Localized bimodal response of neurite extensions and structural proteins in dorsal-root ganglion neurons with controlled polydimethylsiloxane substrate stiffness

Abstract

Neuron morphology, adhesion, axon or neurite outgrowth, and neuron-glial cell interactions are influenced by cues from growth factors as well as extracellular matrix molecules linked to the structural scaffolding. Both chemical and physical events affect neural response, as cells respond to soluble, and insoluble chemical cues and neuron-material interface cues including the mechanical properties of the substrate itself. Both types of cues directly influence neural behaviors and the array of structural elements including microtubules, actin filaments, neurofilaments, and filament-associated proteins. In this manuscript, we examine the relationship between the physical substrate environment and neuron morphology in primary dorsal-root ganglia (DRG) neuron co-cultures including glial cells and DRG neurons. By culturing DRGs on polydimethylsiloxane (PDMS) substrates of varying elasticity we found that structural protein responses, neurite extensions, and protein distributions varied between substrates, indicating a physical relationship between cultured surface rigidity and cellular morphology. In addition, we found higher cell densities for both DRG neurons and glial cells grown on semi-rigid polydimethylsiloxane substrates (PDMS ratio of base to curing agent of 35:1) than found on more rigid (15:1) or more flexible (50:1) substrates, indicating a localized bimodal response within a very small difference of elasticity on PDMS. These results imply that physiological relevancy may be best discovered by examining and replicating physical parameters such as tissue stiffness. This work is important in fields including biomaterials, neuron-material interactions, and neuroscience.