Function Of Polymer Composition Research Articles

Tuning Polymer Composition Leads to Activity-Stability Tradeoff in Enzyme-Polymer Conjugates.

Protein-polymer conjugation provides an opportune means to adjust the local environment of proteins and enhance protein stability, performance, and solubility. Although much attention has been focused on tuning protein-polymer interactions, the properties of polymer-modified proteins may also be altered by polymer-polymer interactions. Herein, we sought to better understand the influence of polymer-polymer interactions on Candida rugosa lipase, which was modified with random co-polymers composed of sulfobetaine methacrylate (SBMA) and poly(ethylene glycol) methacrylate (PEGMA). Our findings suggest that there is an apparent activity-stability tradeoff as a function of polymer composition. Specifically, as the ratio of SBMA to PEGMA increased, lipase stability was enhanced, whereas activity decreased. By tuning the monomer ratio, we showed that lipase productivity could be optimized. These findings are discussed in the context of complex enzyme-polymer and polymer-polymer interactions and ultimately may enable more informed conjugate designs and improved enzyme productivity in industrial biotransformations under harsh or extreme conditions.

Development and characterisation of cytocompatible polyester substrates with tunable mechanical properties and degradation rate

Although it has been repeatedly indicated the importance to develop implantable devices and cell culture substrates with tissue-specific rigidity, current commercially available products, in particular cell culture substrates, have rigidity values well above most tissues in the body. Herein, six resorbable polyester films were fabricated using compression moulding with a thermal presser into films with tailored stiffness by appropriately selecting the ratio of their building up monomers (e.g. lactide, glycolide, trimethylene carbonate, dioxanone, ε-caprolactone). Typical NMR and FTIR spectra were obtained, suggesting that the fabrication process did not have a negative effect on the conformation of the polymers. Surface roughness analysis revealed no apparent differences between the films as a function of polymer composition. Subject to polymer composition, polymeric films were obtained with glass transition temperatures from -52 °C to 61 °C; contact angles in water from 81 ° to 94 °; storage modulus from 108 MPa to 2,756 MPa and loss modulus from 8 MPa to 507 MPa (both in wet state, at 1 Hz frequency and at 37 °C); ultimate tensile strength from 8 MPa to 62 MPa, toughness from 23 MJ/m3 to 287 MJ/m3, strain at break from 3 % to 278 %, macro-scale Young's modulus from 110 MPa to 2,184 MPa (all in wet state); and nano-scale Young's modulus from 6 kPa to 15,019 kPa (in wet state). With respect to in vitro degradation in phosphate buffered saline at 37 °C, some polymeric films [e.g. poly(glycolide-lactide) 30 / 70] started degrading from day 7 (shortest timepoint assessed), whilst others [e.g. poly(glycolide-co-ε-caprolactone) 10 / 90] were more resilient to degradation up to day 21 (longest timepoint assessed). In vitro biological analysis using human dermal fibroblasts and a human monocyte cell line (THP-1) showed the potential of the polymeric films to support cell growth and controlled immune response. Evidently, the selected polymers exhibited properties suitable for a range of clinical indications.

Direct ink writing of polycaprolactone / polyethylene oxide based 3D constructs

There has been increasing interest over recent years in the application of three-dimensional (3D) printing technologies in the biomedical field. One such method is Direct Ink Writing (DIW); this approach has the potential advantage of allowing room-temperature deposition of materials, presented as an ink, to build complex architectures. DIW offers the ability to process biomaterials containing temperature-sensitive components. Due to the fabrication principles of DIW, there are specific rheological requirements that the ink must exhibit for the 3D construction. For this reason, hydrogel-based liquid feed stocks have been the focal point of ink development. As a consequence, studies based on inks comprising hydrophobic biomaterials, which are insoluble in water and hence unsuited to the hydrogel approach, have been limited.In this study, we investigate novel inks that utilize polycaprolactone (PCL), a hydrophobic polymer, as the primary constituent by dissolving the polymer in solvent systems based on dichloromethane (DCM) and acetone (ACE). Moreover, polyethylene oxide (PEO) was incorporated into the PCL systems in order to extend the range of hydrophilicity of the systems. The rheological properties of the inks were investigated as a function of polymer composition and solvent system. Woodpile constructs of PCL and PCL/PEO were fabricated using DIW method and were assessed by a series of material characterisation. The type of solvent system had a noticeable impact on the ink rheology, which ultimately affected the surface properties. The incorporation of PEO particularly enhanced the roughness and wettability of the constructs. Our results support the use of DIW as a new means to process hydrophobic polymers for biomedical applications.

