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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Development of a non-adhesive wound drressing

Author: HAROLD, Stephanie

Year: 1992

Supervisor(s): Edgar Andrews

A non-adhesive wound dressing was prepared, based on a segmented polyetherurethane, modified with polydimethylsiloxane, (PDMS), such that it was superhydrophobic at its surface and hydrophilic throughout its bulk. A /lq diffuse-like' schematic structure was envisaged, whereby one end of a monofunctional PDMS was attached mainly to the polyurethane surface. Semi-telechelic carbinol-terminated PDMSs of low MW (1000-10,000) were chosen for incorporation.
Preparation of monohydroxy-terminated PDMS was carried out via a 5-step synthesis (involving ring-opening of hexamethyltrisiloxane monomer, initiated by 1-ethyoxyethyl-3-lithiopropyl ether). The polysiloxane was subsequently incorporated into polyurethane, at various percentage levels (0.1, 0.5, 1.0, 2.5, 3.0, 5.0, 7.0, 10.0%), using 1- and 2-stage hot melt bulk polymerisations, allowing for water content in the formulations; optimal conditions were investigated and established in both instances.

Bulk polyurethane-PDMS polymers were dissolved in a methylated spirits/dichloromethane (70/30 volume ratio respectively) solvent mix, and the resulting solutions cast as films of c. 0.01-0.02mm thickness by hand spreading.

Mechanical properties of the films, such as ultimate tensile strength, hysteresis at various strain levels (100, 200, 300 and 400% ), and resistance to fracture propagation, were determined by stress-strain and tear testing respectively. Adherency was determined via a recently developed peel test, using gelatine as a substrate, which was designed to provide a hydrogen-bonded adherend resembling wound exudate in its adherency. Water permeability of the films was also measured by permitting drying of the gelatine only through the dressing film. The use of such tests significantly reduced the number of animal tests required to evaluate candidate films for wound adherency.