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Abstract:
This article discusses the morphology and thermomechanical properties of graphene oxide (GO) paper sheets and GO paper composites reinforced with carbon fibers. GO paper was fabricated using GO paste obtained by the condensation of GO aqueous solution synthesized using the Hummers' method. Carbon fibers were implemented to improve the mechanical properties of the pristine GO paper. All the investigated papers were subjected to thermal treatment to check thermo-related morphological and mechanical properties. The results presented in this study allowed for the deeper insight into morphological, structural, and mechanical volume and surface-related properties of pristine GO and GO-based composite materials reinforced with carbon fibers. We showed that there are two important factors that should be taken into consideration for the design and fabrication of GO-based papers. These factors were the concentration of the reinforcing agent and the thermal reduction of the papers. Both factors have influenced the final properties of the resulting GO-based papers. For the first time, it was revealed how the addition of the reinforcing material affects the GO paper thermal expansion coefficient.

Keywords:
Flake graphene, Graphene oxide, Graphene oxide paper, Carbon fibers, Mechanical properties

Abstract:
Fused Deposition Modelling (FDM) technique has been widely utilized in fabrication of 3D porous scaffolds for tissue engineering (TE) applications. Surprisingly, although there are many publications devoted to the architectural features of the 3D scaffolds fabricated by the FDM, none of them give us evident information about the impact of the diameter of the fibres on material properties. Therefore, the aim of this study was to investigate, for the first time, the effect of the diameter of 3D-printed PCL fibres on variations in their microstructure and resulting mechanical behaviour. The fibres made of poly(ε-caprolactone) (PCL) were extruded through commonly used types of nozzles (inner diameter ranging from 0.18 mm to 1.07 mm) by means of FDM technique. Static tensile test and atomic force microscopy working in force spectroscopy mode revealed strong decrease in the Young's modulus and yield strength with increasing fibre diameter in the investigated range. To explain this phenomenon, we conducted differential scanning calorimetry, wide-angle X-ray-scattering, Fourier-transform infrared spectroscopy, infrared and polarized light microscopy imaging. The obtained results clearly showed that the most prominent effect on the obtained microstructures and mechanical properties had different cooling and shear rates during fabrication process causing changes in supramolecular interactions of PCL. The observed fibre size-dependent formation of hydrogen bonds affected the crystalline structure and its stability. Summarising, this study clearly demonstrates that the diameter of 3D-printed fibres has a strong effect on obtained microstructure and mechanical properties, therefore should be taken into consideration during design of the 3D TE scaffolds.

Keywords:
fused deposition modelling, polycaprolactone, mechanical properties, hydrogen bonds, microstructure

Abstract:
Liquid-crystal-based biomaterials provide promising platforms for the development of dynamic and responsive interfaces for tissue engineering. Cholesteryl ester liquid crystals (CLCs) are particularly well suited for these applications, due to their roles in cellular homeostasis and their intrinsic ability to organize into supramolecular helicoidal structures on the mesoscale. Here, we developed a nonwoven CLC electrospun scaffold by dispersing three cholesteryl ester-based mesogens within polycaprolactone (PCL). We tuned the ratio of our mesogens so that the CLC would be in the mesophase at the cell culture incubator temperature of 37°C. In these scaffolds, the PCL polymer provided an elastic bulk matrix while the homogeneously dispersed CLC established a viscoelastic fluidlike interface. Atomic force microscopy revealed that the 50% (w/v) cholesteryl ester liquid crystal scaffold (CLC-S) exhibited a mesophase with topographic striations typical of liquid crystals. Additionally, the CLC-S favorable wettability and ultrasoft fiber mechanics enhanced cellular attachment and proliferation. Increasing the CLC concentration within the composites enhanced myoblast adhesion strength promoted myofibril formationin vitrowith mouse myoblast cell lines.

