Axonal growth on surfaces with periodic geometrical patterns

Abstract

The formation of neuron networks is a complex phenomenon of fundamental importance for understanding the development of the nervous system, and for creating novel bioinspired materials for tissue engineering and neuronal repair. The basic process underlying the network formation is axonal growth, a process involving the extension of axons from the cell body towards target neurons. Axonal growth is guided by environmental stimuli that include intercellular interactions, biochemical cues, and the mechanical and geometrical features of the growth substrate. The dynamics of the growing axon and its biomechanical interactions with the growing substrate remains poorly understood. In this paper, we develop a model of axonal motility which incorporates mechanical interactions between the axon and the growth substrate. We combine experimental data with theoretical analysis to measure the parameters that describe axonal growth on surfaces with micropatterned periodic geometrical features: diffusion (cell motility) coefficients, speed and angular distributions, and axon bending rigidities. Experiments performed on neurons treated Taxol (inhibitor of microtubule dynamics) and Blebbistatin (disruptor of actin filaments) show that the dynamics of the cytoskeleton plays a critical role in the axon steering mechanism. Our results demonstrate that axons follow geometrical patterns through a contact-guidance mechanism, in which high-curvature geometrical features impart high traction forces to the growth cone. These results have important implications for our fundamental understanding of axonal growth as well as for bioengineering novel substrates that promote neuronal growth and nerve repair.

Submicron Topographically Patterned 3D Substrates Enhance Directional Axon Outgrowth of Dorsal Root Ganglia Cultured Ex Vivo

“…Besides our DRG ex vivo cultures, another study plated dissociated cortical embryonic rat neurons onto substrates with sine wave-like periodic patterns with 1–6 µm pitch sizes, which is slightly different to our square wave-like patterns. The dissociated neurons produced axons that were tightly aligned with 4 µm and 5 µm pitch sizes, and that alignment was abolished by taxol and blebbistatin treatments that disrupted the cytoskeleton [ 31 ]. Taken together, this suggests that there may be an ideal “sweet spot” when designing biomaterials with ridge and groove feature sizes to optimally direct nerve regeneration by controlling cytoskeleton arrangements.…”

“…Indeed, nano- and micropatterned substrates have been used as tools to guide axons along a defined path and demonstrate their capacity to respond to topographical features in their microenvironments [ 28 , 29 , 30 , 31 , 32 ]. However, exactly how axons respond to biophysical information and the dynamics of axonal movement are still poorly understood.…”

Combined Traction Force–Atomic Force Microscopy Measurements of Neuronal Cells

“…The brain tissue isolation protocol was approved by Tufts University Institutional Animal Care and Use Committee in accordance with the NIH Guide for the Care and Use of Laboratory Animals. For cell dissociation and culture, we used established protocols reported in our previous work [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Cortical neurons were cultured on poly acrylamide (PAA) substrates coated with poly D-lysine (PDL), at a density of 5000 cells/cm 2 .…”

“…To date, despite important recent advances, researchers still lack a fully quantitative description of growth dynamics, which incorporates the physical interactions between the neuron and the surrounding environment. In particular, there are still numerous basic unanswered questions about the mechanisms that determine neuron biomechanical behavior, such as neuron-substrate interactions, cellular response to various external cues, and how these interactions affect the formation and function of neuronal networks [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. A detailed knowledge of these interactions is essential, because these stimuli together control the wiring of neuronal circuits and their function, from growth to homeostasis and cellular health.…”

The Role of Tissue Geometry in Spinal Cord Regeneration

“…What is clear from the available literature is that different surface topographies result in differences in both the rate and pattern of neurite outgrowth, even when no specific attempt has been made to alter the chemical composition of the surface. Another consideration that may have relevance to the development of prosthetic materials are the constraints imposed by intrinsic factors such as the energy costs and biomechanical limits associated with neurite turning and branching [182][183][184].…”