Lithium Cycling, Limiting Current, and Electrochemical Characterization in Solid Polymer Electrolytes

Successful prevention of lithium dendrite growth would enable the use of lithium metal as an anode material in next-generation secondary batteries. Mechanically stiff solid polymer electrolytes have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth. A series of diblock copolymers of high modulus and molecular weight were synthesized, and their nanostructures and electrochemical properties were characterized as a function of polymer composition and lithium salt concentration, including measurements of the limiting current. X-ray tomography was used to observe lithium metal plating and cycling through these solid polymer electrolyte membranes under a range of electrochemical conditions. Insight into the interplay between electrochemical and mechanical properties, polymer microstructure, and lithium electrodeposition morphology will aid in the design of next-generation electrolytes.

Effect of Micro fillers on Two Body Abrasive Wear Behavior of Polyamide 66 and Polypropylene (PA66/PP) Blend Based Composites

The hybrid effect of micro fillers on two body abrasive wear behavior of PA66/PP blend based composites is studied. Three composites PA66/PP/MoS2, PA66/PP/MoS2/SiC and PA66/PP/MoS2/SiC/Al2O3 are prepared using melt mix method by twin screw extrusion technique. The test is carried out on a water proof SiC abrasive paper (180 and 320 Grit) for a load of 10 N in multi pass condition. The results revealed that abrasive wear volume is a function of polymer composition, grit size and abrading distance. The effect of interparticulate distance seems to be detrimental to improve abrasive wear resistance. The negative effect of wear is due to the major reduction in ductility of composites which is due to hybrid effect of fillers. The surface counter modification also affects wear behavior. Deep micro grooving, micro cutting and abrasive ploughing are major mechanisms observed during the test. Among the studied micro composites, PA66/PP/MoS2 exhibited better abrasive wear behavior. The abraded surfaces are analyzed by using scanning electron microscope (SEM) photographs

Electrospun poly(dimethyl siloxane)-based meshes as a platform for t cell expansion

Event Abstract Back to Event Electrospun poly(dimethyl siloxane)-based meshes as a platform for t cell expansion Alex Dang1, Sarah E. De Leo1, Danielle R. Bogdanowicz1, Helen H. Lu1 and Lance C. Kam1 1 Columbia University, Biomedical Engineering, United States Introduction: Recent advances in the genetic manipulation of T cells have led to striking successes in immunotherapy of cancer. However, advances in cell production and manufacturing are needed to fully realize the power of this approach. The current gold standard for initiating clinical ex vivo expansion of T cell populations consists of rigid (GPa) polystyrene beads presenting activating antibodies to CD3 and CD28. Recent work by our lab demonstrated that improved human T cell stimulation can be achieved using softer poly(dimethyl siloxane) (PDMS) substrates (~30 kPa – 2 MPa)[1]m[2]. In this report, we leverage this mechanosensing property of T cells in a fiber-based mesh system to improve human T cell expansion on a clinically relevant scale. This format preserves the high surface area provided by beads while reducing the risks associated with incomplete removal of these structures from the final cell product. We herein examine the effect of composition, rigidity, fiber density, and pore size of electrospun polymer fibers on long-term (19 days) T cell expansion on clinically relevant scales. Materials and Methods: Fibrous meshes were synthesized via electrospinning of NuSil MED-4086 PDMS mixed with poly(ε-caprolactone) (PCL) in a 3:1 v/v dichloromethane (DCM) / N,N-dimethylformamide (DMF) solution at 10 – 12 kV onto a grounded collection electrode with a working distance between 10-12 cm. Polymer concentration was varied from 19 to 50% wt/wt. Meshes were coated with goat-anti-mouse IgG linkers followed by a 1:4 ratio of mouse IgG-anti-human CD3 (OKT3) to mouse IgG-anti-human CD28 (9.3) (2 h, 23 °C). Cells were subjected to a carboxy-fluorescein succinimidyl ester (CFSE) assay and seeded at 1 million cells / mL at either small-scale (1 mL) or clinical scale (15-20 mL) volumes. Cell proliferation studies were performed in vitro with human naïve CD4+/CD8+ T cells as previously described[1]. Assays for CD107b expression and IFNγ secretion were performed upon completion of blast phase and in vitro re-stimulation for 4 and 12 hours, respectively. Assays for memory markers CD45RO and CCR7 were performed following re-stimulation. Results and Discussion: Scanning electron microscopy (SEM) revealed tunable pore sizes and fiber densities as a function of polymer composition. Long-term culture for 17-19 days coupled with approximately 9.8 maximum doublings for PDMS/PCL meshes indicated a robust system for expansion of T cells. Expansions on experimental meshes yielded up to 3.2 and 4 times more cells compared to Dynabead® and pure PCL mesh controls, respectively (see fig. 1). Flow cytometry revealed higher levels of proliferation on experimental meshes than on the current gold standard and pure PCL controls. Assays for CD107b / CD45RO / CCR7 expression and IFNγ secretion showed PDMS/PCL mesh-expanded cell activation levels on par with or higher than cells expanded on the current gold standard (see fig. 2). Memory marker analysis revealed high levels of central memory T cells after re-stimulation (data not shown). Conclusion: We have shown that electrospun, antibody-functionalized PDMS/PCL fibrous meshes with microscale diameters and pore sizes can increase T cell proliferation. Cells produced yielded substantially higher population doublings and were shown to have equal or better levels of effector cell function than the current gold standard. This platform holds significant promise in the ex vivo expansion of T cells. National Institutes of Health (R01AI088377); Wallace H. Coulter Foundation; National Science Foundation GRFP; Columbia University Medical Center Flow Cytometry Core

