A strong and tough interpenetrating network hydrogel with ultrahigh compression resistance

Abstract

A novel interpenetrating network (IPN) hydrogel with ultrahigh compressive strength and fracture strain has been prepared using the copolymer of 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and acrylamide (AM) [P(AMPS-co-AM)] or N-isopropylacrylamide (NIPAM) [P(AMPS-co-NIPAM)] as the primary network and polyacrylamide (PAM) as the secondary network. The as-prepared IPN hydrogel of P(AMPS-co-AM)/PAM has a significantly high compressive strength (91.8 MPa), which is 4 times greater than that of the common PAMPS/PAM IPN hydrogel as well as the compressively strongest hydrogel reported in the literature. The P(AMPS-co-AM)/PAM IPN hydrogel is tough enough not to fracture even when the compressive strain reaches 98%. Synchrotron radiation small-angle X-ray scattering (SAXS) analysis has indicated that the presence of an AM comonomer changes the size of the physically cross-linked domains in the IPN hydrogel, which may partially account for its unique mechanical properties. This study has presented the compressively strongest hydrogel reported to date and also provided a novel and feasible method to prepare the highly strong and tough hydrogel.

Extremely Compressible Hydrogel via Incorporation of Modified Graphitic Carbon Nitride

“…2 wt% g‐CN‐AHPA hydrogel is flexible enough under compression and can withstand stress up to 2 MPa, even when the force is received nonuniformly. Due to physical changes upon compression (regardless of initial shape and surface area), a rough calculation of the compressive strength value for the presented hydrogel yields approximately 10 MPa, which is remarkable for a covalent hydrogel, especially when compared to systems with non‐covalent reinforcements and having the high water content of the presented hydrogel in mind (Table S3, Supporting Information) . The mechanical performance of the hydrogel is clearly in the range to meet the criteria for tough cartilage‐joint systems where the average cyclic stress ranges from 6 MPa up to 14 MPa with daily activities like walking or running .…”

“…Being weak under regular synthesis conditions, significant effort was invested in reinforcing hydrogels to increase their mechanical properties and to mimic natural systems . Common approaches for reinforcement utilize double network systems, nano composite hydrogels, host–guest systems, and solid reinforcer additions . Reinforcers act as a stress absorbing material and ideally distribute the stress equally through the polymeric network.…”

“…Due to physical changes upon compression (regardless of initial shape and surface area), a rough calculation of the compressive strength value for the presented hydrogel yields approximately 10 MPa, which is remarkable for a covalent hydrogel, especially when compared to systems with non-covalent reinforcements and having the high water content of the presented hydrogel in mind (Table S3, Supporting Information). [4,6,15,16,34] The mechanical performance of the hydrogel is clearly in the range to meet the criteria for tough cartilage-joint systems where the average cyclic stress ranges from 6 MPa up to 14 MPa with daily activities like walking or running. [35,36] One important, distinct characteristic of the presented hydrogel lies beneath its softness, which allows improved stress load distribution compared to tough hydrogels.…”

Supplementary Networking of Interpenetrating Polymer System (SNIPSy) Strategy to Develop Strong & High Water Content Ionic Hydrogels for Solid Electrolyte Applications

“…[ 16 ] Interpenetration of networks via one‐step or sequential procedure was able to increase the compressive strength above 90 MPa and the tensile strength to 1.3 MPa. [ 17 ] Polymeric [ 18 ] and metallic nanoparticles [ 19 ] served as reinforcing agents and strengthened the tensile properties and stretchability of the hydrogels. In most of the reported strategies, the water content was limited between 70 to 90%.…”

Mechanics of composite hydrogels approaching phase separation

“…Frequently, nanoparticles are added to such hydrogels, to modify either their biofunctionality or their mechanical properties: for example, adding silver nanoparticles makes PVA/gum acacia hydrogels antibacterial [9], and magnetic nanoparticles allow for hydrogels to be remotely controlled by magnetic fields [10]. Nanoparticles are also used to modulate the mechanical properties of hydrogels, since their presence often strongly influences the hydrogel stiffness [11], porosity [12]and fracture resistance [13], which are all crucial for many applications. For instance, cartilage substitutes need to be resistant to high compressive stresses but at the same time have have tunable stiffness [14].…”