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PubMed1999

Effect of molecular weight and polydispersity on kinetics of dissolution and release from ph/temperature-sensitive polymers.

N-isopropylacrylamide (NIPAAm) polymers exhibit a lower critical solution temperature (LCST). Aqueous solutions of these polymers are soluble below their LCST and precipitate above their LCST. The LCST is dependent on pH for polymers with ionizable groups because of a change in hydrophilicity with ionization and electrostatic repulsion that cause a shift in the LCST. We have designed a novel polymeric delivery system that utilizes linear, pH/temperature-sensitive terpolymers of NIPAAm, butyl methacrylate (BMA) and acrylic acid (AA). This system allows the aqueous loading of drugs in polymeric beads with high loading efficiency while preserving the bioactivity of the protein drug. Furthermore, the unique properties of the pH/temperature-sensitive polymeric bead make it a potential system for oral drug delivery of peptide and protein drugs to different regions of the intestinal tract. This study aims at investigating the effect of polydispersity and molecular weight (MW) of terpolymers of poly(NIPAAm-co-BMA-co-AA) with feed mol ratio of NIPAAm/BMA/AA 85/5/10 on the polymer dissolution rate and on the release kinetics of a model protein, namely insulin. Varying the weight average MW (Mw) and polydispersity of the polymer modulated the polymer dissolution rate and the release rate of insulin from pH/temperature-sensitive polymeric beads. An increase in the polydispersity of the polymer through the addition of high MW polymer chains caused a decrease in the release rate of insulin and in the polymer dissolution rate. High MW polymer chains impose a certain degree of interaction between polymer chains due to chain entanglement. There is a limiting value of MW above which chain entanglement has no effect on drug release rate.

Acrylamides↗

PubMed1997

Polymer of proline analogue with sustained antifibrotic activity in lung fibrosis.

Inhibitors of collagen such as cis-4-hydroxy-L-proline (cHyp) may ameliorate bleomycin (bleo)-induced pulmonary fibrosis. An alternating polymer of poly(ethylene glycol) (PEG)-lysine (PEG-Lys) with cHyp attached as a pendant side chain was prepared for intratracheal delivery with bioinactive trans-Hyp (tHyp) polymer as control. To test whether the cHyp polymer has prolonged lung retention and sustained antifibrotic activity, we first instilled 3H- and 14C-labeled cHyp polymer in normal rats. Lung retention was 86 +/- 9% at 6 h and 29 +/- 3% at 7 d (n = 5). Next, rats were instilled intratracheally with either saline (sal) or 1.2 U bleo, and the following treatment groups were studied: Bleo/sal; Bleo/cHyp polymer; Bleo/tHyp polymer; and Bleo/PEG-Lys + cHyp. The dose of the test agents was 150 mg/kg polymer containing 8.5 mg/kg cHyp or tHyp instilled intratracheally at 7 and 14 d after bleo. At 21 d, hydroxyproline content (mg/lung) was: Control, 1.8 +/- 0.1; Bleo/sal 4.0 +/- 0.1*; Bleo/cHyp polymer, 2.8 +/- 0.3*+; Bleo/tHyp polymer, 4.4 +/- 0.2*; and Bleo/PEG-Lys + cHyp, 4.0 +/- 0.1* (*p < 0.05 versus Control; +p < 0.05 versus Bleo/sal; n = 5/group). The cHyp polymer also reduced lung total protein content, but the decrease was not significant. The dose required to produce 50% inhibition of lung collagen was approximately 700-fold less than monomeric cHyp. Thus, the cHyp polymer is a potent, long-acting antifibrotic agent which may be useful in treating lung fibrosis.

Animals↗

PubMed1976

Determination of the subunit composition of haptoglobin 2-1 polymers using quantitative densitometry of polyacrylamide gels.