Novel alkyd-type coating resins produced using cationic polymerization

Novel, partially bio-based poly(vinyl ether) copolymers derived from soybean oil and cyclohexyl vinyl ether (CHVE) were produced by cationic polymerization and investigated for application as alkyd-type surface coatings. Three different polymers were produced and cured clear coatings and free films characterized as a function of CHVE comonomer content and curing conditions. CHVE comonomer content was varied at 0, 25, and 50 wt%, and the three different curing conditions were 1 week at room temperature, 120°C for 1 h, and 150°C for 1 h. The results of the study showed that the thermal, mechanical, and physical properties of the coatings produced from these novel polymers varied considerably as a function of polymer composition and cure temperature. Overall, the results suggest a good potential for these novel copolymers to be used for coatings cured by autoxidation. Compared to conventional alkyd resins, which are produced by high temperature melt condensation polymerization, these poly(vinyl ether)s provide several advantages. These advantages include milder, more energy efficient polymer synthesis, elimination of issues associated with gelation during polymer synthesis, production of polymers with well-defined composition and relatively narrow molecular weight distribution, and elimination of film formation and physical property issues associated with entrained monomers, dimers, trimers, etc.

Engineering adhesion to thermoresponsive substrates: effect of polymer composition on liquid-liquid-solid wetting.

Adhesion control in liquid-liquid-solid systems represents a challenge for applications ranging from self-cleaning to biocompatibility of engineered materials. By using responsive polymer chemistry and molecular self-assembly, adhesion at solid/liquid interfaces can be achieved and modulated by external stimuli. Here, we utilize thermosensitive polymeric materials based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x = MEO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y = OEGMA), that is, P(MEO2MAx-co-OEGMAy), to investigate the role of hydrophobicity on the phenomenon of adhesion. The copolymer ratio (x/y) dictates macromolecular changes enabling control of the hydrophilic-to-lipophilic balance (HBL) of the polymer brushes through external triggers such as ionic strength and temperature. We discuss the HBL of the thermobrushes in terms of the surface energy of the substrate by measuring the contact angle at water-decane-P(MEO2MAx-co-OEGMAy) brush contact line as a function of polymer composition and temperature. Solid supported polyelectrolyte layers grafted with P(MEO2MAx-co-OEGMAy) display a transition in the wettability that is related to the lower critical solution temperature of the polymer brushes. Using experimental observation of the hydrophilic to hydrophobic transition by the contact angle, we extract the underlying energetics associated with liquid-liquid-solid adhesion as a function of the copolymer ratio. The change in cellular attachment on P(MEO2MAx-co-OEGMAy) substrates of variable (x/y) composition demonstrates the subtle role of compositional tuning on the ability to control liquid-liquid-solid adhesion in biological applications.

