PubMed Health⌕ Search

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 847 records · Page 47Linked to original sources

Randomized trial of a nonpolymer-based rapamycin-eluting stent versus a polymer-based paclitaxel-eluting stent for the reduction of late lumen loss.

BACKGROUND: Although drug-eluting stents (DESs) constitute a major achievement in preventing restenosis, concerns remain regarding the increased inflammatory and thrombogenic responses associated with the polymers used. Recently, we showed that a nonpolymer on-site coating with rapamycin not only is feasible and safe but also leads to a dose-dependent reduction in restenosis. METHODS AND RESULTS: To assess whether polymer-free stents coated on-site with 2% rapamycin solution are inferior to polymer-based paclitaxel-eluting stents for the prevention of restenosis, we randomly assigned a total of 450 patients with de novo lesions in native coronary vessels, excluding the left main trunk, to either the polymer-free, rapamycin-coated Yukon DES (rapamycin stent) or the polymer-based, paclitaxel-eluting Taxus stent (paclitaxel stent). The primary end point was in-stent late lumen loss. Secondary end points were angiographic restenosis and target lesion revascularization. The study was designed to test the noninferiority of the rapamycin stent compared with the paclitaxel stent with respect to late lumen loss according to a noninferiority margin of 0.13 mm. Follow-up angiography was completed in 81% of the patients. The mean difference in in-stent late lumen loss between the rapamycin-stent group and the paclitaxel-stent group was 0.002 mm, and the upper limit of the 1-sided 95% confidence interval was 0.10 mm (P=0.02 from test for noninferiority). No significant differences were observed regarding angiographic restenosis rates (14.2% with the rapamycin stent and 15.5% with the paclitaxel stent) and target lesion revascularization rates due to restenosis (9.3% in both groups). CONCLUSIONS: The polymer-free, rapamycin-coated stent has an antirestenotic effect that is not inferior to that observed with the polymer-based paclitaxel-eluting stent.

Aged↗

A decrease in Sendai virus infection potency by interactions with cationic thermo-responsive polymers.

Three types of synthetic cationic polymers were incubated with Sendai virus (HVJ), and virus infection of Rhesus monkey kidney cells, LLCMK2, was measured by the plaque assay method. One composition poly(N-isopropylacrylamide-co-N,N-dimethylaminopropyl acrylamide-co-butylmethacrylate) of (P(IP-27DA-16BM)) showed substantial decreases in the infection potency of the virus over a wide range of polymer concentrations. This polymer expressed a significant virus titer decrease even at a very low concentration (2 x 10(-4) wt%), and its virus titer reduction was found to be incubation temperature-dependent. As the virus was incubated with this polymer above the phase transition temperature of this polymer over a long period, the virus titer reduction was larger. Selectivity to the virus titer reduction in comparison with cytotoxicity to LLCMK2 cells was evaluated. This P(IP-27DA-16BM) polymer was revealed to possess a higher selectivity to virus reduction than sodium dodecyl sulfate. This indicates the feasibility of this polymer for a virus-specific inactivating agent.

Acrylic Resins↗

Synthesis and characterization of poly(L-alanine)-block-poly(ethylene glycol) monomethyl ether as amphiphilic biodegradable co-polymers.

Di-block co-polymers of poly(L-alanine) with poly(ethylene glycol) monomethyl ether (MPEG) were synthesized as amphiphilic biodegradable co-polymers. The ring-opening polymerization of N-carboxy-L-alanine anhydride (NCA) in dichloromethane was initiated by amino-terminated poly(ethylene glycol) monomethyl ether (MPEG-NH2, M(n) = 2000) to afford poly(L-alanine)-block-MPEG. The weight ratio of two blocks in the co-polymers could be altered by adjusting the feeding ratio of NCA to MPEG-NH2. Their chemical structures were characterized on the basis of infrared spectrometry and nuclear magnetic resonance. According to circular dichroism measurement, the poly(L-alanine) chain on the co-polymers in an aqueous medium had a alpha-helix conformation. Two melting points from MPEG block and poly(L-alanine), respectively, could be observed in differential scanning calorimetry curves of the co-polymers, suggesting that a micro-domain phase separation appeared in their bulky states. The co-polymers could take up some water and the capacity was dependent on the ratio of poly(L-alanine) block to MPEG. Such co-polymers might be useful in drug-delivery systems and other biomedical applications.

