Three‐Level Hierarchical 3D Network Formation and Structure Elucidation of Wet Hydrogel of Tunable‐High‐Strength Nanocomposites

Abstract

The structural characterization of wet gel state hydrogels at multi‐length scales ranging from nanometers to micrometers is very challenging and rarely reported. Herein, tunable high‐strength nanocomposite hydrogels based on cellulose nanofibers with various cross linkers are synthesized and characterized. Synchrotron tomography and small‐angle X‐ray scattering methods are combined to quantitatively elucidate 3D hierarchically wet gel state network structures, providing an understanding on the structure–properties relationship of hydrogels. The hierarchical 3D network of wet gel demonstrates three levels of structures: 1) the bundle aggregated by cellulose nanofibers; 2) physically crosslinked bundle networks; and 3) fractal‐structure agglomerates composed of aggregated network domains. The finding of fractal agglomerate structures tuned by crosslinker characteristics provides fundamental knowledge to explain a variation of several orders of magnitude of mechanical properties and reveals different formation mechanisms, opening a new and flexible prospect for wet gel state material design and processing control.

Block Sequence Effects on the Self-Assembly Behaviors of Polypeptide-Based Penta-Block Copolymer Hydrogels

“…The ability to measure the morphology of the hydrogel plays a crucial role in optimizing the hydrogel composition and functionality. However, all of the existing characterization methods have inherent limitations in sample preparation, measurement resolution, local variation, and statistical data treatment . Electron microscopy (called the direct method) provides the real space image with resolution up to the submicrometer scale to the nanoscale, but this technique requires a dehydrated gel (dry sample) with a distorted structure and misleading information.…”

“…However, all of the existing characterization methods have inherent limitations in sample preparation, measurement resolution, local variation, and statistical data treatment. 51 Electron microscopy (called the direct method) provides the real space image with resolution up to the submicrometer scale to the nanoscale, but this technique requires a dehydrated gel (dry sample) with a distorted structure and misleading information. The rapid cooling of cryo-SEM and cryo-TEM causes geometry expansion or gel structural change.…”

Injectable Hydrogel Guides Neurons Growth with Specific Directionality

“…The chemical structures of CNF, poly-L-lysine-based, and the crosslinkers (PLL and PLLGA) are shown in Figure 3. The crosslinkers were synthesized in our laboratory accordingly to established methods [45]. The parallel needle walls of a co-injection syringe were used to align the CNF and crosslinker solutions, respectively.…”

“…The chemical structures of CNF, poly-L-lysinebased, and the crosslinkers (PLL and PLLGA) are shown in Figure 3. The crosslinkers were synthesized in our laboratory accordingly to established methods [45]. To determine an appropriate hydrogel composition for neurite growth study, we first considered the biotoxicity of the scaffolds by quantifying cell viability using AlamarBlue assay, a redox indicator for cell proliferation.…”

“…A polarized optical microscope (POM) and transmission X-ray microscope (TXM) were used to analyze the alignment structures of our hydrogels in the micro-and nano-scales, respectively. They are the techniques to examine the morphologies of hydrogels in situ without using high vacuum techniques such as SEM or TEM which would distort the wet gel structures [45]. PC12 cells are regularly used as a model of sympathetic neurons and neuronal differentiation [46].…”