Transparent biocompatible wool keratin film prepared by mechanical compression of porous keratin hydrogel

We could prepare a transparent wool keratin film by mechanical compression of the keratin hydrogel, which was prepared by our method previously reported. Optical transmittance of the keratin film was approximately 70% at 400 nm and 80% at 550 nm. The keratin film had higher mechanical strength than the keratin hydrogel estimated from the tensile test. Young's modulus of the keratin film and that of keratin hydrogel were 0.582 ± 0.294 MPa and 0.041 ± 0.008 MPa, respectively. We evaluated degradability of keratin film by tryptic digestion in vitro and that also by implantation test in vivo. The keratin film showed slower degradation rate in the presence of trypsin in vitro, and also that as a subcutaneous implant in mouse in vivo. Biocompatibility is also a key factor for application of keratin as biomaterials. Within several days after subcutaneous implantation of the sample in mouse, an apparent symptom of acute inflammation of tissues, such as swelling of the reddish skin, was not observed. Keratin film remained in the original morphology of sheet-like structure while keratin hydrogel was degraded with many cracks and gaps after implantation for several weeks. We concluded from those results that keratin film was mostly biocompatible without provoking inflammation nor encapsulation, mechanically stronger than the keratin hydrogel, and was more resistant to degradation than the keratin hydrogel.