Star‐shaped polycaprolactone/chitosan composite hydrogels: fabrication and characterization

Star‐shaped polycaprolactone (stPCL)/chitosan composite hydrogel was fabricated by simply melt/solution blending between chitosan/dicarboxylic acid solution and melted stPCL, using 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and N‐hydroxysuccinimide as conjugating agents to obtain a composite hydrogel. Here, stPCL and modified stPCL were investigated. The stPCL was modified to have a carboxyl‐terminated chain (stPCL‐COOH). The composite hydrogels were transparent. The network structure of the composite hydrogels was investigated. stPCL‐OH had no chemical bond to the chitosan network but stPCL‐COOH could co‐crosslink with the chitosan network. The porous structure and porosity of the composite hydrogels were similar to those of chitosan hydrogel. However, the hydrophobicity of stPCL resulted in a lower swelling ratio compared to chitosan hydrogel. The rheological analysis of the composite hydrogel exhibited a stable crosslinked network. Compression testing of the composite hydrogel obtained from stPCL‐COOH at a mole ratio of stPCL‐COOH and chitosan of 1:1 had optimum compressive mechanical properties comparable to chitosan hydrogel due to a synergistic effect of the flexibility in stPCL and the co‐crosslinking of stPCL‐COOH with the chitosan network. © 2020 Society of Chemical Industry     

Effect of incorporation of star-shaped polycaprolactone on structure-properties relationship of chitosan-based networks via urethane/urea linkage

A chitosan-based network was fabricated using hexamethylene diisocyanate as a crosslinking agent. The effect was investigated of incorporating star-shaped polycaprolactone (stPCL) into chitosan-based networks (CS/stPCL), where the stPCL content varied from 10 to 50 wt%. Quantitative analyses of the urethane/urea linkages and of the stPCL content in the networks were determined based on curve fitting and Soxhlet extraction, respectively. The optimum weight ratio was 80:20 for CS and stPCL (80CS20stPCL), with the highest urethane/urea linkages and stPCL content in the network (30.73%). The compressive testing and rheological analysis indicated that incorporating stPCL enhanced the compressive strength and rheological properties of the chitosan-based network. In addition, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay of the CS/stPCL network had a cell viability percentage greater than 70%. The CS/stPCL network promoted the formation of an apatite layer on the surface, indicating that the CS/stPCL network could be a promising candidate for tissue engineering.     

Amphiphilic chitosan nanospheres: Factors to control nanosphere formation and its consequent pH responsive performance

Chitosan grafted with hydrophobic and hydrophilic groups initiates the formation of amphiphilic chitosan nanospheres. The molecular weight of mPEG plays an important role to control the particle size. As compared to mPEG 2000, which gives a bimodal nanosphere (∼200, and ∼300 nm), mPEG 5000 initiates a monodispersed nanosphere with the smaller size (150 nm). In aqueous solution, the nanosphere surface is negatively charged resulting in a well dispersion in neutral to high pH but a significant precipitation in low pH. A model drug incorporation using lidocaine is successful when amphiphilic chitosan nanospheres were dissolved in good solvent followed by allowing mixing with drug solution before dialysis. The particle size of the drug incorporated chitosan is significantly increased, that is, from 100-150 nm to approximately 400-500 nm when the amount of incorporated lidocaine was about 0.68 mg per mg of lidocaine-loaded nanosphere.     

Modification of epoxidized natural rubber as a PLA toughening agent

In the present study, the modification of epoxidized natural rubber (ENR) was investigated to improve toughness of PLA. ENR-PLA copolymers were synthesized by 2 steps reactions. Acid hydrolysis of ENR to prepare macroinitiator (ENR-OH) and copolymerization with lactide to obtain ENR-PLA copolymers. The reaction time of acid hydrolysis and the lactide monomer loading was investigated. The optimum conditions were 8 h acid hydrolysis with 5wt% lactide loading to obtain ENR8-PLA5 copolymers. A series of samples of PLA blended with ENR-PLA copolymers was prepared using melt-blending. The blend of PLA with ENR8-PLA5 copolymers at 1 phr substantially improved the tensile properties. The elongation at break was increased 67%, and toughness was increased 64% compared to neat PLA. These results indicate that ENR8-PLA5 has potential as toughening agent for PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48267.