Staff

Abstract:
The four most popular water models in molecular dynamics were studied in large-scale simulations of Brownian motion of colloidal particles in optical tweezers and then compared with experimental measurements in the same time scale. We present the most direct comparison of col- loidal polystyrene particle diffusion in molecular dynamics simulations and experimental data on the same time scales in the ballistic regime. The four most popular water models, all of which take into account electrostatic interactions, are tested and compared based on yielded results and re- sources required. Three different conditions were simulated: a freely moving particle and one in a potential force field with two different strengths based on 1 pN/nm and 10 pN/nm. In all cases, the diameter of the colloidal particle was 50 nm. The acquired data were compared with experimental measurements performed using optical tweezers with position capture rates as high as 125 MHz. The experiments were performed in pure water on polystyrene particles with a 1 μm diameter in special microchannel cells.

Keywords:
Brownian motion,molecular dynamics,optical tweezers,ballistic regime

Abstract:
One of the most fascinating areas in the field of smart biopolymers is biomolecule sensing. Accordingly, multifunctional biomimetic, biocompatible, and stimuli-responsive materials based on hydrogels have attracted much interest. Within this framework, the design of nanostructured materials that do not require any external energy source is beneficial for developing a platform for sensing glucose in body fluids. In this article, we report the realization and application of an innovative platform consisting of two outer layers of a nanocomposite plasmonic hydrogel plus one inner layer of electrospun mat fabricated by electrospinning, where the outer layers exploit photoinitiated free radical polymerization, obtaining a compact and stable device. Inspired by the exceptional features of chameleon skin, plasmonic silver nanocubes are embedded into a poly(N-isopropylacrylamide)-based hydrogel network to obtain enhanced thermoresponsive and antibacterial properties. The introduction of an electrospun mat creates a compatible environment for the homogeneous hydrogel coating while imparting excellent mechanical and structural properties to the final system. Chemical, morphological, and optical characterizations were performed to investigate the structure of the layers and the multifunctional platform. The synergetic effect of the nanostructured system’s photothermal responsivity and antibacterial properties was evaluated. The sensing features associated with the optical properties of silver nanocubes revealed that the proposed multifunctional system is a promising candidate for glucose-sensing applications.

Abstract:
Intrinsically conducting polymers (ICPs) are widely used to fabricate biomaterials; their application in neural tissue engineering, however, is severely limited because of their hydrophobicity and insufficient mechanical properties. For these reasons, soft conductive polymer hydrogels (CPHs) are recently developed, resulting in a water-based system with tissue-like mechanical, biological, and electrical properties. The strategy of incorporating ICPs as a conductive component into CPHs is recently explored by synthesizing the hydrogel around ICP chains, thus forming a semi-interpenetrating polymer network (semi-IPN). In this work, a novel conductive semi-IPN hydrogel is designed and synthesized. The hybrid hydrogel is based on a poly(N-isopropylacrylamide-co-N-isopropylmethacrylamide) hydrogel where polythiophene is introduced as an ICP to provide the system with good electrical properties. The fabrication of the hybrid hydrogel in an aqueous medium is made possible by modifying and synthesizing the monomers of polythiophene to ensure water solubility. The morphological, chemical, thermal, electrical, electrochemical, and mechanical properties of semi-IPNs were fully investigated. Additionally, the biological response of neural progenitor cells and mesenchymal stem cells in contact with the conductive semi-IPN was evaluated in terms of neural differentiation and proliferation. Lastly, the potential of the hydrogel solution as a 3D printing ink was evaluated through the 3D laser printing method. The presented results revealed that the proposed 3D printable conductive semi-IPN system is a good candidate as a scaffold for neural tissue applications.

Abstract:
Multifunctional nanomaterials with the ability torespond to near-infrared (NIR) light stimulation are vital for thedevelopment of highly efficient biomedical nanoplatforms with apolytherapeutic approach. Inspired by the mesoglea structure ofjellyfish bells, a biomimetic multifunctional nanostructured pillowwith fast photothermal responsiveness for NIR light-controlled on-demand drug delivery is developed. We fabricate a nanoplatformwith several hierarchical levels designed to generate a series ofcontrolled, rapid, and reversible cascade-like structural changesupon NIR light irradiation. The mechanical contraction of thenanostructured platform, resulting from the increase of temper-ature to 42°C due to plasmonic hydrogel−light interaction, causesa rapid expulsion of water from the inner structure, passing through an electrospun membrane anchored onto the hydrogel core. Themutual effects of the rise in temperature and waterflow stimulate the release of molecules from the nanofibers. To expand thepotential applications of the biomimetic platform, the photothermal responsiveness to reach the typical temperature level forperforming photothermal therapy (PTT) is designed. The on-demand drug model penetration into pig tissue demonstrates theefficiency of the nanostructured platform in the rapid and controlled release of molecules, while the high biocompatibility confirmsthe pillow potential for biomedical applications based on the NIR light-driven multitherapy strategy.

Keywords:
bioinspired materials, NIR-light responsive nanomaterials, multifunctional platforms, electrospun nanofibers, plasmonic hydrogel, photothermal-based polytherapy, on-demand drug delivery

Abstract:
This work describes the morphological, optical, and thermo‐optical properties of a temperature‐sensitive hydrogel poly(N‐isopropylacrylamide‐co‐N‐isopropylmethacrylamide) [P(NIPAm‐co‐NIPMAm]) film containing a specific amount of gold nanorods (GNRs). The light‐induced thermoplasmonic heating of GNRs is used to control the optical scattering of an initially transparent hydrogel film. A hydrated P(NIPAm‐co‐NIPMAm) film is optically clear at room temperature. When heated to temperatures over 37 °C via light irradiation with a resonant source (λ = 810 nm) to the GNRs, a reversible phase transition from a swollen hydrated state to a shrunken dehydrated state occurs. This phenomenon causes a drastic and reversible change in the optical transparency from a clear to an opaque state. A significant red shift (≈30 nm) of the longitudinal band can also be seen due to an increased average refractive index surrounding the GNRs. This change is in agreement with an ad hoc theoretical model which uses a modified Gans theory for ellipsoidal nanoparticles. Morphological analysis of the composite film shows the presence of well‐isolated and randomly dispersed GNRs. Thermo‐optical experiments demonstrate an all‐optically controlled light attenuator (65% contrast ratio) which can be easily integrated in several modern optical applications such as smart windows and light‐responsive optical attenuators.

Keywords:
active plasmonics, gold nanorods, hydrogels, optical attenuators, optical transparency, plasmonic nanoparticles, polymers

Abstract:
The dynamics of highly flexible micro- and nano-filaments are important to a variety of biological, medical, and industrial problems. The filament configuration variation and cross-stream migration in a microchannel are affected by thermal fluctuations in addition to elastic and viscous forces. Here, hydrogel nano-filaments with small bending Young's moduli are utilized to elucidate the transitional behavior of elastic Brownian filaments in an oscillatory microchannel flow. A numerical model based on chain elastic dumbbells similar to the Rouse-Zimm model accounting for elastic, viscous, and random Brownian forces is proposed and implemented. In addition, a theoretical model to describe the average orientation–deformation tensor evolution for an ensemble of filaments in an oscillatory flow is proposed. The results are compared with the evolution observed in the experiments.

Abstract:
Body tissues and organs have complex functions which undergo intrinsic changes during medical treatments. For the development of ideal drug delivery systems, understanding the biological tissue activities is necessary to be able to design materials capable of changing their properties over time, on the basis of the patient's tissue needs. In this study, a nanofibrous thermal‐responsive drug delivery system is developed. The thermo‐responsivity of the system makes it possible to self‐regulate the release of bioactive molecules, while reducing the drug delivery at early stages, thus avoiding high concentrations of drugs which may be toxic for healthy cells. A co‐axial electrospinning technique is used to fabricate core–shell cross‐linked copolymer poly(N‐isopropylacrylamide‐co‐N‐isopropylmethacrylamide) (P(NIPAAm‐co‐NIPMAAm)) hydrogel‐based nanofibers. The obtained nanofibers are made of a core of thermo‐responsive hydrogel containing a drug model, while the outer shell is made of poly‐l‐lactide‐co‐caprolactone (PLCL). The custom‐made electrospinning apparatus enables the in situ cross‐linking of P(NIPAAm‐co‐NIPMAAm) hydrogel into a nanoscale confined space, which improves the electrospun nanofiber drug dosing process, by reducing its provision and allowing a self‐regulated release control. The mechanism of the temperature‐induced release control is studied in depth, and it is shown that the system is a promising candidate as a "smart" drug delivery platform.

Keywords:
biomimetic nanomaterials, electrospun core–shell nanofibers, hierarchical nanostructures, smart drug delivery, thermo‐responsive hydrogels

Abstract:
Materials for the treatment of cancer have been studied comprehensively over the past few decades. Among the various kinds of biomaterials, polymer-based nanomaterials represent one of the most interesting research directions in nanomedicine because their controlled synthesis and tailored designs make it possible to obtain nanostructures with biomimetic features and outstanding biocompatibility. Understanding the chemical and physical mechanisms behind the cascading stimuli-responsiveness of smart polymers is fundamental for the design of multifunctional nanomaterials to be used as photothermal agents for targeted polytherapy. In this review, we offer an in-depth overview of the recent advances in polymer nanomaterials for photothermal therapy, describing the features of three different types of polymer-based nanomaterials. In each case, we systematically show the relevant benefits, highlighting the strategies for developing light-controlled multifunctional nanoplatforms that are responsive in a cascade manner and addressing the open issues by means of an inclusive state-of-the-art review. Moreover, we face further challenges and provide new perspectives for future strategies for developing novel polymeric nanomaterials for photothermally assisted therapies.

Abstract:
Over the past few decades, there has been strong interest in the development of new micro- and nanomaterials for biomedical applications. Their use in the form of capsules, particles or filaments suspended in body fluids is associated with conformational changes and hydrodynamic interactions responsible for their transport. The dynamics of fibres or other long objects in Poiseuille flow is one of the fundamental problems in a variety of biomedical contexts, such as mobility of proteins, dynamics of DNA or other biological polymers, cell movement, tissue engineering, and drug delivery. In this review, we discuss several important applications of micro and nanoobjects in this field and try to understand the problems of their transport in flow resulting from material-environment interactions in typical, crowded, and complex biological fluids. Our aim is to elucidate the relationship between the nano- and microscopic structures of elongated polymer particles and their flow properties, thus opening the possibility to design nanoobjects that can be efficiently transported by body fluids for targeted drug release or local tissue regeneration.

