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PubMed2004

Effects of gel composition on the radiation induced density change in PAG polymer gel dosimeters: a model and experimental investigations.

Due to a density change that occurs in irradiated polyacrylamide gel (PAG), x-ray computed tomography (CT) has emerged as a feasible method of performing polymer gel dosimetry. However, applicability of the technique is currently limited by low sensitivity of the density change to dose. This work investigates the effect of PAG composition on the radiation induced density change and provides direction for future work in improving the sensitivity of CT polymer gel dosimetry. A model is developed that describes the PAG density change (delta(rho)gel) as a function of both polymer yield (%P) and an intrinsic density change, per unit polymer yield, that occurs on conversion of monomer to polymer (delta(rho)polymer). %P is a function of the fraction of monomer consumed and the weight fraction of monomer in the unirradiated gel (%T). Applying the model to experimental CT and Raman spectroscopic data, two important fundamental properties of the response of PAG density to dose (delta(rho)gel dose response) are discovered. The first property is that delta(rho)polymer)depends on PAG %C (cross-linking fraction of total monomer) such that low and high %C PAGs exhibit a higher deltarho(polymer)than do more intermediate %C PAGs. This relationship is opposite to the relationship of polymer yield to %C and is explained by the effect of %C on the type of polymer formed. The second property is that the delta(rho)gel dose response is linearly dependent on %T. From the model, the inference is that, at least for %T < or = 2%, monomer consumption and delta(rho)polymer depend solely on %C. In terms of optimizing CT polymer gel dosimetry for high sensitivity, these results indicate that delta(rho)polymer can be expected to vary with each polymer gel system and thus should be considered when choosing a polymer gel for CT gel dosimetry. However, delta(rho)polymerand %P cannot be maximized simultaneously and maximizing %P, by choosing gels with intermediate %C and high %T, is found to have the greatest impact on increasing the sensitivity of PAG density to dose. As such, future research into new gel formulations for high sensitivity CT polymer gel dosimetry should focus on gels that exhibit an intrinsic density change and maximizing polymer yield in these systems.

Acrylic Resins↗

PubMed2007

Biocompatibility and drug release behavior of spontaneously formed phospholipid polymer hydrogels.

Hydrogels containing 2-methacryloyloxyethyl phosphorylcholine (MPC) moieties were formed from aqueous solutions with water-soluble MPC polymers with carboxylic acid and alkyl groups because of hydrogen bonding formation. To investigate the biocompatibility and drug release behavior of the hydrogels, we used random- and block-type carboxylic acid MPC polymers, such as poly [MPC-co-methacrylic acid (MA)] (rPMA), poly[MPC-co-4-(2-methacryloyloxyethyl) trimellitic acid (MET)] (rPMT), poly (MA-block-MPC-block-MA) (bPMA) and poly(MET-block-MPC-block-MET) (bPMT), and alkyl MPC polymers, such as poly[MPC-co-n-butyl methacrylate] (PMB) and poly(MPC-co-benzyl methacrylate) (PMBz). We investigated the biocompatibility of the spontaneously formed MPC polymer hydrogels by a hemolysis test and an in vivo injection test. The random MPC polymers having carboxylic acid groups expressed more hemolytic activity compared to the block polymers. The results of the in vivo injection test also indicated low biocompatibility of the carboxylic acid polymers especially at high concentration. The alkyl MPC polymers, the PMB and PMBz showed excellent biocompatibility in both hemolysis and in vivo injection test. However, the hydrogels, the rPMA/PMB hydrogel (rABgel) and the rPMT/PMBz hydrogel (rTZgel) lowered the hemolytic activity of elemental polymers, the rPMA and rPMT. Thus, suppression of the ionization of the carboxylic acid groups is necessary for biocompatibility. We also investigated the drug release behavior with attention to the interaction between the polymer and the drugs. The release behavior of a relatively low-molecular-weight hydrophilic drug, 5-fluorouracil, did not depend on the structure of the polymers. The higher-molecular-weight drugs, ketoprofen and indomethacin, were released faster from the block polymer hydrogel than the random polymer hydrogel, the rABgel, while the highest-molecular-weight drug, doxorubicin, was released faster from the random polymer hydrogel. A probable reason for this is the difference in the molecular structure; that is, the separated hydrophilic and hydrophobic sections in the block polymers constructed pathways where a drug can diffuse. In addition, the rTZgel suppressed the release of a drug with a large number of aromatic rings probably because of the stacking effect. The results of the compression test also suggested the existence of the stacking effect between the rTZgel and the drugs. Based on these results, control of drug release is possible by selecting a reservoir with an appropriate chemical structure to interact with the drug. For example, release of a relatively linear-structured drug with less aromatic rings can be suppressed in the rABgel rather than in the rTZgel. Thus, it can be concluded that if the ionization is suppressed, these MPC polymer hydrogels can be used as a material for a drug reservoir that can be selected according to the drug.

