Three-Dimensional Tomography of Cellulose Nanofibers- Polypeptides Nanocomposite Hydrogels

Cellulose nanofiber (CNF) is a promising material in tissue engineering for tunable surface chemistry, robust mechanical strength, excellent biocompatibility, and abundance in nature. Rather than crosslink CNF hydrogel with a multivalent metal cation, we fabricated a CNF hydrogel using a synthetic cationic polypeptide, PLLGA, to enhance its biophysics and biochemistry properties, such as adhesion to biomolecules. In this research, we focused on the microstructure of cellulose nanofiber (CNF) hydrogels crosslinked by either CaCl₂, a metal cation commonly used in literature, or polypeptide (PLLGA). We insight into their microstructure from nanometer to macro-scale using polarized microscopy (POM), scanning electron microscopy (SEM), small angle X-ray scattering spectroscopy (SAXS) and transmission X-ray microscopy (TXM). TXM can also probe the three-dimensional network structure of CNF/CaCl₂ hydrogel in hundreds micrometer scale. Based on SAXS results, we assumed CNFs assemble into bundles after crosslinked by PLLGA. This assumption was confirmed by POM images of CNF/PLLGA hydrogel. We expect this microstructural difference from the crosslinker type will result in a fundamental difference in CNF/PLLGA hydrogel's biophysics properties. Comparing with the conventional method using SEM to study hydrogel structure, TXM can be operated under ambient conditions. Thus, TXM images provide a more realistic understanding to hydrogel network comparing with SEM images because hydrogel samples can be prevented from structural distortion during freeze-drying.