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PubMed1984

Monomer-polymer equilibria in the axon: direct measurement of tubulin and actin as polymer and monomer in axoplasm.

The monomer-polymer equilibria for tubulin and actin were analyzed for the cytoskeleton of the squid giant axon. Two methods were evaluated for measuring the concentrations of monomer, soluble (equilibrium) polymer, and stable polymer in extruded axoplasm. One method, the Kinetic Equilibration Paradigm ( KEP ), employs the basic principles of diffusion to distinguish freely diffusible monomer from proteins that are present in the form of polymer. The other method is pharmacological and employs either taxol or phalloidin to stabilize the microtubules and microfilaments, respectively. The results of the two methods agree and demonstrate that 22-36% of the tubulin and 41-47% of the actin are monomeric. The in vivo concentration of monomeric actin and tubulin were two to three times higher than the concentration required to polymerize these proteins in vitro, suggesting that assembly of these proteins is regulated by additional mechanisms in the axon. A significant fraction of the polymerized actin and tubulin in the axoplasm was stable microtubules and microfilaments, which suggests that the dissociation reaction is blocked at both ends of these polymers. These results are discussed in relationship to the axonal transport of the cytoskeleton and with regard to the ability of axons to change their shape in response to environmental stimuli.

Actins↗
PubMed1998

Comparative histological evaluation of new tyrosine-derived polymers and poly (L-lactic acid) as a function of polymer degradation.

Previous studies demonstrated that poly(DTE carbonate) and poly (DTE adipate), two tyrosine-derived polymers, have suitable properties for use in biomedical applications. This study reports the evaluation of the in vivo tissue response to these polymers in comparison to poly(L-lactic acid) (PLLA). Typically, the biocompatibility of a material is determined through histological evaluations as a function of implantation time in a suitable animal model. However, due to changes that can occur in the tissue response at different stages of the degradation process, a fixed set of time points is not ideal for comparative evaluations of materials having different rates of degradation. Therefore the tissue response elicited by poly(DTE carbonate), poly(DTE adipate), and PLLA was evaluated as a function of molecular weight. This allowed the tissue response to be compared at corresponding stages of degradation. Poly(DTE adipate) consistently elicited the mildest tissue response, as judged by the width and lack of cellularity of the fibrous capsule formed around the implant. The tissue response to poly(DTE carbonate) was mild throughout the 570 day study. However, the response to PLLA fluctuated as a function of the degree of degradation, exhibiting an increase in the intensity of inflammation as the implant began to lose mass. At the completion of the study, tissue ingrowth into the degrading and disintegrating poly(DTE adipate) implant was evident while no comparative ingrowth of tissue was seen for PLLA. The similarity of the in vivo and in vitro degradation rates of each polymer confirmed the absence of enzymatic involvement in the degradation process. A comparison of molecular weight retention, water uptake, and mass loss in vivo with two commonly used in vitro systems [phosphate-buffered saline (PBS) and simulated body fluid (SBF)] demonstrated that for the two tyrosine-derived polymers the in vivo results were equally well simulated in vitro with PBS and SBF. However, for PLLA the in vivo results were better simulated in vitro using PBS.

Animals↗
PubMed1993

Osteoblast-like cell (MC3T3-E1) proliferation on bioerodible polymers: an approach towards the development of a bone-bioerodible polymer composite material.

An osteogenic cell line (MC3T3-E1) was used to study the potential of bioerodible polymers and ceramics to support osteoblast growth for a proposed bone-polymer composite for skeletal tissue repair. MC3T3-E1 cells were seeded on to 50:50 poly(lactide-co-glycolide), hydroxyapatite, 50:50 hydroxyapatite/poly(lactide-co-glycolide), and the poly(anhydride), poly(bis(p-carboxyphenoxy) propane surfaces. Cell attachment and growth on these surfaces was found to be highest on poly(lactide-co-glycolide), the least on hydroxyapatite and hydroxyapatite/poly(lactide-co-glycolide) combinations gave intermediate values. The order of adhesion and growth of MC3T3-E1 cells on the polymer and ceramic systems was poly(lactide-co-glycolide) is greater than hydroxyapatite/poly(lactide-co-glycolide) which is greater than hydroxyapatite. Negligible growth was found on poly(bis(p-carboxyphenoxy) propane. High alkaline phosphatase activity for the cells grown on poly(lactide-co-glycolide) and hydroxyapatite/poly(lactide-co-glycolide) confirmed retention of the osteoblast phenotype. This in vitro evaluation suggests that poly(lactide-co-glycolide) and hydroxyapatite/poly(lactide-co-glycolide) combinations may be candidate biomaterials for the construction of a cell-polymer matrix for skeletal tissue regeneration.

