Neural Pathfinding on Uni- and Multidirectional Photopolymerized Micropatterns

Abstract

Overcoming signal resolution barriers of neural prostheses, such as the commercially available cochlear impant (CI) or the developing retinal implant, will likely require spatial control of regenerative neural elements. To rationally design materials that direct nerve growth, it is first necessary to determine pathfinding behavior of de novo neurite growth from prosthesis-relevant cells such as spiral ganglion neurons (SGNs) in the inner ear. Accordingly, in this work, repeating 90° turns were fabricated as multidirectional micropatterns to determine SGN neurite turning capability and pathfinding. Unidirectional micropatterns and unpatterned substrates are used as comparisons. Spiral ganglion Schwann cell alignment (SGSC) is also examined on each surface type. Micropatterns are fabricated using the spatial reaction control inherent to photopolymerization with photomasks that have either parallel line spacing gratings for unidirectional patterns or repeating 90° angle steps for multidirectional patterns. Feature depth is controlled by modulating UV exposure time by shuttering the light source at given time increments. Substrate topography is characterized by white light interferometry and scanning electron microscopy (SEM). Both pattern types exhibit features that are 25 μm in width and 7.4 ± 0.7 μm in depth. SGN neurites orient randomly on unpatterned photopolymer controls, align and consistently track unidirectional patterns, and are substantially influenced by, but do not consistently track, multidirectional turning cues. Neurite lengths are 20% shorter on multidirectional substrates compared to unidirectional patterns while neurite branching and microfeature crossing events are significantly higher. For both pattern types, the majority of the neurite length is located in depressed surface features. Developing methods to understand neural pathfinding and to guide de novo neurite growth to specific stimulatory elements will enable design of innovative biomaterials that improve functional outcomes of devices that interface with the nervous system.

Microtopographical features generated by photopolymerization recruit RhoA/ROCK through TRPV1 to direct cell and neurite growth

“…Interestingly, fibroblasts fail to respond to these topographical cues, which may allow for reduced electrode encapsulation and lower electrode resistance [5, 33, 34]. SGN neurite and SGSC responses to these micro- and nano-channels depend on feature amplitude, periodicity, slope, and complexity; all of which can be finely tuned to modulate contact guidance [5, 35, 36]. Despite abundant evidence that cells respond to surface topographical features, the mechanisms by which cells sense and respond to these biophysical cues have not been elucidated.…”

Intracellular calcium and cyclic nucleotide levels modulate neurite guidance by microtopographical substrate features

“…Neurites prefer to grow in the grooves compared to the ridges of these micropatterned substrates 12,15 . This observation implies that either the ridge features act as a repulsive signal and/or that the groove acts as a permissive substrate.…”

3D-Printed pHEMA Materials for Topographical and Biochemical Modulation of Dorsal Root Ganglion Cell Response

“…10,11 Programming the spatial arrangement of neuronal circuits ex vivo has been widely explored via a variety of approaches including chemically and topographically guided neuronal process outgrowth and interconnection (e.g. within microchannel architectures 12–15 or via chemical/textural features established by micropatterning 16–19 ).…”