Wet spinning and radial self-assembly of a carbohydrate low molecular weight gelator into well organized hydrogel filaments

In this work, we describe how a simple single low molecular weight gelator (LMWG) molecule - N-heptyl-D-galactonamide, which is easy to produce at the gram scale - is spun into gel filaments by a wet spinning process based on solvent exchange. A solution of the gelator in DMSO is injected into water and the solvent diffusion triggers the supramolecular self-assembly of the N-heptyl-D-galactonamide molecules into nanometric fibers. These fibers entrap around 97% of water, thus forming a highly hydrated hydrogel filament, deposited in a well organized coil and locally aligned. This self-assembly mechanism also leads to a very narrow distribution of the supramolecular fiber width, around 150 nm. In addition, the self-assembled fibers are oriented radially inside the wet-spun filaments and at a high flow rate, fibers are organized in spirals. As a result, this process gives rise to a high control of the gelator self-assembly compared with the usual thermal sol-gel transition. This method also opens the way to the controlled extrusion at room temperature of these very simple, soft, biocompatible but delicate hydrogels. The gelator concentration and the flow rates leading to the formation of the gel filaments have been screened. The filament diameter, its internal morphology, the solvent exchange and the velocity of the jet have been investigated by video image analysis and electron microscopy. The stability of these delicate hydrogel ropes has been studied, revealing a polymorphic transformation into macroscopic crystals with time under some storage conditions. The cell viability of a neuronal cell line on the filaments has also been estimated.