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PubMed1998

Use of a bioabsorbable polymer for the delivery of ofloxacin during experimental osteomyelitis treatment.

This study was performed to investigate the potential utility of ofloxacin-impregnated bioabsorbable polymers for osteomyelitis therapy. Pseudomonas aeruginosa osteomyelitis was induced in 48 New Zealand White rabbits. Four weeks after infection, the animals were randomized to one of four treatment groups: drug-free polymer, ofloxacin polymer, systemic ofloxacin, or ofloxacin polymer plus systemic ofloxacin. Twenty-eight days later, radiographs were taken of the affected area, the animals were killed, and bone was obtained for histologic evaluation, culture, and determination of ofloxacin concentrations. The percentage of sterile bone cultures was 33, 83, 75, and 91 for the groups treated with drug-free polymer, ofloxacin polymer, systemic ofloxacin, and ofloxacin polymer plus systemic ofloxacin, respectively. When compared with the drug-free polymer, both the ofloxacin polymer and the ofloxacin polymer plus systemic ofloxacin significantly improved the rate of sterilization. The mean concentrations of the drug in bone for the groups treated with ofloxacin polymer, systemic ofloxacin, and ofloxacin polymer plus systemic ofloxacin were 34.9 (range: 2-160), 1.9 (range: 0.8-3), and 26.0 microg/g (range: 9-100 microg/g), respectively. These data suggest that the DL-lactide:glycolide polymer studied is a suitable vehicle for the delivery of high local concentrations of ofloxacin and that these concentrations result in eradication of the bacterial pathogen in this rabbit model.

Animals↗

PubMed1996

Interstitial delivery of carboplatin via biodegradable polymers is effective against experimental glioma in the rat.

PURPOSE: Carboplatin has shown promise experimentally as an antineoplastic agent against both primary central nervous system (CNS) tumors and several solid tumors that frequently metastasize to the brain. Unfortunately, carboplatin is limited in its clinical use for tumors in the CNS by systemic toxicity and poor penetration through the blood brain barrier. Recent advances in polymer technology have made feasible the intracranial implantation of a biodegradable polymer capable of local sustained delivery of chemotherapy for brain neoplasms. This study assessed the toxicity and efficacy of carboplatin delivered from intracranial sustained release polymers in the treatment of experimental gliomas in rodents. METHODS: Two biodegradable anhydride polymer systems were tested: a copolymer of 1,3-bis-(p-carboxyphenoxy propane) and sebacic acid, and a copolymer of fatty acid dimer and sebacic acid. The polymers were loaded with carboplatin and dose escalation studies evaluating toxicity were performed by implanting carboplatin-loaded polymers into the brains of rats. Next, efficacy was tested. F-98 glioma cells were injected intracranially into rats, and 5 days later polymers containing the highest tolerated doses were implanted at the site of tumor growth. The survival of animals receiving carboplatin-loaded polymer was compared with that of animals receiving intraperitoneal doses of the same agent. RESULTS: Carboplatin-polymer was well tolerated at doses up to 5% loading in both polymer systems. Locally delivered carboplatin effectively prolonged survival of rats with F98 gliomas. Maximal treatment effect was seen with 5% loading of either polymer, with median survival increased threefold over control (P < 0.004). Systemic carboplatin also significantly prolonged survival, but the best intracranial polymer dose was significantly more effective than the best systemic dose tested. CONCLUSIONS: Carboplatin can be safely delivered intracranially by biodegradable sustained- release polymers. This treatment improves survival in rodents with experimental gliomas, with locally delivered carboplatin being more effective than systemic carboplatin.

Animals↗

PubMed2003

Effect of poly-hydroxy aliphatic ester polymer type on amoxycillin release from cylindrical compacts.

