Nanomedicine, Volume IIA: Biocompatibility
© 2003 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003
188.8.131.52 Biocompatibility of Teflon-Coated Prostheses
The first implantation of bulk Teflon into the dog peritoneal cavity was reported in 1949 by Leveen and Barbario . Teflon has been used as a solid implant in cardiovascular surgery (e.g., cardiac valves, vascular patches and catheters), orthopedics (e.g., hip prostheses), facial surgery (e.g., maxillary and orbital implants), and neurosurgery (e.g., dura mater implants, derivation valves) .
While Teflon is non-antigenic [1196-1198], complement activation has been demonstrated by Teflon tubes in contact with whole venous blood for 10 minutes , and Teflon suture and graft materials cause significant activation of C5a complement .
Teflon coatings have often been applied to prostheses to achieve anti-adhesive effects , but with a mixed record of success. For example, after a long period of widespread use [1362, 1363], Proplast-Teflon temporomandibular joint (TMJ) interpositional implants manufactured by Vitek had to be removed from the market in 1995 by the FDA. This was due to complications including severe bony destruction of both condyle and fossa as a result of extensive granulomatous and exuberant foreign body giant cell reactions , cerebrospinal fluid leak , fibrosis, calcification, inflammation and pain , soft tissue destruction  and the exacerbation of existing connective tissue or autoimmune disease problems . Failed Proplast-Teflon TMJ implants  had to be replaced, and removal led to increased rates of immune-mediated and somatization-related conditions, allergies, or symptoms of environmental sensitivity .
Other problems occur infrequently with mechanical Teflon prostheses. There is at least one case of an eroded prosthetic Teflon cardiac disc valve in the tricuspid position that became embolic, producing foreign material that was later found in the vessels, vessel walls, and parenchyma of the lung, associated with a foreign body type of inflammatory reaction [1277, 1368]. A case of Teflon embolization to the lungs from Teflon pledgets deployed during cardiac surgery, with pathological changes found in the pulmonary arteries, has also been reported .
Teflon aortic grafts have been implanted in human patients undergoing abdominal aortic aneurysmectomy . Other Teflon arterial prostheses have been studied in humans [1221-1225], and grafts in other arteries have been studied in baboon [1201, 1204] and canine  models. In one study , Teflon prostheses placed arterially in human patients for periods from 2 months to 18 years were initially permeated by thrombus containing platelet antigens. This became organized and converted to granulation, and then to fibrous, tissue. The newly formed tissue contained foreign body giant cells in contact with the prosthesis and showed evidence of permeation by plasma proteins. The oldest grafts also showed stenosis, calcification, or aneurysm formation . A Teflon coated aortic stent implanted in dogs for 1-4 weeks reacted only moderately with the vessel wall, producing a neointimal layer 115 microns thick . By comparison, gold-coated stents produced the fewest macroscopic and histopathologic changes in the aorta with an 83.9-micron-thick neointima, while a copper-coated stent produced severe erosion of the vessel wall, marked thrombus formation, and aortic rupture . But while large-diameter (>5 mm diameter) vascular grafts can remain excellent for >10 years after implantation, smaller-diameter Teflon vascular grafts may occlude rapidly upon implantation .
Early Teflon catheters implanted to provide drainage in the bile duct over periods from 1 week to 8 months were at best partially effective. There was insufficient drainage and bile duct infection in most patients, spontaneous dislocation of the endoprosthesis in many patients, and death in one patient due to an intrahepatic aneurysm adjacent to the puncture tract . More recently, in vitro studies of biliary stents have shown less clogging and sludge formation in Teflon biliary stents, but clinical studies have given conflicting results [1228-1231, 5018]. Part of the continuing difficulty may be due to the irregular surface which features multiple shallow pits and ridges with multiple particles projecting into the lumen, which are visible at the submicron scale under SEM examination . Venous Teflon catheters used for parenteral nutrition produced the most extensive thromboses among the five major types of catheter materials tested . Intravenous Teflon catheters have a slightly increased risk  of catheter-induced phlebitis compared to Vialon (PTFE) catheters, even though both materials are fluorocarbons.
