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Combating Infection at the Nano Level

Mon, 03/12/2007 - 1:18pm
Nanotechnology is still very much in the development phase in terms of having a meaningful impact on healthcare treatment options. However, one of the first products made available out of this area is a silver nanoparticle coating that can be applied to medical devices to take advantage of the antimicrobial properties inherent in the materials. This article examines this technology.

By Jack Rubinger
In the medical device industry, innovation is key. Thanks to a robust market for medical devices, competition among device manufacturers is fierce. Also high are the expectations of hospital administrators and physicians who have come to demand that a continual stream of unique products flows into the marketplace.

The ON-Q SilverSoaker devices before (right) and after the SilvaGard antimicrobial treatment process (left). ON-Q PainBuster offers the ON-Q SilverSoaker antimicrobial catheter.
As a result, non-differentiated or “me-too” products have quickly been driven down to the commodity level. Medical device makers are under increasing pressure to shorten product development cycles, incorporate technological innovations, and produce products that offer clear advantages. Innovations that increase the devices’ efficacy and safety are paramount in this regard.

Over the past decade, the drive for innovation has led to particularly extraordinary advancements in the field of bioengineering and nanotechnology. Breakthroughs in these areas have changed, and will continue to transform, the way we detect and treat diseases. In the development of medical devices, nanotechnology holds the promise of shrinking devices, such as micro sensors and pacemakers, while increasing functionality and performance. Advances in nanotechnology, combined with further refinement of products, will revolutionize the way devices safely deliver drugs, combat infections, and monitor a patient’s health.

As exciting as future prospects for this technology may be, the medical use of nanotechnology has remained almost exclusively in the experimental realm. Recently, a breakthrough in the field has opened the door to one of the first medical applications of nanotechnology—one that promises to transform the way medical devices are treated to curtail the spread of deadly nosocomial infections.

The antimicrobial treatment of products is nothing new to the medical device industry. In an attempt to limit the role that devices play in the spread of infections, manufacturers have used a variety of methods to impart antimicrobial properties to their products. In some cases infection-fighting agents such as ionic silver have been directly incorporated into the material of the device. More common have been methods to spray or dip coat antibiotics, antiseptics, or antimicrobial silver onto the outside surface of finished products. While these methods offer some degree of antimicrobial benefit, their limitations have led the industry to search for a broader, more effective solution.

Biofilms are read utilizing spectrophotometry analysis of density.
   
Research scientists at AcryMed Inc., who had already been awarded patents for the use of silver as an antimicrobial, discovered a way to effectively harness silver’s broad-spectrum antimicrobial ability through the application of silver nanoparticles. As innovators in the fields of advanced wound care and infection control, AcryMed was the first company to successfully incorporate infection-fighting silver into an antimicrobial gel. Their development of SilvaGard silver antimicrobial technology represents one of the first real medical uses of nanotechnology—a significant breakthrough in the antimicrobial treatment of medical devices and ultimately, the fight against nosocomial infections.

Fourth Leading Cause of Death

Reducing nosocomial infections (also called Healthcare Acquired Infections or HAIs) is no small matter for the healthcare industry. U.S. hospitals report that the number of HAI cases is on the rise. According to the Centers for Disease Control, more than two million people each year who enter U.S. healthcare facilities contract infections unrelated to their initial healthcare concern. These infections increase a patient’s average hospital stay from 4.5 to 21.1 days and kill 90,000 U.S. patients each year.1

The cost of treatment is also staggering. HAIs add an average of $57,000 to a patient’s hospital bill—that is $28 billion to $30 billion added to the nation’s healthcare costs each year.2Of particular concern to the medical device industry is evidence that shows a large number of HAIs are transmitted to patients during the use of medical products—particularly implanted, indwelling, and other percutaneous devices. In the most thorough study of its kind, the state of Pennsylvania recently audited the rate and cause of HAIs in Pennsylvania hospitals and concluded that the rise of nosocomial infections was related in part to the increase in use of invasive devices such as catheters.3The rise in nosocomial infections has been exacerbated by the use, and overuse, of antibiotics, which have increased the number of antibiotic resistant strains of bacteria. Between 1983 and 1993, the percentage of patients receiving antibiotics rose from 1.4% to 45%. In a 1994 study reported in the New England Journal of Medicine, this increased use of antibiotics directly parallels the increase in antibiotic resistance.4To reduce the overuse of antibiotics, the medical community has turned to other antimicrobials, most notably silver. While antibiotics kill bacteria by targeting and disrupting a single specific site of that bacterium, silver’s unique properties allow it to simultaneously attack several sites. This multi-pronged attack disrupts the bacteria’s ability to mutate into resistant strains.Silver has also proven to be effective across a broad spectrum of microorganisms, gram-positive and gram-negative bacteria, and fungi. Research has shown that silver even kills Methicillin-resistant Staphylococcus aureus and other bacteria dubbed “superbugs” due to their strong resistance to traditional antibiotic treatments.

A Breakthrough Process

SilvaGard represents a tremendous advance in the use of antimicrobial silver. Until recently, silver’s use in treating medical devices was significantly curtailed due to limitations in how the element was, and could be, applied. By working with silver in its nanoparticle form, AcryMed was able to develop a new medical device treatment process that offers significant advantages while eliminating many former limitations.

