Italian researchers look to cellulose and carbon for ingestible devices

Over the past decade, ingestible electronics have made a number of exciting advances. From gut health monitors to cardiac pacemakers, miniaturized devices housed inside biocompatible enclosures designed to be swallowed are playing an increasingly important role in the field of medical diagnostics. One of the remaining challenges with these devices is finding better ways to power them. Today’s batteries are made with a range of non-recyclable and potentially toxic materials. In addition, they have a limited lifetime within the body, so for patients, that might mean undergoing an additional operation to enable the device’s removal.

A group of Italian researchers are proposing an alternative – edible generators and capacitors, made from food-grade ingredients, that can be safely ingested, and which then degrade in the human body after completing their function. Writing in Nano Energy [DOI: 10.1016/j.nanoen.2023.108168], the authors describe a series of electrically-conductive composites they made using two materials. The first was ethylcellulose, a sugar, food additive, and derivative of cellulose, known in the food safety industry as E462. The second was activated carbon (E153), an additive with a smoky taste that is stable in the gastrointestinal tract and wholly excreted in faeces.

The fabrication of these composite films was descried as “a simple one-pot synthesis processes”. Varying quantities of activated carbon (AC) was dispersed in a solution of ethylcellulose (EC) in ethanol. The resulting dispersion was cast in a petri dish and the ethanol allowed to evaporate. This process, accompanied by gravity-induced phase separation, generated a series of films “with opposite faces showing completely different electrical properties: a conductive bottom layer rich in AC, where EC acts as a binder, and a top layer consisting of pure EC.”

Electrical characterisation of these films showed that Ohmic behaviour was achieved at 10% activated carbon, but the sheet resistance was excessively high (~ 250 k?/sq). At higher concentrations of carbon (60%), the resistance drops to ~1 k?/sq. Resistivity stayed consistent for all filler concentrations above 10%. As a result of these initial tests, the authors chose to proceed with a 40% activated carbon composite. They further modified the films by adding a range of edible additives. Myristic acid (E570) and sunflower oil, which both act as ethylcellulose plasticizers, decreased the film’s Young modulus by almost 30%. Citric acid (E330) – an effective crosslinking agent for cellulose, and a modifier for activated carbon – enhanced the film stiffness, increasing the Young modulus while reducing the maximum sustained stress and strain. This range of films were immersed in simulated gastric fluid for 72 hours. All were found to remain mechanically and electrically stable.

The films – specifically, the pure ethylcellulose side – were then used as the electropositive material in a series of triboelectric nanogenerators (TENGs), with Teflon (interfaced with an aluminium electrode) acting as the negative material. Higher instant peak power output was measured for those TENGs made with additive-enhanced films, and their performance compared very favourably with edible devices reported elsewhere in the literature.

In addition, the unmodified composite films (with a 90:10 carbon to cellulose weight ratio) were used as the electrodes of a fully edible supercapacitor. Edible gold leaf acted as the current collector, and nori – a seaweed widely used in Japanese cuisine – soaked in an electrolyte, was the separator. The device was then encased in beeswax to protect it, and the total assembly was 3 cm in length. At 3.36 mW h g-1, the energy density of the edible supercapacitor was approximately one-third that of a commercial device. It had a maximum capacity of ~9 mAh g−1, and showed excellent stability over 1000 cycles.

The authors conclude that the use of these composites “….in edible energy harvesting and storage devices with promising figures of merits, combined with simple and scalable fabrication schemes, shows a concrete path to fulfil the energetic requirements of envisioned edible systems.”


Leonardo Lamanna, Giuseppina Pace, Ivan K. Ilic, Pietro Cataldi, Fabrizio Viola, Marco Friuli, Valerio Galli, Christian Demitri, Mario Caironi. “Edible cellulose-based conductive composites for triboelectric nanogenerators and supercapacitors,” Nano Energy 108 (2023) 108168. DOI: 10.1016/j.nanoen.2023.108168