Abstract:
Highly efficient single-material organic solar cells (SMOCs) based on fullerene-grafted polythiophenes were fabricated by incorporating electrospun one-dimensional (1D) nanostructures obtained from polymer chain stretching. Poly(3-alkylthiophene) chains were chemically tailored in order to reduce the side effects of charge recombination which severely affected SMOC photovoltaic performance. This enabled us to synthesize a donor–acceptor conjugated copolymer with high solubility, molecular weight, regioregularity, and fullerene content. We investigated the correlations among the active layer hierarchical structure given by the inclusion of electrospun nanofibers and the solar cell photovoltaic properties. The results indicated that SMOC efficiency can be strongly increased by optimizing the supramolecular and nanoscale structure of the active layer, while achieving the highest reported efficiency value (PCE = 5.58%). The enhanced performance may be attributed to well-packed and properly oriented polymer chains. Overall, our work demonstrates that the active material structure optimization obtained by including electrospun nanofibers plays a pivotal role in the development of efficient SMOCs and suggests an interesting perspective for the improvement of copolymer-based photovoltaic device performance using an alternative pathway.

Abstract:
The recent progress in bioengineering has created great interest in the dynamics and manipulation of long, deformable macromolecules interacting with fluid flow. We report experimental data on the cross-flow migration, bending, and buckling of extremely deformable hydrogel nanofilaments conveyed by an oscillatory flow into a microchannel. The changes in migration velocity and filament orientation are related to the flow velocity and the filament's initial position, deformation, and length. The observed migration dynamics of hydrogel filaments qualitatively confirms the validity of the previously developed worm-like bead-chain hydrodynamic model. The experimental data collected may help to verify the role of hydrodynamic interactions in molecular simulations of long molecular chains dynamics.

Abstract:
Composite nanofibers made of a polyaniline-based polymer blend and different thiol-capped metal nanoparticles were prepared using ex situ synthesis and electrospinning technique. The effects of the nanoparticle composition and chemical structure on the electrical properties of the nanocomposites were investigated. This study confirmed that Brust's procedure is an effective method for the synthesis of sub-10 nm silver, gold, and silver-gold alloy nanoparticles protected with different types of thiols. Electron microscopy results demonstrated that electrospinning is a valuable technique for the production of composite nanofibers with similar morphology and revealed that nanofillers are well-dispersed into the polymer matrix. X-ray diffraction tests proved the lack of a significant influence of the nanoparticle chemical structure on the polyaniline chain arrangement. However, the introduction of conductive nanofillers in the polymer matrix influences the charge transport noticeably improving electrical conductivity. The enhancement of electrical properties is mediated by the nanoparticle capping layer structure. The metal nanoparticle core composition is a key parameter, which exerted a significant influence on the conductivity of the nanocomposites. These results prove that the proposed method can be used to tune the electrical properties of nanocomposites.

Abstract:
Objective
Due to the capacity of the amniotic membrane (Am) to support re-epithelisation and inhibit scar formation, Am has a potential to become a considerable asset for reconstructive urology i.e., reconstruction of ureters and urethrae. The application of Am in reconstructive urology is limited due to a poor mechanical characteristic. Am reinforcement with electrospun nanofibers offers a new strategy to improve Am mechanical resistance, without affecting its unique bioactivity profile. This study evaluated biocomposite material composed of Am and nanofibers as a graft for urinary bladder augmentation in a rat model.

Material and Methods
Sandwich-structured biocomposite material was constructed from frozen Am and covered on both sides with two-layered membranes prepared from electrospun poly-(L-lactide-co-E-caprolactone) (PLCL). Wistar rats underwent hemicystectomy and bladder augmentation with the biocomposite material.

Results
Immunohistohemical analysis (hematoxylin and eosin [H&E], anti-smoothelin and Masson’s trichrome staining [TRI]) revealed effective regeneration of the urothelial and smooth muscle layers. Anti-smoothelin staining confirmed the presence of contractile smooth muscle within a new bladder wall. Sandwich-structured biocomposite graft material was designed to regenerate the urinary bladder wall, fulfilling the requirements for normal bladder tension, contraction, elasticity and compliance. Mechanical evaluation of regenerated bladder wall conducted based on Young’s elastic modulus reflected changes in the histological remodeling of the augmented part of the bladder. The structure of the biocomposite material made it possible to deliver an intact Am to the area for regeneration. An unmodified Am surface supported regeneration of the urinary bladder wall and the PLCL membranes did not disturb the regeneration process.

Conclusions
Am reinforcement with electrospun nanofibers offers a new strategy to improve Am mechanical resistance without affecting its unique bioactivity profile.

Keywords:
Bladder, Smooth muscles, Muscle regeneration, Bionanotechnology, Renal system, Urothelium, Urology, Nanomaterials

Abstract:
In this article, we report on the production by electrospinning of P3HT/PEO, P3HT/PEO/GO, and P3HT/PEO/rGO nanofibers in which the filler is homogeneously dispersed and parallel oriented along the fibers axis. The effect of nanofillers' presence inside nanofibers and GO reduction was studied, in order to reveal the influence of the new hierarchical structure on the electrical conductivity and mechanical properties. An in-depth characterization of the purity and regioregularity of the starting P3HT as well as the morphology and chemical structure of GO and rGO was carried out. The morphology of the electrospun nanofibers was examined by both scanning and transmission electron microscopy. The fibrous nanocomposites are also characterized by differential scanning calorimetry to investigate their chemical structure and polymer chains arrangements. Finally, the electrical conductivity of the electrospun fibers and the elastic modulus of the single fibers are evaluated using a four-point probe method and atomic force microscopy nanoindentation, respectively. The electrospun materials crystallinity as well as the elastic modulus increase with the addition of the nanofillers while the electrical conductivity is positively influenced by the GO reduction.

Keywords:
electrospun composite nanofibers, poly(3-hexylthiophene), graphene oxide, electrical conductivity, mechanical properties

Abstract:
The role of mechanical properties is essential to understand molecular, biological materials, and nanostructures dynamics and interaction processes. Atomic force microscopy (AFM) is the most commonly used method of direct force evaluation, but due to its technical limitations this single probe technique is unable to detect forces with femtonewton resolution. In this paper we present the development of a combined atomic force microscopy and optical tweezers (AFM/OT) instrument. The focused laser beam, on which optical tweezers are based, provides us with the ability to manipulate small dielectric objects and to use it as a high spatial and temporal resolution displacement and force sensor in the same AFM scanning zone. We demonstrate the possibility to develop a combined instrument with high potential in nanomechanics, molecules manipulation and biological studies. AFM/OT equipment is described and characterized by studying the ability to trap dielectric objects and quantifying the detectable and applicable forces. Finally, optical tweezers calibration methods and instrument applications are given.

Keywords:
optical trap, nanomanipulation, nanomechanics, femtonewton forces

Abstract:
Recent biomedical hydrogels applications require the development of nanostructures with controlled diameter and adjustable mechanical properties. Here we present a technique for the production of flexible nanofilaments to be used as drug carriers or in microfluidics, with deformability and elasticity resembling those of long DNA chains. The fabrication method is based on the core-shell electrospinning technique with core solution polymerisation post electrospinning. Produced from the nanofibers highly deformable hydrogel nanofilaments are characterised by their Brownian motion and bending dynamics. The evaluated mechanical properties are compared with AFM nanoindentation tests.

Correction: Hydrogel Nanofilaments via Core-Shell Electrospinning, Nakielski P., Pawłowska S., Pierini F., Liwińska W., Hejduk P., Zembrzycki K., Zabost E., Kowalewski T.A., PLOS ONE, ISSN: 1932-6203, DOI: 10.1371/journal.pone.0133458, Vol.10, No.7, pp.e0133458-1-2, 2015

Keywords:
Gels, Nanomaterials, Atomic force microscopy, Polymerization, Bending, Mass diffusivity, Mechanical properties, Hydrodynamics

Abstract:
Drug delivery systems based on nanofibrous mats appear to be a promising healing practice for preventing brain neurodegeneration after surgery. One of the problems encountered during planning and constructing optimal delivery system based on nanofibrous mats is the estimation of parameters crucial for predicting drug release dynamics. This study describes our experimental setup allowing for spatial and temporary evaluation of drug release from nanofibrous polymers to obtain data necessary to validate appropriate numerical models. We applied laser light sheet method to illuminate released fluorescent drug analog and CCD camera for imaging selected cross-section of the investigated volume. Transparent hydrogel was used as a brain tissue phantom. The proposed setup allows for continuous observation of drug analog (fluorescent dye) diffusion for time span of several weeks. Images captured at selected time intervals were processed to determine concentration profiles and drug release kinetics. We used presented method to evaluate drug release from several polymers to validate numerical model used for optimizing nanofiber system for neuroprotective dressing.

Keywords:
neural therapy, brain phantom, drug delivery, laser light sheet, computational modeling, nanofibers

Abstract:
This paper is a third of a series of the three where eccentric cases of flow in silo models recorded by the DPIV technique are presented and discussed in detail. The methodology of empirical descriptions of velocities, flow rate and stagnant zone boundaries on the base of registered velocity fields in eccentric filling and discharge in 2D silo model was discussed. In previous two papers [1] and [2] we analyzed also eccentric flows but with different locations of the outlet. It was stated that in practice even tiny eccentricity of filling or discharge processes may lead to quite an unexpected behavior of the silo structure. During asymmetrical processes, flow patterns and wall stresses may be quite different. It is therefore crucial to identify how flow patterns developed in the material during eccentric filling or discharge and to determine both the flow rate and wall stresses occurring under such state of loads. Thus, we discuss here the third case of discharge — located in the center of the silo bottom. A comparison of these three cases of discharge mode will be presented in the next paper. Empirical descriptions of eccentric flow velocities in silo model by the linear and nonlinear regressions are presented here with specific functions like the Gaussian function and “the double logarithmic function”. In both methods the velocity was also descripted by linearization and in the Gaussian method also by the nonlinear method of Gauss–Newton and in the case of the method of double logarithm — the nonlinear method of Levenberg–Marquardt was applied. Velocities were predicted by using interpolation due to the nonlinear model of the Gaussian type and to the nonlinear function of “the double logarithm”.

Keywords:
Eccentric granular flow, Silo model, Empirical description, Linear and nonlinear regression, Gaussian description, Double logarithm

Abstract:
The effect of laser wavelength on single-wall carbon nanotubes synthesis yield and their properties was studied. A double-pulse Nd:YAG laser, working at a wavelength of 355 or 1064 nm, was used for carbon nanotubes production. The synthesized carbon nanotubes (CNTs) were investigated using the SEM/STEM microscopy and Raman spectroscopy. The results show that the useful range of UV laser radiation fluence is narrower and the properties of synthesized CNTs depend much more on the laser fluence than in the case of infrared laser radiation.

