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PubMed2005

In vitro and ex vivo intestinal tissue models to measure mucoadhesion of poly (methacrylate) and N-trimethylated chitosan polymers.

PURPOSE: The adhesion of a range of polymers based on poly(2-(dimethylamino-ethyl) methacrylate (pDMAEMA) was assessed using human mucus-secreting and non mucus-secreting intestinal cell monolayers, HT29-MTX-E12 (E12) and HT29 monolayers, as well as excised non-everted intestinal sacs from rats. Differentiation of mucoadhesion from bioadhesion was achieved by pre-treatment with the mucolytic agent, N-acetyl cysteine (NAC). Adherence of pDMAEMA polymers was compared to that obtained with the mucoadhesive, N-trimethylated chitosan (TMC). METHODS: The quantity of adherent coumarin 343-conjugated polymers to HT29, E12, and intestinal sacs was measured by fluorescence. Confocal laser scanning microscopy (CLSM), light microscopy, and fluorescent microscopy were used to provide direct evidence. Measurements of transepithelial electrical resistance (TEER), permeability to FITC-dextran 4000 (FD-4), and the release of lactate dehydrogenase (LDH) were used to assess potential cytotoxicity of polymers. RESULTS: Adherence of unquaternized and of 10%, 24%, and 32% methyl iodide-quaternized pDMAEMA polymers was measured in E12, HT29, and sacs. All pDMAEMA polymers showed significantly higher levels of adhesion to mucus (mucoadhesion) than to epithelium (bioadhesion). Colocalization of pDMAEMA with mucus was confirmed in E12 by microscopy. TMC showed equally high levels of mucoadhesion as unquaternized and 24% quaternized pDMAEMA, but displayed higher levels of bioadhesion. pDMAEMA-based polymers demonstrated lower levels of adherence to E12 and rat sacs in the presence of NAC, whereas adherence of TMC was unchanged. pDMAEMA significantly decreased the permeability of FD-4 across E12 monolayers and sacs and was less cytotoxic in E12 than in HT29. In contrast, TMC increased the permeability of FD-4 across E12 and sacs and was less cytotoxic in E12 than in HT29. CONCLUSIONS: Human mucus-producing E12 monolayers can be used to assess polymer mucoadhesion and give similar data to isolated rat intestinal sacs. pDMAEMA displayed similar levels of mucoadhesion and lower levels of bioadhesion than a chitosan derivative and it was not cytotoxic. pDMAEMA decreased FD-4 flux in the presence of mucus, whereas TMC increased it. The combination of mucus and methacrylate polymers appears to increase barrier function of the apical membrane.

Animals↗

PubMed2006

Theoretical and practical approaches for prediction of drug-polymer miscibility and solubility.

PURPOSE: Crystallization of drugs formulated in the amorphous form may lead to reduced apparent solubility, decreased rate of dissolution and bioavailability and compromise the physical integrity of the solid dosage form. The purpose of this work was to develop thermodynamic approaches, both practical and theoretical, that will yield a better understanding of which factors are most important for determining the ability of polymers to stabilize amorphous active pharmaceutical ingredients (API). MATERIALS AND METHODS: Lattice based solution models were used to examine miscibility criteria in API-polymer blends. Different methods were used to estimate the Flory-Huggins interaction parameter for model API-polymer systems consisting of felodipine or nifedipine with poly(vinylpyrrolidone) (PVP). These were melting point depression and determination of solubility parameters using group contribution theory. The temperature and enthalpy of fusion of crystalline API alone and the fusion temperature of the API in the presence of the polymer were measured by differential scanning calorimetry. The resultant thermal data were used to estimate the reduced driving force for crystallization and the solubility of the API in the polymer. RESULTS: Flory-Huggins theory predicts that, for typical API-polymer systems, the entropy of mixing is always favorable and should be relatively constant. Due to the favorable entropy of mixing, miscibility can still be achieved in systems with a certain extent of unfavorable enthalpic interactions. For the model systems, interaction parameters derived from melting point depression were negative indicating that mixing was exothermic. Using these interaction parameters and Flory-Huggins theory, miscibility was predicted for all compositions, in agreement with experimental data. A model was developed to estimate the solubility of the API in the polymer. The estimated solubility of the model APIs in PVP is low suggesting that kinetic rather than thermodynamic stabilization plays a significant role in inhibiting crystallization. CONCLUSIONS: The thermodynamics of API-polymer systems can be modeled using solution based theories. Such models can contribute towards providing an understanding of the compatibility between API and polymer and the mechanisms of physical stabilization in such systems.

