SEARCH · PubMed Health

Results for “Polymers”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources

PubMed1997

[Injectable bioerodible polymer with 5-fluorouracil used in filtration surgery in rabbits].

OBJECTIVE: A prospective randomized and placebo-controlled study was performed to evaluate the effect and toxicity of injectable bioerodible polymer with 5-fluorouracil (5-Fu) on the filtration surgery in rabbits. METHODS: Posterior lip sclerectomies were performed on both eyes of 23 rabbits. Injectable bioerodible polymer impregnated with 2.5% 5-Fu 10 mg was injected subconjunctivally in 16 eyes, and 2.5% 5-Fu 10 mg was injected subconjunctivally in 14 eyes every other day for three times in the first week and every two days for three times in the second week post-operatively. Another 16 eyes received the drug-free polymer after surgery and served as controls. RESULTS: The bleb in the eyes treated with drug-free polymer failed in the postoperative 7 days and the bleb in the eyes treated with 5-Fu injection failed in 20-30 days, while the bleb in the eyes treated with 5-Fu polymer remained successful throughout the experimental period. From 7 to 30 postoperative days, the rate of scleral fistula occlusion was 6.7% in the eyes treated with 5-Fu polymer, 41.7% in the eyes treated with 5-Fu injection and 100% in the eyes treated with drug-free polymer. Corneal epithelial defects appeared in 3 eyes treated with 5-Fu polymer, in 8 eyes treated with 5-Fu injection and in 2 eyes treated with drug-free polymer. CONCLUSION: Injectable bioerodible polymer with 5-Fu may significantly prevent bleb scarring and subsequent blockage of the filtering tract, enhance success rate of filtering surgery in rabbits and reduce the toxicity of 5-Fu. This drug delivery system has considerable value for clinical use.

Animals↗

PubMed1999

Development of a new biodegradable intravascular polymer stent with simultaneous incorporation of bioactive substances.

OBJECTIVE: Due to the thrombogenicity and permanent implant nature of metallic stents, bioresorable synthetic polymers have been proposed for stents and local drug delivery systems. Bioresorbable polyesters like poly(D,L-lactide) demonstrated excellent biocompatibility in various tissues. This paper describes a novel method for the molding of these polymers. The specific CESP-process (Controlled Expansion of Saturated Polymers) is characterised by the use of the plasticizer carbon dioxide and allows the incorporation of bioactive substances at physiologic temperatures into the polymer bulk and the production of complex designed implants. METHODS: The CESP-process is characterised by the exposure of an amorphous polymer to an inert gas at high pressure with a significant lower glass transition point. The plasticizing effect makes it possible to process polylactides at a temperature close to room temperature. The low process temperature constitutes a key advantage for thermally sensitive polymers and allows the incorporation of thermally sensitive pharmaceutical additives. To obtain some preliminary information on the biocompatibility, in vitro cell toxicity testing as well as drug release assessment was performed. RESULTS: Different polymer sheets were produced using the CESP-process. Cytotoxicity was not observed in any molded polymer material. According to the mechanical and biocompatibility results Poly(D,L-lactide) (P-DL-LA) was investigated in the CESP-process. Finite element analysis was used to test the possible geometry of an adequate stent. A helical design was chosen and a stent-prototype was produced using the CESP-process. Peroxidase activity as an incorporated marker enzyme could be measured over 6 weeks. Different drug release profiles were obtained due to various pore sizes of the polymer. CONCLUSIONS: The new CESP-process can be used to process biodegradable polymers and to mold different stent geometries without inducing cytotoxic effects to the material. Furthermore, this procedure permits the simultaneous incorporation of bioactive substances during the molding process. Drug release kinetics can be regulated by different pore sizes of the material.

Absorbable Implants↗

PubMedDate not supplied

Quantitative methods for evaluating optical and frictional properties of cationic polymers.

