Dual-stage reverse-dialysis-engineered cartilage-biomimetic hydrogels: Highly resilient anti-swelling double-layer architectures

Although hydrogels show immense promise in biomedical and engineering applications, they face critical limitations in mechanical property versatility and inadequately stable anti-swelling capacities. Inspired by the graded structure of articular cartilage—where a dense, wear-resistant outer layer integrates with a compliant, shock-absorbing inner layer—this study proposes a dual-stage reverse-dialysis strategy for fabricating a chitosan/polyvinyl alcohol (CS/PVA) and silk nanofiber/polyvinyl alcohol (SNF/PVA) double-layer biomimetic hydrogel by precisely regulating the internal dialysate (a CS/PVA solution), external polyethylene glycol concentration, and molecular weight to form a soft inner structure. Subsequently, a rigid, densely structured SNF/PVA outer layer was fabricated without requiring any chemical crosslinkers, synergistically enhancing the mechanical property of the hydrogel: The compression strength surged from 345.07 to 2490.23 kPa (for the single inner and double layers, respectively) at 70 % strain by optimizing the solution concentration and enhancing the mechanical properties of the outer hydrogel. Crucially, this method enables robust, chemical-crosslinker-free interfacial bonding (shear strength >390 kPa) through physical crosslinking, overcoming weak interlayer adhesion in conventional methods. The hydrogel exhibits exceptional anti-swelling properties (mass swelling ratio = 24.55 % after 168 h) and resilience (91.47 % stress retention over 10 compression cycles). This strategy provides a green and scalable route to develop structurally stable, double-layer hydrogels.