Sub-nanoscale free volume and local elastic modulus of chitosan–carbon nanotube biomimetic nanocomposite scaffold-materials by Axpe, E, Bugnicourt, L, Merida, D, Goiriena-Goikoetxea, M, Unzueta, I, Sanchez-Eugenia, R, Garcia, J, Plazaola, F, Contera, S