Calcium phosphate cement (CPC) is a good biomaterial for bone defect repair and as a delivery system for active agents. The aim of this study was to explore the physicochemical properties and in vitro soaking and release behaviors of gentamicin-loaded CPC with and without alginate; in particular, for biocompatibility. MTT colorimetric assay and RT-PCR were used to detect U2OS cell viability and level of cyclooxygenase-2 (COX-2), respectively. As a result, the setting time increased after the addition of 0.5% alginate and 5% gentamicin, reaching 19 min—significantly higher than the 8 min taken by the CPC control, demonstrating the adverse effect of alginate and gentamicin on the setting reaction of CPC. Gentamicin might reduce the diametral tensile strength, while alginate did not affect the strength. The rate of gentamicin release from CPC can be extended by the presence of alginate. The addition of gentamicin did not show signs of impaired cell viability, but alginate enhanced the cell viability. COX-2 expression of U2OSs cultured in the alginate-containing cement extract was about one-third level of the cement extract without alginate. Alginate-containing CPC is not only useful as a reservoir for antibiotic delivery but it also helps stimulate bone regeneration.
