Mechanical and tribological properties of poly(hydroxyethyl methacrylate) hydrogels as articular cartilage substitutes

Poly(hydroxyethyl methacrylate) (p(HEMA)) hydrogels have been proposed as promising biomaterials to replace damaged articular cartilage. A major obstacle to their use as replacement bearing tissue is their poor mechanical properties in comparison with healthy articular cartilage. The purpose of this study was to obtain p(HEMA) hydrogels with physicochemical and mechanical properties close to healthy articular cartilage, by introducing a hydrophilic monomer, namely acrylic acid (AA). Formulations of hydrogels with different amounts of hydrophilic monomer (acrylic acid, AA) were synthesized and tested: p(HEMA), p(HEMA-co-5%AA), p(HEMA-co-25%AA). The macro-mechanical tests were reproduced at nanoscale in order to verify if the superficial properties of the hydrogels are similar to the bulk ones. ► In this study we obtained a HEMA hydrogel substitute of articular cartilage. ► Hydrogels with different amounts of hydrophilic monomer were synthesized and tested. ► HEMA–5%AA hydrogel has mechanical properties similar with the articular cartilage. ► Increase in %AA decreases the homogeneity of hydrogel at macro and nanoscales. ► The HEMA hydrogels exhibit a similar cartilage boundary lubrication mechanism.