The objective of the work was to investigate the effects of a range of poly-hydroxy aliphatic esters (poly-lactide (PLA) and poly-lactide-co-glycolide (PLGA)) of different molecular weight and composition on the release and stability of the amphoteric drug amoxycillin. The effect of this amphoteric drug on the extent and kinetics of polymer degradation was also investigated. The polymers were used to prepare drug-free and drug-loaded cylindrical discs. Drug release profiles were determined while changes in polymer composition were monitored by weight loss and molecular weight change. The extent of drug release was highly dependent on polymer molecular weight and composition, with earlier complete release occurring with the lower molecular weight and lower lactide containing polymers. A larger proportion of drug was released by polymer degradation control with the higher lactide containing polymer. The proportion of drug released intact was influenced by the polymer molecular weight, with a greater proportion of intact drug being released from the higher molecular weight systems. The inclusion of amoxycillin influenced polymer degradation and resulted in slower polymer hydrolysis. Model parameters obtained for polymer degradation indicated that this retardation effect increased with increasing lactide content of the polymer. The results suggest that small amounts of amoxycillin or its degradation products may bind or cross link with the polymers, thus retarding their degradation.

Amoxicillin↗

PubMed1999

Flexural properties of acrylic resin polymers reinforced with unidirectional and woven glass fibers.

STATEMENT OF PROBLEM: Fiber-reinforced plastics for dental applications have been under development for some time. A major difficulty in using reinforcing fibers with multiphase acrylic resins, such as powderliquid resins, has been improper impregnation of fibers with the resin. PURPOSE: The aim of this study was to describe and test a novel system to use polymer-preimpregnated reinforcing fibers with commonly used multiphase acrylic resins. MATERIAL AND METHODS: Continuous unidirectional and woven preimpregnated glass fiber reinforcements (Stick and Stick Net) were used to reinforce heat-curing denture base and autopolymerizing denture base polymers. A temporary fixed partial denture polymer was also reinforced with Stick reinforcement material. Five test specimens were fabricated for unreinforced control groups and for Stick- and Stick Net-reinforced groups. A 3-point loading test was used to measure transverse strength and flexural modulus of the materials and ultimate strain at fracture was calculated. Cross-sections of test specimens were examined with a SEM to evaluate degree of impregnation of fibers with polymer matrix. Quantity of fibers in test specimens was determined by combustion analysis. RESULTS: Transverse strength of heat-curing denture base polymer was 76 MPa, Stick reinforcement increased it to 341 MPa, and flexural modulus increased from 2550 to 19086 MPa. Stick Net reinforcement increased transverse strength of heat-curing denture base polymer to 99 MPa and flexural modulus to 3530 MPa. Transverse strength of autopolymerizing denture base polymer was 71 MPa; Stick increased it to 466 MPa; and flexural modulus increased from 2418 to 16749 MPa. Stick Net increased the transverse strength of autopolymerizing denture base polymer to 96 MPa and flexural modulus to 3573 MPa. Transverse strength of temporary fixed partial denture polymer increased from 58 to 241 MPa and flexural modulus from 1711 to 7227 MPa. ANOVA showed that reinforcement type and polymer brand affected transverse strength and modulus (P <.001). Stick Net reinforcement increased the strain at fracture, whereas Stick reinforcement decreased the strain values. SEM examination revealed well-impregnated glass fibers with polymer matrix. Quantity of glass fibers varied from 6 to 28 vol-%, the lowest being with Stick Net reinforcement and the highest with Stick reinforcement. CONCLUSIONS: Novel glass fiber reinforcements may considerably enhance flexural properties of multiphase dental polymers, which is due to proper impregnation of fibers with polymer matrix. By using Stick or Stick Net reinforcement, the strain at fracture of the material can be modified.

Acrylic Resins↗

PubMed2001

Preparation and performance of protein-adsorption-resistant asymmetric porous membrane composed of polysulfone/phospholipid polymer blend.

