A Medical Device Designer’s Guide to Skin-Related Products

 In Engineering, Medical Product Design

The approximate 20 square feet that we call our skin is astonishing at allowing us to move, to control our body temperature, and to survive life’s tumbles. Thankfully this exterior organ is very good at repairing itself, but it has limits. These limitations are very specific to us as individuals. When placing a “foreign body”, i.e., medical device on our skin, there are factors that affect our skin’s resilience.

First off, there is a small percent of the human population whose skin reacts negatively to everything except natural fibers. This reaction is are called dermatitis. Dermatitis is a category of skin reactions that range from small red rash to a large crusty blisters.

From the practitioner’s perspective, it is important to understand the end-user’s personal history with various materials. The device designer’s responsibility is to use the most bio-compatible, breathable materials possible. But picking the ideal material sometimes isn’t enough.


Anticipating different material needs for different areas of the body

The sensitive, thin-skinned areas of our body are simply more delicate than those with thicker skin. As well, skin over a joint or bone protrusion is less resilient than skin over large muscles . Here, thin skin areas simple do not have enough compliance for it to be a good intermediary between the underlying tissues and a more rigid medical device. So the designer may be required to use synthetic stretchy, foamy materials. One example of such a material is silicone. It comes in a variety of configurations: mild adhesives, gentle fabric coatings through to soft foams. Yes there are material options— but then we get older.

So why does our grandparents bruise so easily? As we get older, the skin thins and becomes less elastic; what’s even more problematic is that the blood vessel walls thin, causing them to break more easily. For the elderly, even clothing that is slightly constricting can cause sub-dermal bleeding. The elderly, especially, need a medical device to land gently. Additionally, as in real estate biz, location matters.

One size does not fit all when designing medical devices for different patients

We recently developed a medical device that mounts to the jaw through the front, mid region of the throat. Very challenging to say the least. There are bony areas adjacent to soft tissue with nerve clusters. This region also has a huge anatomy variation between users and this region allows for complex movement. One size will NOT fit all, but there cannot be 78 sizes either. Even if the patient is comatose, the device must be capable of some motion— even if just so the patient can swallow (and, chewing and talking may be good too).

The concern with motion, and of course improper device attachment, is that these causes potentially damaging forces on the skin. Anytime the device is pushing in, pulling on, or trying to slip side-ways on the skin there is reason for concern. There can be shearing loads parallel and perpendicular to the skin. As well as pressure loads force into or pulling on the skin.

Over time, these forces are a concern. Healthy skin and tissues rejuvenate themselves via adequate vascular flow. This flow requires arteries and veins to be uninterrupted so that oxygen and nutrient can replenish tissues. Here, again, the medical device must be designed and installed properly to allow proper vascular flow.

In spite of these mentioned skin interaction and device placement concerns, technology has progressed. Devices are smaller, and their applied treatments are more targeted to the aliment. Medical designers are creating medical devices capable of being successfully worn by a larger percentage of the population which are easily and safely purchased over-the-counter and worn longer term with little side effects.

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