Development of novel biodegradable nanocomposites for bone repair applications

The main goal of this research is to introduce novel series of biodegradable nanocomposites that closely mimic the characteristics of real bone such as mechanical and thermal properties. These nanocomposites are composed of cotton-sourced cellulose microcrystals (MCC), hydroxyapatite nanoparticles (HA) and Poly L-Lactic Acid (PLLA). A novel fabrication route is used to manufacture MA and MH series of nanocomposites. MA series was developed to find an optimum range for weight fraction of each constituent required for design of the MH series. Evaluation of the thermal properties of MA series showed that increasing of weight ratio of MCC and HA from 0 to 21 Wt% increased the crystallinity up to 38%. Compression test results of them revealed that increasing the weight fraction of MCC or HA from 0 to 21Wt% enhanced the compressive yield stress from 0.127 to 2.2 MPa and the Young’s modulus from 6.6 to 38 MPa. The cytotoxicity assay results showed there was no sign of toxic material affecting on viability of cells. The MH series was designed and fabricated by selecting a narrower range of weight fraction of the constituents. A design of experiments was used to alter the composition of the constituents to assess their contributions and their effect onto the mechanical properties and biodegradation behaviour of the MH series of the nanocomposites. The weight ratio of MCC to HA, the concentration of PLLA, and the porogen content were chosen as varying factors. A model that accurately predicts the optimum parameter setting was created. Analysis of variance statistical analysis showed that the ratio of MCC to HA was the most influential factor affecting the compressive yield and the mass loss, while the porogen content was the most detrimental factor affecting the Young’s modulus of MH series of nanocomposites had no significant effect on their rate of the mass loss. The nanocomposites with highest weight ratio 4 of MCC to HA, showed maximum mechanical strength and the lowest water absorption and the lowest mass loss. It was found two series of nanocomposites was comparable to trabecular bone from a compositional, structural, thermal, mechanical point of view.