Bisphosphonates such as Risedronate (RIS) are drugs of choice in treatment of several systemic bone diseases because of their well-known ability to inhibit osteoclast mediated bone resorption. Influence of RIS on non-resorbing bone cells is also discussed. Polyelectrolytecomplex (PEC) nanoparticles (NP) show promising features for functionalizing implant surfaces including water stable adherence and retarded drug release. To investigate whether PEC-NP are suitable as a drug delivery system for RIS on the surface of implanted material in bone healthy and osteoporotic conditions, this study evaluates cellular compatibility of PEC-NP functionalized Ti-40Nb with human mesenchymal stem cells (hMSC).
hMSC of 5 bone healthy and 5 osteoporotic donors were harvested from bone reaming-debris and seeded on different combinations of implant materials in 24-well plates. Cells were cultured in osteogenic differentiation medium for 35 days. Tested materials consisted of Ti-40Nb plates that were covered with either RIS-loaded PEC-NP, pure RIS-film, unloaded PEC-NP or were left untreated. Osteogenic differentiation was studied using light microscopy and measuring Ca2+ uptake, as well as osteocalcin concentrations in the supernatant. After differentiation period cell viability was assessed via MTT-test.
Microscopic observation revealed that in presence of RIS-containing material cells became detached and formed aggregates shortly after seeding, particularly where RIS was released from PEC-NP. Among all groups mineral production became visible after 6 days of differentiation. MTT assay also showed significantly reduced (p < 0.005) cell viability in vicinity of RIS-loaded PEC-NP when compared to PEC-NP without RIS, which presented the highest viability. In bone healthy cells RIS decreased the Ca2+ uptake in a material dependent manner. Significant reduction in Ca2+ uptake was observed for RIS-loaded PEC-NP compared to the non-RIS containing materials (p < 0.05). Pure RIS-film led to significantly reduced Ca2+ consumption compared to RIS-free PEC-NP (p < 0.05), that exhibited the highest calcium uptake. In osteoporotic donors Ca2+ uptake was reduced. Osteocalcin concentration in the supernatant varied strongly between donors seemingly uninfluenced by RIS.
In conclusion, our results demonstrate that the concentrations of RIS used here led to increased cellular toxicity. Effects were stronger, when RIS was loaded to PEC-NP. PEC-NP without RIS loading did not decrease the viability of hMSC. Thus, PEC-NP seems to be a good drug delivery system for the functionalization of metallic osteosynthetic materials.