Kazutaka Murata

Optical anisotropy in polymer–clay nanocomposite hydrogel and its change on uniaxial deformation

Optical anisotropy was observed in nanocomposite hydrogels with polymer–clay network structures and was found to exhibit unique changes when the gels were deformed uniaxially. Birefringence measurements showed distinct maxima and sign inversions that depend on strain and gel composition.

Proliferation and harvest of human mesenchymal stem cells using new thermoresponsive nanocomposite gels

For tissue engineering and regenerative medicine, stem cells should be effectively cultured in vitro. New thermoresponsive nanocomposite gels (MD-NC gels), consisting of inorganic clay (hectorite) and copolymers composed of hydrophobic 2-methoxyethyl acrylate (MEA) and hydrophilic N,N-dimethylacrylamide (DMAA) units, could be applied in cell culture and cell harvesting without trypsinization, specifically using mesenchymal stem cells (MSCs). The composition of the MD-NC gel (the ratio of the two monomer types and the clay content) was found to determine its swelling properties in the culture medium, thermosensitivity, protein adsorption, and cell attachment and proliferation. Various kinds of human cells, including MSCs, osteoblast (HOS) cells, fibroblast (NHDF) cells, and epithelial cells could be effectively cultured on MD-NC gels. In particular, on an MD10-NC2 gel with relatively low DMAA and clay content, the cells could be harvested by decreasing the temperature, either as a cell sheet (MSCs or NHDF cells) or as a population of suspension cells (HOS cells). Further, it was found that the MD10-NC2 gel is suitable for stem cell differentiation. Because of their thermosensitivity, controllable modulus, and surface properties, MD-NC gels are promising cell culture substrates useful for tissue engineering and regenerative medicine.

Thermoresponsible Cell Adhesion/Detachment on Transparent Nanocomposite Films Consisting of Poly(2-Methoxyethyl Acrylate) and Clay

Soft, transparent and mechanically tough nanocomposite (M-NC) films composed of poly(2-methoxyethyl acrylate) (PMEA) and inorganic clay (hectorite) were studied as substrates for a living cell harvest system. It was found that five cell types could all be cultivated to confluence on the surface of M-NC n films with clay content (n = 10–23 wt%), although the cells hardly cultivated on the surface of chemically-cross-linked PMEA and linear PMEA films. Further, it was found that the cells cultured on the surfaces of M-NC films can be detached, without any enzymatic digestion, by decreasing the medium temperature and/or simultaneously using gentle pipetting. The detached cell was obtained as a single cell or a contiguous cell sheet, both of which were viable and recultured. From the compositions and surface properties, it was estimated that the cell culture and subsequent cell detachment were attributed to the unique PMEA/clay network. The new soft nanocomposite is potentially a very promising substrate for tissue engineering.

Morphology and mechanical properties of polymer blends with photochemical reaction for photocurable/linear polymers

The relationship between morphology and mechanical properties were investigated in a binary blend of photocurable polymer (2,2-bis(4-(acryloxy diethoxy)phenyl)propane; BPE4) and linear polymer (polysulfone; PSU). The blend films are prepared by in situ photopolymerization of homogeneous mixtures of BPE4-monomer and PSU. The tensile strength and modulus reach a maximum in the blends having vague domain structures with a diffusion-phase boundary, at which the underdeveloped small BPE4-rich domains are wrapped with the PSU-rich matrix. The higher strength and modulus are caused by a strong interfacial adhesion between the BPE4-rich domain and the PSU-rich phase, which is brought about by incomplete phase separation in the PSU-rich phase. The tensile strength and modulus decrease as the bicontinuous structures clear due to deterioration of the interfacial adhesion. The mechanical properties also deteriorate in the blends with semi-IPN structures due to the lower conversion of BPE4. The composition dependencies on the tensile strength and the modulus for blends cured at optimum cure temperatures were found to give convex curves reaching maximums greater than those of pure components.