Health care embraces many rubber compounds

CLEVELAND—With all the polymer choices available for the health care industry, it's important to make sure all parties involved with medical device development understand the application and regulatory hurdles involved.

That's what the International Elastomer Conference's Advanced Elastomers for Health Care seminar, held recently in Cleveland, sought to clear up—identifying the key applications for some of the core rubber materials and educating companies on the regulatory hurdles involved.

"It's a little bit of a new direction for the Rubber Division, coming from a tire background and moving into health care," said Judit Puskas, professor of chemical and biomolecular engineering at the University of Akron and chair of the seminar, as well as the recipient of the 2017 Charles Goodyear Medal.

"But even I didn't realize that some of the rubber processing companies around this area have now over 50 percent of their business in health care. I think this is a very important meeting."

Dow Chemical's Uma Kale said the global health care market is growing at 4-6 percent annually with emerging geographies exceeding that. However, the American and European regions account for about 75 percent of the health care market, which Kale estimates to exceed $300 billion.

Aging population and the rise of chronic diseases are driving this growth, but Kale said advancement in science, materials and a shift to outpatient/home care is driving the need for stronger regulations.

"The modern medical devices are much more sophisticated than what you had about 50 or 60 years ago," Kale said. "Those devices were primarily tools to aid the diagnosis and treatment of diseases. What you see now are medical devices that have evolved into being minimally invasive and can be adjusted very precisely without needing surgery and the risks associated with that surgery."

Variety of rubbers

Many different types of rubber compounds have made their way into the health care industry—butyl, butadiene and isoprene rubbers in addition to both high consistency and liquid silicones. Dana Adkinson, technical development manager within Arlanxeo's Tire and Specialty Rubber business unit, outlined that butyl rubber lends itself to a number of applications, namely rubber stoppers, plungers and sealing applications.

While the specific type of butyl rubber varies depending on the application, Adkinson said butyl is usually the best choice when strong impermeability, low water absorption and excellent resistance to mineral oils is required.

Comparatively, butadiene and isoprene rubber lack in their resistance to gas and moisture, but have low-water absorption properties, she said. If the drug vial is to be penetrated multiple times by a needle, isoprene's strength is that is has excellent re-fragmentation resistance.

These compounds also need to have strong resistance to sterilization chemicals.

"All of these different kinds of medical parts undergo at least one sterilization step in their lifecycle," Adkinson said. "Different sterilization techniques include steam, radiation and ethylene oxide, but they can undergo anywhere from one type of sterilization to multiple types of sterilizations from when they actually make the stopper to when it's in its final form."

Silicone implantables

Adkinson added that while butyl and other kinds of rubbers are excellent for some applications, their main weakness is that they cannot be used for implantable medical device applications. Silicone, however, does not share that problem and its biocompatibility is one of the reasons it's widely used in many short- and long-term implantable applications.

Eric Reynolds, applications engineer for Dow Corning health care, outlined that silicones are used mainly because they have high temperature stability (able to thrive in both hot and cold environment), have high gas permeability, do not interact with many chemicals, but most importantly can stay in the body without breaking down or adversely affecting it.

But because silicone compounds are used inside the body, the regulatory environment on these types of medical devices is stricter. In the U.S., devices are broken into three classes—Class 1 being the least strict and Class 3 being the most stringent.

Kale outlined the differences between each class of device.

• Class 1—Low risk to patients, general controls sufficient to ensure these devices are safe and effective;
• Class 2—Typically cleared a 510K process, clearance is not approval; and
• Class 3—Premarket approval, life sustaining and supporting devices.

Reynolds outlined the typical testing requirements for each class of material, stressing that there could be variances either way depending on the specific application. He said Class 1 materials are very close to an industrial grade, usually just requiring a one-time or intermittent U.S. Pharmacopeia Class VI testing and produced in ISO 9001 environment. Examples of usage include wound drains, handles, basically devices that do not significantly impact the patient.

Class 2 is the most standard health care grade. Reynolds said these usually have the phrase health care in the title. They require Class VI testing, but also need skin sensitization and irritation studies and 30-day implant studies, typically produced in health care facilities. Materials in this class are more suitable for short-term implantables that are in the body for less than 30 days.

The strictest level of testing is found on Class 3 because these materials are used to make devices that will stay in the body for 30 days or more. Reynolds said this includes a Class VI study and 90-day implant studies among others, but most importantly he said suppliers want to see and approve the kind of applications this material is going to be used for. These materials are used in long-term drug release applications. Typically for these, suppliers will have drug master files.

"The idea for this is to provide a choice for the consumer, to be able to look at what your device is doing and see what kind of regulatory support you're really going to need," Reynolds said. "The original equipment manufacturer needs to make that choice, to look at the device and determine what is an appropriate manufacturing environment."

Reynolds said, though, that he doesn't know of a health care silicone supplier who isn't proactive in at least looking at the applications its material is going into. Many suppliers also limit what their materials can be used in.

Suppliers also will limit the applications their grades will be used for. Reynolds said Dow Corning will not sell a lower grade regulatory material to an OEM that requires a higher level of testing.

"This isn't risk-free for the suppliers," Reynolds said. "We need to be able to mitigate our risk as well as make sure you're mitigating your risk as well. Even if you have an application that's agreed upon, even if you have the right grade for that, there are contractual obligations many suppliers put in place."