Animals↗

PubMed2004

Effect of surface grafted polymers on the adsorption of different model proteins.

Adsorption of a model protein to a surface with end-grafted polymers was studied by Monte Carlo simulations. In the model the effect on protein adsorption in the presence of end-grafted polymers was evaluated by calculating the change in free energy between an end-grafted surface and a surface without polymers. The change in free energy was calculated using statistical mechanical perturbation theory. Apart from ordinary athermal polymer-polymer and protein-polymer interactions we also study a broad selection of systems by varying the interaction between proteins and polymers and effective polymer-solvent interactions. The interactions between the molecules span an interval from -0.5 to +0.5 kT. Consequently, general features of protein adsorption to end-grafted surfaces is investigated by systematically changing properties like hydrophilicity/hydrophobicity of the polymer, protein and surface as well as grafting density, degree of polymerization and protein size. Increasing grafting density as well as degree of polymerization decreases the adsorption of protein except in systems with attractive polymer-protein interactions, where adsorption increases with increasing chain length and higher grafting density. At a critical polymer-protein interaction neither chain length nor grafting density affects the free energy of adsorption. Hydrophilic polymers were found to prevent adsorption better than hydrophobic polymers. Very small particles with radii comparable to the size of a polymer segment were, however, better excluded from the surface when using hydrophobic than hydrophilic polymers. For systems with attractive polymer-protein interaction not only the volume of the protein was shown to be of importance but also the size of the exposed surface.

Adsorption↗

PubMed2005

Simulation of interaction forces between nanoparticles in the presence of Lennard-Jones polymers: freely adsorbing homopolymer modifiers.

The force between two nanoscale colloidal particles dispersed in a solution of freely adsorbing Lennard-Jones homopolymer modifiers is calculated using the expanded grand canonical Monte Carlo simulation method. We investigate the effect of polymer chain length (N), nanoparticle diameter (sigma(c)), and colloid-polymer interaction energy (epsilon(cp)) on polymer adsorption (Gamma) and polymer-induced forces (F(P)(r)) between nanoparticles in the full thermodynamic equilibrium condition. There is a strong correlation between polymer adsorption and the polymer-mediated nanoparticle forces. When the polymer adsorption is weak, as in the case of smaller diameters and short polymer chain lengths (sigma(c) = 5, N = 10), the polymers do not have any significant effect on the bare nanoparticle interactions. The adsorbed amount increases with increasing particle diameter, polymer chain length, and colloid-polymer interaction energy. In general, for strong polymer-particle adsorption the polymer-governed force profiles between nanoparticles show short-range repulsion and long-ranged attraction, suggesting that homopolymers would not be ideal for achieving stabilization in nanoparticle dispersions. The attraction is likely due to bridging, as well as polymer segment-segment interactions. The location and magnitude of attractive minimum in the force profile can be controlled by varying N and epsilon(cp). The results show partial agreement and some marked differences with previous theoretical and experimental studies of forces in the limit of flat walls in an adsorbing polymer solution. The difference could be attributed to incorporation of long-ranged colloid-polymer potential in our simulations and the influence of the curvature of the nanoparticles.

Journal Article↗

PubMed2001

Effect of molecular weight of thermoreversible polymer on in vivo retention of rhBMP-2.

