TITLE:
Effect of Protein Adsorption onto the Dissolution of Silicon-Substituted Hydroxyapatite
AUTHORS:
Claudia Manuela Botelho, Roger Brooks, Masanobu Kanitakahara, Chikara Ohtsuki, Serena Best, Maria Ascensão Lopers, Neil Rushton, William Bonfield, José Domingos Santos
KEYWORDS:
Biomaterials, Silicon, Surface Properties, Proteins, Dissolution
JOURNAL NAME:
Journal of Encapsulation and Adsorption Sciences,
Vol.1 No.4,
December
9,
2011
ABSTRACT: Several authors have shown the beneficial role to incorporate silicon into hydroxyapatite lattice, although, the mechanism behind the enhanced bioactivity of this Si-hydroxyapatite (Si-HA) is poorly understood. The incorporation of Si into the HA lattice alters the surface charge of HA, leading to more negative values. Due to the importance of the surface properties on the interaction between biomaterials, physiological fluids, and the host tissue, it is important to further characterize the surface of Si-HA by determining its surface energy and wettability. Our results showed that the incorporation of Si increased the hydrophilicity of HA, leading to a higher interfacial tension. Another important property for osteointegration is the formation of an apatite layer. The dissolution of Si-HA in the presence of serum-free simulated body fluid (SBF) started at early time points and using atomic force microscopy (AFM) it was possible to observe the dissolution at the grain boundaries and grains, therefore an apatite layer was formed in a short period of time. As the dissolution-precipitation process is much more complex in vivo, we tried to mimic the initial stages of the in vivo reaction by incubating the Si-HA in serum-SBF. It was shown that the dissolution kinetics in serum-SBF was slower when compared to the dissolution in serum free-SBF. At the same time point, no significant dissolution features were observed or apatite layer was visualized. The phase imaging AFM indicated the presence of a layer on top of these materials that could be a proteinaceous layer, as XPS analysis detected an increase on the concentration of nitrogen on the surface of the samples incubated in the presence of proteins.