The Mechanical Properties of Spinal Cord Organoids Depend on Their Age and Composition

Spinal cord organoids are valuable human in vitro models of development and disease. Many aspects of cell behavior and function in the spinal cord are regulated by mechanical signals, but the mechanical properties of human spinal cord organoids remain largely uncharacterized.

Here, we quantify the elastic and viscoelastic properties of human spinal cord organoids at four ages (days 51, 87, 132, and 179) using microindentation.

The average effective Young's modulus across all organoids was 731 ± 336 Pa, and stiffness increased with age (R² = 0.49, p < 0.0001). Stress relaxation testing revealed pronounced viscoelasticity, with age-dependent increases most pronounced at short relaxation times and more modest at long relaxation times, suggesting that maturation selectively stiffens the short-time response while leaving long-time equilibrium stiffness largely unchanged. Immunohistological analysis revealed that neurofilament heavy chain (NFH) immunoreactivity increased with age and correlated significantly with effective Young's modulus, while glial fibrillary acidic protein (GFAP) immunoreactivity, despite increasing with age, did not correlate with stiffness, suggesting that neuron maturation contributes to age-dependent stiffening.

These findings establish quantitative mechanical properties for human spinal cord organoids, provide age-specific material parameters for computational modeling and synthetic neural interface design, and inform the design of experiments related to assembloid interactions and durotaxis in the developing central nervous system.