A facile approach to construct three-dimensional oriented chitosan scaffolds with in-situ precipitation method

Fast contact of solid-liquid interface created high strength multi-layered cellulose hydrogels with controllable size

Novel onion-like and multi-layered tubular cellulose hydrogels were constructed, for the first time, from the cellulose solution in a 7% NaOH/12% urea aqueous solvent by changing the shape of the gel cores. In our findings, the contacting of the cellulose solution with the surface of the agarose gel rod or sphere loaded with acetic acid led to the close chain packing to form immediately a gel layer, as a result of the destruction of the cellulose inclusion complex by acid through inducing the cellulose self-aggregation. Subsequently, multi-layered cellulose hydrogels were fabricated via a multi-step interrupted gelation process. The size, layer thickness and inter-layer space of the multi-layered hydrogels could be controlled by adjusting the cellulose concentrations, the gel core diameter and the contacting time of the solid-liquid interface. The multi-layered cellulose hydrogels displayed good architectural stability and solvent resistance. Moreover, the hydrogels exhibited high compressive strength and excellent biocompatibility. L929 cells could adhere and proliferate on the surface of the layers and in interior space, showing great potential as tissue engineering scaffolds and cell culture carrier. This work opens up a new avenue for the construction of the high strength multi-layered cellulose hydrogels formed from inner to outside via a fast contact of solid-liquid interface.

Prevention of browning of depolymerized chitosan obtained by gamma irradiation

In this paper, effect of oxygen and pH on the browning of chitosan exposed to gamma radiation was investigated. It was found that oxygen and pH value could play important roles in the inhibiting browning of irradiated chitosan. When the pH value of chitosan solution was below 3.0, sufficient oxygen could inhibit browning of irradiated chitosan in aqueous solution. As a result of irradiation of chitosan solution (pH<3) with sufficient oxygen, the irradiated chitosan solutions obtained were colorless and pellucid. FT-IR, (13)C NMR, and UV-vis spectra confirmed that the irradiation in the presence of oxygen cannot result in chemical modification of irradiated chitosan. An effective technology was developed for the inhibition of browning of irradiated chitosan during depolymerization of chitosan by gamma irradiation.

Dual stimuli-responsive N-phthaloylchitosan-graft-(poly(N-isopropylacrylamide)-block-poly(acrylic acid)) copolymer prepared via RAFT polymerization

In order to develop stimuli-responsive hydrogel, chitosan graft copolymer with chitosan back-bone and poly(N-isopropylacrylamide)-block-poly(acrylic acid) (PNIPAAm-b-PAA) branch chains was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF. The chain transfer agent was obtained by modification of chitosan with 3-benzylsulfanyl thiocarbonylsulfanyl propionic acid (BPATT) with 68% the degree of substitute. The graft polymerizations possessed controlled/living characteristics. The behavior of the graft copolymer in aqueous solution was investigated by dynamic light scattering, transmission electron microscopy, and UV-visible spectrophotometer. N-Phthaloylchitosan-graft-(poly(N-isopropylacrylamide)-block-poly(acrylic acid)) copolymer (N-phthaloylchitosan-g-(PNIPAAm-b-PAA)) could assemble to micelles in aqueous solution in range of 200-300 nm with narrow size distribution, and the hydrodynamic diameter could be controlled dependent on length of branch chains and temperature. The LCST values of micelle could be modulated from 34 to 40 °C by controlling the constitution of branch chains, pH, and concentration.