Preparation of ZnSO4 cross-linked double-network hydrogels via synergistic ionic and Hofmeister effects as in-situ fruit packaging integrating cushioning and monitoring

To reduce postharvest mechanical damage, an in-situ fruit packaging solution integrating both force cushioning and real-time sensing functions is proposed. This was achieved using the synergistic effects of ion cross-linking and the Hofmeister effect to create ZnSO 4 cross-linked double-network hydrogels directly on the fruit surface. The results show that the hydrogels exhibited superior compressive strength, deformability, and Young’s modulus. With increasing concentrations of the ZnSO 4 solution, the compressive property, Young’s modulus, and cross-linking density of the hydrogels increased, while their energy dissipation rate decreased. The hydrogels cross-linked with a 0.3 M ZnSO 4 solution was the optimal one, achieving an energy dissipation rate of 35.2 %, while their compressive strength was 3.5 times that of the uncross-linked hydrogels, along with 3.9 times higher ionic conductivity and 75.9 % lower resistance. The optimal hydrogels could output electrical signals in response to strain at different rates and proportions and exhibited stable sensing over 100 compression cycles. Furthermore, the performance of the optimal hydrogels was evaluated using ripe and fragile kiwifruit. The cushioning test results show that the hydrogels could reduce vibration, compression and dropping damage, therefore effectively protecting the fruit. Besides, the hydrogels could quantitatively detect the compression force acting on fruit surfaces by outputting electrical signals in real-time. Additionally, the hydrogels achieved 96.8 % biodegradation within 6 h and had good biocompatibility. Overall, the present study proposed an idea of fabricating an in-situ fruit packaging with both cushioning and real-time sensing functions to reduce mechanical damage and facilitate inspection for fruit during postharvest transportation.