Minimally invasive implants based on passive electronics for selective electrical stimulation

The line of research on which Antoni Ivorra, head of the Biomedical Electronics Research Group (BERG) at the Department of Information and Communication Technologies (DTIC) at UPF is working is a new method to implement very slim and flexible electronic implants inside the human body. These devices are aimed at electrically stimulating the peripheralnerves mainly to restore motor function in people with paralysis.

A study published in PLoS One this July by BERG members Laura Becerra-Fajardo and Antoni Ivorra demonstrates in vivo that the methodology proposed by the authors will enable developing sufficiently "smart" implants as to respond to external instructions according to stimulation needs.

Digital implants capable of being selectively activated

The addressing of implants is an almost indispensable feature for applications aimed at recovering motor function in paralysed patients, since in such cases it is necessary to selectively activate a series of nerves following a pattern.

The study published by Becerra-Fajardo and Ivorra in PLoS One presents a prototype of the addressable electronics (not yet implantable; 5 cm x 5 cm) that, sufficiently miniaturized, will fit inside future smart implants and may be directed externally with selective stimulation.

Slimmer, more flexible implants

"We use the human body as a conductor for transmitting the energy from external electrodes to the implants", explain Becerra-Fajardo and Ivorra. The implants transform these harmless high frequency currents into low frequency currents capable of producing stimulation. "Our method is feasible and safe because the currents we pass through the human body are high frequency and in the form of short bursts", they add.

In this way, the implants can be much slimmer and more flexible than those that currently exist because they do not use either of the two common methods (electrochemical energy and inductive coupling) to provide power to the electronics. These other two methods of providing energy require components that are bulky and rigid (batteries and coils). In contrast, the method under study only requires a small core of passive electronics and two peripheral electrodes.

A highly non-invasive implantation process

The fact that the implants can be very slim means that in practice they can be very compact and flexible and can be implanted by means of a procedure very similar to an injection. We could even speak of " injectable neurostimulators". In short, all of this means that both the implants and the implantation process are very little invasive. This is something that the authors had already demonstrated previously with electronics that were not addressable.
At present, Becerra-Fajardo is working on a new version of these "smart" devices that will enable performing implants with a diameter of just some 2 mm and a length of about 4 cm.

Reference work:
Laura Becerra-Fajardo, Antoni Ivorra (2015), " In Vivo Demonstration of Addressable Microstimulators Powered by Rectification of Epidermically Applied Currents for Miniaturized Neuroprostheses", PloS One, 6 July, DOI: 10.1371/journal.pone.0131666.

Previous related studies:

Antoni Ivorra, Laura Becerra-Fajardo (2014), " Flexible Thread-like Electrical Stimulation Implants Based on Rectification of Epidermically Applied Currents Which Perform Charge Balance" (2014), Replace, Repair, Restore, Relieve - Bridging Clinical and Engineering Solutions in NeurorehabilitationBiosystems & Biorobotics, Volume 7, pp 447-455.