A macromonomer approach to the synthesis of poly(1,1‐bis(ethoxycarbonyl)‐2‐vinyl cyclopropane‐graft‐dimethyl siloxane)

AbstractPoly(1,1‐bis(ethoxycarbonyl)‐2‐vinyl cyclopropane (ECVP)‐graft‐dimethyl siloxane) copolymers were prepared using a macromonomer approach. Poly(dimethyl siloxane) (PDMS) macromonomers were prepared by living anionic polymerization of cyclosiloxanes followed by sequential chain‐end capping with allyl chloroformate. These macromonomers were then copolymerized with ECVP. MALDI‐ToF mass spectrometry and 1H NMR spectroscopy were used to show that the macromonomers had approximately 80% of the end groups functionalized with allyl carbonate groups. Gradient polymer elution chromatography showed that high yields of the graft copolymers were obtained, along with only small fractions of the PECVP and PDMS homopolymers. Differential scanning calorimetry showed that the low glass transition temperature (Tg) of the PDMS component could be maintained in the graft copolymers. However, the Tg was a function of polymer composition and the polymers produced had Tgs that ranged from −50 to −120 °C. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Non-monotonous variation of the LCST of light-responsive, amphiphilic poly(NIPAM) derivatives

The response to light of macromolecules in aqueous media is a significant concern for the design of complex fluids, and (bio)materials imparted with stimuli-triggered properties. It is common knowledge that polymer chains containing photochrome groups can be tailored to undergo a transition between poor and good solvent conditions upon exposure to light, thanks to the photoswitch of the polarity/hydrophobicity of their photochromes. In water, marked photo-responses are typically achieved in the vicinity of the low critical solution temperature (LCST) of polymers. To understand and optimize the variation of the LCST of amphiphilic polymers in response to exposure to UV-visible light, we studied the LCST properties of a homologous set of derivatives of poly(N-isopropylacrylamide). The chains contained a hydrophilic oligo(ethylene oxide) side group (at 20 mol%) and a light-responsive azobenzene introduced at a varying integration level (ranging from 0% to 24 mol%). Turbidity measurements showed that the LCST passes through a minimum value upon increasing the density of the hydrophobic azobenzene. At a low % of azobenzene, the LCST displayed the conventional decrease with increasing hydrophobicity of the polymers, from ca. 56 °C in the absence of azobenzene down to ca. 35 °C for the polymer containing 5 mol% azobenzene. Conversely, beyond 11 mol% azobenzene, the LCST increased upon increasing the hydrophobicity of the polymers, and a “reverse” response to exposure to light was observed. Namely the LCST decreased by up to 5 °C upon the photoconversion of azobenzene from the trans, apolar isomer, to the cis, polar, i.e. more water soluble isomer. This counterintuitive behavior was accompanied by the formation of clusters of chains, whose diameter (∼20 nm) was measured by dynamic light scattering. AFM and UV-visible spectra confirmed the presence of hydrophobic associates between the azobenzene groups. We ascribed the origin of the “reverse” responses to the presence of these clusters. We proposed accordingly a model of the partitioning of azobenzene between water and the hydrophobic core of the clusters, which allowed us to calculate the LCST as a function of polymer composition. Fitting experimental data to the model quantitatively indicated that self-assemblies scavenge the hydrophobic photochromes and in turn tune their contribution to the LCST.

Colloidal phase behavior of pH-responsive, amphiphilic PEGylated poly(carboxylic acid)s and effect on kinetic solubility under acidic conditions

PEGylated poly(carboxylic acid)s, PEG-b-PCAs, were evaluated as additives for solubilized oral formulations of weakly acidic compounds. Micelles of poly(ethylene glycol)-block-poly(acrylic acid), PEG-b-PAA, and poly(ethylene glycol)-block-poly(methacrylic acid), PEG-b-PMAA, were prepared. Fluorescence spectroscopy and dynamic light scattering revealed that both polymers assemble into nanoscopic structures (< 200 nm) in acidic media and exhibit pH-sensitive colloidal phase behavior. Using a solvent evaporation technique, the block copolymers and corresponding PCA homopolymers were incorporated into PEG3350-based solid dispersions. The kinetic solubility profile of a BMS compound, BMS-A (Seq ~ 12.5 μg/mL at pH 1.1) in 0.1 N HCl was monitored as a function of polymer composition. While BMS-A precipitated rapidly in 0.1 N HCl in the absence of PEG-b-PCAs, a supersaturated level of ca. 400 μg/mL was maintained for variable lengths of time in the presence of PEG-b-PCAs. Although the kinetic solubility of BMS-A was also enhanced in the presence of the PCA homopolymers, the relative magnitude and duration of supersaturation as a function of polymer composition suggests that micellar solubilization, rather than specific interaction, contributes to enhanced solubility of BMS-A in 0.1 N HCl. Under acidic conditions, pH-responsive PEG-b-PCAs may offer the kinetic supersaturation necessary to minimize precipitation of compounds which have limited solubility in acidic milieu.

