2.3.3 Materials to Interface Electronic Devices with Living Systems

One of the main goals of bioelectronics is to achieve efficient communication between

living systems and electronic devices. The biggest challenge of this objective is the de­

velopment of interfaces that allow the union between different conduction modes since

the most conventional electronic devices transport electric charge by electron mobility;

while in living systems, charge transport takes place by ionic fluxes and it is strongly

influenced by the water-rich biological medium. At a cellular level, communication oc­

curs through the combination of mechanical, thermal, biological, chemical, and electrical

signals; the electrical signals are given by peaks of flows of ions, mainly cations, which are

released in response to differences in potential inside and outside the cell. When the ions

are released, they alter the potential of the tissue, which induces communication. The

integration between electrical devices and biological systems through capturing these

signals allows the control of adhesion, proliferation, and apoptosis cellular. While at

the tissue level, integration provides information on the biological functioning and allows

the formation of regeneration structures, stimulation, drug release, and disease modeling.

Specific applications of this technology include support for people with chronic brain

diseases such as paralysis, artificial retinas, and new technologies to model, monitor, and

influence cellular behavior [52].

In order to facilitate communication between the living and artificial systems, biotic/

abiotic interfaces have been developed that serve as ionic/electronic couplers, which are

usually composed of a hybrid circuit that facilitates interaction. In addition, current re­

searches are searching for the development of artificial devices based on ion transport

that allows greater affinity with nature. In both cases, the most common ion transport

mechanisms in synthetic materials are the formation of an electrical double layer and

electrochemical reactions. The former involves the redistribution of ions on the charged

surface by electrostatic forces, which generates a local dipole field that allows the

transport of ions and the detection and interpretation of biological signals (Figure 2.5);

and the latter involves oxidation-reduction processes that allow the transfer of electrons.

The organic electrical ion pumps (OEIPs) are an example of these ionic interfaces, which

allow controlling the flow of ions in physiological processes. The OEIPs generally contain

a film of a mixed conductive copolymer of PEDOT: PSS. In 2007, the first OEIP was

published, which successfully allowed the transport of small cations. From this, the

FIGURE 2.5

The schematization of the ion transport mechanism of the electrical double layer.

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Bioelectronics