Synthesis of bioengineered heparin chemically and biologically similar to porcine-derived products and convertible to low MW heparin.

Heparins have been invaluable therapeutic anticoagulant polysaccharides for over a century, whether used as unfractionated heparin or as low molecular weight heparin (LMWH) derivatives. However, heparin production by extraction from animal tissues presents multiple challenges, including the risk of adulteration, contamination, prion and viral impurities, limited supply, insecure supply chain, and significant batch-to-batch variability. The use of animal-derived heparin also raises ethical and religious concerns, as well as carries the risk of transmitting zoonotic diseases. Chemoenzymatic synthesis of animal-free heparin products would offer several advantages, including reliable and scalable production processes, improved purity and consistency, and the ability to produce heparin polysaccharides with molecular weight, structural, and functional properties equivalent to those of the United States Pharmacopeia (USP) heparin, currently only sourced from porcine intestinal mucosa. We report a scalable process for the production of bioengineered heparin that is biologically and compositionally similar to USP heparin. This process relies on enzymes from the heparin biosynthetic pathway, immobilized on an inert support and requires a tailored N-sulfoheparosan with N-sulfo levels similar to those of porcine heparins. We also report the conversion of our bioengineered heparin into a LMWH that is biologically and compositionally similar to USP enoxaparin. Ultimately, we demonstrate major advances to a process to provide a potential clinical and sustainable alternative to porcine-derived heparin products.

Surface modification of a polyethylene film for anticoagulant and anti-microbial catheter.

A functional anticoagulant and anti-bacterial coating for polyethylene (PE) films is described. The stepwise preparation of this nanocomposite surface coating involves O2 plasma etching of PE film, carbodiimide coupling of cysteamine to the etched PE film, binding of Ag to sulfhydryl groups of cysteamine, and assembly of heparin capped AgNPs on the PE film. The nanocomposite film and its components were characterized by 1H-nuclear magnetic resonance spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and field emission-scanning electron microscopy. The resulting PE films demonstrate anticoagulant activity using a hemoglobin whole blood clotting assay, and anti-bacterial activity against Bacillus cereus 3551 (Gram-positive) and Escherichia coli BL21 (Gram-negative) bacteria. The hydrophilicity of the heparin coated PE was determined by contact angle measurements; and the stability of the nanocomposite film, with respect to Ag leaching, was assessed by atomic absorption spectroscopy.

Can natural fibers be a silver bullet? Antibacterial cellulose fibers through the covalent bonding of silver nanoparticles to electrospun fibers.

Natural cotton was dissolved in a room-temperature ionic liquid 1-ethyl-3-methyl acetate and wet-jet electrospun to obtain nanoscale cotton fibers with a substantially reduced diameter-and therefore an increased surface area-relative to natural cotton fibers. The resulting nano-cotton fibers were esterified with trityl-3-mercaptopropionic acid, which after selective de-tritylation afforded nano-cotton fibers containing reactive thiol functionality. Silver nanoparticles that were covalently attached to these sulfhydryl groups were assembled next. The microstructure of the resulting nanocomposite was characterized, and the antibacterial activity of the resulting nano-cotton Ag-nanoparticle composite was also studied. This nanocomposite showed significant activity against both Gram-negative and Gram-positive bacteria.

Synthesis of Heparin-Immobilized, Magnetically Addressable Cellulose Nanofibers for Biomedical Applications.

Magnetically responsive heparin-immobilized cellulose nanofiber composites were synthesized by wet-wet electrospinning from a nonvolatile, room-temperature ionic liquid (RTIL), 1-methyl-3-methylimidazolium acetate ([EMIM][Ac]), into an aqueous coagulation bath. Superparamagnetic magnetite (Fe3O4) nanoparticles were incorporated into the fibers to enable the manipulation of both dry and wet nanofiber membranes with an external magnetic field. Three synthetic routes were developed to prepare three distinct types of nanocomposite fibers: cellulose-Fe3O4-heparin monofilament fibers, cellulose-Fe3O4-heparin core-shell fibers with heparin covalently immobilized on the fiber surface, and cellulose -Fe3O4 core-shell fibers with heparin physically immobilized on the fiber surface. These nanocomposite fibers were characterized by electron microscopy to confirm their coaxial structure and the fiber dimensions (fiber diameter 0.2-2.0 µm with 0.1-1.1 µm core diameter). Thermogravimetric analysis, liquid chromatography-mass spectrometry, Fourier transform infrared and X-ray diffraction spectroscopy provided detailed compositional analysis for these nanocomposite fibers, confirming the presence of each component and the surface accessibility of the heparin. The anticoagulant activity of immobilized heparin on the nanocomposite fiber surfaces was evaluated and confirmed by antifactor Xa and antifactor IIa assays.

Functionalization of nitrogen-doped carbon nanotubes with gallium to form Ga-CN(x)-multi-wall carbon nanotube hybrid materials.

In an effort to combine group III-V semiconductors with carbon nanotubes, a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes has been developed. With an aqueous solution of a gallium salt (GaI(3)), it was possible to form covalent bonds between the Ga(3+) ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride-carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy.

High-sensitivity bolometers from self-oriented single-walled carbon nanotube composites.

