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New Options for Fighting Hospital-Acquired Infections

NEWS TRENDS

The Glovegard is a gloved-hand sanitizer that works in a matter of seconds.

Hospital-acquired infections are a scourge. Not only do they harm patients, killing as many as 99,000 a year, but they cost $5.5 billion a year to treat. Some payers, including CMS, have had enough and will no longer be covering treatments necessitated by infections caused by prior treatments.

CMS will cease Medicare coverage for four such conditions in October. They are infections associated with urinary catheters, blood lines, heart bypass surgery, and certain elective surgeries. It is proposing to stop paying for treatments of some other infection-related conditions by fall 2009.

This development should accelerate research to find solutions to curb the problem. A number of efforts are already under way, and many of the proposed solutions will require buy-in from medical device manufacturers. One idea in development is a device itself.

Some ideas were passed around at the eighth annual conference of the Multidisciplinary Alliance against Device-Related Infections (MADRI). “One benefit of the conferences is that many relationships have been formed that are resulting in collaborative research,” says Rabih Dariouche, MD, MADRI's founder. He is also director of the Center for Prostheses Infection at Baylor College of Medicine (Houston).

One area being studied is ventilator-initiated pneumonia. Ventilators' endotracheal tubes are the culprits, and they need anti­infective coatings, he says. “We must combine strict infection-control measures with anti­infective technology,” he says. This applies to other implanted devices as well, he adds.

Solutions to the problem need to have two qualities, he explains. First, they must be able to easily achieve a reduced rate of infection. Second, they must be durable. “You can't rely on human rates of compliance when it comes to infection-control measures,” he says. “Once an implant with a truly effective antiinfective is put in the patient, its job is essentially done.”

Gene and Peter Gordon, the founders of Germgard Lighting LLC (Dover, NJ), are tackling the problem from a different angle. They say that not only are current hospital practices inadequate for keeping pathogens out of patients, but that coating devices won't fully solve the problem, either. The main reason is that treating devices doesn't do anything about the pathogens that the caregiver can transmit to the patient.

What is needed, they say, is a way to make caregivers' hands sterile. “Personal protective equipment is a huge part of the infection prevention business, but all it does is protect the worker from the patient,” says Peter Gordon, who is Gene's son. Alcohol rubs kill some germs but not spores. Hand washing removes pathogens but doesn't kill them.

Instead, says Gene Gordon, “We have to figure out a way to sterilize hands within a very short time—seconds—and do it conveniently and with no irritation. So that all the excuses that healthcare workers and hospital administrators make will go down the drain.”

Ultraviolet C is used to sterilize the glove on a caregiver's hand. It is emitted through a germicidal tube.

So Germgard is developing several technologies to address that. The closest to fruition is the Glovegard, a gloved-hand sanitizer. It uses Ultraviolet C to sterilize the glove on a caregiver's hand to the tune of a 4 log reduction in pathogens or better.

The Ultraviolet C is emitted through a germicidal tube, in a way that does not cause cancer. It can cause redness of the skin, but that's not an issue on gloved hands. The caregiver sticks his hand into a box and spreads his fingers. The opening is sealed, and the tubes emit the radiation. The sanitizing process at this point takes 3 seconds. Eventually, the Gordons would like to get the process down to 1 second.

Germgard is also developing a bare-hand sanitizer, an air sterilizer, and a surgical instrument sterilizer.

Hospitals have been reluctant to embrace these concepts, the Gordons say, but that could change once they are on the hook financially for treatments of infections contracted at their facilities.

Copyright ©2008 Medical Device & Diagnostic Industry

The Academic Connection

BUSINESS PLANNING & TECHNOLOGY DEVELOPMENT

Sidebars:

At the same time local governments are seeking ways to spur economic development in the life sciences industries or revitalize neighborhoods, many medical device manufacturers are seeking ways to decrease costs and form partnerships. University scientific research parks represent the perfect marriage for many device manufacturers and local government officials, as they facilitate connections and close collaboration among talented people. The resulting combinations have the power to create energetic atmospheres of innovation for the companies and economic renaissances for the communities.

