Preparation of keratin and chemically modified keratin hydrogels and their evaluation as cell substrate with drug releasing ability

Keratin was extracted as a reduced form from wool, which was then subjected to acetamidation, carboxymethylation or aminoethylation at abundant free cysteine residues to give acetamidated keratin (AAK), carboxymethylated keratin (CMK) and aminoethylated keratin (AEK). Hydrogels were prepared from intact and three chemically modified keratins simply by concentrating their aqueous solution and subsequent cooling. The lowest concentration to form a hydrogel without fluidity was 110mg/ml for AAK, 120mg/ml for AEK, 130mg/ml for keratin and 180mg/ml for CMK. Comparing with a hydrogel just prepared (swelling ratio: 600-700), each hydrogel slightly shrank in an acidic solution. While AAK hydrogel little swelled in neutral and basic solutions, other hydrogels became swollen and CMK hydrogel reached to dissolution. Hydrogels of keratin, AAK and AEK were found to support cell proliferation, although cell elongation on AAK and AEK hydrogel was a little suppressed. On the other hand, CMK hydrogel did not seem to be suitable for a cell substrate because of its high swelling in culture medium. Evaluation of the hydrogels as a drug carrier showed that keratin and AAK hydrogels were good sustained drug release carriers, which showed the drug release for more than three days, while the release from AEK and CMK hydrogels completed within one day. Thus, keratin and chemically modified keratin hydrogels, especially keratin and AAK hydrogels, were promising biomaterials as a cell substrate and a sustained drug release carrier.