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Neural pathfinding on uni- and multidirectional photopolymerized micropatterns.

Tuft BW, Xu L, White SP, Seline AE, Erwood AM, Hansen MR, Guymon CA - ACS Appl Mater Interfaces (2014)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biochemical Engineering, University of Iowa , Iowa City, Iowa 52242, United States, United States.

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.

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SGN survival, total and primary neurite length (NL), andbranching on unpatterned controls and on parallel and 90° anglemicropatterns of HMA-co-HDDMA polymer substrates.(A) SGN survival on unpatterned and micropatterned substrates normalizedto a tissue culture plastic (TCP) control. (B) Total and primary SGNneurite lengths are significantly shorter than corresponding lengthson parallel patterns and unpatterned controls (*p < 0.05, ANOVA). (C–D) Significantly more branches perneurite length and per neurite on 90° angle patterns are observedcompared to neurites on parallel patterns and unpatterned controls(*p < 0.05, ANOVA). Error bars represent standarderror of the mean (SE).
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fig4: SGN survival, total and primary neurite length (NL), andbranching on unpatterned controls and on parallel and 90° anglemicropatterns of HMA-co-HDDMA polymer substrates.(A) SGN survival on unpatterned and micropatterned substrates normalizedto a tissue culture plastic (TCP) control. (B) Total and primary SGNneurite lengths are significantly shorter than corresponding lengthson parallel patterns and unpatterned controls (*p < 0.05, ANOVA). (C–D) Significantly more branches perneurite length and per neurite on 90° angle patterns are observedcompared to neurites on parallel patterns and unpatterned controls(*p < 0.05, ANOVA). Error bars represent standarderror of the mean (SE).

Mentions: To compare differences in neurite behavior on varied directionalsurface cues, dissociated SGNs were cultured on unpatterned controls,unidirectional (parallel) patterns, and repeating angle (90°angle) patterns. Neuronal survival, neurite length, and branchingwere examined as an initial comparison (Figure 4). SGN survival on unpatterned and micropatterned poly(HMA-co-HDDMA) is comparable to survival on a tissue cultureplastic (TCP) control (p > 0.05). Further, nosignificant difference is evident between primary neurite length,i.e. the longest neurite from each neuron, on unpatterned controlscompared to unidirectional micropatterns. Total neurite length, thatis, primary neurite length plus branch length, on unpatterned andunidirectional substrates is also similar. However, both primary andtotal neurite lengths are approximately 20% shorter on repeating anglepatterns, relative to unpatterned and parallel pattern substrates.Neurites on multidirectional surfaces may be shorter due to the presentationof a higher density of potential encounters with feature edges tothe advancing neural growth cone compared to fewer such encounterson smooth or unidirectional surfaces. Each encounter with a featureedge is likely associated with growth cone stalling and the underlyingfocal adhesion formation or removal and cytoskeleton rearrangementevents which reduce the rate of neurite extension.58


Neural pathfinding on uni- and multidirectional photopolymerized micropatterns.

Tuft BW, Xu L, White SP, Seline AE, Erwood AM, Hansen MR, Guymon CA - ACS Appl Mater Interfaces (2014)

SGN survival, total and primary neurite length (NL), andbranching on unpatterned controls and on parallel and 90° anglemicropatterns of HMA-co-HDDMA polymer substrates.(A) SGN survival on unpatterned and micropatterned substrates normalizedto a tissue culture plastic (TCP) control. (B) Total and primary SGNneurite lengths are significantly shorter than corresponding lengthson parallel patterns and unpatterned controls (*p < 0.05, ANOVA). (C–D) Significantly more branches perneurite length and per neurite on 90° angle patterns are observedcompared to neurites on parallel patterns and unpatterned controls(*p < 0.05, ANOVA). Error bars represent standarderror of the mean (SE).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4215840&req=5

fig4: SGN survival, total and primary neurite length (NL), andbranching on unpatterned controls and on parallel and 90° anglemicropatterns of HMA-co-HDDMA polymer substrates.(A) SGN survival on unpatterned and micropatterned substrates normalizedto a tissue culture plastic (TCP) control. (B) Total and primary SGNneurite lengths are significantly shorter than corresponding lengthson parallel patterns and unpatterned controls (*p < 0.05, ANOVA). (C–D) Significantly more branches perneurite length and per neurite on 90° angle patterns are observedcompared to neurites on parallel patterns and unpatterned controls(*p < 0.05, ANOVA). Error bars represent standarderror of the mean (SE).
Mentions: To compare differences in neurite behavior on varied directionalsurface cues, dissociated SGNs were cultured on unpatterned controls,unidirectional (parallel) patterns, and repeating angle (90°angle) patterns. Neuronal survival, neurite length, and branchingwere examined as an initial comparison (Figure 4). SGN survival on unpatterned and micropatterned poly(HMA-co-HDDMA) is comparable to survival on a tissue cultureplastic (TCP) control (p > 0.05). Further, nosignificant difference is evident between primary neurite length,i.e. the longest neurite from each neuron, on unpatterned controlscompared to unidirectional micropatterns. Total neurite length, thatis, primary neurite length plus branch length, on unpatterned andunidirectional substrates is also similar. However, both primary andtotal neurite lengths are approximately 20% shorter on repeating anglepatterns, relative to unpatterned and parallel pattern substrates.Neurites on multidirectional surfaces may be shorter due to the presentationof a higher density of potential encounters with feature edges tothe advancing neural growth cone compared to fewer such encounterson smooth or unidirectional surfaces. Each encounter with a featureedge is likely associated with growth cone stalling and the underlyingfocal adhesion formation or removal and cytoskeleton rearrangementevents which reduce the rate of neurite extension.58

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biochemical Engineering, University of Iowa , Iowa City, Iowa 52242, United States, United States.

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.

Show MeSH
Related in: MedlinePlus