Fabrication of Tough Hydrogel Composites from Photoresponsive Polymers to Show Double-Network Effect

Abstract

Inspired by the toughening mechanism of double-network (DN) gels, tough hydrogel composites with a sandwich structure were fabricated from photoresponsive polymers. By copolymerization of hydrophilic monomers, 2ureidoethyl methacrylate (UM), and photoresponsive hydrophobic monomers, (2-nitrobenzyloxycarbonylaminoethyl methacrylate (NBOC)) at high concentrations, physical hydrogels that are soft and highly stretchable are formed due to the hydrophobic associations of NBOC, serving as dynamic crosslinkers. By UV irradiation, the physical crosslinking switches into chemical crosslinking, and the soft physical hydrogels transform into rigid and less stretchable chemical hydrogels. By UV curing the surface layers of the physical hydrogels, we prepared hydrogel composites having a sandwiched structure with two rigid outer layers and a soft inner layer. The molecular-level continuous interfaces and matched swelling ratios between the layers ensure the macroscale hydrogel composites' high strength and toughness with a DN gel effect. The outer layers fracture preferentially at deformation, playing a role like the first network of a DN gel, while the inner layer maintains the integrity, playing a role resembling the second network. The evolution of the fracture morphology of the rigid layers gives useful insight into the internal fracture process of DN gels.

3D Printing of Strong and Tough Double Network Granular Hydrogels

“…Indeed, this strategy enables the design of extremely tough hydrogels that can be stretched up to 50 times. [ 16–18 ] However, these tough hydrogels are typically rather soft such that they cannot bear significant loads under tension. To overcome this shortcoming, double network (DN) hydrogels composed of two interpenetrating polymeric networks have been introduced.…”

“…By contrast, synthetic hydrogels typically have an ill‐defined microstructure and their composition is most often homogeneous. Variations in the composition can be introduced using magnetic nanoparticle gradients, [ 22 ] ultraviolet (UV) patterning, [ 23 ] micro‐molding, [ 24 ] photo‐triggered chemical cross‐linkers, [ 18 ] or micro‐phase separation. [ 25 ] Another remarkable example of controlling the microstructure of soft synthetic materials is the incorporation of liquid crystals into polymer chains.…”

Highly Elastic Slide‐Ring Hydrogel with Good Recovery as Stretchable Supercapacitor

“…Another strategy is to optimize the polymer network structure of chemically cross‐linked hydrogels to make it easily disperse internal stress. A very typical example is the double‐network gel, in which two polymer networks with different chain lengths are interspersed with each other, and the short‐chain polymer network is ruptured for energy dissipation, but the long‐chain polymer network maintains the high elasticity of the gel [1f, g, 5] . Practice has proved that these gel have excellent mechanical properties as well as good stability, which is superior to physical polymer hydrogels.…”

Renormalized Flory‐Huggins lattice model of physicochemical kinetics and dynamic complexity in self‐healing double‐network hydrogel

“…Furthermore, the effect of molar concentration of network component on the mechanical property of DN hydrogel has been studied using the proposed model. Three groups of experimental data 41 of UM/NBOC (UM: ureidoethyl methacrylate, NBOC: nitrobenzyloxycarbonylaminoethyl methacrylate) DN hydrogels with a variety of molar concentration of NBOC network ( f NBOC , f NBOC = 0.1, 0.15, and 0.2), have been employed to verify the proposed model. All parameters used in the model are listed in Table 2.…”

“…Comparison between analytical results using Equation ) and experimental data 41 of the UM/NBOC double‐network hydrogels with a variety of molar concentration of the NBOC network of f NBOC (mol%) = 0.1, 0.15, and 0.2. (a) the simulated parameters are originated from Table 2.…”