Alkaline Phosphatase↗
PubMed2004

Chiral separations in microemulsion electrokinetic chromatography. Use of micelle polymers and microemulsion polymers.

In this study, microemulsions of the chiral surfactant polysodium N-undecenoyl-D-valinate (poly-D-SUV) was utilized for enantiomeric separation by investigating two approaches using polymeric chiral surfactant in microemulsion electrokinetic chromatography (MEEKC). In the first approach, poly-D-SUV was used as an emulsifier surfactant along with 1-butanol and n-heptane. Enantioseparation of anionic or partially anionic binaphthyl derivatives, anionic barbiturates, and cationic paveroline derivatives were achieved by varying the mass fraction of 1-butanol, n-heptane and poly-D-SUV. For anionic or partially anionic analytes, relatively lower mass fractions of n-heptane, and poly-D-SUV were found to give optimum chiral separations as compared to that for cationic solutes. In the second approach, the chiral microemulsion polymer was prepared by polymerizing mixtures of 3.50% (w/w) of sodium N-undecenoyl-D-valinate (D-SUV) and 0.82% (w/w) of n-heptane (core phase) at varying concentration of 1-butanol. After polymerization, the n-heptane and 1-butanol were removed to yield solvent free microemulsion polymers (MPs) which were then utilized for the separation of anionic binaphthyl derivatives and anionic barbiturates. When MPs of D-SUV were utilized for chiral separation, 1.00% (w/w) 1-butanol and 3.50% (w/w) 1-butanol was optimum for enantioseparation of (+/-)-BNP and (+/-)-BOH, respectively. On the other hand, for anionic (+/-)-barbiturates very low concentration of butanol (0.25%, w/w) provided optimum resolution. Compared with micellar electrokinetic chromatography (MEKC), the use of micelle polymers or microemulsion polymers in MEEKC showed dramatic enhancement for resolution of (+/-)-BNP, while this enhancement was less dramatic for other binaphthyls [(+/-)-BOH, (+/-)-BNA] as well as for (+/-)-barbiturates and (+/-)-paveroline derivatives. However, higher separation efficiency of the enantiomers was always observed with MEEKC than in MEKC.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2000

Laterally attached liquid crystalline polymers as stationary phases in reversed-phase high-performance liquid chromatography. II. Optimization of the molecular parameter of the polymer.

Stationary phases obtained by coating side-chain liquid crystalline polymers (LCPs) with the mesogenic rod like units laterally attached to a polysiloxane backbone via a flexible spacer have been already reported. These phases show excellent planarity and shape recognition for polynuclear aromatic hydrocarbon (PAH) solutes in reversed-phase liquid chromatography. Optimization of these stationary phases in terms of molecular parameters of the polymer is here described. Fifteen stationary phases have been prepared varying different parameters such as the spacer length, the aliphatic tail length, and the proportion of laterally attached mesogenic units along the polymer chain. The results show that the combination of a long spacer and long terminal chains, which generates a smectic phase in the polymer bulk, leads to the best chromatographic performances towards planarity and shape recognition for PAH solutes.

Chromatography, High Pressure Liquid↗
PubMed2000

Bioencapsulation within synthetic polymers (Part 2): non-sol-gel protein-polymer biocomposites.