Abstract:
One promising strategy to reconstruct bone defects relies on 3D printed porous structures. In spite of several studies having been carried out to fabricate controlled, interconnected porous constructs, the control over surface features at, or below, the microscopic scale remains elusive for 3D polymeric scaffolds. In this study, we developed and refined a methodology which can be applied to homogeneously and reproducibly modify the surface of polymeric 3D printed scaffolds. We have demonstrated that the combination of a polymer solvent and the utilization of ultrasound was essential for achieving appropriate surface modification without damaging the structural integrity of the construct. The modification created on the scaffold profoundly affected the macroscopic and microscopic properties of the scaffold with an increased roughness, greater surface area, and reduced hydrophobicity. Furthermore, to assess the performance of such materials in bone tissue engineering, human mesenchymal stem cells (hMSC) were cultured in vitro on the scaffolds for up to 7 days. Our results demonstrate a stronger commitment toward early osteogenic differentiation of hMSC. Finally, we demonstrated that the increased in the specific surface area of the scaffold did not necessarily correlate with improved adsorption of protein and that other factors, such as surface chemistry and hydrophilicity, may also play a major role.

Keywords:
surface modification, solvent treatment, polycaprolactone, BMP-2 adsorption

Abstract:
Biodegradable 3D-printed polycaprolactone scaffolds for bone tissue engineering applications have been extensively studied as they can provide an attractive porous architecture mimicking natural bone, with tunable physical and mechanical properties enhancing positive cellular response. The main drawbacks of polycaprolactone-based scaffolds, limiting their applications in tissue engineering are: their hydrophobic nature, low bioactivity and poor mechanical properties compared to native bone tissue. To overcome these issues, the surface of scaffolds is usually modified and covered with a ceramic layer. However, a detailed description of the adhesion forces of ceramic particles to the polymer surface of the scaffolds is still lacking. Our present work is focused on obtaining PCL-based composite scaffolds to strengthen the architecture of the final product. In this manuscript, we report qualitative and quantitative evaluation of low temperature plasma modification followed by detailed studies of the adhesion forces between chemically attached ceramic layer and the surface of polycaprolactone-nanohydroxyapatite composite 3D-printed scaffolds. The results suggest modification-dependent alteration of the internal structure and morphology, as well as mechanical and physical scaffold properties recorded with atomic force microscopy. Moreover, changes in the material surface were followed by enhanced adhesion forces binding the ceramic layer to polymer-based scaffolds.

Keywords:
surface modification, low temperature plasma, atomic force microscopy, bone tissue engineering

Abstract:
Composite scaffolds of bioactive glass (SiO2-CaO) and bioresorbable polyesters: poly-L-lactic acid (PLLA) and polycaprolactone (PCL) were produced by polymer coating of porous foams. Their structure and mechanical properties were investigated in micro and nanoscale, by the means of scanning electron microscopy, PeakForce Quantitative Nanomechanical Property Mapping (PF-QNM) atomic force microscopy, micro-computed tomography and contact angle measurements. This is one of the first studies in which the nanomechanical properties (elastic modulus, adhesion) were measured and mapped simultaneously with topography imaging (PF-QNM AFM) for bioactive glass and bioactive glass – polymer coated scaffolds. Our findings show that polymer coated scaffolds had higher average roughness and lower stiffness in comparison to pure bioactive glass scaffolds. Such coating-dependent scaffold properties may promote different cells-scaffold interaction.

Keywords:
bone tissue engineering, composite scaffold, bioactive glass, mmechanical properties

Abstract:
In this paper, the effect of the presence of L929 fibroblast cells and a cyclic load application on the kinetics of the degradation of amorphous PLGA films was examined. Complex micro and nano morphological, mechanical and physico-chemical studies were performed to assess the degradation of the tested material. For this purpose, molecular weight, glass transition temperature, specimen morphology (SEM, μCT) and topography (AFM) as well as the stiffness of the material were measured. The study showed that the presence of living cells along with a mechanical load accelerates the PLGA degradation in comparison to the degradation occurring in acellular media: PBS and DMEM. The drop in molecular weight observed was accompanied by a distinct increase in the tensile modulus and surface roughness, especially in the case of the film degradation in the presence of cells. The suspected cause of the rise in stiffness during the degradation of PLGA films is a reduction in the molecular mobility of the distinctive superficial layer resulting from severe structural changes caused by the surface degradation. In conclusion, all the micro and nanoscale properties of amorphous PLGA considered in the study are sensitive to the presence of L929 cells, as well as to a cyclic load applied during the degradation process.

