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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: Synthesis of polyurethanes for medical use: biodegradable low adherence films for the prevention of adhesions after surgery.

Author: REHMAN, Ihtesham

Year: 1992

Supervisor(s): Ray Smith

Adhesions commonly occur after internal disease or surgery. The natural healing response leads to the formation of vascular and avascular adhesions after inflammatory diseases and surgical interventions. A barrier film could be incorporated during surgery between layers of tissues that must not adhere to one-another. The film would be biodegradable so that it disappears over a period of time, and would ideally be two sided, allowing relative movement at that interface, while being firmly anchored on the opposite side to prevent displacement.
In order to produce a biodegradable low adherence material for incorporation during surgery to prevent adhesions between tissues which should move relative to one-another the prime requirement is to identify a suitable substrate film. This must already be a material that has proven non toxic properties. Polyurethanes are among the many polymers that have been used inside the living body. The films produced must be soft, pliable, biocompatible and sufficiently strong to be handled and to retain their integrity over a suitable period in vivo.

Polyesterurethane-polydimethylsiloxane graft polymers were synthesized. Films were prepared using cast technique, casting on glass slides from 5 - 7% solution in tetrahydrofuran. Chemical characterization of the polymer was done by using nuclear magnetic resonance and fourier transform infrared spectroscopy and gel permeation chromatogrpahy. Tensile strength of the films was measured on a J.J. Instrument's tensile testing machine.

In-vitro hydrolytic degradation was carried out in which films were immersed at 37oC in alkaline solution. Sodium hydroxide was used in the case of hydrolytic degradation. Degradation was assessed by tensile testing as a function of time to determine the degradation of mechanical strength, infrared spectroscopy, and mass loss. Titration method was also used to quantitatively determine the hydrolytic degradation.

In order to study the adhesions of films, in-vitro model based on a gelatin test, which is simple and rapid was used. Adhesions were measured by using a peel test on either sides of the film using a J.J. Instrument's tensile testing machine.