In-vitro osteogenesis of synovium stem cells induced by controlled release of bisphosphate additives from microspherical mesoporous silica composite

In this study, in-vitro osteogenesis was successfully induced in the highly chondrogenic synovium mesenchymal stem cells (SMSCs) by controlled release of a nitrogenous bisphosphonate additive – alendronate (AL) from a mesoporous silica (MS)–hydroxyapatite (HA) composite that was mediated in poly(lactic-co-glycolic acid) (PLGA) microspheres. This microspherical based controlled release system is constructed with three levels of degradable structures: (1) the AL drug was first hybridized with HA nanoparticles; (2) the HA–AL complexes were filled into the mesopores of MS particles by self-assembly in situ; and (3) the HA–AL-laden MS constructs (MSH–AL) were built in the bulk of PLGA microspheres. In comparison with any mono-component construct, the superiority of this multi-component system comes from two aspects of functionalities: (1) significantly greater loading capacity of the extremely hydrophilic drug-AL; and (2) better controlled profile of AL release. Based on this newly developed PLGA/MSH–AL releasing system, as recipients the SMSCs, which usually exhibit exclusively high chondrogenesis, demonstrated a strong osteogenic commitment. The results were verified by alkaline phosphatase (ALP) activity assay, calcium secretion assay, real time PCR and immunohistochemistry analysis. Considering the renewable source and high proliferative profile of SMSCs, the achievement of engineered SMSC osteogenesis with this PLGA/MSH–AL controlled release system would open a new door to major bony reparation and regeneration.