Human haptoglobin (Hp), a hemoglobin-binding glycoprotein containing two types of polypeptide chains, alpha and beta, in equimolar amounts linked by disulfide bonds, exists in three major phenotypes determined by the properties of the alpha chain: Hp 1-1 (alpha1), Hp 2-2 (alpha2), and Hp 2-1 (alpha1 and alpha2). Hp 2-2 and Hp 2-1 form a series of alpha-disulfide-linked polymers. The subunit composition of the Hp 2-1 series was studied by isolation of single Hp 2-1 polymers by polyacrylamide gel electrophoresis. After reductive disulfide cleavage and alkylation the relative content of alpha2 and alpha1 polypeptide chains was determined by quantitative densitometry of acid/urea polyacrylamide gels stained with Coomassie brilliant blue R250. The molar ratios alpha2/alpha1 for the Hp 2-1 polymers. P1 through P5 (in order of decreasing electrophoretic mobility), were found to be: P1, 0.0 (alpha1 only); P2, 0.48; P3, 0.97; P4, 1.6; P5, 2.0. Since one alphabeta-Hb half-molecule is known to bind to each Hp beta chain, the beta polypeptide chain content of each of the Hp 2-1 polymers could be estimated by by counting the number of Coomassie blue bands formed after electrophoresis of isolated Hp 2-1 polymers fractionally saturated with cyanmethemoglobin (Hb). The number of beta chains present in Hp 2-1 polymers P1 through P4 was determined to be: P1, 2; P2, 3; P3, 4 and P4, 5. Molecular weights of the Hp 2-1 polymers were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresus using as standards the almost homologous Hp 2-2 polymer series whose molecular weights are known from ultracentrifugation studies. Molecular weights for the first five Hp 2-1 polymers were estimated to be 107,000; 162,000; 217,000, 274,000; and 331,000, respectively. These data are consistent with the previously proposed model for the subunit composition of the Hp 2-1 polymer series when P1 = (alpha1 beta)2 and the subsequent polymers in order are represented as (alpha1 beta)2(alpha2 beta)n where n = 1,2,3,4...

Densitometry↗

PubMed1998

Assessment of an experimental bone wax polymer plus TGF-beta 1 implanted into calvarial defects.

The study reported describes an experimental biodegradable polymer ceramic composite with wax-like handling properties that was combined with 2.0 micrograms of recombinant human transforming growth factor beta (rhTGF-beta(1)). The polymer/rhTGF-beta(1) combination was introduced into standard-sized calvarial defects in rabbits to evaluate biodegradability, biocompatibility, hemostasis control, and bone promotion. The experimental wound model was a standard-size circular calvarial defect 8 mm in diameter. The experimental design included 24 skeletally mature New Zealand white rabbits divided evenly between two time periods (6 and 12 weeks) and among three experimental treatments (untreated defects and defects treated with polymer with or without rhTGF-beta(1)). Evaluations consisted of clinical examinations, standarized radiography, radiomorphometry, as well as histology and histomorphometry. Data were analyzed by an Analysis of Variance (ANOVA) and Fisher's Protected Least Significant Difference test at each time period (level of significance p < or = 0.05). Radiomorphometry data indicated that standard-sized defects treated with the wax-like polymer alone and the polymer plus 2.0 micrograms of TGF-beta(1) were significantly more radiopaque than control sites at both 6 and 12 weeks. Histomorphometric data revealed the amount of new bone was significantly greater at 6 weeks in the polymer plus 2.0 micrograms of TGF-beta(1) and in the control group than in the polymer alone. Moreover, at 12 weeks, there was significantly more new bone in the control than in either the polymer alone or the polymer plus 2.0 micrograms of TGF-beta(1). We speculate the incomplete biodegradation of the polymer ceramic composite contributed to the radiopacity and may have retarded osseous regeneration. It is important that the bone wax-like polymer material was biocompatible and acted as a hemostatic agent.

Animals↗

PubMed2000

Spherical crystal agglomeration of ibuprofen by the solvent-change technique in presence of methacrylic polymers.

