Elastic-Plastic Transformation of Polyelectrolyte Complex Hydrogels from Chitosan and Sodium Hyaluronate

Hydrogels formed by the chemically or physically crosslinked polymers with mechanical properties adjustable over a wide range are the most promising materials for artificial tissue and organs, due to their low modulus and high water content. The physical hydrogels from the biopolymers without any chemical additives are promising candidates for biomedical applications because they are bio-compatible and eco-friendly.

In this work, the mechanically strong polyelectrolyte complex hydrogels from a pair of oppositely charged biopolymers – positive chitosan and negative sodium hyaluronate (HA) were synthesized by tuning the composition of the hydrogels. From the tensile and stress relaxation measurements, we found that the HA/chitosan hydrogels exhibit quite different mechanical properties in comparison to the properties of hydrogels formed by complexation of oppositely charged synthetic polyelectrolytes. The synthetic polyelectrolyte complex hydrogels, formed either by two-step polymerization or by simple mixing of the oppositely charged synthetic polyelectrolytes, are highly viscoelastic materials over a wide range of strain rates even at small deformation. They exhibit yield but sustain large deformation after yield. No flow occurs even at fracture and strong finite chain extensibility effects have been observed in synthetic polyelectrolyte complex hydrogels. By contrast, HA/chitosan hydrogels are elastic-like at small strains, almost independent of the strain rate, but become plastic-like at large strains, exhibiting yield, flow, and fracture that are delayed at high strain rates. The transformation of HA/chitosan hydrogels from elastic to plastic-like and their difference from synthetic polyelectrolyte complex is related to the difference in charge density and chain flexibility between biological and synthetic hydrogels. We demonstrate that polyelectrolyte complex hydrogels have rich mechanical properties that can be tuned by adjusting their structure.

This result has been published in Macromolecules, 2018, 51, 8887-8898. The first co-authors are Dr. Ran SHI (Hokkaido University, Japan) and Dr. Taolin SUN (AISMST, South China University of Technology). The corresponding author is Dr. Jianping GONG (Hokkaido University, Japan). 

The link for the paper is as follows: https://pubs.acs.org/doi/10.1021/acs.macromol.8b01658

Source from South China Advanced Institute for Soft Matter Science and Technology

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