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The treatment of oily wastewater remains a technological challenge. Membrane separation methods can offer solutions with high throughput and low operating cost if suitable membranes can be developed. In this work, an electrospun polymer composite membrane containing metal–organic framework (MOF) particles and carbon nanotubes (CNTs) is presented, which performs both high water flux and high separation efficiency. Polyacrylonitrile (PAN), which has excellent fiber-forming properties, is used as the polymer matrix. The MOF zeolitic imidazole framework-8 (ZIF-8) increases membrane hydrophilicity and imparts nanopores. The MOF particles are tightly associated with CNTs, increasing the MOF binding and providing mechanical stability and increased surface area to the composite fiber membrane. The result is a high-flux, high-separation efficiency, and recyclable polyacrylonitrile/zeolitic imidazolate framework-8/carbon nanotube (PAN/ZIF-8/CNT) nanofiber membrane. The membrane has a high water contact angle (WCA > 130°) and exhibits underwater oleophilicity and underoil hydrophobicity. The PAN/ZIF-8/CNT membrane has a hierarchical porous structure of microscale and nanoscale channels, resulting in good porosity that greatly improves oil–water separation performance. The membrane has a high separation flux of 2139 L m–2 h–1 for oil–water emulsion in a gravity-fed apparatus and excellent oil/water separation efficiency (>98.5%). In addition, even under acidic, alkaline, saline, and abrasive conditions, the prepared membrane also exhibits excellent hydrophobic and oleophilic properties. This work offers prospects for water purification and oily wastewater remediation. [ABSTRACT FROM AUTHOR]

Oil pollution has always been an important issue affecting the ecological and residential environment, and the development of a highly efficient oil/water separation membrane has become a hot topic. In this paper, Janus polyacrylonitrile (PAN) nanofiber membranes (PNM) were prepared by co-blending hydrophilic SiO2 nanoparticles, carbon nanotubes (CNTs) doped with PAN (PNM-SiO2 and PNM-CNT, respectively) and then using sequential multilayer electrospinning. The existence of electrostatic mutual gravitational force between SiO2 and CNTs makes the binding between the multilayer membranes exist more firmly, which is conducive to withstand the osmotic pressure brought by the liquid. In addition, Janus PAN membranes have different wetting properties; they have a micro/nanopore structure that forms a permeable channel for liquids, thus enabling efficient separation of water-in-oil and oil-in-water emulsions, which separates oil/water emulsions with flux as high as 2188 L m–2 h–1 and separation efficiency as high as 99.8%. This experiment further develops the application of Janus membranes in oil/water separation. [ABSTRACT FROM AUTHOR]

In this study, we investigated engineered nanoparticle (ENP) release associated with the contamination of personal protective clothing during the simulated motion of the human wearing the ENP-contaminated protective clothing and evaluated the relative ENP retention on the fabric. The release of airborne ENPs can contribute to inhalation exposure, which is the route of exposure of most concern to cause adverse health effects in the pulmonary system. The evaluation focuses on four popular fabric materials making the laboratory coats (cotton, polypropylene, polyester cotton blend, and Tyvek) and three types of ENPs (Al2O3, carbon black (CB), and carbon nanotube (CNT)). The magnitudes of particle contamination and resuspension were investigated by measuring the number concentration increase of airborne particles in sizes of 10 nm to 10 μm and the weight changes on fabric pieces. Collected aerosol particles and contaminated fabric surfaces were further characterized for understanding particle morphology, elements, agglomeration, and surface contamination status. The particle resuspension from the contaminated lab coat fabric was found to vary by the type of fabric material. Cotton fabric showed the highest level of particle resuspension for all three tested ENPs. Data were evaluated to determine the dominant forces responsible for ENP adhesion on the surface of the fabric. Tyvek fabric was determined as the best fabric for trapping Al2O3 and carbon black ENPs, indicating less resuspension of particles, meaning lower subsequent release, but not durable enough to wear for the long term compared with other fabrics. [ABSTRACT FROM AUTHOR]

Eu 3+ -induced polystyrene- co -poly(acrylic acid) aggregates (EIPAs) were synthesized using a self-assembly approach, and their structures and photophysical characteristics were examined to achieve effective monochromatic red emission in polymer light-emitting diodes (PLEDs). By adjusting the monomer ratio in RAFT polymerization, the size of Eu 3+ -induced block copolymer nanoaggregates can be regulated, thereby modulating the luminescence intensity. High-performance bilayer polymer light-emitting devices were fabricated using poly(9,9-dioctylfluorene) (PFO) and 2-( tert -butylphenyl)-5-biphenylyl-1,3,4-oxadiazole (PBD) as the host matrix, with EIPAs as the guest dopant. The devices exhibited narrow red emission at 615 nm with a full width at half-maximum (fwhm) of 15 nm across doping concentrations of 1, 3, 5, and 10 wt %. At a doping concentration of 3 wt %, the device achieved a maximum brightness of 1864.48 cd/m 2 at 193.82 mA/cm 2 and an external quantum efficiency of 3.20% at a current density of 3.5 mA/cm 2 . These results indicate that incorporating polystyrene- co -poly(acrylic acid) with Eu 3+ complexes enhances the excitation and emission intensity, as well as the structural stability of the emitting layer in PLEDs, thereby improving the device performance.

