Cosmetic Potential of a Structural Protein Copolymer Based on Silk, Elastin, and Keratin

The hair cosmetic industry is constantly searching for new ingredients and innovative materials that can help enhance properties, such as softness, shine, shape, and color. However, conventional products contain harmful chemicals. In this study, we developed a biobased alternative using a recombinant protein composed of repetitions of consensus motifs from the structural proteins silk, elastin, and keratin, termed SELP::KP. This protein was expressed in <i>Escherichia coli</i> and purified by a nonchromatographic method to high purity. Fourier-transform infrared spectroscopy (FTIR) confirmed the β-sheet-rich structure, characteristic of silk and SELP-like proteins. Calorimetry studies confirmed the high thermal stability of SELP::KP. When applied to hair, SELP::KP colocalized at both the cuticle and cortex, indicating strong penetration capacity. Mechanical testing of treated virgin hair showed significant improvements: Young's modulus increased by 34.9%, and extensibility improved by 12.4% compared to untreated controls, indicating enhanced strength and elasticity. Additionally, the protein's potential as a safer perming agent was evaluated, maintaining a curling effect similar to the chemical treatment but with lower damaging effects. Furthermore, SELP::KP was shown to reduce by half the combing strength needed, acting as an effective conditioning agent. This research highlights SELP::KP as a promising biobased copolymer for hair cosmetics, offering both styling benefits and improved hair health, as a leave-in treatment or a hair mask that aids in combability and perming service.