Phase-Separation-Induced Porous Hydrogels from Amphiphilic Triblock Copolymer with High Permeability and Mechanical Strength

Porous hydrogels, possessing both high mechanical strength and high permeability, are sought after in energy storage, soft robotics, solar vapor generation, and tissue engineering. However, there is always a trade-off between mechanical strength and permeability. In general, high porosity promotes molecular mass transportation (permeability) but sacrifices mechanical strength. To address this issue, in this work, micro/nanoporous hydrogels with high mechanical strength are fabricated from the self-assembly of amphiphilic triblock copolymers consisting of hydrophilic end blocks and hydrophobic midblocks. The chemically distinct blocks induce the phase separation, yielding a hydrogel network consisting of nanopores dispersed in the micrometer-thick sponge-like base support with an ordered lamellar structure. The soft water-depleted phase is dynamic, forming a transient network that allows chain exchange and coalescence between different phases. This reversible process not only dissipates energy to toughen hydrogels but also enables self-recovery. By systematically altering the length of end blocks and midblocks, one can synthesize hydrogels with tunable mechanical properties, including an elastic modulus of 87–884 kPa, a fracture stress of 63–584 kPa, a fracture strain of 1–20, and work of extension of 217–2104 kJ/m3. The gels with a porous size in the range of 1–8 μm also exhibit self-recovery behavior and a high permeability of 10–12 and 10–11 m2. The porous hydrogels show a fracture energy of ∼2000 J/m2, several orders of magnitude higher than common porous hydrogels (gelatin, agarose, and polyacrylamide) and comparable to soft biological tissues. The preparation process also endows the foreseeable potential as injectable hydrogels for applications in soft robotics and 3D printing.