Analysis of polydisperse polymer adsorption on porous cellulose fibers.

The adsorption of cationic water-soluble polymers onto negatively charged porous wood pulp fibers is an essential aspect of papermaking. Adsorption data can be displayed as a direct plot of the amount adsorbed, Γ, versus the amount of polymer added or as an isotherm plot showing the amount adsorbed versus the residual unadsorbed polymer. In either data presentation, the analysis is more transparent if the units of each axis are the same (e.g., mg/g or meq/g), giving dimensionless slopes. Values for Γmax, ΓI, f I , and Γme can be extracted from many isotherms where: Γmax is the maximum capacity of the fibers to adsorb polymer; ΓI is the y-axis isotherm intercept and gives the maximum dose that can be fully adsorbed; f I is the slope of the direct plot at ΓI, and f I is the mass fraction of the added polymer that can access interior (pore) surfaces; and, Γme is the saturated amount of polymer adsorbed on exterior surfaces. Additionally, the molecular weight distribution of the adsorbing polymer in conjunction with the adsorption isotherm can be used to estimate the molecular weight distributions of adsorbed polymer on interior and exterior fiber surfaces as functions of the polymer dose.

Low Molecular Weight Shuttle Molecules Enhance Polychloramide Antimicrobial Activity.

Investigated were the influences of succinimide (SI), 5,5-dimethylhydantoin (DMH), and 3-(hydroxymethyl)-5,5-dimethylhydantoin (HDMH) on the biocidal activity of chlorinated, water-soluble polyamide prepared by the reaction of isopropylamine with poly(styrene-alt-maleic anhydride). The resulting polymer was a negatively charged, water-soluble polymer bearing a carboxylic acid and an isopropylamide moiety on nearly every repeat unit. Subsequent treatment with NaOCl chlorinated the polymers to up to 4.4% Cl while inflicting some polymer chain scission. SI, DMH, or HDMH increased the biocidal activity of polychloramides toward planktonic Escherichia coli and Staphylococcus aureus. Independent solution studies confirmed that oxidative chlorine spontaneously transferred from aqueous polychloramides to small molecules. We concluded that SI, DMH, and HDMH acted as shuttles that extracted oxidative Cl from the polymer chloramides and transported oxidative Cl more efficiently to microbial surfaces. Succinimide was the most effective shuttle. These results warn that some low molecular weight soluble molecules in antimicrobial testing solutions may exaggerate the effectiveness of the polymer or immobilized antimicrobial agents.

Purification of phage for therapeutic applications using high throughput anion exchange membrane chromatography.

As cases of multidrug resistant bacterial infections increase, scientists and clinicians around the world are increasingly turning to bacteriophages as alternatives to antibiotics. Even though our understanding of phage has increased significantly since the early days of its discovery, over a century ago, the currently used tools and technologies for phage purification for therapeutic applications are severely limited. Bacteriophages are produced by bacterial cultures, and impurities such as endotoxins must therefore be removed before clinical use. We present an anion exchange bind-and-elute membrane chromatographic method for purifying T7 bacteriophage from Escherichia coli culture supernatant that removes undesirable impurities, while ensuring a high viable phage count in the purified product. Our method does not involve the use of chemicals such as organic solvents and caesium chloride that could typically leave residual toxicity in the final product. It also does not require expensive equipment, such as an ultracentrifuge. Using our method, that is based on an in-house designed membrane module, 65% of viable T7 phage was recovered, and up to 94% endotoxins could be removed. The method, which took approximately 15 min, is rapid and scalable, and produces quite pure bacteriophage samples in a single step. It therefore potentially represents a major improvement over the status quo, and shows the way ahead for streamlining phage manufacturing for therapeutic use.

Impacts of non-microbial soils on polychloramide disinfectants.