This paper presents three quantitative methods to examine gloss, opacity, and friction of cationic polymers. The adsorption of cationic polymers onto hair and skin can be regarded as a thin film coating. Therefore, optical and frictional properties of polymer films are of significant relevance to the applications of cationic polymers in hair care products. Such properties reflect the desirable hair condition attributes consumers seek in shampoo and conditioner products. Using these test methods, polyquaternium-10 and cationic guar samples of varying molecular weight and cationic substitution were compared. The effect of an anionic surfactant, sodium dodecyl sulfate (SDS), on polymer film properties was also investigated. Neat guar hydroxypropyl trimonium chloride imparts less friction than polyquaternium-10 but dulls the substrate employed in this study. The optical data show that polyquaternium-10 provides greater film clarity and gloss than cationic guars. In the presence of SDS, polyquaternium-10 also displays similar or lower friction than cationic guar. The comparative optical and frictional results are in good agreement with the visual assessment of the cationic polymer films. These results clearly demonstrate that polyquaternium-10 exhibits superior film properties in the forms of both neat polymer and polymer/surfactant complex. In addition, microscopic techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) provide powerful explanations for the differences noted between the two popular classes of cationic polymers. The test methods described in this paper can be utilized to differentiate the upper performance potential of cationic polymers. These objective and standardized test methods derived from the coatings industry are not affected by the variability of hair or the formulation complexity of end products. They can be useful tools in the product development process in quickly screening the relative performance of different polymers.

Cations↗

PubMed1994

In vivo versus in vitro degradation of controlled release polymers for intracranial surgical therapy.

Intracranial studies to analyze the degradation kinetics of the bioerodible polymer poly[bis(p-carboxyphenoxy)propane-sebacic acid] [p(CPP-SA) 20:80] copolymer wafers were conducted in a rat model. Rats were separated into four groups: those receiving 1) polymer, 2) polymer loaded with the chemotherapeutic agent BCNU, 3) drug-loaded polymer with previous tumor implantation, and 4) polymer and an absorbable hemostatic material. A polymer wafer was surgically implanted into the brain of each animal. Residual polymer was harvested at varying times for chromatographic analysis. In vitro effects of pH, mixing, and water availability on degradation were also studied. The results of in vitro and in vivo studies were compared to understand the behavior of polymers in a clinical setting. We found that degradation of p(CPP-SA) initially occurred more slowly in vivo than in vitro. The presence of BCNU, tumor, and absorbable hemostatic material did not affect the ultimate time of polymer degradation in vivo, and the intrinsic polymer degradation time of 1 mm thick p(CPP-SA) 20:80 disks in vivo was 6-8 weeks.

Animals↗

PubMed1997

Stabilization of Liposomes Attached to Polymer Surfaces Having Phosphorylcholine Groups

The adsorption state of liposomes on a polymer surface containing a phosphorylcholine group, that is, omega-methacryloyloxyalkyl phosphorylcholine (MAPC) polymer, was evaluated using a quartz crystal microbalance and an atomic force microscope. After a quartz crystal resonator coated with the MAPC polymer or poly[2-hydroxyethyl methacrylate (HEMA)] was equilibrated with distilled water, the quartz crystal was contacted with a dipalmitoylphosphatidylcholine (DPPC) liposomal suspension. The resonance frequency change during liposome adsorption on the poly(HEMA)-coated resonator was larger than that on the MAPC polymer-coated resonator. The temperature response based on the phase transition of adsorbed DPPC liposomes, that is, the liquid crystalline state to gel state, on the MAPC polymer-coated resonator was more sensitive than that on the poly(HEMA)-coated resonator. Moreover, when the DPPC liposomes adsorbed on the polymer surfaces were disintegrated with a nonionic surfactant, it took longer for the frequency to return to the initial value of the poly(HEMA)-coated resonator than to that of the MAPC polymer-coated resonator. According to atomic force microscopic observation of the polymer surface after treatment with the liposomal suspension, the DPPC liposomes adsorbed on the MAPC polymers maintained their spherical shape well. We conclude that DPPC liposomes adsorbed on the poly(HEMA) surface can penetrate a hydrated layer and its ordered structure. On the other hand, DPPC liposomes may adsorb to the MAPC polymer surface without change in their original structure. Copyright 1997Academic Press

Journal Article↗

PubMed2000

Flow-Induced Anisotropy in Mixtures of Associative Polymers and Latex Particles.

