Tensile properties, water absorption and enzymatic degradation studies of polyethylene/starch filled hydroxyapatite blend for orthopaedic applications
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Date
2016-06
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KNUST
Abstract
Linear low-density polyethylene (LLDPE)/starch blends filled with hydroxyapatite have been
synthesized by injection moulding. The aim was to control the rate of biodegradation of
LLDPE/starch blends for bone screw fixation using hydroxyapatite (HA). Hydroxyapatite
contents were varied from 1.0% to 3.0% in intervals of 0.5% by parts and the blend phases were
characterised using X-ray diffractometry (XRD) and scanning electron microscopy (SEM).
Biodegradation was studied by performing water absorption and enzymatic tests. Water uptakes
by the samples were carried out according to ASTM D570 and enzymatic test was carried out on
samples in phosphate buffered saline (PBS) containing α-amylase. Tensile properties of the
samples before and after enzymatic degradation were determined using Titan and Testometric’s
universal testing machine while the surface changes were determined with Meiji Techno optical
microscope. Seven different samples were formed for the study, two of the samples; one composed
of LLDPE only and the other of 60% LLDPE, 40% starch and 0% hydroxyapatite, were used as
controls. The results obtained show that the incorporation of starch granules into the LLDPE
reduces the tensile strength but almost doubles the tensile modulus and this was attributed to starch
granules expanding the amorphous tie chain of LLDPE. Addition of hydroxyapatite into the blend
gave an increase in the tensile strength. The increase in strength with increasing HA content was
statistically significant at a p-value of 0.0008 and the improvement slowed the rate at which the
blend degraded. Hydroxyapatite is suspected to have affected the intermediate phase of the
LLDPE by the hydroxyl group through hydrogen bonding. The water absorption by the blends
showed that as hydroxyapatite content increased, the moisture uptake of the blends increased and
enzymatic degradation rate increased, giving rise to high percentage loss in tensile strength and
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modulus. Conversely there was a high gain in percentage elongation. Optical micrographs of the
surfaces of the degraded samples showed surface erosion and agglomerates. The samples that
showed higher erosion and more agglomerates had the highest water uptake and highest
percentage loss in tensile strength and those with less erosion and fewer agglomerates had less
water uptake and less percentage loss in tensile strengt
Description
Thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Materials Science) College of Science