In this work, films of horizontally aligned single-walled carbon nanotubes were thermally and electrically characterized in order to determine the bolometric performance. An average thermal time constant of τ = 420 µs along with a temperature coefficient of resistance of TCR = -2.94% K(-1) were obtained. The maximum voltage responsivity and detectivity obtained were R(V) =230 V/W and D* = 1.22 × 10(8) cm Hz(1/2)/W, respectively. These values are higher than the maximum voltage responsivity (150 V/W) and maximum temperature coefficient of resistance (1.0% K(-1)) previously reported for carbon nanotube films at room temperature. The maximum detectivity was obtained at a frequency of operation of 1.25 kHz.

Electrospun polyvinylpyrrolidone fibers with high concentrations of ferromagnetic and superparamagnetic nanoparticles.

Electrospun polymer fibers were prepared containing mixtures of different proportions of ferromagnetic and superparamagnetic nanoparticles. The magnetic properties of these fibers were then explored using a superconducting quantum interference device. Mixed superparamagnetic/ferromagnetic fibers were examined for mesoscale magnetic exchange coupling, which was not observed as theoretically predicted. This study includes some of the highest magnetic nanoparticle loadings (up to 50 wt%) and the highest magnetization values (≈ 25 emu/g) in an electrospun fiber to date and also demonstrates a novel mixed superparamagnetic/ferromagnetic system.

Electrospinning of nanomaterials and applications in electronic components and devices.

Electrospinning of nanomaterial composites are gaining increased interest in the fabrication of electronic components and devices. Performance improvement of electrospun components results from the unique properties associated with nanometer-scaled features, high specific surface areas, and light-weight designs. Electrospun nanofiber membrane-containing polymer electrolytes show improved ionic conductivity, electrochemical stability, low interfacial resistance, and improved charge-discharge performance than those prepared from conventional membranes. Batteries with non-woven electrospun separators have increased cycle life and higher rate capabilities than ones with conventional separators. Electrospun nanofibers may also be used as working electrodes in lithium-ion batteries, where they exhibit excellent rate capability, high reversible capacity, and good cycling performance. Moreover, the high surface area of electrospun activated carbon nanofibers improves supercapacitor energy density. Similarly, nanowires having quasi-one-dimensional structures prepared by electrospinning show high conductivity and have been used in ultra-sensitive chemical sensors, optoelectronics, and catalysts. Electrospun conductive polymers can also perform as flexible electrodes. Finally, the thin, porous structure of electrospun nanofibers provides for the high strain and fast response required for improved actuator performance. The current review examines recent advances in the application of electrospinning in fabricating electronic components and devices.

Conductive cable fibers with insulating surface prepared by coaxial electrospinning of multiwalled nanotubes and cellulose.

Core-sheath multiwalled carbon nanotube (MWNT)-cellulose fibers of diameters from several hundreds of nanometers to several micrometers were prepared by coaxial electrospinning from a nonvolatile, nonflammable ionic liquid (IL) solvent, 1-methyl-3-methylimidazolium acetate ([EMIM][Ac]). MWNTs were dispersed in IL to form a gel solution. This gel core solution was electrospun surrounded by a sheath solution of cellulose dissolved in the same IL. Electrospun fibers were collected in a coagulation bath containing ethanol-water to remove the IL completely and dried to form core-sheath MWNT-cellulose fibers having a cable structure with a conductive core and insulating sheath. Enzymatic treatment of a portion of a mat of these fibers with cellulase selectively removed the cellulose sheath exposing the MWNT core for connection to an electrode. These MWNT-cellulose fiber mats demonstrated excellent conductivity because of a conductive pathway of bundled MWNTs. Fiber mat conductivity increased with increasing ratio of MWNT in the fibers with a maximum conductivity of 10.7 S/m obtained at 45 wt % MWNT loading.

Noncovalent functionalization as an alternative to oxidative acid treatment of single wall carbon nanotubes with applications for polymer composites.

We have created stable dispersions of single wall carbon nanotubes (SWNTs) in water by employing a noncovalent functionalization scheme that allows carboxylic acid moieties to be attached to the SWNT surface by a pi-pi stacking interaction. Pyrenecarboxylic acid (PCA) is noncovalently attached to the surface of SWNTs and affords highly uniform and stable aqueous dispersions. This method was developed to provide a noncovalent alternative to the commonly used oxidative acid treatment functionalization of carbon nanotubes. This alternative strategy avoids the damage to the carbon nanotube structure inherent to oxidative acid treatments. Carbon nanotubes are commonly functionalized with oxidative acid treatment schemes to create polymer-nanotube composites and improve the adhesion between the polymer and carbon nanotubes. Composites of SWNTs and polycarbonate were prepared and tested to determine the effect of PCA on the adhesion of the SWNTs to the polymer matrix. These tests confirmed that PCA improved the SWNT-polycarbonate adhesion and improved the dispersion of the SWNTs throughout the matrix. This study demonstrates that stable dispersions of SWNTs can be achieved without substantial cutting, introduction of defects, or covalent modification, by employing a simple and effective noncovalent functionalization with PCA.

Heparin-cellulose-charcoal composites for drug detoxification prepared using room temperature ionic liquids.

We report novel heparin-cellulose-charcoal composites prepared using room temperature ionic liquids (RTILs) to enhance the biocompatibility and blood compatibility of activated charcoal beads while decreasing the size of their active pores.