Biocompatible Materials↗

Dynamics of cellular entry and drug delivery by dendritic polymers into human lung epithelial carcinoma cells.

Dendrimers and hyperbranched polymers are emerging as potentially ideal drug delivery vehicles because they provide a significant amount of tailorability and a large density of functional groups. This study explores the dynamics of cellular entry of dendrimers and hyperbranched polymers alone, and in the complexed form with ibuprofen, into A549 human lung epithelial carcinoma cells using UV/Vis spectroscopy, flow cytometry and fluorescence microscopy. Both dendrimers and hyperbranched polymers appear to enter these cells rapidly. The polyamidoamine (PAMAM) dendrimers, with NH2 and OH end functionalities appear to enter cells (in approx. 1 h) faster than the hyperbranched polyol (OH functionality) (in approx. 2 h). Cellular entry of PAMAM-NH2 was detected as early as 5 min. All branched polymers and their ibuprofen complexes entered A549 lung epithelial cells rapidly when compared to the pure drug. The drug payload was about 50% by weight in the complexes formed by PAMAM-NH2 dendrimers and was about 30% in the encapsulated form for Polyol-OH and PAMAM-OH. The complexation and encapsulation of ibuprofen with the polymers appear to facilitate rapid cellular entry of ibuprofen. The anti-inflammatory effect of the polymer-complexed drug was demonstrated by more rapid suppression of COX-2 mRNA levels than that achieved by the pure drug. This suggests that these dendritic polymers can act as efficient drug carriers, delivering high 'payloads' of drug even with complexation and encapsulation.

Anti-Inflammatory Agents, Non-Steroidal↗

Biodegradable polymers as biomaterials.

Biomaterials are used in prostheses and medical devices for different purposes. Polymers are the most diverse class of biomaterials. All biomaterials must meet certain criteria and regulatory requirements before they can be qualified for use in medical applications. Biocompatibility is one of the most important requirements. Both nondegradable polymers are designed to degrade in vivo in a controlled manner over a predetermined time. The main mechanism of in vivo degradation of polymers is 'hydrolytic degradation', in which enzymes may also play a role (i.e. 'enzymatic degradation'). Both natural e.g., collagen, and synthetic e.g., poly(alpha-hydroxy) acids, biodegradable polymers are used in biomedical applications. Many of the current polymers and processing techniques need to be improved in order to produce polymers with better performance in biological media. An important trend in related research and development is the synthesis of novel polymers, which would exhibit improved biocompatibility, and be bioresponsive.

Animals↗

Elastic protein-based polymers in soft tissue augmentation and generation.

Five elastic protein-based polymers, designed as variations of polymer I, (GVGVP)251, elicited different responses when injected as subcutaneous implants in the guinea pig, a preclinical test used to evaluate materials for soft tissue augmentation and specifically for correction of urinary incontinence. All six polymers, prepared using recombinant DNA technology, expressed at good levels using transformed E. coli fermentation. These E. coli-produced polymers were purified for the first time to the exacting levels required for use as biomaterials where a large quantity could disperse into the tissues in a few days. Time periods of 2 and 4 weeks were used. Polymer I functioned as a bulking agent around which a fine fibrous capsule formed. Inclusion of (GVGVAP)8, a chemoattractant toward monocytes and elastin-synthesizing fibroblasts in the sequence of polymer I, resulted in an appropriate tissue response of invasion of macrophages. Inclusion of lysine residues, for lysyl oxidase cross-linking, suggested a possible remodeling of the implant toward fibers. Most promising however, when the cell attachment sequence, GRGDSP, was added to polymer I, the implant elicited tissue generation with a normal complement of collagen and elastic fibers, spindle-shaped histiocytes and angiogenesis. If this response is retained over time, the desired soft tissue augmentation and generation will have been achieved. Our working hypothesis is that on formation of elastin, with a half-life of the order of 70 years, a long lasting soft tissue augmentation would result rather than scar tissue as occurs with Contigen, the currently approved injectable implant for soft tissue augmentation.

