Natural rubber as a biomineralization template in natural rubber/hydroxyapatite composites

Biomineralization is a process present in living organisms in which organic molecules act as templates in the formation of nanocrystals of inorganic minerals, influencing features as crystallite size and orientation. Human bone is an example of natural composite material with a complex hierarchical structure that is only possible because of the biomineralization process. In attempts to mimic the process of bone formation, researchers have synthesised hydroxyapatite(HAp) in the presence of different organic molecules. Proteins, Lipids, carbohydrates and polymers with negatively charged groups have successfully improved control over particle size and dispersion. Natural rubber (NR) is a bioactive natural polymer with an interesting chemical structure, consisting of a long poly(cis-1,4-isoprene) chain with a protein and a lipid as terminal groups, making it a possible biomineralization template for hydroxyapatite. In this work we developed a precipitation method that allows the use of natural rubber as a biomineralization template in the fabrication of hydroxyapatite/natural rubber composites. The formation of crystalline Hap at room temperature was confirmed by X-ray diffraction (XRD), microstructural features were analysed by scanning electron microscopy(SEM) and thermogravimetric analysis (TGA) was used to obtain the yield of the reaction. We believe that negatively charged groups in the proteins and lipids present in the NR chains play an important role in the dispersion of HA since it was not possible to produce composites by the same precipitation method when NR was not present in solution during reaction. (author)