Algorithms↗

PubMed1981

1H-NMR study of the effect of synthetic polymers on the fluidity, transition temperature and fusion of dipalmitoyl phosphatidylcholine small vesicles.

The interaction of water-soluble polymers with dipalmitoyl phosphatidylcholine small vesicles and the effect on vesicle fusion were studied by means of 1H-NMR spectrometry. The motion of dipalmitoyl phosphatidylcholine molecules decreased on interaction with the polymers and was detected as a change in the signal intensity. The interaction behavior of polymers is very sensitive to the chemical structure of the applied polymers. Poly(styrene sulfonic acid) and poly(ethylene glycol) decreased the motion of the choline methyl group, predominantly through coulombic and hydrophobic interaction forces, respectively. For example, in the case of the poly(styrene sulfonic acid)-containing system, the signal intensity of the choline methyl group was decreased about 15% while those of the hydrophobic methylene and terminal methyl groups were scarcely decreased by the addition of polymer to a final concentration of 4.0 x 10(-2) unit mol/l. These polymers are considered to interact with the surface of the vesicle membrane. On the other hand, poly(L-glutamic acid) and poly(N-vinyl-2-pyrrolidone) decreased the signal intensities of not only the choline methyl group, but also those of the hydrophobic methylene and terminal methyl groups. This result suggests that part of these polymers might be incorporated into the hydrophobic region of the vesicle membrane. Addition of the non-ionic polymers inhibited vesicle fusion considerably. This effect was explained by the stabilization of dipalmitoyl phosphatidylcholine vesicles by complexation with these polymers.

Kinetics↗

PubMed1994

Poly(ethylene glycol) on the liposome surface: on the mechanism of polymer-coated liposome longevity.

The hypothetical model is built explaining the molecular mechanism of protective action of poly(ethylene glycol) on liposomes in vivo. The protective layer of the polymer on the liposome surface is considered as a statistical 'cloud' of polymer possible conformations in solution. Computer simulation was used to demonstrate that relatively a small number of liposome-grafted molecules of hydrophilic and flexible polymer can create a dense protective conformational cloud over the liposome surface preventing opsonizing protein molecules from contacting liposome. A more rigid polymer fails to form this dense protective cloud, even when hydrophilic. Computer simulation was also used to reveal possible heterogeneity of reactive sites on a polymer-coated liposome surface, and to estimate the optimal polymer-to-lipid ratio for efficient liposome protection. Experiments have been performed with the quenching of liposome-associated fluorescent label (nitrobenzoxadiazole or fluorescein) with protein (rhodamine-ovalbumin or anti-fluorescein antibody) from solution. It was shown that poly(ethylene glycol) grafting to liposomes hinders protein interaction with the liposome surface, whereas liposome-grafted dextran (more rigid polymer) in similar quantities does not affect protein-liposome interaction. Highly-reactive and low-reactive populations of chemically identical reactive sites have been found on polymer-coated liposomes. Experimental data satisfactory confirm the suggested mechanism for the longevity of polymer-modified liposome.

Binding Sites↗

PubMed1994

Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effects on the biocompatibility, in vivo.

