Preparation of in situ forming and injectable alginate/mesoporous Sr-containing calcium silicate composite cement for bone repair

Abstract

Injectable biomaterials to aid bone regeneration are worth investigating in bone tissue engineering due to minimized invasive damages. In this study, a novel in situ formed composite cement consisting of alginate and Sr-containing mesoporous calcium silicate nanoparticles (mSCS) has been designed. Firstly, mSCS were fabricated with Sr-substitution for Ca in mesoporous calcium silicate nanoparticles. The morphology, particle size, element mapping and mesoporous structure of the mSCS nanoparticles were characterized. The results showed that the nanoparticles were in the range from 200 nm to 300 nm, and had a surface area of about 312 m² g⁻¹. Then the mSCS materials were mixed with a sodium alginate solution. The alginate component in the composite cement was internally crosslinked by locally released Ca²⁺/Sr²⁺ cations from mSCS through the addition of D-gluconic acid δ-lactone (GDL). Characterization results showed that GDL accelerated the gelation rate of cement and thus increased the injectability coefficient to more than 90% after 2 minutes of setting. The higher amount of GDL enhanced the tridimensional network formation rate and improved the compressive strength and Young's modulus of the cement. In addition, scanning electron microscopy (SEM) observations demonstrated that the alginate hydrogel provided extra micropores (tens of micrometers) for cell growth. The mSCS induced fast bone-like apatite deposition on the surface of all the cements after 3 days of SBF immersion. In vitro human bone mesenchymal stem cell (hBMSC) tests, including Cell Counting Kit-8 (CCK-8) assay and alkaline phosphatase (ALP) activity evaluation, revealed that the injectable mSCS–alginate cement had significant biocompatibility and low cytotoxicity, and moreover could support hBMSC proliferation and osteogenesis differentiation.