Since the introduction of sol-gel bioencapsulation and the demonstration that biological function can be incorporated into, and preserved within, polymer matrices, a number of alternative polymers have been used to immobilize proteins. Various enzymes have been trapped in such diverse polymers as epoxy-amine resins, polyvinyl plastics, polyurethane foams and silicone elastomers. Together with sol-gel encapsulates, these biocomposites represent a powerful approach for immobilizing biological materials for applications as biosensors and biocatalysts, and hold promise as bioactive, fouling-resistant polymers for environmental, food and medical uses. Although still at the developmental stage, these biocomposites promise to revolutionize the whole arena of high-performance bioimmobilization.

Biocompatible Materials↗
PubMed2000

Affinity partitioning of a poly(histidine)-tagged integral membrane protein, cytochrome bo3 ubiquinol oxidase, in a detergent--polymer aqueous two-phase system containing metal-chelating polymer.

A system has been developed for selective partitioning of membrane proteins. For the first time, an integral membrane protein, cytochrome bo3 ubiquinol oxidase from Escherichia coli, has been affinity partitioned in an aqueous two-phase system. The systems used were different detergent/polymer aqueous two-phase systems containing a metal-chelating polymer, such as poly(ethyleneglycol)-iminodiacetic acid-Cu(II) as well as dextran-iminodiacetic acid-Cu(II). Many non-ionic detergents, such as alkyl(polyethyleneoxide) (CmEOn), Triton, Tween and alkylglucosides, form two-phase systems in mixture with polymers, such as dextran and poly(ethyleneglycol), i.e., a micelle-enriched phase in equilibrium with a polymer-enriched phase are formed. In general, membrane proteins partition strongly to the micelle phase. We show that it is possible to selectively partition a poly(histidine)-tagged integral membrane protein into the polymer phase by metal affinity partitioning, with a shift in the partitioning coefficient from 0.015 to 4.8 (300-fold). The affinity partitioning was characterized and the effects of ligand concentration, pH, time, salts, buffer type, imidazole and charged detergent are discussed. Thus, a fast and mild affinity procedure for the purification of integral membrane proteins can be developed in affinity detergent/polymer aqueous two-phase systems, and the method is especially suitable for the purification of labile integral membrane proteins, such as receptors.

Chelating Agents↗
PubMedDate not supplied

Synthesis of well-defined amphiphilic block copolymers having phospholipid polymer sequences as a novel biocompatible polymer micelle reagent.

To realize safer and effective drug administration, novel well-defined and biocompatible amphiphilic block copolymers containing phospholipid polymer sequences were synthesized. At first, the homopolymer of 2-methacryloyloxyethylphosphorylcholine (MPC) was synthesized in water by reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The "living" polymerization was confirmed by the fact that the number-average molecular weight increased linearly with monomer conversion while the molecular weight distribution remained narrow independent of the conversion. The poly(MPC) thus prepared is end-capped with a dithioester moiety. Using the dithioester-capped poly(MPC) as a macro chain transfer agent, AB diblock copolymers of MPC and n-butyl methacrylate (BMA) were synthesized. Associative properties of the amphiphilic block copolymer (pMPC(m)-BMA(n)) with varying poly(BMA) block lengths were investigated using NMR, fluorescence probe, static light scattering (SLS), and quasi-elastic light scattering (QELS) techniques. Proton NMR data in D2O indicated highly restricted motions of the n-butyl moieties, arising from hydrophobic associations of poly(BMA) blocks. Fluorescence spectra of N-phenyl-1-naphthylamine indicated that the probes were solubilized in the polymer micelles in water. The formation of polymer micelles comprising a core with poly(BMA) blocks and shell with hydrophilic poly(MPC) blocks was suggested by SLS and QELS data. The size and mass of the micelle increased with increasing poly(BMA) block length. With an expectation of a pharmaceutical application of pMPC(m)-BMA(n), solubilization of a poorly water-soluble anticancer agent, paclitaxel (PTX), was investigated. PTX dissolved well in aqueous solutions of pMPC(m)-BMA(n) as compared with pure water, implying that PTX is incorporated into the hydrophobic core of the polymer micelle. Since excellent biocompatible poly(MPC) sequences form an outer shell of the micelle, pMPC(m)-BMA(n) may find application as a promising reagent to make a good formulation with a hydrophobic drug.

