Polymer implantable membranes

A survey is made of developments in the use of polymers in biomedical applications, including vascular prostheses, orthopaedic implants, membranes for haemodialysis and haemofiltration, intraocular and contact lenses, controlled drug release, artificial skin and artificial pancreases. 19 refs. 

Feng, K., Shen, Y., Liu, D. et al. 2010. Ni-Cr Co-implanted 316L stainless steel as bipolar plate in polymer electrolyte membrane fuel cells. Jnternational Journal of Hydrogen Energy 35 690-700. 

Spin coating is one of the simplest techniques for applying thin films, but it is no use for low solubility polymers (HaU et aL, 1998). Chemical vapour deposition solves this problem because monomers are delivered to the surface in the vapour phase, eliminating the need to dissolve macromolecules. They then undergo simultaneous polymerization, resulting in the formation of a thin film. Moreover, the substrate compatibility obtained using this method is excellent for biomedical devices such as implants, membranes and microfluidic devices (Asatekin et al., 2010). 

Dubois, P., Rosset, S., Koster, S., Bufom, J.M., Stauffer, J., Mikhailov, S., Dadras, M., Rooij, Nico- F. de., and Shea, H., Microactuators based on ion-implanted dielectric electroactive polymer membranes (EAP), Presented at 13th International Conference on Solid-State Sensors, Actuators and Microsystems, Seoul, Korea, June 5-9, 2005, 2048. 

Step 3 Biocompatibility. The biocompatibility of selected polymers, identified in Steps 1 and 2, were evaluated by implanting flat membranes into a C57/B16 mouse (Jackson Labs, Bar Harbor, ME). The membranes and capsules were implanted at various internal sites or in the back tissue under the skin. The results of these tests are not reported herein and will be discussed in a subsequent publication. They do, however, have important implications as to the ultimate selection of a polymeric system. 

It is well recognized that in vitro angiogenesis assays can have clear advantages. However, the major drawback of all of these assays is that they require the endothelial cells to be removed from their natural microenvironment, which alters their physiological properties. To study angiogenesis in vivo, the most frequently used assay systems exploit chicken chorio-allanto-ic membrane (CAM) [28,60], the corneal pocket [61], transparent chamber preparations such as the dorsal skin fold chamber [62,63], the cheek pouch window [64] and polymer matrix implants [65,66]. 

Siloxane-containing devices have also been used as contact lenses, tracheostomy vents, tracheal stents, antireflux cuffs, extracorporeal dialysis, ureteral stents, tibial cups, synovial fluids, toe joints, testes penile prosthesis, gluteal pads, hip implants, pacemakers, intra-aortic balloon pumps, heart valves, eustachian tubes, wrist joints, ear frames, finger joints, and in the construction of brain membranes. Almost all the siloxane polymers are based on various polydimethylsiloxanes. 

Nondegradable polymers are also useful as matrices for ocular implants. This application requires the polymer to be hydrophilic, to minimize local tissue irritation. Need for ocular implants stems from the challenges posed to conventional ocular medicines (i.e., eye drops) such as rapid dilution, tear washout, poor patient compliance, and limited bioavailability. Ocular implants from hydrophilic polymer matrices that provide localized sustained release may overcome the above limitations. The first polymeric sustained release product to reach the market was Ocusert , a pilocarpin sustained release ocular implant developed by Alza. Ocusert has the drug reservoir as a thin disc of pilocarpine-alginate complex sandwiched between two transparent discs of microporous membrane fabricated from ethylene-vinyl acetate copolymer. The microporous membranes permit the tear fluid to penetrate into the drug reservoir compartment to dissolve pilocarpine from the complex. Pilocarpine molecules are then released at a constant rate of 20 or 40 pg/hr for a four- to seven-day management of glaucoma. 

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