Keywords:
carbon nanotubes, laser radiation fluence, pulsed laser vaporization, Raman spectra

Abstract:
The aim of this study was to compare two different acellular scaffolds: natural and synthetic, for urinary conduit construction and ureter segment reconstruction. Acellular aortic arch (AAM) and poly(L-lactide-co-caprolactone) (PLCL) were used in 24 rats for ureter reconstruction in both tested groups. Follow-up period was 4 weeks. Intravenous pyelography, histological and immunohistochemical analysis were performed. All animals survived surgical procedures. Patent uretero-conduit junction was observed only in one case using PLCL. In case of ureter segment reconstruction ureters were patent in one case using AAM and in four cases using PLCL scaffolds. Regeneration of urothelium layer and focal regeneration of smooth muscle layer was observed on both tested scaffolds. Obtained results indicates that synthetic acellular PLCL scaffolds showed better properties for ureter reconstruction than naturally derived acellular aortic arch.

Keywords:
Ureter, Muscle regeneration, Kidneys, Collagens, Urine, Surgical and invasive medical procedures, Smooth muscles, Inflammation

Abstract:
The purpose of this study was to compare: a new five-layered poly (L–lactide–co–caprolactone) (PLC) membrane and small intestinal submucosa (SIS) as a control in rat urinary bladder wall regeneration. The five-layered poly (L–lactide–co–caprolactone) membrane was prepared by an electrospinning process. Adipose tissue was harvested from five 8-week old male Wistar rats. Adipose derived stem cells (ADSCs) were seeded in a density of 3×106 cells/cm2 onto PLC membrane and SIS scaffolds, and cultured for 5-7 days in the stem cell culture medium. Twenty male Wistar rats were randomly divided into five equal groups. Augmentation cystoplasty was performed in a previously created dome defect. Groups: (I) PLC+ 3×106ADSCs; (II) SIS+ 3×106ADSCs; (III) PLC; (IV) SIS; (V) control. Cystography was performed after three months. The reconstructed urinary bladders were evaluated in H&E and Masson's trichrome staining. Regeneration of all components of the normal urinary bladder wall was observed in bladders augmented with cell-seeded SIS matrices. The urinary bladders augmented with SIS matrices without cells showed fibrosis and graft contraction. Bladder augmentation with the PLC membrane led to numerous undesirable events including: bladder wall perforation, fistula or diverticula formation, and incorporation of the reconstructed wall into the bladder lumen. The new five-layered poly (L–lactide–co–caprolactone) membrane possesses poorer potential for regenerating the urinary bladder wall compared with SIS scaffold.

Keywords:
urinary bladder regeneration, electrospinning

Abstract:
The study was conducted to evaluate the cytocompatibility and hydrolytic degradability of the new poly(lactic acid)/polyethylene glycol-polyhedral oligomeric silsesquioxane (peg-POSS/PLLA) nanocomposite as potential material for cartilage regeneration. PLLA scaffolds containing 0 to 5% of peg-POSS were fabricated by electrospinning. Human mesenchymal stem cells (hMSC’s) were cultured in vitro to evaluate the cytocompatibility of the new nanocomposite material. Hydrolytic degradation studies were also carried out to analyze the mass loss rate of the nanocomposites through time. The addition of the peg-POSS to the PLLA did not affect the processability of the nanocomposite by electrospinning. It was also observed that peg-POSS did not show any relevant change in fibers morphology, concluding that it was well dispersed. However, addition of peg-POSS caused noticeable decrease in mean fiber diameter, which made the specific surface area of the scaffold to rise. hMSC’s were able to attach, to proliferate, and to differentiate into chondrocytes in a similar way onto the different types of electrospun peg-POSS/PLLA and pure PLLA scaffolds, showing that the peg-POSS as nano-additive does not exhibit any cytotoxicity. The hydrolytic degradation rate of the material was lower when peg-POSS was added, showing a higher durability of the nanocomposites through time. Results demonstrate that the addition of peg-POSS to the PLLA scaffolds does not affect its cytocompatibility to obtain hyaline cartilage from hMSC’s.

Keywords:
PLLA, peg-POSS, nanocomposite, electrospinning, chondrocyte, stem cells, scaffold, cartilage repair, hydrolytic degradation

Abstract:
Traumatic/surgical brain injury can initiate a cascade of pathological changes that result, in the long run, in severe damage of brain parenchyma and encephalopathy. Excessive scarring can also interfere with brain function and the glial scar formed may hamper the restoration of damaged brain neural pathways. In this preliminary study we aimed to investigate the effect of dressing with an L-lactide-caprolactone copolymer nanofiber net on brain wound healing and the fate of the formed glial scar. Our rat model of surgical brain injury (SBI) of the fronto-temporal region of the sensorimotor cortex imitates well the respective human neurosurgery situation. Brains derived from SBI rats with net-undressed wound showed massive neurodegeneration, entry of systemic inflammatory cells into the brain parenchyma and the astrogliosis due to massive glial scar formation. Dressing of the wound with the nanofiber net delayed and reduced the destructive phenomena. We observed also a reduction in the scar thickness. The observed modification of local inflammation and cicatrization suggest that nanofiber nets could be useful in human neurosurgery.

Keywords:
brain injury, L-lactide-caprolactone copolymer nanofiber net, glial scar, neurodegeneration

Abstract:
Thermochromic liquid crystals (TLC) and true-colour digital image processing have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. Thin coatings of TLC at surfaces are utilized to obtain detailed temperature distributions and heat transfer rates for steady or transient processes. Liquid crystals also can be used to make the temperature and velocity fields in liquids visible by the simple expedient of directly mixing the liquid crystal material into the liquid (water, glycerol, glycol, and silicone oils) in very small quantities to use as thermal and hydrodynamic tracers. In biomedical situations, e.g., skin diseases, breast cancer, blood circulation and other medical application, TLC and image processing are successfully used as an additional non-invasive diagnostic method especially useful for screening large groups of potential patients. The history of this technique is reviewed, principal methods and tools are described and some examples are presented. Also steady-state and transient liquid crystal thermography (LCT) is used to measure local heat transfer on a plate equipped with transverse vortex generators. Automated evaluation allows determining the heat transfer coefficient without arbitrary influence of human interpretation.

Keywords:
Liquid Crystal Thermography, Steady-State and Transient Method, Vortex Generators, Biomedicine

Abstract:
Excessive cicatrisation or epidural fibrosis in the operative field is an inappropriate event occasionally occurring after neurosurgical procedures (i.e., spine procedures and craniotomies). This excessive process may disturb the postopera­tive course and render reoperations more difficult and risky. The literature describes this phenomenon as accompanying up to 20% of neurosurgical procedures. The scar tissue that forms postoperatively adheres to the dura mater, penetrates into the spinal canal and can cause narrowing symptoms, neurological deficits and pain. The incidence and spread of this excessive scar or epidural fibrosis can be prevented through the modification of the surgical technique by incorporating endoscopic or microscopic access to minimize the operative field and the use of isolating substances (autogenous or heterogeneous) administered intraoperatively.

The aim of this experimental study was to morphologically assess the cicatrisation process, adhesion and to prevent excessive scar formation with the local use of membranes manufactured by an electrospinning process (nanotechnology). We also investigated whether the biodegradable nanofibrous net triggers or modifies the immunological response or the local inflammatory process.

Micro-nanofibrous membranes were produced by the electrospinning process. A biodegradable, medically certified copolymer poly(L-lactide-co-caprolactone) (PLCL) was used as the electrospun material.

An experimental rat model was used in this study. Experimental and control groups were formed with specified follow-up times of 4, 14 and 30 days. During the operation, a two-level laminectomy in the thoracic segment was performed. The operative field was divided into two regions. Isolating material was used on the dura mater and surface of the spinal cord in the area where the laminectomy was performed. The material was analysed with the use of light and electron microscopy.

Local cicatrisation can be modified using nanomaterials. Scar formation and epidural fibrosis can be limited and modi­fied locally. No local inflammation process was observed.

Initial observations indicate the potential for the effective use of materials obtained in the electrospinning process to prevent cicatrisation.

Keywords:
neurosurgery, cicatrisation, epidural fibrosis, copolymer, poly(L-lactide-co-caprolactone), nanofibrous net, rat model

Abstract:
This work presents our attempts to characterize release of two model drugs from electrospun polymer nanofibers. Such drug delivery system offers great potential for applications in medicine especially as neurosurgery protective membranes. Proper delivery of drugs requires precise control of the drug diffusion process during the release for days or even weeks. Lipophilic model drug Rhodamine B and hydrophilic Bovine Serum Albumin conjugated with Fluoresceine (BSA - FITC) were embedded in electrospun poly(L -lactide-co -ε-caprolactone) (PLC) nanofibers. Release of Rhodamine B showed saturation in cumulative release profile at 60% and 86% for 1.5% and 3% wt. initial drug content, respectively. Nanofibers electrospun from emulsion released almost entire drug encapsulated in water vesicles inside the nanofibers. Possible location of vesicles close to the surface of the nanofibers exposed them for surrounding fluid and caused leaching of the drug. In this case encapsulation of drug in emulsion prevented the initial burst release.Dependence of a drug release and composition of nanofiber is essential for production of drug delivery systems. Mathematical model constructed with this data allows to avoid tedious experimental work. This research was supported by Ministry of Science and Higher Education, National Centre for Research and Development Project grant no. R13008110. The first author has been supported with a scholarship from the European Social Fund, Human Capital Operational Programme.

Keywords:
nanofibres, drug delivery, vesicles

Abstract:
Comprehensive studies of drug transport in nanofibres based mats have been performed to predict drug release kinetics. The paper presents our approach to analyze the impact of fibers arrangement, one of the parameters varied in our parallel experimental studies. Drug encapsulation in submicron fibers and subsequent controlled release of drugs is a tedious task due to the large number of process and material parameters involved. In the numerical study we constructed a 3D finite element geometry representing nanofibrous cubic element. COMSOL Multiphysics has been used to assess the impact of the various purposed arrangements of fibers within the mat. Drug release from nanofibers was modeled by adsorption -desorption and diffusion equation, where drug diffusion coefficient in the fluid between the fibers was altered depending on porosity of the material. Our study shows that for the same material porosity drug release from the matrix of regularly oriented fibers is slower than from randomly oriented, isotropic nanofibrous material. Also by decreasing distance between the fibers drug transport rate is reduced.

