To design and successfully sell medical devices, manufacturers must ask themselves a number of key questions. What range of functions should this product offer? In what type of environment will this product need to perform? Is there competition from similar technologies? One of the most critical, and often most complex, factors to consider is the regulatory standards to which medical devices must adhere. With many nuanced requirements from government agencies, industry organizations, and widely accepted third-party entities, identifying the necessary and valuable certifications to meet can be uniquely challenging for engineers.

Fig. 1 – It is vital that medical device components are tested for biocompatibility.

The consequences of performance failure in a medical device can be devastating and even life threatening for a patient. As a result, each element of the product must be thoroughly tested and verified—down to the wire and cable components (See Figure 1). One commonly recognized certification for medical cable and integrated plastics is USP Class VI Testing.

Understanding the Components of USP Class VI Testing

The U.S. Pharmacopeial Convention (USP) was established in 1820 to create a national set of requirements for pharmaceuticals and health products. Today, the non-profit organization has expanded to include hundreds of experts worldwide who create standards for medications, ingredients in food, dietary supplements, healthcare technologies, and more. Broadly considered official regulatory criteria, USP standards are recognized by and integrated into US federal legislation and used in more than 140 countries.

In addition to medicines, the USP publishes biocompatibility protocols for the plastics and polymers used in medical devices or surgical equipment that may come in contact with human tissue. Initially, these requirements were meant for the packaging of pharmaceuticals. The compounds in packaging materials had to be durable and resistant to environmental factors, highly protective, non-absorbent, and non-toxic. This strict standard was recognized as a good test for other applications, as it provided a substantial amount of biocompatibility metrics. Now, the standard has evolved for use in a large variety of medical applications. Depending on the specific use of the plastic, as well as other factors such as the length of patient contact time (limited, prolonged, or permanent), materials are categorized into one of six classes. The USP Class VI designation is considered the most stringent and, therefore, most useful for medical applications.

USP Class VI Testing involves three in vivo biological reactivity evaluations, generally performed on mice or rabbits to mimic use in humans. They are:

  • Acute Systemic Toxicity (Systemic Injection) Test: Measures toxicity and irritation when a sample of the compound is administered orally, applied to the skin, and inhaled.
  • Intracutaneous Test: Measures toxicity and localized irritation when the sample is in contact with live subdermal tissue (specifically, the tissue that the medical device is intended to contact).
  • Implantation Test: Measures toxicity, infection, and irritation of an intramuscular implantation of the compound into a test animal over several days.
Fig. 2 – Cables play a critical role in a wide range of medical equipment.

In addition to demonstrating an extremely low level of toxicity by passing these three tests, the material will be subjected to several temperature assessments for set periods of time. Consequently, compounds that do meet USP Class VI standards are very valuable for medical device manufacturers. It generally ensures a high quality level and better acceptance with the FDA and USDA. Most importantly, use of Class VI certified materials substantially reduces the risk of causing harm or increased stress to a patient from reaction to a toxic material.

USP Class VI Testing is only one standard of biocompatibility, however. Though not a limited series of tests, some biocompatibility requirements for medical devices may exceed the testing performed in USP Class VI. A more rigorous standard for the biological evaluation of medical devices is ISO-10993. This standard also utilizes systemic toxicity and intracutaneous reactivity testing. However, it also includes additional cytotoxicity, genotoxicity, chronic toxicity, and hemocompatibility tests, as well as more involved systemic toxicity testing. The additional intensity of ISO-10993 testing is due to it primarily being required for medical devices that will be permanently or semi-permanently implanted into a patient. Therefore, for devices that are not intended to be implanted or will have limited contact with patients, ISO-10993 testing may be more extensive than necessary.

Determining the Most Valuable Accreditation for Medical Device Cable

There is a wide array of medical devices whose wire and cable components require a level of biocompatibility. New robotics, communication, and vision systems technologies require cable for power, instrumentation, and control. From miniature cameras and surgical tools to metabolic monitors, pacemakers or medicine pumps, dental equipment and similar devices, any parts that touch the skin for prolonged periods of time, are in contact with an open wound, or enter the body, generally demands biological reactivity testing (See Figure 2). Most often, the materials in question are the plastic compounds and polymers used for cable insulation and outer jacketing.

