Substrate Curvature Influences the Direction of Nerve Outgrowth

Abstract

Nerve outgrowth in the developing nervous system utilizes a variety of attractive and repulsive molecules found in the extracellular environment. In addition, physical cues may play an important regulatory role in determining directional outgrowth of nervous tissue. Here, by culturing nerve cells on filamentous surfaces and measuring directional growth, we tested the hypothesis that substrate curvature is sufficient to influence the directional outgrowth of nerve cells. We found that the mean direction of neurite outgrowth aligned with the direction of minimum principle curvature, and the spatial variance in outgrowth direction was directly related to the maximum principle curvature. As substrate size approached the size of an axon, adherent neurons extended processes that followed the direction of the long axis of the substrate similar to what occurs during development along pioneering axons and radial glial fibers. A simple Boltzmann model describing the interplay between adhesion and bending stiffness of the nerve process was found to be in close agreement with the data suggesting that cell stiffness and substrate curvature can act together in a manner that is sufficient to direct nerve outgrowth in the absence of contrasting molecular cues. The study highlights the potential importance of cellular level geometry as a fidelity-enhancing cue in the developing and regenerating nervous system.

Controlled cellular orientation on PLGA microfibers with defined diameters

“…On grooved surfaces, Bettinger et al examined the alignment of endothelial cells on patterns with round cross-section and reported that cells oriented along the substrate patterns as spacing decreased from 5 to 2.5 μm (Bettinger et al 2006). On the cylindrical substrates, cultured nerve cells on filamentous substrates and reported that substrate curvature influenced the direction of nerve outgrowth (Smeal et al 2005). However, to our knowledge there has not been a systematic study that analyzed the effects of microfiber diameter in the range of ten to hundreds of micrometers.…”

“…When a cell measured angle θ b at distance b from the center line of fiber radius r, cell orientation θ t=0 at the center line of a fiber is, And the curvature of a cell τ is (Smeal et al 2005;Weisstein 2008…”

“…These reports have observed cell alignment along the fibers. However, many observations were performed on small diameter fibers such as nanofibers that were fabricated by electrospinning Murugan and Ramakrishna 2007;Chew et al 2008;Tian et al 2008), relative to only few studies on individual microfibers (Neumann et al 2003;Smeal et al 2005;Bashur et al 2006). Therefore the ability to engineer biodegradable fibers of defined diameters can be used to systematically study these observations to determine the effects of fiber size on cell alignment.…”

“…A number of previous studies have aimed to analyze cell alignment on fibrous substrates (Neumann et al 2003;Smeal et al 2005;Bashur et al 2006;Murugan and Ramakrishna 2007;Chew et al 2008;Tian et al 2008). These reports have observed cell alignment along the fibers.…”

Phosphate glass fibres and their role in neuronal polarization and axonal growth direction

“…Smeal et al [49] studied the directional growth of DRG neurons on polymeric fibres with diameters ranging between 35 and 500 lm. They found that substrate curvature is sufficient to influ-ence the directional outgrowth of DRG neurites.…”