The effect of associative polymers on the structure and rheological behavior of colloidal suspensions is discussed. Adding associative polymer is known to increase the viscosity of the suspensions. At high shear rates the increase is close to what could be expected on the basis of the hydrodynamic effects of the added polymer. At low shear rates the viscosity increases much more. Small-angle light scattering (SALS) during flow is used here to investigate the underlying structural mechanisms. The SALS patterns indicate that the associative polymer changes the particulate structure: characteristic butterfly patterns appear even at relatively low particle volume fractions. They are not present in the suspensions without associative polymer. The patterns indicate that fluctuations in particle concentration are more pronounced in the flow direction than in the vorticity direction and that anisotropic particulate structures with an orientation along the vorticity direction develop. The evolution of their characteristic length scale during flow has been followed over time. Changing the hydrophilic part of the polymer from polyacrylamide to polyacrylic acid induces stronger associative interactions. In the suspensions this results in a reduction of the relative viscosity rather than an increase. The difference in degree of associativity between the polymers also has an effect on the SALS patterns in the suspensions both at rest and during flow. The rheology as well as the SALS suggest the presence of a strong polymer network in the second system. The competition between adsorption of the associative polymer on the particles with the intermolecular associations between the polymer chains seems to be responsible for the observed differences. Copyright 2000 Academic Press.

Journal Article↗

PubMed2003

Depletion-induced phase separation in colloid-polymer mixtures.

Phase separation can be induced in a colloidal dispersion by adding non-adsorbing polymers. Depletion of polymer around the colloidal particles induces an effective attraction, leading to demixing at sufficient polymer concentration. This communication reviews theoretical and experimental work carried out on the polymer-mediated attraction between spherical colloids and the resulting phase separation of the polymer-colloid mixture. Theoretical studies have mainly focused on the limits where polymers are small or large as compared to the colloidal size. Recently, however, theories are being developed that cover a wider colloid-polymer size ratio range. In practical systems, size polydispersity and polyelectrolytes (instead of neutral polymers) and/or charges on the colloidal surfaces play a role in polymer-colloid mixtures. The limited amount of theoretical work performed on this is also discussed. Finally, an overview is given on experimental investigations with respect to phase behavior and results obtained with techniques enabling measurement of the depletion-induced interaction potential, the structure factor, the depletion layer thickness and the interfacial tension between the demixed phases of a colloid-polymer mixture.

Journal Article↗

PubMed1991

Polymer-mediated electrostatic interactions between charged lipid assemblies and electrolyte solutions: a tentative model of the polyethylene glycol-induced cell fusion.

We developed a theoretical model to investigate the interaction between charged lipid aggregates and a water solution containing ions and uncharged polymers. The local concentration of ions and polymer chains around the lipid aggregate have been treated as variational parameters which can be found by minimizing the total energy of the system. We divided the energy into the following main contributions: (a) Solvation energy of the ions. This depends on the local polymer concentration through the variation of the solvent dielectric properties. (b) Ions-lipid aggregate interactions. These depend on the local concentrations both of the ion cloud and polymer chains. (c) Conformational energy of the polymer. This term is related to the inhomogeneous spatial density of the polymer segments. Any direct interaction between the charged lipid surface and the polymer coils has been intentionally neglected. The minimization procedure leads to a non-linear Poisson-Boltzmann equation coupled with a non-linear algebraic equation describing the polymer distribution. The solution of the above system allows one to calculate the ions and polymer spatial distribution around the lipid aggregate. The knowledge of such parameters is useful to predict the effect of non-ionic polymers on the structure and properties of lipid assemblies such as the mean area per lipid molecule, the aggregation number, the critical micellar concentration and the formation of immiscibility gaps in mixed lipid systems. A possible involvement of these parameters into the fusion process between lipid vesicles is discussed.

