Implantable polytetrafluoroethylene

F 754 Specification for Implantable Polytetrafluoroethylene (PTFE) Polymer Fabricated in Sheet, Tube, and Rod Shapes... 

Ethylene vinyl acetate has also found major applications in drug delivery. These copolymers used in drug release normally contain 30-50 wt% of vinyl acetate. They have been commercialized by the Alza Corporation for the delivery of pilocarpine over a one-week period (Ocusert) and the delivery of progesterone for over one year in the form of an intrauterine device (Progestasert). Ethylene vinyl acetate has also been evaluated for the release of macromolecules such as proteins. The release of proteins form these polymers is by a porous diffusion and the pore structure can be used to control the rate of release (3). Similar nonbiodegradable polymers such as the polyurethanes, polyethylenes, polytetrafluoroethylene and poly(methyl methacrylate) have also been used to deliver a variety of different pharmaceutical agents usually as implants or removal devices. 

Figure 1. Implantation of electrons in polytetrafluoroethylene films to form electric transducer of high stability and sensitivity.

Hurst BS. Permanent implantation of expanded polytetrafluoroethylene is safe for pelvic surgery. United States Expanded Polytetrafluoroethylene Reproductive Surgery Study Group. Human Reproduction 1999, 14, 925-927. 

U., Zilla, P., In vitro endothelialization of expanded polytetrafluoroethylene grafts a clinical case report after 41 months of implantation. J. Vase. Surg., 1997, 25(4) 757-763. 

The best known fluorocarbon polymer is polytetrafluoroethylene (PTFE), commonly known as Teflon (DuPont). Other polymers containing fluorine are polytrifluorochloroethylene (PTFCE), polyvinylfluor-ide (PVF), and fluorinated ethylene propylene (FEP). Only PTFE will be discussed here since the others have rather inferior chemical and physical properties and are rarely used for implant fabrication. 

Fig 1 22 Boston Scientific Endotak quadripolar Reliance G implantable cardioverter-defibrillator lead. Two expanded polytetrafluoroethylene (ePTFE or Gore-Tex) jackets black arrows) cover the shock coils to prevent tissue ingrowth (courtesy of Boston Scientific)... 

Commonly used natural fibres are cotton and silk, but also included are the regenerated cellulosic fibres (viscose rayon) these are widely used in non-implantable materials and healthcare/hygiene products. A wide variety of products and specific applications utilise the unique characteristics that synthetic fibres exhibit. Commonly used synthetic materials include polyester, polyamide, polytetrafluoroethylene (PTFE), polypropylene, carbon, glass, and so on. 

Charnley develops the technique of low friction arthroplasty (LFA). Usirig polytetrafluoroethylene (PTFE) as the bearing material (Charnley 1961) implants were fabricated either by Charnley in his home workshop or in the machine shop at Wrightington and chemically sterilized. 

The unique invention that led to PTFE polymer products expanding and becoming desirably porous made the material suitable for use as implants. The modified structure consists of nodes interconnected by very small fibrils (Fig. 1.11). Briefly, the process is as follows. A fine powder of un-sintered polytetrafluoroethylene is uniformly mixed with a Uquid lubricant and then shaped into a product (sheet, rod or tube) by extrusion. After removal of the... 

Several known and commonly used biomedical polymers are categorised under the USP Class VI classifications. This includes polytetrafluoroethylene (Pl FE) (used in artificial ligaments and grafts and as catheter liners), fluorinated ethylene propylene (FEP) (used in electrocautery devices and fusing sleeves), PEEK (used in implantables, orthopaedic and dental devices). For Class VI materials, as defined by the USP, the most stringent testing procedures are performed. Any substance that may have leaked from the material is usually captured in extract solutions of NaCl, 5% EtOH, cotton-seed oil or polyethylene glycol. 

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