The effects of Eudragit(R) nature on the formation and spherical agglomeration of ibuprofen microcrystals have been examined when solvent change (ethanol-water) technique is applied. Four methacrylic polymers (Eudragit(R) S100, L100, RS, and RL), with different solubility and solubilizing ability, were used. The extrapolated points of maximum temperature deviation rate in crystallization liquid that reflect the maximum crystallization rate and the corresponding water addition were determined, as well as crystal yielding and incorporation of drug and polymer in the agglomerates. The physicomechanical properties of the agglomerates, such as size, sphericity, surface roughness and porosity, as well as flow and packing or compression behavior during tableting, were evaluated for different drug/polymer ratios. It was found that crystal yield is greatly reduced in the presence of water-insoluble polymers and that formation of the microcrystals and incorporation of drug and polymer are affected by the polymer nature. Crystal formation changes are attributed to alterations in the metastable zone, whereas the changes in drug and polymer incorporation and crystal yield are caused by changes in the polymers' solubility and micellization. The size of agglomerates depends on the polymer nature and its interactions with the ibuprofen microcrystals formed. Sphericity, surface roughness, and intraparticle porosity of agglomerates increase, in general, with the presence of polymer owing to changes in habit and growth rate of the microcrystals and to their coating before binding into spherical agglomerates. The particle density or intraparticle porosity and size changes determine flow or packing behavior and densification of agglomerates at low compression. The incorporation and brittleness of the polymer determine the deformation under higher compression pressure, expressed as yield pressure, Py.

Acrylic Resins↗

PubMed2006

Polymer therapeutics: concepts and applications.

Polymer therapeutics encompass polymer-protein conjugates, drug-polymer conjugates, and supramolecular drug-delivery systems. Numerous polymer-protein conjugates with improved stability and pharmacokinetic properties have been developed, for example, by anchoring enzymes or biologically relevant proteins to polyethylene glycol components (PEGylation). Several polymer-protein conjugates have received market approval, for example the PEGylated form of adenosine deaminase. Coupling low-molecular-weight anticancer drugs to high-molecular-weight polymers through a cleavable linker is an effective method for improving the therapeutic index of clinically established agents, and the first candidates have been evaluated in clinical trials, including, N-(2-hydroxypropyl)methacrylamide conjugates of doxorubicin, camptothecin, paclitaxel, and platinum(II) complexes. Another class of polymer therapeutics are drug-delivery systems based on well-defined multivalent and dendritic polymers. These include polyanionic polymers for the inhibition of virus attachment, polycationic complexes with DNA or RNA (polyplexes), and dendritic core-shell architectures for the encapsulation of drugs. In this Review an overview of polymer therapeutics is presented with a focus on concepts and examples that characterize the salient features of the drug-delivery systems.

Amino Acid Sequence↗

PubMed2001

IUdR polymers for combined continuous low-dose rate and high-dose rate sensitization of experimental human malignant gliomas.

Local polymeric delivery enhances IUdR radiosensitization of human malignant gliomas (MG). The combined low-dose rate (LDR) (0.03 Gy/h) and fractionated high-dose rate (HDR) treatments result in cures of experimental MGs. To enhance efficacy, we combined polymeric IUdR delivery, LDR, and HDR for treatments of both subcutaneous and intracranial MGs. In vitro: Cells (U251 MG) were trypsinized and replated in triplicate 1 day prior to LDR irradiation in media either without (control) or with 10 microM IUdR. After 72 hr, LDR irradiation cells were acutely irradiated (1.1 Gy/min) with increasing (0, 1.25, 2.5, 5.0, or 10 Gy) single doses. Implantable IUdR polymers [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebaic acid (PCPP:SA), 20:80] (50% loading; 10 mg) were synthesized. In vivo: For flank vs. intracranial tumors, mice had 6 x 10(6) subcutaneous vs. 2 x 10(5) intracranial cells. For intracranial or subcutaneous MGs, mice had intratumoral blank (empty) vs. IUdR polymer treatments. One day after implantation, mice had immediate external LDR (3 cGy/h x 3 days total body irradiation) or HDR (2 Gy BID x 4 days to tumor site) or concurrent treatments. For the in vitro IUdR treatments, LDR resulted in a striking increase in cell-killing when combined with HDR. For the in vivo LDR treatments of flank tumors, the growth delay was greater for the IUdR vs. blank polymer treatments. For the combined LDR and HDR, the IUdR treatments resulted in a dramatic decrease in tumor volumes. On day 60 the log V/V0 were -1.7 +/- 0.22 for combined LDR + HDR + IUdR polymer (P < 0.05 vs. combined LDR + HDR + blank polymer). Survival for the intracranial controls was 22.9 +/- 1.2 days. For the blank polymer + LDR vs. blank polymer + LDR + HDR treatments, survival was 25.3 +/- 1.7 (P = NS) vs. 48.1 +/- 3.5 days (P < 0.05). For IUdR polymer + LDR treatment survival was 27.3 +/- 2.3 days (P = NS). The most striking improvement in survival followed the IUdR polymer + LDR + HDR treatment: 66.0 + 6.4 days (P < 0.05 vs. blank polymer + LDR + HDR). The polymeric IUdR delivery plus combined continuous LDR and HDR treatments results in growth delay and improved survival in animals bearing the MG xenografts. This treatment may hold promise for the treatment of human MGs.

