The use of PThs as phototransducers for neurostimulation has opened new and exciting

avenues for rescuing biological functions and treating diseases [32,33], including their use

as retinal prostheses. In this case, PThs offers important advantages as compared with

other materials, namely photovoltaic functioning, high biocompatibility, mechanical re­

silience, and a relatively high light sensitivity. In this regard, Maya-Vetencourt et al. have

developed a P3HT-based device composed of a flexible and highly conformable silk

substrate covered with photoactive layers (Figure 4.4), which was able to rescue vision in

dystrophic rats [34]. The further evolution of such an approach was the development of

injectable P3HT sub-micro particles in suspension. This approach simplifies the surgery

and provides a much better and diffuse retina coverage [35]. These results have inspired

other works, such as the work of Ghezzi et al., in which the prostheses are composed of a

P3HT/PCBM layer over a PDMS substrate [36]. Other works employ either organic

pigments or semiconducting carbon nanotubes and will be described in the relevant

sections below.

4.4 Small Molecules

Traditionally, small molecules have been employed widely in bioelectronics to modify

chemically the surface of electrodes, i.e. to enhance cell-to-electrode attachment and

electron transfer [37]. Some relevant examples relate to microbial fuel cells, whose effi­

ciency greatly depends on bacteria-electrode attachment. For instance, Cheng et al. re­

ported the ammonia treatment of neutral carbon cloth at elevated temperature, which

leads to the improvement of the start-up time and power production in mixed culture

microbial fuel cells [38]. Apart from these applications in which small molecules are

employed as passive components, in the last couple of decades, they have been in­

creasingly used as active bioelectronic systems, i.e. for triggering bioelectric signaling.

FIGURE 4.4

(a) Scanning electron microscopy images of the prosthetic device (top) and of its cross-section. (b) Scheme of the

implant approach. Adapted with permission [ 34]. Copyright (2017) Springer Nature.

Materials for Organic Bioelectronics

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