Stephen Charron, Mechanical Engineering Manager

Will your medical device perform the intended function effectively without adverse effects on the patient or practitioner? A key consideration when designing your medical device is determining the type of contact that will occur between the device and the patient as well as between the device and the practitioner. The types of contact can be broken down into two distinct types, direct contact and indirect contact. The FDA defines the two types of contact as follows:

Direct contact – “term used for a device or device component that comes into physical contact with body tissue”

Indirect contact – “term used for a device or device component through which a fluid or gas passes, prior to the fluid or gas coming into physical contact with body tissue (in this case the device or device component itself does not physically contact body tissue)”Selecting biocompatible materials is a necessary step when your medical device will have contact with the patient. The FDA guidance now requires that the practitioner is also considered when reviewing the biocompatible aspects of the materials in your medical device.  A question the medical device developer must consider is…how will you know that your medical device will do no harm? The FDA guidance documents provide assistance to understand the path toward a successful submission of your medical device to the FDA for market approval. Refer to the link below for info on FDA guidance on use of ISO 10993-1, “Biological evaluation of medical devices – Part 1: Evaluation and testing within a risk management process”.

FDA MedicalDevices/GuidanceDocuments/ ISO-10993-1, “Biological evaluation of medical devices- Part 1: Evaluation and testing within a risk management process”

When evaluating your medical device for biocompatibility, the FDA recommends that you create a risk based evaluation plan.  The plan should include a review of the device and materials, including processing of the materials during the manufacturing process and any residuals from peripheral steps used during the manufacturing process.  It is important to keep in mind that the FDA does not approve individual materials; the FDA only considers finished medical devices, Final Finished Form (FFF). The biocompatibility evaluation of the finished medical device can begin after all manufacturing processes have been completed, including sterilization (if applicable) and packaging. This way the evaluation of the device will include the effects of all possible contaminations to your device during the manufacturing process.  

When considering your plan for biocompatibility evaluation of your device, refer to Attachment A in the ISO-10993-1 FDA guidance document, which provides a framework for determining the relevant biocompatibility endpoints for the evaluation of your device. It is important to note that the chart is merely a guide and is not to be considered a check list.  While considering all of the endpoints identified in Attachment A is important, it does not mean that you are required to test them all, nor is it intended to be an exhaustive list.  A careful assessment of your particular device and the intended use is required. To further assist in evaluating your justification and test data, refer to “Attachment D: Biocompatibility Evaluation Flow Chart” in the ISO-10993-1.

The flow chart helps you navigate the question of whether or not you need additional biocompatibility evaluation on the type of device contact with the patient or practitioner’s body tissue, and evaluation of the type of material utilized in the medical device. The flow chart in Attachment D guides the medical device manufacturer back to the Attachment A with the biological endpoints.

When choosing materials for your medical device, it is important to consider where the part will be used in the structure of your device, if it comes into contact with the patient or practitioner and how long the material will be in contact with the body tissue. After you determine the duration of contact and you understand the type of material you need, it would be beneficial to select a material that has a history of doing the task at hand and is already recognized by the FDA as an approved material. Raw materials must be tested for biocompatibility in compliance with ISO-10993 or testing as per United States Pharmacopeia Class I-VI, (USP class I-VI). USP testing is sometimes referred to today to assess plastics.   

Metals, plastics, ceramics, textiles, and other materials are often selected for use in medical devices.  It is common for today’s medical devices to utilize single use disposables that come into contact with the patient.  Many of the materials specified into disposables are engineered plastics to keep the disposable costs down.

There are a number of raw material suppliers who support medical device applications.  If your material selection includes plastics, some available engineered plastics for consideration include; Acetal, Peek, Ultem, among others offered by Rὂchling Engineered Plastics, and SABIC Innovative Plastics. If your material selection falls under elastomers, consider Dow Corning Healthcare.

In summary, medical device development that includes physical contact with the patient or practitioner must carefully consider the type of materials selected during the design process to support biocompatibility requirements. Furthermore, the manufacturing process in which to achieve the device’s Final Finished Form must not introduce any additional biocompatibility hazards.  Refer to the following link for more on the FDA definition of Final Finished Form. (FDA MedicalDevices/GuidanceDocuments, Refer to Section III paragraph A). At Cogmedix, we are dedicated to supporting our customers in material selection and regulatory compliance through our DFcx process.  Click here to read more on DFcx™.