Incorporation of Hydroxyapatite Sol Into Collagen Gel to Regulate the Contraction Mediated by Human Bone Marrow-Derived Stromal Cells

In this paper, hydroxyapatite (HA) sol composed of nanosized HA particles was incorporated into collagen gel to regulate cell-mediated collagen contraction. Human bone marrow derived stromal cells (hMSCs) were cultured for 37 days in gels with HA to collagen ratios of 0:1, 0.5:1, 1:1, 1.5:1, and 2:1, respectively. The contraction of gels was evaluated by measuring diameter change with incubation time, and the microstructure of gels at the end of culture was visualized by SEM. The cytotoxicity of HA sol was evaluated according to the percentage of maximum lactate dehydrogenase (LDH) release from hMSCs. A combination of Hoechst 33342, propidium iodide, and calcein esters was used for imaging the live/dead cells and the distribution of loaded cells within the constructs. By incorporating HA sol into the collagen gel, the hMSCs medicated contraction was delayed and the extent of contraction was reduced as the proportion of HA relative to the collagen increased. Depending on the ratio of HA sol incorporated within the collagen gel, hMSC cells revealed different morphology and a change in the distribution of loaded cells within the gels. No significant cytotoxicity was noticed as a consequence of incorporating HA sol into the collagen lattice.