Keywords:
Electrospinning, ZnO nanofibers, ZnFeO, Room temperature ferromagnetism, Magnetic oxides

Abstract:
The potential of polarizing-interference Pluta microscope for determination of optical birefringence of individual nanofibers formed by electrospinning was shown. This technique can be applied for measurements of fiber birefringence, practically at diameter above 300 nm. The molecular orientation of individual polycaprolactone (PCL) nanofibers was determined from birefringence assuming the same orientation of both phases, crystal and amorphous. The molecular orientation was determined using DSC crystallinity, crystal intrinsic birefringence calculated for the first time for PCL from bond polarizabilities as well as estimated value of amorphous intrinsic birefringence. Our results indicate that the birefringence and thus molecular orientation are strongly inhomogeneous along the nanofibers, reflecting a complex nature of forces acting during electrospinning process. The average molecular orientation is weak if any, being dependent together with fiber thickness and crystallinity on electrospinning parameters, like applied voltage, concentration and type of solvent. The obtained results indicate that the average molecular orientation displays similar dependence on applied voltage as fiber diameter. Relatively low melting temperature of electrospun nanofibers suggests low crystal size and/or high concentration of defects in crystals. This observation corresponds with low crystallinity and molecular orientation, indicating together relatively low degree of crystal ordering due to high rate of cooling and solvent evaporation during electrospinning, limiting thus crystallization process.

Keywords:
Nanofibers, Electrospinning, Birefringence, Polarizing-interference microscopy, Polycaprolactone

Abstract:
In this report, experiments mimicking some aspects of cloud-clear-air mixing in a laboratory chamber are discussed. A saturated plume containing small droplets of water (a surrogate of an atmospheric cloud) is mixed with unsaturated environmental air in order to study effect of evaporative cooling at the interfaces between cloudy and clear air filaments on small-scale turbulence. Two components of the turbulent velocity at a small scale are determined using particle imaging velocimetry of the cloud droplets. Enhanced velocity fluctuations between the Kolmogorov (η ≈ 0.8 mm) and Taylor (λ ≈ 8 mm) microscales are observed.
The characteristic feature of these microscales is anisotropy with a preferred vertical direction. A straightforward dependence of the observed effects on the relative humidity of the environment indicates the importance of buoyancy production by evaporative cooling. This conclusion is in agreement with previous numerical experiments described in the literature and suggests that, under certain conditions, effects similar to the above may influence the smallest scales of turbulence in natural clouds.

Keywords:
Small-scale turbulence, Atmospheric turbulence, Evaporative cooling, Cloud-clear-air mixing

Abstract:
In this paper we continue empirical description of eccentric granular flow registered by the DPIV (Digital Particle Image Velocimetry) technique. The first results concerning eccentric flow with the outlet located on the right were published in Sielamowicz et al. [30]. Here we present a methodology of empirical descriptions of velocities, flow rate and the flow channel boundary (FCB) in another eccentric case. The analysis is based on the experimental results (velocity profiles) obtained in the DPIV technique. Statistical analysis of the experimental results was also performed. We show how to fit the proper type of function to describe flow parameters in the silo model. The presented methodology is universal and can be applied in any case of eccentric flow of any granular material.

Keywords:
Universal methodology of empirical analysis, DPIV technique, Eccentric granular flow, Discharge on the left, Vertical model, Plexiglas, Velocity, Gaussian type function, Ch function, Multiple regression, “Joined functions”, Flow channel boundary (FCB)

Abstract:
DPIV (Digital Particle Image Velocimetry) is often used to record the flows in silo models and to recognise the flow in two-dimensional structures. Flow in a two-dimensional laboratory model with transparent walls was recorded using the DPIV technique. Recorded images were processed and the velocities of the flowing material were obtained. Statistical analysis of the readings taken from velocity profiles was also performed. To describe the flow the theoretical model of velocity presented in Choi, Kudrolli, and Bazant (2005) was modified. An empirical description of the flow rate was carried out. An analysis of the kinematic parameter b was carried out and compared to the solutions given by Medina, Córdova, Luna, and Treviño (1998) and Choi et al. (2005). Comparisons between the experimental measurements and the empirical descriptions are presented. Comparing the Gaussian based kinematic model of Choi et al. (2005) and a modified empirical kinematic model, a better description of velocity was obtained by using the latter. In further comparisons using the two aformentioned models and a parabolic description the best description of velocity was given by the parabolic function. Flow rate was analysed using the three types of functions. Both the Gaussian and modified empirical kinematic model gave almost the same values for calculated levels h = 5, 10 cm. Using the parabolic description the value of flow rates differed slightly. The flow channel boundary was analysed using parabolic and hyperbolic descriptions. Both descriptions were good because the correlation coefficients, had values ranging from 0.928 to 0.997.

Abstract:
This paper presents numerical and experimental analysis of the hydrodynamic flow focusing in a rectangular microchannel. Aim of the study is to improve performance of the Particle Image Velocimetry (PIV) technique app lied to micro-scale flow analysis. The symmetric flow focusing system of two channels crossed at right angle is investigated. The numerical model is used to analyse the e ffect of Reynolds number on the flow focusing mechanism. In the experiment, the flow foc using is applied to concentrate seeding tracers into a thin sheet at the channel axis. Such a modification removes the out of focus images of the seeding particles, effe ctively improving PIV evaluation of vector fields in microchannel. Based on the exp erimental and numerical results we have found that expected improvement is possible for the flow at Reynolds number less than 10 only.

Keywords:
selective seeding, flow focusing

Abstract:
Recent developments in Computational Fluid Dynamics (CFD) increased interest in quantifying quality of the numerical models. One of the necessary steps is the so-called code validation procedure, an assessment of a numerical simulation by comparisons between simulation results and laboratory measurements. The focus of the present review is application of modern full field experimental techniques, mostly based on the digital image analysis, in validating numerical solutions of complex flow configurations. Each validation procedure opens new issues of quantifying its outcome to find directions for model updating, limits of computer simulation quality, and to perform uncertainty quantification.

Keywords:
CFD validation, experimental methods

Abstract:
The impact of the transversely-oriented sinusoidal wall corrugation on the hydraulic drag is investigated numerically for the flow through the channel of finite width and with flat sidewalls. The numerical method, based on the domain transformation and Chebyshev-Galerkin discretization, is used to investigate the flow resistance of the laminar, parallel and pressure-driven flow. The obtained results are compared to the reference case, i.e., to the flow through the channel with rectangular cross section of the same aspect ratio. Simple explanation of the gain in the volumetric flow rate observed in the flow through spanwise-periodic channel with long-wave transversely-oriented wall corrugation is provided. In the further analysis, pressure drop in the flows with larger Reynolds numbers are studied numerically by means of the finite-volume commercial package Fluent. Preliminary experimental results confirm the predicted tendency.

Keywords:
Drug reduction, finite volume flow modeling, corrugated walls

Abstract:
Electrospun nonwovens have recently been successfully applied as a dressing material in spinal neurosurgery. Scarring is known to be one of the major post-operative complications for neurosurgery. If it occurs, it may trap a nerve, so that when a patient moves the nerve becomes stretched, causing nerve damage, pain, and internal scarring of the nerve. This causes subsequent complications related to ingrowths of connective tissue onto the spinal canal. The formation of an astroglial scar is another serious postoperative complication of brain neuro-surgery. The use of bio-absorbable isolative materials as anti-liaison protection and as possible carriers for neuroprotective drug delivery is expected to help in solving such problems. The nanostructured material acts as an anti-bacterial and anti-liaison barrier while enabling transport of oxygen, nutrients, and metabolites, facilitating the healing process of the surgical wound.

Keywords:
Nanofibres for neurosurgery, protection of scar formation

Abstract:
In this paper we aim to create an experimental and numerical model of nano and micro filaments suspended in a confined Poiseuille flow. The experimental data obtained for short nanofibres will help to elucidate fundamental questions concerning mobility and deformation of biological macromolecules due to hydrodynamic stresses from the surrounding fluid motion. Nanofibres used in the experiments are obtained by electrospinning polymer solutions. Their typical dimensions are 100–1000 μm (length) and 0.1–1 μm (diameter). The nanofibre dynamics is followed experimentally under a fluorescence microscope. A precise multipole expansion method of solving the Stokes equations, and its numerical implementation are used to construct a bead-spring model of a filament moving in a Poiseuille flow between two infinite parallel walls. Simulations show typical behaviour of elongated macromolecules. Depending on the parameters, folding and unfolding sequences of a flexible filament are observed, or a rotational and translation motion of a shape-preserving filament. An important result of our experiments is that nanofibres do not significantly change their shape while interacting with a micro-flow. It appeared that their rotational motion is better reproduced by the shape-preserving Stokesian bead model with all pairs of beads connected by springs, omitting explicit bending forces.

Keywords:
Nanofibres suspension, Microchannels, Filament dynamics, Stokesian dynamics, Multipole expansion

Abstract:
The paper presents the methodology of empirical description and statistical analysis of velocity profiles that were depicted by the Digital Particle Image Velocimetry technique (DPIV). Experimental runs were recorded by the high resolution camera in the model with vertical walls. Here we analyze the eccentric discharge with the outlet located in the bottom close to the right vertical wall of the model. On the base of the experimental results we present an empirical analysis of velocities and calculation of the flow rate in two proposed descriptions of the flow. Velocity functions were presented by the exponential function (the modi fi ed Gauss type), by the multiple regression and by the ch function. Also the fl ow rate was calculated for two presented descriptions. Empirical calculations of the stagnant zone boundary was also presented using the readings from velocity profiles.

Keywords:
Particle Image Velocimetry, granular flow, Multiple regression

Abstract:
Clusters made of a small number of close solid spherical particles at a random configuration, sedimenting through a viscous fluid at small Reynolds number, were experimentally investigated at a short-time scale. The cluster settling velocities were measured and shown to be well approximated by the ensemble-averaged formula derived earlier for the uniform distribution of the point particles inside a spherical volume. It was emphasized that the “effective radius” of this volume in general should be smaller than the actual radius of a cluster made of the spheres, and the relation between both radii was determined. The formula was also shown to account well for the gravitational settling of rigid conglomerates, measured and computed elsewhere.

Keywords:
cluster of sendimenting particles, small Reynolds number

Abstract:
Biodegradable polymeric nanofibrous coatings were obtained by electrospinning different polymers onto sintered 45S5 Bioglass®-based glass-ceramic pellets. The investigated polymers were poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and a composite of poly(caprolactone) (PCL) and poly(ethylene oxide) (PEO) (PCL–PEO). The fibrous coatings morphology was evaluated by optical microscopy and scanning electron microscopy. The electrospinning process parameters were optimised to obtain reproducible coatings formed by a thin web of polymer nanofibres. In-vitro studies in simulated body fluid (SBF) were performed to investigate the bioactivity and mineralisation of the substrates by inducing the formation of hydroxyapatite (HA) on the nanofiber-coated pellets. HA crystals were detected on all samples after 7 days of immersion in SBF, however the morphology of the HA layer depended on the characteristic fibre diameter, which in turn was a function of the specific polymer-solvent system used. The bioactive and resorbable nanofibrous coatings can be used to tailor the surface topography of bioactive glass-ceramics for applications in tissue engineering scaffolds.

