**6. Conclusion**

for vision recovery lost due to retinal degeneration. Such observation emphasizes that nanowires are starting point in the progress for regeneration and implantable

*Schematic of electron movement and holes toward the n-type and p-type silicon at the neural cell membrane for simulating the light senses. Light with receive to the n-type silicon containing the positive ions causes to the movement of electrons to the p-type silicon layer containing negative ions cause to senses the light and transfer produced faradic current to the cells [69]. (Refer to ACS ChemMatters online archive 2013–2014).*

We believe that future strategies could involve incorporating smart

nanostructures to simulate the extracellular matrix in addition to extracellular electric based on the intracellular electric charges to follow the polarization and adhesion of cells in the retina. For example, when the level of light changes, the system would control the transferred electrical signals by implants. Therefore we believe that nanostructures such as carbon nanotubes could serve to control the extracellular electrical charge incorporation nanoparticles such as gold nanoparticles for light sensation with a size of less than 10 nm to control the thermal stability. **Figure 5** is showing the retinal cell polarization when external electrical charge

*The confocal microscopy image of seeded retinal ganglion cells into the random polypyrrole/graphene/poly (lactic-co-glycolic acid) nanofibers (a), polypyrrole/graphene nanofibers (b), the aligned polypyrrole/ graphene/poly (lactic-co-glycolic acid) nanofibers (c), the SEM mapping of loaded gold nanoparticles into the polyvinylpyrrolidone nanofiber (d) and the energy-dispersive X-ray for loaded gold nanoparticles into the*

artificial photoreceptors.

**Figure 4.**

*Regenerative Medicine*

**Figure 5.**

**128**

*polyvinylpyrrolidone nanofibers (e) [24, 26].*

**5. Challenges and prospects**

Nanowires have had a substantial impact on retinal applications and still, have great potential to advance therapeutic implants for retinal regeneration. The development of new structures, and their incorporation into the simulation of the extracellular matrix, extracellular electric and light senses may lead to improvement of advanced structure for developing artificial retina. However, challenges still need to be addressed in controlling the local charges and light sensation improvement. It is believed that engineered nanowires with high efficiency will be increasingly used in retinal implantations. In recent years, several in vitro and in vivo reports have indicated the possibility of a significant effect of nanowires on the recovery of vision that lost due to retinal degeneration. Another challenge that must be addressed is the extracellular matrix to create a 3D scaffold, where it did not discuss in reports that have been done for nanowires usage in vision recovery, due to a limitation in synthesizing of nanowires. Also, it is crucial to discover the key factor promoting the assemblies of different layers of the retina and create specific scaffolds for polarization and construction of cells for transferring the neural signals to the brain. Developing nanowires to control the neural signals and guide the cells for polarization will be useful for engineering complex architecture as well as the retina.

### **Acknowledgements**

This research was supported by the Shinshu University, Nano Fusion Technology Research Group, Division of Frontier Fibers, Institute for Fiber Engineering (IFES), Interdisciplinary Cluster for Cutting Edge Research.

#### **Competing interests**

The authors declare no competing interests.

*Regenerative Medicine*