The presence of some nonmicrobial chemicals and surfaces, herein called "soils", are known to degrade the performance of biocides, and biocidal assays often include mixtures of materials to mimic the effects of soils. We hypothesized that water-soluble anionic polychloramide biocides were less sensitive to soil interference than cationic polymeric biocides. The relationships between soil composition and antimicrobial polymer biocidal activity were compared for an anionic polychloramide, a cationic polychloramide, and a cationic poly(quaternary ammonium) biocide. The nanoscale soil models individually investigated were polyacrylic acid (PAA), cellulose nanocrystals (CNCs), and bovine serum albumin. The low molecular weight model soils were ammonium chloride, glycine, and succinimide. Three types of soil impacts were identified: 1) sequestration, whereby the soil physically inhibited transport of the biocide to microbes; 2) extraction, whereby the soil reduced or extracted oxidative chlorine, decreasing or eliminating the oxidative chlorine strength; and 3) extraction whereby the biocidal activity increases in the presence of a low molecular weight chemical that carries oxidative Cl from the polymer to the microbes. PAA and CNCs inhibit cationic biocides by sequestration but have little impact on anionic polychloramide. Glycine and BSA extract oxidative chlorine, lowering the biocidal activity of the anionic and cationic polychloramides while not impacting the poly(quaternary ammonium) biocide. Finally, the presence of succinimide increased bacteria deactivation of both anionic and cationic polychloramides. We propose that succinimide extracts oxidative chlorine from the polychloramides and transports it to the bacteria.

Optimization of fluid flow in membrane chromatography devices using computational fluid dynamic simulations.

Flow uniformity within the device is critically important in membrane chromatography. Recent studies have shown that the design of the device has a significant impact on flow uniformity, and thereby on separation efficiency. The main premise of this work is that computational fluid dynamics (CFD) could serve as a fast and inexpensive tool for preliminary optimization of the design of a membrane chromatography device. CFD also helps in identifying factors that affect flow uniformity. In this paper, CFD is used to compare the fluidic attributes of conventional membrane chromatography devices such as the stacked disc and radial flow devices with those of more recently developed ones such as the different versions of the laterally-fed membrane chromatography (LFMC) device. These are compared based on pulse tracer solute dispersion, which is a useful metric for measuring flow uniformity, and is thereby a good predictor of chromatographic separation performance. The poor separation performance typically observed with conventional membrane chromatography devices could be attributed to the high degree of solute dispersion within these devices. CFD is then used to analyze the impact of factors such as membrane aspect ratio, and channel dimensions on the performance of z2-laterally-fed membrane chromatography (z2LFMC) devices. The results discussed in the paper demonstrate that CFD could indeed serve as a powerful optimization and performance prediction tool for membrane chromatography.

Modeling the Impact of Polychloramide Solution Properties on Bacterial Disinfection Kinetics.

Anionic water-soluble polychloramide biocides are of interest because, compared to conventional cationic antimicrobial polymers, anionic biocides are less likely to be sequestered or deactivated by contact with non-microbial soil. Although electrostatics can prevent anionic polymers from adsorbing on microbes, water-soluble polychloramides appear to transfer oxidative chlorine during transient contacts between polymer chains and microbe surfaces. The Chick-Watson model of disinfection kinetics has been modified to account for the contributions of polychloramide molecular weight (MW) and the polychloramide configuration in solution estimated from the overlap concentration, C*, below which dilute polymer chains exist as discrete objects in solution. The key assumption in the modeling was that the transfer rate of oxidative chlorine from polychloramide chains to microbe surfaces impacts the disinfection kinetics. Because both C* and MW are measurable, the polymer-modified Chick-Watson (PCW) model has one less unknown parameter than the two-parameter Chick-Watson equation. The PCW model predicts that lower MW polymers are more effective biocides compared with high MW counterparts. Additionally, polymers with more compressed configurations in solution are more effective biocides. Experimental evidence supports these conclusions. Based on the estimated time scale of bacteria/polymer collisions compared with disinfection kinetics, arguments are made that bacteria surfaces must be contracted many times by polychloramide chains to achieve sufficient Cl transfer to deactivate bacteria.

Water-soluble anionic polychloramide biocides based on maleic anhydride copolymers.

