bioelectronics, rather we want to provide an overview of the main class of CPs that are

representative of the entire literature on the field. The most used CPs in bioelectronics are

displayed in Figure 4.2. The first two CPs employed as organic semiconductors were

polyanilines (PANIs) and polypyrroles (PPys), while poly(3,4-ethylene dioxythiophene):

poly(styrene sulfonate) (PEDOT:PSS) and polythiophenes (PThs) were introduced more

recently. Note that PANIs, PPys, and PEDOT:PSS are conductive polymers, while PThs

display a semiconducting behavior.

4.3.1 Polyaniline

PANI is an important conductive polymer that has been used extensively in bioelec­

tronics. Despite its relatively good bioelectronic properties, PANI exhibits some dis­

advantages, such as its limited solubility in many solvents and its poor conductivity at

high pH values. This latter issue has been solved by adding crystalline nanocellulose to

PANI (CNC-PANI): the high density of hydroxyl groups of the nanocellulose stabilizes

the polymer structure via hydrogen bonding [18]. A very recent and interesting example

of the use of PANI as an abiotic interface has been reported by Deisseroth, Bao, and

coworkers [19]. Here, the authors show that modification of neurons with conductive

PANI, which is synthesized by genetically instructing cells, increased their membrane

capacitance and decreased spike number. In addition, this method was also applied in

vivo, to modify the motor functions of Caenorhabditis elegans. Although this approach can

pose some cytotoxicity issues due to the monomer or radical side products, it can pave

the way towards the development of biocompatible hybrids that are directly synthesized

by cells.

4.3.2 Polypyrrole

PPy represents another important class of conductive polymers, owing to the easiness of

its synthesis, high biocompatibility, and environmental stability [20]. This material is

usually produced as conductive monolithic sheets that display appreciable mechanical

strain upon application of an external bias. This property has rendered PPys a perfect

choice for the fabrication of artificial muscles or mechano-modulators [21]. Despite these

sheets being intrinsically stretchable, they do not adhere effectively to cells and tissues

due to their hydrophobicity. This is a serious disadvantage since to efficiently sense or

stimulate a desired target molecule or cell, the device must be able to integrate with the

bio-target. To overcome this issue, PPys have been often coupled to other stretchable

materials, such as hyaluronic acid and poly(dimethylsiloxane) (PDMS) [20]. In regards to

PPys applications, Golabi et al. studied the effect of PPy ion dopants on bacterial dif­

ferentiation. In particular, the authors found that the adhesion of specific bacterial strains

FIGURE 4.2

Chemical structure of the most commonly used conjugated polymers for bioelectronics applications.

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Bioelectronics