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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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Related in: MedlinePlus

Channel amplitude is modulated by shuttering the UV light sourceat specific time increments. Feature depth for parallel and 90°angle patterns is similar at each exposure. Each point indicates mean± SD.
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fig3: Channel amplitude is modulated by shuttering the UV light sourceat specific time increments. Feature depth for parallel and 90°angle patterns is similar at each exposure. Each point indicates mean± SD.

Mentions: To compare neuralpathfinding on both uni- and multidirectional patterns, microfeatureamplitude was controlled by shuttering the photopolyermization reactionat specific UV exposure times (Figure 3). Polymerizationrate rapidly decreases upon shuttering of the radiation source asno new radicals are formed to initiate propagation reactions and asexisting radicals terminate by combination and disproportionationreactions. Temporal control of the reaction, thus afforded, enableskinetic trapping of specific microchannel amplitudes that allow fordirect comparisons between pattern directionalities. To generate channelamplitudes of 7.4 ± 0.7 μm for both pattern types, UV lightexposure was shuttered at 77 and 85 s for unidirectional and multidirectionalpatterns, respectively. Under the given reaction conditions, parallelpattern amplitude ranged from approximately 1.3 to 8 μm and90° angle pattern amplitude ranged from 2 to 9 μm. Amplitudeprofiles as a function of UV exposure time for both pattern typesare very similar, with slight variations likely being attributableto differences in light diffraction patterns that alter incident lightintensities locally at the substrate surface. Microfeature amplitudeincrease and subsequent decrease occur nearly symmetrically arounda maximum amplitude UV exposure time step. Decreases in amplitudeare likely due to backfilling of masked regions as reactive speciesdiffuse into shadowed areas and as more photons are allowed to reachthe area through light diffraction and internal reflectance withinthe system.


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)

Channel amplitude is modulated by shuttering the UV light sourceat specific time increments. Feature depth for parallel and 90°angle patterns is similar at each exposure. Each point indicates mean± SD.
© Copyright Policy
Related In: Results  -  Collection

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

fig3: Channel amplitude is modulated by shuttering the UV light sourceat specific time increments. Feature depth for parallel and 90°angle patterns is similar at each exposure. Each point indicates mean± SD.
Mentions: To compare neuralpathfinding on both uni- and multidirectional patterns, microfeatureamplitude was controlled by shuttering the photopolyermization reactionat specific UV exposure times (Figure 3). Polymerizationrate rapidly decreases upon shuttering of the radiation source asno new radicals are formed to initiate propagation reactions and asexisting radicals terminate by combination and disproportionationreactions. Temporal control of the reaction, thus afforded, enableskinetic trapping of specific microchannel amplitudes that allow fordirect comparisons between pattern directionalities. To generate channelamplitudes of 7.4 ± 0.7 μm for both pattern types, UV lightexposure was shuttered at 77 and 85 s for unidirectional and multidirectionalpatterns, respectively. Under the given reaction conditions, parallelpattern amplitude ranged from approximately 1.3 to 8 μm and90° angle pattern amplitude ranged from 2 to 9 μm. Amplitudeprofiles as a function of UV exposure time for both pattern typesare very similar, with slight variations likely being attributableto differences in light diffraction patterns that alter incident lightintensities locally at the substrate surface. Microfeature amplitudeincrease and subsequent decrease occur nearly symmetrically arounda maximum amplitude UV exposure time step. Decreases in amplitudeare likely due to backfilling of masked regions as reactive speciesdiffuse into shadowed areas and as more photons are allowed to reachthe area through light diffraction and internal reflectance withinthe system.

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