New biodegradable polyhydroxyacids and polyurethane scaffolds for tissue engineering
Abstract of thesis entitled
?ew Biodegradable Polyhydroxyacids and Polyurethane Scaffolds for Tissue Engineering?Submitted by
TSUI Yuen Kee
for the Degree of Master of Philosophy
at The University of Hong Kong
in March 2005
This thesis presents the results of the study on biodegradable polyhydroxyacids and polyurethanes as candidate biomaterials for tissue engineering. New polyhydroxyacids with enhanced hydrophobicity were synthesized to evaluate the concept whether osteoblasts having hydrophobic properties will better attach and proliferate on surfaces with higher hydrophobicity. As yet, there has been no detailed study that addressed this issue. Poly(DL-lactic acid-co-2-hydroxybutyric acid) (PLBA), poly(DL-lactic acid-co-2-hydroxy-3-methylbutyric acid) (PLMBA), poly(DL-lactic acid-co-2-hydroxyhexanoic acid) (PLHA), poly(DL-lactic acid-co-2-hydroxyoctanoic acid) (PLOA), and poly(DL-lactic acid) (PDLLA) used as a control were synthesized by melt-polycondensation. The polymers were transformed into thin films, and their chemical and surface properties were characterized. Human osteoblasts SaOS-2 were used to evaluate their potential to facilitate the cell attachment, proliferation and activity. It has been found that PLMBA and PLHA with an intermediate hydrophobicity enhanced attachment, proliferation and activity of osteoblasts. As osteoblasts response to these new PLMBA and PLHA polyhydroxyacids was better than the
PDLLA control, PLMBA and PLHA might potentially become more favourable biomaterials for bone tissue engineering than presently available polyhydroxyacids. The limitation of these new polyhydroxyacids synthesized in the study is, however, their low molecular weight which makes it difficult to process them into porous scaffolds with adequate mechanical properties.
The polymers which are free from those drawbacks and can be processed into porous scaffolds for tissue engineering are new biodegradable polyurethanes. These polymers were studied in the second part of the thesis with the purpose to design processes for the preparation of porous membranes. The primary application of these membranes could be for artificial periosteum, skin or in cardiovascular surgery. The phase-inversion process was applied and various polymer coagulation methods were evaluated to produce membranes with homogeneous and interconnected porous structure. In addition, several factors which affect the formation of porous membranes were also studies. These factors included the coagulation technique, the type of solvent, polymer concentration, the thickness of cast solution layer, solvent evaporation time, and the presence of additives. It has been found that the membrane with best properties can be produced from a 5 weight/volume-% solution of the polyurethane based on poly(e-caprolactone) diol with a molecular weight of 530 daltons in N,N-dimethylformamide, water should be used as a coagulant, no additives should be used, and the membranes should be cast for only one day. Such membrane may be potentially used as a ?kin substitute?in tissue engineering. Potentially, this technique may also be applied to prepare membranes from other polymers.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:polyurethanes biomedical materials design and construction tissue engineering
Date of Publication:01/01/2005