The biological performance of bone graft substitutes based on calcium phosphate bioceramics is dependent
on a number of properties including chemical composition, porosity and surface micro- and nanoscale
structure. However, in contemporary bioceramics these properties are interlinked, therefore making
it difficult to investigate the individual effects of each property on cell behavior. In this study we have
attempted to investigate the effects of calcium and inorganic phosphate ions independent from one
another by preparing composite materials with polylactic acid (PLA) as a polymeric matrix and calcium
carbonate or sodium phosphate salts as fillers. Clinically relevant bone marrow derived human mesenchymal
stromal cells (hMSCs) were cultured on these composites and proliferation, osteogenic differentiation
and ECM mineralization were investigated with time and were compared to plain PLA control
particles. In parallel, cells were also cultured on conventional cell culture plates in media supplemented
with calcium or inorganic phosphate to study the effect of these ions independent of the 3D environment
created by the particles. Calcium was shown to increase proliferation of cells, whereas both calcium and
phosphate positively affected alkaline phosphatase enzyme production. QPCR analysis revealed positive
effects of calcium and of inorganic phosphate on the expression of osteogenic markers, in particular bone
morphogenetic protein-2 and osteopontin. Higher levels of mineralization were also observed upon
exposure to either ion. Effects were similar for cells cultured on composite materials and those cultured
in supplemented media, although ion concentrations in the composite cultures were lower. The approach
presented here may be a valuable tool for studying the individual effects of a variety of soluble compounds,
including bioinorganics, without interference from other material properties.