Processing and Characterization of PCL- and PLGA-HA Composites for Bone Tissue Engineering.

摘要

The focus of this research is to advance the processing techniques of fabricating scaffolds for tissue engineering and to gain a better understanding of the scaffold properties and behaviours. To achieve these objectives, the fundamental properties of two widely used biomaterials, poly(lactide-co-glycolide acid) (PLGA), poly(ε-caprolactone) (PCL), and their composites with hydroxyapatite were examined. Though increasing the mechanical properties of the bulk polymers, the addition of hydroxyapatite did not affect the thermal and viscoelastic properties, suggesting little interactions may exist between the polymer and the particles. Interestingly, though the addition of the fillers increased the mechanical properties of the bulk materials, the particles worsened the mechanical properties of gas foamed/salt leached scaffolds possibly due to the struts of the porous structure having similar thicknesses as the particles. In such a case, the filler acted as stress raisers and decreased the properties of the struts. The viscoelasticity of the scaffolds was also not affected by the fillers but was affected by the testing environment. An aqueous environment caused the PLGA, but not PCL, to transition such that the porous structure was altered. These results suggest that PLGA may not be ideal for scaffolds for load bearing applications. For electrospinning, a parametric study was performed to control the scaffold morphology, but more importantly, a novel process to fabricate 3D electrospun scaffolds was developed. The novel technique exploited the plasticizing effect of pressurized carbon dioxide on the polymer such that multiple layers of the thin meshes can be sintered together without the use of heat. The process was optimized for adhering layers of PLGA and its composite with nano-hydroxyapatite, and these scaffolds have a high open-porosity and better mechanical properties compared to the gas foamed/salt leached scaffolds. Finally, a model was derived for the viscoelasticity of the bulk materials and their scaffolds by applying fractional calculus on the classical standard linear solid model based on a system of springs and dashpots. The model fitted the data, and correlations between the static mechanical properties and the fitting parameters were found such that by performing static mechanical tests, the viscoelastic behaviours can be approximated.