Our goal was to develop film-forming polymers to extend the antimicrobial lifetimes of cleaned and disinfected surfaces. Antimicrobial polymers were prepared by first reacting poly(ethylene-alt-maleic anhydride) with isopropylamine, partially consuming the anhydride groups, followed by hydrolysis to give water-soluble, highly anionic polyamide PC3. Chlorination with NaOCl gave PC3Cl with oxidative chlorine contents up to 9 wt%. Dried, 5 µm thick, PC3Cl films, gave log 4 reductions in the concentration of Escherichia coli or Staphylococcus aureus exposed to films. A unique feature of the maleic anhydride copolymer platform was the ability to form covalent grafts to surfaces via anhydride reactions. PC3 solution was impregnated into cellulosic filter paper, heated to form ester linkages with cellulose, followed by chlorination with sodium dichloroisocyanurate dihydrate giving grafted PC3Cl. The treated paper (0.3 wt% PC3Cl) gave a log 4 reduction of E. coli concentration in 30 min.

High Yield Poly(ethylene-alt-maleic acid) Grafting to Wood Pulp while Minimizing Fiber/Fiber Wet Adhesion.

Heating bleached kraft pulps treated with poly(ethylene-alt-maleic acid) (PEMAc) can lead to high yields of carboxylated polymer grafted to fibers. However, in many cases, the cured, dry pulp cannot be effectively repulped (redispersed in water) because the wet strength is too high. Impregnation with PEMAc solutions at pH 4 followed by high temperature (120-180 °C), catalyst-free curing for short times can give fixation yields >85% while maintaining repulpability. The combination of high fixation yields with low wet strength is possible because the extent of curing required for high grafting yields is less than the curing requirement for high wet strength. Two challenges in moving this technology to practicable applications are (1) identifying the optimum laboratory pulp curing conditions and (2) translating laboratory curing conditions to industrial processes. A modeling tool was developed to meet these challenges. The model is based on the observation that for curing conditions giving high fixation yields the wet tensile indices of grafted pulp sheets showed a power-law dependence on the ßΓ product where ß is the conversion of the succinic acid moieties in PEMAc to the corresponding succinic anhydride groups in the curing step and Γ is the amount of polymer applied to the pulp. For two PEMAc molecular weights and two pulp types, the power-law slopes were 0.6; however, the pre-exponential terms depended upon the specific polymer and pulp type combination. We propose that the relationships between the wet tensile index and ßΓ, from polymer-treated, laboratory pulp handsheets, can be used to predict if proposed curing conditions for larger-scale processes will produce a repulpable product.

Preventing the release of copper chlorophyllin from crop spray deposits on hydrophobic surfaces.

The chlorophyll derivative copper chlorophyllin and related chlorins have promise as environmentally friendly agricultural chemicals, however, spray application is hindered by the propensity of dried spray deposits to wash off leaf surfaces during rain or irrigation. HYPOTHESIS: Polyelectrolyte complexes formed between anionic carboxymethyl cellulose and cationic polyamidoamine-epichlorohydrin can prevent the release of copper chlorophyllin from dried spray deposits on leaf surfaces when exposed to water. EXPERIMENTS: Sessile drops on parafilm and containing polyelectrolyte complex and copper chlorophyllin or Brilliant Sulfaflavine, an anionic water-soluble dye, were dried to form deposits that were physical models for crop spray drop deposits on hydrophobic leaf surfaces. Larger buffer drops were placed on the dried deposits and the release of copper chlorophyllin or the dye were measured. FINDINGS: Copper chlorophyllin showed some immediate (burst) release upon exposure to buffer whereas the remainder was immobilized on the parafilm. By contrast, Brilliant Sulfaflavine displayed rapid release following square root time dependence, typical of a diffusion-controlled process. The unusual behavior of copper chlorophyllin is attributed to the presence of CuChl nanoparticles when dispersed in water. The nanoparticles are encased in the polyelectrolyte complex that adheres to parafilm. The fraction of the added copper chlorophyllin lost in the burst release can be controlled by varying the polyelectrolyte complex composition and concentration.

Challenges to Achieving Strong but Fully Degradable Adhesive Joints between Wet Cellulose Surfaces.