To obtain protein-adsorption-resistant membrane for hemodialysis, we prepared a polymer blend composed of polysulfone and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer (PSf/MPC polymer). The content of the MPC polymer in the PSf was 7 and 15 wt%. The asymmetric porous membrane was obtained by the dry/wet membrane processing method. The surface characterization of the PSf/MPC polymer membrane by X-ray photoelectron spectroscopy revealed that the MPC polymer located at the surface. The mechanical strength of the PSf/MPC polymer membrane did not change compared with that of the PSf membrane. On the other hand, the permeability of solute below a molecular weight (Mw) of 2.0 x 10(4) through the PSf membrane increased with the addition of the MPC polymer, which is considered to be an effect of the hydrophilic character of the MPC polymer. The amount of protein adsorbed on the PSf membrane from plasma was reduced by the addition of the MPC polymer. The permeability of low-molecular-weight protein (Mw = 1.2 x 10(4)) did not change even after the PSf/MPC polymer membrane was contacted with plasma protein solution for 4 h, whereas it decreased dramatically in the case of the PSf membrane. Platelet adhesion was also effectively suppressed on the PSf/MPC polymer membrane. Based on these results, the MPC polymer could serve as a doubly functional polymeric additive, that is, to generate a protein-adsorption-resistant characteristic and to render the membrane hydrophilic.

Adsorption↗

PubMed1998

Synthetic, implantable polymers for local delivery of IUdR to experimental human malignant glioma.

PURPOSE: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We evaluated whether we could similarly deliver halogenated pyrimidines to experimental intracranial human malignant glioma. To address this issue we studied the in vitro release from polymers and the in vivo drug delivery of IUdR to experimental human U251 glioblastoma xenografts. METHODS AND MATERIALS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions of IUdR in synthetic [(poly(bis(p-carboxyphenoxy)-propane) (PCPP):sebacic acid (SA) polymer discs were serially incubated in buffered saline and the supernatant fractions were assayed. In vivo: To compare local versus systemic delivery, mice bearing flank xenografts had intratumoral or contralateral flank IUdR polymer (50% loading) treatments. Mice bearing intracranial (i.c.) xenografts had i.c. versus flank IUdR polymer treatments. Four or 8 days after implantation of polymers, mice were sacrificed and the percentage tumor cells that were labeled with IUdR was measured using quantitative microscopic immunohistochemistry. RESULTS: In vitro: Increasing percentage loadings of IUdR resulted in higher percentages of release: 43.7 + 0.1, 70.0 + 0.2, and 90.2 + 0.2 (p < 0.001 ANOVA) for the 10%, 30%, and 50% loadings, respectively. In vivo: For the flank tumors, both the ipsilateral and contralateral IUdR polymers resulted in similarly high percentages labeling of the tumors versus time. For the ipsilateral IUdR polymers, the percentage of tumor cellular labeling after 4 days versus 8 days was 45.8 +/- 7.0 versus 40.6 +/- 3.9 (p = NS). For the contralateral polymer implants, the percentage of tumor cellular labeling were 43.9 +/- 10.1 versus 35.9 +/- 5.2 (p = NS) measured 4 days versus 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentage of tumor cellular labeling was low: 13.9 +/- 8.8 and 11.2 +/- 5.7 measured 4 and 8 days after implantation. For the i.c. tumors having the i.c. IUdR polymers, however, the percentage labeling was comparatively much higher: 34.3 +/- 4.9 and 35.3 +/- 4.0 on days 4 and 8, respectively. For the i.c. tumors, examination of the percentage cellular labeling versus distance from the implanted IUdR polymer showed that labeling was highest closest to the polymer disc. CONCLUSION: Synthetic, implantable biodegradable polymers provide the local, controlled release of IUdR and result in the high, local delivery of IUdR to experimental intracranial human malignant glioma. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Animals↗

PubMed2005

Ligand-receptor interactions in tethered polymer layers.

