3-D structures with tunable porosity for in vitro anisotropic neural models

INTRODUCTION: Organized networks are common in nature, where cells can be found isotropically or anisotropically distributed [1]. While progress was achieved organizing cells in two-dimension (2-D), reported fabrication techniques for aligned networks in 3-D are limited [2]. Here, we describe the use of a biomimetic extra-cellular matrix system to engineer anisotropic in vitro neural models.

METHODS: Polymeric blends of methacrylated gelatin and gellan gum were varied.  Crosslinking and freezing were used as a mechanism to tune pore orientation, pore size and mechanical properties. 3-D neural constructs were developed culturing primary neurons isolated from embryonic mouse cortex. Heterotypic cultures with endothelial cells were performed in a custom microfluidic device.

RESULTS: The degradation rate and mechanical properties were controlled by adjusting the ratio of the polymeric blend, while the 3-D anisotropic structure and its pore size were tuned by varying the temperature of the freezing step and guiding the crosslinking. The top-down fabricated oriented porous structures in a single step process resulted in pore sizes ranging from 18μm to 376μm overcoming the resolution of similar techniques and ranging the size of human neocortex columns. As a model system, neurons were injected in the 3-D oriented porous systems creating 3-D neural anisotropic constructs at a large millimeter scale, which has not been achieved before.  Further, we also aligned primary neurons interfaced with endothelial cells under dynamic conditions controlled by a microfluidic platform designed for co-cultures as an organ-on-chip type model.

DISCUSSION & CONCLUSIONS: The presented system can potentially be used to model several tissues in vitro, especially anisotropic neural tissues characterized by aligned neurites outgrowing from primary neurons. Degradation and mechanical properties were tuned by material engineering techniques with a meaningful neuronal organization. Degenerative conditions in the brain result in degradation, regional stiffness changes, altered neuron networks morphology and ultimately neuronal function loss as observed during aging, and degenerative disorders.

ACKNOWLEDGEMENTS: Funding from FLAD and the FCT grant SFRH/BD/92565/2013.

REFERENCES

[1] Griffith LG & Swartz MA. Nat Rev Mol Cell Biol. 2006; 7:211-224

[2] Bouyer C et al, Adv Mater. 2016; 28:161-167