Many start-up life science companies cannot justify or afford to purchase expensive resources and equipment for research and development purposes with the limited financial resources they possess. By locating in a research park, companies can often gain access to university laboratories and equipment through agreements that allow companies to purchase time on expensive equipment owned by the host institution.

Companies can also gain access to the specialized knowledge possessed by university researchers, as the lead researchers are often faculty members themselves. The close proximity of research parks to universities enables the faculty member to maintain good working relationships with both the university and the company and its executives. This article takes a look at the varied benefits that university research parks can offer medical device manufacturers and provides examples of successful ongoing collaborations.

Building from the IP Up

(click to enlarge)
Researchers at the nonprofit InMotion Musculoskeletal Institute in Memphis work with industry to improve the treatment of musculoskeletal disease.

Intellectual property is, without a doubt, one of the most valuable assets of a medical device manufacturer, and such assets can originate from a variety of sources. While some companies that partner with university research parks bring their core intellectual property with them, others look to the universities themselves as valuable sources of ideas.

For example, Piedmont Triad Research Park, affiliated with Wake Forest University, has an office of technology asset management that works with university researchers to license or form start-up companies with university intellectual property, to achieve their goals of technology commercialization. Wake Forest University Health Sciences is foremost in the expansion of a new park, which was designed by Sasaki Associates (San Francisco). The Biomedical Research Campus District alone will encompass 72 acres out of the 200-acre park.

When developing a relationship with a university research park, manufacturers will find that many points are up for negotiation, including issues surrounding the ownership of intellectual property that is brought into or emerges from the collaboration. Some research parks may want to have an equity stake in a company or its IP as part of the tenancy deal. Others may not. During negotiations, clear communication and detailed assessment of the value that both parties bring to the collaboration are key to settling on a fair and mutually beneficial arrangement.

Finding Funding

Venture capitalists often participate actively in investment opportunities that become available in university research parks, and such parks actively maintain relationships with venture capital groups. These relationships frequently help start-ups finding their first angel investors. The investors provide both funding and management skills to the nascent companies. This managerial guidance is invaluable to researchers, who are often not familiar with the business side of the process.

Varied Research Offerings

The resources available at university research parks across the country vary greatly, as do the types of endeavors supported by the parks. Certain universities and their parks are designed to support specialized interests, such as specific device sectors, nanotech, biotech, clinical chemistry, clinical trials, or others. When considering a partnership with a particular park, manufacturers must consider the establishment's history in terms of the types of companies that the park has traditionally supported.

Likewise, the types of university departments that support or have relationships with the park—such as biomedical engineering, surgery, or molecular biology departments—speak volumes with regard to the type of intellectual capital that will be available to a budding company. The same can be said for the park's partnerships or other connections with large medtech companies.

In addition to intellectual resources, physical features of research parks run the gamut, and many parks are in the process of expanding or updating their facilities. For example, Technology Enterprise Park (Atlanta) is in the process of building an 11-acre park that will include a biotechnology complex just outside Georgia Tech University. The planned four buildings will feature open space inside each building, and customization of that open space for small manufacturers. The Emerging Technology Center, a 60,000-sq-ft wet lab and bioscience incubator located on the campus of Louisiana State University is another example of a facility that offers shared resources to medical device companies such as MaxiFlex LLC, which manufactures urological surgical devices.

Likewise, University Park at the Massachusetts Institute of Technology, developed by Forest City Science and Technology Group (Cambridge, MA), goes beyond simple access to a premier research institution. It is a 27-acre mixed-used development that combines 1.3 million sq ft of biotech research space with residential housing, a hotel, and commercial properties. It was the winner of the Urban Land Institute's 2004 Award for Excellence.

Another Forest City property, the Science and Technology Park at Johns Hopkins University, will offer similar amenities, along with 1.1 million sq ft of lab and office space. The facilities and access to Johns Hopkins University School of Medicine will offer medical device companies an excellent avenue for partnership formation.

Building Businesses

Many research parks offer direct business assistance to park companies. For example, the Virginia Biotechnology Research Park includes the Virginia Biosciences Development Center. The center provides assistance by evaluating potential university technologies, with the intent to spawn companies derived from university research. Once a company is established, the development center assists with business strategies and provides mentors to companies located in the park's incubator. The BioBiz program also places graduate-level business students inside biotechnology companies to assist with solving various business-related issues.

