<p> The objective of this work was to investigate the potential of poly(vinyl
pyrrolidone) (PVP) as a protein resistant biomaterial. Two types of PVP surface
were studied: (1) plasma polymerized N-vinyl pyrrolidone monomer on
polyethylene (PE), and (2) grafted PVP surfaces formed by reaction of the
activated polymer with plasma polymerized allyl amine on PE. Surfaces were
also prepared by grafting polyethylene oxide (PEO), a known protein repellent, to
plasma polymerized allyl amine and for comparison to PVP. The surfaces were
characterized chemically by water contact angle and X-ray photoelectron
spectroscopy (XPS). Protein interactions were studied using radiolabeled
fibrinogen in PBS buffer. </p> <p> Plasma polymerized N-vinyl pyrrolidone surfaces were prepared in a
microwave plasma reactor. Reactions were carried out both at room temperature
and at 50°C (increased vapour pressure) in an attempt to increase the extent of
plasma polymer deposition. The resulting surfaces showed structures chemically
different from conventional linear PVP. XPS analysis suggested the presence of
a variety of functional groups, including amines, amides, hydroxyls, carbonyls
and urethanes. Mechanisms for the reactions occurring could not be ascertained
but it appeared that the monomer was extensively fragmented in the plasma.
Although these surfaces were hydrophilic (contact angles of 20 to 30°), they did not resist fibrinogen adsorption: in fact they showed adsorption levels
approximately 10% greater than unmodified polyethylene. </p> <p> Methods for direct grafting of polyvinyl pyrrolidone and polyethylene oxide
to plasma polymerized allyl amine (PPAA) surfaces were designed on the
assumption that the PPAA surfaces would be rich in amino groups for reaction
with appropriate polymer chain ends. Although there was 8-12% of nitrogen on
the surfaces, the C1 s high resolution showed that amide and urethane
functionalities are also present in addition to amines. The hydroxyl end groups of
preformed PEO and PVP chains were activated by reaction with either 1-[3-
(dimethylamino) propyl], 3-ethylcarbodiimide and N-hydroxy succinimide
(EDC/NHS), and N-N-disuccinimidyl carbonate (DSC). NMR spectra of the
products of these reactions showed that for PEO, the yields were moderate, and
for PVP, the yields were low. Surfaces grafted using polymers activated with
EDC/NHS were more hydrophilic than surfaces grafted with DSC-activated
polymers. XPS data did not provide clear evidence that significant polymer
grafting had occurred in any of the systems. It was concluded that changes in
the allyl amine plasma polymer in different environments following plasma
polymerization may affect the efficiency of grafting subsequently. XPS data
suggested that the allyl amine plasma surfaces undergo oxidation over time in
air. Also the films may be partly removed from the polyethylene surface when
placed in buffer as suggested by XPS and contact angle data. Various parameters were examined in an attempt to improve the allyl amine plasma
polymerization process for greater stability of the film. Increasing the treatment
time from 1 0 to 30 minutes gave surfaces that showed a slower change in
contact angle when stored in air. </p> <p> Despite the lack of strong chemical evidence of extensive polymer
grafting, all of the grafted surfaces were found to be significantly protein
repellent, with reductions of 10 to 36 % compared to unmodified polyethylene.
The PEO surfaces were more repellent than the PVP, although the differences
were not significant. Surfaces grafted using polymers activated with EDC/NHS
were more protein repellent than those grafted with DSC-activated polymers.
Protein adsorption was not affected by PVP molecular weight in the range 2,500
to 10,000. Since there is considerable overlap of the molecular weight
distributions (MWD) of these two polymers, it is speculated that the MWDs of the
grafted polymers may be more similar than those of the polymers themselves,
possibly due to "selection" of similar, presumably optimal molecular weights. </p> <p> Discussion of the possible reasons for the better protein resistance of
PEO compared to PVP is given in terms of chain structure in relation to the steric
exclusion and water barrier theories of protein repulsion. </p> / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19280 |
| Date | 04 1900 |
| Creators | Thomas, Sal |
| Contributors | Brash, John, Sheardown, Heather, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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