The stability of biomedical polymers in physiological environments is crucial for the normal operation of devices, as well as determining their effect on the tissue response. Degradation is an important factor in polymer biocompatibility, since the environment of the human body can be aggressive to polymers. Most implanted polymers suffer degradation to some extent, and the kinetics and mechanisms of the processes can be affected significantly by various biologically active species, especially enzymes, lipids, peroxides, free radicals and phagocytic cells. The degradation of poly(caprolactone) and poly(DL-lactic acid) under controlled in vivo conditions was studied using a poly(methyl methacrylate) chamber designed to control the exposure of polymers to physiological environments. In particular they may be designed to allow access of extracellular exudate only or access to cells as well as the fluid. The chambers, sealed with filters of pore size either 0.45 micron (impervious to cells) or 3.0 microns (allowing cells to enter the chamber), were implanted subcutaneously into experimental animals for 10, 20 and 30 wk periods. Degradation and molecular interactions of the polymers were characterized by gel permeation chromatography and scanning electron microscopy. The extracellular exudate formed within the implanted chamber is active in promoting the degradation of some biomedical polymers. Inflammatory cells are involved in the biodegradation of implanted polymers by releasing biologically active species such as free radicals into the area surrounding the implant. The data have demonstrated that the hydroxyl radical is likely to be one of the main causes of polymer degradation.

Animals↗

PubMed1995

Antibacterial activity of MDPB polymer incorporated in dental resin.

OBJECTIVES: Previously, we have reported that dental composite incorporating the new monomer methacryloyloxydodecylpyridinium bromide (MDB) showed no release of antibacterial components after being cured but still exhibited antibacterial activity against Streptococcus mutants on its surface. In this study, in order to elucidate the mechanism of the antibacterial effect of immobilized MDPB, the bactericidal activity of MDPB polymer in water-soluble and -insoluble form was investigated, and the effect of MDPB polymer on bacterial attachment was estimated. METHODS: Solutions of homo-polymer of MDPB and co-polymer of MDPB with acrylamide were prepared and the viability of seven major oral streptococci was determined after incubation with each polymer solution. For the estimation of bactericidal activity of insolubilized MDPB polymer, bacteria were kept in contact with cured unfilled Bis-GMA-based resin discs with or without MDPB, and the recovery of viable cells was measured. Attachment of streptococci to cured resin discs with or without MDPB was also compared using radiolabelled bacteria. RESULTS: Water-soluble homo-polymer of MDPB and co-polymer with acrylamide showed bactericidal activity against oral streptococci. However, cured resin incorporating MDPB, which is in water-insoluble form, had little bactericidal activity. Attachment of streptococci, including species which are early colonizers in dental plaque formation, to the cured resin containing MDPB was significantly less than to the control without MDPB. CONCLUSIONS: These results indicate that the bactericidal activity of MDPB polymer is reduced after immobilization, but MDPB on the surface of a resin-based material still shows a bacteriostatic effect and antiadhesion property against oral streptococci.

Analysis of Variance↗

PubMed2004

Microcellular polyHIPE polymer supports osteoblast growth and bone formation in vitro.

A novel micro-cellular polymer with a well-defined and uniform micro-architecture has been developed as a three-dimensional support matrix for in vitro tissue engineering applications. This material is manufactured through a high internal phase emulsion (HIPE) polymerization route and may be modified with hydroxyapatite. The generic form of the support is known as PolyHIPE Polymer (PHP). By changing the chemical composition of the emulsion and the processing conditions, the pore size can be altered from sub-micron range to a few hundred microns and the porosity varied from 70% to 97%. Our work has investigated the use of this micro-porous polymer as a biomaterial to support the growth of osteoblasts, the bone forming cells in vitro. Three groups of polymers were used that had pore sizes of 40, 60 and 100 microm. Results demonstrated in vitro cell-polymer compatibility, with osteoblasts forming multicellular layers on the polymer surface and also migrating to a maximum depth of 1.4mm inside the scaffold after 35 days in culture. PHP was also able to support the differentiation of osteoblasts and the production of a bone-like matrix. The effect of modifying the polymer with hydroxyapatite was also studied and showed that there was a significant increase in osteoblast numbers penetrating into the polymer. There were few differences, between the pore sizes studied, on the overall penetration of osteoblasts into the polymer but the rate of movement into 100 microm PHP was significantly higher compared to the other sizes investigated. This study shows that osteoblasts seeded onto PHP demonstrate cellular attachment, proliferation and ingrowth leading to the support of an osteoblastic phenotype. Therefore this highly porous scaffold has a potential for bone tissue engineering.

