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Silver Antimicrobials Start Proving Their Mettle

The first components made from polymers compounded with silver-based antimicrobials are establishing a toehold in the North American and European medical markets. Proponents hope that these pioneering applications will prove the worth of the materials and lead to their widespread use. However, demonstrating to potential users the real cost-benefit of the expensive additives remains an issue.

Nosocomial infections — those picked up in hospitals — are a big problem and cost billions of dollars each year. In Germany, more people die from catheter-related infections than from traffic accidents, notes Michael Wagener, managing director of antimicrobial developer Bio-Gate Bioinnovative Materials, Nürnberg, Germany, formed in September 2000.

Silver has been used since antiquity as an antimicrobial, and has been seeing a resurgence in interest. Organic antimicrobials like triclosan have limitations, due to temperature sensitivity and varying compatibility with different polymer matrices, explains Andrew Barclay, technical manager of compounder Wells Plastic, Stone, England.

Silver is widely recognized as being safe and has high heat stability (over 500°C) and low volatility, making it suitable for use with engineering polymers, notes Barclay. It also provides long-lasting effectiveness and wash resistance.

Current commercial products generally rely on a zeolite or ceramic as a carrier for silver. Silver ions are released by the presence of moisture or another metallic ion. Most of the antimicrobials are produced by firms in Japan, even if marketed by non-Japanese firms.

Asia-Pacific has led the use of silver antimicrobials, notes Fred Gastrock, project manager at market researcher BRG Townsend, Mt. Olive, NJ. Indeed, only a few years ago, the region accounted for close to 100% of global consumption, which he reckoned was 5 million to 10 million lb in 2001. Demand has steadily been increasing in North America and Europe, with each now accounting for about 6 to 7% of the market. Gastrock expects overall silver-antimicrobial use to grow 5 to 6%/yr, with gains concentrated mainly in North America and Europe.

Doctor’s Research Group, Plymouth, CT, introduced in the fourth quarter of 2001 SafeSeal stethoscope diaphragm covers with about a 5% level of AgIon antimicrobial from AgION Technologies, Wakefield, ma. DRG has made over 10 million of the injection molded thermoplastic elastomer covers, says Dwayne Poteet, sales vp. The covers are marketed worldwide.

There are 16 million stethoscope wearers in the U.S. alone, notes Poteet. So far, response has been greater from emergency-care staff than from hospital infection-control specialists. He believes the latter are loathe to admit to an infection-control problem. This hinders the broader acceptance of medical goods containing silver antimicrobials, say other observers.

Edwards Lifesciences, Irvine, CA, started selling Vantex central venous catheters with an undisclosed level of Oligon antimicrobial from Bioenvision, New York, in June 2000. The extruded polyurethane catheters are sold globally and come in a variety of sizes in 2-, 3-, and 4-lumen configurations. It compounds the pur internally, and says tested antimicrobial efficacy is over one year in the body.

Vygon, Ecouen, France, has offered Multicath Expert central venous catheters with AgIon since 2001. The extruded pur catheters, which are marketed in Europe, come in various sizes in 2-, 3-, 4-, and 5-lumen configurations. Acceptance in the U.K. has been excellent, says Alan Martin, business development manager for Vygon U.K., Cirencester, England. It uses an undisclosed level of AgIon and claims 30-day-plus efficacy.

Ravi Bhatkal, AgION’s vp. for strategy and business development, sees promise for antimicrobials for other types of catheters and in implants, such as components for pacemakers and orthopedic devices. AgIon uses a zeolite carrier.

Ensinger, Nufringen, Germany, provides stock shapes containing AgIon for applications like polyetheretherketone handles for dental instruments. Surgical handles should be out in 2003, as should thermoformed polyphenylene sulfone sterilization trays for surgical instruments. Tests of the trays have shown no loss of antimicrobial efficacy after 50 autoclaving cycles.