Amino Acid Sequence↗

Insulin release from islets of Langerhans entrapped in a poly(N-isopropylacrylamide-co-acrylic acid) polymer gel.

A copolymer of N-isopropylacrylamide (98 mol% in feed) and acrylic acid, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAAm-co-AAc)), was prepared by free radical polymerization for development of a thermally reversible polymer to entrap islets of Langerhans for a refillable biohybrid artificial pancreas. A 5 wt% solution of the polymer in Hanks' balanced salt solution forms a gel at 37 degrees C that exhibits no syneresis. Diffusion of fluorescein isothiocyanate (FITC) dextrans having molecular weights of 4400 and 70000 were used to evaluate mass transport in the gel at 37 degrees C. Insulin secretion from islets in the polymer gel was also investigated in both static and dynamic systems. The polymer gel exhibited excellent diffusion of FITC dextran 4400 and FITC dextran 70000 with diffusion ratios, D/D0 (ratio of diffusion in the gel to diffusion in water), of 0.20+/-0.04 and 0.35+/-0.17, respectively. Human islets entrapped in the polymer gel showed prolonged insulin secretion in response to basal (5.5 mM) glucose concentration compared to free human islets. Rat islets showed prolonged insulin secretion in response to high (16.5 mM) glucose concentrations compared to free rat islets. Rat islets in the polymer gel maintained insulin secretion in response to the higher glucose concentration for over 26 days. Rat islets entrapped by the polymer also released higher quantities of insulin more rapidly in response to changes in concentrations of glucose and other stimulants than rat islets entrapped in an alginate control. These results suggest that this material would provide adequate diffusion for rapid insulin release in an application as a synthetic extracellular matrix for a biohybrid artificial pancreas.

Acrylamides↗

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers.

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylatel copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.

Adsorption↗

Enhancement of ionic conductivity of PEO based polymer electrolyte by the addition of nanosize ceramic powders.

The ionic conductivity of polyethylene oxide (PEO) based solid polymer electrolytes (SPEs) has been improved by the addition of nanosize ceramic powders (TiO2 and AL2O3). The PEO based solid polymer electrolytes were prepared by the solution-casting method. Electrochemical measurement shows that the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte has the best ionic conductivity (about 10(-4) S cm(-1) at 40-60 degrees C). The lithium transference number of the 10 wt% TiO2 PEO-LiClO4 polymer electrolyte was measured to be 0.47, which is much higher than that of bare PEO polymer electrolyte. Ac impedance testing shows that the interface resistance of ceramic-added PEO polymer electrolyte is stable. Linear sweep voltammetry measurement shows that the PEO polymer electrolytes are electrochemically stable in the voltage range of 2.0-5.0 V versus a Li/Li+ reference electrode.

Aluminum Oxide↗

Polymer-encapsulated PC-12 cells demonstrate high-affinity uptake of dopamine in vitro and 18F-Dopa uptake and metabolism after intracerebral implantation in nonhuman primates.