Carboxymethyl Cellulose:Polyvinylamine Complex Hydrogel Swelling

The swelling behavior of the polyelectrolyte complex films made from polyvinylamine (PVAm) or poly(vinylformamide-co-vinylamine) copolymers and carboxymethyl cellulose (CMC) was studied as a function of polymer composition, pH, and salt concentration. Swelling is determined by the balance between ionic cross-link density, opposing swelling, with solvation and Donnan effects promoting swelling. Films containing excess ammonium groups gave the greatest swelling at low pH, whereas excess carboxyl groups enhanced swelling at high pH. Films with balanced charge stoichiometry (CMC:PVAm 3:1 w:w) gave the minimum swelling. High concentrations of sodium chloride increased swelling due to the decomposition (screening) of ionic cross-links, whereas calcium ion decreased swelling possibly because of calcium dicarboxylate cross-links. A simple swelling model based on the ionization behavior of dilute polymers and ionic cross-linking predicted the major swelling behaviors, including the effects of pH and polymer compos...

Optimization of Pressure Response in HPDLC Gratings Based on Polymer Composition

This paper reports on the pressure response of Bragg gratings formed by reflective Holographic Polymer Dispersed Liquid Crystals (HPDLCs) as a function of polymer composition. Pressure response is determined by measuring the variation in reflected wavelength intensity in response to hydrostatic pressure applied parallel to the HPDLC grating vector. The pressure response of di- and tri-functional urethane polymer HPDLCs is reported here. These polymer gratings demonstrate a correlation between pressure response sensitivity and polymer functionality and polymer composition. A maximum response of 1.6 nm of wavelength shift over 20 psi of pressure variation is recorded for a di-functional polymer HPDLC.

Molecular Engineering of Silk-Elastinlike Polymers for Matrix-Mediated Gene Delivery: Biosynthesis and Characterization

The unique advantage of genetic engineering techniques for the design and development of polymers for controlled gene delivery lies in exquisite control over polymer structure. In this article we report the biosynthesis and characterization of a series of new silk-elastinlike protein polymers (SELPs), namely, SELP415K, with larger elastin blocks per monomer unit than SELP47K previously studied for matrix-mediated gene delivery. A new cloning strategy was used, where a block of eight elastin units (8E) was integrated into the existing DNA sequence of SELP47K monomer genes using appropriate restriction endonuclease recognition sites. Following random multimerization, multimer gene segments of desired size were selected, expressed, and purified on Ni-agarose columns. The molecular weight and sequence composition of the purified SELPs were determined by MALDI-TOF and amino acid analysis, respectively. The influence of structural changes on the rheological properties of the polymers was investigated. In addition, hydrogel disks were prepared from 47K and 415K-8mer polymer solutions, and the effects of cure time and environmental conditions on the hydrogel equilibrium swelling ratio as a function of polymer composition were studied. DNA sequencing and agarose gel electrophoresis confirmed the successful cloning of the monomer gene segment of SELP415K consisting of 312 bp. Random concatemerization of SELP415K monomer gene segments resulted in a library of SELP415K multimer sequences of 6, 8, and 10 repeats respectively, each yielding a polymer with exact molecular weight and sequence. Rheometric measurements showed that both complex shear modulus (G*) and gelation point were influenced by polymer composition. Equilibrium swelling studies on hydrogel disks prepared from 47K and 415K-8mer polymer solutions showed that changes in polymer composition resulted in different gelation patterns and increased sensitivity toward changes in temperature and ionic strength but not pH. Together these results demonstrate the potential of recombinant techniques in engineering polymers with defined structures which allows the study of the structural parameters affecting matrix-mediated delivery of genes and bioactive agents.

