Potentials of Polylactide-Chitin Composites as Femoral Scaffold in Orthopaedics
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
Over the last two decades, several materials such as metals, polymers and composites have been used as implants in the body. Metallic implants have proven to cause stress shielding, toxic corrosion products and necessity for re-surgery. On the other hand, synthetic polymers possess poor stiffness and cause inflammation. The quest in making up for the disadvantages of these materials has culminated in a paradigm shift to the use of biodegradable and biocompatible polymers such as polylactide (PLA). However, PLA is hydrophobic and displays very low elastic modulus (1.9 - 4.1 GPa) compared to that of bone human (10 – 30 GPa). The low elastic modulus inhibits load transfer to the healing bone while hydrophobicity induces low affinity for living tissues. Therefore, this study is aimed at increasing the elastic modulus of PLA and making it hydrophilic by reinforcing with -chitin (a structural polysaccharide), which is biodegradable and biocompatible. Chemical treatment method was employed in extracting chitin from crab and shrimp exoskeletons with the use of 0.4, 0.8 and 1.2M concentrations of both HCl and NaOH for demineralization and deproteinization processes respectively. Characterizations such as Fourier Transform Infrared Spectroscopy (FTIR), thermogravimetric analysis (TGA), Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) were carried out on the extracted samples. The PLA-chitin composites were produced via slip casting where PLA was dissolved in dichloromethane (DCM) at room temperature (32 0C) and 10, 20 and 30 wt. % -chitin with the lowest acetylation degree (DA) were added. In vitro degradation examination was carried out by immersing samples in phosphate buffered solution (PBS) maintained at pH 7.4 and at 37 0C for designated periods. Biodegradation of samples were studied by determining times of hydrolysis TH and diffusion TD. The presence of two amide I peaks formed between 1661-662 cm-1 and 1626-1628cm-1 in the FTIR spectra of treated shells revealed that chitin extracted from these two sources have -form. Increasing concentrations of HCl and NaOH reduced DA from 99.4 - 63.7%. X- Ray reflections were observed on (021), (110), (120) and (013) planes. The crystalline index (Crl) ranged between 65.5 and 87.4 %, while thermal stabilities measured from activation energy (Ea) were between 100.12 and 139.63kJ/mol. There was reduction of hydrogen bond energy (EH) from 5.25 - 4.52 kCal for -chitin samples with increase in concentrations of HCl and NaOH. The addition of -chitin to PLA increased its elastic modulus from 3.64 GPa to 10.1- 33 GPa. Composites of PLA-chitin degraded via bulk hydrolysis as TH >> TD where 16.13-11.8 x 106 s and 33.67-15.00 m2/s were measured for TH and TD respectively. Hydrolysis of PLA was accelerated on addition of hydrophilic chitin with weight loss from 16.22 - 66.02 %. The results of this study also showed non-toxic degradation products as the pH of PBS stood between 7.4 and 7.37 at 37 0C, which is similar to human physiological conditions. Thus, PLA-chitin composites can serve as a potential substitute for metallic and fossil based polymers as femoral scaffolds in orthopaedic applications.