Keywords:
Electrospinning, Nanofibers, Bioglass®, Polyhydroxyalkanoates, Tissue engineering

Abstract:
Electrospinning is based on so-called bending instability which results in an erratic spiralling motion of the liquid jet as it proceeds towards a collecting electrode, where it is eventually de posited as a mat of micro/nanosized fibres. Most electrospinning models formulated within the slender approximation rely, however, on an inconsistent description of electrostatic interactions which renders them grossly inappropriate whenever the discretization is either too coarse or too fine. The present work aims at proposing a discrete slender model which is numerically consistent (allowing use of arbitrary fine meshes) and remains accurate even for coarse meshes. At the same time, efficient numerical techniques based on hierarchical charge clustering are introduced that drastically decrease computational times. Finally, a versatile boundary value method is implemented to enforce fixed-potential boundary conditions, allowing realistic electrode configurations to be investigated.

Keywords:
Electrospinning numerical model, boundary value method, bending instability

Abstract:
Small-scale mixing between cloudy air and unsaturated clear air is investigated in numerical simulations and in a laboratory cloud chamber. Despite substantial differences in physical conditions and some differences in resolved scales of motion, results of both studies indicate that small-scale turbulence generated through cloud–clear air interfacial mixing is highly anisotropic. For velocity fluctuations, numerical simulations and cloud chamber observations demonstrate that the vertical velocity variance is up to a factor of two larger than the horizontal velocity variance. The Taylor microscales calculated separately for the horizontal and vertical directions also indicate anisotropy of turbulent eddies. This anisotropy is attributed to production of turbulent kinetic energy (TKE) by buoyancy forces due to evaporative cooling of cloud droplets at the cloud–clear air interface. Numerical simulations quantify the effects of buoyancy oscillations relative to the values expected from adiabatic and isobaric mixing, standardly assumed in cloud physics. The buoyancy oscillations result from microscale transport of liquid water due to the gravitational sedimentation of cloud droplets. In the particular modeling setup considered here, these oscillations contribute to about a fifth of the total TKE production.

Keywords:
laboratory cloud formation, TKE of cloud air, microscale cloud turbulence

Abstract:
Electrospinning of the globular protein, bovine serum albumin (BSA), was optimized to obtain proteinous fibers suitable asbiosensors. It was shown that the as-spun protein preserves its native form, whereas solubility of the cross-linked in the ambient conditions BSA nanofibers evidently decreases. Insoluble BSA fibers can be easily modified to be used as two-dimensional biosensors. Here, we show the micro pH sensor obtained from the BSA fiber stained with a fluorescein derivative (FITC).

Keywords:
Electrospinning BSA, pH sensor

Keywords:
mikroprzepływy, eksperymentalna mechanika płynów

Abstract:
Praca zawiera opis badań zjawiska opadania cząstek kulistych w cieczy o dużej lepkości, a w szczególności wzajemnych oddzaiływań między poszczególnymi, opadającymi razem cząstkami. Opisano stanowisko badawcze, sposób przeprowadzenia pomiarów oraz przedstawiono wybrane wyniki badań.

Keywords:
gliceryna, kilka cząsteki szklanych, eksperyment, trajektorie cząstek, dynamika

Abstract:
Turbulent flow of water in an 1 mm long and 0.4 mm high gap of an emulsifier is investigated experimentally using micro-PIV technique and compared with numerical predictions. The purpose of the investigations is to develop a procedure for well-controlled generation of mono-disperse suspension of micro-droplets. The micro-flow measurements are based on epi-fluorescence illumination and high-speed imaging. The experimental data are compared with the numerical results obtained using direct simulation and turbulent flow model. From the turbulent modelling (k−ε) was found that, the maximum of turbulent energy dissipation rate takes place mainly in the micro-channel gap. However, measured and directly simulated (DNS) velocity fields indicate that flow turbulization is delayed and develops shortly behind the gap. Experimental and numerical results are used to predict droplet dimension of two different oil emulsions. Very low amount of oil-phase fraction in investigated emulsions justifies us to use flow characteristics evaluated for pure water to predict mean diameter of oil droplets. These predictions are validated using experimental data on statistics of droplets size.

Keywords:
Micro-flow, Micro-PIV, Particle Image Velocimetry, Turbulence, Micro-channel, Emulsion

Abstract:
Turbulent flow of water in a short 0.4 mm high micro-channel of an emulsifier is investigated experimentally using a micro-PIV technique and compared with numerical predictions. The micro-flow measurements are based on epi-fluorescence illumination and high-speed imaging. Velocity fields obtained from the measurements and direct numerical simulations indicate that flow turbulization is delayed and develops only at the outlet region of the micro-channe

Keywords:
micro-channel, micro-PIV, turbulence

Abstract:
The flow evolution of an amaranth seed is being investigated in a wedge-shaped model made of Plexiglas. The objective of this paper is to recognise flow patterns in the flowing material, and also to depict evolution of velocity fields, flow field discontinuities, velocity profiles for cross-sections of the model, shear zones and flow streamlines using the digital particle image velocimetry (DPIV) optical technique. It is demonstrated that the DPIV technique used in the experiments enables quantitative analysis of the flow zones geometry. The technique also allows to reveal boundaries between flowing and stagnant zones and to extract velocity profiles at any selected sections of the model.

Keywords:
Optical technique, DPIV, Granular material flows, Converging hopper, Particle, Plug flow, Shear zones, Discharge flow rate

Abstract:
Cloudy air, containing small water droplets, undergoes mixing with the unsaturated environment inside the cloud chamber in the process resembling smallest scales of entrainment and mixing in real clouds. Particle Image Velocimetry (PIV) applied to images from the chamber interior is used to investigate dynamics of the process in scales from 1.2 mm to few centimeters. A special algorithm, allowing for investigation of droplets motion, is developed, tested and adapted to the experimental data. Two velocity components retrieved in the vertical cross-section through the chamber interior indicate anisotropy of small-scale turbulent motions, with the preferred vertical direction. This result confirms earlier numerical studies, indicating that evaporation of cloud droplets at the cloud – clear air interface may substantially influence the small-scale turbulence in clouds.

Keywords:
Atmospheric turbulence, Turbulence in clouds, Small-scale turbulence, Laboratory investigations of atmospheric turbulence, Particle Image Velocimetry

Abstract:
The aim of this paper is to present the evolution of plug flow developing in three densely packed granular materials in the model of a hopper made of Plexiglas. For this purpose, the digital particle image velocimetry (DPIV) technique is applied to analyse the flow field of the granular material. When discharge starts, a plug flow zone in the flowing material expands upward. This zone changes its width reaching the upper surface of the material. The plug flow evolution as a function of time is described using DPIV. This technique yields the velocity profiles of flowing granular materials, velocity magnitude contours, vector fields, velocity distributions on certain levels in the model and traces of the selected particles. The results obtained for the evolution of the vertical velocity, height and width of the plug flow zone as a function of time, measured at the symmetry axis of the model for the amarantus seed are compared to the results obtained by Waters and Drescher. Measurements of the stagnant boundary as a function of time are compared to the results available in the literature

Keywords:
Optical technique, Experiments, Granular, Materials, Flow, Particle, Plug flow

Abstract:
A steady-state natural convection in a differentially heated cavity for temperatures in a vicinity of the freezing point is used to investigate and compare performance of four different numerical methods: finite differences, finite volume, finite elements and mesh-free diffuse approximation method. A primary aim of the exercise is to define a new numerical benchmark solution for natural convection problems, which includes challenging configuration of strongly non-linear buoyancy term. This configuration is used to test the performance of two popular commercial codes (Fluent and Fidap) and to compare them with two classical finite difference codes and the new promising mesh-free implementation.

Keywords:
numerical simulation, numerical benchmarks, mesh-free methods, natural convection

Abstract:
Very thin liquid jets can be obtained using electric field, whereas an electrically-driven bending instability occurs that enormously increases the jet path and effectively leads to its thinning by very large ratios, enabling the production of nanometre size fibres. This mechanism, although it was discovered almost one century ago, is not yet fully understood. In the following study, experimental data are collected, with the dual goal of characterizing the electro-spinning of different liquids and evaluating the pertinence of a theoretical model.

Keywords:
nanofibres, electrospinning, polymer fibres, electrified liquid jet

Abstract:
The temporal evolution of a thermal pattern observed on a heated wall by infrared camera is correlated with the propagation velocity of the thermal perturbations calculated by DNS. In the experiment the propagation velocity was measured by using PIV-based analysis of infrared images of the thermal pattern on the wall. To verify the experimental technique of image analysis, a sequence of synthetic images, simulating thermal patterns on the wall, was generated from the DNS solution, and the convective velocity was evaluated. It was found that the convective velocity of thermal structures obtained by PIV-based analysis of the experimental and synthetic images was in relatively good agreement with that calculated from the DNS solution. The present study confirmed that for a high Prandtl number fluid (water) the propagation velocity of the thermal perturbations is only about half of the convective velocity of the velocity perturbations. It was also found that the convection velocity observed for hot spots is distinctly lower than that for the cold spots.

Abstract:
Measurements were conducted on an eastern slope of the Salt Lake Basin (SLB) as a part of the Vertical Transport and Mixing Experiment (VTMX) conducted in October 2000. Of interest was the nocturnal boundary layer on a slope (in particular, katabatic flows) in the absence of significant synoptic influence. Extensive measurements of mean flow, turbulence, temperature, and solar radiation were made, from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred. The results show that near the surface (<25–50 m) the nocturnal flow is highly stratified and directed downslope, but at higher levels winds strongly vary in magnitude and direction with height and time, implying the domination of upper levels by air intrusions. These intrusions may peel off from different slopes surrounding the SLB, have different densities, and flow at their equilibrium density levels. The turbulence was generally weak and continuous, but sudden increases of turbulence levels were detected as the mean gradient Richardson number (GRN) dropped to about unity. With a short timescale GRN fluctuated on the order of a few tens of seconds while modulating with a longer (along-slope internal waves sloshing) timescale of about half an hour. The mixing efficiency (or the flux Richardson number) of the flow was found to be a strong function of GRN, similar to that found in laboratory experiments with inhomogeneous stratified shear flows. The eddy diffusivities of momentum and heat were evaluated, and they showed a systematic variation with GRN when scaled with the shear length scale and the rms vertical velocity of turbulence.