Solution Properties of Water–Poly(ethylene glycol)–Poly(N-vinylpyrrolidone) Ternary System

Viscosity and density measurements as well as determination of binodal curves were made for a water–PEG–PVP ternary system. In the system, a hydrodynamic interaction parameter Δb23 suggested that a repulsive interaction worked between PEG and PVP molecules and the strength of interaction became strong with increasing molecular weight of the samples. Temperature dependence of partial specific volume v could be explained in terms of the amount of hydrated water attracted by each polymer chain. Molecular weight and temperature dependence of binodal curves were obviously related to those of Δb23. Consequently, it is considered that Δb23 is closely related to the Flory–Huggins interaction parameter χ23. However, binodal curves were only partially consistent with the Flory–Huggins theory for the solvent 1–polymer 2–polymer 3 ternary system. To explain the binodal behavior, χ23 is not only a function of temperature but also a function of polymer-composition as well as that of Δb23. The hydration of each polymer chain relating to interaction parameters χ21 and χ31 is also an important factor for the binodal behavior.

Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties

AbstractA major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three‐dimensional architecture, increased hydrophilicity of poly(lactic‐co‐glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2‐sulfobutyl‐vinyl alcohol) and poly(diethylaminoethyl‐vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge‐containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three‐dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core–corona‐like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged‐groups‐containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic–hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Metal ion-sensitive holographic sensors.

Holographic sensors for Na+ and K+ have been fabricated from crown ethers incorporated into polymeric hydrogels. The methacrylate esters of a homologous series of hydroxyether crown ethers were synthesized and copolymerized with hydroxyethyl methacrylate and the cross-linker ethylene dimethacrylate (3 mol %) to form stable hydrogel films (approximately 10 m thick) containing covalently bound (0-97 mol %) 12-crown-4, 15-crown-5, and 18-crown-6 pendant functionalities. The films were transformed into silver-based volume holograms using a diffusion method coupled with a holographic recording using a frequency-doubled Nd:YAG laser. The resulting holographic reflection spectrum was used to characterize the shrinkage and swelling behavior of the holograms as a function of polymer composition and the nature and concentration of alkali, alkaline earth, and NH4+ ions in the test media. Optimized film compositions containing 50 mol % crown ether showed substantial responses (< or = 200 nm) within 30 s at ion concentrations of < or = 30 mM, which could be rationalized on the basis of the known complexation behavior of the crown ethers. An 18-crown-6 holographic film was shown to be able to quantitate K+ concentrations over the physiologically relevant range. It was virtually unaffected by variations in the Na+ background concentration within the normal physiological variation (approximately 0.13-0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.

Associative phenomena in galactomannan-deacetylated xanthan systems

The interaction between mesquite seed galactomannan (MSG; d-mannose to d-galactose ratio ( M/ G)∼1.1) and deacetylated xanthan (DX) in 5 mM NaCl leading to synergistic gel formation at 25 °C was investigated and compared with the far more studied system made of xanthan and locust bean gum (LBG; M/ G∼3.5). Rheology and differential scanning calorimetry were used to measure temperatures of gel formation and transition enthalpy as a function of polymer composition, while circular dichroism was used to probe the conformation of DX in the LBG–DX system. MSG and DX associate at 25 °C with a well defined stoichiometry of 0.6:1.0 (w/w) at low ionic strength favouring the disordered coil state of DX. When LBG was used in place of MSG in water or 5 mM NaCl, two types of mechanisms of interpolymeric association are envisaged.

Combining molecular and continuum mechanics concepts for constitutive equations of polymer melt flow

Molecular-level modelling of linear viscoelastic properties of a polymer melt is combined with a continuum-based model for the recoverable deformation in domains of fluid in a flow field to predict nonlinear viscoelastic properties. A nonlinear differential constitutive equation is derived, whose parameters are elemental linear viscoelastic properties which can be calculated as a function of polymer composition and environmental conditions. The model is demonstrated by means of examples of important nonlinear effects: recoverable strain and Non-Newtonian shear viscosity, extrudate swell, nonlinear stress relaxation, the onset of shear, and elongational viscosity.

Development of a conducting polymer‐based microelectrode array detection system

AbstractAn individually addressable microelectrode array system has been developed in the course of this work. The performance of this system was investigated using conventional electrochemistry (oxidation/reduction or ferrocene carboxylic acid) to demonstrate that independent potential control and current measurement at each of the array components was possible. The practical utility of this system has been demonstrated using a conducting polymer based microarray detection system subsequent to Ion Chromatography. The detection of simple electroinactive ions (e.g., Cl−, SO42−, K+, NH4+) using the array system was achieved and the response at each of the array components was studied as a function of polymer composition.