Gene

Cell biology

Amyotrophic lateral sclerosis

Neurite

Neuroscience

Spinal muscular atrophy

Biology

Microfluidics

Biomedical engineering

Materials science

Neuromuscular junction

Myogenesis

Motor neuron

Biochemistry

Nanotechnology

Spinal cord

Anatomy

Embryonic stem cell

In vitro

Myocyte

Medicine

Biological system

Disease

Pathology

Science Advances

Motor units are the fundamental elements responsible for muscle movement. They are formed by lower motor neurons and their muscle targets, synapsed via neuromuscular junctions (NMJs). The loss of NMJs in neurodegenerative disorders (such as amyotrophic lateral sclerosis or spinal muscle atrophy) or as a result of traumatic injuries affects millions of lives each year. Developing in vitro assays that closely recapitulate the physiology of neuromuscular tissues is crucial to understand the formation and maturation of NMJs, as well as to help unravel the mechanisms leading to their degeneration and repair. We present a microfluidic platform designed to coculture myoblast-derived muscle strips and motor neurons differentiated from mouse embryonic stem cells (ESCs) within a three-dimensional (3D) hydrogel. The device geometry mimics the spinal cord-limb physical separation by compartmentalizing the two cell types, which also facilitates the observation of 3D neurite outgrowth and remote muscle innervation. Moreover, the use of compliant pillars as anchors for muscle strips provides a quantitative functional readout of force generation. Finally, photosensitizing the ESC provides a pool of source cells that can be differentiated into optically excitable motor neurons, allowing for spatiodynamic, versatile, and noninvasive in vitro control of the motor units.

Microfluidic device for the formation of optically excitable, three-dimensional, compartmentalized motor units