Animals↗

PubMed2005

Characterization of physico-mechanical properties of indomethacin and polymers to assess their suitability for hot-melt extrusion processs as a means to manufacture solid dispersion/solution.

The objective of the study was to characterize the physical and viscoelastic properties of binary mixtures of drug and selected polymers to assess their suitability for use in the hot-melt extrusion (HME) process as a means to improve solubility by manufacturing either solid dispersion or solid solution. Indomethacin (INM) was selected as a model drug. Based on comparable solubility parameters, the selected polymers were Eudragit EPO (EPO), polyvinylpyrrolidone/vinyl acetate copolymer (PVP-VA), polyvinylpyrrolidone K30 (PVPK30), and poloxamer 188 (P188). The various drug and polymer systems were characterized for thermal and rheological properties as a function of drug concentration to provide an insight into miscibility and processibility of these systems. From the thermal analysis studies, a single T(g) was observed for the binary mixtures of INM/EPO, INM/PVP-VA, and INM/PVPK30, indicating miscibility of drug and polymer in the given ratios. In the case of mixtures of INM/P188, two melting endotherms were observed with decreasing drug melting point as a function of polymer concentration indicating partial miscibility of drug in polymer. As part of the rheological evaluation, zero rate viscosity (eta(o)) and activation energy (E(a)) was determined for the various systems using torque rheometer at varying shear rates and temperatures. The eta(o) for binary mixtures of drug and EPO, PVP-VA and PVPK30 were found to be significantly lower as compared to pure polymer, indicating disruption of the polymer structure due to miscibility of the drug. On the other hand, INM/P188 mixtures showed a higher eta(o) compared to pure polymer indicating partial miscibility of drug and polymer. With respect to E(a), the mixtures of INM/EPO showed an increase in E(a) with increasing drug concentration, suggesting antiplasticization effect of the drug. These findings corroborate the thermal analysis results showing increase T(g) for the various binary mixtures. The mixtures of INM/PVP-VA showed a decrease in the E(a) with the increasing drug concentration suggesting a plasticization effect of the drug. The understanding of thermal and rheological properties of the various drug/polymer mixtures help established the processing conditions for hotmelt extrusion (such as extrusion temperatures and motor load) as well as provided insight into the properties of the final extrudates. Using the actual hot-melt processing, a model was developed correlating the zero rate viscosity to the motor load determined by rheological evaluation.

Acrylates↗

PubMed1997

Environmental fate assessment of two synthetic polycarboxylate polymers.

In order to estimate the proportion which may enter the aquatic environment and characterize exposure potential, the environmental fate properties of two polycarboxylate polymers in activated sludge were determined. The polycarboxylates studied were a polymer emulsion (PE), a high-molecular-weight polymer (MW 50,000-60,000), and a resin polymer (RP), a low-molecular-weight polymer (MW 4500 to 9000). Both polymers exhibited a high degree of sorption to sludge solids in a series of sorption/ desorption studies, indicating a high potential for removal during wastewater treatment. In isotherm tests, the adsorption coefficient, Koc, was 1060 and 2730 for the RP and the PE, respectively. The biodegradation of the two polymers was measured under aerobic conditions in a 60-day semicontinuous activated sludge test and in a 60-day modified Sturm test using 14C-labeled compounds. In both studies, polymers accumulated in sludge solids over time and there was no evidence of significant biodegradation, although small amounts of radiolabeled CO2 were produced, suggesting the potential for biodegradation. Testing confirmed that the lack of biodegradation was not due to inhibition of microbial respiration by the polymers. High removals of PE and RP during wastewater treatment were confirmed in a field study at a facility receiving polymer inputs from households and manufacturing plants.

Biodegradation, Environmental↗

PubMed1996

A study of the mechanisms of slow religation to sickle cell hemoglobin polymers following laser photolysis.