Animals↗

PubMed2001

Haemoproteus and Schistosoma synthesize heme polymers similar to Plasmodium hemozoin and beta-hematin.

Many parasites digest hemoglobin as an amino acid source, but only a few produce heme polymer pigment instead of catabolizing heme via heme oxygenase. This work compares purified heme polymers produced by Haemoproteus columbae and Schistosoma mansoni to that of Plasmodium falciparum hemozoin and synthetic beta-hematin. Fourier-transform infrared spectroscopy identifies the signature peaks of the common iron-carboxylate bond characteristic in all four heme polymers. However, all pigments could be distinguished by quite different three-dimensional structure visualized by Field Emission Inlens Scanning Electron Microscopy. Both P. falciparum and H. columbae heme polymers had a symmetrical shape unlike the amorphous S. mansoni heme polymer and beta-hematin. All four heme pigments serve as templates for heme polymer extension, which was inhibitable by chloroquine and other quinoline antimalarials. The polymers showed different levels of resistance to hydrogen peroxide degradation. This work identifies another genus, Haemoproteus, capable of intracellular heme polymer formation. The different three-dimensional structures of each pigment implicate genus specific formation of heme polymer, variation of inhibition of polymer extension by the quinolines and degradation by hydrogen peroxide.

Animals↗

PubMed2000

Development of a poly(ortho ester) prototype with a latent acid in the polymer backbone for 5-fluorouracil delivery.

A study has been carried out to determine whether the latest family of poly(ortho esters) can be converted into a practical delivery system. This polymer differs from the previously described polymers in that it incorporates a short segment of a latent acid in the polymer backbone. The following issues were specifically addressed: (a) can the erosion and drug release be reproducibly controlled to yield the desired drug release kinetics and erosion rates? (b) Is the polymer stable during radiation sterilization, on storage and on fabrication? (c) Can the polymer be prepared reproducibly at the desired molecular weights and molecular weight distribution? (d) Is the polymer safe for its intended application and does the in vivo erosion proceed to completion? (e) Can the polymer be easily fabricated into desired configurations? Studies have shown that if the synthesis is carefully controlled, the desired molecular weights can be reproducibly prepared, that the polymer is reasonably stable after irradiation at 24 kGy and during storage at room temperature under anhydrous conditions, and that it can be safely thermally fabricated at temperatures in the neighborhood of 120 degrees C. When polymer devices were implanted intraperitoneally in rats the polymer eroded to completion without any overt toxicity as determined by the measured parameters.

Acids↗

PubMed2001

Lattice model calculations of interactions between proteins and surface grafted polymers with tethered affinity ligands.

Monte Carlo calculations of protein binding to affinity ligands tethered to a surface by polymers have been done and analyzed with statistical mechanical perturbation theory. The interaction of the polymers with the surface, the solvent and the protein has been varied. Different solution conditions of the polymers have been investigated, varying from collapsed polymer structures on a surface to structures extending out in the solution (athermic condition) or to mushroom like structures (hydrophobic polymers grafted on hydrophilic surface). The variation in binding of model proteins of different sizes and interactions with polymers has been studied. In general, smaller proteins bind better than larger proteins. Two types of polymer collapses have been studied. One type is due to increased polymer-surface attraction. The second type is due to increased polymer-self attraction. In the former case the binding, as a function of degree of collapse, decreases monotonically except for small proteins with attraction to the polymer. For collapses of the second type the loss of binding goes through a maximum except for large proteins.

Journal Article↗

PubMed2003

Quartz crystal microbalance sensor for organic vapor detection based on molecularly imprinted polymers.

