The e-skin market is expected to be worth $1,719 million by 2025. And much of this growth will be from devices designed for medical use.
There is one major issue, however, that could hamper its seemingly unstoppable growth. And that’s its power source.
It’s not just a problem for e-skin, but for all medical devices. As they become more flexible, thinner and smaller, the available space for the batteries that must power them shrinks and shrinks and shrinks.
- They must be embedded in the device, rather than located in a battery compartment
- They must be highly waterproof and protected from the effects of all other fluids
- And often they must also allow the device to bend, expand and contract as flexibly as human skin
But the possible problems are even more complicated than this, as devices like pacemakers are not worn on the skin but must operate internally.
This means that, should they need recharging, invasive surgery – with all its risks and discomfort – is required to prolong their duration.
And, of course, as medical devices become functionally more powerful, they invariably consume more power.
The result: ever more demand on our already beleaguered batteries. And that’s increasingly a problem.
Is lithium-ion the solution?
Lithium-ion rechargeable batteries offer medical devices numerous advantages over non-rechargeable batteries. Their high energy-density chemistry can be custom manufactured to enable the miniaturisation of devices and their excellent cycle and calendar life can extend the lifespan of devices.
As such they are ideal for active implantable medical devices, such as pacemakers. Currently available systems have a lifespan of 9–25 years, compared to the typical 2–5 offered by non-rechargeable batteries.
Yet, high-profile hazards associated with the failure of these batteries – recently those of the Samsung Note 7 mobile hit the news – include excessive release of heat, electrolyte leakage causing toxic exposure and the malfunction of devices caused by battery capacity depletion.
Inevitably such risks have been addressed and mitigated but they have led to the search for alternative means for powering and charging medical devices.
Beyond the battery: AC/DC voltage induction
Of course, not all devices are powered by batteries.
Other medical devices run from the mains but even here it is vital that precautions are taken into consideration when designing each device.
It’s critical that the power supply is properly regulated and has reliable isolation to minimise the risk of electric shock. For electronic equipment to be approved for medical applications, it must meet IEC 60601 safety standards.
It must have effective and reliable isolation between the AC input and the power supply, its internal high voltage stages and its DC output. It also needs sufficient spacing between the conductors and the electronic components for proper isolation and doubled or reinforced insulation to meet leakage requirements.
Alternative power sources
Researchers from Dartmouth College, in collaboration with clinicians at the University of Texas, have recently created pacemaker “devices which will be self-charged by the energy harvested directly from the human body.”
Although still undergoing advanced tests this approach could significantly extend the lifetime of implantable medical devices and remove the need for surgery to replace the batteries.
In essence, these devices use dual-cantilever structured thin films made of piezoelectric materials to convert kinetic energy into electrical energy that can be used to power the battery.
Elsewhere, other researchers – working with e-skin at Binghamton University – are looking close to successfully using human sweat to create electrical energy.
Commenting on his research, Seokheun Choi noted that ‘biochemical energy harvested from human sweat is the most suitable energy source for skin-contacting devices. Sweat is readily and constantly available in sufficient quantities, can be acquired non-invasively and contains a rich variety of chemical and biological entities that can produce electricity.’
Extending the battery: wireless charging
Wireless charging – due to the contactless nature of the technology – is ideal for implantable medical devices using batteries and also for the rapidly growing market for wearable monitoring devices.
In relation to implantable devices, rigorous testing is required to ensure that the device is not susceptible to unintended charging arising from nearby devices.
For all devices the charging circuit needs to be protected to guarantee that the cell cannot be charged beyond specifications, even if a third-party wireless charger is used by the patient.
Helping you to understand and build battery and power systems for the medical device market
Risk management, quality and accuracy are essential in the increasingly stringent regulatory requirements that apply to every step of a medical device’s life cycle. We embed checks, best practices, monitoring and recording into every stage.
Traceability is particularly important, using specified and verified components with fully defined finishes, battery types, temperature ranges, and so on.
The latest version of the requirements for a quality management system that meets the rigorous needs of the medical devices industry is ISO 13485:2016.
Our sales director, John Johnston, commented on successfully transitioning to the latest requirements:
‘It’s a huge privilege for us to be involved with some of the most pioneering medical projects in the world, something we take great pride in.
In order for us to deliver the very best for our customers, it’s vital that we take quality and processes extremely seriously. Standards such as the ISO 13485:2016 are an excellent mark of our commitment to quality, allowing us to credibly demonstrate our excellence in medical electronics manufacturing.’
And we’re here to help you overcome challenges as you design, prototype, test and deliver your products to market.