Medical implants provide numerous benefits to patients who cannot afford to have regular visits from a doctor or travel to their GP. But if they are really going to make an impact in healthcare, they need a power source that's more efficient than batteries.
That is what researchers at the Institute of Electrical and Electronics Engineers (IEEE) have been working on in their recent paper Remote Powered Medical Implants for Telemonitoring, from the <i>Proceedings of the IEEE</i>.
Patients with conditions like diabetes mellitus and dementia – where constant monitoring is required – would benefit from small sensors implanted inside a patient's body to remotely monitor vital signs, the researchers said.
The researchers devised a 'telemedical sensor implant system' that wirelessly powers medical implant devices, guaranteeing autonomous operability for practical high data rates and realistic attenuation losses due to the human body.
It transmits data to an external platform that periodically reports a patient’s physical condition to a remote station using a wireless link.
The researchers first looked at the benefits of medical implants that closely monitor vital signs such as blood pressure, temperature, glucose, oxygen, blood lipids and pulse. First, the system will detect early anomalies in the vital signs so that mild treatment or care can be provided before it escalates into a bigger problem.
The research paper said today's medical care is expectant and reacting. A person has to become ill first, before being treated with a standardised medicine.
"In contrast, future medicare... is preventive, predictive, participatory, and personalised. That means health problems become foreseeable and can therefore be treated prophylactically before the illness breaks out," the paper said.
Also, if the patient forgets to take their medicine the system will be able to alert the patient through an acoustic signal or dedicated call.
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Another benefit is if the patient does not move for an usually long period of time outside of typical sleeping hours, a 'beeper' or acoustic signal is set off where the patient deactivates if everything is okay. If the patient doesn't deactivate then an emergency situation is assumed and emergency services can take action.
Batteries not effective enough
A part of ensuring medical implants deliver these benefits is to ensure they stay powered for long periods of time without having to make the patient undergo surgery or any other abrasive means to recharge power.
According to the research paper, batteries – which are the most common way to power in-body devices – are not an effective way to go about powering medical implants.
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Lithium solid-state cells use a high amount of energy with energy density of ~260Wh/kg, requiring high data rates and large wireless link distances. Also, as lithium is a chemical agent, to implant that into a human body could cause additional health risks.
An alternative to this that offers "high potential" is the 'inductive link' technique, the paper said. High transmission frequencies are not suitable for transferring energy into a human body with a medical implant, so therefore lower frequencies are needed for wireless power transfer.
"Due to the advantages of inductive power transfer – especially the independence of the electrical characteristics of surrounding materials – a system based on the presented results is implemented at the ISM [Industrial, Scientific and Medical] frequency of 13.56 MHz.
"This frequency is very well suited for inductive coupling because it does not endanger biological tissue if FCC [US Federal Communications Commission] limits are respected."
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The researchers looked at the geometry, distance and angle between the antenna coils to achieve high efficiency of the inductive link.
According to the paper, the inductive link allows for remote powering of medical implants that also don't require any maintenance.
The researchers' next steps is to look at how a watch could communicate between the medical implant and a smartphone, as well processing the data through a smartphone.
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