Design News for Mechanical and Design Engineers

Understanding and meeting a real clinical need with appropriate technology is the heart and soul of a successful medical device. Technology is important, but it should not overshadow the clinical need. Paul Yock, M.D., head of the Stanford University Biodesign program, says, “The successful, effective people in medical technology invention start with a clinical need and understand how important it is. That is more than half of the secret to successful inventing.”

How about the importance of understanding the regulatory environment?

It's vital to any development effort. Without the clearance of the Food and Drug Administration (FDA), a drug or medical device may not be sold legally in the U.S. Medical devices have been regulated since 1976. For medical devices, the relevant FDA office is the Center for Devices and Radiological Health.

FDA regulates devices according to their level of risk: Exempt, Class I, Class II and Class III, with Class III being the highest risk. But there is also another wrinkle to this framework, which involves classifications 510(k) and PMA. There were many devices on the market before 1976 that were being used safely and a classification has been established called the “510(k)” for newer devices “substantially equivalent” to those on the market before 1976. PMA means “Pre Market Approval” for devices without a predicate, or representing high risk. Regulations surrounding medical devices can be a very complicated area that requires competent professional help. A good place to start for learning more about the regulatory environment is the Regulatory Affairs Professional Society (RAPS). There's no question that complying with all the regulations can be a very expensive process. But it is even more expensive when you get it wrong.

What are some regulatory areas that engineers need to address most?

A very important one is biocompatibility of materials. Any material used in a medical device must be “friendly” to the human body. You must choose materials not only for their performance in the hostile environment of the human body, but also for their compatibility with body tissues and fluids. The type and duration of contact a material has with the body is a key consideration. Something that sits for a short time on the skin has different requirements than a material permanently implanted into the body.

Any material in a medical device must be tested for biocompatibility before being used in a medical device for human use. Companies such as Pacific Bio Labs (Hercules, CA) offer these services. Pacific Bio offers a useful publication, “Assessing Biocompatibility,” available for download from its website. This material is also included in “The Medical Device R&D Handbook.” Another useful book on this subject is “Biomaterials Science,“ edited by Buddy Ratner.

Recently, some materials' suppliers have begun to offer medical grade materials that are pre-certified. For example, Bayer offers its “MD” grades of Makrolon™ polycarbonate and Lustran™ ABS, which have been tested to ISO 10993-1 standards and designed for human tissue contact of 30 days or less. Using these materials can help trim time and expense from your development program.

How about the options for manufacturing your device?

Medical devices in different specialties can require very different manufacturing skills. For example, orthopedics devices typically involve metalworking, casting, forging, machining and polishing. Cardiology products use specialized extrusion and fabrication methods to produce devices such as catheters, stents and guidewires. To learn more about production methods for particular devices, I would suggest publications like Knowledge Enterprise's “BONEZone™,” as well as medical device trade shows, such as OMTEC and Cannon Communications' MD&M show.

The rapid prototyping industry is also beginning to provide more support for medical device development. Stratasys, for example, offers an FDA-compliant polycarbonate material for use in its RP systems. The Society of Manufacturing Engineers (SME) has recently released a video, “Medical Applications of Rapid Prototyping,” showcasing innovative use of rapid prototyping in medical. “The Medical Device R&D Handbook” also includes a detailed chapter on the topic.

Just how much does an engineer need to know about the medical environment?

It is important to understand the history, development and culture of any medical specialty for which you are designing medical devices. Arthroscopy, Cardiology, Urology, Laparoscopy have all developed idiomatic ways of treating patients. Each area of the body being treated also has very different requirements from delicate cardiac vascular surgery with hair-fine sutures to orthopedic surgery with mallets, chisels and screws that can resemble a species of carpentry.

It is especially important to directly observe how a medical device will be used in actual clinical practice. Some things that seem to make perfect sense to an outsider might not work in a clinical setting. By observing medical procedures, you will learn things that just can't be picked up from a book or even from an expert's descriptions. Your medical affairs specialist can help you gain access to an operating room and instruct you in the finer points of OR etiquette. Designers owe it to themselves to observe first-hand and their managers owe it to the designer, the company and the patient to let them. It is also very important to get the consent of both the facility and patient before taking any pictures in an OR. And you must always respect federal patient privacy regulations.

		Ted Kucklick is chief technical officer for Cannuflow, Inc, a Silicon Valley based company that develops and markets innovative fluid management solutions for arthroscopic surgery. He is also the author of The Medical Device R&D Handbook.
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