Intracranial implantation of polymer-encapsulated PC-12 cells has been shown to improve motor behavioral performance in animal models of Parkinson's disease. The purpose of this blinded study was to examine whether such improvement is associated with the active uptake and metabolism of dopamine precursors by intracerebrally implanted polymer-encapsulated PC-12 cells. In an in vitro experiment we demonstrate that 3H-dopamine uptake by PC-12 cells was 10(8) fmol/min x 10(6) cells, and that this uptake can be specifically blocked 88% by the addition of 10nM of nomifensine. In the in vivo experiments, polymer-encapsulated PC-12 cells were implanted in four MPTP-treated monkeys into the left deep parietal white matter (R1) or left striatum (R2-4). A fifth MPTP-treated monkey (R5) served as a control and received left striatal implants of empty capsules. 18-F-Dopa Positron Emission Tomography (PET) imaging was performed on each monkey before and after implantation surgery by blinded investigators. PET images obtained 5-13 wk after implantation demonstrated well delineated focal areas of high 18F-dopa uptake in R1, R2, and R4. The focal area of high 18F-dopa uptake in R1 precisely coregistered on a brain magnetic resonance image to the site of implantation. R3 (in whom the polymer-encapsulated PC-12 cells demonstrated poor cell survival upon explantation) and R5 (empty capsules) failed to demonstrate any area of increased 18F-dopa uptake in their PET images. Histological examination of the host brain revealed no sprouting of dopaminergic nerve terminals around the implantation sites of the polymer-encapsulated PC-12 cells. These results indicate that the previously noted behavioral improvement after intrastriatal implantation of polymer encapsulated PC-12 cells is at least in part due to their highly specific uptake and metabolism of dopamine precursors. Furthermore, these data suggest that polymer-encapsulated PC-12 cells can store, reuptake, and functionally replenish dopamine and therefore, may be an effective treatment for Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

Influence of hydrophilic polymers on celecoxib complexation with hydroxypropyl beta-cyclodextrin.

Complexation of celecoxib with hydroxypropyl beta-cyclodextrin (HPbetaCD) in the presence and absence of 3 hydrophilic polymers-polyvinyl pyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), and polyethylene glycol (PEG)-was investigated with an objective of evaluating the effect of hydrophilic polymers on the complexation and solubilizing efficiencies of HPbetaCD and on the dissolution rate of celecoxib from the HPbetaCD complexes. The phase solubility studies indicated the formation of celecoxib-HPbetaCD inclusion complexes at a 1:1M ratio in solution in both the presence and the absence of hydrophilic polymers. The complexes formed were quite stable. Addition of hydrophilic polymers markedly enhanced the complexation and solubilizing efficiencies of HPbetaCD. Solid inclusion complexes of celecoxib-HPbetaCD were prepared in 1:1 and 1:2 ratios by the kneading method, with and without the addition of hydrophilic polymers. The solubility and dissolution rate of celecoxib were significantly improved by complexation with HPbetaCD. The celecoxib-HPbetaCD (1:2) inclusion complex yielded a 36.57-fold increase in the dissolution rate of celecoxib. The addition of hydrophilic polymers also markedly enhanced the dissolution rate of celecoxib from HPbetaCD complexes: a 72.60-, 61.25-, and 39.15-fold increase was observed with PVP, HPMC, and PEG, respectively. Differential scanning calorimetry and X-ray diffractometry indicated stronger drug amorphization and entrapment in HPbetaCD because of the combined action of HPbetaCD and the hydrophilic polymers.

2-Hydroxypropyl-beta-cyclodextrin↗

A new drug delivery system using plasma-irradiated pharmaceutical aids. VII. Control release of theophylline from plasma-irradiated polymer-coated granules.

With a view to expanding the application of a drug delivery system (DDS) preparation using plasma-irradiated pharmaceutical aids for various dosage forms, we studied the theophylline release property from plasma-irradiate polymer-coated granules, the polymers of which differ in the plasma irradiation effect. We used a new type of rotational plasma-irradiation reactor to perform plasma-irradiation uniformly on the surface of polymer-coated granules based on scanning electron microscope (SEM) observation. It was shown that an increase in theophylline release rate with an increase in plasma duration was observed in all polymer-coated granules, although the factors of such release properties vary with the polymers, as evidenced by the SEM observations. Such results provided the criteria for selecting polymer structures for granule coating. Thus, the present method for the control of drug release is considered principally applicable not only to polymer-coated granules but also to various drug forms under consideration of the above criteria.

