Mechanical and Viscoelastic Properties of Cellulose Nanocrystals Reinforced Poly(ethylene glycol) Nanocomposite Hydrogels

Abstract

The preparation and mechanical properties of elastomeric nanocomposite hydrogels consisting of cellulose nanocrystals (CNCs) and poly(ethylene glycol) (PEG) are reported. The aqueous nanocomposite CNC/PEG precursor solutions covalently cross-linked through a one-stage photocross-linking process. The mechanical properties of nanocomposite hydrogels, including Young's modulus (E), fracture stress (σ), and fracture strain (ε), were measured as a function of CNC volume fraction (φCNC, 0.2-1.8%, v/v) within polymeric matrix. It was found that the homogeneously dispersed nanocomposite hydrogels can be prepared with φCNC being less than 1.5%, whereas the heterogeneous nanocomposite hydrogels were obtained with φCNC being higher than 1.5%. The nanocomposite hydrogels exhibited higher strengths and flexibilities when compared with neat PEG hydrogels, where the modulus, fracture stress, and fracture strain enhanced by a factor of 3.48, 5, and 3.28, respectively, over the matrix material alone at 1.2% v/v CNC loading. Oscillatory shear data indicated the CNC-PEG nanocomposite hydrogels were more viscous than the neat PEG hydrogels and were efficient at energy dissipation due to the reversible interactions between CNC and PEG polymer chains. It was proposed that the strong gel viscoelastic behavior and the mechanical reinforcement were related to "filler network", where the temporary interactions between CNC and PEG interfered with the covalent cross-links of PEG.

Inelastic behaviour of bacterial cellulose hydrogel: In aqua cyclic tests

“…Frensemeier et al [18] also reported that a release of water was a critical deformation mechanism in compressive behaviour, regarding it as the main event to cause plastic deformation. Although the latter is considered to be a permanently irreversible process, a self-recovery phenomenon was reported by Yang et al [19], confirming the crucial role of reversible sacrificial hydrogen bonds in the deformation behaviour of nanocomposite hydrogels.…”

“…A high content of interstitial water is in the space between fibre layers (Fig. 1c), and it can be easily squeezed out [19,28]. The weak cross-links are insufficient to support layers of fibres in re-absorption of squeezed water, leading to poor resilience in compression at all force levels (Fig.…”

“…The effect of microfibrils on tensile behaviour of BC hydrogels was discussed by Frensemeier et al [18]; they also considered the influence of an irreversible process of water squeezing in tensile deformation. The failure of cross-links, not leading to crack propagation, was of importance for the overall high-level ductility of such materials, resulting in the release of potential energy and plastic deformation [11,19]. Due to external tension, fibrils reorient themselves along a loading direction and reorganize their positions [12,13,16,20].…”

Enhanced Mechanical Properties in Cellulose Nanocrystal–Poly(oligoethylene glycol methacrylate) Injectable Nanocomposite Hydrogels through Control of Physical and Chemical Cross-Linking

“…Of note, the ultra-high CNC loading PO 100 -4.95 hydrogel has a 35-fold higher G' than the control PO 100 -0 hydrogel, which for tissue engineering applications would mechanically match much stiffer tissues including cartilage or pre-calcified bone to a degree not possible without the use of the CNC nanophase. 61 As such, the dramatic increase in mechanical performance shown here (35-fold increase in modulus with < 5 wt % CNCs) is the largest improvement reported to date compared with other injectable/minimally invasive PEG-based hydrogels and is achieved by simple mixing of native CNCs into the gel matrix without the need for CNC surface modification.…”

Stable, self-healing hydrogels from nanofibrillated cellulose, poly(vinyl alcohol) and borax via reversible crosslinking

“…Nanocellulose derivatives have readily been utilised in hydrogel preparation (6)(7)(8)(9), primarily to impart mechanical reinforcement into the hydrogel but also to encourage crosslinking and provide stimuli-responsive behaviour. Amongst nanocellulosic materials, nanofibrillated cellulose (NFC) is a promising choice for hydrogel material (10)(11)(12)(13).…”