Animals↗

PubMed2005

Liquid chromatography of polymers under limiting conditions of desorption II. Tandem injection and quantitative molar mass determination.

Liquid chromatography under limiting conditions of desorption (LC LCD) is a method which allows molar mass independent elution of various synthetic polymers. A narrow, slowly moving zone of small molecules, which promotes full adsorption of one kind of polymer species within column (an adsorli) acts as an impermeable barrier for the fast moving macromolecules. The latter accumulate on the barrier edge and elute nearly in total volume of liquid within column. At the same time, transport of less adsorptive macromolecules is not hampered so that these are eluted in the size exclusion (SEC) mode. As result, polymers differing in their polarity and adsorptivity can be easily separated without molar mass interference. Three methods of barrier creation are discussed and compared. It is shown that a fraction of sample may elute unretained if the adsorli sample solvent is used as a barrier in connection with a narrow-pore column packing. One part of excluded macromolecules likely breaks-out from the adsorli zone and this results in partial loss of sample and distortion of the LC LCD peaks. This problem can be avoided if the adsorli zone is injected immediately before sample solution. Applicability of the LC LCD method for polymer separation has been demonstrated with a model mixture of poly(methyl methacrylate) (adsorbing polymer) and polystyrene (non adsorbing polymer) using bare silica gel as a column packing with a combination of tetrahydrofuran (a desorption promoting liquid -a desorli) and toluene (adsorli). It has been shown that the LC LCD procedure with tandem injection allows simple and fast discrimination of polymer blend components with good repeatability and high sample recovery. For quantitative determination of molar masses of both LC LCD and SEC eluted polymers, an additional size exclusion chromatographic column can be applied either in a conventional way or in combination with a multi-angle light scattering detector. A single eluent is used in the latter column, which separates the mixed mobile phase, system peaks and the desorli zone from the polymer peaks so that measurements are free from disturbances caused by the changing eluent composition. The resulting LC LCD x SEC procedure has been successfully applied to poly(methyl methacrylate) samples.

Chromatography, Liquid↗

PubMed2005

Hydrogen bonding interactions between adsorbed polymer molecules and crystal surface of acetaminophen.

The objective of this work was to investigate whether or not the hydrogen bonding interaction between polymer and crystal surface can be detected by the etching pattern changes in the presence of polymers. The (010) face of acetaminophen single crystal was used as a model solid surface. The etching patterns on the (010) face of acetaminophen crystal by water are in the directions of a- and c-axes, which are the same as the directions of the dominant attachment energies on the (010) face. In the presence of polymer, the hydrogen bonding interactions between adsorbed polymer and crystal surface can affect surface diffusion of acetaminophen molecules and change the etching patterns in the direction of a-axis, i.e., the direction of one hydrogen bond chain. Studies with 2-hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) showed that polymers, which can form hydrogen bonds with acetaminophen crystal surface, can change etching patterns in the direction of a-axis. Study with Dextran suggested that if a polymer cannot form hydrogen bonds with crystal surface due to steric repulsion, it will not change the etching pattern in the direction of a-axis. Studies with poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) further confirmed that only if a polymer can form hydrogen bonds with acetaminophen on crystal surface, the etching patterns in the direction of a-axis will be affected. The study results suggest that in the presence of polymers, the etching pattern change in the direction of hydrogen bond chain, the a-axis of acetaminophen crystals, can be used to indicate the existence of the hydrogen bonding interactions between adsorbed polymers and acetaminophen crystal surface.

Acetaminophen↗

PubMed2005

Controlled release of the herbicide simazine from computationally designed molecularly imprinted polymers.