Keywords:
L929, aliphatic polyester, stiffness rise

Abstract:
Electrospun nanofibrous scaffolds are willingly used in tissue engineering applications due to their tunable mechanical, chemical and physical properties. Additionally, their complex openworked architecture is similar to the native extracellular matrix of living tissue. After implantation such scaffolds should provide sufficient mechanical support for cells. Moreover, it is of crucial importance to ensure sterility and hydrophilicity of the scaffold. For this purpose, a low temperature surface plasma treatment can be applied. In this paper, we report physico-mechanical evaluation of stiffness and adhesive properties of electrospun mats after their exposition to low temperature plasma. Complex morphological and mechanical studies performed with an atomic force microscope were followed by scanning electron microscope imaging and a wettability assessment. The results suggest that plasma treatment can be a useful method for the modification of the surface of polymeric scaffolds in a desirable manner. Plasma treatment improves wettability of the polymeric mats without changing their morphology.

Keywords:
Atomic force microscopy, Surface modification, Electrospun fibers, RF plasma treatment, Tissue engineering, Nanomaterial

Abstract:
Tissue engineering holds great potential in the production of functional substitutes to restore, maintain or improve the functionality in defective or lost tissues. So far, a great variety of techniques and approaches for fabrication of scaffolds have been developed and evaluated, allowing researchers to tailor precisely the morphological, chemical and mechanical features of the final constructs. Electrospinning of biocompatible and biodegradable polymers is a popular method for producing homogeneous nanofibrous structures, which might reproduce the nanosized organization of the tendons. Moreover, composite scaffolds obtained by incorporating nanoparticles within electrospun fibers have been lately explored in order to enhance the properties and the functionalities of the pristine polymeric constructs. The present study is focused on the design and fabrication of biocompatible electrospun nanocomposite fibrous scaffolds for tendon regeneration. A mixture of poly(amide 6) and poly(caprolactone) is electrospun to generate constructs with mechanical properties comparable to that of native tendons. To improve the biological activity of the constructs and modify their topography, wettability, stiffness and degradation rate, we incorporated silica particles into the electrospun substrates. The use of nanosize silica particles enables us to form bead-on-fiber topography, allowing the better exposure of ceramic particles to better profit their beneficial characteristics. In vitro biocompatibility studies using L929 fibroblasts demonstrated that the presence of 20 wt% of silica nanoparticles in the engineered scaffolds enhanced cell spreading and proliferation as well as extracellular matrix deposition. The results reveal that the electrospun nanocomposite scaffold represents an interesting candidate for tendon tissue engineering.

Abstract:
Four kinds of biodegradable polymers were employed to prepare bioresorbable coatings on Mg-2.0Zn-0.98Mn (ZM21) alloy to understand the relationship between polymer characteristics, protective effects on substrate corrosion, cytocompatibility and cell functionality. Poly-l-lactide (PLLA), poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or poly(lactic-co-glycolic) acid (PLGA) was spin-coated on ZM21, obtaining a smooth, non-porous coating less than 0.5 μm in thickness. Polymer coating characterization, a degradation study, and biocompatibility evaluations were performed. After 4 w of immersion into cell culture medium, degradation of PLGA and PLLA coatings were confirmed by ATR-FTIR observation. The coatings of PLLA, PHB and PHBV, which have lower water permeability and slower degradation than PLGA, provide better suppression of initial ZM21 degradation and faster promotion of human osteosarcoma cell growth and differentiation.

Keywords:
Biodegradable metal, Magnesium alloy, Biodegradable polymer, SaOS-2 differentiation, Calcification