The binding of small proteins to ligands that are attached to the free ends of polymers tethered to a planar surface is studied using a molecular theory. The effects of changing the intrinsic binding equilibrium constant of the ligand-receptor pair, the polymer surface coverage, the polymer molecular weight, and the protein size are studied. The results are also compared with the case where ligands are directly attached to the surface without a polymer acting as a spacer. We found that within the biological range of binding constants the protein adsorption is enhanced by the presence of the polymer spacers. There is always an optimal surface coverage for which ligand-receptor binding is a maximum. This maximum increases as the binding energy and/or the polymer molecular weight increase. The presence of the maximum is due to the ability of the polymer-bound proteins to form a thick layer by dispersing the ligands in space to optimize binding and minimize lateral repulsions. The fraction of bound receptors is unity for a very small surface coverage of ligands. The very sharp decrease in the fraction of bound ligand-receptor pairs with surface coverage depends on the polymer spacer chain length. We found that the binding of proteins is reduced as the size of the protein increases. The orientation of the bound proteins can be manipulated by proper choice of the grafted layer conditions. At high polymer surface coverage the bound proteins are predominantly perpendicular to the surface, while at low surface coverage there is a more random distribution of orientations. To avoid nonspecific adsorption on the surface, we studied the case where the surface is covered by a mixture of a relatively high molecular weight polymer with a ligand attached to its free end and a low molecular weight polymer without ligand. These systems present a maximum in the binding of proteins, which is of the same magnitude as when only the long polymer-ligand is present. Moreover, when the total surface coverage in the mixed layers of polymers is high enough, nonspecific adsorption of the proteins on the surface is suppressed. The use of the presented theoretical results for the design of surface modifiers with tailored abilities for specific binding of proteins and optimal nonfouling capabilities is discussed.

Adsorption↗

PubMed2000

Polymer chemotherapy for head and neck cancer.

OBJECTIVES: To study a new method of delivery of chemotherapy for the treatment of squamous cell carcinomas (SCCs) of the head and neck, to evaluate the pharmacokinetics of four anticancer agents (cisplatin, fluorouracil [5-FU], methotrexate [MTX], and paclitaxel) loaded into the biodegradable polymer, polyanhydride polymer poly(FAD:SA), and to evaluate the effectiveness and toxicity of the drug-polymer combination against human SCCs, both in vitro and in vivo. STUDY DESIGN: Poly(FAD:SA) was loaded with different chemotherapeutic drugs and its in vitro and in vivo drug release and tissue penetration characteristics were studied. The biocompatibility and toxicity of the polymer-drug combination were determined. The effectiveness of the drug-polymer was evaluated against three different human SCCs (larynx O11, pharynx FADU, and floor of mouth UM- SCC1) cultured in vitro and in nude mice carrying human SCC xenografts. METHODS: The in vitro drug release pharmacokinetics of the drugs were performed using atomic absorption spectrometry for cisplatin and high-pressure liquid chromatography for the 5-FU, MTX, and paclitaxel studies. In vitro tumor cytotoxicity was assessed by growth assay. In vivo cytotoxicity was assessed by growth rate inhibition in a nude mouse model. RESULTS: All four chemotherapy drugs demonstrated a continuous release that followed first-order kinetics from the polymer. More than 95% of the MTX and 5-FU, 70% of the cisplatin, and 20% of the paclitaxel was released within the 10 days of the assay. Tumor cytotoxicity revealed that the polymer was very effective against the human SCCs O11, FADU, and UM- SCC1 in vitro. When a small amount of polymer (1-2 g) was added to the cell culture and left for 7 days, 96.6% of the UM-SCC1 cells, 86.9% of the FADU cells, and 94.6% of the O11 cells were killed. When the culture medium was then changed every 2 days to remove the effect of nutrient depletion or chemicals released by the degrading polymer, 74% of the UM-SCC1 cells, 94.5% of the FADU cells, and 66.1% of the O11 cells were killed at 7 days. The tumor animal model was the nude mouse carrying human floor of mouth SCC xenografts. Different amounts of cisplatin were incorporated into the polymers (5% and 7% drug/polymer at a weight/weight [wt/wt] load). Thirty-five days after implantation of the polymer in nude mice, the mean treated tumor size was 65.5% of controls in the 5% group and 31.8% in the 7% group. Seventy days after implantation the mean treated tumor size was 41.4% of controls in the 5% group and 38.1% in the 7% group, indicating a statistically significant delay of tumor growth compared with controls or with intraperitoneally injected cisplatin. The blank polymer was well tolerated by the mouse and had no effect on tumor growth. CONCLUSIONS: The study results indicate that polymer chemotherapy is effective against a variety of SCCs of the head and neck, both in vitro and in vivo, and may become a useful therapeutic option for head and neck cancer.

