Mechanical and Chemical Characterization of Chitosan Hydroxyapatite Composites

Abstract

Hydroxyapatite is a very interesting ceramic that has been explored recently for various biomedical applications ranging from bone pastes and cements to tissue scaffolds due to its biodegradability and biocompatibility. However, its ceramic behavior makes it hard to use due to its high brittleness. It has been demonstrated in the literature that a composite of Chitosan polymer and hydroxyapatite has high mechanical strength. Chitosan is biocompatible, biodegradable, nontoxic, anti-bacterial, and is soluble in diluted acidic solutions. In this thesis, we study the effects of varying the processing parameters on the mechanical and chemical properties of the composite. The processing parameters studied include using different Hydroxyapatite/ Chitosan concentrations, the use of different acids such as malic and acetic acids, the presence of nano-hydroxyapatite, and the immersion in sodium hydroxide. Fourier transform infrared spectroscopy (FTIR) as well as X-Ray Absorption Fine Structure (XAFS) are used to study resulting chemical variations as a result of the use of different parameter. The results suggest that there are chemical interactions between the composite's components. The chitosan's amino group and the carboxyl group from the acid act as the glue that holds the composite together. Also, three point bending test is used to measure the flexural strength of each composite. The three point bending test shows the weakening effect of immersion in sodium hydroxide. The flexural strength and elasticity decreased by a factor of 1/3. In addition, a three point bending test for a wet specimen that has been immersed in sodium hydroxide as well as water shows that the mechanical properties of the composite decreased by a factor of 1/100 as compared to the samples just treated with sodium hydroxide and tested dry. Other processing parameters such as changing the acid used from malic acid to acetic acid showed similar mechanical properties. This was assumed to be due to the fact that both acetic acid and malic acid have carboxyl group in common. Also, since FTIR suggests that the carboxyl is the glue that holds the composite together, it was not surprising to see similar mechanical properties when these two acids are exchanged. Scanning electron Microscopy, SEM, was used to study the fracture surface of composite. It was shown by SEM that there was good cohesion between chitosan and hydroxyapatite. However, it was confirmed that cohesion is weakened significantly once the composite is immersed in sodium hydroxide.