R Dhamodharan

The preparation of porous films (average size variation from 1 to 32 μm) of a 1:1 blend of chitosan with poly(EG-ran-PG) by the controlled evaporation of water from a 2 wt % aqueous acetic acid solution is reported. Interestingly, the blend exhibited porosity that could be tailored from 1 to 32 μm with the temperature of preparation of the blend film. The powder X-ray diffraction, Fourier transform infrared, and differential scanning calorimetry analyses of the films suggested the formation of partially miscible blends. Temperature-induced phase separation of the blend appears to be the mechanism of pore formation. The tensile strength, cytotoxicity, and biocompatibility of the blend films for the growth of mesenchymal stem cells were assessed vis-a-vis chitosan. The 1:1 blend film was observed to lack cytotoxicity and was also viable for the growth of mesenchymal stem cells. The tensile properties of the 1:1 blend were superior to those of the chitosan film. The simple preparation of porous, nontoxic, and biocompatible films could find use as a scaffold in the growth of tissue, and especially bone tissue, in wound dressing, and in filtration if a better control over pore size is achieved.

Mechanical degradation of polymers reported so far, utilize cutting, impact or attrition for size reduction, which is very different from the low-magnitude forces experienced by the polymers during their service life. In this work, we have studied the effect of such low-magnitude forces, on the polymeric materials, using a low-energy rolling compression-type wet-grinder. The rolling compression action produces shear and compression on the polymer, leading to abrasion and resulting in the formation of crazes, micro-cracks and chip-offs, akin to the wearing. Measurements using Raman spectroscopy showed that the shear forces, generated upon grinding, produced strains on the polymer backbone, which upon sufficient build-up, results in chain scission at the points of physical entanglement. These homolytic chain scissions produced “mechano”radicals, which were confirmed by radical-scavenging using DPPH. The ensuing reduction in the molecular weight was further analyzed using GPC, light scattering and viscometry. Surprisingly, XRD measurements showed strain-induced crystallization as well. In order to theoretically validate the studies, a probabilistic model, explaining the “complex” response of the molecular weight distribution and the PDI upon mechanical degradation, has also been presented. Crosslink density function was incorporated to explain the preferential chain scission of the high molecular weight species, leading to a gradual reduction in the average molar mass.

Biocompatible hydrogels were prepared by mixing aqueous-acidic solution of chitosan with alkali lignin, a major by-product of the paper producing industries, for the first time, by sustainable means. Electrostatic interactions between the phenoxide groups in lignin and the ammonium groups on the chitosan backbone were found to be responsible for the ionotropic cross-linking. These gels were non-toxic to Mesenchymal stem cells, in vitro, and to zebrafish up to 100 μg/ml, in vivo. In addition, these gels provided a conducive surface for cell attachment and proliferation, making it suitable for application as scaffolds in tissue engineering. In presence of the hydrogel, NIH 3T3 mouse fibroblast cells showed good cell migration characteristics suggesting that the gel might be suitable for wound healing application. The chitosan-alkali lignin gelation system was further capable of removing ferric ions from contaminated water by way of complexation and coagulation. Cross-linked films of chitosan and alkali lignin could also be prepared by simply immersing chitosan films into a solution of alkali lignin. Alkali lignin was observed to diffuse into the chitosan “crystal”, forming electrostatic cross-links between the chitosan chains. The choice of lignin, in comparison to the other ionotropic cross-linkers for chitosan, makes the cross-linking system, inexpensive and sustainable.