Implantation of hydrophilic and hydrophobic titanium discs in rat tibia: cellular reactions on the surfaces during the first 3 weeks in bone.

In a previous study, a method for evaluation of short-time (1-8 days) healing of titanium implants in rat tibiae was described (J. Biomed. Mater. Res. 66A(3) (2003) 662). The implants were disc-shaped and cells and tissue on the surface were investigated, not the adjacent tissue. In this study healing during the first 3 weeks in bone was examined and the healing response between hydrophilic and hydrophobic titanium was compared. Immunofluorescence techniques were used to detect signs of bone formation on the surfaces. Cell viability, alkaline phosphatase (ALP) activity, presence of osteocalcin and cells positive for bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) were investigated. Both viable and non-viable cells were found on both surfaces during the first week. Only initially was there a difference between them; 4% viable cells on hydrophilic discs compared to 56% on hydrophobic ones. More BMP-2 positive cells were found on hydrophilic discs than on hydrophobic ones after 1 week. VEGF was detected after 8 days on both surfaces. Osteocalcin positive cells were found from 2 weeks. ALP positive cells were found after 8 days, while at 2-3 weeks ALP positive tissue was abundant on both surfaces. In conclusion, signs of bone formation were detected during the period investigated. Surface energy appeared to be of more importance initially, with higher surface energy resulting in more rapid cell activation and differentiation than lower.