The effect of organic molecules on magnesium degradation
Magnesium (Mg) and its alloys have been widely investigated as biomaterials due to their remarkable biodegradability and bioresorbability. The discrepancy of degradation results between in vitro and in vivo observations demands a much better understanding for the mechanism of the degradation processes. However, the roles of organic molecules in Mg degradation remain unclear. In this thesis, several typical organic components, L-ascorbic acid, L-glutamine, L-alanyl-L-glutamine, bovine serum albumin, fibrinogen and fetal bovine serum were chosen to elucidate the effects of organic components on the degradation of pure Mg under cell culture conditions. The results reveal that the influence of organic components on the degradation of pure Mg is time- and medium-dependent. Small organic molecules increase the degradation rate of pure Mg after relatively long-term immersion, while proteins generally reduce the degradation of Mg. On the other hand, they play an important role in the formation of the degradation products. The addition of organic components favours the precipitation of crystalline nesquehonite rather than hydromagnesite in the ‘outer’ layer in HBSS. Whereas, in HBSSCa and DMEM organic components accelerate the formation of Ca/P-rich products in the top of degradation layer, presenting an in vivo-like degradation layer. Moreover, proteins seem to stabilize the top of Ca/P-rich layer and protect the integrity of degradation layer, which are of importance to Mg degradation. The formation of Ca/P-rich products reduces the surface roughness and changes the surface chemistry and charge, eventually weakening the adsorption of proteins. A promising result is that the addition of organic molecules, especially FBS, can weaken the difference of Mg degradation caused by the different conditions used, such as the composition of media, the ratio of medium volume to sample and the static or semi-static conditions, which enables the results more comparable.
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