Molecularly imprinted polymers on quartz crystal microbalances (QCM) are examined for their ability to detect vapors of small organic molecules with greater sensitivity and selectivity than the traditional amorphous polymer coatings. Hydroquinone and phenol serve as noncovalently bound templates that generate shape-selective cavities in a poly(acrylic) or poly(methacrylic) polymer matrix. The imprinted polymers are immobilized on the piezoelectric crystal surface via a precoated poly(isobutylene) layer. The behavior of the imprinted polymer films is characterized by the dynamic and steady-state response of the QCM frequency to pulses of organic vapors in dry air. The apparent partition coefficients are determined for imprinted and nonimprinted polymers prepared by two synthetic methods and for varying mole ratios of template to monomer. The hydroquinone-imprinted polymers and, to a lesser extent, the phenol-imprinted polymers exhibit greater sensitivity and higher selectivity than the nonimprinted polymers toward organic vapors that are structurally related to the templates. These results indicate that molecularly imprinted polymers are promising for the development of selective piezoelectric sensors for organic vapor detection.

Journal Article↗

PubMed2006

Soluble narrow band gap and blue propylenedioxythiophene-cyanovinylene polymers as multifunctional materials for photovoltaic and electrochromic applications.

A family of soluble narrow band gap donor-acceptor conjugated polymers based on dioxythiophenes and cyanovinylenes is reported. The polymers were synthesized using Knoevenagel polycondensation or Yamamoto coupling polymerizations to yield polymers with molecular weights on the order of 10 000-20 000 g/mol, which possess solubility in common organic solvents. Thin film optical measurements revealed narrow band gaps of 1.5-1.8 eV, which gives the polymers a strong overlap of the solar spectrum. The energetic positions of the band edges were determined by cyclic voltammetry and differential pulse voltammetry and demonstrate that the polymers are both air stable and show a strong propensity for photoinduced charge transfer to fullerene acceptors. Such measurements also suggest that the polymers can be both p- and n-type doped, which is supported by spectroelectrochemical results. These polymers have been investigated as electron donors in photovoltaic devices in combination with PCBM ([6,6]-phenyl C(61)-butyric acid methyl ester) as an electron acceptor based on the near ideal band structures designed into the polymers. Efficiencies as high as 0.2% (AM1.5) with short circuit current densities as high as 1.2-1.3 mA/cm(2) have been observed in polymer/PCBM (1:4 by weight) devices and external quantum efficiencies of more than 10% have been observed at wavelengths longer than 600 nm. The electrochromic properties of the narrow band gap polymers are also of interest as the polymers show three accessible color states changing from an absorptive blue or purple in the neutral state to a transmissive sky-blue or gray in the oxidized and reduced forms. The wide electrochemical range of electrochromic activity coupled with the strong observed changes in transmissivity between oxidation states makes these materials potentially interesting for application to electrochromic displays.

Journal Article↗

PubMed2006

Self-organization-induced three-dimensional honeycomb pattern in structure-controlled bulky methacrylate polymers: Synthesis, morphology, and mechanism of pore formation.

