Substrate Modulus Directs Neural Stem Cell Behavior

Abstract

Although biochemical signals that modulate stem cell self-renewal and differentiation were extensively studied, only recently were the mechanical properties of a stem cell's microenvironment shown to regulate its behavior. It would be desirable to have independent control over biochemical and mechanical cues, to analyze their relative and combined effects on stem-cell function. We developed a synthetic, interfacial hydrogel culture system, termed variable moduli interpenetrating polymer networks (vmIPNs), to assess the effects of soluble signals, adhesion ligand presentation, and material moduli from 10-10,000 Pa on adult neural stem-cell (aNSC) behavior. The aNSCs proliferated when cultured in serum-free growth media on peptide-modified vmIPNs with moduli of >/=100 Pa. In serum-free neuronal differentiation media, a peak level of the neuronal marker, beta-tubulin III, was observed on vmIPNs of 500 Pa, near the physiological stiffness of brain tissue. Furthermore, under mixed differentiation conditions with serum, softer gels ( approximately 100-500 Pa) greatly favored neurons, whereas harder gels ( approximately 1,000-10,000 Pa) promoted glial cultures. In contrast, cell spreading, self-renewal, and differentiation were inhibited on substrata with moduli of approximately 10 Pa. This work demonstrates that the mechanical and biochemical properties of an aNSC microenvironment can be tuned to regulate the self-renewal and differentiation of aNSCs.

Regulation of Endothelial Cell Adherence and Elastic Modulus by Substrate Stiffness

“…Mammalian cells are commonly attached to their surrounding cells or extracellular matrix, which are associated with young's modulus in the range of 10 Pa-10 kPa (Yeung et al 2005;Saha et al 2008). Therefore to assess cellular responses, previous studies have used different elastic moduli of substrates (for instance, 42 Pa-280 kPa (Stroka & Aranda-Espinoza 2011a) and 10 Pa-10 kPa (Saha et al 2008)).…”

“…While numerous studies have confirmed the importance of surface chemistry in cell-substrate interaction for successful performance of implants or tissue engineered constructs, the impact of mechanical parameters of substrate, such as stiffness on cellular functions has only been studied in the past 10 years Yeung et al 2005;Saha et al 2008;Byfield et al 2009;Stroka & Aranda-Espinoza 2011a;Yeh et al 2012;Huang et al 2013;Ataollahi et al 2015).…”

Moving from static to dynamic complexity in hydrogel design

“…Additional related studies have emphasized the critical role of hydrogel stiffness in skeletal muscle stem cell self-renewal 12 , neural stem cell behavior 13 and megakaryocyte poiesis 14 . 3D mechanical properties are similarly important in controlling adult stem cell fate in alginate hydrogels incorporating adhesive ligands 4 .…”

Stiffening hydrogels to probe short- and long-term cellular responses to dynamic mechanics

“…In the last decade, matrix stiffness alone has been implicated in regulating cellular functions, such as contraction 3,4 , migration 5,6 , proliferation 7,8 and differentiation 9,10 . With this in mind, a variety of natural (for example, gelatin, collagen) and synthetic (for example, polyacrylamide) polymer systems were used in vitro to mimic the elasticity of native tissues, which varies significantly throughout the body (for example, brain: ~0.2-1 kPa (refs [11][12][13], muscle: ~10 kPa (ref. 10), osteoid: ~30-45 kPa (ref.…”