The present study describes the development of materials suitable for environmental control of algae. Molecularly imprinted polymers (MIPs) were used as simazine carriers able to provide the controlled release of simazine into water. Three polymers were designed using computational modelling. The selection of methacrylic acid (MA) and hydroxyethyl methacrylate (HEM) as functional monomers was based on results obtained using the Leapfrog algorithm. A cross-linked polymer made without functional monomers was also prepared and tested as a control. The release of simazine from all three polymers was studied. It was shown that the presence of functional monomers is important for polymer affinity and for controlled release of herbicide. The speed of release of herbicide correlated with the calculated binding characteristics. The high-affinity MA-based polymer released approximately 2% and the low-affinity HEM-based polymer released approximately 27% of the template over 25 days. The kinetics of simazine release from HEM-based polymer show that total saturation of an aqueous environment could be achieved over a period of 3 weeks and this corresponds to the maximal simazine solubility in water. The possible use of these types of polymers in the field of controlled release is discussed.

Eukaryota↗

PubMed2005

Polymer conjugates: nanosized medicines for treating cancer.

Interdisciplinary research at the interface of polymer chemistry and the biomedical sciences has produced the first polymer-based nanomedicines for the diagnosis and treatment of cancer. These water-soluble hybrid constructs, designed for intravenous administration, fall into two main categories: polymer-protein conjugates or polymer-drug conjugates. Polymer conjugation to proteins reduces immunogenicity, prolongs plasma half-life and enhances protein stability. Polymer-drug conjugation promotes tumor targeting through the enhanced permeability and retention (EPR) effect and, at the cellular level following endocytic capture, allows lysosomotropic drug delivery. The successful clinical application of polymer-protein conjugates (PEGylated enzymes and cytokines) and promising results arising from clinical trials with polymer-bound chemotherapy (e.g. doxorubicin, paclitaxel, camptothecins) has provided a firm foundation for more sophisticated second-generation constructs that deliver the newly emerging target-directed anticancer agents (e.g. modulators of the cell cycle, signal transduction inhibitors and antiangiogenic drugs) in addition to polymer-drug combinations (e.g. endocrine- and chemo-therapy).

Antineoplastic Agents↗

PubMed1998

Problems encountered for food safety with polymer packages: chemical exchange, recycling.

When a polymer is in contact with a liquid, generally some matter transfers take place: the liquid enters the polymer, while some additives leave the polymer. This fact is responsible for a reduction in the properties of the polymer and pollution of the liquid food is obtained. However, it is sure that, on account of their outstanding properties, food packages are becoming more and more based on polymers. The process of mass transfers is controlled by transient diffusion, and these theoretical problems are so complex that only numerical models are able to resolve them. New difficult problems appear with the desire of recycling old food packages made of polymers by reusing them as new food packages. Of course, because of the potential contamination brought with this recycled polymer, the package is made of bi-layer or tri-layer films where the reused polymer is located between two virgin polymer layers. As it takes some time for the contaminant to diffuse through the virgin layer, this latter plays the role of a functional barrier to pollution. The various difficulties in the whole problem are considered in succession: the coextrusion of the films where a contaminant transfer already occurs; and the effect of the liquid food which may enhance the diffusion of the contaminant. Various master curves are drawn by using dimensionless numbers, so as to make the results quite general and of use from a practical point of view.

Conservation of Natural Resources↗

PubMed2003

Protein partitioning in thermoseparating systems of a charged hydrophobically modified ethylene oxide polymer.