Animals↗

PubMed1991

Chemical and molecular weight analyses of prosthodontic soft polymers.

A number of studies have been made investigating the properties of dental prosthodontic soft polymer materials. In such materials, which are used as short-term denture soft liners, the polymer component is complexed with one or more plasticizers. This lowers the glass transition temperature, Tg, of the polymer by allowing greater chain mobility and produces a more flexible material. Little information is available relating to the polymer components of such soft-lining materials. The chemical composition and molecular-weight distribution of a polymer help to determine its ability to form a plasticized soft polymer-gel. In the present work, both pyrolysis depolymerization/gas chromatography (GC) and size exclusion chromatography (SEC) have been used to characterize 11 commercial polymer powders. By use of SEC and polymer standards having a narrow molecular-weight range, it has been possible for accurate molecular-weight distributions to be determined for all 11 powders. The peak molecular weights were found to be between 1.79 x 10(5) and 3.28 x 10(5). These values are above the molecular weight at which chain entanglement occurs. The polydispersity ratios (Mw/Mn) were between 2.09 and 4.48. Methacrylate polymers can be readily decomposed thermally to their constituent monomers, which, once recovered, can be analyzed by gas chromatography. The simple pyrolysis apparatus used in the present study was easily assembled and was capable of producing both qualitative and quantitative results. None of the commercial polymers analyzed gave methacrylate decomposition products with pendant chains greater than ethyl (-CH2-CH3). All of the commercial polymers successfully studied by the pyrolysis test method proved to be poly(ethyl [100-79%]/methyl [0-21%] methacrylate) polymers or co-polymers.

Chromatography, Gas↗

PubMed2002

Polymers in nephrology. Characteristics and needs.

Polymers employed as biomaterials in nephrology serve for different applications: they form membranes for dialysis and plasmapheresis, are used as materials for dialyser housings and as a potting mass for capillary membranes, they make up tubing-systems for extracorporeal circuits and - in the form of beads - act as parts of adsorber columns for hemoperfusion or immunoadsorption. However, generally speaking, many polymers have not yet been designed for their final application. To date, many polymers are still taken from the chemist's shelf according to their alleged performance properties or to their sterilisability. When used in medical application, polymers must show a high purity. Uncontrolled leaching of oligomers from the polymer backbone or of additives from or during the manufacturing process must be avoided. Blood and other body fluids are extremely effective in extracting any loosely bound polymers. During long-term application, e.g. in patients suffering from chronic diseases, these effects may lead to an accumulation of these compounds in circulating blood, tissue, or joints. Consequently, polymers should show an excellent biostability and not degrade during their ageing process. The amount of extractable material should be kept low in order to avoid inflammatory reactions. Polymers must have high blood compatibility in terms of minimized cell- and complement activation. Polymers for medical application should at best be able to stand high temperatures in order to survive steam sterilisation. If this is impossible, their release kinetics for residual quantities of sterilizing agents should be fast. Finally, protein adsorption should appear under controlled conditions, otherwise a reduced performance through protein adsorption will take place. Further, the uncontrolled activation of biochemical cascades, such as the coagulation, complement or contact phase cascade, following blood/material contact must be minimized. A final aspect has been recently made responsible for adverse patients reactions, the interaction between polymers and medicinal drugs. This drug/material interaction must be low, at best zero, apart form those situations, where a controlled drug-release is wanted. The chemical variety of polymers for medical application is large. However, all typical requirements cannot be met by one single polymer. Compromises have to be found between properties and application. Polymer selection for application in nephrology has always to be made under the premise of final application.

Adsorption↗

PubMedDate not supplied

Strength of relined denture base polymers subjected to long-term water immersion.

