Yoshikazu Kumashiro

Enzymatic Degradation of Semi‐IPN Hydrogels Based on N‐Isopropylacrylamide and Dextran at a Specific Temperature Range

The temperature-dependent enzymatic degradation of semi-IPN hydrogels consisting of dextran grafted with thermo-responsive chains (lower cloud point) and a thermo-responsive crosslinked matrix (higher cloud point) was examined. Enzymatic degradation of the semi-IPN hydrogel was significantly inhibited below the lower and above the higher cloud point. Only between both cloud points, enzymatic degradation proceeded. The designed semi-IPN hydrogel is therefore advantageous to achieve enzymatic degradation at a specific temperature range.

Temperature-controlled erosion of poly(N-isopropylacrylamide)-based hydrogels crosslinked by methacrylate-introduced hydrolyzable polyrotaxane

Abstract Biodegradable hydrogels for temperature-controlled erosion were prepared by co-crosslinking N-isopropylacrylamide (NIPAAm) and methacrylate (MA)-introduced polyrotaxane (PRX) in which many α-cyclodextrins (α-CDs) arethreaded onto a poly(ethylene glycol) chain capped with bulky end-groups via ester linkages. The amount of MA attached to hydroxyl group of α-CDs in PRX could be varied by the feed ratio of GMA and PRX. The prepared hydrogels were transparent below lower critical solution temperature (LCST) of PNIPAAm matrix (32 °C). By elevating temperature above the LCST, water contents were slightly decreased, and the hydrogels became opaque. Elevating temperature in an aqueous condition above the LCST led to dehydration of the PNIPAAm matrix, which accompanies α-CD sliding to expose the ester linkage to the medium and enhances erosion of the hydrogels.

Thermoresponsive Nanostructured Surfaces Generated by the Langmuir–Schaefer Method Are Suitable for Cell Sheet Fabrication

Thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-immobilized surfaces for controlling cell adhesion and detachment were fabricated by the Langmuir-Schaefer method. Block copolymers composed of polystyrene and PIPAAm (St-IPAAms) having various chain lengths and compositions were synthesized by reversible addition-fragmentation chain transfer radical polymerization. The St-IPAAm Langmuir film at an air-water interface was horizontally transferred onto a hydrophobically modified glass substrate while regulating its density. Atomic force microscopy images clearly visualized nanoscaled sea-island structures on the surface. By adjusting both the composition of St-IPAAms and the density of immobilized PIPAAms, a series of thermoresponsive surfaces was prepared to control the strength, rate, and quality of cell adhesion and detachment through changes in temperature across the lower critical solution temperature range of PIPAAm molecules. In addition, a two-dimensional cell structure (cell sheet) was more rapidly recovered on the optimized surfaces than on conventional PIPAAm surfaces. These unique PIPAAm surfaces are suggested to be useful for controlling the strength of cell adhesion and detachment.

Stripe-Patterned Thermo-responsive Cell Culture Dish for Cell Separation without Cell Labeling

A stripe-patterned thermo-responsive surface is prepared to enable cell separation without labeling. The thermo-responsive surface containing a 3 μm striped pattern exhibits various cell adhesion and detachment properties. A mixture of three cell types is separated on the patterned surface based on their distinct cell-adhesion properties, and the composition of the cells is analyzed by flow cytometry.

Preparation of Thermoresponsive Nanostructured Surfaces for Tissue Engineering

Thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-immobilized surfaces for controlling cell adhesion and detachment were fabricated by the Langmuir-Schaefer method. Amphiphilic block copolymers composed of polystyrene and PIPAAm (St-IPAAms) were synthesized by reversible addition-fragmentation chain transfer (RAFT) radical polymerization. A chloroform solution of St-IPAAm molecules was gently dropped into a Langmuir-trough apparatus, and both barriers of the apparatus were moved horizontally to compress the film to regulate its density. Then, the St-IPAAm Langmuir film was horizontally transferred onto a hydrophobically modified glass substrate by a surface-fixed device. Atomic force microscopy images clearly revealed nanoscale sea-island structures on the surface. The strength, rate, and quality of cell adhesion and detachment on the prepared surface were modulated by changes in temperature across the lower critical solution temperature range of PIPAAm molecules. In addition, a two-dimensional cell structure (cell sheet) was successfully recovered on the optimized surfaces. These unique PIPAAm surfaces may be useful for controlling the strength of cell adhesion and detachment.

Differences in dynamic behavior of single diatom cells caused by changing wavelengths.

We investigate a motion of diatom cells stimulated by a halogen lamp irradiation. Diatom cells are single-celled organisms which have chloroplast. Chloroplast contains photosynthetic pigment which absorbs blue light (wave length of the light is 400u202fnm-450u202fnm) and red one (650u202fnm-700u202fnm). Light intensity of the halogen lamp is fixed about 500u202fLx during the experiment. We used colored films to cut the blue or red light and observed motion of diatom cells by using the optical microscope. We found that the speed of diatom cells decreases when the colored film is inserted, and it increases after ejecting the film. It is noted that the light intensity is constant during the experiment, which means that we change wave length of the irradiated light. Our results show that the average speed of diatom cells is influenced by not the light intensity but the wave length of the light.

Removal of excess polymer from a suspension containing hybrids of thermoresponsive polymer and carbon nanotubes using aggregation phenomenon

Hybrids of organic molecules and single-walled carbon nanotubes (SWNTs) are attractive candidates for nanobiodevices. The removal of organic molecules after dispersing the SWNTs in organic media is a significant step in the preparation of these hybrid suspensions. We investigated the aggregation phenomenon in hybrids of poly(N-isopropylacrylamide) (PNIPAAm) and SWNTs. Our results indicate that the hybrids efficiently precipitated when a buffer or salt solution was added to the suspension at 25 degrees C. 4mM tris(hydroxymethyl) aminomethane hydrochloride (Tris-HCl) buffer was sufficient to precipitate the hybrids. Then, by repeated centrifugations and replacements of solvents, excess PNIPAAm molecules were efficiently removed from the suspension. Results of UV-vis spectroscopy and atomic force microscopy (AFM) suggest that the PNIPAAm-SWNT hybrids retained their hybridized structures even after the treatment process. However, the aggregation phenomenon was not observed at 4 degrees C