Hyaluronic acid nanoparticles titrate the viscoelastic properties of viscosupplements.

Hyaluronic acid (HA) is a glycosaminoglycan with diverse biomedical applications including viscosupplementation of synovial fluid for the treatment osteoarthritis. Current HA viscosupplements such as Synvisc, Orthovisc, and Hyalgan have shown positive effects of reducing pain and improving joint function. The therapeutic efficacy, however, is highly transient, and these viscous fluids suffer from poor injectability. HA nanoparticles were found to modify the rheological properties of a model of the HA viscosupplement Orthovisc. Nanoparticles were successfully synthesized from 17 and 1500 kDa HA. Nanoparticle suspensions of HA were studied at different concentrations and in blends with the model viscosupplement. Nanoparticles made from 1500 kDa HA reduced the viscosupplement viscosity and elasticity to a much greater degree than nanoparticles made from 17 kDa HA. The difference in the nanoparticle effect on viscoelasticity suggested that nanoparticles made from 17 kDa HA may have dangling surface polymers that facilitated interactions with HA in solution. This hypothesis was supported by the greater compressibility of 17 kDa nanoparticles as determined by ultrasonic vibrational spectroscopy. Rheological investigations showed that the viscoelasticity of viscosupplements could be discretely titrated by modulating the concentration and type of HA nanoparticle additive (hard sphere or hairy). Thus, the injectability of viscosupplements may be enhanced while maintaining high elasticity.