As there are many options for biocompatibility testing that often depend on specific uses of the individual cable and medical device design, it can be difficult to identify the most valuable evaluations. When choosing or creating cable for medical assemblies, manufacturers often commit one of two common mistakes.

Fig. 3 – Companies like Northwire provide USP Class VI tested cables that meet a variety of other needs.

The first mistake is to spend too much time and money on high-level certifications that are not needed. It can be tempting to hold to the philosophy of “better safe than sorry,” especially with medical equipment, but this can incur exorbitant expenses and greatly slow down the time to market. Testing to the highest ISO-10993 standards can add months of time and be very costly, according to the “Medical Device Testing Guide” by Toxikon, Inc. Depending on the device’s application, and how the cable components will interact with the patient, this higher level testing may not be needed.

USP Class VI testing, alternatively, can be completed in four to six weeks and adds only nominal costs to production. Medical equipment that only employs internal wire and cable systems, or has cable parts intended for limited external patient contact, may not even need full USP Class VI testing.

Another common mistake in medical manufacturing, usually made after the biocompatibility tests have been decided on, is failing to continue to verify the approval from supply chain partners. Purchasers should always ask for a certification (“cert”) instead of assuming that, because the part has met the standard in the past, it will continue to in the future. Purchasers tell anecdotes about products that, while they met all the requirements, had never officially been validated and vendors who stop using certified compounds without giving notice. These situations resulted in large recalls, which could have been prevented.

Finding the right balance between cost savings and adequate protection is critical for medical device and cable manufacturers, especially with industry risks that include patient harm, lawsuits, and FDA recalls. Due to relatively quick turnaround and lower costs, completing the full battery of USP Class VI tests can be advantageous and offer a level of security. For suppliers whose products need a robust level of biocompatibility without incurring additional time or cost, achieving USP Class VI approval can be decidedly beneficial.

“If you want to play it safe in the medical arena by ‘overprotecting’ products, explore USP Class VI testing,” suggests Mark S. Perrott, a subject matter expert in custom cable for medical manufacturing. “Most medical devices do not need to perform to the intensive standard set by ISO-10993, but manufacturers still spend huge amounts of time and money to gain approval. Even if your product doesn’t quite need USP Class VI, it’s the most worthwhile certification from a cost/benefit perspective. You gain a widely recognized approval that engineers are familiar with and avoid spending too much and slowing time to market.”

Saving Time and Money by Being Proactive and Involved

How can a medical equipment provider identify needed tests while saving money and keeping the product on-track to market? A key step is to thoroughly understand the device’s application. Answer questions such as:

  • Will this device or integrated cable assemblies directly come in contact with a patient?
  • If so, will the contact be limited (<24 hours), prolonged, or permanent?
  • Will contact be purely external (e.g., touching the patient’s skin) or will there be internal contact (e.g., surgical cameras and vision systems)?

When the full application is clear, individual suppliers equipped with knowledgeable subject matter experts can be an important resource in meeting the appropriate standard. For example, medical wire and cable manufacturers can help with material selection by avoiding jacketing that has potentially hazardous compounds while also fulfilling peripheral needs such as sterilization requirements or high-flex capabilities (See Figure 3).

It is always valuable to be proactive and involved with suppliers. Often, companies will be well versed in industry standards such as USP Class VI and may even have subject matter experts and experienced engineers that can provide guidance and navigation through complex regulations and testing.

USP Class VI testing is an excellent option for many medical device and medical cable manufacturers. Com monly understood by suppliers and engineers, it provides a solid level of biocompatibility with marginal costs and added time. Even for products that may not need the full battery of USP Class VI tests, its status internationally and competitive level of investment make it ideal for a wide range of medical components.

This article was written by Joe Mustari, SME - Custom Cable & Wire for Medical Manufacturing, Northwire Inc., Osceola, WI. For more information, Click Here .