Papers by Author: Lay Poh Tan

Abstract: This project aims to optimize the process parameters for fabricating Poly (L-Lactide-co-ε-Caprolactone) (PLCL) electrospun scaffolds to achieve fiber diameters within the ranges of ~500nm, 500nm~1µm and 1~3µm. Electronspun PLCL solutions of different concentrations (4wt% - 12wt%) were prepared using chloroform and dimethylformamide as solvents. The driving voltage and flow rate were varied from 10kV-30kV and 1ml/hr12ml/hr respectively while the gap distance was kept constant at 15cm. The effects of polymer concentration and process parameters on the properties of the scaffolds fabricated such as Youngs modulus, degree of crystallization and porosity were studied. Scanning electron microscopy (SEM) was used to check the structural integrity (absence of beading and uniform diameter) of the fibers. An increase in polymer concentration resulted in an increase in fiber diameter. Flow rate also showed a positive correlation with fiber diameter. Results showed that Youngs modulus decreased with increasing fiber diameter. Porosity of 76% to 94% was achieved. The potential application of PLCL electrospun scaffolds in the tissue engineering of soft tissues was discussed.

Abstract: Palmitic acid was added into drug-loaded poly(L-lactide) (PLLA) to modify the drug release profiles of the polymer. The acid was added in different concentrations and gradients across the thickness of the polymer. Drug release was monitored using a UV spectrometer over a period of 90 days. Degradation was studied using gel permeation chromatography and differential scanning calorimetry (DSC) to follow the change in the molecular weight and glass transition temperature respectively. Addition of palmitic acid was found to accelerate the degradation of PLLA and resulted in an accelerated release of the drug as expected. Modification of release profiles by designing the acid gradient was also attempted. It was found that the total acid concentration is still the dominant factor over the gradient design in affecting the degradation and subsequently the release profiles. Different drug concentrations also played a role in the different release profiles exhibited. Surprisingly the sample with lower drug concentration (2wt%) showed a much higher initial burst than the 5wt% loaded samples. This was due to the induced nucleation of the polymer by the drug at low concentration resulting in higher crystallinity of the polymer and consequently overall lower solubility of the drug.

Abstract: The effects of compatibilization and mould geometry on the fibrillation of liquid crystalline polymer were investigated in this study. The blend is composed of polycarbonate (PC) and LC5000, a thermotropic liquid crystalline polymer consisting of 80/20 wt% of hydroxybenzoic acid and poly(terephthalate). The effect of compatibilization was investigated by studying the morphological properties of injection moulded plaques and significant enhancement in the fibrillation of LCP was observed in the moulded samples after addition of the compatibilizer. The effect of mould geometry was studied by comparing results obtained from three types of specimens, namely, specimens cut from large rectangular plaques, moulded rectangular bar specimens and molded dog-bone specimens. It was found that mould geometry had a direct influence on the magnitude of the elongational and shear stresses in the melt during molding and thus affected the degree of LCP fibrillation. Moreover, it was observed that the constriction at the “neck” of the dogbone geometry actually facilitated development of LCP fibre in the blend by increasing shear stress during moulding and promoting LCP fibre coalescence.