Chitosan-poly(acrylic acid) polyelectrolyte complex membranes: preparation, characterization and permeability studies

Polyelectrolyte complex (PEC) membranes were obtained by mixing solutions of two polymers of opposite charges, chitosan (Chi) and poly(acrylic acid) PAA. Three membranes were obtained: one made of pure chitosan and two membranes with chitosan mixed with PAA at a ratio of 95:5 (one prepared using PAA solution in 3.5% formic acid, named ChiPAA3.5, and another one using a PAA solution in 10% formic acid, named ChiPAA10). The membranes were characterized by swelling experiments, FT-IR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical properties and permeability studies in relation to a drug model (sodium sulphamerazine). The calculation of degree of ionization showed that the lower the formic acid concentration was, the higher the PAA dissociation degree. Polyelectrolyte complex formation was characterized by FT-IR. Water uptake results showed that PEC membranes were more hydrophilic than pure chitosan, ChiPAA3.5 being the most. Morphological analysis by SEM and AFM showed that PAA addition changed the membranes morphology, especially for ChiPAA3.5. Mechanical properties indicated that PEC membranes were more rigid than pure chitosan membranes and that the morphology has an influence on tensile strength values. Permeability values decreased with complex formation and were lower for ChiPAA10 than ChiPAA3.5. However, as drug concentration was increased, the difference between the two complex membranes disappeared. The results were discussed considering the drug-membrane interactions. Diffusion coefficient values indicated that ChiPAA3.5 had a higher drug retention capacity than ChiPAA10.     

Chitosan-poly(acrylic acid) polyelectrolyte complex membranes: preparation,characterization and permeability studies

Polyelectrolyte complex (PEC) membranes were obtained by mixing solutions of two polymers of opposite charges, chitosan (Chi) and poly(acrylic acid) PAA. Three membranes were obtained: one made of pure chitosan and two membranes with chitosan mixed with PAA at a ratio of 95:5 (one prepared using PAA solution in 3.5% formic acid, named ChiPAA3.5, and another one using a PAA solution in 10% formic acid, named ChiPAA10). The membranes were characterized by swelling experiments, FT-IR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical properties and permeability studies in relation to a drug model (sodium sulphamerazine). The calculation of degree of ionization showed that the lower the formic acid concentration was, the higher the PAA dissociation degree. Polyelectrolyte complex formation was characterized by FT-IR. Water uptake results showed that PEC membranes were more hydrophilic than pure chitosan, ChiPAA3.5 being the most. Morphological analysis by SEM and AFM showed that PAA addition changed the membranes morphology, especially for ChiPAA3.5. Mechanical properties indicated that PEC membranes were more rigid than pure chitosan membranes and that the morphology has an influence on tensile strength values. Permeability values decreased with complex formation and were lower for ChiPAA10 than ChiPAA3.5. However, as drug concentration was increased, the difference between the two complex membranes disappeared. The results were discussed considering the drug–membrane interactions. Diffusion coefficient values indicated that ChiPAA3.5 had a higher drug retention capacity than ChiPAA10.     

In vitro and in vivo biocompatibility of chitosan-xanthan polyionic complex

A novel hydrogel, CHITOXAN(TM) (CH-X), has potential as a vehicle for controlled drug delivery. The hydrogel is obtained by complexation of two polysaccharides, chitosan and xanthan. In the present work we investigated the biocompatibility of the complex using in vitro and in vivo models. The cytotoxic effects of CH-X microspheres as well as their degradation products at different concentrations were assessed on fibroblasts (fibroblast cell line L-929) using 3-(4,5-dimethylthiazole-2yl)-2,5-triphenyl tetrazolium) (MTT). The test is based on mitochondrial dehydrogenase cell activity as an indicator of cell viability. Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) cytokines as well as nitric oxide (NO) production by macrophages (macrophage cell line J-774) were examined as indicators of cell activation. In vivo biocompatibility assessment was performed for 1 to 12 weeks. This study was performed using tablets obtained after compression of CH-X particles implanted at the subcutaneous level in male Wistar rats. CH-X biocompatibility and degradation were investigated using histological studies. Light and transmission electron microscopy (TEM) analyses were used to determine the foreign-body reaction and phagocytosis of the implants by macrophages. Fibroblast exposition to CH-X particles and degradation products did not show cytotoxic effects as measured by MTT test. TNF-alpha production was dependent on CH-X particles concentration, whereas IL-1beta production was found to be dose independent. CH-X extract products stimulated TNF-alpha secretion when used at the highest concentration (10 mg/mL), notably after 28 days' degradation time. No effect was observed on IL-1beta production when CH-X extracts were used in comparison to the control. The effects of CH-X particles on NO secretion were similar as on TNF-alpha. Histological studies showed that CH-X tablets broke down into particles which progressively degraded into smaller fragments. A significant fraction of the fragments was ingested by the macrophages after 12 weeks of implantation. Light microscopy studies showed a weak foreign-body reaction as a function of time and the fibrous layer thickness decreased with time of implantation.     