To investigate the effect of polymer molecular weight (MW) on rhBMP-2 delivery by thermoreversible polymers, four polymers with similar lower critical solution temperatures (20 degrees -22 degrees C) but different MWs were studied. Thermoreversible polymers were based on N-isopropylacrylamide (NiPAM), ethyl methacrylate (EMA), and N-acryloxysuccinimide (NASI), and had MWs of either approximately 49 kDa or approximately 400 kDa. The NASI content was either 0 or 1-1.6%. High MW polymers, irrespective of their NASI content, formed a stable gel with significantly lower water uptake and exhibited a dense micelle with average pore size smaller than the low MW polymers. NiPAM/EMA polymers without NASI did not conjugate with recombinant human bone morphogenetic protein-2 (rhBMP-2). NiPAM/EMA polymers containing NASI, however, gave conjugation with rhBMP-2. For polymers without NASI, a high MW was essential for rhBMP-2 retention when injected intramuscularly in Sprague-Dawley rats. For NASI-containing polymers, the MW of the polymer did not make a significant difference because rhBMP-2 retention was equivalent for different size polymers. We conclude that polymer MW affects rhBMP-2 retention in vivo in polymers designed for physical entrapment of rhBMP-2, but not in polymers designed for chemical conjugation with rhBMP-2.

Animals↗

PubMed2003

Pharmacokinetics in mice of four oligomer-conjugated polymers for amplification targeting.

UNLABELLED: For use in amplification targeting, an oligomer-conjugated polymer must display adaptable chemistry, minimal steric hindrance, low toxicity, and favorable pharmacokinetics. In particular, the polymer must remain in circulation sufficiently long to permit target localization. OBJECTIVES: To evaluate their properties for amplification targeting, the biodistribution in normal mice was determined for four polymers conjugated with multiple copies of a phosphorodiamidate morpholino (MORF) oligomer. METHODS: An amine-derivatized 25-mer MORF oligomer was radiolabeled with 99mTc. Three polymers of succinylated polylysine (PL) with initial weight average molecular weights (Mw) of 30, 100, and 200 KDa, and one poly (methyl vinyl ether-alt-maleic acid) (PA) with initial Mw of 45 KDa polymer, were each conjugated with an amine derivatized 25-mer complementary MORF (i.e., cMORF). The average number of attached cMORF groups on each polymer molecule (i.e., gpm) was estimated by a high performance liquid chromatography (HPLC) shift assay after the addition of trace 99mTc-MORF to the unpurified polymer, while the average number of accessible cMORF on each polymer was determined by adding radiolabeled MORF at increasing concentrations to the purified cMORF polymer solution until saturation. After purification, each polymer was radiolabeled by incubation with trace 99mTc-MORF. The biodistribution was then established in normal CD1 mice at a constant dosage of 2-4 micrograms of cMORF. RESULTS: The gpm varied from about 12 on 30 KDa PL to 40 on 45 KDa PA. The biodistribution results show that the pharmacokinetics of the radiolabel is a function of both the type of polymer as well as its gpm. Of the four polymers, the 30 KDa PL showed the most favorable pharmacokinetic profile, with the lowest liver accumulation and the highest blood values compared to the remaining three polymers. CONCLUSION: The biodistribution of the four polymers showed characteristic differences, with one polymer (30 KDa PL) showing the most favorable properties for amplification targeting.

Animals↗

PubMed1999

Synthetic, implantable polymers for IUdR radiosensitization of experimental human malignant glioma.

BACKGROUND: Recently, polymeric controlled delivery of chemotherapy has been shown to improve survival of patients with malignant glioma. We tested the delivery of IUdR via polymers for radiosensitization of experimental intracranial human malignant glioma. To assess efficacy, we measured the in vitro release, the in vivo delivery of IUdR and the resultant radiosensitization of experimental human U251 glioblastoma xenografts. METHODS: 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 vs. 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. vs. 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. For comparisons of radiosensitization, mice bearing i.c. xenografts had i.c. vs. flank IUdR polymers and cranial fractionated external beam irradiation (2 Gy BID x 4 days). 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 vs. time. For the ipsilateral IUdR polymers, the percentages of tumor cellular labeling after 4 vs. 8 days were 45.8 +/- 7.0 vs. 40.6 +/- 3.9 (p = NS. For the contralateral polymer implants, the percentages tumor cellular labeling were 43.9 +/- 10.1 vs. 35.9 +/- 5.2 (p = NS) measured 4 vs. 8 days after implantation. For the i.c. tumors treated with extracranial IUdR polymers, the percentages of tumor cellular labeling were 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 percentages labeling were 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 vs. distance from the implanted IUdR polymer showed labeling was highest closest to the polymer disc. Radiosensitization: For mice bearing i.c. tumors and receiving flank vs. intracranial IUdR polymer treatments, the survival after external beam irradiation was significantly higher for the intracranial treatments: 49 + 8.9 vs. 80 + 4.1 (p = 0.03) days, respectively. CONCLUSIONS: 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. The local delivery and labeling result in improved survival following radiotherapy. This technique holds promise for the local delivery of IUdR for radiosensitization of human brain tumors.

