Caroline L. Schauer

A Review: Electrospinning of Biopolymer Nanofibers and their Applications

Electrospinning is a fabrication technique, which can be used to create nanofibrous non‐wovens from a variety of starting materials. The structure, chemical and mechanical stability, functionality, and other properties of the mats can be modified to match end applications. In this review, an introduction to biopolymers and the electrospinning process, as well as an overview of applications of nanofibrous biopolymer mats created by the electrospinning process will be discussed. Biopolymers will include polysaccharides (cellulose, chitin, chitosan, dextrose), proteins (collagen, gelatin, silk, etc.), DNA, as well as some biopolymer derivatives and composites.

Carboxymethyl Chitosan as a Matrix Material for Platinum, Gold, and Silver Nanoparticles

Carboxymethyl chitosan (CMC) was evaluated for its use in the synthesis and stabilization of catalytic nanoparticles for the first time. Many studies have reported on the ability of chitosan to bind with metal ions and support metal nanoparticles. CMC has a higher reported chelation capacity than chitosan, which has potential implications for improved catalyst formation and immobilization. Platinum, gold, and silver nanoparticles were synthesized in both chitosan and CMC. Particle size, morphology, and aggregation were examined using transmission electron microscopy (TEM). Complexation of nanoparticles was studied through Fourier transform infrared spectroscopy (FTIR). Similar nanoparticle size distributions were observed in the two polymers; however, CMC was observed to have higher rates of aggregation. This indicates that the carboxymethyl groups did not change nanoparticle formation; however, poor cross-linking and a limited anchoring ability of CMC led to the inability to immobilize the catalyst materials effectively.

Color changes in chitosan and poly(allyl amine) films upon metal binding

The intense coloration of butterflies, snakes, hummingbirds and arthropods is due to reflective interference by stacked thin film layers of alternating high and low index of refraction materials. By controlling film thickness, it is also possible to create a single layer film of similar materials with well-defined color. Cross-linked chitosan and poly(allyl amine) hydrochloride thin films were assembled by dropping a dilute solution onto a spinning silicon substrate. Film quality and reproducibility were investigated, as well as the effects of cross-linking. Control of thickness could be used to determine film color. When dipped into a variety of metal ion solutions, the cross-linked films changed in thickness and color.

Biodegradable and conducting hydrogels based on Guar gum polysaccharide for antibacterial and dye removal applications

Conducting hydrogels possessing antibacterial activity were developed using a two-step free-radical aqueous polymerization method to incorporate polyaniline chains into an adsorbent Guar gum/acrylic acid hydrogel network. The material properties of the synthesized samples were characterized using FTIR spectroscopy, thermal analysis and scanning electron microscopy techniques. Conducting hydrogels were tested for antibacterial activities against gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria and demonstrated antibacterial activity. Synthesized hydrogel samples can be potential adsorbent materials for dye removal applications.

Non-covalent crosslinkers for electrospun chitosan fibers

Electrospun chitosan fibers have numerous potential in biomedical, food, and pharmaceutical applications. However, the mats formed are often not chemically stable in a wide range of pHs unless crosslinked. Here, we report on the use of glycerol phosphate (GP), tripolyphosphate (TPP) and tannic acid (TA) as a new set of non-covalent crosslinkers for electrospun chitosan fibers. Crosslinking with or without heat or base activation were performed either prior to (one-step or activated one-step) or after (two-step or activated two-step) electrospinning with either GP or TA. TPP crosslinking was performed in two-step and activated two-step. FESEM, FTIR and UV-vis transmittance at 600 nm were used to determine fiber surface morphology, chemical interactions and solubility in 1M AA (pH 3), water (~pH 6) and 1 M NaOH (pH 13), respectively. Crosslinking of chitosan with GP and TA yields fibers with a mean diameter range of 145-334 nm and 143-5554 nm, respectively. TPP crosslinking produced branched fibers with mean diameters of 117-462 nm range. Two-step chitosan-TA did not dissolve in 1M AA even after 72 h while all chitosan-TPP, activated two-step chitosan-TA and two-step heat activated chitosan-GP fibers survived in water after 72 h.

Thin chitosan films as a platform for SPR sensing of ferric ions

Homogeneous chitosan films of various thicknesses (10-65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe(3+) were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe(3+) of 9.49 x 10(5) M(-1) was determined with a detection limit as low as 250 ppb.