The Louisiana Business and Technology Center at Louisiana State University's South Campus Research Park offers management assistance, financial modeling, and small business innovation research grants to incubator and research park clients in the medical device and life sciences fields. The center employs full-time business counselors, including eight MBA graduate assistants and a counselor who holds both MBA and MD degrees, to assist technology companies.

Conclusion

Today, university research parks have evolved well beyond simply providing four walls and a floor to their harbored companies. Medtech companies can now find research parks with offerings that support nearly every stage of their development.

To find out more about research and science parks, and the benefits they can offer to medical device companies, contact the Association of University Research Parks, a 350-member organization that actively encourages and promotes university-industry interaction. The organization can be found on the Web at www.aurp.net.

Charles F. D'Agostino is executive director of the Louisiana Business and Technology Center and LSU South Campus Research Park (Baton Rouge).

Copyright ©2008 MX

Preemption Trouble Ahead: Proposed Legislation Brings Possible Turmoil

The development of new and innovative medical technologies is often a costly and lengthy process. Navigating the rigorous FDA requirements for premarket approval (PMA) can take years and tens of millions of dollars. Yet some on Capitol Hill are challenging the robustness of the current PMA review process. They would rather have a medical product's safety and efficacy be determined by a layperson in a jury than by FDA engineers and scientists who have spent years reviewing clinical data about the device. If this change were to occur, it would undermine the current regulatory process and stifle innovation.

Novelli
Novelli:The post-Riegel dispute.

The principle of federal preemption over state laws is driving a debate in Washington about whether injured parties should be permitted to bring liability suits against PMA devices in state courts. The principle of preemption is generally defined as federal law preempting, or being supreme over, state laws or regulations. This was the issue at stake in a recently decided Supreme Court case involving a device manufacturer.

The Supreme Court addressed the preemption doctrine head-on in the case of Riegel v. Medtronic. In the Riegel case, plaintiffs brought suit alleging that a Medtronic catheter was negligently designed and manufactured. The plaintiff's contention was that Medtronic was explicitly liable for injuries incurred because of the product's design.

The overall issue, however, was the legal doctrine of federal preemption. As the doctrine relates to the case, the conflict focused on whether claims of product liability under various state tort liability laws were preempted by the PMA process under the Federal Food, Drug, and Cosmetic Act. In an 8–1 decision, the Court held that the PMA process preempts competing state tort laws and thereby limits the liability that companies can face in a product liability lawsuit.

Where the Trouble Lurks

While the Supreme Court's decision was welcome news for many in the medical technology industry, opponents of the decision quickly denounced the ruling and began setting the stage for dissenting action. In May, Representative Henry Waxman (D–CA), as chairman of the House Committee on Oversight and Government Reform, called a hearing to examine the implications of preemption of state liability laws. The highly publicized event specifically examined the central question of the Riegel decision, focusing on whether FDA regulation of drugs and devices should bar injured patients from compensation under state law. Following the hearing, Waxman requested documents related to FDA's position on preemption of state liability lawsuits for both drugs and devices.

These actions culminated in the June introduction of the Medical Device Safety Act of 2008 (HR 6381) in the House of Representatives, and the July introduction of a Senate bill of the same name (S 3398). The legislative proposal aptly states, “Nothing in this section shall be construed to modify or otherwise affect any action for damages or the liability of any person under the law of any State.” Notwithstanding possible constitutional challenges to this legislation itself, the proposal, in effect, negates the Supreme Court's holding and would allow for seemingly endless litigation against PMA products—no matter how rigorous the federal approval process might be.