PURPOSE: This study was undertaken to characterize the long-term equilibrium flexural strength at proportional limit (FSp) of 4 denture reline polymers processed onto 4 denture base polymers. MATERIALS AND METHODS: A 3-point flexural test was applied on rectangular specimens of each denture base polymer-denture reline polymer. Each specimen was immersed in water for 4 months prior to and 4 months after reline. RESULTS: Significant differences existed among the relined specimens because of the denture base polymer variable, the denture reline polymer variable, and their interaction (P < 0.05). The descending order in FSp according to the denture base polymer, arranged in terms of statistical significance was: Acron approximately Acron MC > Triad > Palapress Vario, where approximately denotes no significant difference between Acron and Acron MC. The descending order in FSp according to the denture reline polymer, arranged in terms of statistical significance was: Triad > Rebaron > Rebaron LC > Tokuso Rebase. Significant difference existed among all of the denture reline polymers. CONCLUSION: The present study showed that the long-term equilibrium strengths of 4 denture reline polymers processed onto 4 denture base polymers were different. The strength of the relined specimen of a denture base is dependent on the strength of the denture base polymer and that of the reline polymer.

Acrylic Resins↗

PubMedDate not supplied

Viscosity of polymer solution phase and other factors controlling the dissolution of theophylline microspheres prepared by the emulsion solvent evaporation method.

The objectives of this investigation are to evaluate the effect of the viscosity of polymer solution phase on microsphere properties, especially the drug release characteristics since no studies on this formulation variable have been reported. Also, since it is known that polymer molecular weight affects both the viscosity of the polymer solution and the release properties of microspheres, the interaction of these factors was studied. Microspheres with 33% theoretical drug loading of anhydrous theophylline core material were prepared by the emulsion solvent evaporation method. Two cellulose acetate butyrate polymers, (CAB381-2, CAB381-20), chemically similar but having different molecular weights, were used to prepare different polymer solutions having different apparent viscosities in acetone. A Brookfield viscometer was used to evaluate the viscosities of polymer solutions. Dissolution rates of microspheres prepared from the polymer solutions were inversely related to the initial polymer solution viscosities for both CAB381-2 and CAB381-20. The times for the release of 30 and 50% of the drug from the microspheres have a linear relationship with initial polymer solution viscosity. Initial release was significantly decreased with increasing polymer solution viscosity. Unlike CAB381-2 microspheres which follow Higuchi spherical matrix release kinetics, microspheres prepared from the higher molecular weight polymer (CAB381-20) showed extended release dissolution profiles with near zero order kinetics. It is evident that both the polymer solution viscosity and the molecular weight have an effect on the drug release from microspheres. These results suggest that release rates of matrix microspheres could be predictably optimized by adjusting the viscosity of polymer solutions.

Delayed-Action Preparations↗

PubMed2001

Preparation of Colloidal Low-Density Polyethylene Latexes by Flow-Induced Phase Inversion Emulsification of Polymer Melt in Water.

The aim of this study is to prepare colloidal polymeric latexes by using the flow-induced phase inversion emulsification method given by G. Akay [Chem. Eng. Sci. 53, 203 (1998)] of polymer melts followed by the solidification of polymer melt droplets. We also investigate the mechanism of emulsification and stabilization in polymeric dispersions which undergo a phase change after emulsification. The history of the emulsification and emulsion structure are monitored by using a process rheometer and off-line scanning electron microscopy with energy-dispersive X-ray analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and particle size measurements. It is shown that the molecular structure of the surface-active material is the most important parameter in achieving phase inversion emulsificationin polymer melts. Molecular surfactants could not be used to provide surface activity in polymeric melts. Several experimental polymeric surfactants are used and their ability to form a [water-in-polymer melt] emulsion is tested. The successful polymeric surfactants are known as hydrophobically modified water-soluble polymers. It is postulated that the surface-active materials should conform at the water/polymer melt interface and not be removed from the interface by surface deformations. The ability of hydrophobically modified water-soluble polymers to remain at the interface is reduced if the hydrophobic moeties which anchor into the polymer melt have chain length approaching 18 carbons or more. After the first phase inversion and subsequent dilution of the [polymer melt-in-water], if mixing is carried out while cooling, a second phase inversion takes place from [polymer melt-in-water] to [water-in-solid polymer] despite high water content of the polymer/water system. If the water content is high (25-40% investigated) the second phase inversion yields a powdered material with encapsulated water. A third phase inversion occurs if the powdered microcapsules from the second phase inversion is heated while mixing to yield a [(water-in-polymer)-in-water] multiple emulsion which can be inverted back to [polymer melt-in-water] emulsion by increasing the temperature and subjecting the emulsion to high deformation rate flows. However, if this last phase inversion is not allowed to proceed to completion, and the [(water-in-polymer)-in-water] multiple emulsion is cooled, microporous polymeric particles are obtained. Copyright 2001 Academic Press.