Time-resolved linear dichroism (TRLD) measurements are conducted on gels of sickle cell hemoglobin following laser photolysis of the carbonyl adduct to monitor religation kinetics to hemoglobin S polymers. The return of the polymer phase to its equilibrium ligation state has been found to be about 1000 times slower than that of the solution phase hemoglobin tetramers. Several mechanisms describing this slow religation to the polymer were proposed: (1) religation occurs through a biomolecular process involving all polymer hemes, (2) religation occurs through a bimolecular process in which only hemoglobin molecules at the polymer ends can participate, and (3) religation occurs through the exchange of ligated hemoglobin molecules in the monomer phase with unligated ones in the polymer phase. To test these mechanisms, measurements are performed on gels having different domain sizes. The results show no relation between domain size and religation kinetics. The independence of religation kinetics and domain size is most consistent with the first of the three mechanisms described above (bimolecular recombination involving all polymer hemes). This result is discussed in terms of a model in which diffusion of the ligand is inhibited in the polymer phase. An understanding of the ligand binding kinetics of sickle hemoglobin polymers could have pathophysiological significance in its relevance to polymer formation and melting during red blood cell circulation.

Carbon Monoxide↗

PubMed2004

[Cultivation of human cells on polymer covered biomaterial--a new concept to improve the implant characteristics. Results of an in-vitro-investigation].

BACKGROUND AND PURPOSE: Calcific degeneration with the resulting need for operative replacement remains the major drawback of bioprostheses. Previous studies have shown that cellular surface seeding decreases calcium uptake in vitro and in vivo, but complete coverage remains difficult to achieve. A new approach is presented, masking glutaraldehyde residues with a covalently bound polymer layer thus facilitating cell seeding. The aim of this study was to evaluate different polymers for their ability to promote surface cell adhesion and formation of complete monolayers. MATERIAL AND METHODS: Ten ultrathin polymers, covalently bound to glass and exhibiting different physicochemical characteristics (thickness, molecular weight, hydrophilic properties, electrical charge) were seeded with human endothelial cells. Four of the ten polymers were also seeded with fibroblasts. As a reference, both cell types were seeded on glass surface. Quality of cell growth and coverage was evaluated by light and scanning electron microscopy. RESULTS: Five of ten polymers and glass exhibited excellent growth and complete surface coverage after 2 weeks, two allowed less cell adherence than glass reference, and three showed only poor cellular growth without adherence. Scanning electron microscopy demonstrated an intact monolayer for the five polymers with excellent cell coverage. Fibroblasts grew well on glass but not on the four tested polymers. No correlation was found between molecular weight, thickness, hydrophilic or charge characteristics of the polymers. CONCLUSION: Several ultrathin polymers, seeded with human endothelial cells, permit complete monolayer formation, but without any apparent correlation to physicochemical characteristics. Polymers covalently bound to biologic tissue appear as a promising approach to prevent calcific degeneration of bioprostheses.

Blood Vessel Prosthesis↗

PubMed1992

Effect of anionic polymers on fusion of Sendai virus with human erythrocyte ghosts.

The effect of anionic polymers (dextran sulfate, heparin and chondroitin sulfate) on fusion of Sendai virus with erythrocyte ghosts was studied. The effect of pH on the activity of these anionic polymers was also investigated. In order to examine the interaction of such polymers with the Sendai virion and erythrocyte ghost surfaces, the binding of virions to erythrocyte ghosts and the aggregation of virions and/or erythrocyte ghosts were also measured with respect to the same parameters. It was found that the anionic polymers suppressed the fusion of Sendai virus with erythrocyte ghosts. The order of effectiveness of the polymers in suppression was dextran sulfate greater than heparin greater than chondroitin sulfate, for the application of a same quantity (weight/ml) of the polymers. The lower the pH of the suspending medium, the more effective were the polymers in suppressing virion-erythrocyte ghost aggregation and fusion. The suppression of fusion was dependent on the concentration of the polymers applied: the higher the concentration of the polymer applied, the more the suppression was observed. Evidence from binding studies, turbidity measurements and electrophoretic mobility measurements indicates that the anionic polymers interact preferentially with the virion surface.

Adsorption↗

PubMed1993

Membranes and polymer structures--biocompatibility aspects with respect to production limits.

