Matrices with compliance comparable to that of brain tissue select neuronal over glial growth in mixed cortical cultures

¹ University of Pennsylvania
² Sea Run Holdings

^* To whom correspondence should be addressed. E-mail: pgeorges{at}seas.upenn.edu.

Submitted on August 24, 2005
Revised on October 13, 2005
Accepted on 10 January 2006

	Abstract

Cortical neurons and astrocytes respond strongly to changes in matrix rigidity when cultured on flexible substrates. In this study, existing polyacrylamide gel polymerization methods were modified into a novel method for making substrates capable of engaging specific cell-adhesion receptors. Embryonic cortical dissociations were cultured on polyacrylamide or fibrin gel scaffolds of varying compliance. On soft gels, astrocytes do not spread and have disorganized F-actin compared to the cytoskeletons of astrocytes on hard surfaces. Neurons, however, extend long neurites and polymerize actin filaments on both soft and hard gels. Compared to tissue culture plastic, or stiff gel substrates coated with laminin, on which astrocytes overgrow neurons in mixed cultures, laminin-coated soft gels encouraged attachment and growth of neurons while suppressing astrocyte growth. The growth of astrocytes on soft gels was inhibited even in the absence of mitotic inhibitors normally used to temper the astrocyte population. Dissociated embryonic rat cortices grown on flexible fibrin gels, a biomaterial with potential use as an implant material, display a similar mechano-dependent difference in cell population. Interestingly, the stiffness of materials required for optimal neuronal growth, characterized by an elastic modulus of several hundred Pa is in the range measured for intact rat brain. Together, these data emphasize the potential importance of material substrate stiffness as a design feature in the next generation of biomaterials intended to promote neuronal regeneration across a lesion in the CNS while simultaneously minimizing the ingrowth of astrocytes into the lesion area.

Key Words: Astrocyte, Cytoskeleton, Extracellular Matrix, Mechanotransduction, Neuron

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