Hyaluronic acid-silica nanohybrid gels

Excessive water sorption and low mechanical properties are a severe drawback in some biomedical applications of hyaluronic acid (HA). A way to improve these properties is here explored through the novel concept of nanohybrid hydrogels consisting of a HA matrix including different amounts of silica-derived species. This inorganic filler phase controls the mechanical and swelling properties of HA cross-linked matrices. Below a 2 wt % of silica in the systems, nanoparticle aggregates of tens of nanometers and silica oligomers are distributed more or less homogeneously throughout the organic matrix, without percolating. This morphology of the silica phase is accompanied by an increased swelling degree of the composite when compared with pure HA. For higher silica mass ratios in the composites the inorganic counterpart coalesces, leading to a continuous inorganic silica network interpenetrated with the organic HA network, which coexists with a dispersed phase of silica-nanoparticle aggregates. Silica oligomers originating in the exposition of the nanoparticles to reactives during the composite preparation procedure contribute to the continuity of the silica network. For these compositions, swelling is reduced three times when compared with pure HA, and a significant improvement of the mechanical properties occurs. Water-containing samples of these materials exhibited a glass transition, which pure dry HA does not. None of the compositions studied showed any cytotoxicity. Thus, the materials could be of use in tissue engineering applications where these properties of HA need to be modulated.