4D Printing of Robust Hydrogels Consisted of Agarose Nanofibers and Polyacrylamide

Hydrogels combined with complex 3D shapes and robust mechanical properties are extremely desired soft platforms in the fields of biomaterials, recently, 4D printing has been developed to be further shaped to form required patterns. On the basis of the excellent thixotropy of Laponite and the thermal-reversible sol–gel transition of agarose and easy formation of nanofibers below 35 °C, a 4D printing hydrogel (4D Gel) was fabricated by in situ polymerizing acrylamide in the agarose matrix containing Laponite. The experimental results demonstrated that Laponite played an important role in the improvement of 4D printing, such as endowing the ink with shear-thinning behavior to extrude easily and excellent shape stability after printing. The mechanical properties of 4D Gel were unexpectedly higher than those of both agarose and polyacrylamide hydrogels. The 4D Gel showed the ability to further transform its shapes, and was used successfully to construct a whalelike hydrogel, which opened mouth and cocked tail by treating with an external force and then cooling, as well as the octopus like hydrogel with waved tentacles to seem to “come alive”. This work opened a new avenue for creating more complex architectures than 3D with excellent properties, which is important in the macromolecule fields for the wide applications

High-Strength Films Consisted of Oriented Chitosan Nanofibers for Guiding Cell Growth

Chitosan has biocompatibility and biodegradability; however, the practical use of the bulk chitosan materials is hampered by its poor strength, which can not satisfy the mechanical property requirement of organs. Thus, the construction of highly strong chitosan-based materials has attracted much attention. Herein, the high strength nanofibrous hydrogels and films (CS-E) were fabricated from the chitosan solution in LiOH/KOH/urea aqueous system via a mild regenerating process. Under the mild condition (ethanol at low temperature) without the severe fluctuation in the system, the alkaline-urea shell around the chitosan chains was destroyed, and the naked chitosan molecules had sufficient time for the orderly arrangement in parallel manner to form relatively perfect nanofibers. The nanofibers physically cross-linked to form CS-E hydrogels, which could be easily oriented by drawing to achieve a maximum orientation index of 84%, supported by the scanning electron microscopy and two-dimensional wide-angle X-ray diffraction. The dried CS-E films could be bent and folded arbitrarily to various complex patterns and shapes. The oriented CS-E films displayed even ultrahigh tensile strength (282 MPa), which was 5.6× higher than the chitosan films prepared by the traditional acid dissolving method. The CS-E hydrogels possessed hierarchically porous structure, beneficial to the cell adhesion, transportation of nutrients, and removal of metabolic byproducts. The cell assay results demonstrated that the CS-E hydrogels were no cytotoxicity, and osteoblastic cells could adhere, spread, and proliferate well on their surface. Furthermore, the oriented CS-E hydrogels could regulate the directional growth of osteoblastic cells along the orientation direction, on the basis of the filopodia of the cells to extend and adhere on the nanofibers. This work provided a novel approach to construct the oriented high strength chitosan hydrogels and films

Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers

Mechanically strong cellulose fibers spun with environmentally friendly technology have been under tremendous consideration in the textile industry. Here, by inducing the nanofibrous structure formation, a novel cellulose fiber with high strength has been designed and spun successfully on a lab-scale spinning machine. The cellulose–NaOH–urea solution containing 0.5 wt % LiOH was regenerated in 15 wt % phytic acid/5 wt % Na₂SO₄ aqueous solution at 5 °C, in which the alkali–urea complex as shell on the cellulose chain was destroyed, so the naked stiff macromolecules aggregated sufficiently in a parallel manner to form nanofibers with apparent average diameter of 25 nm. The cellulose fibers consisting of the nanofibers exhibited high degree of orientation with Herman’s parameter of 0.9 and excellent mechanical properties with tensile strength of 3.5 cN/dtex in the dry state and 2.5 cN/dtex in the wet state, as well as low fibrillation. This work provided a novel approach to produce high-quality cellulose multifilament with nanofibrous structure, showing a great potential in the material processing