Biomolecules – biomaterials interactions: IR study of the adsorption, in model conditions, of glycine on Hydroxyapatite and TiO2

Hydroxyapatite (HA), on of the material considered in this thesis, is the main component of hard tissue such as bone and teeth of vertebrates animal and humans. Consequently HA is readily considered as a bioactive material for artificial bone substitution because of its biocompatibility and chemical and biological affinity with the bone tissue.
Calcium hydroxyapatite (Ca5(PO4)3OH) is the primary component of natural bone, but a number of other calcium-phosphorus compounds are also biocompatible, such as octacalciumphosphate (OCP) and tetracalciumphosphate (TCP). This kind of compounds, particularly HA, may show different Ca:P ratio ranging from 1.55 to 2.2. Many of these artificial materials show good biocompatibility so that bone cells tolerate their presence with few deleterious effects and bone mineralization may be enhanced. The role of HA is not a passive one and it contributes to the formation of the CO32- apatite on the surface and promotes the adhesion of matrixproducing cells and organic molecules as a result of surface chemistry and charges. However, it has been observed that the in vivo cellular response could be compromised by highly crystalline HA ceramics, hence some amorphous or soluble phases may result in a more stable interface with biological environment.
Some kinds of low density HA, with highly interconnected porosity have also been employed as viable alternative to bone grafts, without problems of infection and inadequate supply. Furthermore, porous structure favours the growth of bone into the implant, leading to a more securely fixed and integrated repair.
The interfacial strength between bone and the implant material is much greater for these bioactive implant materials compared with other, such as Si, Zr or Al. Moreover, the biocompatibility of HA and the similarities between its structure and bone mineral have led to great interest in the potential of dense HA as a mineral for the augmentation of osseous defects.