The phase behavior of a thermoseparating cationic hydrophobically modified ethylene oxide polymer (HM-EO) containing tertiary amines has been investigated at different pH, salt and sodium dodecyl sulfate (SDS) concentrations, in order to find a water/HM-EO two-phase system suitable for protein partitioning. The used polymer forms micellar aggregates that can be charged. By changing pH and SDS concentrations the netcharge of the SDS/HM-EO aggregate can be shifted from positive to negative. Bovine serum albumin (BSA) and lysozyme were partitioned in the thermoseparated two-phase systems of the cationic polymer at different pH, salt and SDS concentrations. The dominant attractive interactions between the polymer aggregates and the studied proteins were shown to be of electrostatic (Coulomb) nature rather than hydrophobic interaction. At low ionic strength the positively charged polymeric aggregates attracted negatively charged BSA and repelled positively charged lysozyme. Upon addition of SDS the negatively charged aggregates attracted lysozyme and repelled BSA. Thus, it was possible to direct proteins with different charges to the polymeric phase and redirect them to a polymer-depleted phase by changing the netcharge of the polymeric aggregates. The effect of different salts on the partitioning of BSA in a system of slightly positively charged HM-EO was studied. NaCl and KBr have a significant effect on driving the BSA to the polymer-depleted phase, whereas KF and K2SO4 have a smaller effect on the partitioning. The cloud point temperature of the charged polymer decreased upon addition of SDS near the isoelectric molar ratio of SDS to polymer and also upon salt addition. In the latter case the decrease was smaller than expected from model calculations based on Flory-Huggins theory, which were performed for a charged thermoseparating polymer at different charges and salt concentrations.

Ethylene Oxide↗

PubMed2001

Phenanthrene desorption from soil in the presence of bacterial extracellular polymer: observations and model predictions of dynamic behavior.

The extracellular polymer produced by a bacterium isolated from soil was employed in laboratory studies of desorption of a model polynuelear aromatic hydrocarbon (PAH), phenanthrene. The experimental results show that the selected extracellular polymer enhances the extent of release of soil-bound phenanthrene. A kinetic model was developed as an aid in interpreting the alterations in phenanthrene desorption resulting from polymer addition. The model employs a statistical gamma (gamma) distribution to describe spectrum of rate constants for transfer of phenanthrene from soil to water, and assumes instantaneous binding of phenanthrene to polymer and of polymer to the test soil. The relevant distribution coefficients and statistical parameters of the gamma distribution needed for the model were evaluated in independent experiments. Using these measured parameters, the model provides a satisfactory independent prediction of phenanthrene release from soil to aqueous phase at two test polymer concentrations, 50 mg TOC/L and 100 mg TOC/L. The success of the independent model predictions suggests a mechanism for the influence of extracellular polymer on phenanthrene desorption. The intrinsic, soil-specific, rate constants for solid to solution transfer of phenanthrene do not appear to be changed by bacterial polymer. Instead, polymer binding of phenanthrene in solution results in an increase in driving force for desorption by decreasing the solution concentration of the free, unbound, PAH molecule.

Bacteria↗

PubMed2002

Improved haemocompatibility of cysteine-modified polymers via endogenous nitric oxide.

A novel method for improving the haemocompatibility of biomedical materials through endogenous nitric oxide (NO) is presented. L-cysteine was covalently immobilized onto two biomedical polymers: polyurethane (PU) and polyethylene terephthalate (PET). The L-cysteine content on the polymers was approximately 5-8 nmol/cm2 as quantified via a chemiluminescence-based assay. The haemocompatibility of the modified polymers was evaluated in terms of the number of adhered platelets when exposed to a platelet suspension labeled with Cr51. Platelet adherence on the L-cysteine-modified polymers was reduced more than 50% as compared to the control (glycine-modified polymers) when the platelet suspension contained plasma constituents. No difference in platelet adhesion was observed in the absence of plasma constituents. Further experiments demonstrated that NO was easily transferred to the L-cysteine-modified polymers from S-nitroso-albumin in PBS buffer. The NO was then released from the polymer. NO transfer or release was not observed for the control. The results suggest that L-cysteine-modified polymers are effective in reducing platelet adhesion via the transfer of NO from endogenous S-nitrosoproteins in plasma to the polymer followed by the subsequent release of NO. Thus, exploiting endogenous NO is a viable option for improving the haemocompatibility of biomaterials.

Animals↗

PubMed2003

Platelet compatible blood filtration fabrics using a phosphorylcholine polymer having high surface mobility.

