Green Fabrication of Keratin Nanoparticles from Yak Horn by Steam Flash Explosion: Structure-Property Evolution

Yak horn represents a valuable resource for fabricating keratin-derived materials; however, its dense, highly cross-linked protein network resists efficient processing via conventional extraction methods. This study introduces a single-step steam flash explosion (SFE) approach to produce keratin nanoparticles (KNPs) from yak horn. The impact of SFE operating pressure (0-1.6 MPa) on KNP morphology, protein secondary/tertiary structures, thermal behavior, and in vitro biocompatibility was systematically investigated. Morphological evaluations revealed that SFE pressure successfully regulates particle dimensions, yielding optimal uniformity with a minimum average particle height of 11.5 nm at 1.45 MPa. Structural characterization indicated that high-pressure treatment induced a shift in disulfide bonds from stable gauche-gauche-gauche (g-g-g) states (515 cm^-1) toward higher-energy trans-gauche-trans (t-g-t) arrangements (540 cm^-1). This structural deconstruction led to a decrease in thermal degradation temperatures (from 321.9 °C at 0 MPa to <300 °C at 1.6 MPa) but significantly enhanced dehydration efficiency (ΔH = -470.44 J/g at 1.6 MPa). In vitro biocompatibility assessments demonstrated that the prepared KNPs maintain excellent cytocompatibility, supporting L929 and HaCaT cell viabilities above 95%. These findings demonstrated the versatility and effectiveness of SFE as a sustainable strategy for tuning KNP properties, highlighting its great potential in biomedical applications and green material processing.