Oligon may soon find use in pulmonary artery catheters, says Bioenvision, which has received U.S. FDA approval for the application. Oligon technology involves impregnating a polymer with silver, platinum, and carbon particles. When contacted by an ionic fluid such as saline or body fluids, an electrochemical reaction takes place, releasing silver ions.

Milliken Chemicals, Spartanburg, SC, began offering AlphaSan, a zirconium-phosphate-based ceramic ion-exchange resin containing silver, in Europe in 1998 and in the U.S. in 1999, says Geoff Haas, market manager. Unlike other products, it does not impart color, he claims. It is now being used in products such as silicone tubing.

Ciba Specialty Chemicals, Basel, Switzerland, started marketing silver antimicrobials in 2001. Irgaguard B5000 features a zeolite carrier and is being used for medical ancillaries like bed pans. A catheter containing the material should be marketed this year, as should a base and casters for a mobile blood-pressure monitoring unit. Discoloration is not an issue.

Clariant, Muttenz, Switzerland, introduced Sanitized Silver in North America several months ago, says Charlotte, NC-based marketing analyst Marla Brandon. It relies on a glass ceramic carrier and does not pose color-change issues. Medical has not been a prime focus, though applications like hospital flooring and mattresses are in the works, and prosthetics are a possibility.

Bio-Gate is grooming nanosilver technology licensed from the Fraunhofer-Institute for Manufacturing and Advanced Materials, Bremen, Germany. Bio-Gate’s Nanosilver BG uses elemental silver, and comes as a nanoporous powder containing 1- to 5-micron particles, and as 10-micron particles nanodispersed in liquid, notes Wagener. The company is working on about 10 medical applications, including prosthetics. An endotracheal catheter is likely the first to be commercialized, Wagener says.

Wells Plastic launched masterbatches with silver antimicrobials at K98. Its Bactiglas range features versions based on soluble complex glasses. A molded tpe stethoscope diaphragm cover has been commercial for about four years, but the biggest volume is anaesthesia systems like extruded polypropylene and polyethylene tubing and injection molded high-impact polystyrene connectors.

Other compounders like RTP, Winona, MN, and A. Schulman, Akron, oh, are showing more interest in supplying silver antimicrobial materials for medical. Clariant Masterbatches recently started offering masterbatches containing AlphaSan and expects its first medical applications to be commercialized by year end, says Manfred Dicks, Winchester, VA-based vp. and general manager of additive masterbatches for the Americas.

Many suppliers report increasing inquiries about applications over the last year. Applications are rising, but the floodgates haven’t opened yet, admits Barclay. Medical markets are naturally cautious, he explains, adding that development times are longer because of the necessary testing. It seems that a lot of players are waiting for someone else to make the first move, he says, because of the extra cost posed by the antimicrobial.

Clariant’s Brandon quotes a price range of $40 to $90/lb. Barclay notes that a masterbatch generally sells for $30 to $35/lb. Typical addition rates of 0.25 to 0.5% (400:1 to 200:1) give a raw material on-cost of 7 to 17.5¢/lb, he says. Kevin Marshall, RTP medical market manager, reckons a minimum added cost of 75¢/lb, though, while Milliken’s Haas places the figure at $1/lb.

Jody Walker, engineering plastics product manager at stock-shapes distributor Curbell Plastics, Orchard Park, NY, says a shape with a silver antimicrobial is three to four times the cost of one without it.

Price wouldn’t be as much of an issue in the medical market if the value of using the materials to combat nosocomial infections were more fully appreciated. Lack of clinical trials is a factor, and so is lack of market awareness. The inability to claim a health benefit is a big hindrance, many suppliers complain.

The cost issue will diminish as the idea of reducing infections takes hold and as doctors become more convinced to use antimicrobials, says Bio-Gate’s Wagener. It’s just a matter of time, agrees AgION’s Bhatkal. Rengarajan Ramesh, A. Schulman technology vp., sees global volume doubling or tripling in 6 or 7 years.

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