Power source for implantable medical electronics explored


New research from the journal ACS Nano Letters demonstrates the potential of transient enzyme biobatteries (TEBFCs) based on graphene (LIG)/gold nanoparticle (NP) composite electrodes as an energy source in transient electronics and implantable medical devices (IMDs).

​​​​​​​Study: Transient, implantable and ultra-thin biopiles enabled by laser-induced graphene and gold nanoparticle composite. Image Credit: OSORIOartist/Shutterstock.com

Importance of Transient Power Sources in IMDs

In IMDs, miniaturized batteries containing corrosive liquid electrolytes are typically used as power sources, which can lead to graft rejection and damage to surrounding tissues during electrolyte leakage. Thus, a second surgery is often performed after the initial implantation of the IMDs to replace the entire IMD assembly after failure or treatment, or the batteries being depleted, further damaging the implant site.

Transient energy sources with excellent bioresorbability and biocompatibility can effectively solve these problems. EBFC is a suitable device which can efficiently convert biochemical energy into electricity and provide stable and continuous power outputs. Additionally, the EBFC can be developed into an ultrathin and flexible device to reduce foreign body sensation in the implant site. Thus, EBFCs have attracted considerable attention for implantable and wearable device applications.

Carbon nanomaterials are widely used as electrodes in EBFCs due to their excellent electrical properties, good biocompatibility and large surface area. LIG can be obtained by fabricating a thin film of graphene from polyimide (PI) using an infrared carbon dioxide (CO2) laser.

In EBFCs and enzymatic sensors, certain functional materials such as metallic nanoparticles and conductive polymers are used as dopants to improve the output performance or the sensitivity of the sensors. Among these doping materials, gold NPs are the most suitable compared to other dopants due to their large surface area, conductivity and biocompatibility.

In this study, researchers synthesized ultra-thin implantable TEBFCs based on gold NPs/LIG composite electrodes and evaluated their performance.

Summary of the TEBFCs table

A quartz glass served as a temporary support substrate during the synthesis. The glass was cleaned using acetone, ethanol, and deionized (DI) water sequentially. The poly(methyl methacrylate) (PMMA) was spin coated for 30 seconds at 2000 rotations per minute and then heated on a hot plate for 20 minutes at 200 degrees Celsius to prepare a PMMA sacrificial layer.

Subsequently, an 80-micrometer PI tape base sheet was laminated to the glass, and the LIG electrodes were obtained directly from the laminated PI using a 10.64-micrometer infrared CO.2 laser in an ambient environment. The spacing, speed, and power of the laser lines were set at 0.03 millimeters, 1000 millimeters per second, and 1.8 watts, respectively.

The resulting LIG array was immersed in acetone for 12 hours to remove the residual PMMA sacrificial layer, and a photoresist (PR) layer was then spin-coated on the LIG to prevent it from falling off after the dissolution of the LIGs. water soluble strips. Residual LIG electrode and PR on the glass were removed using acetone and water-soluble tapes were used to capture the pattern for transfer printing.

An ultra-thin film of poly(lactic-coglycolic acid) (PLGA) was obtained as a receiving substrate by spin coating a solution of PLGA on the quartz glass. The water-soluble tape with the LIG network was then placed on the PLGA substrate and the sample was immersed in water for 30 minutes to peel off the PLGA film and dissolve the water-soluble tape.

Subsequently, two layers of silver nanowires were dispersed on the PLGA film which served as the connection wire. Finally, another PLGA film was spin coated on top of the as-synthesized sample which served as the encapsulation layer.

During the synthesis of the LIG/gold NPs composite electrodes, the electrodes were treated with ultraviolet ozone (UVO) to improve their hydrophilicity, and then the aqueous solution of chloroauric acid was added to the LIG electrode. The electrode was heated for 20 minutes at 80 degrees Celsius to obtain LIG/gold NPs composite electrodes.

Laccase and glucose oxidase were then added to the cathodes and anodes, respectively, and finally two microliters of chitosan and one microliter of bovine serum albumin (BSA) were added to each electrode to incorporate the enzymes.

Manufacture and evaluation of synthesized samples

Linear scanning voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) were used to characterize the synthesized samples. The researchers also performed in vivo and in vitro studies to assess the biocompatibility and bioresorbability of the samples.

search results

An array of implantable TEBFCs based on a LIG/gold NPs composite electrode was successfully fabricated. The LIG/gold NPs composite electrode demonstrated high surface area and low impedance, which accelerated electron transfer between electrode surfaces and enzymatic active sites.

Fast electron transfer exceptionally improved output performance with an open circuit potential (OCP) of 0.77 Volts, maximum power density of 483.1 μW/cm2and a maximum current density of 3113.5 μA/cm2. Such output performance of LIG-based EBFCs has been achieved for the first time.

Additionally, the ultrathin TEBFC has demonstrated long life and fast response time reaching maximum OCP within one minute. The TEBFC maintained its activities for more than four weeks under a biofluid environment at room temperature. TEBFCs also displayed excellent transient performance and biocompatibility in in vivo and in vitro tests. Thus, they can be implanted for a long time for energy harvesting purposes.

After use, the TEBFCs present on the PLGA substrate degraded in a phosphate buffer solution in less than a month and in 44 days in the body of the animals without causing inflammation.

In summary, the results of this study demonstrated that TEBFCs based on LIG/gold NPs composite electrodes possess significant potential as an energy efficient solution for IMDs and transient electronics. Moreover, the synthesized TEBFCs can be customized according to the requirements of the implantation sites and the output intensities.


Li, J., Li, H., Li, D. et al. (2022) Transient, implantable and ultrathin biofuel cells enabled by laser-induced graphene and gold nanoparticle composite. ACS Nano Letters. https://pubs.acs.org/doi/10.1021/acs.nanolett.2c00864

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