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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
Research Student Awards

PhD Thesis: Polyurethane Membranes for Encapsulation of Implantable Medical Devices

Author: ROOHPOUR, Nima

Year: 2009

Supervisor(s): Ihtesham Rehman

The work in this thesis involved the development of novel encapsulation materials for implantable medical devices. In this study, copolymers of polyether-urethane (PEU) with polydimethylsiloxane (PDMS) were synthesised with the goal of creating materials with low water permeability and high elasticity. PDMS was incorporated into polymer backbone as a part of soft segment during polyurethane synthesis and physical properties as well as water permeability of resulting copolymer were studied in regard to PDMS content. Increase in PDMS content led to increase of microphase separation of the copolymer and corresponding increase in elastic modulus. Surface energy of the polymer was decreased by incorporating PDMS compared to unmodified PEU. PDMS in copolymer formed a hydrophobic surface which caused reduction in water permeability and water uptake of the membranes. Thus, PDMS containing polyurethane with its potent water resistant properties demonstrated a great promise for use as an implantable encapsulation material.

Polyurethane films with different soft segment lengths (PTMO1000, PTMO2000) were prepared by adding different concentrations of isopropyl myristate. The physical and mechanical properties of these polymers were determined using FTIR and Raman spectroscopy, differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Moreover, surface properties, water uptake, water permeability and in vitro stability of the blends were studied. The modified polymers showed improvement in water uptake and permeability compared with unmodified polyurethane for an optimal concentration of 1-2 wt% isopropyl myristate (IPM).

In the final part of this study, possibility of introducing silver lactate as an antibacterial agent in structure of polyether polyurethane was investigated and it was found that the silver end capped polyurethane is stable in vitro.