The dramatic loss of strength upon exposure to water is one of the challenges preventing the widespread substitution of plastic packaging with paper and paperboard. Although treatment with conventional wet strength resins and other adhesive polymers can strengthen wet paper, it is at the expense of green credentials, including easy recycling or rapid composting. The goal of this work was to demonstrate the adhesive requirements for strong, wet cellulose-cellulose joints that can be recycled easily because the joint strength can be destroyed by the presence of a weak reducing agent. Cellulose membrane surfaces were first treated with a bound layer of carboxymethyl cellulose, modified to have covalently tethered hydrazide groups. Joints were fabricated by laminating two hydrazide-modified membranes with a polymeric adhesive bearing aldehyde functionality. Aldehydes spontaneously condense with hydrazide to give hydrazone bonds. When the adhesive was oxidized dextran, the wet laminates had an intermediate strength. Upon exposure to a reducing agent, the joint strength was reduced to nearly zero because every hydrazone moiety connecting two cellulose surfaces included a cleavable disulfide linkage. By contrast, glyoxalated cationic polyacrylamide gave very strong wet joints. However, the wet adhesion was dominated by polyelectrolyte complexation, and the presence of hydrazone linkages had little influence on the wet adhesion. We conclude that robust joint degradability will require cleavable linkages in the adhesive backbone while minimizing polyelectrolyte complexation.

Deposited Nanoparticles Can Promote Air Clogging of Piezoelectric Inkjet Printhead Nozzles.

Piezoelectric inkjet printing is susceptible to printhead clogging when printing with inks that contain dispersed particles. This paper investigates the mechanisms by which 28-530 nm nanoparticle dispersions induce printhead clogging without forming large aggregates or thick deposited layers on printhead surfaces. Printing experiments were combined with nanoparticle deposition studies and with experiments where inks were pumped through printheads at a constant flow rate with a syringe pump. Submonolayer coverages of hydrophobic cationic polystyrene nanoparticles adhering to printhead surfaces promote rapid clogging by trapped air that enters from the nozzle opening. We propose that the deposited particles distort the shape of the ink/air meniscus, possibly causing air entrainment, and promote air bubble adhesion to the interior printhead surfaces. The printer's purge-blot cleaning procedure removes air clogs, but the clogs quickly reform when printing is resumed because the adsorbed nanoparticles are not removed by the cleaning procedure. Nondepositing anionic hydrophobic nanoparticles cause much less clogging, possibly because of filtration of trace large aggregates. Colloidal stability is a necessary but not sufficient criterion for ink dispersions; the ink particles must not adsorb onto the printhead surfaces. Thus, alternate surface chemistries for the printhead and ink particle surfaces may be required to print hydrophobic ink materials.

Choosing mineral flotation collectors from large nanoparticle libraries.

Polystyrene nanoparticles can promote froth flotation of mineral particles if the nanoparticles are sufficiently hydrophobic and are colloidally stable in the high ionic strength solutions typical of commercial flotation operations. A library of 80 unique polystyrene nanoparticle types was prepared with click chemistry and used to determine if particles that were sufficiently hydrophilic to be colloidally stable in high ionic strength and high pH solutions, were also capable of promoting flotation. The conflicting requirements of colloidal stability and hydrophobicity can be achieved in 9 mM sodium carbonate, a very challenging environment. Instead of testing all 80 samples with laborious flotation testing, automated assays measuring colloid stability and nanoparticle hydrophobicity were employed. The colloid stability assay measured the critical coagulation concentrations (CCC). Nanoparticle hydrophobicity was characterized by water contact angle, measurements (CA). A smaller cohort of the most promising nanoparticle candidates for detailed flotation testing were identified by mapping nanoparticle properties on the CA versus CCC plain - a "Flotation Domain Diagram". We believe that this work was the first time that combinatorial synthesis and high throughput screening have been used in the development of flotation chemicals. Finally, based on the accumulated evidence, effective nanoparticle flotation collectors are likely to be ∼50 nm in diameter, with a soft hydrophobic polymer shell and with surface functional group densities in the order of magnitude of 0.1 nm-2.

Relating Redox Properties of Polyvinylamine-g-TEMPO/Laccase Hydrogel Complexes to Cellulose Oxidation.