The Medical Device Safety Act maintains a thinly coded shell of self-righteousness that barely covers the inherent and substantial flaws of the policy it seeks to advance. To begin, the proposal assumes that FDA's rigorous PMA process is flawed and should, without debate, be subject to the second guessing of the medical ‘expertise' of hundreds of different and competing authorities (aka juries). However, the legislative statutes the proposal attacks (the Medical Device Amendments of 1976) have prevented, and continue to prevent, the safety problems the proposal's authors believe are inherent in the current law. The PMA process was incorporated into the Federal Food, Drug and Cosmetic Act by way of the Medical Device Amendments of 1976. Prior to this change, the FDA did not possess any real authority to determine whether a product was safe or efficacious prior to approval. Instead, the agency employed police authority to determine safety and efficacy ex post facto of a device approval. In turn, if a product was neither effective nor safe, the FDA could seek legal recourse for possible product misbranding or adulteration. The overall consequence of the Medical Device Safety Act essentially would be the ability of state courts to challenge, and perhaps determine, whether a medical device is safe or efficacious.

What existed prior to the 1976 device amendments was a mélange of competing, and often conflicting, state regulations established to determine the safety and efficacy of a medical device. As it became apparent that innovations in the device industry were pervasive and that the industry itself was burgeoning, Congress rightly acted to establish a single, consistent and risk-based system to determine whether a device was safe and efficacious prior to that product entering the stream of commerce. The Medical Device Safety Act will, in effect, ignore what Congress sought to establish to deal with potentially unsafe products regulated at the state level. The proposal will allow for numerous state courts to question the validity of the PMA process and, ultimately, the very mission of the FDA. The agency and its Center for Devices and Radiological Health continue to be the “gold standard” in the world in ensuring medical device safety and efficacy. This reputation is built on the nearly 1000 scientists, researchers, physicians and engineers who devote their career to the agency's mission. Absent this single national authority, we are left with the mélange of conflicting state regulations that was problematic to the pre-device amendments era.

The authors of the Medical Device Safety Act continually argue that the legislation is about preserving and improving patient safety. However, the outcome of the legislation, if passed, could have the opposite effect. The hodgepodge effect of a medical device's safety and efficacy being challenged at numerous state levels significantly undermines the tried and true PMA process. In turn, patient access to innovative and lifesaving medical devices could be limited, resulting in greater negative clinical outcomes and substantial increases in overall healthcare spending. At a time when our country should be encouraging the development of new technologies, the passage of this legislation would have opposite outcome.

A Flawed Proposal

Questioning the motivation of the creation of legislation such as the Medical Device Safety Act almost seems to be sacrosanct. Through a convoluted cloud of sanctimonious rhetoric, the stated intent of the legislation is to protect patient safety. Again, the bill's authors assume that patient safety is ignored under the current approval scheme. In constructing their argument, legislators claim that patients injured by a device can seek no other legal recourse in pursuing damages for their injuries. This is a false claim, as the court's decision in Riegel does not deny a plaintiff complete legal recourse. Rather, it simply conveys a long-held constitutional principle of implied preemption of federal law. The Supreme Court rightly concluded that impracticalities that could arise from a patchwork of competing state courts would significantly undermine the authority of a single, scientific authority. Given the obvious flow of commerce from state to state, the PMA process provides such a scientific authority and has been proven to be the best facility to ensure device safety and efficacy. What appears to be a chivalrous and cavalier advancement for patient safety is more akin to the motivations of plaintiffs' attorneys.

The passage of this legislation remains unclear for the remainder of 2008. Congress has a plateful of other non-health-related issues to address prior to its adjournment. The fact that 2008 is an election year also will dampen most legislators' appetites to address any controversial issue. Many experts speculate that 2009 will be a watershed year for health reform, and possibly, an opportunity will exist to pass the Medical Device Safety Act. For innovation's sake, let's hope there are more motivated engineers and innovators than there are trial attorneys.

Thomas C. Novelli is director of federal affairs for the Medical Device Manufacturers Association (Washington, DC). He can be reached by phone at 202/354-7175 or via e-mail at tnovelli@medicaldevices.org.


© 2008 Canon Communications LLC

Return to MX: Issues Update.

Okay Industries Wins Quality Award

Okay Industries also won the 2008 Ulbrich Award for Competitive Excellence in Product Development for developing a device used in minimally invasive surgery. The award acknowledges a firm that develops and manufactures a product that best uses metal to replace a nonmetal competitive material. Okay Industries makes precision metal stampings and subassemblies for the medical market.

