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OPINION | AUGMENTATION TECHNIQUES | thus more resistant to biodegradation

(and hence producing longer-lasting effects) appeared in 1985. However, despite the screening of patients, hypersensitivity to bovine collagen was a problem in a small proportion, and as newer products appeared, the use of Zyderm/Zyplast declined.

Human origin Newer products are based on materials of human origin. Examples of commercial human-derived donor materials currently used for facial augmentation include LifeCellÕs

have been used in facial implants. Silicone, of course, is widely used in medical devices that come into contact with the body, and has a long history of such use. In the present context, silicone has a number of qualities that make it suitable for use in implants: ■ It can be produced in either liquid (gel) or solid forms

■ The solid form is easy to manipulate into the desired shape by a moulding process or by being carved during the implantation procedure

Cymetra, a micronised,

injectable form of human skin tissue; InamedÕs CosmoDerm and CosmoPlast, which are based on collagen bioengineered from a single cell line; and Fascia BiosystemsÕ Fascian, which consists of preserved particulate fascia made from irradiated human cadaveric fascia lata (the deep fascia of the thigh). It appears that the implanted fascia lata is digested as extraneous tissue and replaced with native collagen, creating a vascularised sheet of collagen that essentially restores the original elements found in native fascia in a process known as ÔrecollagenationÕ. Non-biologic materials such as precious

metals, paraffin wax and acrylic polymers, and even products of animal origin such as ivory, have also been used as fillers or bone substitutes, although the use of these particular materials is now mainly of historic interest. However, one product that still has a place in facial remodelling is Suneva MedicalÕs Artefill, the latest iteration of a series of products originally developed by SunevaÕs predecessor company, Artes Medical. Artefill consists of non-resorbable polymethyl- methacrylate (PMMA) microspheres, 30–50 m m in diameter, suspended in a buffered aqueous carrier gel containing 3.5% bovine collagen and 0.3% lidocaine hydrochloride for patient comfort. The collagen in the product provides immediate filling and, as it is gradually resorbed, the PMMA microspheres provide a support matrix for the patientÕs own collagen to take over. Meta-Crill is a similar product that

originates in Brazil and consists of microspheres of PMMA in a colloidal suspension without protein. More recently, other synthetic polymers

such as silicone, polytetrafluoroethylene (PTFE) and high-density polyethylene

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■ It is easy to sterilise ■ It is easy to remove in the event of complications

■ It is relatively inexpensive. Allergan is one company

Non-biologic materials

such as precious metals, paraffin wax and acrylic

that offers a range of silicone facial implants, manufactured by the California company Spectrum Designs Medical. Others include Implantech, based in Washington DC, and Lugoff, South Carolina- based Surgiform Technology, both of which also manufacture PTFE implants.

PTFE implants PTFE is a synthetic polymer with a myriad of uses ® it was originally developed by DuPont, whose Teflon product is famous for imparting Ônon-stickÕ properties to cooking utensils. As well as this surface property, PTFE is biologically inert and non-biodegradable, which make it attractive as an implant material. Teflon has been used in paste form for medical applications, such as the treatment of vocal cord disorders, although this use has now been discontinued. One PTFE product with a long history

of usage in the manufacture of endoprostheses is WL GoreÕs Gore-Tex, originally developed as a waterproof but breathable fabric. Gore-Tex is an expanded PTFE (ePTFE) sheet composed of fine PTFE fibrils held together by solid expanded PTFE nodes. Its porous nature permits macrophage migration and tissue ingrowth, and it is used in a wide range of implantable materials, including vascular grafts, sutures and surgical staple reinforcers, and hernia repair products for example. In the context of facial implants, early Gore-Tex implants consisted of strands of

June 2012 |

ePTFE. Aesthetically, the results were not always as pleasing as anticipated; for example, the shape of the implant was sometimes visible or could be felt through the skin. Subsequently, a tubular form of Gore-Tex known as SoftForm was developed, which allows the ingrowth of blood vessels. Products made from SoftForm PTFE were more effective than ePTFE strands, although they still reportedly had some technical issues, such as shortening of the strands over time. The next generation of the SoftForm implants was the Ultrasoft implants, which are claimed to be three times softer than their predecessors. A more recent

polymers, and even products of animal origin such as ivory, have also been used as fillers or bone substitutes.

development has been a new type of solid Gore-Tex implant, known as Gore- Tex S.A.M. (subcutaneous augmentation material), which is available in a variety of preformed shapes and patches. It is also possible to carve the product precisely into the

shape desired by the surgeon, which may help to improve the outcome of nasal and chin reconstructions, or cosmetic augmentations. A newer ePTFE product is the Advanta

implant, manufactured by Atrium Medical (recently acquired by the Swedish Getinge Group). The dual- porosity Advanta implant comprises a soft, high-porosity centre surrounded by a smooth, medium-porosity outer layer. This structure reportedly provides a good foundation for the overgrowth of the patientÕs own collagen, leading to a more natural healing process. Because of these properties Advanta is the ePTFE implant preferred by many surgeons.

PHDPE implants Porous high-density polyethylene (PHDPE) is another synthetic polymer used for reconstructive and cosmetic procedures. It is marketed in the US by Porex Surgical under the trade name Medpor, and is manufactured by heating small particles of high-density polyethylene to create a material that is both strong and firm, and that can be contoured after softening in hot water. It is porous, with pore sizes varying from 100 m m to 250 m m, with 50% of the pores being larger than 150 m m. The pores are

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