Delayed-Action Preparations↗

Influence of water-soluble polymers on the dissolution of nifedipine solid dispersions with combined carriers.

The objective of this investigation was to clarify the influence of water-soluble polymers on the dissolution behavior of nifedipine from solid dispersions with combined carriers. All the solid dispersions of nifedipine were prepared by the fusion method using nicotinamide and 4 different water-soluble polymers, hydroxypropylmethyl-cellulose (HPMC), polyvinylpyrrolidone (PVP), partially hydrolyzed polyvinyl alcohol (PVA) and pullulan. HPMC, PVP or PVA dissolved in the fused liquid of nicotinamide and operated efficiently on the amorphous formation of nifedipine in solid dispersions. In dissolution studies, the drug concentration for these dispersions increased to more than twice intrinsic drug solubility. The rank order of the drug concentration was HPMC > PVP > PVA. However, since pullulan did not dissolve in the fused nicotinamide, nifedipine was present as a crystalline state in the solid dispersion; the supersaturation behavior of the drug was scarcely observed. The compatibility, namely, the solubility and miscibility, between nicotinamide or nifedipine and the polymers, was determined by differential scanning calorimetry using the mixtures treated with fusing and subsequent rapid cooling. Both HPMC and PVP exhibited high compatibility not only with nicotinamide but also with nifedipine. The crystallization behavior of nifedipine from a supersaturated solution containing nicotinamide or the polymers was studied. The inhibitory effect of HPMC or PVP for drug crystallization was evident, which would be related not to the solubilizing effect but to the adhesive force of the polymer for the drug. Therefore, it was understood that the use of a polymer with high compatibility and adhesion with nifedipine provides a high supersaturation level of the drug in dissolution. Further, the solubility parameter was found to be useful for selecting a suitable polymer as a component of combined carriers.

Calcium Channel Blockers↗

Chemical and biological properties of polymer-modified proteins.

Modification with polymers such as polyethylene glycol (PEG) can increase circulating lifetime, reduce immunogenicity and simplify the handling of pharmaceutical proteins. These benefits are currently exploited in six marketed polymer-modified protein therapeutics and about a dozen product candidates in clinical trials. However, traditional protein modification techniques are restricted by the limited control over polymer structure and the location and number of polymer attachment sites. New technology, in the form of chemical protein synthesis and the generation of precision polymers, has been applied to generate synthetic erythropoiesis protein (SEP). This promising treatment for anaemia has been synthesised with precision polymer modification methodology to improve the target protein pharmaceutical. The chemical and biological properties of proteins prepared by both traditional and novel approaches are contrasted in this discussion of chemical protein synthesis and polymer modification in protein drug discovery.

Amino Acid Sequence↗

Polymer conjugates. Pharmacokinetic considerations for design and development.

Soluble polymer conjugates have only recently been introduced into clinical practice. They can be subdivided into 2 main categories: polymer-protein conjugates, so far the most widely studied; and polymer-drug conjugates, particularly those containing conventional antitumour agents, that are still at an early stage of development. Polymer conjugation can be used to alter the biodistribution, elimination and rate of metabolism of covalently bound drugs. In the case of protein adducts, polymer conjugation prolongs the protein plasma elimination half-life (5- to 500-fold increases in elimination half-life have been reported), reduces proteolytic degradation and has the added benefit of reducing immunogenicity. Cellular uptake of low molecular weight drugs convalently bound to polymeric carriers is restricted to the endocytic route. Thus, the organ and subcellular distribution of the drug can be modified. Cellular uptake has been used to facilitate drug targeting and decreased toxicity. In this review, the theoretical rationale for polymer conjugation is described, as is the limited clinical pharmacokinetic experience with polymer conjugates. As an alteration of the pharmacokinetic profile of a drug was one of the underlying arguments for creation of polymeric conjugates, more clinical pharmacokinetic studies are urgently needed to permit the validation of appropriate pharmacokinetic models that can be used in the future to assist in the optimisation of clinical protocols, and improved conjugate design.

