The Roles of an Aluminum Underlayer in the Biocompatibility and Mechanical Integrity of Vertically Aligned Carbon Nanotubes for Interfacing with Retinal Neurons.

William J Watterson,David Miller,Conor Rowland,Richard P Taylor,Benjamín J Alemán,Julian H Smith,Saba Moslehi,Julie E Chouinard,Kara M Zappitelli,Stephen L Golledge,Maria-Thereza Perez

doi:10.3390/mi11060546

William J Watterson, David Miller + Show 9 more

Open Access

https://doi.org/10.3390/mi11060546

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Journal: Micromachines	Publication Date: May 28, 2020
Citations: 11	License type: CC BY 4.0

Affiliation: University of Oregon, Lund University

Abstract

Retinal implant devices are becoming an increasingly realizable way to improve the vision of patients blinded by photoreceptor degeneration. As an electrode material that can improve restored visual acuity, carbon nanotubes (CNTs) excel due to their nanoscale topography, flexibility, surface chemistry, and double-layer capacitance. If vertically aligned carbon nanotubes (VACNTs) are biocompatible with retinal neurons and mechanically robust, they can further improve visual acuity—most notably in subretinal implants—because they can be patterned into high-aspect-ratio, micrometer-size electrodes. We investigated the role of an aluminum (Al) underlayer beneath an iron (Fe) catalyst layer used in the growth of VACNTs by chemical vapor deposition (CVD). In particular, we cultured dissociated retinal cells for three days in vitro (DIV) on unfunctionalized and oxygen plasma functionalized VACNTs grown from a Fe catalyst (Fe and Fe+Pl preparations, where Pl signifies the plasma functionalization) and an Fe catalyst with an Al underlayer (Al/Fe and Al/Fe+Pl preparations). The addition of the Al layer increased the mechanical integrity of the VACNT interface and enhanced retinal neurite outgrowth over the Fe preparation. Unexpectedly, the extent of neurite outgrowth was significantly greater in the Al/Fe than in the Al/Fe+Pl preparation, suggesting plasma functionalization can negatively impact biocompatibility for some VACNT preparations. Additionally, we show our VACNT growth process for the Al/Fe preparation can support neurite outgrowth for up to 7 DIV. By demonstrating the retinal neuron biocompatibility, mechanical integrity, and pattern control of our VACNTs, this work offers VACNT electrodes as a solution for improving the restored visual acuity provided by modern retinal implants.

Highlights

Photoreceptor degeneration in the retina can lead to blindness in patients with retinitis pigmentosa (RP) or age-related macular degeneration (AMD) [1,2]
The uniform vertically aligned carbon nanotubes (VACNTs) fabricated for the biocompatibility tests were densely packed (Figure 1a,d) and there were no observable differences in carbon nanotubes (CNTs) nanotopography via scanning electron microscopy (SEM) imaging between any of the four preparations
VACNTs grown without the Al underlayer (Fe and Fe+Pl preparations) delaminated from the substrate, and in some cases already during sample handling (Figure S3a, these samples were not used in the cell cultures)

Summary

Introduction

Photoreceptor degeneration (i.e., loss of rods and cones) in the retina can lead to blindness in patients with retinitis pigmentosa (RP) or age-related macular degeneration (AMD) [1,2]. Electrode materials must resist degradation in the physiological environment of neural tissue and should support surface functionalization to increase their hydrophilicity, thereby preventing neuronal cell death and stimulating neurite outgrowth [12], and reduce the voltage threshold needed for neuronal stimulation [13]. They need to be strong and yet flexible to reduce inflammation and glial scarring in the surrounding tissue [14,15,16]. Soft materials (i.e., mechanically compliant) [17,18] and materials with rough, textured surfaces [19,20] can enhance neurite outgrowth, elongation rate, and branching

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