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September/October 2009

Devices and Materials

From Metal Alloys to Tissue Engineering, ASTM Committee F04 Standards Aid the Medical Field

In a first aid clinic, a nurse uses tweezers to remove a splinter.

In an operating room, a surgeon sets a broken leg and places a synthetic material to fill a cavity left by a badly damaged piece of bone.

The metals in the tweezers and the material for the bone repair, as different as they may seem, share something in common. The materials can be specified to standards developed by ASTM International Committee F04 on Medical and Surgical Materials and Devices.

From its early and ongoing focus on specifying metal alloys such as titanium and cobalt-chrome-molybdenum destined for medical devices to its cutting edge work on tissue engineering and computer-assisted orthopaedic surgical technologies, Committee F04 continues to add to its more than 250 standards used by device companies and clinicians alike. Today, more than 1,000 members representing 32 countries collaborate in the work of the committee’s 35 standards developing subcommittees.

“This particular activity [F04] has had a great impact on medical products at large,” says Jack Lemons, Ph.D., a professor at the University of Alabama at Birmingham and former F04 chair. “The purpose is to have the best possible medical products, and standards are a significant part.”

“The oldest and most used relevant standards that are still being updated and kept in the books are for the materials,” says Jack E. Parr, Ph.D., president, Medical Technology Development Inc., Memphis, Tenn., current F04 chair and past member of the ASTM International board of directors. And for today’s F04 activities, he says, “We look for areas of need from each stakeholder group … to write standards in a timely fashion.”

Tissue Engineering and F04

One of the most active F04 divisions is F04.04, Division IV — Tissue Engineered Medical Products. Reflecting a burgeoning area of research and engineering, TEMPs combine biomaterials and engineering to repair or regenerate cells, tissues and organs. The six F04 TEMPs subcommittees cover classification and terminology, biomaterials and biomolecules, cells and tissue engineered constructs, assessment, adventitious agents safety and cell signaling.

“We’ve specialized in certain areas,” says Warren Haggard, Ph.D. “This group in ASTM is leading the world in developing standards in the tissue engineering area.” Haggard is professor and Herff chair of excellence in biomedical engineering at the University of Memphis, Memphis, Tenn., a member of the ASTM board of directors and co-chair of the F04 TEMPs division. To date, the division has produced more than 25 standards with 25 more in the pipeline.

Companies and clinicians alike can refer to a standard guide from the F04 division that addresses in vivo assessment of implantable devices to repair or regenerate the tissue that allows knees and elbows to bend: F2451, Guide for In Vivo Assessment of Implantable Devices Intended to Repair or Regenerate Articular Cartilage. They can characterize collagen-containing biomaterials, used for hemostatic sponges, soft tissue augmentation and drug delivery with F2212, Guide for Characterization of Type I Collagen of Starting Material for Surgical Implants and Substrates for Tissue Engineered Medical Products. And they can check models, surgical considerations and tissue process with F2721, Guide for Pre-Clinical In Vivo Evaluation in Critical Size Segmental Bone Defects.

TEMPs draft standards under way in F04.04 groups, to name a few, detail methods for determining the mass of sodium alginate and chitosan, characterizing hydrogels, quantifying mineralized matrix and cell viability, and evaluating demineralized bone and TEMPs for tendon repair.

Surgery and Testing: CAOS and MRI

Technology advances have become part of operating rooms today as surgeons use computer-assisted devices to aid in the accuracy of positioning implants or other instrumented tasks in the operating room as well as diagnose health care situations with magnetic resonance imaging.

In an activity initiated by surgeons on the F04 committee, F04.05 on Computer Assisted Orthopaedic Surgical Systems is standardizing a technique to measure and report the accuracy of surgical navigation and robotic positioning devices. Their purpose is to allow users to compare different computer-assisted surgical systems.

“Positional accuracy of the systems is the basis for completing more complex surgical tasks in an accurate manner,” says William Mihalko, M.D., Ph.D., a physician at Campbell Clinic Orthopaedics, Memphis, Tenn., an associate professor at the University of Tennessee, and director of orthopaedic reconstructive research, InMotion Orthopaedic Research Laboratory, Memphis, Tenn.