SCS Acquired by Private Investment Firm

SCS was previously owned by Bunker Hill Capital LP for two and a half years, during which the company experienced strong growth. SCS is the global leader in parylene conformal coating services and materials. The coating is used on a range of products including stents, catheters, electronics, electrosurgical tools, and cardiac assist devices. SCS has nine coating plants worldwide. In addition to parylene coatings, the company also provides liquid coating systems such as spray, spin, and dip coating systems, and ionic contamination test systems.

Never Assume When It Comes to Precision Medical Manufacturing

If there’s one thing we know for sure about the manufacturing of precision medical devices, it’s that there is almost no margin for error. The smaller a part you have to make, the more accurate and repeatable the manufacturing process has to be. Since many of these products are implanted in the body or cut tissue, an error in manufacturing that is allowed to go unnoticed could very well mean an injury to a patient. And when you are talking about parts that are in some cases microscopic, it is very easy for errors to go unnoticed.

That’s why you can’t assume that what works in the manufacturing of conventional medical devices will work in the manufacturing of precision medical devices. Miniaturized parts need processes optimized for miniaturization.

Many of the articles in this, the first Fall Edition of Med-Tech Precision, show you what you can do instead of making assumptions.

One way in which we are trying to help is by presenting a special section on micromolding. Some medical manufacturers don’t understand the difference between small part molding and micromolding. Others assume that conventional molding equipment can handle molding jobs of any part size. Both attitudes can lead to faulty manufacturing processes. Freelance writer Beth Orenstein explains what micromolding is all about, what techniques are being used to optimize the process, and what forces are driving its adoption in the precision medical field. Scott Herbert, president of Rapidwerks Inc. (Pleasanton, CA), explains what can go wrong when a precision medical device maker tries to make a micromolded part with a conventional molding machine.

Eric Schwarzenbach, president of Rollomatic Inc. (Mundelein, IL), discusses how the design and manufacturing of orthopedic cutting tools suffer from faulty assumptions as well. In particular, the tools are often not made in a way that complements the design of the implants. In an article you can find here, he reviews what orthopedics manufacturers need to know to do proper cutting-tool design and manufacturing.

If a precision medical device is going into the body, it needs to have a good coating in order to ensure that it will not cause an adverse reaction in the patient. And not just any coating will do. In afeature, Lonny Wolgemuth, senior medical marketing specialist for Specialty Coating Systems (Indianapolis), discusses one family of conformal coatings, parlyene. It has a very good track record of preventing adverse reactions, and of use on cardiological and minimally invasive surgical devices.

If you’re reading this magazine, chances are you’re making a product that is no ordinary medical device. Therefore, you shouldn’t be content with ordinary manufacturing processes and material choices. We hope you find the insights in this issue’s articles helpful.

Johnson Medtech Establishes Global Network, Opens Cleanrooms

Johnson Medtech (Shelton, CT) has established a global network of eight medical innovation centers. They are in China, Germany, Switzerland, Israel, the United Kingdom, and the United States. The facilities feature design and prototyping services for device subsystems and components. Each center has local sales and technical support experts to increase efficiency and streamline product development. Johnson Medtech also opened four cleanrooms at its Shajing, China facility. The cleanrooms, which encompass 14,000 m2, increase the company’s manufacturing capacity by 1 million additional Class II and III devices and subassemblies per year. The new facilities each also have an engineering office, a testing lab, and a document control room.

Asahi Intecc and MediGuide Collaborate in Cardiology

“This collaboration brings together the most advanced guidewires and sophisticated imaging and guidance technology, providing an exciting opportunity to improve CTO [chronic total occlusion] in the future,” says Martin Leon, MD, professor of medicine at Columbia University Medical Center (New York). The G-Wire guidewire is a submillimeter tracking sensor that combines Asahi wire technology with MediGuide’s navigation technology and 3-D imaging. It will enable doctors to visually track orientation of the guidewire, along with the 3-D spatial tip position of the wire, while manipulating the device in real time.

