Moisturizing efficiency of silk protein hydrolysate: Silk fibroin

Abstract

A biomimetic approach of composition and natural function of natural moisturizing factor (NMF) with the amino acid content of silk fibroin was advantageously used to reconstruct the skin moisturizing system. The isolation of silk hydrolysate with water and sodium chloride treatment was complete in one hour. Lithium ion from LiBr effectively penetrated crystal domains of fibroin and gave desired solubility. Silk fibroin from <i style="">Bombyx mori</i> cocoons was non-allergic and biocompatible in skin and rabbit eye tests. The concentration dependent moisturizing efficacy of fibroin (1-5% w/v) in solution and cream form has been demonstrated by TEWL <i style="">in vitro</i> and in volunteers. As compared to dry and normal skin the fibroin containing cream revealed increased substantivity. The increased hydroxproline content was responsible for retaining higher moisture in the skin. This in turn maintained the skin in soft and supple state. The significant drop in impedance was observed within 1 hr of the application of fibroin and the effect was sustained for more than 6 hrs. Thus, increased hydration level in stratum corneum was achieved by fibroin treatment. The SEM of fibroin treated skin replicas showed a desired attribute of soft, smooth skin texture and improved flexibility. The increased state of hydration caused interdigitating of cell edges as evident in microphotographs. The rapid and sustained moisturizing efficiency observed with silk fibroin was well substantiated by the results of skin substantivity and impedance tests.