Emilija Zdraveva

Synthetic vs natural scaffolds for human limbal stem cells

Aim To investigate the impact of synthetic electrospun polyurethane (PU) and polycaprolactone (PCL) nanoscaffolds, before and after hydrolytic surface modification, on viability and differentiation of cultured human eye epithelial cells, in comparison with natural scaffolds: fibrin and human amniotic membrane. Methods Human placenta was taken at elective cesarean delivery. Fibrin scaffolds were prepared from commercial fibrin glue kits. Nanoscaffolds were fabricated by electrospinning. Limbal cells were isolated from surpluses of human cadaveric cornea and seeded on feeder 3T3 cells. The scaffolds used for viability testing and immunofluorescence analysis were amniotic membrane, fibrin, PU, and PCL nanoscaffolds, with or without prior NaOH treatment. Results Scanning electron microscope photographs of all tested scaffolds showed good colony spreading of seeded limbal cells. There was a significant difference in viability performance between cells with highest viability cultured on tissue culture plastic and cells cultured on all other scaffolds. On the other hand, electrospun PU, PCL, and electrospun PCL treated with NaOH had more than 80% of limbal cells positive for stem cell marker p63 compared to only 27%of p63 positive cells on fibrin. Conclusion Natural scaffolds, fibrin and amniotic membrane, showed better cell viability than electrospun scaffolds. On the contrary, high percentages of p63 positive cells obtained on these scaffolds still makes them good candidates for efficient delivery systems for therapeutic purposes.

On a Relationship Between Normal-Shear Coefficients and Tensile Moduli in Anisotropic Materials

In general, stress and deformation tensors of anisotropic linear elastic materials are related by the fourth order compliance/elasticity tensor. It has been observed that in the case of a planar (2D) orthotropic material the off-diagonal component of the compliance tensor known as normal-shear coefficient is equal to one half of the derivative of corresponding tensile compliance with respect to the angle of rotation of coordinate axes. A detailed analysis of the transformation law for the components of the compliance tensor is given, including the proof that the same relation also holds in the general case of planar anisotropic materials. In the selected illustrative examples polar diagrams of tensile moduli and normal-shear coefficients are shown for representative cases of woven fabrics and textile composites.

The efficacy of electrospun polyurethane fibers with TiO2 in a real time weathering condition

This study focuses on the behavior of electrospun polyurethane fibers filled with nano, micro spheres and nanotube TiO2, thus nTiO2, mTiO2 or TiNT, under real time ultraviolet (UV) radiation. Analyses were conducted using scanning electron microscopy (SEM), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis and differential scanning calorimetry (DSC) techniques. Significant changes of thermoplastic polyurethane (TPU) + 0.5% nTiO2 and TPU + 0.5% mTiO2 fibers morphology, that is, agglomerated TiO2 particles, were observed on material surfaces due to TPU fiber degradation, also supported by FTIR spectra given as reduction in the peaks intensities after UV radiation, especially in the case of TPU + 0.5% nTiO2. Further, after UV radiation, the initial degradation temperature reduction of the hard segment for all materials was up to 40℃. A significant reduction in the final degradation temperature (from 397.8℃ to 274.1℃) was noticed for the mTiO2 filled fibers, suggesting their photocatalytic activity, while Tg was increased up to 20℃ for almost all fillers added to TPU, thus indicating lower molecular chain mobility upon UV radiation.

Photooxidative Stability of Polyurethane/Polycarbonate Blends

In this work the photooxidative stability of polyurethane/polycarbonate (PU/PC) blends was studied. Poly (ester–urethane) elastomers based on poly (caprolactone) glycol and an aromatic type of diisocyanate (MDI) were synthesized by a prepolymer procedure. Blends of PU and PC with different weight ratios were prepared using a Brabender mixer. Thermal and mechanical properties were evaluated after UV irradiation (200 hours) performing DSC, DMA, TGA and tensile tests. DMA results indicated partial miscibility of PC and PU in the PU/PC blends with higher hard segment content, attributed to favourable interactions between the ester groups from the soft segments and urethane groups from the hard segments. The photochemical degradation of the polyurethane is associated with the scission of the urethane group and photooxidation of the central CH2 group between the aromatic rings. The processes of photooxidative degradation are less pronounced in PU/PC blends with higher hard segment content in the polyurethane.

Parameters Dependence of Fibers Diameter and Pores Area in Electrospinning

Electrospinning has become the most popular nanofibers production technique that many scientists around the world were intrigued by. It is based on electrostatic forces stretching a polymer solution that undergoes bending instability and eventually results in number of fine nanoscaled filaments. The study reports of four processing parameters effect on electrospun polyethylene oxide (PEO) fibers diameter and pores area. Fibers diameter increase results from the increase of time, volume flow rate and tip to collector distance with a critical value of the first two parameters. The pores area showed both decrease and increase after a critical value of the electrical voltage at 19 kV, while the mean pores area decreased with the time increase. Irregular trends of increasing and decreasing trends of the means pores area were noticed with the change of the volume flow rate and tip to collector distance..