Abstract:
This paper deals with measurements of convective velocity of large-scale thermal structures, using the thin foil technique and infrared thermography to visualize the thermal pattern on the wall. An image correlation method is proposed to track the displacement of the observed thermal pattern. The idea of the method is similar to that of particle image velocimetry, but the thermal patterns on the heated wall are used, rather than tracing particles. On this basis, the thermal patterns created by the coherent structures of turbulent channel flow are examined. Particular attention is paid to the determination of the optimal parameters of image acquisition, including spatial and temporal separation. An attempt is made to relate momentum and scalar transport analyses by considering the propagation velocity of large-scale temperature structures. The proposed technique appears to be an attractive alternative for non-intrusive analysis of turbulent flow, especially, where opaqueness of channel walls excludes the use of optical methods.

Abstract:
An experimental and numerical study has been made of transient natural convection of water freezing in a cube-shaped cavity. The effect of the heat transfer through the side walls is studied in two configurations: with the cavity surrounded by air and with the cavity immersed in an external water bath of constant temperature. The experimental data for the velocity and temperature fields are obtained using liquid crystal tracers. The transient development of the ice/water interface is measured. The collected data are used as an experimental benchmark and compared with numerical results obtained from a Finite-difference code with boundary fitted grid generation. The computational model has been adopted to simulate as closely as possible the physical experiment. Hence, fully variable fluid properties are implemented in the code, and, to improve modelling of the thermal boundary conditions, the energy equation is also solved inside the bounding walls. Although the general behaviour of the calculated ice front and its volume matches observations, several details of the flow structure do not. Observed discrepancies between experimental and numerical results indicate the necessity of verifying and improving the usual assumptions for modelling ice formation.

Keywords:
Natural convection, freezing, phase change, experimental benchmark, water density anomaly, liquid crystals, particle image velocimetry and thermometry, boundary fitted grid, finite differences vorticity-vector potential method

Abstract:
The three-dimensional instability of an axisymmetric natural convection flow is investigated numericaUy using a global spectral Galerkin method. The linear stability problem separates for different azimuthal modes. This aUowsus to reduce the problem to a sequence of 2D-like problems. The formulation of the numerical approach and several test calculations are reported. The numerical results are successfully compared with an experiment on natural convection of water in a vertical cylinder, which shows an axisymmetry-breaking instability with a high azimuthal wavenumber.

Keywords:
Axisymmetry-breaking instability, natural convection, global Galerkin method

Abstract:
A semi-implicit finite element method (FEM) is presented for the two-dimensional computer simulation of solid-liquid phase change controlled by natural convection and conduction. The algorithm is based on a combination of (1) a projection method to uncouple velocity calculations from pressure calculations for incompressible fluid flow, (2) the backward Euler and explicit Adams-Bashforth schemes to effectively integrate diffusion and advection in time, and (3) an enthalpy-porosity approach to account for the latent heat effect on a fixed finite element grid. Credibility of the obtained numerical predictions is investigated through computational model verification and validation procedures. Commonly used benchmark problems are employed to verify the algorithm accuracy and performance. The natural convection of freezing pure water is studied experimentally through the use of sophisticated full-field acquisition experimental techniques. The measured velocity and temperature fields are compared with the pertinent calculations. The range of congruity of the experimental and numerical results is thoroughly studied, and potential reasons of some disparity in a local structure of the natural convection flow and in the interface shape are discussed.

Abstract:
A numerical and experimental study of unsteady natural convection during freezing of water is presented. The mathematical model for the numerical simulations is based on the enthalpy-porosity method in vorticity-velocity formulation, equations are discretised on a fixed grid by means of a finite volume technique. A fully implicit method has been adopted for the mass and momentum equations. Experiments are performed for water in a differentially heated cube surrounded by air. The experimental data for natural convection with freezing in the cavity are collected to create a reference for comparison with numerical results. The method of simultaneous measurement of the flow and temperature fields using liquid crystal tracers is used. It allows us to collect transient data on the interface position, and the temperature and velocity fields. In order to improve the capability of the numerical method to predict experimental results, a conjugate heat transfer problem was solved, with finite thickness and internal heat conductivity of the non-isothermal walls. These results have been compared with the simulations obtained for the idealised case of perfectly adiabatic side walls, and with our experimental findings. Results obtained for the improved numerical model shown a very good agreement with the experimental data only for pure convection and initial time of freezing process. As time passes the discrepancies between numerical predictions and the experiment became more significant, suggesting a necessity for further improvements of the physical model used for freezing water.

Abstract:
An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation, the solution of the Navier-Stokes equation for the axial components of the streaming velocity. The theoretical model was verified experimentally using a 32 MHz pulsed Doppler unit. The experimental acoustical fields were produced by three different 4 mm diameter flat and focused transducers driven by the transmitter generating the average acoustic power within the range from 1 microW to 6 mW. The streaming velocity was measured along the ultrasonic beam from 0 to 2 cm. Streaming was induced in a solution of water and corn starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water, changed from 0.3 to 40 grams of starch in 1 l of distilled water. For applied acoustic powers, the streaming velocity changed linearly from 0.2 to 40 mm/s. Both, the theoretical solutions for plane and focused waves and the experimental results were in good agreement. The streaming velocity field was also visualised using the particle image velocimetry (PIV) and two different evaluation methods. The first based on the FFT-based cross-correlation analysis between small sections for each pair of images and the second employing the algorithm of searching for local displacements between several images.

Abstract:
An optical Flow technique based on the use of Dynamic Programming has been applied to Particle Image Velocimetry thus yielding a significant increase in the accuracy and spatial resolution of the velocity field. Results are presented for calibrated synthetic sequences of images and for sequences of real images taken for a thermally driven flow of water with a freezing front. The accuracy remains better than 0.5 pixel/frame for tested two-image sequences and 0.2 pixel/frame for four-image sequences, even with a 10% added noise level and allowing 10% of particles of appear or disappear. A velocity vector is obtained for every pixel of the image.

Abstract:
Our aim is to explore, both experimentally and theoretically, the cumulative effects of small particle–liquid density difference, where the particles are used as tracers in recirculating flow. As an example we take a flow field generated in a differentially heated cavity. The main flow structure in such a cavity consists in one or two spiraling motions. Long‐term observations of such structures with the help of tracers (small particles) indicated that accumulation of the particles may set in at some flow regions. For theoretical insight into the phenomenon, a simple analytical model of recirculating (rotating) flow was studied. It was assumed that particles are spherical and rigid, and their presence does not affect the flow field. The particle Reynolds number is negligibly small, hence only the effects of particle–liquid density difference are of importance. Besides buoyancy, the effects of Saffman’s force and the inertial forces are also taken into account when calculating particle trajectories. Both cases were analyzed, particles with density slightly higher and lower than the fluid. It was found that in our case the inertial forces are egligible. In the numerical experiment trajectories of particles were investigated. The particles were allocated at random in the flow field obtained by numerical solution of the natural convection in the differentially heated cavity. In the experimental part, behavior of a dilute particle suspension in the convective cell was explored. In the model‐analytical study of a simple spiraling motion, it was found that due to the interaction of the recirculating convective flow field and the gravity‐buoyancy force, the particles may be trapped in some flow regions, whereas the rest of the flow field becomes particle‐free. This prediction agrees fairly well with the numerical and experimental findings.

Abstract:
The droplet separation from a liquid jet was investigated experimentally. Details of the shape of the thin liquid neck joining the droplet to its parent body were studied in terms of the fluid viscosity and the jet diameter. As the viscosity increased, the neck rapidly elongated creating a long thread. Its final diameter before rupture was approximately one micrometer and seems to be constant within wide range of parameters varied. One or multiple breakups of the micro-thread were observed, which produced micro-satellites, i.e. droplets in a micrometer range. The experimental results only partly confirmed the predictions of Eggers' (Phys. Rev. Lett. 71 (1993) 3458) similarity solution. The predicted shape of the pinch-off region well overlaps the long thread observed for very viscous liquids. However, the final jet diameter, retraction velocity of the thread and presence of multiple breakups differentiate the experimental evidence from the model expectations.

Abstract:
Nonlinear viscous droplet oscillations are analysed by solving the Navier-Stokes equation for an incompressible fluid. The method is based on mode expansions with modified solutions of the corresponding linear problem. A system of ordinary differential equations, including all nonlinear and viscous terms, is obtained by an extended application of the variational principle of Gauss to the underlying hydrodynamic equations. Results presented are in a very good agreement with experimental data up to oscillation amplitudes of 80% of the unperturbed droplet radius. Large-amplitude oscillations are also in a good agreement with the predictions of Lundgren & Mansour (boundary integral method) and Basaran (Galerkin-finite element method). The results show that viscosity has a large effect on mode coupling phenomena and that, in contradiction to the linear approach, the resonant mode interactions remain for asymptotically diminishing amplitudes of the fundamental mode.

Abstract:
The problem of transient natural convection in a cube-shaped cavity is investigated experimentally and numerically. The motion is driven by a sudden temperature difference applied to two opposite side walls of the vessel. The experiments are performed at a Rayleigh number of 1.66 × 105 and a Prandtl number of 1109, inside a 5 × 5 × 5 cm3 cavity made of Plexiglas, with two isothermal copper walls kept at a prescribed temperature. Numerical simulation has been performed using a finite difference vorticity-velocity model of the Navier-Stokes equation with the Boussinseq approximation. The theoretical predictions are found to be in good agreement with the experimental results.

Abstract:
The behavior of evaporating small diameter jets in a low‐pressure environment is studied experimentally. Charged coupled device (CCD) cameras connected to a computerized data logging system are employed for high‐speed imaging. Experiments at different jet velocities and environmental pressures have been performed with pure ether and ethanol, and also the mixtures of the two. Complex instability structures during the evaporation of the jet were observed. The recorded experimental evidences of these structures are presented and discussed.

Abstract:
An optical measuring method has been applied to determine the dynamic surface tension of aqueous solutions of heptanol. The method uses the frequency of an oscillating liquid droplet as an indicator of the surface tension of the liquid. Droplets with diameters in the range between 100 and 200 μm are produced by the controlled break-up of a liquid jet. The temporal development of the dynamic surface tension of heptanol-water solutions is interpreted by a diffusion controlled adsorption mechanism, based on the “three-layer” model of Ward and Tordai. Measured values of the surface tension of bi-distilled water, and the pure dynamic and static (asymptotic) surface tensions of the surfactant solutions are in very good agreement with values obtained by classical methods.