Proteoglycans (PGs) play many important roles in biology, contributing to the mechanical properties of tissues, helping to organize extracellular matrix components, and participating in signaling mechanisms related to mechanotransduction, cell differentiation, immune responses, and wound healing. Our lab has designed two different types of PG mimics: polyelectrolyte complex nanoparticles (PCNs) and PG-mimetic graft copolymers (GCs), both of which are prepared using naturally occurring glycosaminoglycans. This work evaluates the enzymatic stability of these PG mimics using hyaluronidases (I-S, IV-S, and II), chondroitinase ABC, and lysozyme, for PG mimics suspended in solution and adsorbed onto surfaces. Hyaluronan (HA)- and chondroitin sulfate (CS)-containing PG mimics are degraded by the hyaluronidases. PCNs prepared with CS and GCs prepared with heparin are the only CS- and HA-containing PG mimics protected from chondroitinase ABC. None of the materials are measurably degraded by lysozyme. Adsorption to polyelectrolyte multilayer surfaces protects PG mimics from degradation, compared to when PG mimics are combined with enzymes in solution; all surfaces are still intact after 21 days of enzyme exposure. This work reveals how the stability of PG mimics is controlled by both the composition and macromolecular assembly of the PG mimic and also by the size and specificity of the enzyme. Understanding and tuning these degradation susceptibilities are essential for advancing their applications in cardiovascular materials, orthopedic materials, and growth factor delivery applications.

Blood-contacting materials are critical in many applications where long-term performance is desired. However, there are currently no engineered materials used in cardiovascular implants and devices that completely prevent clotting when in long-term contact with whole blood. The most common approach to developing next-generation blood-compatible materials is to design surface chemistries and structures that reduce or eliminate protein adsorption to prevent blood clotting. This work proposes a new paradigm for controlling protein-surface interactions by strategically mimicking key features of the glycocalyx lining the interior surfaces of blood vessels: negatively charged glycosaminoglycans organized into a polymer brush with nanoscale domains. The interactions of two important proteins from blood (albumin and fibrinogen) with these new glycocalyx mimics are revealed in detail using surface plasmon resonance and single-molecule microscopy. Surface plasmon resonance shows that these blood proteins interact reversibly with the glycocalyx mimics, but have no irreversible adsorption above the limit of detection. Single-molecule microscopy is used to compare albumin and fibrinogen interactions on surfaces with and without glycocalyx-mimetic nanostructures. Microscopy videos reveal a new mechanism whereby the glycocalyx-mimetic nanostructures eliminate the formation of fibrin networks on the surfaces. This approach shows for the first time that the nanoscale structure and organization of glycosaminoglycans in the glycocalyx are essential to (i) reduce protein adsorption, (ii) reversibly bind fibrin(ogen), and (iii) inhibit fibrin network formation on surfaces. The insights gained from this work suggest new design principles for blood-compatible surfaces. New surfaces developed using these design principles could reduce risk of catastrophic failures of blood-contacting medical devices.

The endothelial glycocalyx lining the inside surfaces of blood vessels has multiple features that prevent inflammation, blood clot formation, and infection. This surface represents the highest standard in blood compatibility for long-term contact with blood under physiological flow rates. Engineering materials used in blood-contacting biomedical devices, including metals and polymers, have undesirable interactions with blood that lead to failure modes associated with inflammation, blood clotting, and infection. Platelet adhesion and activation are key events governing these undesirable interactions. In this work, we propose a new surface modification to titanium with three features inspired by the endothelial glcyocalyx: First, titanium surfaces are anodized to produce titania nanotubes with high surface area. Second, the nanostructured surfaces are coated with heparin-chitosan polyelectrolyte multilayers to provide glycosaminoglycan functionalization. Third, chitosan is modified with a nitric oxide-donor chemistry to provide an important antithrombotic small-molecule signal. We show that these surfaces are nontoxic with respect to platelets and leukocytes. The combination of glycocalyx-inspired features results in a dramatic reduction of platelet and leukocyte adhesion and platelet activation.