The structure and electrochemical properties of adsorbed complexes based on mixtures of polyvinylamine-g-TEMPO (PVAm-T) and laccase were related to the ability of the adsorbed complexes to oxidize cellulose. PVAm-T10 with 10% of the amines bearing TEMPO moieties (i.e., DS = 10%), adsorbed onto gold sulfonate EQCM-D sensor surfaces giving a hydrogel film that was 7 nm thick, 89% water, and encasing laccase (200 mM) and TEMPO moieties (33 mM). For DS values >10%, all of the TEMPOs in the hydrogel film were redox-active in that they could be oxidized by the electrode. With hydrogel layers made with lower-DS PVAm-Ts, only about half of the TEMPOs were redox-active; 10% DS appears to be a percolation threshold for complete TEMPO-to-TEMPO electron transport. In parallel experiments with hydrogel complexes adsorbed onto regenerated cellulose films, the aldehyde concentrations increased monotonically with the density of redox-active TEMPO moieties in the adsorbed hydrogel. The maximum density of aldehydes was 0.24 µmol/m2, about 10 times less than the theoretical concentration of primary hydroxyl groups exposed on crystalline cellulose surfaces. Previous work showed that PVAm-T/laccase complexes are effective adhesives between wet cellulose surfaces when the DS is >10%. This work supports the explanation that TEMPO-to-TEMPO electron transport is required for the generation of aldehydes necessary for wet adhesion to PVAm.

Hydrazide-Derivatized Microgels Bond to Wet, Oxidized Cellulose Giving Adhesion Without Drying or Curing.

Hydrazide-derivatized poly(N-isopropylacrylamide-co-acrylic acid) microgels gave strong adhesion to wet, TEMPO oxidized, regenerated cellulose membranes without a drying or heating step. Adhesion was attributed to hydrazone covalent bond formation with aldehyde groups present on the cellulose surfaces. This is one of only three chemistries we have found that gives significant never-dried adhesion between wet cellulose surfaces. By contrast, for cellulose joints that have been dried and heated before wet testing, the hydrazide-hydrazone chemistry offers no advantages over standard paper industry wet strength resins. The design rules for the hydrazide-microgel adhesives include: cationic microgels are superior to anionic gels; the lower the microgel cross-link density, the higher the adhesion; longer PEG-based hydrazide tethers offer no advantage over shorter attachments; and, adhesion is independent of microgel diameter. Many of these rules were in agreement with predictions of a simple adhesion model where the microgels were assumed to be ideal springs. We propose that the unexpected, high cohesion between neighboring microgels in multilayer films was a result of bond formation between hydrazide groups and residual NHS-carboxyl esters from the preparation of the hydrazide microgels.

Mineral-mineral particle collisions during flotation remove adsorbed nanoparticle flotation collectors.

Flotation of 43µm diameter, hydrophilic glass beads with hydrophobic cationic polystyrene nanoparticle flotation collectors revealed that bead-bead collisions during conditioning and flotation caused the irreversible abrasion of the adsorbed nanoparticles. The abraded particles were present in the suspension as large aggregates. Nanoparticle abrasion explains why small polystyrene particles are more effective than larger ones, and why, much higher dosages of larger nanoparticles are required for the same flotation performance. These behaviors also were demonstrated with a phenomenological model of the abrasion dynamics.

Automating multi-step paper-based assays using integrated layering of reagents.

We describe a versatile and simple method to perform sequential reactions on paper analytical devices by stacking dry pullulan films on paper, where each film contains one or more reagents or acts as a delay layer. Exposing the films to an aqueous solution of the analyte leads to sequential dissolution of the films in a temporally controlled manner followed by diffusive mixing of the reagents, so that sequential reactions can be performed. The films can be easily arranged for lateral flow assays or for spot tests (reactions take place sequentially in the z-direction). We have tested the general feasibility of the approach using three different model systems to demonstrate different capabilities: 1) pH ramping from low to high and high to low to demonstrate timing control; 2) rapid ready-to-use two-step Simon's assays on paper for detection of drugs of abuse utilizing a 2-layer stack containing two different reagents to demonstrate the ability to perform assays in the z-direction; and 3) sequential cell lysing and colorimetric detection of an intracellular bacterial enzyme, to demonstrate the ability of the method to perform sample preparation and analysis in the form of a spot assay. Overall, these studies demonstrate the potential of stacked pullulan films as useful components to enable multi-step assays on simple paper-based devices.

Redox Properties of Polyvinylamine-g-TEMPO in Multilayer Films with Sodium Poly(styrenesulfonate).

