Biomaterials for osteoarticular applications: role of functionalization

This work was focused on the development of functionalized materials with potential applications for the substitution/repair of damaged tissues. The materials utilized as substrates were calcium orthophosphates, namely hydroxyapatite, β-tricalcium phosphate, monetite and brushite, and gelatin films. This choice was based on a biomimetic strategy: the inorganic component of the hard tissues of vertebrates is a basic calcium phosphate similar to synthetic hydroxyapatite, and gelatin is a degradation product of the main proteic component of the human body, collagen. Functionalization of calcium phosphates was performed through ionic substitution, adsorption of metallic nanoparticles, organic molecules, amino and polyamino acids. The results indicated that the possibility of ionic substitution depends both on the type of calcium phosphate and of the foreign ion. Strontium substitutes for calcium up to 100at% in the structure of monetite an up to about 80at% in β-tricalcium phosphate, whereas the replacement is limited to 38at% in brushite. The maximum incorporation of zinc into β-tricalcium phosphate is much lower. Hydroxyapatites were utilized as supports for Pt nanoparticles and β-lactams. The amount of adsorbed β-lactam can reach values greater than 20wt% and depends both on the type of molecule and on the polarity of the loading solution. Adsorption of Pt nanoparticles provided materials with very good anti-oxidant properties. Both Pt nanoparticles and β-lactams displayed a controlled release over time. The interaction of aspartic acid and polyaspartic acid with brushite revealed that both molecules inhibit crystallization. However, the specific interaction of polyaspartic acid causes its adsorption up to 2.3wt%, whereas aspartic acid is not adsorbed at all. Both molecules inhibit brushite hydrolysis. Finally the properties of gelatin films were modified using two polyphenols, quercetin and curcumin, which are known for their good anti-inflammatory, anti-oxidant and anti-cancer activities. The results indicate that the functionalizing agents provide new materials with enhanced beneficial characteristics.