Novel self-gelling, injectable composites for bone regeneration based on gellan gum hydrogel and calcium and magnesium carbonate microparticles

摘要

Introduction: Hydrogels are becoming more popular biomaterials for bone regeneration due to their injectability and the ease of incorporation of inorganic particles, e.g. calcium phosphate (CaP). Carbonates, e.g. CaCO3 have been successfully applied as bone regeneration materials and are more soluble than CaP. Carbonate particles could potentially serve as delivery vehicles for slow release of calcium (Ca) or magnesium (Mg) ions to crosslink anionic polysaccharides such as gellan gum (GG) to form homogeneous hydrogels. Carbonate microparticles containing Ca and/or Mg can be formed easily by mixing Ca2+ and Mg2+ and CO32- ions in varying concentrations. In this study, carbonate microparticles containing different amounts of Ca and Mg were added to a GG solution. Ca2+ and Mg2+ released from microparticles crosslinked GG to yield hydrogel-microparticle composites. The effect of Mg content on gelation, cytocompatibility and cell growth was studied. Methods: Ca2+/Mg2+ solutions of different Ca:Mg elemental ratios and CO32- solution were prepared. Particles were separated off by centrifugation, dried and autodaved and subjected to physiochemical characterization using FTIR, XRD, SEM, Raman, AAS and DLS. To generate self-gelling GG-microparticle composites, microparticles were resuspended in ddH2O and mixed with autodaved GG solution at 37° C. Final micropartide and GG concentrations were 2.5% and 0.66%, respectively (w/v). Gelation speed, micropartide distribution and cytocompatibility were investigated by rheometry, Micro-CT and MG-63 osteoblast-like cell culture in eluate from composites and directly on composites, respectively. Results: In the absence of Mg, calcite with some vatertie was formed. At low Mg content, magnesian calcite was formed. Increasing Mg content further increased general amorphicity. Microparticles of calcite, vaterite and magnesium caldte did not induce hydrogel formation. Addition of Mg-richer microparticles induced gelation within 25 min. Micropartide dispersion in hydrogels was homogeneous. All composites were cytocompatible. Cell growth after 7 d was highest on composites containing particles with an equimolar Ca:Mg ratio. Discussion: Increasing Mg content in the microparticles increased their amorphicity, in turn increasing their solubility, resulting in enhanced ion release and GG crosslinking and, in turn, hydrogel formation. Other studies have reported a beneficial effect of Mg as a component of CaP on cell proliferation, as observed in this study. Conclusion: Carbonate microparticles containing a sufficient amount of Mg induce GG hydrogel formation, resulting in injectable, cytocompatible hydrogel-micropartide composites.