Medical Electronics
How small can medical implanted devices become?
By Denis Pasero, product commercialisation manager, Ilika W
hen designers plan a new product, they rarely think about the battery first. The early focus lies with the core functionality of
the product, in line with the company’s own unique technology. In automotive this can, for example, be the driving performance of a car; in IoT, this could be ways of measuring, communicating and analysing data; in MedTech, taking the example of pacemakers, it is to send electrical pulses to help the heart beat at normal pace or rhythm. Powering these products is peripheral to their core functionality and is sometimes taken for granted. But the world is changing, and there are now political, legislative, societal and environmental pushes to optimise resources available in the world. In automotive, internal combustion engines will make way for rechargeable batteries to reach Net Zero and lower greenhouse gas emissions. In IoT, the demand for Big Data requires multitudes of small size sensors placed in hard-to-reach places where electrical cables cannot be used: for example, developers are placing sensors on the blades of wind turbines to optimise their aerodynamics. No place for a cable here and instead small batteries are needed.
In MedTech, one current goal is to reduce the reliance on prescription drugs to treat medical conditions. The over-prescription of opioids in the USA and Canada has led to addiction, abuse and the death of over 600,000 people in the last two decades. At the same time, technologies have improved greatly beyond pharmaceutical medicine and can often cure diseases more effectively than drugs, generally improving the health and well-being of patients. Looking into the future, the concept of WBAN, Wireless Body Area Network, is becoming realistic thanks to progress in science, medicine, electronics and product design.
WBAN describes a network of very small devices, implanted or placed on the body, that measure physical and bodily parameters, and
40 October 2023
communicate these data wirelessly to a hub, for example people’s mobile phones. Through this transfer of data (transmit and receive), sensing devices can learn how to best monitor certain parameters, whilst active devices can optimise therapies. There would be no need to visit a doctor or hospital to be examined or modify a treatment.
Whilst the vision of WBAN can look far in the future, the technologies for sensing or treating therapies using devices exists now. Cardiac monitors, defibrillators and pacemakers are the most widespread example of an Active Implanted Medical Device (AIMD). Whilst first implanted in 1958, the size of pacemakers in the 1970s was similar to that of old-fashioned pocket watches. Nowadays, pacemakers are less than 15 cm3 in volume and can simultaneously provide heart rate monitoring and pacing. A new generation of even smaller, leadless pacemakers exists that can be implanted directly inside the heart. Cochlear implants are another well-known example of bioelectronic devices, which are partly implanted and partly external: work is underway to miniaturise hearing devices to the extent that they could one day be
Components in Electronics
implanted directly in the middle ear. Neurostimulators are another type of AIMD which have greatly improved in terms of functionalities whilst decreasing in size. Neurostimulators can treat multiple conditions by providing electrical pulses to nerves. TENS (Transcutaneous Electrical Nerve Stimulation) machines were first developed in the 1970s to improve the comfort of pregnant women, and were initially external devices. Current devices are only a few cm3 in volume, implanted in the body in one of the few, large enough pockets in the body (chest, lower back) and connected to the targeted nerve via internal leads. In fact, next-generation devices will be much smaller than 1 cm3 and placed directly onto nerves, making the treatments more efficient and implantation procedures less costly and risky. The potential of neurostimulation is broad and largely already proven: spinal cord stimulators can reduce chronic pain; deep brain stimulators can treat Parkinson’s disease or obsessive compulsive disorder; Vagus nerve stimulators are effective for epilepsy and depression; hypoglossal stimulators can reduce sleep apnoea, and sacral nerve implants incontinence.
Prosthetic joints are also becoming smart. Up to now, the success of artificial knee, hip or shoulder implant surgery has been evaluated through examination by doctors and assessment of the patient’s pain levels. Research is taking place to develop small devices inserted inside the new joint which will measure temperature and position for example, and communicate data wirelessly, providing information about the surgery, risk of infection, possible movements and re-growth of the bone in the joint. These medical advances have been made possible through advancements in product design, packaging and micro-electronics. In particular, great care has been taken to optimise the energy consumption of new AIMD. Whilst the battery is not in the designer’s thoughts at first, the availability of a battery small enough to match the product requirements, in terms of size and energy, can be a barrier to development. Currently, most AIMD are powered by a primary, non- rechargeable battery; in fact, no life-critical implanted device has yet been approved for implantation which contains a secondary,
www.cieonline.co.uk.uk
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