Jeffrey Ortega, ZPower

Whether they’re detecting a life-threatening change in vitals or helping to manage chronic pain, wearable medical devices have the potential to enhance the quality of life and deliver advanced care to people with health issues ranging from the emergency to the long term. Wireless connectivity and Internet of Things technological advancements are resulting in innovations that have the potential to combine real-time data analysis with monitoring and treatment for more successful personally administered and caregiver-administered therapies. It truly is a revolutionary time to be in the medical device design industry.

But all of this capability and potential is not without its challenges – one of which is finding safe, reliable battery power.

Identifying and engineering products with batteries that are both safe and powerful enough to get the job done is an ordeal with which just about every R&D department is familiar, and while battery pitfalls are not a problem isolated to the med-device industry, failures or malfunctions in medical devices can be significantly costlier in terms of potential harm.

Concessions in Battery-Powered Medical Devices

It seems that with every viable battery option, there is a concession that must be made. Designers are confronted with challenges that impact the device on multiple levels, including functionality, sustainability and safety.

Some of these issues include:

• High capacity and stable chemistry, but low run time.
• High capacity and long run time, but unstable chemistry.  
• High capacity and long run time, but cannot withstand high-temperature sterilization.
• High capacity and long runtime, but must be sealed into the device on account of high toxicity and mishandling danger.
• High capacity and long run time, but are not available in the required form factor.

Workarounds abound to try to address these issues. For capacity and drainage issues, products are often designed with two batteries instead of one to ensure that the device has a life span long enough to be useful. But this is not an ideal fix. The National Institute of Health reports that current endoscopic capsules used for bowel imaging and diagnostics for upper and lower gastrointestinal disorders use two silver-oxide batteries that deliver 20 mW of energy. The report points out that this is enough capacity to power the endoscope as it is today, but it will not meet the needs of tomorrow’s iterations. Meanwhile, the two batteries take up much of the room in the capsule, making it impossible to add the therapeutic and diagnostic elements that represent the future of capsule endoscopy technology.

Elsewhere, sealing in batteries that are known to be toxic is one way to mitigate issues regarding battery mishandling and accidental ingestion, as well as helping with form factor complications. But this type of design impacts the device’s repair potential and end-of-life recyclability – issues that are not sustainable over the long term. Right-to-repair legislation in states across the country is being initiated to address the e-waste issues associated with sealed-in batteries within common consumer electronics such as cell phones and tablets; and while the attention is not currently being directed at the medical device industry, it is likely just a matter of time before the spotlight is turned in this direction. Especially considering that the wearable medical device industry is slated for an 18.3% compound annual growth rate for a valuation of $14.4 billion by 2022, according to research firm Markets and Markets. The non-recyclable trash potential in an industry this size is monumental.

The bottom line is that medical devices, whether they run on primary or secondary battery power, must be reliable, safe and sustainable – and, historically, it has been impossible to meet these three capabilities in a single power solution.

Silver-Zinc Battery – A Revolutionary Battery Chemistry That Provides Safety, Reliability and Sustainability

Thankfully, there is now an option that does meet all three criteria in a microbattery format: silver zinc. Available as either a primary or a secondary option, silver-zinc chemistry delivers the highest energy density and capacity in a microbattery format compared to all currently available microbattery chemistries. This is critically important because smaller-sized devices do not necessarily have smaller power requirements. Devices with wireless connectivity typically require a higher capacity and greater energy density than their non-wireless counterparts.

With silver zinc, medical device designers don’t have to choose between short run time vs. short lifetime. Case in point: Over the last few years, the international hearing aid industry has made great advancements in its product designs that feature wireless connectivity, but it did not have a good rechargeable battery option to ensure that these devices lasted long enough to be truly valuable to the wearer. Traditional rechargeable microbattery options had neither the capacity nor the life span to keep these more sophisticated hearing aids running all day, every day; and while disposable batteries worked, powering these devices results in about 100 batteries thrown away each year per hearing aid.

But advancements in silver-zinc rechargeable battery technology were happening concurrently, and now the two technologies have been united, resulting in dependable, long-lasting rechargeable devices that have the potential to improve the quality of life of millions. Nearly every major hearing aid manufacturer in the world now offers a hearing-aid device powered by rechargeable silver-zinc batteries. And while there are wireless hearing aids that are powered by batteries with chemistries other than silver zinc, these batteries must be sealed into the devices for patient safety. This means that they cannot be changed out in the event that the battery dies or if the wearer forgets to charge their hearing aids and wants to use a disposable battery. It also means that when the battery dies, the hearing aid dies with it, creating difficult-to-disassemble e-waste that will likely end up in a landfill, unable to be recycled.  

Benefits of Silver-Zinc Microbattery Chemistry:

• High energy density, long runtime, stable water-based chemistry
• Non-toxic, non-flammable – does not need to be sealed into the device
• Can withstand high-temperature sterilization
• Silver-zinc primary batteries have the safety combined with a high capacity and energy density ideal for ingestible applications (such as endoscopic capsules)
• 100% recyclable
• Can withstand up to 1,000 discharge cycles without losing significant energy

Silver-zinc, relied upon for decades by NASA and the military to power everything from spacecraft to torpedoes, is a chemistry that is, by comparison, more powerful the smaller it gets. For safety, sustainability and power, there is no other microbattery chemistry currently available that offers what silver zinc can, and for the medical device industry, where safety is of paramount importance and design is becoming more sophisticated by the day, that is exactly what is needed.

Jeffrey V. Ortega joined ZPower (Camarillo, Calif.) in 2008 and has made numerous contributions to the understanding and improvement of silver-zinc batteries. He has a bachelor’s of science degree in chemistry from California State University, Los Angeles and a Ph.D. in chemistry from the University of California at Irvine.

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.