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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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Schematic of micropatternfabrication process for neural pathfinding studies. (A) Photopolymerizablemonomer is selectively exposed to UV light through a photomask resultingin micropatterns across the substrate surface. (B,C) Representationof transparent (white) and reflective (black) band size of the photomasks.(D,E) White light optical profiling 3D images of parallel and 90°angled micropatterned HMA-co-HDDMA substrates representing100 μm2 areas and channel amplitudes of 7 μm.
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fig1: Schematic of micropatternfabrication process for neural pathfinding studies. (A) Photopolymerizablemonomer is selectively exposed to UV light through a photomask resultingin micropatterns across the substrate surface. (B,C) Representationof transparent (white) and reflective (black) band size of the photomasks.(D,E) White light optical profiling 3D images of parallel and 90°angled micropatterned HMA-co-HDDMA substrates representing100 μm2 areas and channel amplitudes of 7 μm.

Mentions: Accordingly, unidirectional parallelline-space gratings were made by masking the prepolymer formulationwith Ronchi rule optics that have alternating transparent (glass)and reflective (chrome) bands (Figure 1). Eachband is a straight line with a width of 25 μm and extends acrossthe entire length of the mask. Multidirectional or angled patternswere generated by masking the reaction with repeating reflective angles.Masking the photopolymerization reaction in this manner locally modulatespolymerization kinetics,48,49 which results in microscaleperiodic raised and depressed features that match the width of thephotomask bands. Surface depressions occur beneath reflective bandsand raised features appear beneath transparent bands. Final thin filmsurface topography is composed of uniform, gradually transitioningmicrofeatures that contrast with stark, on–off type featuresgenerated via multistep lithographic etching methods.33,41,50 The gradual transitions betweenmicrofeatures are likely due to the diffraction of light as it passesthrough microscale photomask bands51,52 and due todiffusion of monomer toward reactive regions as demonstrated in interferencepatterning holographic photopolymerization.53 Once the light source is shuttered, the reaction rate rapidly decreasesas no new radicals are generated via photon absorption.54 Uni- and multidirectional micropatterns weremeasured and characterized by white light interferometry (Figure 1 D–E). As expected, micropattern spacingclosely matches photomask band spacing.


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)

Schematic of micropatternfabrication process for neural pathfinding studies. (A) Photopolymerizablemonomer is selectively exposed to UV light through a photomask resultingin micropatterns across the substrate surface. (B,C) Representationof transparent (white) and reflective (black) band size of the photomasks.(D,E) White light optical profiling 3D images of parallel and 90°angled micropatterned HMA-co-HDDMA substrates representing100 μm2 areas and channel amplitudes of 7 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig1: Schematic of micropatternfabrication process for neural pathfinding studies. (A) Photopolymerizablemonomer is selectively exposed to UV light through a photomask resultingin micropatterns across the substrate surface. (B,C) Representationof transparent (white) and reflective (black) band size of the photomasks.(D,E) White light optical profiling 3D images of parallel and 90°angled micropatterned HMA-co-HDDMA substrates representing100 μm2 areas and channel amplitudes of 7 μm.
Mentions: Accordingly, unidirectional parallelline-space gratings were made by masking the prepolymer formulationwith Ronchi rule optics that have alternating transparent (glass)and reflective (chrome) bands (Figure 1). Eachband is a straight line with a width of 25 μm and extends acrossthe entire length of the mask. Multidirectional or angled patternswere generated by masking the reaction with repeating reflective angles.Masking the photopolymerization reaction in this manner locally modulatespolymerization kinetics,48,49 which results in microscaleperiodic raised and depressed features that match the width of thephotomask bands. Surface depressions occur beneath reflective bandsand raised features appear beneath transparent bands. Final thin filmsurface topography is composed of uniform, gradually transitioningmicrofeatures that contrast with stark, on–off type featuresgenerated via multistep lithographic etching methods.33,41,50 The gradual transitions betweenmicrofeatures are likely due to the diffraction of light as it passesthrough microscale photomask bands51,52 and due todiffusion of monomer toward reactive regions as demonstrated in interferencepatterning holographic photopolymerization.53 Once the light source is shuttered, the reaction rate rapidly decreasesas no new radicals are generated via photon absorption.54 Uni- and multidirectional micropatterns weremeasured and characterized by white light interferometry (Figure 1 D–E). As expected, micropattern spacingclosely matches photomask band spacing.

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