Animals↗

PubMed1996

Protein adsorption and platelet adhesion on polymer surfaces having phospholipid polar group connected with oxyethylene chain.

We evaluated the blood compatibility of various amphiphilic polymers, that is, n-butyl methacrylate (BMA) copolymers with methacrylates having a phosphorylcholine (PC), hydroxy (OH) or methoxy (MeO) group as an end polar group in the oxyethylene side chain. The amount of proteins adsorbed on the PC-polymer from human plasma was smaller than that on not only the poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate) but also the OH-polymer and MeO-polymer. The PC group could weaken the interaction between plasma proteins and polymer surfaces. The amount of adsorbed proteins on the PC-polymer decreased with an increase in the mole fraction of the PC units in the polymers. We could observe an effect of the oxyethylene chain length (n is the number of repeating units of oxyethylene) on protein adsorption between n = 2 and n = 3. The platelet adhesion on these polymer surfaces was evaluated using rabbit platelet-rich plasma. On the polymers without the PC group, that is, poly(BMA), OH-polymer, and MeO-polymer, many platelets adhered and a considerable shape change in the adherent platelets occurred. On the other hand, the PC-polymers could effectively suppress platelet adhesion. The platelet adhesion behavior on the polymers was strongly dependent on the adsorbed proteins. Platelet adhesion was completely inhibited on all of the PC-polymers studied having a 0.3 PC unit mole fraction. However, it was observed that the oxyethylene chains on the PC-polymers with a 0.1 PC unit mole fraction affected platelet adhesion.

Adsorption↗

PubMed2005

Preparation and in vitro evaluation of propylthiouracil microspheres made of Eudragit RL 100 and cellulose acetate butyrate polymers using the emulsion-solvent evaporation method.

The objectives of this investigation are to evaluate the encapsulation efficiency of the anti-thyroid agent 6-n-propyl-2-thiouracil using two polymers of different characteristics (cellulose acetate butyrate polymer, (CAB-551-0.01) and ammonio methacrylate copolymer (Eudragit RL 100) and to study the effect of this encapsulation on the drug release properties. Polymers were used separately and in combination to prepare different microspheres. Also, the effect of polymer solution phase viscosity was studied for each of the polymers and for their combinations. An Ostwald viscometer was used to evaluate the relative viscosities of polymer solution phases and their combinations. Microspheres with 25% theoretical drug loading of 6-n-propyl-2-thiouracil core material were prepared by the emulsion solvent evaporation method. Microspheres prepared from CAB-551-0.01, which has higher relative polymer phase viscosity than Eudragit RL 100, showed significantly lower drug release rates and a noticeable lag time. Polymer combinations of CAB-551-0.01 and Eudragit RL 100 (1:1) showed an interesting synergistic increase in relative polymer solution viscosities at all concentrations. Unlike microspheres prepared from the two polymers separately which follow Higuchi spherical matrix release kinetics, microspheres prepared using a combination (1:1) of the two polymers showed near zero order with faster rates compared to those prepared using CAB-551-0.01 equivalent polymer concentrations. The results of this study suggest that 6-n-propyl-2-thiouracil was successfully and efficiently encapsulated and release rates of matrix microspheres are related to polymer solution phase viscosity, but when polymer combinations were used other factors such as structural effects must be considered.

Cellulose↗

PubMed2000

Synthesis, characterization, biodegradation, and drug delivery application of biodegradable lactic/glycolic acid polymers: I. Synthesis and characterization.