Journal Article↗

PubMed1996

Aggregation of phospholipid vesicles by water-soluble polymers.

Water-soluble polymers such as dextran and polyethylene glycol are known to induce aggregation and size growth of phospholipid vesicles. The present study addresses the dependence of these processes on vesicle size and concentration, polymer molecular weight, temperature, and compartmentalization of the vesicles and polymers, using static and dynamic light scattering. Increasing the molecular weight of the polymers resulted in a reduction of the concentration of polymer needed for induction of aggregation of small unilamellar vesicles. The aggregation was fully reversible (by dilution), within a few seconds, up to a polymer concentration of at least 20 wt %. At relatively low phosphatidylcholine (PC) concentrations (up to approximately 1 mM), increasing the PC concentration resulted in faster kinetics of aggregation and reduced the threshold concentration of polymer required for rapid aggregation (CA). At higher PC concentrations, CA was only slightly dependent on the concentration of PC and was approximately equal to the overlapping concentration of the polymer (C*). The extent of aggregation was similar at 37 and 4 degrees C. Aggregation of large unilamellar vesicles required a lower polymer concentration, probably because aggregation occurs in a secondary minimum (without surface contact). In contrast to experiments in which the polymers were added directly to the vesicles, dialysis of the vesicles against polymer-containing solutions did not induce aggregation. Based on this result, it appears that exclusion of polymer from the hydration sphere of vesicles and the consequent depletion of polymer molecules from clusters of aggregated vesicles play the central role in the induction of reversible vesicle aggregation. The results of all the other experiments are consistent with this conclusion.

Dextrans↗

PubMed2002

Two-dimensional rhombohedral grid coordination polymers [M(bbbt)(2)(NCS)(2)](n)(M = Co, Mn, or Cd; bbbt = 1,1'-(1,4-butanediyl) bis-1H-benzotriazole): synthesis, crystal structures, and third-order nonlinear optical properties.

In this paper, treatment of 1,1'-(1,4-butanediyl) bis-1H-benzotriazole (bbbt) and KSCN with Co(II), Mn(II), or Cd(II) afforded three two-dimensional rhombohedral grid coordination polymers [M(bbbt)(2)(NCS)(2)](n)(M = Co, 1; Mn, 2; Cd, 3). The two-dimensional rhombohedral grids are parallel to the crystallographic ac plane. The rhombohedral grid consists of 44-membered rings of M(4)(bbbt)(4), and gives the dimensions of 12.913 x 10.764 A for polymer 1, 13.106 x 10.797 A for polymer 2, and 13.256 x 10.870 A for polymer 3. The three polymers' third-order nonlinear optical (NLO) properties were determined by Z-scan technique in DMF solution. The results show that all three polymers show very large NLO absorption and strong NLO refraction properties. The third-order NLO absorptive coefficients alpha(2) are 5.4 x 10(-9) m W(-1) for polymer 1, 5.2 x 10(-9) m W(-1) for polymer 2, and 5.0 x 10(-9) m W(-1) for polymer 3. The alpha(2) values are larger than those of all the reported cluster compounds. The NLO refractive index values n(2) of the three polymers are 5.73 x 10(-19), 3.55 x 10(-19), and 3.07 x 10(-19) m(2) W(-1), respectively. Their hyperpolarizability gamma values are calculated to be 2.40 x 10(-30) esu for polymer 1, 1.52 x 10(-30) esu for polymer 2, and 1.50 x 10(-30) esu for polymer 3. The gamma values are comparable to those of clusters and better than those of organometallic compounds, semiconductors, and fullerene.

