Surface modification of titanium with phosphonic acid to improve bone bonding:: Characterization by XPS and ToF-SIMS

Commercially pure titanium (cp Ti) is widely used in dental implantology. However, it is only passively integrated in bone and the resulting fixation in the bone, which is necessary for the function, is mainly mechanical in its nature. With the objective of increasing the chemical interaction between the implant and bone tissue, several phosphonic acids were synthesized and grafted onto titanium disks. The bare polished Ti disks (Ti P) and the grafting of three phosphonic acids (methylenediphosphonic acid (MDP), propane-1,1,3,3-tetraphosphonic acid (PTP), and ethane-1,1,2-triphosphonic acid (ETP)) on these disks were characterized with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). These surface analytical techniques provided strong indications of the formation of a chemical link between the Ti implant and the phosphonic acid molecule. The bioactivity of the modified Ti disks was evaluated by incubating these disks in a physiological solution (Hank's balanced salt solution (HBSS)) for 1, 7, and 14 days. Modified surfaces showed only slightly higher calcium levels in the XPS analysis compared to the reference Ti P surface. Among them, the surface modified with ETP (Ti P + ETP) induced the highest calcium phosphate deposition after 14 days incubation.