What Makes a Material Medical Grade?

Materials used in the healthcare and medical setting must often carry the title "medical grade." But what defines a material as "medical grade"? Biocompatibility refers to "the ability of a material to perform with an appropriate host response in a specific application" (William's definition), and can be measured in different ways, depending on the context of the medical device. Because they come in contact with the human body, materials are tested for biocompatibility and safety in order to receive the "medical grade" designation.

Medical Grade Polymers 

In the United States, the Food and Drug Administration (FDA) Center for Devices and Radiological Health (CDRH) regulates devices implanted into the body. Rightly so, patient safety drives manufacturing processes that minimize polymerization residues and results in the careful selection of additives such as plasticizers and antioxidants.

Plastics are valued for use in the medical setting for many reasons, including:

• toughness
• transparency
• sterility
• transportability
• flexibility

Many medical devices contain silicone (polysiloxane) polymers. Medical grade silicones are generally grouped into three categories: non-implantable, short-term implantable, and long-term implantable. Silicones are highly useful in the healthcare setting because they exhibit the following characteristics:

• low toxicity
• low chemical reactivity
• thermal stability
• resistance to oxygen, ultraviolet (UV) light, and ozone
• electrical insulation properties
• high gas permeability
• the ability to repel water and form watertight seals

How Materials Earn the "Medical Grade" Designation

USP Testing

The purpose of testing is to answer this most basic and logical question, "Is this material compatible with the human body and is the intended contact safe for each potential human user?" The industry answer is found in the performance of a series of "USP" tests. The U.S. Pharmacopeial Convention (USP) is a scientific, nonprofit organization that sets standards for the identity, strength, purity, and quality of food ingredients, medicines, medical materials and dietary supplements manufactured, distributed and consumed worldwide. Their standards are enforceable in the United States by the Food and Drug Administration (FDA), and they are also used in more than 140 countries.

Specific USP tests are used to evaluate biological response to elastomerics, plastics, and other polymeric material that may come into direct or indirect contact with a patient. Silicone manufacturers have assisted their medical customers in selecting their materials by noting to what Grade levels the specific silicone compound has been tested and whether the material is suitable for short-term (less than 29 days) or long-term (greater than 29 days) implants. Medical grade materials are usually USP Class VI (systemic and intracutaneous toxicity) certified or compliant.

ISO 10993

The International Organization for Standardization (ISO) "develops and publishes documents that provide requirements, specifications, guidelines, or characteristics that can be used consistently to ensure that materials, products, processes, and services are fit for their purpose."

The ISO standard for medical grade materials is 10993. Some of the considerations for biocompatibility are:

• Cytotoxicity/growth inhibition (ISO 10993-5)
• Hemolysis (ISO 10993-4)
• Chemical analysis/"fingerprinting" (ISO 10993-18)
• Biological-toxicological evaluation (ISO 10993-1)

Manufacturers and suppliers of medical grade materials will often label their products as such and provide statements of certification to specific OEM material specifications, which usually contain references to relevant regulatory requirements.

ASTM Testing

ASTM International has developed over 12,000 standards that operate globally. Developed by top healthcare practitioners, engineering leaders, and other technical experts, they advance human health by improving care delivery, supporting medical research and drug development, enhancing product manufacturing, and much more.

Some of the ASTM standards guiding medical devices include:

• Standard Guide for Accelerated Aging of Sterile Barrier Systems for Medical Devices (F1980-16)
• Standard Practice for Care and Handling of Orthopedic Implants and Instruments (F565-04/2018)
• Standard Specification for Rubber Surgical Gloves (D3577-09/2015)
• Standard Practice for Extraction of Medical Plastics (F619-14)

Watch our video series about biomedical innovation.

The Future of Medical Grade Materials

The very characteristics that give medical grade materials their current advantages are being improved on and engineered to create new uses and treatments. Because the human body tends to reject anything that is not totally inert, biocompatible thermoplastics are being developed based on their chemical structure or by chemical modification.

Bioengineers are conducting research with nano-scale surface texture, where they have found that some nano-scale patterns can kill off cells while others encourage cell growth. They see the possibilities for advancement and practical applications of new medical grade materials. The successful development and manufacture of these new products will benefit countless patients in the future. 

Conclusion

Materials used in medical applications are tested for biocompatibility.  There are a number of governing bodies that develop standards, testing methods, and specifications around what an appropriate immune response and repair entails. Materials and devices can be approved as medical grade for applications dependent on the function and duration of contact.