Along the margins in the definition of “bioactivity”, the term “bioactivity” was coined to refer to those materials that can develop a direct, adherent, and strong bonding with the bone tissue. To evaluate the bioactivity of the materials, it has been proposed that materials that form an apatite on their surfaces in the SBF also can form the apatite in a living body and can bond to bone through the apatite layer. In other words, the apatite-forming ability in the SBF is a measure of in vivo bioactivity.
A cellular SBF was used for in vitro experiments. The SBF solution was prepared according to the procedure described by Kokubo and Takadama. Ion concentrations of SBF are similar to those in human blood plasma .
There are histological techniques for measuring new bone formation that should work for chemical apatite deposition. These require adding compounds that are incorporated into calcium phosphate crystals as a pulse label so that crystals growing at the time of labeling take up the compound. Tetracycline can be added to water for living animals or culture medium for in vitro experiments, and regions of uptake are detected by fluorescence in microtome sections (or epoxy-embedded ground sections if mineralization is too hard for cutting microtome sections). Lead acetate can be similarly added and detected by precipitation of black lead sulfide after exposure to hydrogen sulfide (more toxic than tetracycline, but permanent).
It appears that your question pertains to in vitro analysis. If you are sure that what forms is apatite then periodic UV Spec measurement of SBF for calcium concentration can give fairly good idea of rate of deposition.
How to measure bone-like apatite rate? – by weight changing of your samples during the fixed periods of time (e.g., the initial weight was 1 g, after 24 hours of soaking it became 1.1 g, therefore, the rate was 0.1 g/24 hours). Similar calculations can be done by following the concentration decreasing of the major ions.
or From SEM of soaked sample how to measure the rate of apatite formation? – by thickness increasing of the deposits during the fixed periods of time. To get the best results, a combination of all 3 techniques (weight changing, concentration decreasing and thickness increasing) should be used.
Is there any formula or software? – no it is not.
You can check the cross-section under SEM, and then measure the apatite layer thickness. Another method is using XRF depth profile.
@sergy V. dorozhkin Thanks for your excellent advice. But I have a question do you think degradation and dissolution in the SBF might be a meaurment by chance which you may investigate by ICP or EDX. In the case of evaluationg with SEM, just you are considering caultiflower area and white tiny space. I agree with your suggestion about thickness. It seems more practical. I am honor to review your excellemt and wonderful papers...so amazing
do you think degradation and dissolution in the SBF might be a measurement by chance which you may investigate by ICP or EDX? – everything depends on both the accuracy of your experiments, including solution preparation, and the sensitivity of the measurement techniques you are able to use. Similar is valid for SEM investigations and any other approach. Therefore, the proper combination of various techniques (the more techniques – the better) will always be the best choice. You just need to work, analyze, read, gain the experience, think, etc.
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