Sweet test for diabetics

Medical devices are the ultimate design challenge. Not only must they be super-efficient and meet rigorous regulations, they now have to be attractive too.

Design forms the bridge between technology and usability, but in the medical sector it arguably has the greatest influence — and faces its most stringent challenges.

Designers must incorporate some of the most highly advanced science into devices that are used under highly stressed conditions, where hygiene and safety are often crucial.

Some devices are for users with very specific needs and difficulties.

‘The job of a medical product designer is somewhat different from a consumer product designer,’ explained Jim Dawton, director of Pearson Matthews, a design consultancy that specialises in the healthcare sector. While product design is often a marketing-related discipline, transferring some form of technology into a usable and attractive form, the task in the medical field is more one of defining a technology than designing it.

‘Someone might have seen a need in a hospital, or they might have a piece of technology and an idea. What we do is help them find out the value of their idea, make it tangible, so they can raise some money to go on to the next stage. And we can go all the way through the process to deliver the product itself.’

One example of this was UK company Hypoguard, which came to Pearson Matthews with a concept for a disposable blood glucose meter for diabetics.

‘The accepted view from the market leaders was that you couldn’t make money from disposable meters, because the components needed, especially the PCB, would push up the price,’ explained James Aitken, senior designer on the project, ‘but Hypoguard came to a different conclusion.’

The company came up with the idea of combining cheaper electronics with having the test strips incorporated into the meter, making a single unit that could be thrown away once the strips were exhausted.

Pearson Matthews accepted the task of making this concept, dubbed the Flight Meter, a reality.

Although the technology for glucose meters, depending on a biochemical reaction that detects the amount of glucose in a drop of blood, is well known, transferring this into a disposable meter proved to be a significant design challenge.

Dawton explained that at the start of the project nobody had any idea what the Flight Meter might look like. ‘We looked at all sorts of things: features off disposable cameras, everything. But there were constraints — because it was a medical device the regulations didn’t allow us to assume the device could just be dropped and then thrown away. So there was a certain level of robustness we had to design in.’

The design process started with some basic assumptions. ‘We knew there would be a display screen, and some kind of lever mechanism to dispense the test strips,’ said Aitken. ‘So we put together a series of wooden block models, with sprung levers, displays and memory buttons all in different positions. And in parallel to that, we had a range of concept models in different types of materials and construction methods. All these were put to focus groups, to see which configuration and which materials consumers would find acceptable.’

The most popular shape was a smooth injection-moulded form, with a rotating lever at the base, and the display positioned at the opposite end.

‘The advantage of the rotating lever over a sliding one is that someone with the limited dexterity you can get with advanced diabetes can grasp the whole machine in their hand and roll it against their other arm or a hard surface to work the lever,’ Aitken explained.

The rotating action defined the type of mechanism that would be needed inside the machine. There would be three main components: a cartridge holding 100 test strips, held inside the meter with a desiccant to control the humidity; a sprung door, to keep the chamber sealed but still allow strips to be removed; and a rotating drum, operated by the lever.

This had to open the door, remove the top strip from the stack, release the door so the spring could close it, and present it through the slot so the blood test could be carried out.

The team refined the drum and door designs until they had a mechanism that was a low enough level of complexity to be made at a low enough price for a disposable meter — but then an unforeseen problem raised its head.

‘The strips have to be held at five per cent humidity,’ Aitken said. ‘Having a door opening and closing wasn’t a problem, because humidity changes at a slow pace — you can keep the door open for a minute, in fact. The problem was in finding a material for the meter that would keep the moisture out when the door was shut.’

The meter also needed a polymer that provided good dimensional stability, and the team looked at several options that, according to their data sheets, should have provided the required moisture protection.

‘We did some test mouldings, but we found that they were in fact significantly worse than our interpretation of the data led us to believe,’ Aitken said.

‘At that point we had to go back and mould test plaques in dozens of different materials. We eventually found that the only materials that would give us the barrier properties we needed were polyethylene or polypropylene, and that was exactly where we didn’t want to be, because they aren’t the most rigid of plastics and they didn’t provide the dimensional stability.’

The solution turned out to be glassreinforced polypropylene, but even that wasn’t simple. ‘We found a grade of PP that was reinforced with 40 per cent weight of glass beads. We couldn’t even use a fibre-reinforced grade, because the fibres made pathways in the shell that the moisture could travel through.’

The final design had to undergo extensive humidity testing, which was audited by the German certification agency TÜV.

‘Clinical equipment has to be audited by a disinterested third party,’ Dawton explained. One problem was the test strips themselves. ‘The crown jewels, for Hypoguard, was the biochemistry on the strips, but we had input into the proportions of the strips and the contacts,’ Aitken said.

‘They’re screenprinted on to the substrate, but the problem was guillotining them accurately. The guillotine was made in California by one of only two firms in the world that can make guillotines to cut to the tolerances we needed. It cost around £1m.’

Transferring the design from prototype to production carried its own issues. ‘The prototype mouldmaker would make the meters lovingly, so they were perfect, but in a production environment you have to set the tool running and walk away. You can’t have that level of attention to detail. We tried strenuously to make the transfer to production smooth, but it was very hard to maintain all the shapes and tolerances, and we had to make a further round of fine modifications.’

The final result, from three and a half years of work, was a meter incorporating 100 strips, which cost the same as the strips alone for a comparable model from a competitor. Hypoguard has signed a deal to distribute the meter through Wal-Mart in the US under the name NewTek.

Although there is a no-frills look to the device, it incorporates features such as a temperature sensor which prevents it from operating if it has, for example, been left on a dashboard in full sun. The moisture protection ensures a long shelf life.

‘For some type II diabetics, who don’t have to test every day, 100 strips might last a year,’ said Dawton.

The FlightMeter exemplifies a growing trend for consumerism and brand consciousness in medical design, said Dawton.

‘Five years ago you could design a medical device like a blood glucose meter, and it didn’t really matter what it looked like or how appropriate it was. It just had to work. We’re convinced that’s changing. When you can go into a shop and buy a glucose meter off the shelf, it has to be attractive to consumers: both in terms of how it looks, and how it works.’