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Abstract:
A novel metal matrix composites (MMC) with Mg matrix reinforced with natural filler in the form of Didymosphenia geminata frustules (algae with distinctive siliceous shells) are presented in this work. Pulse plasma sintering (PPS) was used to manufacture Mg-based composites with 1, 5 and 10 vol.% ceramic filler. As a reference, pure Mg was sintered. The results show that the addition of 1 vol.% Didymosphenia geminata frustules to the Mg matrix increases its corrosion resistance by supporting passivation reactions, and do not affect the morphology of L929 fibroblasts. Addition of 5 vol.% the filler does not cause cytotoxic effects, but it supports microgalvanic reactions leading to the greater corrosion rate. Higher content than 5 vol.% the filler causes significant microgalvanic corrosion, as well as increases cytotoxicity due to the greater micro-galvanic effect of the composites containing 10 and 15 vol.% diatoms. The results of contact angle measurements show the hydrophilic character of the investigated materials, with slightly increase in numerical values with addition of amount of ceramic reinforcement. The addition of Didymosphenia geminata frustules causes changes in a thermo-elastic properties such as mean apparent value of coefficient of thermal expansion (CTE) and thermal conductivity (λ). The addition of siliceous reinforcement resulted in a linear decrease of CTE and reduction in thermal conductivity over the entire temperature range. With the increasing addition of Didymosphenia geminata frustules, an increase in strength with a decrease in compressive strain is observed. In all composites an increase in microhardness was attained.
The results clearly indicate that filler in the form of Didymosphenia geminata frustules may significantly change the most important properties of pure Mg, indicating its wide potential in the application of Mg-based composites with a special focus on biomedical use.

Keywords:
Metal-matrix composites (MMCs),Pulse plasma sintering (PPS),Ceramic filler,Microstructure,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:
One promising strategy to reconstruct osteochondral defects relies on 3D bioprinted three-zonal structures comprised of hyaline cartilage, calcified cartilage, and subchondral bone. So far, several studies have pursued the regeneration of either hyaline cartilage or bone in vitro while—despite its key role in the osteochondral region—only few of them have targeted the calcified layer. In this work, we present a 3D biomimetic hydrogel scaffold containing β-tricalcium phosphate (TCP) for engineering calcified cartilage through a co-axial needle system implemented in extrusion-based bioprinting process. After a thorough bioink optimization, we showed that 0.5% w/v TCP is the optimal concentration forming stable scaffolds with high shape fidelity and endowed with biological properties relevant for the development of calcified cartilage. In particular, we investigate the effect induced by ceramic nano-particles over the differentiation capacity of bioprinted bone marrow-derived human mesenchymal stem cells in hydrogel scaffolds cultured up to 21 d in chondrogenic media. To confirm the potential of the presented approach to generate a functional in vitro model of calcified cartilage tissue, we evaluated quantitatively gene expression of relevant chondrogenic (COL1, COL2, COL10A1, ACAN) and osteogenic (ALPL, BGLAP) gene markers by means of RT-qPCR and qualitatively by means of fluorescence immunocytochemistry.

Keywords:
alginate, gelatin methacrylate, ß-tricalcium phosphate TCP, bioprinting, coaxial needle, calcified cartilage

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

Abstract:
The progress in the treatment of chronic diseases of civilization that occurred in recent years, led to a significant prolongation of median survival time of the developed countries societies. Organ transplantation has revolutionized medicine as it became possible to replace an irreversibly diseased organ. However, at the moment we can observe a significant shortage of organs for transplantation, which forces doctors to accept those coming from more and more expanding criteria donors. No doubt, the number of donors, at best, will certainly not grow. Tissue engineering and regenerative medicine methods are extremely promising, in particular bioprinting of tissues and organs, which begun to develop at the beginning of the XXI century. Article highlights possible future direction of organ transplantation.