Abstract:
Finite-amplitude, axially symmetric oscillations of small (0.2 mm) liquid droplets in a gaseous environment are studied, both experimentally and theoretically. When the amplitude of natural oscillations of the fundamental mode exceeds approximately 10% of the droplet radius, typical nonlinear effects like the dependence of the oscillation frequency on the amplitude, the asymmetry of the oscillation amplitude, and the interaction between modes are observed. As the amplitude decreases due to viscous damping, the oscillation frequency and the amplitude decay factor reach their asymptotical values predicted by linear theory. The initial behaviour of the droplet is described quite satisfactorily by a proposed nonlinear inviscid theoretical model.

Abstract:
The thermal convection in a cubic cavity, with two opposite vertical walls kept at prescribed temperatures, is investigated experimentally. The Rayleigh numbers ranged from 104 to 2 × 107 and the Prandtl numbers from 5.8 to 6 × 103. The velocity and vorticity fields are shown. The temperature fields were visualized with the help of liquid crystals suspended as small tracer particles in the medium. It is observed that convection in the cavity is strongly three-dimensional. The streamlines spiral from the foci on the walls toward the foci in the vertical midplane and vice versa. The disappearance of one of the vortices midway between the center and the front or back wall is observed for RA > 6 × 104. The topological structures are discussed. The experimental observations are compared with numerical calculations found in the literature.

Keywords:
natural convection, rectangular enclosures

Abstract:
The distribution of droplets in a plane Hagen-Poiseuille flow of dilute suspensions has been measured by a special LDA technique. This method assumes a well defined relation between the velocity of the droplets and their lateral position in the channel. The measurements have shown that the droplet distribution is non-uniform and depends on the viscosity ratio between the droplets and the carrier liquid. The results have been compared with a theory by Chan and Leal describing the lateral migration of suspended droplets.

Abstract:
Two optical methods, light absorption and LDA, are applied to measure the concentration and velocity profiles of droplet suspensions flowing through a tube. The droplet concentration is non-uniform and has two maxima, one near the tube wall and one on the tube axis. The measured velocity profiles are blunted, but a central plug-flow region is not observed. The concentration of droplets on the tube axis and the degree of velocity profile blunting depend on relative viscosity. These results can be qualitatively compared with the theory of Chan and Leal.

Abstract:
Materials containing suspended micro- or nanomaterials are used extensively in multiple fields of research and industry. In order to understand the behavior of nanomaterials suspended in a liquid, the knowledge of particle stability and mobility is fundamental. For this reason, it is necessary to know the nanoscale solid-solid interaction and the hydrodynamic properties of the particles. In the presented research we used a hybrid Atomic Force Microscope coupled with Optical Tweezers system to measure the femtonewton scale interaction forces acting between single particles and the walls of a microchannel at different separation distances and environmental conditions. We show an important improvement in a typical detection system that increases the signal to noise ratio for more accurate position detection at very low separation distances.

Keywords:
Optical Tweezers, Atomic Force Microscopy, particle-wall interaction, colloid stability

Abstract:
The current task of contemporary fluid mechanics evidently moves from modeling large scale turbulence to lower, molecular scale limit, where assumption of a continuous and deterministic description becomes questionable again. Once the scaling length of flow becomes comparable with structure dimensions, transport phenomena are strongly modulated by molecular interactions and its proper interpretation needs involvement of deeper physics. New experimental tools largely help in understanding transport phenomena at nanoscales. In the following review we give few examples of problems appealing for new theoretical and numerical models embracing continuous flow modeling with molecular scale phenomena.

Abstract:
Comprehensive studies of drug transport in nanofibres based mats have been performed to predict drug release kinetics. The paper presents our approach to analyze the impact of fibers arrangement, one of the parameters varied in our parallel experimental studies. Drug encapsulation in submicron fibers and subsequent controlled release of drugs is a tedious task due to the large number of process and material parameters involved. In the numerical study we constructed a 3D finite element geometry representing nanofibrous cubic element. COMSOL Multiphysics has been used to assess the impact of the various purposed arrangements of fibers within the mat. Drug release from nanofibers was modeled by adsorption -desorption and diffusion equation, where drug diffusion coefficient in the fluid between the fibers was altered depending on porosity of the material. Our study shows that for the same material porosity drug release from the matrix of regularly oriented fibers is slower than from randomly oriented, isotropic nanofibrous material. Also by decreasing distance between the fibers drug transport rate is reduced.

Keywords:
Nanofibres, finite elements, drug release modelling

Abstract:
In this preliminary work we introduce a new method for verification of the no-slip boundary condition on the liquid-solid interface, by analyzing variations in Brownian motion coefficients of colloidal nanoparticles as a function of distance from the wall. The experimental investigations are performed in a small channel using an epi-fluorescent microscope. For precise measurements close to the wall an evanescent wave illumination is used. The experimental data obtained for 300nm particles gave us evidence of relatively large (0.3μm) slip length. The experiments are supplemented by two-dimensional Molecular Dynamics simulations.

Keywords:
small-scale turbulence, cloud, cloud droplets, evaporation

Abstract:
This paper presents numerical analysis of the hydrodynamic flow focusing in rectangular microchannels. The low Reynolds numer pressure driven flow in symmetric system of crossed channels with three inlets and one outlet is investigated. The numerical model is used to elucidate the origin of broadening of the focused flow sheet observed experimentally close to the side walls of the outlet channel. It is found that the observed broadening is mainly due to the residual flow inertia and can be totally eliminated if flow Reynolds number is less than one.

Abstract:
A fast discrete model for the simulations of thin charged jets produced during the electrospinning process is derived, based on an efficient implementation of the boundary element method for the computation of electrostatic interactions of the jet with itself and with the electrodes. Short-range electrostatic forces are evaluated with slender-body analytical approximations, whereas a hierarchical force evaluation algorithm is used for long-range interactions. Qualitative comparisons with experiments is discussed.

Keywords:
modelling electrospinning, electrostatic interactions, BEM

Abstract:
Gaining knowledge of the solid-solid interactions and hydrodynamic and mechanical properties is crucial for understanding the processes and dynamics of molecular interactions, biological and nano- structures and also to find their future applications. Atomic force microscopy (AFM) is a versatile technique for nanoscale imaging purposes and for quantify analysis of force at the nanonewton scale. Unfortunately, due to technical limitations and restrictions related to the mechanical properties of cantilevers, this technique cannot detect small forces on the femtonewton scale and analyse the stiffness of very soft materials such as biological tissues or hydrogels. AFM is also use to manipulate materials, however, AFM-based manipulation systems are slow and imprecise. To distinguish, Optical Tweezers (OT) are scientific instruments that can trap small particles and manipulate nano- and micro-materials with much higher precision. The AFM / OT hybrid system is a high-resolution imaging instrument with a lower force limit of detection. It is capable of non-invasively manipulating of nanomaterials, single molecules and living cells, measuring forces with femtonewton accuracy, detecting motion with nanometer (10-9 m) precision and to manipulate objects, but also to obtain images directly in the same sample. The combination of AFM with Optical Tweezers will provide significant advances in biophysical research and in the study of the mechanical properties of nanomaterials [1]. In our system we combine Optical Tweezers with commercial AFM to create an instrument capable of working in hybrid mode. It allows simultaneous manipulation of biological systems of greater complexity and the analysis of their properties. Performed by us, experiments showed that AFM/OT system is a unique technique for visualization of the analysed materials, trapping single micro-objects and measure the interactions (in the range of femtonewton) between single particles. The results obtained by AFM/OT confirm that this equipment is a very useful technique also for determination the mechanical properties of very soft materials (e.g. hydrogels) [2].

Abstract:
Pulsatile drug delivery systems are gaining a lot of interest because of their numerous advantages, especially when compared to conventional pharmaceutical dosage forms [1]. These materials are time- and site-specific drug delivery systems which can minimize deleterious side effects of conventional drug administration systems. Nevertheless, the delivery systems that are of particular interest are the ones with reversible on-off switching capability, because they allow the delivery of therapeutic agents at the proper time after a predetermined lag time. Among the polymers used for biomedical applications, hydrogels are a class of materials of particular significance, because they can provide spatial and temporal control over the release of various types of drugs. Stimuli-responsive hydrogels can release drugs on-demand with a fast release rate through different mechanisms. The effectiveness of this process can be maximized using nanostructured materials with a large surface-area-to-volume ratio such as electrospun nanofibers. Current challenges in the development of hydrogel electrospun fibrous nanomaterials lie in the lack of spinnability of pure hydrogel precursor solutions. Addressing this issue, we firstly designed a new core-shell nanofibrous material in which the poly(N-isopropylacrylamide)-derivative hydrogel is confined within a shell of a spinnable polymer (Figure 1a). Alternatively, we developed a scaffold material in which electrospun nanofibers loaded with different bioactive molecules where surrounded by a stimuli-responsive hydrogel (Figure 1b). Morphological and chemical characterization as well as drug release studies were carried out to confirm the material’s ability to supply different doses of drugs on demand and to study the release mechanism.

Abstract:
Single-material organic solar cells (SMOCs) based on fullerene-grafted polythiophenes are considered promising devices for organic solar cells (OSCs). The main efforts in this field focus on the chemical tailoring of polymer molecules to reduce the side effects of charge recombination. These advances have made it possible to obtain a power conversion efficiency (PCE) close to conventional bulk heterojunction (BHJ) cells. So far, however, SMOCs still show inadequate efficiencies due to ineffective charge transport. Here we show how SMOC efficiency can be strongly increased by optimizing the supramolecular and nanoscale structure of the active layer, while achieving the highest reported efficiency value (PCE = 5.58%) [1]. The enhanced performance may be attributed to well-packed and properly oriented polymer chains. The hierarchical structure is given by the incorporation of electrospun one-dimensional nanostructures obtained from polymer chain stretching. Our results suggest that the active material optimization obtained by the use of electrospun nanofibers plays a key role in the development of efficient SMOCs.

Abstract:
Stimuli-responsive drug delivery systems are gaining a lot of interest due to their numerous advantages, especially when compared to conventional pharmaceutical dosage forms. One of the examples is photo stimulation that together with nanometer size agents, having high absorption in the near-infrared region, generate heat due to the interaction with light. Stimuli-responsive hydrogels with gold nanorods (AuNRs), that are used as photothermal converters, can aid in releasing drugs on-demand with a fast release rate through different mechanisms. Here we report an easy method for preparing AuNRs encapsulated in a poly(N-isopropylacrylamide) (PNIPAm) hydrogel that release water-soluble drugs due to photo stimulation. PNIPAm-AuNRs demonstrated remote, pulsatile drug release and ex vivo action after irradiation using a NIR laser. Morphological and chemical characterization as well as drug release studies were carried out to confirm the material’s ability to supply different doses of drugs on demand and to study the release mechanism. By combining the photothermal property of AuNRs and thermal-responsive effect of PNIPAm, the hydrogel shows fast thermal/photoresponse, high heating rate, high structural integrity and increased drug release due to phase change mechanism.

