## 4 Electroceticals--Intelligent Environments
### Artificial Retina
This proposed device has the capability to be implemented in both eyeball sites, epiretinal and subretinal sites, known as epiretinal implants and subretinal implants, as visualized in Figure 6b. In epiretinal implants, the electrodes are in contact with ganglion cells. The light is incident on the opposite side where the microelectrodes are formed and reach the nanowire photodetection circuits (NWPDs). While in the case of subretinal implants, microelectrodes are contacted with photoreceptors. The light is incident on the same side where the microelectrodes are formed and reaches the NWPDs. Scanning electron microscopy images of the fabricated device are illustrated in Figure 6b. The prosthesis device consists of a voltage regulator and current driver in which silicon nanowires help as similar functions of a photodetector and field-effect transistor such as detecting light and generating stimulation signals according to the light intensity [113]. The device demonstrations suggested that this generated stimulation pulses to retinal tissues; the ratio is high and directly proportional to the light intensity. Therefore, this significant development is a step forward in retinal prosthetic systems that has the enhancing visual resolution capability. Recently demonstrated silicon nanowire arrays shown in Figure 7a rod shape Figure 7b cone shape at different molar ratios of SiCI4/H2 fabricated via e-beam lithography, could be thought of as a novel electrode system for retinal prosthetic devices [114] because of their systematic periodic arrangements and can be integrated with the retinal implant to deliver the stimulative signals to the retinal neurons at a constant field intensity and currents over a wide band of light energy while maintaining uniform stimulative signal distributions. With this significant advantage of the electrode array system, a high-resolution retinal prosthetic system that competes with traditional ones could be realized. Figure 6: _Cont._  
[PERSON] et al. developed novel subretinal implants based on photovoltaic arrays, which induce localized stimulations to the retinal neurons revealed after experimenting on rats [115]. The photovoltaic array module and its electronic configuration are illustrated in Figure 8a,b. The photovoltaic module comprises a 70 \(\upmu\)m wide photovoltaic element separated by 5 \(\upmu\)m trenches arranged in a 1 mm wide hexagonal pattern. The circuit configuration of each photovoltaic element is shown in the subsequent Figure 8a. Each photovoltaic window consists of three photodiodes connected between central active (1) and surrounding return. The visible light triggers the stimulations through the photodiodes located between central active and surrounding return. At the same time, much brighter pulsed illumination generates the biphasic pulses of current in the stimulating photovoltaic cell [115]. All the above electrode configurations and systems are gaining energy wirelessly. Among them, photo energy-based prosthetic systems with high contrast, spatial resolution, and miniaturized capability could greatly stimulate the photoreceptors' function or replace the function of the photoreceptors for restoring vision in visually blinded persons. This significant advantage is because of their adaptability within the retinal system and operation  
Figure 6: **(a)**. The concept of the neural stimulation device is to activate neurons with light energy. Reprinted with permission from [PERSON] et al., Sensors 16, no. 12 (2016): 2035. Copyright 2016 MDPI Publishers. **(b)** Scanning electron microscopy images: fabricated for neural stimulation device. Reprinted with permission from [PERSON] et al., Sensors 16, no. 12 (2016): 2035. Copyright 2016 MDPI Publishers. Figure 7: FESEM images of fabricated Si nanowire arrays **(a)** rod shape **(b)** cone shape at different molar ratios of \(\mathrm{SiCI_{4}/H_{2}}\) using e-beam lithography may be helpful for neural stimulation. Reprinted with permission from [PERSON] et al., ACS nano 5, no. 1 (2011): 656–664.