A New Look at Parylene Conformal Coatings

Parylene is the generic name for a unique series of polymeric organic coating materials that are polycrystalline and linear in nature. They possess useful dielectric and barrier properties per unit thickness, and are chemically inert. Parylene coatings are ultrathin, pinhole-free, and truly conform to components due to their molecular level polymerization—basically “growing” onto the deposition surface one molecule at a time.

Parylenes provide unmatched moisture, chemical, and dielectric protection. They also provide surface lubricity. But the greatest benefit may be their biocompatibility, especially with the growth of new minimally invasive surgical procedures and implant technologies. Parylenes not only do not affect the body in any negative way, but they can be used on devices to enhance their acceptance within the body.

ISO biological evaluations have demonstrated very low levels of fibrous capsule formation, nearly nonexistent toxicological responses, and excellent hemocompatibility.1

Parylene is also the only family of conformal coating materials that are applied via a vapor deposition process. This process ensures that the coating can provide 100% coverage. It means the coating can penetrate deeply into the smallest crevices where other types of coatings simply cannot reach, or would bridge over the area, leaving the potential for delamination of the coating or even damaging small devices, components, or electrical connections by the sheer weight of the coating material itself.

Vapor Deposition Polymerization

Devices to be coated are placed in a room-temperature deposition chamber. A powdered raw material, known as dimer, is placed in the vaporizer at the opposite end of the system. The double-molecule dimer is heated, causing it to sublimate directly to a vapor, then is heated again to a very high temperature that cracks it into a monomeric vapor. This vapor is transferred into the ambient temperature deposition chamber where it spontaneously polymerizes onto all surfaces, forming an ultrathin, uniform, and extremely conformal parylene film. The parylene coating process is carried out in a closed system under a controlled vacuum. The deposition chamber and parts to be coated remain at room temperature throughout the process. No solvents, catalysts, or plasticizers are used in the coating process. No curing process or added steps are required.

Because there is no liquid phase in this deposition process, there are no subsequent meniscus, pooling, or bridging effects as seen in the application of liquid coatings. As a result, dielectric properties are never compromised. The molecular “growth” of parylene coatings also ensures not only a uniform, conformal coating at the thickness specified by the manufacturer, but because parylene is formed from a gas, it penetrates into every crevice, regardless of how seemingly inaccessible. This assures complete encapsulation of the substrate without blocking, or bridging, even the smallest openings.

Parylene Variants and Capabilities

Parylene N is a carbon-hydrogen molecule, poly(para-xylylene), a completely linear, highly crystalline material. Parylene N is a primary dielectric, exhibiting a very low dissipation factor, high dielectric strength, and a low dielectric constant invariant with frequency. The penetrating power of Parylene N is second only to that of Parylene HT.

Parylene C is a carbon-hydrogen molecule with a chlorine atom on the benzene ring. It is produced from the same dimer as Parylene N but modified with the substitution of a chlorine atom for one of the aromatic hydrogens. Parylene C has a most useful combination of electrical and physical properties plus very low permeability to moisture and corrosive gases.

Parylene D is produced from the same dimer as Parylene N, modified by the substitution of chlorine atoms for two of the aromatic hydrogens. Parylene D is similar in properties to Parylene C, with the added ability to withstand higher use temperatures (up to 125°C). Parylene D is generally not used in the medical device industry, as it lacks the necessary biocompatibility credentials.

The newest formulation is Parylene HT, which was developed by replacing the alpha hydrogen atom of the Parylene N dimer with fluorine. This formula provides protection in high temperature environments up to 350°C (short-term, up to 450°C), and offers long-term UV stability not available with the other parylenes. It also has the lowest coefficient of friction, a very low dielectric constant and, because of its extremely small molecular size, it has the highest crevice-penetrating capability of all the parylenes. (Parylene HT is a registered trademark of Specialty Coating Systems.)

All parylene film coatings are free of fillers, stabilizers, solvents, catalysts, and plasticizers. They are extremely lightweight, offering excellent barrier properties without adding dimension or significant mass to delicate components. They are typically applied in thicknesses ranging from 500 Å to 75 µm. A 25-µm coating, for example, will have a dielectric capability in excess of 5,000 V. No other coating materials can be applied as thinly as parylene and still provide the same level of protection. One key benefit of parylene is that it can actually strengthen delicate wire bonds by an estimated factor of 10. Another attribute is parylene’s transparency to visible light, enabling its use on optical devices and components.

