Electrospinning of Cyclodextrin–Pseudopolyrotaxane Nanofibers

Abstract

Cyclodextrins (CDs) are distinctive molecules that can form noncovalent host–guest complexes with a variety of molecules to yield intriguing supramolecular structures. Electrospinning has gained enormous attention since this versatile technique enables production of multifunctional nanofibers made from various polymers, polymer blends, composites, and ceramics. Electrospun nanofibers containing cyclodextrin inclusion complexes are particularly attractive because of the unique properties obtained by combining the large surface area of a polymer nanofiber carrier with the specific chemical structure of the CD complex. Herein we report the first results from electrospinning cyclodextrin inclusion complexes and/or cyclodextrin pseudopolyrotaxanes. Cyclodextrins are cyclic oligosaccharides with a toroidshaped molecular structure consisting of a(1,4)-linked glucopyranose units (Figure 1a). The most common natural CDs have either six, seven, or eight glucopyranose units and are referred to as a-, b-, and g-cyclodextrins, respectively (Figure 1b). The hydrophobic cavity of CDs allows them to form host–guest complexes with various small molecules and macromolecules. The stability of CD complexes depends on many factors such as the size or shape match between host and guest, chemical environment, and the binding forces (e.g., hydrophobic interactions, van der Waals attractions, hydrogen bonding, and electrostatic interactions) between the host CD and guest molecules. Since the physical and chemical properties of incorporated guest compounds can be tailored by CD complexation, CDs are used in a variety of application areas, such as pharmaceuticals (e.g., enhancement of drug solubility and stability, bioavailability, controlled drug delivery, and reduction of drug toxicity), 15] functional food additives (stabilization of volatile or unstable flavors and masking or removal of unwanted tastes and odor), cosmetics and home or personal care (releasing fragrances and masking unpleasant odors), and textiles (stabilization and controlled release of textile additives). CD pseudopolyrotaxanes, formed by threading a polymer chain or long molecule through many CD rings, have fascinating supramolecular structures with unusual properties. It has been shown that CD pseudopolyrotaxanes can be formed with various synthetic polymers, biopolymers, conducting polymers, dyes, polypeptides, proteins, and enzymes, and that the huge variety of supramolecular structures are extremely useful in many diverse areas. The nanostructure or microstructure and the functionality of the guest molecules are altered when encapsulated by CD molecules; furthermore, CD rings assist the stabilization and protection of the guest molecules and can control or sustain their delivery. CDs are natural, nontoxic, and slowly biodegradable, and consequently CD polyrotaxanes are very attractive candidates for smart materials, controlled or sustained delivery systems, sensor devices, molecular switches, or other diagnostic systems. Electrospinning is as a versatile and cost-effective technique for producing multifunctional nanofibers. Nanofibers and their mats have several remarkable characteristics such as large surface area to volume ratios, pore sizes in the nanometer range, unique physical and mechanical properties, and the chemical, physical, and functional properties of the nanofiber surfaces are fairly easy to modify. It has been shown that the very interesting properties and the multifunctionality of the nanofibers make them favorable candidates for use in many areas including biotechnology (tissue engineering, controlled or sustained release systems), textiles (delivery and stabilization of additives) and membranes/filters. The incorporation of CD-pseudopolyrotaxanes into nanofibers is extremely interesting since such the resulting CDcomplex-containing nanowebs will have unique characterFigure 1. a) Chemical structure of a-CD; b) approximate dimensions of g-, b-, and a-CDs; schematic representation of packing structures of c) cage-type and d) channel-type a-CD crystals.