Understanding structural-property relationships in keratin hydrogels

Abstract

There has been research done using human hair keratin hydrogels as a relevant biomaterial for the rapid regeneration of peripheral nerves, for supporting the sustained release of bioactive ciprofloxacin in drug delivery, and also for the support of fibroblast attachment and proliferation. However, the relationship between the mechanical properties and the structure of keratin hydrogels is still not well established and understood even though it has been known that keratin contains a lot of disulphide bridges which contribute to its integral structure.

The objectives of this research were: 1) Fabricate keratin hydrogels and to characterise their 3-D structures, 2) Understand and relate the structure of keratin hydrogels to their mechanical properties, 3) Evaluate the influence of crosslinker thiolation on the mechanical properties of keratin hydrogels. Keratin was extracted from human hair and the fabrication of keratin involved crosslinking of keratin chains using the Poly(acrylic acid)-cysteine complex system. Results have shown the promising effect of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) to be used as a catalyst for successful attachment of cysteine molecules on the Poly(acrylic acid) of 450 kDa in molecular weight, PAA450, that the 200 mM EDAC used was able to increase the thiol group concentration to 45.38 μM as compared to 0.942 μM measured in control using a thiol group assay. EDAC was incorporated for the preparation of the PAA450-cysteine complex.

By crosslinking keratin chains using PAA450-cysteine complex system for hydrogel fabrication, it was observed to have an increase in the Storage modulus, G’, to up to more than 4 times to 30.8 Pa as compared to Blank keratin hydrogels without the addition of PAA450-cysteine complex system in rheology test. This thus helped to relate the mechanical properties to the structure of the hydrogels through affecting the disulphide bonds in the keratin chains. By increasing the amount of crosslinks through disulphide bonding in keratin hydrogels, the mechanical properties could be improved.

Even though the max G’ observed was 30.80 Pa, which is far from simulating human body tissues’, the concept of introducing PAA450-cysteine complex as a crosslinking system for keratin chains was analysed and has proven its capability in improving the mechanical properties.