Keywords:
drug delivery systems, nanofibers

Abstract:
Atomic force microscopy (AFM) is an evolution of scanning tunnelling microscopy that immediately gained popularity thanks to its ability to analyse nanomaterials. Initially, AFM was developed for nanomaterials imaging purposes, however the development of new features made it the most commonly used tool for studying the biophysical properties of biological samples. On the other hand, atomic force microscopy has limited use for examining sub-piconewton forces. Few techniques have been developed to measure forces below the AFM limit of detection. Among them, optical tweezers (OT) stand out for their high resolution, flexibility, and because they make it possible to accurately manipulate biological samples and carry out biophysics experiments without side effects thanks to their non-invasive properties. The combination of AFM with other techniques in the last decades has significantly extended its capability. The improvement of the AFM force resolution by developing a hybrid double probe instrument based on the combination of AFM and OT has great potential in cell or molecular biology. [1] We outline principles of atomic force microscopy combined with optical tweezers (AFM/OT) developed by our team underlying the techniques applied during the design, building and instrument use stages. We describe the experimental procedure for calibration of the system and we prove the achievement of a higher resolution (force: 10 fN – spatial: 0.1 nm – temporal: 10 ns) than the stand alone AFM. We show the use of the hybrid equipment in a number of different biophysics experiments performed employing both AFM and OT probes. The presented studies include the demonstration of simultaneous high-precision nanomanipulation and imaging, the evaluation of single biomolecule mechanical properties and the single cell membrane activation and probing. Finally, we show the further potential applications of our AFM/OT.

Keywords:
AFM, Optical Tweezers

Keywords:
thermal fluctuations, lateral migration, flexible filaments

Abstract:
Electrospun nanofibers are increasingly studied thanks to their potential applications in biomedical devices that include drug delivery systems and tissue engineering scaffolds [1]. Numerous synthetic and natural polymers were used to develop nanofibrous materials. Nanostructured materials high porosity, surface-to- volume ratio together with the ease in surface functionalization and drug incorporation, make them perfect candidates for the development of hemostats. Immediate hemorrhage management becomes crucial to preventing death and serious injury in emergency situations. Severe injuries caused by e.g. traffic accidents are the third leading cause of death worldwide [2]. Research on medical incidents of soldiers stationed in Iraq in 2003-2004 showed that the main cause of death was massive hemorrhage that led to death in about 51% of the rescued soldiers [3]. There is no universal dressing and despite the development of new hemostats, they fail in many preclinical studies. Therefore, there is a need to define most important nanofibrous material characteristics that are responsible for rapid and effective bleeding arrest. There is little research on nanostructured hemostats, regarding the impact of nanofibrous surface on blood and its components. Nonetheless, because of the wide use of nanofibres in wound dressings, artificial blood vessels as well as heart valves, there is knowledge helpful in determining material surface chemistry, wettability and other, which can affect blood coagulation. The very first findings appeared in the research where it was found that even polymers having excellent antiplatelet adhesion abilities, triggered increased platelet adhesion and activation when they were in the form of nanofibers. In several other studies, scaffold morphology, was found to have larger impact on platelet adhesion and activation than differences in the chemistry of the polymers used [4]. More specifically, it was found that materials with fiber diameter higher than 1 µm triggered higher platelet adhesion and aggregation than smaller fibers. In other research, nanofiber stiffness was assessed as more dominating than biological moieties and surface roughness of the nanofiber [5]. In spite of all, analyzed literature presents many contradictory results or findings that had low or no impact on blood clotting in research results of other groups. Hence, additional research and novel experimental methods are needed to find nano features that impact hemostat efficiency.

Keywords:
blood-biomaterial interactions, nanofibers, clotting

Keywords:
Atomic force microscopy/optical tweezers, Nanomanipulation, Single particles analysis, Interaction force measurement, DLVO theory

Keywords:
Hydrogel Nanofilaments, Bending Dynamics, Poiseuille Flow, Electrospinning

Abstract:
Atomic force microscopy (AFM) is the most commonly used method of direct force evaluation, but due to its technical limitations this single probe technique is unable to detect forces with femtonewton resolution. We present the development of a combined atomic force microscopy and optical tweezers (AFM/OT) instrument. The optical tweezers system provides us the ability to manipulate small dielectric objects and to use it as a high spatial and temporal resolution displacement and force sensor in the same AFM scanning zone. We demonstrate the possibility to develop a combined instrument with high potential in nanomechanics, molecules manipulation and biologic al studies. The presented study is aimed to quantify the interaction forces between two single polystyrene particles in the femtonewton scale by using the developed AFM/OT equipment.

Keywords:
optical trap, nanomanipulation, femtonewtons

Abstract:
Mobility of hydrogel nanofilaments suspended in liquid is investigated to gain basic knowledge on hydrodynamic interactions biased by Brownian fluctuations. Typical for long macromolecules effects like spontaneous conformational changes and cross-flow migration are observed and evaluated. The collected experimental data can be used to validate assumptions present in numerical models describing intercellular transport of long biomolecules.

Keywords:
persistence length, macromolecules, electrospinning, DNA, Brownian motion

Abstract:
We propose a microscale experimental model in form of highly deformable nanofilaments, which permits for precise optical measurements and to evaluate hydrodynamic interactions (mobility). The conducted research includes determination of the mechanical properties of elastic hydrogel nanofilaments obtained by electrospinning that can serve as experimental benchmark to validate theoretical and numerical models describing dynamics of long biological molecules (e.g. proteins, DNA). Nanofilaments mechanical properties are determined by studying their dynamic bending. in shear flow and deformations due to the thermal fluctuations (Brownian motion). These results are compared with AFM nanoindentation measurements. Data obtained from this research project will be a base to crea te biocompatible nanoobjects that can become tools for the regeneration of tissue (e.g. neural tissue).

Keywords:
Biocompatible nanoobjects, highly deformable nanofilaments, regeneration of tissue

Abstract:
Controlled drug delivery systems are used to improve the conventional administration of drugs. One of the main challenges is to synthesize materials able to find a defined target and to release drugs in a controlled manner [1]. Several research tasks have been focused on developing ideal drug delivery systems made by hydrogel due to their unique properties [2]. The present study is based on the idea that soft and flexible nanomaterials can easily travel in crowed environments of body fluids and biological tissues. Modification of their mechanical properties obtained by changing of the cross-linker amount may give us the possibility to tune the material rigidity according to desired application. Here, we describe a novel method based on coaxial electrospinning for obtaining highly flexible hydrogel nanofilaments able to transport and release dedicated molecules. Two different types of hydrogels (poly(N,Nisopropyl acrylamide) and polyacrylamide) with three polymer/cross-linker ratios were produced and deeply studied. The nanofilaments morphology was characterized and the release of bovine serum albumin as a function of time was quantified. Mechanical properties of highly deformable hydrogel nanofilaments were evaluated by bending dynamics and Brownian motion observation techniques. The calculated mechanical properties were compared with data obtained by nanoindention. The results highlight the crucial role of morphology and stiffness on mobility of nanofilaments colloid systems. The information gained are fundamental to design nanoobjects with well-defined chemical and physical behaviour.

Keywords:
Nanofilaments, electrospinning, core-shell method, hydrogel

Abstract:
In this talk we would like to tackle general question of contemporary fluid dynamics, how far its assumption of a continuous, smooth medium remains useful when size and time scales start to approach molecular ones. The question is not trivial and seems to depend on several additional factors usually minored. For example, when full Navier-Stokes equations are replaced by their linear approximation we are loosing basic characteristics of convective motion, and still we use such approach. Once our fluid becomes granular matter with its own internal properties, proper interpretation of flow interactions with other molecular structures probably needs deeper physics. But still we try to convert such problem to the classical macro/micro scale description. Hence a general question arises, how small does a fluid have to be before it is not a fluid anymore?

Keywords:
microfluidics, nanofluids, Brownian motion, nanofilaments

Keywords:
Nanofilaments, hydrogel filaments, nanofibres, long nanoobjects deformability

Keywords:
nanofilaments, hydrogel, long molecules flexibility

Keywords:
drug delivery, electrospinning, mathematical modeling, nanofibres

Keywords:
elektroprzędzenie, nanowłókna, uwalnianie leków, TBI

Keywords:
nanomaty, modelowanie uwalniania leku

Keywords:
laser ablation, graphite, carbon nanotubes

Keywords:
electrospinning, flexible nanorods, Brownian motion

Keywords:
nanomanipulation, optical trap, optical tweezers

Keywords:
microfluidics, lab on a chip, droplets, T-junction

Keywords:
Nanoparticles, Brownian motion, hydrodynamic diameter

Keywords:
Nanoparticles, polystyrene beads, surface properties, atomic force microscopy, hydrodynamic properties

Keywords:
brain, drug delivery, nanofibres, mathematical modelling

Abstract:
The paper contains our attempts to estimate diffusion parameters of nanofibers actually applied as protective mats for neurosurgery. Measurements of concentration profiles of fluorophore released from stained nanofibres are performed. The two release systems are investigated: solid nanofibres and core-shell nanofibres with targeted drug simulator encapsulated inside nanofibres. The gathered information allows us to estimate parameters necessary for controlling drug release profiles.

Keywords:
Nanofibers, Electrospinning, Drug Delivery Systems

Abstract:
This paper describes the results of our preliminary studies on Drug Delivery Systems. Two distinct types of drugs are being investigated: lipophylic (soluble in organic solvents) and hydrophylic (soluble in water). Direct measurements of drugs and dye release from nanofibers were done for application in an animat model - rat.

Keywords:
Electrospinnig, Nanofibers, Drug Delivery Systems

Abstract:
Nanofibers produced by electrospinning of biologically active substances became attractive material for encapsulating living cells, bacteria, and drugs for targeted therapy. Here, we aim to use nanofiber matrices as neurosurgery protective membranes and drug carriers. Proper administration of drugs requires precise control of the diffusion process during the time of release of days or even weeks. Construction of such system is a tedious experimental task. To avoid hundreds of tests it is aimed to build a numerical model including essential information about composition, process conditions, and fibers geometry necessary to construct suitable polymer matrices for dedicated drug delivery systems.

Keywords:
drug delivery, electrospinning, nanofibers