Double Network Hydrogels that Mimic the Modulus, Strength, and Lubricity of Cartilage

The development of a hydrogel-based synthetic cartilage has the potential to overcome many limitations of current chondral defect treatments. Many attempts have been made to replicate the unique characteristics of cartilage in hydrogels, but none have simultaneously achieved high modulus, strength, and toughness while maintaining the necessary hydration required for lubricity. Herein, double network (DN) hydrogels, composed of a poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) first network and a poly( N-isopropylacrylamide- co-acrylamide) [P(NIPAAm- co-AAm)] second network, are evaluated as a potential off-the-shelf material for cartilage replacement. While predominantly used for its thermosensitivity, PNIPAAm is employed to achieve superior mechanical properties with its thermal transition temperature tuned above the physiological range. These PNIPAAm-based DNs demonstrate a 50-fold increase in compressive strength (∼25 MPa, similar to cartilage) compared to traditional single network hydrogels while also achieving cartilage-like modulus (∼1 MPa) and hydration (∼80%). In direct comparison to healthy cartilage (porcine), these hydrogels were confirmed to not only parallel the strength, modulus, and hydration of native articular cartilage but also exhibit a 50% lower coefficient of friction (COF). The exceptional cartilage-like properties of the PAMPS/P(NIPAAm- co-AAm) DN hydrogels makes them candidates for synthetic cartilage grafts for chondral defect repair, even in load-bearing regions of the body.