Page 391 - Handbook of Biomechatronics

Current Advances in the Design of Retinal and Cortical Visual Prostheses 385

Fig. 6 Return configuration in retinal electrostimulation. Black circles represent active
electrodes, whereas gray circles are the electrodes used as a return. (A) Monopolar con-
figuration, in which current returns via a distant electrode. (B) Bipolar configuration
where current returns via a neighbor electrode. (C) Multipolar approach where electric
current returns via a group of electrodes.

more meaningful percepts with increased visual resolution, there is a clear
need for new technologies that provide better integration between biology
and the device.

6 CONCLUSIONS AND PERSPECTIVES

In this chapter, we reviewed the progress achieved with the applica-
tion of bioelectronics devices for restoration of visual perception, describing
the different system architectures applied along the visual path, with empha-
sis on retinal and cortical prostheses. We further discuss key challenges facing
current devices focusing on the direct interface between the device and the
neuronal tissue, the electrode.
Recent developments in materials and nanoengineering open new
routes in interfacing with neurons, that diverges from the traditional
approach based on electrical stimulation through metal electrodes. The next
generation of visual prostheses is designed to be minimally invasive,
biocompatible, with high spatial resolution, cell specificity, and improved
safety. A new generation of materials such as carbon nanotubes (CNTs)
(Gabriel et al., 2009; David-Pur et al., 2014; Eleftheriou et al., 2017;
Shoval et al., 2009), nanocrystalline diamond (NCD) (Ganesan et al.,
2014; Hadjinicolaou et al., 2012; Ahnood et al., 2016), conjugated polymers
(CPs) (Samba et al., 2015), and silicon nanowires (Si NWs) (Khraiche et al.,
2011, 2013; Ha et al., 2016) has attracted attention as promising candidates