Regenerated keratin proteins as potential biomaterial for drug delivery

This work aims to preliminarily evaluate the reliability of regenerated keratins (RKs) in the design of microparticulate drug delivery systems by studying their processability and cytotoxicity. RKs were extracted by sulfitolysis from wool waste. A 4.5%w/w RK solution was spray-dried, and microparticles were sterilized by steam vapor under pressure. Scanning electron microscope, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and Fourier transform infrared spectroscopy were used to characterize RKs and microparticles thereof. The in vitro cytotoxicity was determined by assessing the release of lactate dehydrogenase in the human monocytic cell line Tamm-Horsfall glycoprotein-1. RK-based microparticles with a narrow and unimodal particle size distribution (similar to 6 mu m) were obtained. They had a raisin-like structure with a smooth surface. Both microparticle morphology and RK molecular weight were well-preserved after sterilization. The curve fitting of the amide I bands showed that RK in the microparticles was prevalently present in the disordered/-helix secondary structures which made the protein soluble in water. To promote crystallization in the -sheet secondary structure and, therefore, water insolubility, RK-based microparticles were immersed in an aqueous solution of acetic acid at pH3.5 overnight. RK did not induce any appreciable cellular cytotoxicity at any of the concentrations (from 1 up to 1000 mu g sterile microparticles in 1ml cell culture medium) or time-points (24-72h) tested. These preliminary data suggest the feasibility of producing RK biocompatible microparticles using waste wool as starting material.