A series of lactic/glycolic acid polymers with various molar ratios of lactic to glycolic acid and various molecular weights were synthesized using the ring-opening polymerization method. The polymerization conditions for the lactic/glycolic acid polymer synthesis were as follows: 150 degrees C, 700 microm Hg, 3 h, 0.03 wt% of catalyst (stannous 2-ethyl-hexanoate) concentration. The molecular weight of these polymers was controlled by using a molecular weight controller, lauryl alcohol. The synthesized polymers have been characterized with respect to polymer composition, molecular weight, inherent viscosity, and glass transition temperature. The characterization experiments show a good correlation between the polymer compositions and the feed ratios of lactic to glycolic acid. The molecular weight of the lactic/glycolic polymers, ranging from 10,876 to 166,630 D and the intrinsic viscosity of the polymers, ranging from 0.16 to 0.86 dl g(-1), are controlled by the amount of molecular weight controller used. The effect of the amount of the molecular weight controller on the polymer molecular weight and the polymer inherent viscosity was studied. Results indicate that the molecular weight and inherent viscosity of the polymers have a log-log linear relationship with the amount of molecular weight controller used. The lactic/glycolic acid polymers are amorphous, glassy, and transparent. The glass transition temperature of the polymers range from 21.95 to 51.29 degrees C, depending on the polymer molecular weight and the composition.

Biocompatible Materials↗

PubMed1998

Effect of several hydrophilic polymers on the permeation of morphine and salicylic acid through excised hairless rat skin.

Several hydrophilic polymers changed the cumulative amount of morphine (MOR) permeated through excised hairless rat skin from 1% MOR hydrochloride solution containing ethanol and l-menthol at concentrations of 40% and 5%, respectively, as permeation enhancers. Anionic polymers (carboxyvinylpolymer and methylvinylether-maleic anhydride copolymer) in the test solutions decreased the skin permeation of MOR, whereas cationic polymers (polyethyleneimine and chitosan) increased it, compared with that without polymers. Little change, however, was observed by the addition of nonionic polymers (hydroxypropylcellulose and polyethyleneoxide). On the other hand, the cationic and anionic polymers in the test solutions decreased and increased, respectively, the skin permeation of salicylic acid (SA) from the same enhancing system containing sodium salicylate. These opposite results were probably caused by the change in escaping tendency of the drugs from the vehicles, which was due to the drug-polymer interaction. (The escaping tendency has a great effect on the drug partition from the polymer solution to the skin barrier). The effect of hydrophilic polymers on the partition was then evaluated by Donnan membrane theory. The partition of MOR was increased and decreased by the presence of polymers having identical and opposite charge to MOR. The low partition of the drugs to skin may also be caused by low diffusion of the drugs in the polymer solutions. The drug release from the hydrophilic polymer solutions was then measured, and the release rate was found to have decreased in the presence of polymers having opposite charge to MOR and SA. It is suggested that these drug-polymer interactions changed the drug partition to skin thus changing the skin permeation of the drug.

Analgesics, Opioid↗

PubMed2004

Dispersions of polymer ionomers: I.

The principal subject discussed in the current paper is the effect of ionic functional groups in polymers on the formation of nontraditional polymer materials, polymer blends or polymer dispersions. Ionomers are polymers that have a small amount of ionic groups distributed along a nonionic hydrocarbon chain. Specific interactions between components in a polymer blend can induce miscibility of two or more otherwise immiscible polymers. Such interactions include hydrogen bonding, ion-dipole interactions, acid-base interactions or transition metal complexation. Ion-containing polymers provide a means of modifying properties of polymer dispersions by controlling molecular structure through the utilization of ionic interactions. Ionomers having a relatively small number of ionic groups distributed usually along nonionic organic backbone chains can agglomerate into the following structures: (1) multiplets, consisting of a small number of tightly packed ion pairs; and (2) ionic clusters, larger aggregates than multiplets. Ionomers exhibit unique solid-state properties as a result of strong associations among ionic groups attached to the polymer chains. An important potential application of ionomers is in the area of thermoplastic elastomers, where the associations constitute thermally reversible cross-links. The ionic (anionic, cationic or polar) groups are spaced more or less randomly along the polymer chain. Because in this type of ionomer an anionic group falls along the interior of the chain, it trails two hydrocarbon chain segments, and these must be accommodated sterically within any domain structure into which the ionic group enters. The primary effects of ionic functionalization of a polymer are to increase the glass transition temperature, the melt viscosity and the characteristic relaxation times. The polymer microstructure is also affected, and it is generally agreed that in most ionomers, microphase-separated, ion-rich aggregates form as a result of strong ion-dipole attractions. As a consequence of this new phase, additional relaxation processes are often observed in the viscoelastic behavior of ionomers. Light functionalization of polymers can increase the glass transition temperature and gives rise to two new features in viscoelastic behavior: (1) a rubbery plateau above T(g) and (2) a second loss process at elevated temperatures. The rubbery plateau was due to the formation of a physical network. The major effect of the ionic aggregate was to increase the longer time relaxation processes. This in turn increases the melt viscosity and is responsible for the network-like behavior of ionomers above the glass transition temperature. Ionomers rich in polar groups can fulfill the criteria for the self-assembly formation. The reported phenomenon of surface micelle formation has been found to be very general for these materials.

