Toughening hydrogels by immersing with oppositely charged polymers

Cationic Modified PVA Hydrogels Provide Low Friction and Excellent Mechanical Properties for Potential Cartilage and Orthopedic Applications

Poly(vinyl alcohol) (PVA) hydrogel is a promising candidate for articular cartilage repair yet restrained by its mechanical strength and tribological property. Current work reports a newly designed PVA-based hydrogel modified by glycerol (g), bacterial cellulose (BC), and a cationic polymer poly (diallyl dimethylammonium chloride) (PDMDAAC), which is a novel cationic strengthening choice. The resultant PVA-g-BC-PDMDAAC hydrogel proves the effectiveness of this modification scheme, with a confined compressive modulus of 19.56 MPa and a friction coefficient of 0.057 at a joint-equivalent load and low sliding speed. The water content, swelling property, and creep behavior of this hydrogel are also within a cartilage-mimetic range. The properties of PVA-based hydrogels before PDMDAAC addition are likewise studied as a cross-reference. Besides, PDMDAAC-modified PVA hydrogel realizes ideal mechanical and lubrication properties with a relatively low PVA concentration (10 wt.%) and facile fabrication process, which lays a foundation for mass production and marketization in the future.

Mechanically Strong, Tough, and Shape Deformable Poly(acrylamide-co-vinylimidazole) Hydrogels Based on Cu2+ Complexation

Shape deformable hydrogels have drawn great attention due to their wide applications as soft actuators. Here we report a novel kind of mechanically strong, tough, and shape deformable poly(acrylamide-co-vinylimidazole) [poly(AAm-co-VI)] hydrogel prepared by photoinitiated copolymerization and the followed immersing in a Cu²⁺ aqueous solution. Strong Cu²⁺ complexation with imidazole groups dramatically enhances the mechanical properties of the hydrogels, whose tensile strength, elastic modulus, toughness, and fracture energy reach up to 7.7 ± 0.76 MPa, 15.4 ± 1.2 MPa, 23.2 ± 2.5 MJ m^-3, and 22.1 ± 2.3 kJ m^-2, respectively. More impressively, shape deformation (bending) can be easily achieved by coating Cu²⁺ solution on one side of hydrogel strips. Furthermore, precise control of the shape deformation from 1D to 2D and 2D to 3D can be achieved by adjusting Cu²⁺ concentration, coating time, region, and one or two side(s) of hydrogel samples. The Cu²⁺ complexation provides a simple way to simultaneously improve the mechanical properties of hydrogels and enable them with shape deformability. The mechanically strong, tough, and shape deformable hydrogels might be a promising candidate for soft actuators.

Engineering hydrogels by soaking: from mechanical strengthening to environmental adaptation

The soaking strategy could not only strengthen hydrogels with superior mechanical properties but also provide the hydrogels with environmentally adapting properties.

Conductive regenerated silk-fibroin-based hydrogels with integrated high mechanical performances

Strong and tough RSF-based hydrogels that could be used as a strain sensor, a touch screen pen and an electronic skin were developed.

Structured Macroporous Hydrogels: Progress, Challenges, and Opportunities

Structured macroporous hydrogels that have controllable porosities on both the nanoscale and the microscale offer both the swelling and interfacial properties of bulk hydrogels as well as the transport properties of "hard" macroporous materials. While a variety of techniques such as solvent casting, freeze drying, gas foaming, and phase separation have been developed to fabricate structured macroporous hydrogels, the typically weak mechanics and isotropic pore structures achieved as well as the required use of solvent/additives in the preparation process all limit the potential applications of these materials, particularly in biomedical contexts. This review highlights recent developments in the field of structured macroporous hydrogels aiming to increase network strength, create anisotropy and directionality within the networks, and utilize solvent-free or additive-free fabrication methods. Such functional materials are well suited for not only biomedical applications like tissue engineering and drug delivery but also selective filtration, environmental sorption, and the physical templating of secondary networks.

Super-strong and tough poly(vinyl alcohol)/poly(acrylic acid) hydrogels reinforced by hydrogen bonding

Super-strong and tough poly(vinyl alcohol)/poly(acrylic acid) hydrogels based on hydrogen bonding are prepared by the strategy of immersing and cold-drawing.