The proposed CAS (computer-assisted surgery) standard, a draft Practice for Positional Accuracy of Computer Assisted Surgical Systems, addresses the need to evaluate an individual system or to compare systems from different manufacturers. F04.05 decided to standardize accuracy measurements first to enable a basis to review different technologies and their application to various operations.

“After this standard it will be proposed that we then concentrate on standards that test the accuracy of surgical task-oriented algorithms,” Mihalko says.

Another standards activity considers safety concerns regarding magnetic resonance imaging as the result of a request by the U.S. Food and Drug Administration. MRI joins a powerful magnetic field with radio frequency pulses and a computer to examine various parts of the human body and to diagnose conditions and disease. To help prevent accidents when a patient has a pacemaker, a metal joint replacement or other implanted device affected by the magnets and pulses, the behavior of the patient’s implanted device needs to be considered and identified.

To address the implant/MR environment, Committee F04 developed F2503, Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment. The standard provides a uniform marking system to indicate what MR conditions have been determined to be acceptable for a medical device or other item. Consequently, what can and cannot be brought into an MR environment will be clear.

“F2503 is the only internationally agreed-upon set of MR-related terms and markings to satisfy this purpose,” says Daniel Schultz, ASTM F04 staff manager.

A series of standard tests referenced in F2503 provide additional information about implants in the MR environment. Methods cover how to measure magnetically induced displacement force and torque as well as radio frequency induced heating near passive implants and how to evaluate MR image artifacts caused by passive implants.

Regulatory Involvement

Committee F04’s membership, which includes medical and health care professionals, academia, device and material manufacturer representatives and regulators, has long included representation by and standards development activity suggestions from the FDA.

“FDA’s involvement is very active and interactive. The Center for Devices and Radiological Health has a long history of participation with Committee F04,” says Mark Melkerson,
director of FDA’s Division of Surgical, Orthopedic and Restorative Devices of the Office of Device Evaluation, Center for Devices and Radiological Health. He adds that FDA has worked with ASTM since the government group’s formation in 1976 and that the agency takes an active part in standards development to promote and protect public health.

“FDA CDRH’s work with consensus standards organizations like ASTM Committee F04 allows us to actively participate in the developing and revising of standards,” Melkerson says. “Such medical device standards can be used to promote and protect public health.” Standards, he adds, provide ways to understand and evaluate medical devices, establish tests for new devices and identify appropriate levels of preclinical testing.

FDA identifies standardization areas that may be useful in their development of review guidance, and it cites ASTM standards in those documents. Requests, in addition to the current MR work, include pedicle screw spinal fixation systems, ultra high molecular weight polyethylene materials, tissue engineering and more — areas of both current activity and existing standards. Areas where ASTM standards appear in FDA regulatory guidance include external fixators, plasma spray coatings and poly(methylmethacrylate) bone cements, among others.

Beyond Standards: Symposia and Workshops

Committee F04 oversees an ongoing symposia and workshop program as an integral part of its activities. The committee sponsors regular programs that result in books and papers, and that provide relevant and timely information in the field.

The first F04 symposium came soon after the committee’s first meeting in June 1962. That longstanding symposia and workshop tradition continues with a symposium on total knee replacement devices and a workshop on bone graft materials planned for May 2010.

Parr explains that workshops, through presentations and discussions, guide F04 about new standards and activities needs. “They are deliberately targeted to whether there are needs we can discover by having all these people get in the same room,” Parr says. He adds, “Symposia take a snapshot of a process or material that has been in use for quite some time, and you want to summarize what is known about it.” Symposia papers collect in one place the current understanding of a topic for reference and guidance on possible research.

For More Information

Committee F04 will next meet Nov. 10-13 in Atlanta, Ga., as part of the November committee week. All those interested are welcome to participate in Committee F04’s activities. For more information, contact Daniel Schultz, ASTM (phone: 610-832-9716).