Plasmapheresis can be performed by centrifugation and by use of membrane technology. With the latter technique we receive a plasma which is absolutely free from platelets. This is why membranes are gaining market shares in this particular field of medical application. Today plasmapheresis membranes are mostly fabricated from synthetic polymers, such as polypropylene (e.g. PLASMAPHAN), polysulfone, polyacrylonitrile, polymethylmethacrylate, polyvinylalcohol and others, the only exception being cellulose acetate. Parameters determining the biocompatibility of plasmapheresis membranes are generation of complement C3a or C5a, hemolysis and possible thrombus formation. These parameters depend on various properties of the membrane polymer: e.g. the nature of the molecular end/side-groups, the distribution of electrical charges on the polymer surface and the different chemical structures and conformation of the polymer. In addition, membrane properties like pore distribution and geometry or the flow characteristics of a particular device-design may trigger cell activation or influence biocompatibility through the adsorption of various plasmacomponents. Most of the polymers which are used today for manufacturing plasmapheresis membranes have not been developed for this purpose. They were originally selected to be used as textile fibers. Further, no present membrane polymer has been specifically developed to achieve high biocompatibility. The membrane profile was designed in such a way that pheresis properties were met rather than optimizing biochemical blood/polymer interactions. One reason for this decision may be that the market volume of plasmapheresis technology is too small in order to justify specific and high-cost developments of polymers for this purpose. Polymer selection to achieve excellent biocompatibility profiles is determined by polymer-availability, costs, membrane-forming processes and environmental aspects related to possible pollution during the manufacturing process. The production of PLASMAPHAN by the unique Accurel-process combines several of these parameters. The main membrane production processes and especially the Accurel-process are described here. The influence of polymer-surface properties, membrane structure and module-design on the biocompatibility of plasmapheresis treatments are discussed and explained by appropriate examples.

Biocompatible Materials↗

PubMed2005

Thermoresponsive polymers as gene delivery vectors: cell viability, DNA transport and transfection studies.

A range of gene delivery vectors containing the thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAm) was evaluated for effects on cell viability, intracellular trafficking and transgene expression in C2C12 mouse muscle cells. Polymers were complexed with plasmid DNA at pH 7.4 and the ability of the resulting particles to transfect cells was assessed via confocal microscopy and protein expression studies in tissue culture. Cell viability assays indicated that these polymers were toxic at high concentrations when not complexed to DNA or at certain polymer:DNA ratios. Poly(ethyleneimine) co-polymers with side-chain grafted PNIPAm were shown to be less toxic than poly(ethyleneimine) alone or PNIPAm-co-(N,N'-dimethylaminoethylmethacrylate) linear co-polymers and the effects were concentration dependent. Confocal micrographs of labeled polymers and DNA indicated rapid cellular entry for all the complexes but expression of Green Fluorescent Protein was achieved only when the branched PEI-PNIPAm co-polymers were used as vectors. The results indicate that design of appropriate co-polymer components and overall polymer architecture can be used to mediate, and perhaps ultimately control, DNA transport and transgene expression.

Acrylic Resins↗

PubMed1999

Uniform-sized molecularly imprinted polymer for (S)-naproxen selectively modified with hydrophilic external layer.

A uniform-sized molecularly imprinted polymer (MIP) for (S)-naproxen selectively modified with hydrophilic external layer has been prepared. First, the molecularly imprinted polymer for (S)-naproxen was prepared using 4-vinylpyridine and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively, by a multi-step swelling and thermal polymerization method. Next, a 1:1 mixture of glycerol monomethacrylate (GMMA) and glycerol dimethacrylate (GDMA) was used for hydrophilic surface modification, and it was added directly to the molecularly imprinted polymer for (S)-naproxen 4 h after the start of molecular imprinting. The retention factors of all solutes tested were decreased with the surface modified molecularly imprinted polymer, compared with the unmodified molecularly imprinted polymer. However, chiral recognition of racemic naproxen was attained with the surface modified molecularly imprinted polymer as well as the unmodified molecularly imprinted polymer. Further, bovine serum albumin was completely recovered from the surface modified molecularly imprinted polymer. These results revealed that the chiral recognition sites of (S)-naproxen remained unchanged with hydrophilic surface modification, and that the molecularly imprinted polymer for (S)-naproxen was selectively modified with hydrophilic external layer. Preliminary results reveal that the surface modified molecularly imprinted polymer could be applicable to direct serum injection assays of (S)-naproxen.

