Theoretical and experimental quantification of the role of diffusive chemogradients on neuritogenesis within three-dimensional collagen scaffolds

A critical challenge to regenerating close mimics of native axonal pathways under chronic neurodegenerative disease or injury conditions is the inability to stimulate, sustain and steer neurite outgrowth over a long distance, until they reach their intended targets. Understanding neurite outgrowth necessitates quantitative determination of the role of molecular gradients on growth cone navigation under dynamic physiological conditions. High-fidelity biomimetic platforms are needed to computationally and experimentally acquire and analyze spatiotemporal molecular gradient evolution and the growth cone response across multiple conditions along this gradient pathway. In this study, we utilized a simple microfluidic platform in which diffusive gradients were generated within a 3-D porous scaffold in a defined and reproducible manner. The platform's characteristics (spatiotemporal gradient, steepness, diffusion time, etc.) were precisely quantified at every specified location within the scaffold. Using this platform, we show that the cortical neurite response within 3-D collagen scaffolds, at both the cellular and molecular level, is extremely sensitive to subtle changes in localized concentration and gradient steepness of IGF-1 within that region. This platform could also be used to study other biological processes such as morphogenesis and cancer metastasis, where chemogradients are expected to significantly regulate the outcomes. Results from this study might be of tremendous use in designing biomaterial scaffolds for neural tissue engineering, axonal pathway regeneration under injury or disease, and in formulating targeted drug-delivery strategies.