Scientists have developed biodegradable batteries using dissolvable metal foils and polyanhydride packages which may potentially be used as a power source for embedded health sensors.
Digital health technology envisages the use of more and more implantable biomedical devices inside the body for a variety of treatment, monitoring and research applications but powering those devices is a major problem.
Now a team led by materials scientist John Rogers at the University of Illinois at Urbana-Champaign has demonstrated a biodegradable battery that could melt inside the body harmlessly after providing sustained power to embedded biomedical devices for a limited time.
The research article titled "Materials, Designs, and Operational Characteristics for Fully Biodegradable Primary Batteries," is authored by Lan Yin, Xian Huang Hangxun Xu, Yanfeng Zhang, Jasper Lam, Jianjun Cheng and John A. Rogers and is published in the Advanced Materials.
How will the biodegradable battery work to help health sensors?
The study describes of a biodegradable battery made from anodes of magnesium foil and cathodes of iron, molybdenum or tungsten.
Phosphate-buffered saline solution is used as electrolyte and the whole system is packed inside a polyanhydride polymer.
The metals and the package slowly dissolve in the body after use and ions are biocompatible.
The team previously designed many biodegradable silicon chips, powered by induction coils from an external source, to monitor tissue from within a mouse to measure temperature and mechanical strain and then wirelessly transmit the data to external devices and even to heat up tissue after a surgical closure to prevent infection.
However, when the implant is deep within tissue or under bone, transmitting power wirelessly becomes difficult.
Also, using induction coils and the components that receive power from them is complex and take up space. To solve this problem, the University of Illinois team has now created a complete biodegradable battery.
The battery measures one-square-centimeter with 50-micrometre-thick magnesium anode and an 8-micrometre-thick molybdenum cathode and produces a steady current of 2.4 milliamps.
When the battery is completely dissolved, less than 9 milligrams of magnesium is released into the body which is unlikely to cause any problem.
Magnesium, however, is not the only option.
Other metals too can be used at the cathode but the currents and voltages vary depending on the metal.
In December 2013, scientists at Carnegie Mellon University devised an edible sodium-ion battery using electrodes made from melanin pigments. But John Roger’s team reports that magnesium batteries last longer, have more power density and produce higher current.
The battery designed was able to produce a steady output for little more than a day.
Scientists believe that by increasing surface area of the magnesium foil, batteries measuring 0.25 square-centimeter and just one micrometer thick can be built to power implantable health sensors for a day.
As and when these batteries become commercially available, they are expected to have many applications in implantable drug-delivery devices and embedded health sensors to transport medicines to a very specific site in the body or in response to a specific acute condition, such as an epileptic seizure.
Scientists believe that biodegradable batteries may also have other environmental applications such as helping clean oil spills by dropping hundreds of thousands of tiny chemical health sensors that would clean the slick and then later dissolve in the ocean.