Journal Article↗

PubMed2001

Elastic constants of polymer-grafted lipid membranes.

The surface expansion that is induced by the lateral pressure in the brush region of lipid membranes containing grafted polymers is deduced from the scaling and mean-field theories for the polymer brush, together with the equation of state for a lipid monolayer at the equivalence pressure with fluid lipid bilayers. Depending on the length and mole fraction of the polymer lipid, the membrane expansion can be appreciable. Direct experimental evidence for this lateral expansion comes from recent spin-label measurements with lipid membranes containing poly(ethylene glycol)-grafted lipids. The expansion in lipid area modifies the elastic constants of the polymer-grafted membranes in a way that opposes the direct elastic response of the polymer itself. Calculations as a function of polymer lipid content indicate that the net change in isothermal area expansion modulus of the membrane is negative but small, in contrast to previous predictions. A similar situation applies to the curvature elastic moduli of membranes containing short polymer lipids. For longer polymer lipids, however, the direct contribution of the polymer brush to the bending elastic constants dominates, and the increase in bending moduli with increasing polymer lipid content rapidly exceeds the basal values of the bare lipid membrane. The spontaneous (or intrinsic) curvature of the component monolayer of polymer lipid-containing membranes is calculated for the first time. The polymer brush contribution to spontaneous curvature scales quadratically with the polymer length, and at least quadratically with the mole fraction of polymer lipid.

Elasticity↗

PubMed1999

Water sorption, solubility and effect of post-curing of glass fibre reinforced polymers.

Different polymer matrices are used for dental glass fibre composites. The aims of this study were to determine water sorption and solubility of glass fibre composites with different polymer matrices. In addition, the effect of post-curing of matrix polymers with heat on the water sorption and solubility values was investigated. Commercial one-phase and two-phase (powder-liquid) monomer systems were used in polymer matrix of E-glass fibre composite. Rhombic unreinforced and fibre reinforced test specimens were polymerized by autopolymerization or by light only, or additionally post-cured with heat. Water sorption and solubility determination method was based on ISO/DIS 1567-1997 draft for international standard with 7 d immersion time. In addition, water sorption was measured at second time for 30 d immersion time to determine saturation time of test specimens by water. Five test specimens of unreinforced polymer and reinforced polymer were tested and the quantity of fibres was determined by combustion analysis. Water sorption values of different brands of polymer matrices ranged from 0.9 to 8.3 wt% (P < 0.001, ANOVA). High sorption values were explained by microscopic voids in the polymer matrix and by composition of polymer matrix. Solubility values ranged from 0.02 to 2.5 wt% (P < 0.001, ANOVA). Generally, fibre inclusion and post-curing of polymer matrix reduced water sorption and solubility. The results of this study suggest that the water sorption and solubility of fibre composites varies according to the brand of polymer matrix and homogenity of polymer matrix. Water sorption of polymer matrix might influence hydrolytic stability of polymer-glass fibre composite.

Adsorption↗

PubMed2000

Enantioselective ester hydrolysis catalyzed by imprinted polymers.