New crosslinkers for electrospun chitosan fibre mats. I. Chemical analysis

Chitosan (CS), the deacetylated form of chitin, the second most abundant, natural polysaccharide, is attractive for applications in the biomedical field because of its biocompatibility and resorption rates, which are higher than chitin. Crosslinking improves chemical and mechanical stability of CS. Here, we report the successful utilization of a new set of crosslinkers for electrospun CS. Genipin, hexamethylene-1,6-diaminocarboxysulphonate (HDACS) and epichlorohydrin (ECH) have not been previously explored for crosslinking of electrospun CS. In this first part of a two-part publication, we report the morphology, determined by field emission scanning electron microscopy (FESEM), and chemical interactions, determined by Fourier transform infrared microscopy, respectively. FESEM revealed that CS could successfully be electrospun from trifluoroacetic acid with genipin, HDACS and ECH added to the solution. Diameters were 267 ± 199 nm, 644 ± 359 nm and 896 ± 435 nm for CS–genipin, CS–HDACS and CS–ECH, respectively. Short- (15 min) and long-term (72 h) dissolution tests (T600) were performed in acidic, neutral and basic pHs (3, 7 and 12). Post-spinning activation by heat and base to enhance crosslinking of CS–HDACS and CS–ECH decreased the fibre diameters and improved the stability. In the second part of this publication, we report the mechanical properties of the fibres.

New crosslinkers for electrospun chitosan fibre mats. Part II: mechanical properties

Few studies exist on the mechanical performance of crosslinked electrospun chitosan (CS) fibre mats. In this study, we show that the mat structure and mechanical performance depend on the different crosslinking agents genipin, epichlorohydrin (ECH), and hexamethylene-1,6-diaminocarboxysulphonate (HDACS), as well as the post-electrospinning heat and base activation treatments. The mat structure was imaged by field emission scanning electron microscopy and the mechanical performance was tested in tension. The elastic modulus, tensile strength, strain at failure and work to failure were found to range from 52 to 592 MPa, 2 to 30 MPa, 2 to 31 per cent and 0.041 to 3.26 MJ m−3, respectively. In general, neat CS mats were found to be the stiffest and the strongest, though least ductile, while CS–ECH mats were the least stiff, weakest, but the most ductile, and CS–HDACS fibre mats exhibited intermediary mechanical properties. The mechanical performance of the mats is shown to reflect differences in the fibre diameter, number of fibre–fibre contacts formed within the mat, as well as varying intermolecular bonding and moisture content. The findings reported here complement the chemical properties of the mats, described in part I of this study.

Selective detection of hexachromium ions by localized surface plasmon resonance measurements using gold nanoparticles/chitosan composite interfaces

Selective removal of hexavalent chromium ions from aqueous solutions using a chitosan/gold nanoparticles composite film was demonstrated. Localized surface plasmon resonance (LSPR) was used to measure the interface stability and detect the incorporation of chromium ions over time. The effects of pH, ethylenediaminetetraacetic acid (EDTA), and various foreign ions such as trivalent chromium, sodium, calcium, phosphate, sulfate and chloride on the adsorption of hexavalent chromium were investigated.

Silver coordination and hydrogen bonds : A study of competing forces

Abstract A series of six bipyridyl ligands, amino-methylpyridine ureas, and oxalamides have been synthesized and complexes with silver salts have been prepared. The 3-pyridyl ligands form silver complexes with a 2:1 ligand to metal ratio: Ag(3u)2BF4, Ag(3o)2BF4, and Ag(3o)2NO3. In these three complexes the ligands form hydrogen-bonded one-dimensional α-networks in accordance with an anticipated design. Each silver cation is four coordinate, bringing four of the α-networks together to form a channeled solid. The anions, NO3− or BF4−, occupy the channels. The 4-pyridyl and 2-pyridyl ligands form silver complexes with a 1:1 ligand-to-metal ratio. The silver cations of the 4-pyridyl ligand complexes, Ag(4u)NO3·H2O and Ag(4o)NO3, have linear two coordination geometries. The 2-pyridyl urea complex, Ag(2u)BF4, features a three-coordinate silver cation with the third bond coming from the oxygen atom of a neighboring urea functionality. This results in a unique ladder structure. The 2-pyridyl oxalamide structure, Ag(2u)BF4, has two-coordinate silver cations and is helical, with a hydrogen bond between neighboring oxalamide functionalities.