Chromatography, High Pressure Liquid↗

PubMed2002

Mechanistic relationships between polymer microstructure and drug release kinetics in bioerodible polyanhydrides.

This work investigates the relationship between polymer microstructure and drug release kinetics in the bioerodible polyanhydride system, poly[(1,6-bis-p-carboxyphenoxy hexane)-co-(sebacic anhydride)] (CPH-SA). Model drugs, p-nitroaniline (PNA) and disperse yellow 3 (DY), were selected based on compatibility with CPH and SA, respectively. The polymer microstructure and compatibility of the drug with the constituent monomers were determined to have significant influence over the release kinetics of the drugs studied. Polymer systems with homogeneous microstructure, poly(SA) and 50:50 CPH-SA, showed simultaneous polymer degradation and drug release, although the solubility of the drug in the polymer influenced the shape of the release profiles. For the heterogeneous copolymers, 20:80 and 80:20 CPH-SA, individual monomer release kinetics demonstrated the effects of drug partitioning within a phase-separated microstructure. The PNA molecules partition preferentially into the CPH microdomains in the 20:80 CPH-SA copolymer while the DY molecules partition preferentially into the SA microdomains in the 80:20 CPH-SA copolymer. These studies suggest that the drug release mechanism is driven by polymer microstructure, compatibility of the drug with the constituent polymer phases, and solubility of the drug within the polymer. A thorough understanding of drug-polymer interactions as well as the polymer microstructure will pave the way for more accurate predictions of drug release from bioerodible polyanhydrides.

Aniline Compounds↗

PubMed2001

Membrane transport of hydrocortisone acetate from supersaturated solutions; the role of polymers.

Permeation of hydrocortisone acetate (HA) from supersaturated solutions was studied across a model silicone membrane. Supersaturated solutions were prepared using the cosolvent technique with propylene glycol and water (or aqueous polymer solutions) as the cosolvents. In the absence of the polymer, the flux of HA was similar at all degrees of saturation and was not significantly different from the value obtained for a saturated solution. Flux enhancement, as a result of supersaturation, was observed with all the polymers. The flux increased with increasing polymer concentration, reached a maximum and decreased at higher polymer percentages. The amount of polymer required for maximum enhancement differed for each polymer. The decrease of flux at high polymer concentrations is attributed to changes in microviscosity and a marginal increase in solubility. The infrared spectroscopic and differential scanning calorimetry data suggest that HA-polymer interactions occurred through hydrogen bonding thus explaining the proposed mechanism of the anti-nucleant properties of the polymers.

Biological Transport↗

PubMed2003

Evaluation of the stability of polymer-based plasmid DNA delivery systems after ultrasound exposure.

Under ultrasound exposure, the stability of plasmid DNA protected by polymer-based gene delivery system is an important factor for achieving optimal transfection into cells. We have evaluated the effectiveness of various polymer-based plasmid DNA delivery systems, which are interactive polymers and cationic polymers, to avoid shear degradation induced by ultrasound exposure. Alternatively, it is shown that sonication of plasmid DNA for exposure time as low as 10s resulted in total DNA fragmentation and the loss of transfection potency in NIH/3T3 cells. Among these polymer-based plasmid DNA delivery systems, only cationic polymers had the ability to provide the protection of plasmid DNA from ultrasonic degradation as indicated by the reservation in supercoiled circular (SC) and open circular (OC) forms of plasmid DNA on the agarose gel electrophoresis. The DNA stability protected by cationic polymers decreased after ultrasound exposure in 1M sodium chloride solution. Also, higher molecular weight of cationic polymers and sufficient cationic polymer/DNA weight ratios are essential to prevent DNA from degradation under ultrasound exposure in aqueous or salt solution. These results suggest that the protective mechanism by cationic polymers is due to the attractive bonding between cationic polymer and negative plasmid DNA. Whereas, DNA condensation alone provoked by the addition of polyethylene glycols was not sufficient to resist the DNA fragmentation induced by ultrasound exposure.

Animals↗