Postoperative anastomotic complications, such as urinary leakage, remain a critical challenge in bladder enlargement surgery due to tension-induced tissue damage during urine storage. Conventional adhesive hydrogels fail to mitigate mechanical stress owing to their drastically reduced modulus after swelling. This study proposes a novel tension-reducing self-shrinking tough hydrogel patch designed to enhance post-swelling modulus and bioisotropic mechanical reinforcement for anastomotic repair, addressing the limitations of existing materials.

A dual-network hydrogel system composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) was developed. Directional annealing was applied to optimize crosslinking density and polymer chain alignment in the dry state, enabling modulus retention post-swelling. The hydrogel’s adhesive properties were tailored via physical entanglement. Mechanical performance was evaluated through cyclic tensile testing and swelling assays in simulated bladder conditions (37°C, pH 6.8). A rat bladder enlargement model was established to assess in vivo efficacy, with histological (H&E, trichrome) and immunohistochemical (collagen I/III, α-SMA) analyses quantifying tissue integration, inflammation, and biomechanical reinforcement.

Directional annealing increased the hydrogel’s post-swelling modulus by over 8 fold (133 ± 2.1 kPa vs. 15 ± 0.7 kPa in non-annealed controls) while maintaining a self-shrinking strain of 35% to adaptively reduce suture line tension. In vivo, the patch reduced anastomotic leakage incidence by 72% (p < 0.001) compared to traditional hydrogels, with histology demonstrating aligned collagen fibers and minimal fibrosis. Immunofluorescence confirmed enhanced α-SMA expression (2.8-fold increase), indicating active myofibroblast-mediated tissue remodeling.

This work overcomes the inherent trade-off between hydrogel swelling and modulus degradation by leveraging directional annealing to pre-organize the dual-network structure. Unlike isotropic hydrogels, the bioisotropic design mimics native bladder mechanics, preventing stress concentration at the anastomosis. The self-shrinking behavior dynamically accommodates bladder expansion, while covalent-physical hybrid crosslinking ensures durability under cyclic loading. However, long-term biocompatibility and degradation kinetics require further optimization for clinical translation.

The directional-annealed PVA/PAA hydrogel patch represents a breakthrough in anastomotic repair strategies, combining high post-swelling modulus and adaptive self-shrinking to address postoperative tension challenges. Its efficacy in reducing leakage and promoting structured tissue regeneration highlights its potential for improving outcomes in bladder reconstruction and other tension-sensitive surgical applications.