Highly cross-linked network polymers prepared by molecular imprinting catalyzed enantioselectively the hydrolysis of N-tert-butoxycarbonyl phenylalanine-p-nitrophenyl ester (BOCPheONP). The templates were designed to allow incorporation of the key catalytic elements, found in the proteolytic enzyme chymotrypsin, into the polymer active sites. Three model systems were evaluated. These were constructed from a chiral phosphonate analogue of phenylalanine (series A, C) or L-phenylalanine (series B) attached by a labile ester linkage to an imidazole-containing vinyl monomer. Free radical copolymerization of the template with methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA) gave a highly cross-linked network polymer. The templates could be liberated from the polymers by hydrolysis, giving catalytically active sites envisaged to contain an enantioselective binding site, a site complementary to a transition state like structure (series A, C), and a hydroxyl, imidazole, and carboxylic acid group at hydrogen bond distance. As predicted, the enantiomer of BOCPheONP complementary to the configuration of the template was preferentially hydrolyzed with D-selectivity for the series A polymers (kD/kL = 1.9) and L-selectivity for the series B polymers (kL/kD = 1.2). The maximum rate enhancement, when compared with a control polymer, prepared using a benzoyl-substituted imidazole monomer as template, was 2.5, and comparing with the imidazole monomer in solution, a maximum rate enhancement of 10 was observed. The catalytic activity was higher for polymers subjected to the nucleophilic treatment. This was explained by a higher site density and flexibility of the polymer matrix caused by this treatment. In a comparison of template rebinding to polymers imprinted with a template containing either a carboxylate (planar ground state structure) or a phosphonate (tetrahedral transition state like structure) functionality, it was observed that imprinted polymers are able to discriminate between a transition state like and a ground state structure for transesterification. However the influence of transition state stabilization on the observed rate enhancements remains obscure. Only at acidic pH's was catalysis observed, whereas at basic pH's the polymers inhibit the reaction. At a later stage, the catalytic activity of the polymers for nonactivated D- and L-phenylalanine ethyl esters was investigated. A rate enhancement of up to 3 was observed when compared to the blank. Most important, however, the polymers imprinted with a D template preferentially hydrolyzed the D-ethyl ester and exhibited saturation kinetics.

Catalysis↗

PubMed1998

Polymer erosion and drug release characterization of hydroxypropyl methylcellulose matrices.

Polymer erosion of matrices of similarly substituted hydroxypropyl methylcellulose (HPMC) polymers was examined, and drug release in terms of diffusion and erosion contributions was characterized, focusing on matrices containing either polymer alone or a drug content of 25% level with no added excipients. A novel approach was utilized to separate diffusional and erosional contributions to drug release. Diffusional drug release was determined by fitting release data versus (time)0.45, and the drug release due to erosion was quantified by subtracting the percent predicted for diffusional drug release from the total drug release at each specific time point. Drug release resulting from polymer erosion was linear versus time and was found to be a function of the number average molecular weight of the polymer. In contrast, diffusional release rates were comparable for all HPMC grades studied and, thus, were independent of number average molecular weight of the polymers studied. Under stirring conditions of 10-100 rpm as well as static condition, the detachment of individual polymer chains at the matrix surface occurred at a faster rate relative to diffusion away from the matrix surface. The erosion study indicated that polymer diffusion of the HPMC polymer chains through the aqueous diffusion layer was the rate-limiting step for polymer erosion. In general, polymer erosion was found to be inversely related to the polymer number average molecular weight. A scaling law was used to relate polymer erosion rate with the respective polymer number average molecular weight. Similar relationships were obtained for matrices with and without drug at a stirring rate of 100 rpm.

Chemistry, Pharmaceutical↗

PubMed1997

Implantable biodegradable polymers for IUdR radiosensitization of experimental human malignant glioma.

