Silk Plastics with Embedded Enzymes for On-Demand Degradation

A major barrier in developing enzyme-responsive biomaterials is understanding how biomaterial matrix structure regulates enzyme stability, activation, and long-term function. Silk protein-based materials are promising for enzyme immobilization, yet their stabilization mechanisms within dense, semicrystalline matrices remain poorly defined. Here, we fabricate dense silk plastics with embedded pepsin, protease XIV, or α-chymotrypsin using thermoplastic molding and systematically assess how environmental conditions govern enzyme activation and subsequently, silk degradation. Enzyme-free (control) silk plastics are stable under physiological (pH 7.0 and 37 °C) conditions but degrade rapidly under acidic (pH 2.0) or thermal (60 °C) stress. In contrast, plastics with embedded enzymes generated temperature-gated and pH-modulated silk degradation profiles over 70 days. Storage at −20 °C, 4 °C, and 25 °C demonstrates reduced dependence on cold-chain storage for enzyme stability, with frozen, cold, and ambient storage preserving 85–95% of enzymatic activity and maintaining relatively reproducible release kinetics. Across all proteases, thermal activation is the dominant determinant of function, while the semicrystalline nature of silk and the associated β-sheet-mediated confinement broaden the enzyme’s pH tolerance without shifting intrinsic temperature thresholds. These findings position thermoplastic silk materials as a scalable platform for shelf-stable enzyme storage, and for on-demand degradation and delivery across biomedical and industrial applications.