Light-Mediated Shape Transformation of a Self-Rolling Nanocomposite Hydrogel Tube

Stiff and strong hydrogel tube with great mechanical properties and high stability in various solutions

Hydrogel tubes are widely used in fields such as artificial blood vessels, drug delivery, biomedical scaffolds and cell adhesion, yet their application is often limited by unsatisfactory mechanical properties and poor stability in various solutions. Herein, a novel hydrogel tube exhibiting a remarkable mechanical performance and stability in various solutions is prepared by introducing a dual physically cross-linked double network (DN) hydrogel matrix. The obtained hydrogel tube can withstand ∼60 N load without fracture and be stretched to over twice its original length before and after immersing in various solutions. The great mechanical properties and stability in various solutions of hydrogel tubes are due to the introduction of a dual physically cross-linked poly(acrylamide-co-acrylic acid)/carboxymethylcellulose sodium/Fe³⁺ DN hydrogel, which possesses high elastic modulus (3.71 MPa), fracture energy (15.4 kJ m^-2), and great stability in various solutions. In addition, the hydrogel tubes with different thickness, diameters, shapes and the multiple branched hydrogel tubes can also be fabricated to enable further functionalization for application requirements. Therefore, this new type of hydrogel tube presents tremendous potential for applications in biomedical and engineering fields.

Promoting Neuronal Outgrowth Using Ridged Scaffolds Coated with Extracellular Matrix Proteins

Spinal cord injury (SCI) results in cell death, demyelination, and axonal loss. The spinal cord has a limited ability to regenerate, and current clinical therapies for SCI are not effective in helping promote neurologic recovery. We have developed a novel scaffold biomaterial that is fabricated from the biodegradable hydrogel oligo(poly(ethylene glycol)fumarate) (OPF). We have previously shown that positively charged OPF scaffolds (OPF+) in an open spaced, multichannel design can be loaded with Schwann cells to support axonal generation and functional recovery following SCI. We have now developed a hybrid OPF+ biomaterial that increases the surface area available for cell attachment and that contains an aligned microarchitecture and extracellular matrix (ECM) proteins to better support axonal regeneration. OPF+ was fabricated as 0.08 mm thick sheets containing 100 μm high polymer ridges that self-assemble into a spiral shape when hydrated. Laminin, fibronectin, or collagen I coating promoted neuron attachment and axonal outgrowth on the scaffold surface. In addition, the ridges aligned axons in a longitudinal bipolar orientation. Decreasing the space between the ridges increased the number of cells and neurites aligned in the direction of the ridge. Schwann cells seeded on laminin coated OPF+ sheets aligned along the ridges over a 6-day period and could myelinate dorsal root ganglion neurons over 4 weeks. This novel scaffold design, with closer spaced ridges and Schwann cells, is a novel biomaterial construct to promote regeneration after SCI.

Recent progress in the shape deformation of polymeric hydrogels from memory to actuation

Shape deformation hydrogels, which are one of the most promising and essential classes of stimuli-responsive polymers, could provide large-scale and reversible deformation under external stimuli. Due to their wet and soft properties, shape deformation hydrogels are anticipated to be a candidate for the exploration of biomimetic materials, and have shown various potential applications in many fields. Here, an overview of the mechanisms of shape deformation hydrogels and methods for their preparation is presented. Some innovative and efficient strategies to fabricate programmable deformation hydrogels are then introduced. Moreover, successful explorations of their potential applications, including information encryption, soft robots and bionomic systems, are discussed. Finally, remaining great challenges including the achievement of multiple stable deformation states and the combination of shape deformation and sensing are highlighted.

Temperature-Responsive, Manipulable Cavitary Hydrogel Containers by Macroscopic Spatial Surface-Interior Separation

Synthetic macroscopic materials transforming from bulk solid or semisolid to a closed structure with inner cavities and distinct outer and inner microstructures are rarely reported. Here, we report an in situ method for directing spatial surface-interior separation from bulk dynamic hydrogels to closed three-dimensional (3D) hydrogel containers with inner cavities via constructing a competitively cross-linking gradient within dynamic hydrogels. The initial cross-linking of phenylboronic acid/catechol complexes is disrupted by stronger ferric ions/catechol associations, generating gradually weakened cross-linking from the outside to the inside. Both stronger cross-linking in the outer shells and sequentially weaker cross-linked interior generated during swelling closed the hydrogel container with a tunable dense outer shell, fluffy inner layer, and cavities in the core. Cellulose nanocrystals could be used to significantly improve the spatial distinction of gradient cross-linking within hydrogels, leading to an even denser outer shell with tunable shell thickness. Moreover, cavitary hydrogel containers with diverse shapes can be programmed by designing the initial shapes of dynamic hydrogels and macroscopic assembly of individual dynamic hydrogels based on their self-healing capability after subsequent surface-interior separation. These cavitary hydrogel containers demonstrate thermal-responsive gate systems with unique sustained release at higher temperature and potential reaction containers for oxygen generation on demand. This facile spatial surface-interior separation strategy for fabricating closed cavity systems has great potential for various applications.