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You may have seen in the press recently that McDonalds have recalled nearly 33 million ‘Step-it’ activity wrist band toys after receiving more than 70 reports of skin irritations. For those not familiar with Happy Meals, ‘Step-it’ is a range of 6 simple wrist bands that either electronically counts steps on an LCD display or have an LED to indicate activity levels.  Each is linked to a smart phone app.  A great idea to get kids active, but clearly something went wrong for McDonalds in the execution.

Product material safety is regulated in the case of medical devices, but in the rapidly expanding field of consumer wearables it is not always fully considered.

McDonald’s are not alone in having these issues; back in 2014 the market leader Fitbit also experienced a similar product recall. A number of causes were suggested in the media; the specification of the materials used in the clasp, a reaction to the materials in the strap or the adhesives used to assemble the product.  The exact cause is not in the public domain, but creating a wearable product that is safe, comfortable, functional and reliable is not straightforward.

Biocompatible materials do not cause an immune response from the wearer. But in complex biological systems nothing is completely predictable, so how can developers make effective decisions on safety when consumers always want new products quickly and at the right price? Simply testing each new product once it has been designed is not feasible because even if you ignore the ethical considerations, it’s likely that the number of people who will get adverse reactions is very small and quite hard to spot.

The answer is to use the test methods that have been developed and validated by the medical products industry over many years. There are two useful biocompatibility standards: ISO 10993 and USP Class VI. A major factor effecting biocompatibility is the level of interaction with users and ISO 10993 provides a comprehensive test framework to cover a wide range of applications. For activity bracelet materials it suggests:

• Cytotoxicity tests to measure chemicals that might leach from the material and directly impact cell health.
• Sensitisation tests to measure delayed reactions such as redness and swelling caused by repeated exposure.
• Irritation tests to measure the immediate reaction to contact with the material.

Material manufacturers sometimes perform these tests so they can sell pre-qualified materials into the premium healthcare market.  However this is not the end of the story, product design features such as surface finish, texture, permeability to moisture also have an impact. Impermeable plastics can cause a level of sweat build up which may cause a minor rash in itself.  Also decorative finishes that might be applied on the material need close scrutiny, for example metal plating can contain nickel which is undesirable.

Another consideration is the manufacturing process – if not careful material that has been specified biocompatible can easily become incompatible during the process. Even if the supply chain is under control, unwanted chemicals can easily be introduced such as colorants, printing inks or process chemicals such as mould release agents or just factory contamination. Special procedures are required from manufacturers to make sure this does not happen inadvertently.
Much to a product designer’s frustration the range of materials that meet these biocompatibility requirements tend to be limited and more expensive than regular materials. And the ‘flip side’ approach of getting your preferred material tested before launch can be expensive, time consuming and concerning from an animal welfare perspective.

In summary, developing consumer wearable’s requires care to minimise the risks. The medical device biocompatibility standards are the best starting point but they do not offer a complete solution in the consumer product environment.  The risks associated with each product and supply chain must be considered and managed appropriately to succeed.

If you’d like hear about the wearable products we've collaborated on with companies such as Barclaycard and discuss how we could help your company on this journey please get in touch with James at jgb@cambridge-design.co.uk .

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