Proteoglycans (PGs) are important glycosylated proteins found on the cell surface and in the extracellular matrix. They are made up of a core protein with glycosaminoglycan (GAG) side chains. Variations in composition and number of GAG side chains lead to a vast array of PG sizes and functions. Here we present a method for the synthesis of proteoglycan-mimetic graft copolymers (or neoproteoglycans) with tunable GAG side-chain composition. This is done using three different GAGs: hyaluronan, chondroitin sulfate, and heparin. Hyaluronan is functionalized with a hydrazide-presenting linker. Either chondroitin sulfate or heparin is grafted by the reducing end on to the hyaluronan backbone through reductive amination. PG mimics with heparin or chondroitin sulfate side chains and four different ratios of GAG side chain result in graft copolymers with a wide range of sizes. The chemistry is confirmed through attentuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and (1)H NMR. Effective hydrodynamic diameter and zeta potential are determined using dynamic light scattering and electrophoretic mobility measurements. Graft copolymers were tested for their ability to bind and deliver basic fibroblast growth factor (FGF-2) to mesenchymal stem cells (MSCs). The chondroitin sulfate-containing graft copolymers successfully deliver FGF-2 to cells from surfaces. The lowest graft density of heparin-containing PG mimic also performs well with respect to growth factor delivery from a surface. This new method for preparation of GAG-based graft copolymers enables a wide range of graft density, and can be used to explore applications of PG mimics as new biomaterials with tunable biochemical and biomechanical functions.

In the design of scaffolds for tissue engineering biochemical function and nanoscale features are of particular interest. Natural polymers provide a wealth of biochemical function, but do not have the processability of synthetic polymers, limiting their ability to mimic the hierarchy of structures in the natural extracellular matrix. Thus, they are often combined with synthetic carrier polymers to enable processing. Demineralized bone matrix (DBM), a natural polymer, is allograft bone with inorganic material removed. DBM contains the protein components of bone, which includes adhesion ligands and osteoinductive signals, such as important growth factors. Herein we describe a novel method for tuning the nanostructure of DBM through electrospinning without the use of a carrier polymer. This work surveys solvents and solvent blends for electrospinning DBM. Blends of hexafluoroisopropanol and trifluoroacetic acid are studied in detail. The effects of DBM concentration and dissolution time on solution viscosity are also reported and correlated to observed differences in electrospun fiber morphology. We also present a survey of techniques to stabilize the resultant fibers with respect to aqueous environments. Glutaraldehyde vapor treatment is successful at maintaining both macroscopic and microscopic structure of the electrospun DBM fibers. Finally, we report results from tensile testing of stabilized DBM nanofiber mats, and preliminary evaluation of their cytocompatibility. The DBM nanofiber mats exhibit good cytocompatibility toward human dermal fibroblasts (HDF) in a 4-day culture; neither the electrospun solvents nor the cross-linking results in any measurable residual cytotoxicity toward HDF.

The direct delivery of growth factors to sites of tissue healing is complicated by their relative instability. In many tissues, the glycosaminoglycan (GAG) side chains of proteoglycans like aggrecan stabilize growth factors in the pericellular and extracellular space, creating a local reservoir that can be accessed during a wound healing response. GAGs also regulate growth factor-receptor interactions at the cell surface. Here we report the development of nanoparticles for growth factor delivery that mimic the size, GAG composition, and growth factor binding and stabilization of aggrecan. The aggrecan-mimetic nanoparticles are easy to assemble, and their structure and composition can be readily tuned to alter their physical and biological properties. We use basic fibroblast growth factor (FGF-2) as a model heparin-binding growth factor, demonstrating that aggrecan-mimetic nanoparticles can preserve its activity for more than three weeks. We evaluate FGF-2 activity by measuring both the proliferation and metabolic activity of bone marrow stromal cells to demonstrate that chondroitin sulfate-based aggrecan mimics are as effective as aggrecan, and heparin-based aggrecan mimics are superior to aggrecan as delivery vehicles for FGF-2.

Polyelectrolyte multilayers using the polycations chitosan and N,N,N-trimethyl chitosan and the polyanions hyaluronan, chondroitin sulfate, and heparin are studied. Chitosan and hyaluronan behave as a weak polycation and weak polyanion, respectively, whereas N,N,N-trimethyl chitosan, chondroitin sulfate, and heparin behave as strong polyelectrolytes. Hydrophilicity is determined by water contact angle measurements and by comparing wet and dry film thickness measurements. Wet thickness is obtained using Fourier transform surface plasmon resonance, whereas dry thickness is obtained through ellipsometry. For the very thin PEMs studied here, the surface hydrophilicity and swelling in water are highly correlated. The multilayer chemistry is assessed by FT-IR and X-ray photoelectron spectroscopy (XPS). FT-IR and XPS provide information about the composition, degree of ionization, and by inference, the ion pairing. We find that hydrophilicity and swelling are reduced when one polyelectrolyte is strong and the other is weak, whereas ion pairing is increased. By this combination of techniques, we are able to compose a unified description of how the PEM swelling is dictated by the ion pairing in thin polysaccharide-based PEMs.

