Protein and Polysaccharide-Based Fiber Materials Generated from Ionic Liquids: A Review

Abstract

Natural biomacromolecules such as structural proteins and polysaccharides are composed of the basic building blocks of life: amino acids and carbohydrates. Understanding their molecular structure, self-assembly and interaction in solvents such as ionic liquids (ILs) is critical for unleashing a flora of new materials, revolutionizing the way we fabricate multi-structural and multi-functional systems with tunable physicochemical properties. Ionic liquids are superior to organic solvents because they do not produce unwanted by-products and are considered green substitutes because of their reusability. In addition, they will significantly improve the miscibility of biopolymers with other materials while maintaining the mechanical properties of the biopolymer in the final product. Understanding and controlling the physicochemical properties of biopolymers in ionic liquids matrices will be crucial for progress leading to the ability to fabricate robust multi-level structural 1D fiber materials. It will also help to predict the relationship between fiber conformation and protein secondary structures or carbohydrate crystallinity, thus creating potential applications for cell growth signaling, ionic conductivity, liquid diffusion and thermal conductivity, and several applications in biomedicine and environmental science. This will also enable the regeneration of biopolymer composite fiber materials with useful functionalities and customizable options critical for additive manufacturing. The specific capabilities of these fiber materials have been shown to vary based on their fabrication methods including electrospinning and post-treatments. This review serves to provide basic knowledge of these commonly utilized protein and polysaccharide biopolymers and their fiber fabrication methods from various ionic liquids, as well as the effect of post-treatments on these fiber materials and their applications in biomedical and pharmaceutical research, wound healing, environmental filters and sustainable and green chemistry research.

Keywords: biomaterials fabrication; drug delivery; fibers; filtration; green solvents; ionic liquid; polysaccharides; protein; tissue engineering.

Figure 1

Commonly used protein and polysaccharide fiber materials that can be generated from ionic liquids with anions and cations and their natural sources. Protein materials are in red, while polysaccharides are in blue.

Figure 2

Commonly used ionic liquids for fabricating protein and polysaccharide fiber materials.

Figure 3

Examples of electrospinning setups utilized with ionic liquid solvents. (A) Basic horizontal electrospinning setup, with a polymer solution-fed syringe, a high-voltage source and a grounded collector plate. (B) Wet spinning, where fibers are spun into a coagulation bath instead of a grounded collection plate. (A is reproduced with permission from Ref. [154]; Copyright 2014 Elsevier. B is reproduced with permission from Ref. [21]; Copyright 2010 The Royal Society of Chemistry).

Figure 4

SEM images of electrospun nanofibers made from (A) cellulose from [C₂MIM][CH₃CO₂], (B) chitin from [C₂MIM][OAc] and (C) 4.8 wt% and (D) 16.7 wt% cellulose made from [BMIMCl]. (A is used with permission from Ref. [98]; Copyright 2011 The Royal Society of Chemistry. B is used with permission from Ref. [155]; Copyright 2016 European Chemical Societies Publishing. C, D are used with permission from Ref. [99]; Copyright 2018 Elsevier).

Figure 5

SEM images of regenerated cellulose fibers using ionic liquids and a water-based coagulation bath: (A) surface image; (B) cross-section image [100]. (Reproduced with permission from Ref. [100]; Copyright 2018 Wiley).

Figure 6

Water and methanol coagulation agents have different effects on the self-assembly of Thai silk-cellulose polymer composites. (Reproduced with permission from Ref. [102]; Copyright 2017 Elsevier).

Figure 7

(A) Schematic representation of how ion diffusion through a solid electrolyte is dependent on the molecular structure, including the content of various protein structures. (B) Choice of coagulation agent affects the morphology of a polymer, which in turn affects its ability to conduct ions. Results are normalized to the glass transition temperature of each polymer. (Reproduced with permission from Ref. [25]; Copyright 2019 Society of Chemical Industry).

Figure 8

(a,b) Field emission SEM and (c,d) high-resolution TEM micrographs of cellulose/single-walled carbon nanotube (SWCNT) complexes (C/S-Cs) generated through an ionic liquid (BMIMBr); (e) fluorescent microscopy of HeLa cells after 24 h of growth and acridine orange (AO) and ethidium bromide (EB) staining; (f) WST-1 assay shows a significant increase in HeLa cell viability on C/S-C. (Reproduced with permission from Ref. [177]; Copyright 2009 The Royal Society of Chemistry).

Figure 9

Drug release profiles for (A) IBU@2% cellulose micro-nanofibers (CMFs) and IBU@3% CMF matrices compared with a control tea bag and the curve fits based on the Peppas equation for the (B) 2% and (C) 3% samples; (D,E) SEM images of cellulose micro-nanofibers (CMFs) IBU@3% matrices. (Reproduced with permission from Ref. [178]; Copyright 2017 Elsevier).

Figure 10

Cross-section SEM images of (A) cellulose, (B) chitin and (C) cellulose–chitin blend barrier layers prepared by ionic liquid regeneration in 1-ethyl-3-methylimidazolium acetate. Graphs (D–F) show the permeation flux and rejection ratios of (D) cellulose, (E) chitin and (F) chitin-cellulose composite membranes, while (G) compares the distribution of pore sizes in the membranes. (Reproduced with permission from Ref. [179]; Copyright 2011 Elsevier).

Figure 11

(A) A combination of evaporation and freeze crystallization is used to separate and recover ionic liquid mixed with water in this cellulose nanofiber fabrication method. (B) Standard conductivity curves for EMIMAc and EMIMDep used to determine the concentration of ionic liquid in the regenerated solvents. (Reproduced with permission from Ref. [101]; Copyright The Royal Society of Chemistry).