Many electronic surgical systems now include various forms of memory communication and some of the newest systems are starting to interact with radio frequency (RF) and other forms of wireless communication. As precise and undistorted signals are becoming increasingly important, parylene coatings are particularly well suited for these high-frequency devices, given their extremely low dissipation factors and dielectric constants.

Common Applications

Parylene coatings can be applied to almost any material that is vacuum stable. They have been successfully applied to paper, ceramics, plastics, metals, polymers, and even feathers and powders. They are routinely applied to ferrites, nitinol, cobalt chromium, stainless steel, silicones, printed circuit boards, silicon wafers, and numerous other simple and complex components, devices, and systems. Here are some key applications in cardio and surgical areas.

ESU, RF Ablation. Electrosurgery (ESU) devices apply RF currents at frequencies in the range of 300 KHz to 5 MHz to tissue to achieve a surgical result. These processes require precise control of the RF energies to pinpoint only the target and the effects desired.

The active device contacts one surface of the target layer and positions the tissue to ablate through the layer or on its surface. Usually these tools require conductivity only at the tip or on the electrode/probe/hemostat where fulguration is to occur. The rest of the tool needs to be electrically insulated and able to withstand fairly high temperatures.

There are two basic parts to these systems—the RF generator powering the surgical tool, and the active tool that provides the cutting, coagulating, and ablation. Parylene coatings provide a secure moisture and dielectric barrier to protect the critical electronics in the generator and help to insulate and lubricate the active tool.

Electrostimulators: Implantable Cardioverter-Defibrillators (ICDs) and Pacemakers. An ICD is implanted in patients at risk for recurrent, sustained ventricular tachycardia, or fibrillation. The device is connected to leads positioned inside or on the heart’s surface, which are used to sense the heart rhythm and deliver electrical shocks to stimulate the heart as needed. The various leads are tunneled to the pulse generator, which is implanted in a pouch beneath the skin of the chest or abdomen.

A pacemaker also uses electrical impulses to regulate the beating of the heart.

These devices require highly precise and reliable internal circuitry. Life literally depends on it. Parylene coatings provide moisture barrier, dielectric barrier, and biocompatibility properties that are critical to these devices. They prevent short circuit failures. Yet parylene does not add weight or compromise circuitry in any way.

There are, on occasion, patients who are allergic to the enclosure/case metal, titanium, of the pacemaker or ICD. A parylene coating solves this issue quite nicely.

Another scenario where parylene coatings have helped is not one where lives hang in the balance, but one involving discomfort and annoyance for the patient. When the enclosure of a pacemaker also serves as the return electrode, the stimulation signal can cause the adjacent muscles to contract. Coating the entire enclosure, save for a coin-sized space on the chest wall side, with parylene eliminates the muscle twitch.

Pumps: Heart-lung Bypass Pump and Intra-Aortic Balloon Pump. Cardiopulmonary bypass (CPB) is a form of extracorporeal circulation.

It is a technique wherein a device temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and its oxygenation. The CPB pump itself is often referred to as a heart-lung machine or heart-lung pump.

Oxygen-deficient blood withdrawn from the venous circulation is collected (by gravity siphon) in a reservoir. From there, the blood is pumped through an artificial lung, or oxygenator. This is designed to exchange carbon dioxide in the blood for oxygen. As the blood passes through the oxygenator, the blood comes into intimate contact with the surfaces of the exchange membrane. Oxygen and carbon dioxide move across the membrane, permitting the blood cells to release carbon dioxide and absorb oxygen. The oxygen-rich blood is pumped throughout the patient’s body.

The heart-lung pump circuit is a continuous loop. As the oxygenated blood goes into the body, oxygen-depleted blood returns from the body, and is reoxygenated and returned to the patient, completing the circuit.

An intra-aortic balloon pump is a mechanical device that is used to decrease myocardial oxygen demand while at the same time increasing cardiac output. Increasing cardiac output also increases coronary blood flow and thereby myocardial oxygen delivery. The system consists of a cylindrical balloon that is positioned in the aorta where it counterpulsates.