Antineoplastic Agents↗
PubMed1997

Noninvasive in vivo monitoring of drug release and polymer erosion from biodegradable polymers by EPR spectroscopy and NMR imaging.

Biodegradable polymers have attracted much attention as implantable drug delivery systems. Uncertainty in extrapolating in vitro results to in vivo systems due to the difficulties of appropriate characterization in vivo, however, is a significant issue in the development of these systems. To circumvent this limitation, noninvasive magnetic resonance techniques, electron paramagnetic resonance (EPR) and magnetic resonance imaging (MRI), were applied to characterize drug release and polymer degradation in vitro and in vivo. MRI makes it possible to monitor water content, tablet shape, and response of the biological system such as edema and encapsulation. The results of the MRI experiments give the first direct proof in vivo of postulated mechanisms of polymer erosion. Using nitroxide radicals as model drug releasing compounds, information on the mechanism of drug release and microviscosity inside the implant can be obtained by means of 1.2 GHz EPR spectroscopy. To be able to attribute nitroxide mobility to a particular layer of the implant, sandwich-like tablets were manufactured, taking advantage of the distinct spectral features of nitroxides containing different isotopes of nitrogen (15N vs 14N). The use of both noninvasive methods to monitor processes in vivo leads to new insights in understanding the mechanisms of drug release and polymer degradation.

Biodegradation, Environmental↗
PubMed1999

Physical polymer surface modification methods and applications in food packaging polymers.

Continued innovations in the polymer industry have made polymer surface modification methods a subject of intense research. The importance and necessity of surface modification of plastics are explained, and the advantages of physical surface treatments over the less-sophisticated chemical methods are outlined. Currently available physical surface modification methods for food packaging polymers are reviewed from the food packaging perspective. These physical surface modification methods include flame, corona discharge, UV, gamma-ray, electron beam, ion beam, plasma, and laser treatments. The principle of operation of each method is briefly described, and the advantages and disadvantages of each technique are cited. The extent to which each of these methods can produce the specific modifications desired is discussed. Furthermore, the effects of each treatment on barrier, mechanical, and adhesion properties of food packaging polymers are also examined. Finally, an overview of economic aspects of sophisticated surface modification techniques, including ion beam, plasma, and laser treatments, is presented.

Food Packaging↗
PubMed2004

The effects of polymer characteristics on nano particle separation in humic substances removal by cationic polymer coagulation.

Removal of humic substances by coagulation involves nano- and microparticle transport processes. The objective of this paper has been to describe the effects of polymer characteristics on the initial coagulation of nano-sized humic substances and on the aggregates' ability to form larger flocs. The study offers a direct comparison of four different low molecular weight polycations, with charge densities ranging from 4.0 to 7.0 meq/g, as well as of a low and medium molecular weight cationic polyacrylamide with practically equal charge densities. The extent of coagulation of humic substances, determined as the percentage removal of humic substances after filtration through 0.1 microm, could, regardless of the polymer type, be explained by the amount of cationic charge equivalents added per mg TOC of humic substances. The optimal polymer dosage with respect to the extent of flocculation, determined as the percentage removal after filtration through 11 microm could not be explained by this, but the maximum extent of flocculation obtained with each polymer type increased with increasing polyelectrolyte charge density. However, the weak polycation chitosan showed a significantly higher maximum extent of flocculation than would be predicted from its charge density. Polyelectrolyte molecular weight did not show any significant effect on the coagulation of humic substances, nor did it increase the extent of floc separability at 11 microm.

Cations↗
PubMed1999

Surface Modification of Conventional Polymers by Depositing Plasma Polymers of Trimethylsilane and of Trimethylsilane + O2.