It is generally accepted that both surface chemistry and biochemical cues affect mesenchymal stem cell (MSC) proliferation and differentiation. Several growth factors that have strong influences on MSC behavior bind to glycosaminoglycans in interactions that affect their stability and their biochemical activity. The goal of this work was to develop polysaccharide-based polyelectrolyte multilayers (PEMs) to bind and stabilize growth factors for delivery to MSCs. Using the naturally derived polysaccharides chitosan and heparin, PEMs were constructed on gold-coated glass chips, tissue-culture polystyrene (TCPS), and titanium. PEM construction and basic fibroblast growth factor (FGF-2) adsorption to PEMs were evaluated by Fourier transform surface plasmon resonance, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection absorption spectroscopy. The functional response of bone marrow-derived ovine MSCs to FGF-2 on PEM-coated TCPS and titanium was evaluated in vitro, in the presence and absence of adsorbed fibronectin. The effect of FGF-2 dose and presentation on MSC attachment and proliferation was evaluated using low-serum media, over four days. On PEM-coated TCPS, we found that FGF-2 adsorbed to heparin-terminated PEMs with adsorbed fibronectin induces greater cell density and a higher proliferation rate of MSCs than any of the other conditions tested, including delivery of the FGF-2 in solution, at an optimally mitogenic dose. Cell densities on day four were 1.8 times higher when FGF-2 was delivered by adsorption to the PEM than when FGF-2 was delivered in solution. This system represents a promising candidate for the development of surface coatings that can stabilize and potentiate the activity of growth factors for therapeutic applications. Interestingly, the same effects were not observed when FGF-2 was delivered by adsorption to PEMs on titanium. When the polysaccharide-based PEMs were formed on titanium, the proliferative response of ovine MSCs to adsorbed FGF-2 was not as strong as the response to FGF-2 delivered in solution.

The formation of polyelectrolyte complex nanoparticles (PCN) was investigated at different charge mixing ratios for the chitosan-heparin (chi-hep) and chitosan-hyaluronan (chi-ha) polycation-polyanion pairs. The range of 0.08-19.2 for charge mixing ratio (n(+)/n(-)) was examined. The one-shot addition of polycation and polyanion solutions used for the formation of the PCN permitted formation of both cationic and anionic particles from both polysaccharide pairs. The influence of the charge mixing ratio on the size and zeta potential of the particles was investigated. The morphology and stability of the particles when adsorbed to surfaces was studied by scanning electron microscopy (SEM). For most conditions studied, colloidally stable, nonstoichiometric PCN were formed in solution. However, PCN formation was inhibited by flocculation at charge mixing ratios near 1. When adsorbed to surfaces and dried, some formulations resulted in discrete nanoparticles, while others partially or completely aggregated or coalesced, leading to different surface morphologies.

The goal of this work is to explore the effects of solution ionic strength and pH on polyelectrolyte multilayer (PEM) assembly, using biologically derived polysaccharides as the polyelectrolytes. We used the layer-by-layer (LBL) technique to assemble PEM of the polysaccharides heparin (a strong polyanion) and chitosan (a weak polycation) and characterized the sensitivity of the PEM composition and layer thickness to changes in processing parameters. Fourier-transform surface plasmon resonance (FT-SPR) and spectroscopic ellipsometry provided in situ and ex situ measurements of the PEM thickness, respectively. Vibrational spectroscopy and X-ray photoelectron spectroscopy (XPS) provided details of the chemistry (i.e., composition, electrostatic interactions) of the PEM. We found that when PEM were assembled from 0.2 M buffer, the PEM thickness could be increased from less than 2 nm per bilayer to greater than 4 nm per bilayer by changing the solution pH; higher and lower ionic strength buffer solutions resulted in narrower ranges of accessible thickness. Molar composition of the PEM was not very sensitive to solution pH or ionic strength, but pH did affect the interactions between the sulfonates in heparin and amines in chitosan when PEM were assembled from 0.2 M buffer. Changes in the PEM thickness with pH and ionic strength can be interpreted through descriptions of the charge density and conformation of the polyelectrolyte chains in solution.