Injectable self-gelling composites for bone tissue engineering based on gellan gum hydrogel enriched with different bioactive glasses

摘要

Introduction: Gellan gum (GG) is an anionic, calcium-binding polysaccharide produced by bacteria which has been applied in hydrogel form as a tissue engineering (TE) scaffold. Gelation of GG is induced by addition of divalent cations. GG's high affinity for calcium ions means that it is highly mineralizable with calcium phosphate (CaP), which is desirable to improve the material's bioactivity, mechanical properties and osteoblast adhesion and proliferation. Here, GG hydrogels were enriched with bioactive glass particles to enhance ⅰ) mineralization with calcium phosphate (CaP); ⅱ) antibacterial properties and ⅲ) growth of bone-forming cells for future bone regeneration applications. Methods: Three bioactive glasses were compared. One calcium-rich and one calcium-poor preparation (hereafter referred to as A2 and S2) were produced by a sol-gel technique. One preparation of composition close to that of the commonly used 4SS5 type (hereafter referred to as NBG) was produced by flame synthesis. Pre-autoclaved 0.875% (w/v) GG solution and pre-autoclaved bioactive glass suspensions were mixed intensively and then immediately cast at room temperature. Discs of diameter 6 mm and height of 1 mm were cut out and served as samples. The final concentrations of GG and bioactive glass were 0.7% and 1 % w/v, respectively. Samples were then incubated in simulated body fluid (SBF), or subjected to degradation studies, mechanical testing, Micro-CT analysis, antibacterial and cell biological testing. Results: Incubation in SBF for 7,14 and 21 days caused apatite formation in bioactive glass-containing but not in bioactive glass-free samples, as confirmed by FTIR, XRD, SEM, ICP-OES, and measurements of dry mass, i.e. mass attributable to polymer and mineral and not water. Dry mass increases were higher for samples containing S2 and A2 than for those containing NBG. Mechanical testing revealed an increase in compressive modulus in samples containing S2 and NBG but not A2. Samples containing A2 and S2 displayed higher antibacterial activity than samples containing NBG and bioactive glass-free samples against biofilms of meticillin-resistant Staphylococcus aureus (MRSA). Cell biological characterization using rat mesenchymal stem cells (rMSCs) revealed a stimulatory effect of NBG on rMSC differentiation. Discussion: The greater stimulatory effect of S2 and A2 on mineralization and their higher antibacterial effect in comparison to NBG may possibly be due to higher solubility and release of calcium ions, as they are sol-gel derived, while NBG is melt-derived. Conclusion: The addition of bioactive glass thus promotes GG mineralizability and, depending on bioactive glass type, antibacterial properties and rMSC differentiation.