A biodegradable polyurethane-gelatin nanocomposite cryogel with shape-memory properties for information encryption and bilayer actuation.

Abstract

Programming functional asymmetry into soft materials typically relies on compositionally heterogeneous interfaces, which can complicate fabrication and introduce interfacial compatibility concerns. Here, we introduce processing history as a programmable design parameter to imprint pore-architecture contrast into chemically identical polyurethane-gelatin (4:1) cryogels (PUG), thereby enabling reversible actuation, shape-memory programming, and rewritable information handling within a unified material system. Biodegradable PUG cryogels were fabricated by crosslinking gelatin with waterborne dialdehyde-functionalized polyurethane nanoparticles (DFPU) via cryogelation. By modulating the freezing pathway while maintaining identical chemical composition, differences in pore size distribution and water uptake were generated, allowing structural asymmetry to be encoded without introducing compositional heterogeneity. Incorporation of biodegradable crystalline poly(3-hydroxybutyrate) (PHB) segments into the DFPU soft domain endowed the cryogels with improved shape-memory behavior, achieving a shape-fixity ratio of 95.3% with near-complete recovery. The optimized cryogel (PUG2) exhibited high porosity (>90%), a dynamic compressive modulus of approximately 10 kPa, and syringe injectability through a 16G needle with rapid rebound. Pairing processing-differentiated PUG2 and PUG2' layers enabled a bilayer actuator that translated pore-architecture contrast into reversible bending through asymmetric swelling. Beyond actuation, the light-scattering cryogel surface enabled visible information writing through FeCl₃-mediated coordination, while swelling-induced deformation regulated message visibility. Subsequent chemical reduction enabled controllable message erasure, demonstrating rewritable information handling coupled with mechanical deformation. Importantly, PUG cryogels showed cytocompatibility, and the hydrolysable PU segments rendered the network biodegradable. This study establishes a biodegradable multifunctional cryogel platform for information encryption and programmed actuation. STATEMENT OF SIGNIFICANCE: A biodegradable, injectable polyurethane-gelatin cryogel scaffold is developed to integrate reversible actuation and rewritable information processing within a single material system. Functional asymmetry is achieved without chemical heterogeneity by encoding a pronounced pore-architecture contrast through processing history in composition-identical cryogels crosslinked by waterborne dialdehyde-functionalized polyurethane nanoparticles, enabling intrinsically biocompatible actuation with reversible, water-triggered bidirectional bending. Crystalline PHB domains deliver >90% porosity, 16G injectability, and strong shape memory (R_f = 95.3%). The paper-like cryogel surface supports FeCl₃-based writing (including QR codes) and redox erasing, enabling reusable encryption. Cytocompatibility with human mesenchymal stem cells and tunable biodegradation highlight translational biomedical potential, positioning the system as a multifunctional scaffold and an in vitro dry-wet cycling testbed.