Fabrication of Crystalline Gel Fibers By Electrospinning
Authors: Miyazaki Takuya , Mao Yuchun , Gong Jin 
Published: February 2020

The purpose of this research is to develop a new material with a combination of functions of gel and fiber using electrospinning. Gel has a three-dimensional network structure that is usually synthesized by crosslinking the monomers in various ways. It is widely used in hygiene, cosmetic, fragrance, medicine and many others fields. Multi-functions like water absorbability, biocompatibility and flexibility, can be designed and given depending on the chemical structure of monomers and crosslinkers. We developed crystalline gels with high performance via introducing crystalline side chains into the three-dimensional network structure. There are many kinds of crosslinks to form three-dimensional network structure, such as covalent bonds, Coulomb force, hydrogen bonds, coordination bonds, bonds through entanglements, etc. Among these crosslinks, covalent bonds are most suitable for preparing high performance gels. We use photopolymerization to synthesize crystalline gels because it offers advantages including rapid curing rate, minimal heat production and temperature independence, compared to other polymerization techniques. Photopolymerization is a light-based technique that uses to initiate and propagate a polymerization reaction. To create crosslinked gels, at least three reactive components are required: photoinitiator, monomer and crosslinking agent. A photoinitiator creates free radicals upon exposure to specific wavelengths of light, and then initiates polymerization of monomer and crosslinking agent through a photolytic mechanism.

In this research, our aim is to develop a novel gel fiber with a combination of functions of gel and fiber, and ultimately to develop gel nonwoven fabric. The gel nonwoven fabric is expected to have the properties such as water absorbability, biocompatibility, flexibility, and also air permeability, filtration and heat retention. The gel nonwoven fabric could be a promising material for the application in medical treatment due to its air and moisture adjustment function to prevent soaking of wound.

Gel has a three-dimensional network structure, it does not dissolve in an organic solvent to make gel solution, and it is also difficult to be heated to make gel melt. Before gelation, only the droplets but no fibers can be formed via electrospinning because of the too low viscosity of reactive solution. On the other hand, after full gelation, fibers cannot be formed either due to their insolubility and infusibility deriving from three-dimensional network structure. Therefore, the manufacture of gel fibers is difficult.

In this study, electrospinning with pre and post polymerization treatment is used to make gel nonwoven fabric. We propose to use prepolymerized solution with appropriate viscosity to undergo electrospinning. Electrospinning is a method capable of relatively easily preparing nanofibers under a high voltage. An electrospinning device generally consists of a high voltage power supply, a cylinder, and a substrate. The principle of the electrospinning method is that when a positive high voltage is applied to the polymer solution, charges are collected on the droplet surface at the tip of the nozzle and repel each other, and the droplets coming out of the nozzle gradually become conical. When the repulsive force of charge exceeds the surface tension, the solution is jetted straight from the tip of the cone, gradually heading toward the grounded or negatively charged substrate while drawing a spiral. As the ejected solution stream becomes thinner, the surface charge density increases, so the charge repulsion increases and the solution flow is further elongated. Prepolymerized gel solution is set in cylinder, distance between substrate and nozzle is determined, extrusion amount is set, and voltage is given. We run experiments with the procedure of sticking aluminum foil to the metal plate and then spraying the prepolymerizted gel solution onto the board, finally taking aluminum foil off the board and applying postpolymeriation under UV light. SEM observation indicated the fiber diameter is about 400 nm.