Mechanical and tribological assessment of silica nanoparticle-alginate-polyacrylamide nanocomposite hydrogels as a cartilage replacement.

Interpenetrating polymer network (IPN) of alginate-polyacrylamide (ALG-PAAm) has been explored in the past, showing a potential capacity as a structural biomaterial to replace cartilage lesions. In the current study, silica nanoparticles (Si-NPs) were introduced to ALG-PAAm IPN hydrogel as a reinforcement and the mechanical and tribological characteristics of the resultant nanocomposite hydrogel was investigated. Mechanical tests were performed including indentation, unconfined uniaxial compression and stress relaxation to explore the effect of Si-NP concentration on elastic and viscoelastic responses, while friction and wear studies were conducted with the hydrated samples sliding against an alumina ceramic ball. The results were compared with ALG-PAAm hybrid hydrogel samples without nanoparticle reinforcement. Ultra-low coefficient of friction (CoF), coupled with high wear-resistance, and tunable elastic and viscoelastic behaviors observed were mainly attributed to the strong interfacial binding between the nanoparticles and the polymer matrix, allowing effective stress transfer between the two main constituents. This suggests these biomaterials as a promising candidate for use as a cartilage replacement. Samples with 4% concentration of Si-NP, showed considerably robust mechanical performance, high wear-resistance and fairly low CoF.