Journal Article↗

PubMed2004

Polymer bilayer formation due to specific interactions between beta-cyclodextrin and adamantane: a surface force study.

The purposes of this study are to utilize the interactions between an adamantane end-capped poly(ethylene oxide) (PEO) and a cationic polymer of beta-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEO-Ad) mixed with the beta-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the beta-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized beta-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized beta-cyclodextrin polymer in pure water was investigated. It was found that the beta-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the beta-cyclodextrin polymer are rather compact, with a layer thickness of about 60 A (30 A per surface). Upon separation, a very weak attractive force is observed. The beta-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the beta-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive long-range force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the beta-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the beta-cyclodextrin polymer and the adamantane groups.

Adamantane↗

PubMed2005

Theoretical study of cooperativity in multivalent polymers for colloidal stabilization.

Multivalent polymers, i.e., copolymers with multiple binding sites, have been proposed recently for stabilization of fusogentic liposomes and other liposomal colloids useful for drug delivery. The performance of such polymers critically depends on their molecular architecture, in particular the strength and frequency of surface anchoring sites along the backbone of a highly soluble polymer. In this work, we investigate the adsorption and surface forces due to multivalent polymers based on coarse-grained polymer models. We find that for W-type polymers that form dangling tails when all anchoring segments are attached to a surface, increasing the chain length at fixed polymer composition leads to a stronger repulsive barrier in the polymer-mediated surface forces thereby increasing the ability of the polymer to stabilize colloidal particles. This prediction conforms to an earlier experiment indicating that increasing the number of hydrophobic anchors along poly(ethylene glycol) polymers results in the cooperative behavior for both surface adsorption and steric stabilization. For M-type multivalent polymers that have weakly anchoring sites placed at the ends, however, addition of binding sites at fixed polymer composition could lead to negative cooperativity, i.e., the more binding sites, the less the amount of adsorption or the weaker the ability of surface protection. The theory also predicts that polymers with two anchoring sites (e.g., telechelic copolymers) are most efficient for colloidal stabilization.

Journal Article↗

PubMed1997

[Interactions between biospecific polymers and MCF7 cells: modulation of cellular proliferation and expression of estrogen receptors].

Numerous studies on interactions between insoluble polymers and cell membrane receptors indicated modulation of cellular proliferation and cell phenotype by these polymers considered as biospecific. We synthesized several biospecific polymers in order to investigate the interactions between polymers and intracellular receptors as estrogen receptors considered as tumoral indicator of breast cancer. Biospecific polymers were obtained by random substitutions of crosslinked polystyrene beads with suitable chemical groups (sulfonate and amino acid sulfamides). These polymers were used as microcarriers for culture of MCF7 cells, a cellular model of human breast cancer. Quantification of MCF7 cell estrogen receptors was determined by radioligand binding assay for different days of cellular proliferation. The data obtained with MCF7 cells cultured on biospecific polymers show an inverse relationship between polymer induced inhibition of cell proliferation and polymer induced increase of estrogen receptors. Similar inverse relationship was obtained with MCF7 cell cultured on standard polystyrene tissue culture plates. The various interaction between insoluble polymers and MCF7 cells could be related to the proportion and the nature of the substitutive chemical groups. These biospecific polymers could presents sites of interaction with cell membrane receptors leading to modulation of cell biological activity. The different insoluble polymers were used as preliminary models: a practical application could be a methodology of cellular selection using soluble biospecific polymers (for example chemically modified dextrans).

Binding, Competitive↗