Self-Assembled Keratin Nanoparticles Prepared by Partial Hydrolysis and Their Restructuring Response to pH Shifting...

Keratin, an abundant biopolymer in animal byproducts, holds promise as a biomolecule delivery carrier due to its biocompatibility, biodegradability, and low toxicity. However, its intrinsic stability from disulfide bonds limits broader application. Here, we present a strategy to convert waste feather keratin into keratin nanoparticles (KNPs) via partial hydrolysis and pH shifting. At 5% degree of hydrolysis (DH), keratin self-assembled into spherical KNPs with reduced size (∼123 nm) and enhanced solubility (94.5%). These KNPs displayed pH-triggered structural transitions (open state at pH 2.0 → closed at pH 7.0) and high loading efficiency (>93%) for insulin and resveratrol, offering partial protection against gastrointestinal enzymatic degradation and low cytotoxicity. In contrast, higher DH (≥10%) increased β-sheet content and hydrophobic exposure, promoting KNP aggregation and lowering their pH responsiveness and biomolecule encapsulation. Our findings demonstrate the potential of 5% DH KNPs as nanocarriers, providing a sustainable approach for nutrient and pharmaceutical applications.