A series of segmented polyurethanes (SPU's) potentially suitable for blood contacting applications were synthesized. Various soft segment monomers (polypropylene glycol, PPG, MW 1000; PPG 2000; polyethylene glycol, PEG, MW 1500) and chain extenders (ethylene diamine; 1,3 diamino hydroxy propane; and 4,5 dihydroxy-m-benzene disulphonic acid disodium salt, Tiron®) were used to prepare polymers with a range of chemical and physical characteristics. Several of these polymers were novel with respect to the presence of functional groups in the hard segment. The principal objective was to assess the effect of these groups on the physical properties, and to some extent on the blood compatibility of SPU's. Initially the SPU's were characterized to determine the course of the novel polymerizations. Nuclear magnetic resonance (NMR) was used to determine if the hydroxyl group of the chain extender 1,3 diamino hydroxy propane remained unreacted. Although the lack of model compound studies made the results inconclusive, it was estimated, using ¹H NMR, that about 87% of the hydroxyl groups remained unreacted. Sulphur analysis of sulphonate-containing SPU's, formed using Tiron®, showed very low sulphur contents compared to the expected values, suggesting that the repeat units of the SPU's were different from those based on simple stoichiometry. Low angle laser light scattering (LALLS) was used to determine M̅w but did not always produce interpretable results. Electron spectroscopy for chemical analysis (ESCA) was performed on cast films of the polymers to determine chemical composition at the surface. The ESCA data obtained at varying take-off angles showed that the soft segment domains were enriched at the surface. The nitrogen content expected of several of the SPU's was twice that found by ESCA. Again this suggests that the repeat unit of these SPU's is different from the ideal repeat unit based on the stoichiometry used. Mechanically the polymers behaved as expected in terms of stress-strain data. PPG 2000-based SPU's had greater extensibility but lower tensile strength compared to the corresponding PPG 1000-based SPU's. PEG-based polymers had very low mechanical strength and this was attributed to the absorption of water from the environment by these hydrophilic materials. PPG 1000-based polymers showed the best overall mechanical performance from a biomaterial perspective. As a means of assessing the response of blood to these materials, the adsorption of fibrinogen on film coated tubes was studied, both from single protein solutions and from plasma. Fibrinogen "capacity" of the polymer surfaces obtained from the single protein data was strongly dependent on soft segment type and was in the order PPG 1000>PPG 2000> PEG 1500. As with most other materials previously studied, adsorption of fibrinogen from plasma was transient (Vroman effect). This effect was evident as peaks in curves of adsorption versus plasma concentration. The peak heights were found also to be in the order PPG 1000>PPG 2000> PEG 1500. These peak heights are in general also lower than for other, more thrombogenic materials, and may indicate the affinity of the surface for fibrinogen relative to other proteins in plasma. From these observations it is tempting to associate thromboresistance with minimal fibrinogen adsorption. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22935 |
| Date | 08 1900 |
| Creators | Hudson, Charles |
| Contributors | Brash, J. L., Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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