Preferred Growth Orientation of Apatite Crystals on Biological Hydroxyapatite Enriched with Bioactive Glass: A Biomimetic Behavior

The morphological, structural, and chemical transformations during the biomineralization process associated with the apatite formation from bovine-derived hydroxyapatite (BHAp) and BHAp/Nagelschmidtite composite obtained from the mixture of BHAp and Vitryxx bioactive glass are presented. The study is focused on the structural characteristics of apatite formation and the maturation process taking place at the biomaterial surface. The use of a biological HAp is of interest aiming to mimic the natural process of bone mineral matrix formation in the crystallization mechanism. This process was characterized by transmission electron microscopy, where the initial stage was identified as the formation of a hydrated amorphous matrix followed by the appearance of randomly oriented nanocrystals that later coalesce and grow with a preferred orientation to the c-axis. This behavior is a biomimetic process based on the alignment of natural bone apatite along collagen fibrils. The understanding of natural processes of mineral matrix formation at the micro- and nanoscale levels on bioactive materials is of great interest to address the effect of size, structure, and composition of apatite nanocrystals on the biologic phenomena involved in osteointegration.