A Crash Course In Choosing Biocompatible Wearable Tech Materials
By Scott Downen and Veronica Fleck, Anuva
What is the best part about wearable technology products? You can wear them while they work! This also indicates, however, that your wearable device must be made of an appropriate material to be worn safely. Rather than panicking and diving head first into a regulatory whirlpool, let us provide a crash course in how to choose materials that are safe and headed for approval.
When we are talking about being able to wear a device safely, we are talking about biocompatibility. Biocompatibility indicates that a material will perform appropriately without inducing a reaction in a living tissue or cell. In other words, regulating materials for biocompatibility is what allows you to confidently wear a Band-Aid without breaking out in peculiar patches of hives.
Each medical device on the market today that is designed to come in contact with human tissue is regulated primarily by the International Organization for Standardization (ISO) for biocompatibility, almost exclusively through the 10993-1 standard. The best way to approach choosing a biocompatible material for a wearable technology, and to rest assured when you need your next Band-Aid, is to use this standard. Let’s see what ISO has to say.
Standards come hand in hand with classifications, so we first need to ask two simple questions:
- How much does the product touch?
- How long does it touch?
To give you a little more detail, you are deciding here just how invasive the device is so you can narrow down the types of tissues it will contact directly. The device can fall under one of three categories according to the answers to these two questions. Your wearable device will fall under the first or second category, which are described here:
Category I: The device contacts only external body tissues which include skin, mucous membranes, or injured surfaces. Some examples of materials that are currently used for this type of contact are PVC, Polystyrene, and Polyethylene.
Category II: The device contacts internal tissues from the outside, such as a needle, and will come in contact with internal and external tissues including blood, bone, and dentin as well as skin and mucous membranes. This category can be divided further according to the allotted time of contact. If the device is in contact with the listed tissues for a short term, some materials that may be appropriate include Silicone, Polyurethane, and Teflon. Material better suited for longer-term contact is Nylon, Polypropylene, and Polyester.
Category III: The device is totally implantable and thus only contacts internal tissues, such as muscle/fat tissue, bone, and blood. Some materials that are currently used for this type of contact are PMMA, PET, and hydrogels.
The Checklist
Now that we have a solid starting point with your device classification, we can look at the nine major players in passing biocompatibility tests (according to the 10993-1). Make sure to consider each of these carefully when choosing your material.
- Cytotoxicity – Does the material cause a negative effect on body cells, such as cell death or inhibition of cell growth?
- Sensitization – Does the material cause a level of discomfort on contact?
- Irritation – Does the material cause visible irritation, including redness, itchiness, or swelling of the surrounding skin or membrane?
- Intracutaneous Reactivity – Does the material cause a localized reaction from the surrounding tissues?
- Acute Systemic Toxicity – Does the material cause an immune response from the surrounding tissues or body systems upon application?
- Subacute/Sub-chronic Toxicity – Does the material cause an immune response from the surrounding tissues or body systems for an extended period of time?
- Genotoxicity – Does the material cause any gene mutation changes?
- Implantation – Does the material cause any pathological effects on living tissues, such as inducing an internal immune response?
- Hemocompatibility – Does the material have any effect on blood or alter blood components?
Whether it is in raw resin form or a completely finished product, testing is the same for all forms of a material. Therefore, it is essential to make sure that the vendor provides a certificate of biocompatibility regardless of the stage of development you are in when you purchase the material. If you are still unsure about the quality of a material, you can always ask the vendor or your engineering company to provide the risk-management procedures. This will show you how recent their certifications and regulatory procedures are. Whether your design is wearable for portability, aesthetics, or convenience, when it comes to designing this kind of device it is most important that they should be safe.