To obtain a novel polymer for coating on blood filtration devices, which can reduce platelet adhesion and activation when the polymer is in contact with blood under a dry condition, a phosphorylcholine polymer with high mobility of the polymer side chain was designed. The polymer possesses 2-methacryloyloxyethoxyethyl phosphorylcholine unit (PMEO2B) having a diethylene oxide chain between the phosphorylcholine group and the backbone. The surface density of the phosphorylcholine groups and their orientation under aqueous conditions were analyzed with an X-ray photoelectron spectroscope. On the PMEO2B surface, the surface density of phosphorylcholine groups was much higher than that of the theoretical value even when the surface was in air atmosphere. The period for equilibrating the surface of PMEO2B by hydration was shorter than that of the 2-methacryloyloxyethyl phosphorylcholine polymer (PMB). The mobility of the polymer chain with hydration was remarkably improved with the addition of a diethylene oxide chain as a bridging unit. The platelet activation and adhesion were evaluated using a non-woven fabric made from poly(ethylene terephthalate) fibers and that coated with these phosphorylcholine polymers. Even when the platelets were passed through the PMEO2B-coated fabric without prehydration, the activity of the platelets eluted was similar to that of native platelets. Moreover, adherent cells were not observed on the fabric. On the other hand, the platelets adhered to the PET fabric and to that coated with PMB. Based on these results, we concluded that the higher mobility of the polymer chain is very important to reduce interactions with platelets.

Biocompatible Materials↗

PubMed2000

Development of controlled drug release systems based on thiolated polymers.

The purpose of the present study was to generate mucoadhesive matrix-tablets based on thiolated polymers. Mediated by a carbodiimide, L-cysteine was thereby covalently linked to polycarbophil (PCP) and sodium carboxymethylcellulose (CMC). The resulting thiolated polymers displayed 100+/-8 and 1280+/-84 micromol thiol groups per gram, respectively (means+/-S.D.; n=6-8). In aqueous solutions these modified polymers were capable of forming inter- and/or intramolecular disulfide bonds. The velocity of this process augmented with increase of the polymer- and decrease of the proton-concentration. The oxidation proceeded more rapidly within thiolated PCP than within thiolated CMC. Due to the formation of disulfide bonds within thiol-containing polymers, the stability of matrix-tablets based on such polymers could be strongly improved. Whereas tablets based on the corresponding unmodified polymer disintegrated within 2 h, the swollen carrier matrix of thiolated CMC and PCP remained stable for 6.2 h (mean, n=4) and more than 48 h, respectively. Release studies of the model drug rifampicin demonstrated that a controlled release can be provided by thiolated polymer tablets. The combination of high stability, controlled drug release and mucoadhesive properties renders matrix-tablets based on thiolated polymers useful as novel drug delivery systems.

Acrylic Resins↗

PubMed2003

Development of buccal drug delivery systems based on a thiolated polymer.

The purpose of the present study was to investigate the benefit of thiolated polymers (thiomers) for the development of buccal drug delivery systems. L-Cysteine was thereby covalently attached to polycarbophil (PCP) mediated by a carbodiimide. The resulting conjugate displayed 140.5+/-8.4 microM thiol groups per gram polymer. Disintegration studies were carried out with tablets based on unmodified polymer and conjugated polymer, respectively. Due to the formation of disulfide bonds within the thiolated polymer, the stability of matrix-tablets based on this polymer was strongly improved. Additionally tensile studies were carried out, which were in good correlation with further results obtained by mucoadhesion studies, using the rotating cylinder method. These results showed that tablets based on thiolated PCP remained attached on freshly excised porcine mucosa 1.8 times longer than the corresponding control. Moreover, the enzyme inhibitory properties of polymers were evaluated as well. Thiolated PCP increased the stability of the synthetic substrate for aminopeptidase N-leu-p-nitroanilide (N-leu-pNA) and the model drug leucin-enkephalin (leu-enkephalin) against enzymatic degradation on buccal mucosa. Due to the use of thiolated polymers also a controlled drug release for leu-enkephalin was guaranteed over a time period for more than 24 h. Results of the present studies suggest that thiolated polymers represent a very useful tool for buccal delivery of peptide drugs.

Administration, Buccal↗