Evaluation of implant materials (hydroxyapatite, glass-ceramics, titanium) in rat bone marrow stromal cell culture

Bone marrow stromal cells of femora from young adult rats produce bone-like mineralized tissue in culture. We evaluated three implant materials (hydroxyapatite (HA), glass-ceramics (GC) and commercial pure titanium (Ti)), as to their ability to provide an environment for marrow cells to differentiate into osteoblasts and function as suitable for mineralized tissue formation. We did this by measuring the DNA content, alkaline phosphatase (ALP) activity and calcium (Ca) content in culture, and the expression of osteopontin and bone sialoprotein by means of analysis of gene expression using Northern hybridization. DNA measurement showed no difference between each material, but ALP activity and Ca content in the culture on HA and GC were higher than on Ti and the control. An analysis of the gene expression revealed the highest expression of osteopontin and bone sialoprotein in the culture on HA. Mineralized nodule formation (both in area and number) was the most predominant on HA, followed by that on GC. These results showed that HA and GC provided a favourable situation for marrow cells to differentiate osteoblasts, resulting in a large amount of mineralized tissue formation on these surfaces. Present in vitro results could explain the rapid bone bonding of HA and GC in vivo.