Here we report, for the first time, a novel molecular design for three-dimensional honeycomb structures through a self-organization of hydrogen-bonded bulky anchoring group in a methacrylic polymer backbone. The polymerizable monomer design includes a methacrylic double bond linked to various hydrophobic anchoring units such as ethane, n-decane, tricyclodecane (TCD), and adamantane via a hydrogen-bonded cycloaliphatic urethane linkage. The structures of the polymers were confirmed by nuclear magnetic resonance (NMR) and the molecular weights of the polymer were determined by gel permeation chromatography (GPC). The methacrylate polymers having tricyclodecane and adamantane bulky anchoring groups self-organized to produce three-dimensional honeycomb patterns in tetrahydrofuran-water solvent mixture at ambient conditions, whereas its linear analogues (ethane, n-decane) failed to produce any micropattern. The scanning electron microscopy (SEM) analysis of the above-prepared polymer films revealed that the structure of the polymer played a major role in the formation of the honeycomb patterns. The solution Fourier transform infrared (FTIR) measurements confirmed that the bulky tricyclodecane and adamantane polymers have strong hydrogen-bonding interaction compared to that of their linear analogues, which is the driving force for the micropatterns. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the bulky polymers revealed that the polymers exist as vesicles or micelles in the solution, which leads to the formation of the honeycomb pattern. The honeycomb pattern formation in the bulky polymer systems suggests that two cooperative factors such as hydrogen-bonding interaction and hydrophobicity of bulky anchoring units are necessary to induce three-dimensional honeycomb structures. To investigate the effect of molecular weights and its distribution on the self-organization process, both benzoyl peroxide (BPO) initiated free radical and atom transfer radical polymerization (ATRP) techniques were employed for the polymerization. Micropores formed irrespective of differences in molecular weight and polydispersity index (PDI); however, the pore size distribution was influenced by both molecular weights and PDI. Low molecular weight samples afforded polydisperse pores with the ATRP samples with more narrow PDI producing pores with large dimensions. The approach has also been investigated for polystyrene-bulky methacrylic copolymer, and the results revealed that uniform honeycomb patterns were produced for copolymers having more than 50 mol % incorporation of bulky units.

Journal Article↗

PubMed2005

Controlled clustering and enhanced stability of polymer-coated magnetic nanoparticles.

The clustering and stability of magnetic nanoparticles coated with random copolymers of acrylic acid, styrenesulfonic acid, and vinylsulfonic acid has been studied. Clusters larger than 50 nm are formed when the coatings are made using too low or too high molecular weight polymers or using insufficient amounts of polymer. Low-molecular-weight polymers result in thin coatings that do not sufficiently screen van der Waals attractive forces, while high-molecular-weight polymers bridge between particles, and insufficient polymer results in bare patches on the magnetite surface. The stability of the resulting clusters is poor, but when an insufficient polymer is used as primary coating, and a secondary polymer is added to coat remaining bare magnetite, the clusters are stable in high salt concentrations (>5 M NaCl), while retaining the necessary cluster size for efficient magnetic recovery. The magnetite cores were characterized by TEM and vibrating sample magnetometry, while the clusters were characterized by dynamic light scattering. The clustering and stability are interpreted in terms of the particle-particle interaction forces, and the optimal polymer size can be predicted well on the basis of these forces and the solution structure and hydrophobicity of the polymer. The size of aggregates formed by limited polymer can be predicted with a diffusion-limited colloidal aggregation model modified with a sticking probability based on fractional coating of the magnetite cores.

Journal Article↗

PubMed2006

A series of metal-organic polymers assembled from MCl2 (M = Zn, Cd, Co, Cu): structures, third-order nonlinear optical and fluorescent properties.

In this paper four metal-organic polymers {[Zn(fcz)Cl2].CH3OH}n 1, {[Cd(fcz)2Cl2].CH3OH.2H2O}n 2, {[Co(fcz)2Cl2].2CH3OH}n 3 and {[Cu(fcz)2Cl2].2CH3OH}n 4 (fcz = fluconazole: alpha-(2,4-difluorophenyl)-alpha-(1H-1,2,4-triazol-l-ylmethyl)-1H-1,2,4-triazole-l-ethanol) were synthesized and characterized by X-ray single crystal diffraction. Polymer consists of 1-D infinite chains arranged along the b-axis. All of polymers 2-4 exhibit a 2-D rhombohedral grid structure. We study the third-order nonlinear optical properties of fcz and polymers 1-4 in DMF solution by using 8 ns laser pulses at 532 nm, and find that 1 and 4 exhibit different NLO properties from fcz and both 2 and 3 show similar NLO properties to fcz. 1 possesses strong NLO refractive effects and large NLO absorptive behaviors. 2, 3 and fcz exhibit strong refractive effects, but their NLO absorptive behaviors are weaker than that of 1. The NLO effects of 4 are very weak. The study of optical limiting (OL) effects by using 40 ps laser pulses at 532 nm shows that fcz and polymer 3 possess a strong OL effect. The optical limiting threshold values of 0.15 J cm(-2) for fcz and 0.16 J cm(-2) for are comparable to those of many heterothiometallate clusters. Polymers 1, 2 and 4 show a weak OL effect. The fluorescent spectra in DMF solution (concentration: 1 x 10(-4) mol dm(-3)) show that polymers 1-4 exhibit different luminescence properties from fcz. The maximum wavelength of polymers 1-3 are blue shifted gradually by 2-12 nm while polymer 4 exhibits a fluorescent self-quenching phenomenon. These results demonstrate that metal ions play an important part in the NLO and fluorescent properties of coordination polymers.

