Experimental – Apatite – Research

Weitian Zhao (PhD student)

Ti and Ti alloys (such as Ti-6Al-4V) have been widely used as dental and orthopedic implant materials due to their good mechanical properties and biocompatibility. Although on their own these materials hardly bond to living bone when implanted, it is possible to induce bioactivity by simple chemical treatments such as NaOH combined with thermal annealing. The effectiveness of these treatments have been confirmed by both in vitro and in vivo experiments [3, 4]. NaOH and heat treated Ti can therefore be used as a positive control for validating in vitro methods which are aimed at predicting in vivo bioactivity of implant materials.

In the experimental part of the project, we started off with the suggested solution recipe by Bohner and Lemaître and gradually adding more components into the solution. The solution composition is tuned according to our thermodynamic speciation calculations. The essential difference with the ISO method is the use of 5% CO2 as a buffering system, which also results in a higher content of carbonate species in the SBF. After one week of immersion in our SBF in an incubator with 5% CO2 and a constant temperature of 37 °C, apatite formation was found on NaOH treated Ti. The result is consistent with the prediction using the ISO method. Images of Ti surfaces after NaOH treatment and after immersion in our SBF for one week are shown below.


SEM images of NaOH treated Ti surfaces before (a) and after apatite forming ability test (b).
 

Apatite formation was also found on NaOH and heat treated Ti. This demonstrates that our method is capable for accurate prediction of the bioactivity of alkaline treated Ti metals, a first step in validating this new method. Follow up research are currently being conducted focusing on the effect of other inorganic ions in the SBF and the introduction of proteins (e.g. albumin). This project is in collaboration with the Robert Mathys Foundation (RMS) based in Bettlach, Switzerland.

[3] Kim, H.M.; Kokubo, T. Preparation of bioactive Ti and its alloys via simple chemical surface treatment. J. Biomed. Mater. Res. 32, 409–417 (1996).
[4] Nishiguchi, S.; Fujibayashi, S.; Kim, H.-M.; Kokubo, T.; Nakamura, T. J. Biomed. Mater. Res. A 2003, 67, 26–35.