The static wetting properties of TMS (trimethylsilane) and TMS + O2 plasma deposited films on eleven low energy conventional polymers were investigated using the sessile droplet method. The static advancing contact angle is an excellent indication of the change in surface state properties from plasma surface modification. However, traditional contact angle measuring techniques possess a methodological limitation, which can leave a water droplet on the substrate surface for up to 3 min before a measurement is obtained. The static "advancing" contact angles of different size water droplets on teflon and nylon surfaces were observed to change significantly in 2 min while equilibrating with the surface and surroundings. A new quick image-capturing device enables static contact angle measurement 2 to 4 s after contact with the substrate. This technique virtually eliminates the time dependent effects of evaporation and surface state change, which are believed to be responsible for the change in static advancing contact angles. Furthermore, static contact angles independent of droplet volume and contact time may be taken as a surface characteristic property, which is denoted as the intrinsic static contact angle, θS. The static "advancing" contact angle, measured in this fashion, indicated that the wetting properties of TMS and TMS + O2 plasma polymer deposition on 10 conventional polymers were modified virtually independent of the underlying substrate. The average advancing contact angles on TMS and TMS + O2 modified polymers are θS = 94 +/- 2.2 (cos θS = -0.0645) and θS = 32 +/- 6.9 (cos θS = 0.8452), respectively. Copyright 1999 Academic Press.

Journal Article↗
PubMed2006

Carbon-13 labeled polymers: an alternative tracer for depth profiling of polymer films and multilayers using secondary ion mass spectrometry.

13C labeling is introduced as a tracer for depth profiling of polymer films and multilayers using secondary ion mass spectrometry (SIMS). Deuterium substitution has traditionally been used in depth profiling of polymers but can affect the phase behavior of the polymer constituents with reported changes in both bulk-phase behavior and surface and interfacial interactions. SIMS can provide contrast by examining various functional groups, chemical moieties, or isotopic labels. 13C-Labeled PS (13C-PS) and unlabeled PS (12C-PS) and PMMA were synthesized using atom-transfer radical polymerization and assembled in several model thin-film systems. Depth profiles were recorded using a Cameca IMS-6f magnetic sector mass spectrometer using both 6.0-keV impact energy Cs+ and 5.5-keV impact energy O2+ primary ion bombardment with detection of negative and positive secondary ions, respectively. Although complete separation of 12C1H from 13C is achieved using both primary ion species, 6.0-keV Cs+ clearly shows improved detection sensitivity and signal-to-noise ratio for detection of 12C, 12C1H, and 13C secondary ions. The use of Cs+ primary ion bombardment results in somewhat anomalous, nonmonotonic changes in the 12C, 12C1H, and 13C secondary ion yields through the PS/PMMA interface; however, it is shown that this behavior is not due to sample charging. Through normalization of the 13C secondary ion yield to the total C (12C + 13C) ion yield, the observed effects through the PS/PMMA interface can be greatly minimized, thereby significantly improving analysis of polymer films and multilayers using SIMS. Mass spectra of 13C-PS and 12C-PS were also analyzed using a PHI TRIFT I time-of-flight mass spectrometer, with 15-keV Ga+ primary ion bombardment and detection of positive secondary ions. The (12)C7(1)H7 ion fragment and its 13C-enriched analogues have significant secondary ion yields with negligible mass interferences, providing an early indication of the potential for future use of this technique for cluster probe depth profiling of high molecular weight 13C-labeled fragments.

Journal Article↗
PubMed2001

Topological polymer chemistry: systematic classification of nonlinear polymer topologies.

Nonlinear polymer topologies composed of cyclic and branched polymer segments are systematically classified by reference to constitutional isomerism in a series of alkanes (CnH2n+2), monocycloalkanes (CnH2n), and polycycloalkanes (CnH2n-2, CnH2n-4, etc). Thus, the total number of chain ends (termini) and of branch points (junctions) are maintained as invariant parameters, as well as the number of branches at each junction and the connectivity of junction. On the other hand, the distance between two adjacent junctions and that between the junction and terminus are taken as variant parameters. On the basis of the classification of polymer topologies, a novel synthetic strategy by an "electrostatic self-assembly and covalent fixation" technique has been proposed to construct a variety of topologically unique polymer architectures.

Journal Article↗
PubMed2003

Polymer scrambling: macromolecular radical crossover reaction between the main chains of alkoxyamine-based dynamic covalent polymers.

A novel polymer hybridization method, "polymer scrambling", was developed on the basis of the macromolecular radical crossover reaction between the main chains of dynamic covalent polymers. The macromolecular crossover reaction was successfully monitored by GPC and NMR measurements. The present methodology is innovative for the preparation of novel polymer hybrid materials at the nanometer scale.