PURPOSE: The potential of halogenated pyrimidines for the radiosensitization of human malignant gliomas remains unrealized. To assess the role of local delivery for radiosensitization, we tested a synthetic, implantable biodegradable polymer for the controlled release of 5-iodo-2'-deoxyuridine (IUdR) both in vitro and in vivo and the resultant radiosensitization of human malignant glioma xenografts in vivo. MATERIALS AND METHODS: In vitro: To measure release, increasing (10%, 30%, 50%) proportions (weight/weight) of IUdR in the polyanhydride [(poly(bis(p-carboxyphenoxy)-propane) (PCPP): sebacic acid (SA) (PCPP : SA ratio 20:80)] polymer discs were incubated (1 ml phosphate-buffered saline, 37 degrees C). The supernatant fractions were serially assayed using high performance liquid chromatography. To measure modulation of release, polymer discs were co-loaded with 20 microCi 5-125-iodo-2'-deoxyuridine (125-IUdR) and increasing (10%, 30%, or 50%) proportions of D-glucose. To test radiosensitization, cells (U251 human malignant glioma) were sequentially exposed to increasing (0 or 10 microM) concentrations of IUdR and increasing (0, 2.5, 5.0, or 10 Gy) doses of acute radiation. In vivo. To measure release, PCPP : SA polymer discs having 200 microCi 125-IUdR were surgically placed in U251 xenografts (0.1-0.2 cc) growing in the flanks of nude mice. The flanks were reproducibly positioned over a collimated scintillation detector and counted. To measure radiosensitization, PCPP : SA polymer discs having 0% (empty) or 50% IUdR were placed in the tumor or contralateral flank. After five days, the tumors were acutely irradiated (500 cGy x 2 daily fractions). RESULTS: In vitro: Intact IUdR was released from the PCPP : SA polymer discs in proportion to the percentage loading. After 4 days the cumulative percentages of loaded IUdR that were released were 43.7 +/- 0.1, 70.0 +/- 0.2, and 90.2 +/- 0.2 (p < 0.001 ANOVA) for the 10, 30, and 50% loadings. With 0, 10, 30, or 50% D-glucose co-loading, the cumulative release of 125-IUdR from PCPP : SA polymers was 21, 70, 92, or 97% (p < 0.001), respectively, measured 26 days after incubation. IUdR radiosensitized U251 cells in vitro. Cell survival (log10) was -2.02 +/- 0.02 and -3.68 +/- 0.11 (p < 0.001) after the 10 Gy treatment and no (control) or 10 microM IUdR exposures, respectively. In vivo: 125-IUdR Release: The average counts (log10 cpm +/- SEM) (hours after implant) were 5.2 +/- 0.05 (0.5), 4.3 +/- 0.07 (17), 3.9 +/- 0.08 (64), and 2.8 +/- 0.06 (284). Radiosensitization: After intratumoral implantation of empty polymer or intratumoral 50% IUdR polymer, or implantation of 50% IUdR polymers contralateral to tumors the average growth delays of tumors to 4 times the initial volumes were 15.4 +/- 1.8, 20.1 + 0.1, and 20.3 + 3.6 (mean + SEM) days, respectively (p = 0.488 one-way ANOVA). After empty polymer and radiation treatments, no tumors regressed and the growth delay was 31.1 + 2.1 (p = 0.046 vs. empty polymer alone) days. After implantation of 50% IUdR polymers either contralateral to the tumors or inside the tumors, followed by radiation, tumors regressed; growth delays to return to the initial average volumes of 14.0 + 3.6 or 24.2 + 0.2 (p < 0.01) days, respectively. CONCLUSIONS: Synthetic, implantable biodegradable polymers hold promise for the controlled release and local delivery of IUdR for radiosensitization of gliomas.

Animals↗

PubMed1996

Effects of polyacrylic polymers on the degradation of insulin and peptide drugs by chymotrypsin and trypsin.

The purpose of this study was to determine whether carbopol polymers, polyacrylic acid polymers, can inhibit lumenal degradation of insulin, calcitonin and insulin-like growth factor I (IGF-I) by trypsin and chymotrypsin and to understand whether reducing the pH of the incubation medium by these polymers results in inhibition. Further, the effects of carbopol polymers on the in-situ absorption of insulin were studied in rats. In saline, carbopol polymers at 1% and 4% (w/v%) inhibited close to 100% of trypsin and chymotrypsin activities against insulin. In 50 mM Tris buffer, carbopol polymers, including 934P, 974P and 971P, at 0.1% only weakly inhibited degradation of calcitonin and insulin by both enzymes; however, as the polymer concentration increased to 0.4%, degradation of insulin, calcitonin, and IGF-I by both enzymes was complete or almost complete. When the Tris buffer was increased to 100 mM, no inhibition was observed at 0.1%. Determination of the final pH of the incubation medium in the presence of polymers revealed that the inhibitory effects of carbopol polymers correlated with the final pH. When the incubation medium has no or low buffer capacity to buffer the protons released by carbopol polymers, these polymers are able to reduce the pH much lower than the optimum pH for the enzyme activities, and thus inhibit proteolytic degradation. When the buffer capacity of the incubation medium increases, the inhibitory effects of carbopol polymers weaken. In-situ absorption of insulin revealed that carbopol polymers improved insulin absorption and induced a significantly greater decline in blood glucose levels. It is concluded that carbopol polymers with strong bioadhesive properties also can inhibit lumenal degradation of peptide hormones, offering multiple advantages for their uses in oral drug delivery.

Acrylic Resins↗