High-Performance Hydrogels via Alternate Compression-Decompression

Novel bioapplications of hydrogels draw huge attention to the development of strong and tough hydrogels that are easily obtainable with less chemical additions. Here, we demonstrate that pressure, a basic thermodynamic quantity, could enable poly(vinyl alcohol) (PVA) to effectively form a gel. The resulting hydrogels by alternate compression-decompression (ACD) have tunable superior mechanical properties compared with conventional freeze-thawed (FT) PVA hydrogels. The microstructures of the ACD hydrogels under varying parameters, including compression rate, cycles, and holding time, reveal that either a slow compression rate or cyclic compressions favor the physical cross-linking of such single polymer networks. The mechanical results display a wide range of ultimate tensile strength, tensile strain, and maximum compressive strength of ∼0.3 to 2.5 MPa, ∼200 to 550%, and ∼3 to 7 MPa, respectively. Moreover, the load resistance of such hydrogels can be further trained by low-cyclic strain hardening to a maximum compressive strength of ∼50 MPa, followed by a desirable recovery. Upon cyclic compression, the ACD hydrogels exhibit consistent energy dissipation behaviors. More importantly, the effect of modulation of pressure on the hydrogel’s mechanical properties is very likely universal for other hydrogel systems due to the basic mechanism of pressure-induced gelation for the polymers discussed.