Jiří Hodan

Organic–inorganic nanocomposite films made from polyurethane dispersions and colloidal silica particles

Abstract Polyurethane/silica nanocomposites were prepared by solution blending of polyurethane water dispersion (PUD) based on polycarbonate macrodiol with colloidal silica aqueous sol LUDOX TMA. Because of mixing PUDs made from linear polyurethane with the nanofiller, only physical polymer/filler type of interface formed by hydrogen bonds was obtained. As a result the materials were possible to reuse after dissolution in acetone followed by dispersion in water. The effect of colloidal silica content on mechanical, thermal, morphological, and swelling properties of obtained films was tested by tensile test, dynamic mechanical thermal analysis, thermogravimertic analysis, scanning electron microscopy, atomic force microscopy, and swelling analyses. The nanocomposites were classified in three groups differing in the internal structure and functional properties: organic matrix filled with inorganic nanofiller (up to 10 wt% of silica), bicontinous systems (25 and 32 wt% of silica) and inorganic matrix filled with polyurethane (50 and 60 wt% of silica). Only small amount of colloidal silica (up to 10 wt%) improves thermo-mechanical properties, smoothes the materials, and suppresses extent of swelling without changing of the films transparency.

Strong synergistic effects in PLA/PCL blends: Impact of PLA matrix viscosity

Blends of two biodegradable polymers, poly(lactic acid) (PLA) and poly(ϵ-caprolactone) (PCL), with strong synergistic improvement in mechanical performance were prepared by melt-mixing using the optimized composition (80/20) and the optimized preparation procedure (a melt-mixing followed by a compression molding) according to our previous study. Three different PLA polymers were employed, whose viscosity decreased in the following order: PLC ≈ PLA1 > PLA2 > PLA3. The blends with the highest viscosity matrix (PLA1/PCL) exhibited the smallest PCL particles (d∼0.6μm), an elastic-plastic stable fracture (as determined from instrumented impact testing) and the strongest synergistic improvement in toughness (>16× with respect to pure PLA, exceeding even the toughness of pure PCL). According to the available literature, this was the highest toughness improvement in non-compatiblized PLA/PCL blends ever achieved. The decrease in the matrix viscosity resulted in an increase in the average PCL particle size and a dramatic decrease in the overall toughness: the completely stable fracture (for PLA1/PCL) changed to the stable fracture followed by unstable crack propagation (for PLA2/PCL) and finally to the completely brittle fracture (for PLA3/PCL). The stiffness of all blends remained at well acceptable level, slightly above the theoretical predictions based on the equivalent box model. Despite several previous studies, the results confirmed that PLA and PCL could behave as compatible polymers, but the final PLA/PCL toughness is extremely sensitive to the PCL particle size distribution, which is influenced by both processing conditions and PLA viscosity. PLA/PCL blends with high stiffness (due to PLA) and toughness (due to PCL) are very promising materials for medical applications, namely for the bone tissue engineering.

A frame-supported ultrathin electrospun polymer membrane for transplantation of retinal pigment epithelial cells

We report on the design and fabrication of a frame-supported nanofibrous membrane for the transplantation of retinal pigment epithelial (RPE) cells, which is a promising therapeutic option for the treatment of degenerative retinal disorders. The membranous cell carrier prepared from 640 nm-thick poly(DL-lactide) fibres uniquely combines high porosity, large pore size and low thickness, to maximize the nutrient supply to the transplanted cells in the subretinal space and thus to enhance the therapeutic effect of the transplantation. The carrier was prepared by electrospinning, which made it easy to embed a 95 μm-thick circular supporting frame 2 mm in diameter. Implantations into enucleated porcine eyes showed that the frame enabled the ultrathin membrane to be handled without irreversible folding, and allowed the membrane to regain its flat shape when inserted into the subretinal space. We further demonstrated that the minimum membrane thickness compatible with the surgical procedure and instrumentation employed here was as low as 4 μm. Primary porcine RPE cells cultivated on the membranes formed a confluent monolayer, expressed RPE-specific differentiation markers and showed transepithelial resistance close to that of the native RPE. Most importantly, the majority of the RPE cells transplanted into the subretinal space remained viable. The ultrathin, highly porous, and surgically convenient cell carrier presented here has the potential to improve the integration and the functionality of transplanted RPE cells.