 
 
SilvaGard is a wet immersion technology that reduces silver ions to metallic silver atoms. During the process, silver atoms cluster together and “grow” into nanoparticles of metallic silver that become charge bonded to the surface of the material or device.

Due to their small size, of approximately 10 nm in diameter, the nanoparticles create a large surface area, allowing for greater antimicrobial activity. While small in size, these nanoparticles effectively combat bacteria that are actually 100 to 500 times larger then the silver particles themselves.

Upon completion of the process, only submicroscopic silver nanoparticles remain on the surface—particles so small they require a specialized scanning electron microscope to be seen.

While traditional methods of treating devices are often limited to use on certain products or materials, SilvaGard can be used to treat virtually any medical device. Testing has shown that SilvaGard has the ability to create tenacious bonds to any material including plastics, metals, elastic polymers, and even Teflon. The silver nanoparticles have no measurable impact on the physical dimensions and do not interfere with the material’s ability to be repeatedly stretched or flexed; the antimicrobial elements remain in place without chipping or flaking.

The immersion process also makes SilvaGard technology particularly applicable for the treatment of catheters and other devices with interior walls or exposed inner surfaces. With traditional spray-coating processes, only the easy-to-reach outside surfaces of a device are treated. With SilvaGard, the entire device is immersed into the nanoparticle solution ensuring that all bacteria-susceptible surfaces are reached.

Equally important, the application of SilvaGard is nontoxic. In a soon to be published study conducted at Oregon Health and Sciences University, researchers traced silver ions in mice that were implanted with SilvaGard-treated catheters to determine the biodistribution of silver and potential systemic toxicity. After a ten-day period, they found that the majority of the silver remained on the catheter or at the insertion site. The remaining portion that eluted beyond the immediate device was eliminated through the feces. The study confirmed that SilvaGard technology had low toxicity with no silver found in vital organs such as lungs, brain, or skin. Only a trace amount (less than 0.1% of silver) was found in the liver as it was being transitioned into the feces.

Example Materials Treated

PVC Rayon Nylon
Stainless Steel Polyester Silicone
Polypropylene Silicon Polyimide
Polyethylene Titanium PEEK
Polyurethane Ceramic PTFE
Cotton Polysulfone Polycarbonate


With the goal of improving/extending the efficacy of medical devices, manufacturers have also expressed interest in the ability to regulate the duration of the antimicrobial effect. By simply varying the density of silver applied during treatment, users can customize the duration of the antimicrobial agent based upon each device’s particular requirements. A device that resides in tissues for only a few days, for example, would require a lower loading than a permanently implanted device.

Most importantly, SilvaGard is highly effective against a full spectrum of infection-causing bacteria including Staphylococcus aureus, E Coli, Pseudomonas aeruginosa, Enterococcus sp, and Candida albicans.

FDA Approval

The FDA’s initial approval of SilvaGard was granted to I-Flow Corp. for marketing the company’s ON-Q SilverSoaker regional anesthesia delivery catheters. I-Flow began incorporating the SilvaGard treatment into the production process of its SilverSoaker catheters and introduced this product to the market in late 2005.


I-Flow’s ON-Q PainBuster is used after surgery to provide pain relief.
 
Application Brief
In December 2005, the FDA gave its first clearance for the use of SilvaGard technology to I-Flow Corp. for use on the company’s ON-Q SilverSoaker regional anesthesia delivery catheters. According to I-Flow, the catheters offer an added layer of antimicrobial protection against costly surgical site infections, providing reassurance to healthcare providers. A large-scale study recently published in the Journal of American College of Surgeons validated ON-Qs proven patient outcomes.
Since its initial introduction, SilvaGard has gained the attention of manufacturers representing a wide range of medical devices. The versatility of the technology has made it a potential candidate for use on artificial hearts, orthopedic implants, shunts and drainage catheters, respiratory tubes, and central venous catheters.

The rise of nosocomial infections, the growing concern over the overuse of antibiotics, and the continual demand for innovation have all put enormous pressure on medical device manufacturers to investigate the benefits of antimicrobial treatments. SilvaGard represents the first nanotechnology applied solution on the market and offers a significant advance in the battle against healthcare acquired infections.

ONLINE

For additional information on the technologies and products discussed in this article, see the following websites:
  • www.acrymed.com
  • www.iflo.com


  • Jack Rubinger is a technical writer who has written and published several articles related to wound care and infection control technologies.
    References
    1Robert Weinstein, “Nosocomial Infection Update,” Journal of Emerging Infectious Diseases, Vol. 4, No. 3. (Side note: Also, the Centers for Disease Control and prevention estimates that 90,000 people die annually from nosocomial infections, a number that the agency acknowledges they are “working on.” After examining various records pertaining to 5,810 hospitals across the U.S., the Chicago Tribune puts the death rate at 103,000.)

    2The Committee To Reduce Infection Deaths (RID) — www.hospitalinfection.org.

    3Hospital-acquired Infections in Pennsylvania 2005 — Key Findings, PHC4.

    4Ricki Lewis, Ph.D., “The Rise of Antibiotic-Resistant Infections,” FDA Consumer Magazine, September 1995.

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