Parylene coatings provide the moisture and dielectric barriers necessary to prevent short circuits in the control console circuitry of these devices. A shorted circuit in the control console would be a life-threatening event.

Surgical Tools: Electrically & Pneumatically Powered Surgical Instruments. Surgeons rely on powered instruments for bone surgery. Even when the surgery is not on the bone itself, the need to access a critical area may mean going through or removing bone. Pneumatic and electric power sources, along with the development of interchangeable accessories, have revolutionized this surgical instrument field. Procedures are now safer, faster, and less traumatic for the patient.

All electrical and pneumatic powered surgical tools require protection of the motors and circuits that keep them running, and pneumatic tools typically require a hose for connection to the gaseous power supply. Sophisticated control consoles allow the surgeon to precisely control the instrument.

Parylene coatings provide the moisture and dielectric barrier protection required to prevent shorted circuits. Additionally, the pneumatic gas supply hoses are often made of silicone, notorious for its tacky surface and propensity for soiling. These hoses do not have a good hand (feel) and tend to be hard to clean once contaminated. Parylene coatings give these hoses a smooth, nonporous, no-tack hand that facilitates easy cleanup.

Stents, Cardiac Catheters, and NonCoiled Guidewires. Drug-eluting coronary stents come in a variety of sizes and materials, most laser-cut from hypotubes into their intricate spring-like configurations. Stent delivery systems invariably include a guidewire.

As in balloon angioplasty, the coronary stent physically opens the lumen of the narrowed or collapsed coronary artery where it prevents that artery from further collapse.

A parylene coating on the bare-metal stent facilitates drug/polymer combo applications and adherence to the stent. As parylene adheres well to the bare-metal stent material, it in turn provides a surface to which the drug/polymer combo can effectively adhere. In this application, a parylene coating serves as a tie-layer, or primer, for the drug. In addition, parylene can also be applied over a drug to function as a release-control agent.2 It can even be used to control the release of multiple drugs to provide more complex therapeutic activity.3

The lubricity afforded by a parylene coating can enhance the advancement and withdrawal of guidewires and catheters. However, parylene may not be a good candidate for coating coiled guidewires. If the coils actually contact one another, the contact points will remain uncoated. The coating will tend to encapsulate the touching coils into one homogenous construct, reducing the flexibility for which the coiled guidewire was designed. And when the coil is flexed sufficiently to separate the encapsulated coils, uncoated contact points and fractured parylene edges will be exposed.

Intravascular ultrasound (IVUS). IVUS is a medical imaging method that uses a specially designed catheter with a miniaturized ultrasound probe constructed into its distal end. The proximal end of the catheter is attached to computerized ultrasound equipment. Such a catheter allows the application of ultrasound technology to see from inside blood vessels, enabling the doctor to see the vessel’s inner wall.

Intravascular ultrasound systems are comprised of the electronic control console and the catheter containing the ultrasound transceiver sensor. Parylene provides the ultimate moisture and dielectric barrier protection. It helps minimize failures in the console electronics, display circuitry, and components, while providing the same favorable biocompatibility and excellent lubricity to the catheter and its ultrasound sensor elements.

Keeping Pace With New Technology

Isolating instruments, tools and devices from contact with moisture, gases, corrosive biofluids, and chemicals is becoming more important every day—for the devices and for the patients into which many are implanted. Parylene will continue to play an important role in these futuristic devices, its applications limited only by the imaginations of the engineers who use it. The family of parylene coatings also continues to evolve as it keeps pace with the demands of the medical device industry.

Lonny Wolgemuth is the senior medical market specialist for Specialty Coating Systems Inc. (Indianapolis).

 

References

1. N Stark, “Literature Review: Biological Safety of Parylene C,” Medical Plastics and Biomaterials 3, no. 2, (1996): 30-35.

2. A O Regheb et al, Coated implantable medical device, U.S. Patent 6299604, filed Aug. 20, 1999, and issued Oct. 9, 2001.

3. N E Fearnot et al, Coated implantable medical device, U.S. Patent 5609629, filed Jun. 7, 1995, and issued Mar. 11, 1997.