Journal Article↗
PubMed2005

Investigations on the mechanisms of ionic conductivity in PEO-PU/PAN semi-interpenetrating polymer network-salt complex polymer electrolytes: an impedance spectroscopy study.

This paper is a first comprehensive study on the correlated ion transport mechanisms contributing to the overall conductivity behavior in a new class of poly(ethylene oxide)-polyurethane/polyacrylonitrile (PEO-PU/PAN) semi-interpenetrating polymer networks (semi-IPNs)-salt complex polymer electrolytes. A simultaneous investigation of the electrical response on PEO-PU/PAN/LiClO(4) and PEO-PU/PAN/LiCF(3)SO(3) semi-IPNs with varying EO/Li mole ratios (100, 60, 30, 20, 15, 10) has been carried out by impedance spectroscopy. Analysis of the complex plane and spectroscopic plots indicated the presence of two microscopic phases corresponding to the PEO-PU and PAN domains, which leads to space charge polarization in these systems. A suitably modified approach based on the universal power law (UPL) considering the independent contribution from the individual microphases of semi-IPNs facilitates a complete interpretation of the spectroscopic profiles for the real component of conductivity (sigma'(omega)). The sigma'(omega) spectroscopic profiles were fitted with two power law equations, where the frequency region up to approximately 300 kHz is the conductivity profile associated with the PAN phase and beyond this is the superimposed contribution of the PEO-PU phase. Simulated fits using the UPL equation revealed two relaxation times (tau(PEO)(-)(PU), tau(PAN)) related to ionic hopping in the PEO-PU and PAN phases in addition to the conductivity relaxation time (tau(peak)) determined from the Debye peaks. The respective power law exponents (n(PEO)(-)(PU) approximately 0.5-0.8, n(PAN) approximately 1.0-1.6) indicate that though cationic hopping in the softer PEO-PU phase is favored, anionic hopping in the PAN phase contributes significantly to the charge transport processes in these semi-IPNs. Correlation of the experimental results with the simulated fits enable us to distinguish the effects of semi-IPN composition, temperature, morphology, ion-ion, and ion-polymer interactions, which influence the microscopic molecular events, involved in the charge transport in these complex semi-IPN polymer electrolytes.

Journal Article↗
PubMed2005

Steady-state analysis of polymer adsorption at and transport across an interface between two polymer phases.

We consider a mutually incompatible polymer mixture composed of two major components AN and BN and a third minority component C(N). The interactions, parameterized by short-range Flory-Huggins interaction parameters, are chosen such that C wets the A/B interface completely at three-phase coexistence. At sub-saturated conditions the adsorption of C remains necessarily microscopic. We study such a system in a stationary off-equilibrium state: due to imposed chemical potential gradients, polymer AN diffuses from the A-rich bulk phase through the interface to the A-poor bulk phase. Polymer BN travels in the opposite direction. Symmetric conditions are selected for which the polymer CN that accumulates at the A/B-interface has no net flux in the stationary state. This system is described by the Mean Field Stationary Diffusion (MFSD) model, an approach that solves the Scheutjens Fleer self-consistent-field (SF-SCF) equations with the boundary condition that the chemical potentials in the two bulk phases are different (but constant) so that a stationary state can be described. When the chemical potentials in the two bulk phases are the same, MFSD reduces to the equilibrium SF-SCF results. From the MFSD method we obtain the stationary volume fraction profiles and segmental fluxes. By forcing the system further from three-phase coexistence, i.e. by imposing larger concentration gradients, the adsorption of C goes unexpectedly from a thin adsorption layer to a thick adsorption film. The susceptibility partial differential J(A)/partial differential Delta(phi)A of the flux of A (equal to minus the flux of B) with respect to the imposed concentration gradient changes abruptly at the transition in adsorption behaviour. Interestingly, upon variation of the concentration gradients, the fluxes of A and B are enhanced by the accumulation of C at the interface. This means that the adsorbed C-film does not behave as an inert barrier.

Journal Article↗