Teflon transplants following scleroplasty (plastic surgery of the sclera of the eye) have shown good experimental biocompatibility . In one early study, e-PTFE was episclerally implanted for evaluation as an adjunctive material for retinal detachment surgery. The implant demonstrated a minimal inflammatory response and ingrowth of connective tissue, creating a thick, fibrovascular intrascleral implant . A later study using sterilized thin Teflon sheets implanted in surgically prepared pockets in the sclera of rabbit eyes demonstrated excellent compatibility. The implanted sheets elicited histiocytes, fibroblasts, collagen and blood vessels infiltrating the internodal spaces of the highly porous material after 14 days. The number of cells and amount of extracellular matrix material deposited in the implants increased with time . In a 1999 experiment , oval-shaped e-PTFE episcleral implants focally placed in rabbit eyes for 3-11 months elicited a newly formed capsule that constantly encased the implants. The inner surface of the capsule was often covered with numerous giant cells, attesting to a foreign-body granuloma developed against the irregular outline and the hydrophobic character of the implants . No intrusion or extrusion of episcleral implants (which were well tolerated experimentally) was observed. Porosity and surface irregularity of the implant allowed its colonization by a fibrovascular and inflammatory tissue mainly in its peripheral layers. Sclera under the implant was thinned and invaginated . e-PTFE is well tolerated for scleral buckling surgery of rhegmatogenous retinal detachment, with no complications such as migration, infection, erosion, extrusion, or intrusion, and excellent tolerance and biocompatibility over a 14-26 month follow-up period .
Teflon-coated intraocular lenses implanted in vivo in rabbit eyes for 1-2 months showed significantly fewer cell deposits and no iris-lens synechias compared to non-Teflon controls which showed extensive synechias along with lens epithelium proliferation and spindle-shaped cell deposits . e-PTFE alloplasts have shown high biocompatibility and can be ingrown by fibrovascular tissue in vascular, abdominal, and reconstructive surgery. But corneal implants, though well tolerated from a biocompatibility standpoint, show no evidence of fibrovascular ingrowth . An e-PTFE drainage implant with 20- to 50-micron pores for glaucoma filtering surgery was tested in rabbit eyes for 3 months. There was no postoperative hypotony, migration, extrusion, intraocular inflammation, or infection, and there was greatly extended filtering patency compared with conventional trabeculectomy and laser sclerectomy . A PTFE patch graft implanted into anophthalmic patients for 6-13 months was well tolerated without extrusion, granuloma formation, or irritation .
Proplast II is a porous alloplastic composite of Teflon polymer and alumina alleged to have been used successfully as a subperiosteal implant to treat anophthalmic enophthalmos, giving good correction of preoperative upper eyelid sulcus deformity while integrating well with the surrounding tissues and minimizing the risk of subsequent implant migration and extrusion . A Teflon tube has been successfully used as a lacrimal drainage stent in the lower canaliculus, and as a bypass tube in connection with canaliculus laceration repair . For many years, good results in otosclerosis surgery (for the purpose of closing eardrum perforations and rebuilding the ossicular chain, thus rehabilitating conductive hearing loss) have been achieved using a prosthesis made of Teflon-coated platinum wire with gold pistons .
A microporous Teflon tracheal prosthesis  has been tested in rabbits and was successfully incorporated (e.g., luminal side covered by connective tissue and epithelium) within 2-4 weeks without inflammation or granulation tissue at the anastomoses . Two minor complications included infection of the prosthesis before incorporation was complete (which can be overcome by antibiotics) and obstruction of the lumen at the center of the prosthesis by granulation tissue or a deformed Teflon wall (which can be overcome by using a stiffer prosthesis) .
Fluoropolymer-coated polyester fibers have been tested as prosthetic grafts in the surgical management of abdominal hernias [1169, 1194], in cases where the defect is too large or the surrounding tissue is not available for repair. Teflon netting has been employed as a replacement material for subcutaneous tissue and a substitute for superficial fascia destroyed by tumor infiltration involving neurofibroma of the face . Teflon has been used as a nasal septal splint  and as a penile graft implant as a treatment for Peyronie’s disease and erectile dysfunction [5778-5781], and Teflon as Gore-Tex has been used as periodontal material .
Last updated on 30 April 2004