CHAPTER TWO Neuromechanics: From Neurons to Brain Alain Goriely*, Silvia Budday†, Ellen Kuhl{,1 *Mathematical Institute, University of Oxford, Oxford, United Kingdom †Department of Mechanical Engineering, University of Erlangen-Nuremberg, Erlangen, Germany { Departments of Mechanical Engineering and Bioengineering, Stanford University, Stanford, United States 1Corresponding author: e-mail address:
[email protected] Contents 1. Motivation 80 2. Neuroelasticity 82 2.1 Elasticity of Single Neurons 82 2.2 Elasticity of Gray and White Matter Tissue 90 2.3 Elasticity of the Brain 93 3. Neurodevelopment 96 3.1 Growth of Single Neurons 96 3.2 Growth of Gray and White Matter Tissue 103 3.3 Growth of the Brain 106 4. Neurodamage 116 4.1 Neurodamage of Single Neurons 116 4.2 Neurodamage of Gray and White Matter Tissue 119 4.3 Neurodamage of the Brain 126 5. Open Questions and Challenges 128 Acknowledgments 131 Glossary 132 References 133 Abstract Arguably, the brain is the most complex organ in the human body, and, at the same time, the least well understood. Today, more than ever before, the human brain has become a subject of narcissistic study and fascination. The fields of neuroscience, neu- rology, neurosurgery, and neuroradiology have seen tremendous progress over the past two decades; yet, the field of neuromechanics remains underappreciated and poorly understood. Here, we show that mechanical stretch, strain, stress, and force play a critical role in modulating the structure and function of the brain. We discuss the role of neuromechanics across the scales, from individual neurons via neuronal tissue to the whole brain. We review current research highlights and discuss challenges and potential future directions.