Asparaginase↗

Wastewater dewatering polymer affect on biosolids odor emissions and microbial activity.

Odor emissions and microbial activity associated with biosolids dewatered using seven different polyacrylamide cationic polymers were investigated. Nitrogen, sulfur, ketone, and odor unit emissions, and biosolids microbial community metabolic profiles were measured for biosolids containing each polymer. Ammonia represented more than 98% of total nitrogen flux for all polymers, with small concentrations of trimethyl amine. Dimethyl disulfide and carbon disulfide fluxes summed represented 87 to 97% of the sulfur flux for all polymers, with lesser quantities of dimethyl sulfide. Maximum dimethyl disulfide, ammonia, and trimethyl amine concentrations were estimated to be 3.4, 3.2, and 13.5 times greater than published detection limits, respectively. Maximum dimethyl sulfide, carbon disulfide, acetone, and methyl ethyl ketone concentrations were estimated to be 0.028, 0.007, 0.002, and 0.0006 times less than published detection limits, respectively. All treatments were found to volatilize equal odor unit emissions (with the exception of one polymer), and polymers were not found to dramatically affect odor emission from biosolids application. Metabolic fingerprints revealed differences in the ability of microbial communities from certain polymer treatments to degrade amino acids as a sole carbon substrate. In addition, odor unit emissions were significantly correlated with potential for amino acid decomposition.

Amino Acids↗

Bovine serum albumin loaded poly(lactide-co-glycolide) microspheres: the influence of polymer purity on particle characteristics.

To study the influence of polymer purity on microsphere characteristics, bovine serum albumin (BSA) loaded biodegradable microspheres were prepared by spray drying using two samples of poly(lactide-co-glycolide), PLG, (50:50, mwt = 35 and 69 kDa). Polymer properties were varied by DL-lactide and glycolide addition or by ultrafiltration. While the effective drug loading was not affected by polymer purity, Tg was decreased with increasing monomer and oligomer content. The removal of these low molecular weight substances by ultrafiltration led to a narrower molecular weight distribution compared to the untreated PLG. Concerning the polymer with the higher molecular weight, microsphere morphology was also strongly affected by polymer composition. In contrast to the non-modified PLG, monomer addition yielded particles with a much smoother surface structure. Moreover, in vitro cytotoxicity of the microspheres prepared from the polymer pretreated by ultrafiltration was significantly reduced, whereas monomer addition caused a dramatic decrease of cells surviving contact with the microsphere extract. The in vivo degradation rate of the ultrafiltered microspheres was decreased and as a result, protein release at later times was slowed down. Furthermore, depending on the effective drug loading level, monomer addition resulted in a decrease in the initial protein burst. It can be concluded that the effect of low molecular weight impurities in a polymer on microsphere characteristics and on cytotoxicity cannot be ignored. Their elimination is possible by ultrafiltration.

Animals↗

Genetically engineered polymers for drug delivery.

Genetic engineering methodology offers the ability to synthesize protein-based polymers with precisely controlled structures. Protein-based polymers synthesized by recombinant techniques have a well-defined monomer composition and sequence, stereochemistry, and a narrow molecular weight distribution. The structure of the polymeric carrier at the molecular level influences its biological disposition and drug release profile. Current methodologies of polymer synthesis (chemical polymerization) result in the production of polymers with heterogeneous molecular weights, and with monomer sequences and compositions defined in terms of statistical distributions. Genetic engineering methodologies can be used to design new polymeric drug carriers with improved properties, such as better-defined biorecognition, pharmacokinetic, biodegradation, and drug release profiles. In this review article the rationale and methodology of polymer synthesis using genetic engineering techniques, the status of such polymers in drug delivery to-date, and the potential of these polymers for the development of new systems in the future are discussed.

Drug Delivery Systems↗