Originally Published MPMN March 2007

EMERGING AND NANOTECHNOLOGIES

Wireless Technology Sparks New Approach to Powering Implantable Devices

Shana Leonard

Despite boasting a thriving multibillion-dollar market, implantable medical devices are not without their pitfalls. Patients aided by implants often face a number of dangerous power source–related problems, such as limited battery life, infections caused by percutaneous connections, and device discomfort. In an attempt to eliminate these drawbacks, Telemetry Research (Auckland, New Zealand; www.telemetryresearch.com) has developed a technology for powering implantable devices using inductively coupled power transfer.

The wireless technology relies on magnetic fields, rather than batteries or percutaneous connections, to power devices. Transcutaneous energy transfer (TET) requires an external and an internal component. The external part generates a magnetic field from a primary coil. The magnetic field then passes through the skin, without attenuation, and is picked up by an internal component. In turn, the internal component converts the magnetic field into dc power, which powers the device. High power levels, such as 10 W, can be effectively transferred through the skin, according to the company.

“The major differentiation [with conventional power sources] is that you get continuous operation [with TET],” says David Budgett, director of engineering. “It can operate for the lifetime of a patient, as opposed to the lifetime of the battery. After the battery goes flat, the traditional approach is to surgically replace the battery.

Pacemaker batteries last five to seven years. That’s great for patients whose life expectancy won’t exceed that of the battery,” he continues. “But for young people who have a considerable life expectancy ahead of them, there is an option of not having to do repeat surgeries to replace the battery.”

In addition to eliminating fears of finite battery life, the technology offers an alternative to percutaneous connections. Many high-power applications, such as mechanical or electrical pumps, are traditionally powered by running a wire through the patient’s skin from the implanted device to the power source. But because the skin is broken, patients can acquire an infection that could prove fatal, according to Budgett. As a wireless technology, inductively coupled power transfer minimizes such risks.

Telemetry Research also seeks to minimize patient discomfort by enabling energy transfer through loose coupling between the internal and external parts. “The difficulty comes about if you have very close alignment between your external and internal coils; patients can suffer from skin abrasions and discomfort problems,” Budgett says, referring to other companies’ attempts at inductive power-transfer systems. “We’re targeting loose coupling: as long as the coils are within reasonably close proximity—such as 3 cm—it will work effectively without the two coils butting up against each other. Minimal discomfort and minimal heating are key.”

Telemetry Research is now focusing its efforts on penetrating the left ventricular assist device (LVAD) market. By enabling LVADs to operate with high efficiency, the firm’s technology reduces localized heating on the devices, which can be especially dangerous in implantable applications.

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