Journal Article↗

PubMedDate not supplied

Enhancement of wound repair with a topically applied nitric oxide-releasing polymer.

Nitric oxide is an important cytotoxic agent for host defense which also regulates gene expression, signal transduction, and vasodilation. In normal wounds, nitric oxide synthesis and metabolism are significantly increased during inflammation and tissue remodeling. However, nitric oxide production is suppressed in wounds where healing is impaired by diabetes or steroid-treatment. Topical delivery of nitric oxide in therapeutic amounts may alleviate this deficiency and thereby enhance wound repair. Consequently, we developed polyethyleneimine cellulose NONOate polymer, a nonsoluble, nontoxic, polymer-based NONOate--one of a new class of compounds that spontaneously release nitric oxide in a controlled fashion in aqueous media. Polyethyleneimine cellulose NONOate polymer was synthesized from polyethyleneimine cellulose to provide extended nitric oxide release with a half-life of 16 hours. Polyethyleneimine cellulose NONOate polymer or a control polymer was applied topically on full-thickness dermal wounds of rats at the time of wounding and days 3, 7, 10, 14, 17, and 21. Nitric oxide delivery was determined indirectly by measuring urinary nitrate. The first two polyethyleneimine cellulose NONOate polymer applications increased urinary nitrate output twofold to fourfold, whereas urinary nitrate output of control rats did not significantly increase. Nitrate output in polyethyleneimine cellulose NONOate polymer-treated rats was elevated compared with controls after each application, although this was attenuated in later applications. Rate of wound closure was measured with computer-based video imaging. Polyethyleneimine cellulose NONOate polymer-treated wounds were significantly smaller (p < 0.05) on days 7, 10, and 17 relative to controls, based on percentage of wound open relative to initial wound area. In a second experiment, telemetry-implanted rats were wounded to detect potential hypotensive effects as a result of polyethyleneimine cellulose NONOate polymer application. Topical polyethyleneimine cellulose NONOate polymer application to wounds showed no prolonged hypotensive effects, in contrast to a soluble NONOate which suppressed systolic blood pressure for over 6 hours. These results show that a nonsoluble, polymeric NONOate can provide topical nitric oxide delivery to wounds in a controlled manner, which may enhance wound healing. Further studies are in progress with other promising NONOate candidates to establish dose-response effects and therapeutic limits of exogenous nitric oxide release in impaired wound models.

Journal Article↗

PubMed2004

Phase transitions of a polymer threading a membrane coupled to coil-globule transitions.

We theoretically study phase transitions of a polymer threading through a pore imbedded in a membrane. We focus on the coupling between a partition of the polymer segments through the membrane and a coil-globule transition of the single polymer chain. Based on the Flory model for collapse transitions of a polymer chain, we calculate the fraction of polymer segments and the expansion factor of a polymer coil on each side of the membrane. We predict a first-order phase transition of a polymer threading a membrane; polymer segments in one side are discontinuously translocated into the other side, depending on solvent conditions and molecular weight of the polymer. We also discuss the equilibrium conformation of the polymer chain on each side of the membrane.

Journal Article↗