Effect of carbonate content and buffer type on calcium phosphate formation in SBF solutions

Coating of titanium-based biomedical devices with a layer of carbonated, apatitic calcium phosphate increases their bone-bonding ability. Simulated or synthetic body fluids (SBF) have the ability of forming apatitic calcium phosphates on the immersed titanium alloys within a few days to 2 weeks. Apatite-inducing ability of 5 M NaOH-etched surfaces of Ti6A14V strips (10 x 10 x 1 mm) were tested by using three different SBF solutions all concentrated by a factor of 1.5. SBF solutions used in this comparative study were: i) 4.2 mM HCO3- TRIS-HCl buffered SBF (conventional SBF or c-SBF), ii) 27 mM HCO3- TRIS-HCl buffered SBF (Tas-SBF), and iii) 27 mM HCO3- HEPES-NaOH buffered SBF (revised SBF or r-SBF). While the c-SBF of low carbonate ion concentration (4.2 mM) was quite sluggish in forming a coat layer on Ti6A14V strips after 1 week of soaking at 37 degrees C, Tas-SBF with a HCO3- concentration exactly equal to that of human plasma (27 mM) was able to fully coat the immersed strips. Tas-SBF solution was able to coat even the vertically-suspended Ti6A14V strips in 1 week. The coated strips were characterized by using XRD, SEM, and FTIR. The differences in the coating morphology and surface coverage were assessed for each SBF solution of this study. In vitro characteristics of as-coated Ti6A14V strips was compared via the cell attachment, cell viability and total protein amount tests by using rat osteoblasts (7 F2). In vitro tests positively favored the calcium phosphate coatings of the TRIS-buffered, 27 mM HCO3- SBF over those of the c- and r-SBF solutions.