Layer-by-layer (LbL) assemblies of polyvinylamine with grafted TEMPO moieties (PVAm-T) with sodium polystyrenesulfonate (PSS) were prepared on gold-sulfonate surfaces, and the redox properties were measured by cyclic voltammetry. LbL compositions were probed by quartz crystal microbalance (wet) and ellipsometric (dry) film measurements. Approximately 30% of the TEMPO moieties in the LbL assemblies were redox-active when the total TEMPO coverage was varied up to 6 µmol/m2, by either varying the TEMPO content in PVAm-T or by varying the number of LbL bilayers. Three non-redox-active PVAm/PSS blocking bilayers were required to prevent the electrode from oxidizing PVAm-T in the exterior LbL layer. This suggests significant intermixing between the layers in the LbL film. In addition to contributing to the small but growing body of work on redox polymers based on grafted TEMPO, this work serves as a reference point for understanding the redox properties of colloidal PVAm-T-laccase complexes in future work.

Stable Aqueous Foams from Cellulose Nanocrystals and Methyl Cellulose.

The addition of cellulose nanocrystals (CNC) greatly enhanced the properties of methylcellulose (MC) stabilized aqueous foams. CNC addition decreased air bubble size, initial foam densities and drainage rates. Mixtures of 2 wt % CNC + 0.5 wt % MC gave the lowest density foams. This composition sits near the onset of nematic phase formation and also near the overlap concentration of methylcellulose. More than 94% of the added CNC particles remained in the foam phase, not leaving with the draining water. We propose that the nanoscale CNC particles bind to the larger MC coils both in solution and with MC at the air/water interface, forming weak gels that stabilize air bubbles. Wet CNC-MC foams were sufficiently robust to withstand high temperature (70 °C for 6 h) polymerization of water-soluble monomers giving macroporous CNC composite hydrogels based on acrylamide (AM), 2-hydroxyethyl methacrylate (HEMA), or polyethylene glycol diacrylate (PEGDA). At high temperatures, the MC was present as a fibrillar gel phase reinforced by CNC particles, explaining the very high foam stability. Finally, our CNC-MC foams are based on commercially available forms of CNC and MC, already approved for many applications. This is a "shovel-ready" technology.

Rapid Development of Wet Adhesion between Carboxymethylcellulose Modified Cellulose Surfaces Laminated with Polyvinylamine Adhesive.

The surface of regenerated cellulose membranes was modified by irreversible adsorption of carboxymethylcellulose (CMC). Pairs of wet CMC-modified membranes were laminated with polyvinylamine (PVAm) at room temperature, and the delamination force for wet membranes was measured for both dried and never-dried laminates. The wet adhesion was studied as a function of PVAm molecular weight, amine content, and deposition pH of the polyelectrolyte. Surprisingly the PVAm-CMC system gave substantial wet adhesion that exceeded that of TEMPO-oxidized membranes with PVAm for both dried and never-dried laminates. The greatest wet adhesion was achieved for fully hydrolyzed high molecular weight PVAm. Bulk carboxymethylation of cellulose membranes gave inferior wet adhesion combined with PVAm as compared to CMC adsorption which indicates that a CMC layer of the order of 10 nm was necessary. There are no obvious covalent cross-linking reactions between CMC and PVAm at room temperature, and on the basis of our results, we are instead attributing the wet adhesion to complex formation between the PVAm and the irreversibly adsorbed CMC at the cellulose surface. We propose that interdigitation of PVAm chains into the CMC layer is responsible for the high wet adhesion values.

A Colloidal Stability Assay Suitable for High-Throughput Screening.

A library of 32 polystyrene copolymer latexes, with diameters ranging between 53 and 387 nm, was used to develop and demonstrate a high-throughput assay using a 96-well microplate platform to measure critical coagulation concentrations, a measure of colloidal stability. The most robust assay involved an automated centrifugation-decantation step to remove latex aggregates before absorbance measurements, eliminating aggregate interference with optical measurements made through the base of the multiwell plates. For smaller nanoparticles (diameter <150 nm), the centrifugation-decantation step was not required as the interference was less than with larger particles. Parallel measurements with a ChemiDoc MP plate scanner gave indications of aggregation; however, the results were less sensitive than the absorbance measurements.