Interpolymer complex between poly(ethylene oxide) and poly(acrylic acid): Viscometric studies in THF-water mixtures

Systematic studies were performed on interpolymer complex formation between Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) in THF-water mixtures of different compositions. Viscosity behaviour during complex formation in mixed solvents was found to be entirely different from that observed by other workers in aqueous and in pure organic solvents. The result are interpreted in terms of, (a) preferential solvation of the polymer, (b) Probable change in conformation of the polyelectrolyte moleculer. (c) association of complex molecules in a medium of low dielectric constant, and (d) expected disordering of bound water molecules around PEO by THF. Irrespective of solvent composition, interpolymer complex of PAA and PEO was always found to have 1:1 unit mole ratio.     

Efficacy of antibiotics-loaded interpenetrating network (IPNs) hydrogel based on poly(acrylic acid) and gelatin for treatment of experimental osteomyelitis: in vivo study

The safety and efficacy of gentamycin sulphate (GS)- or vancomycin hydrochloride (VCl)-loaded polymer devices based on poly(acrylic acid) and gelatin crosslinked selectively using 0.3 mol % N,N'-methylene bisacrylamide and 1 wt% glutaraldehyde were evaluated by varying the drug concentration onto the devices. The placebo and drug-loaded device of AxGx (acrylic acid:gelatin: 1:1 w/w) were employed for the treatment of experimental osteomyelitis in rabbit. Rabbits were categorized into four groups. Twelve rabbits in each group were treated with 12+/-1 mg of AxGx-1a (22% w/w GS), 12+/-1 mg of AxGx-1b (44% w/w GS), 16+/-1 mg of AxGx-1b (44% w/w GS) and 16+/-1 mg of AxGx-1c (44% w/w VCl). The drug concentration was measured following implantation in the adjacent tissue of femoral cavity, and serum. In femoral cavity maximum drug concentration was found on the 7th day with all the four types of devices. No drug was found after 21 days, at the local site with devices AxGx-1a and AxGx-1b (12+/-1 mg), whereas it was detected after 6 weeks with 16+/-1 mg device (44% w/w GS or VCl). Macroscopic evaluation after treatment revealed that swelling, redness, local warmth and drainage decreased depending upon the drug loading of the implants. Sequential radiographs, histology, microbiologic assay and scanning electron micrography demonstrated devices AxGx-1b and AxGx-1c (16+/-1 mg of 44% w/w drug loading) to be the most suitable device, which heals the infection after 6 weeks of treatment. No significant difference (p>0.05) in the rate of healing was observed between GS- and VCl-loaded devices. None of the implant showed toxic level of drug in serum at any given time.     

The gastrointestinal transit profile of 14C-labelled poly(acrylic acids): an in vivo study

The gastrointestinal distribution profiles for three 14C-labelled poly(acrylic acid)s of different average molecular weights and degrees of cross-linking have been established using the rat model. Despite initial differences in transit times and retention characteristics, these structural features were found to be of little influence to the overall gastrointestinal transit of the materials under consideration. No evidence for the systemic absorption of any of the polymers could be identified.     

Human osteosarcoma cell adhesion behaviour on hydroxyapatite integrated chitosan-poly(acrylic acid) polyelectrolyte complex

A novel degradable composite system has been prepared by integrating hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, (HAP) in a polyelectrolyte complex matrix of chitosan (CHI) and poly(acrylic acid) (PAA). The composite was formulated by integrating 80 wt.% HAP in the polyelectrolyte complex matrix of CHI and PAA in the ratio 40/60 (designated as CPH). The composite could be easily fabricated into clinically significant shapes by a simple moulding procedure intended for bone graft applications. The adhesion behaviour of human osteosarcoma (HOS) cells on this degradable composite system was studied by selecting the polyelectrolyte complex, CHI/PAA 40/60 (designated as CP) as control sample. Light microscopic observations show that cells around CPH retained the typical morphology of HOS cells while cells around the polyelectrolyte complex showed a cytotoxic effect. The adhesion behaviour as well as morphological responses of the seeded cells was further investigated by scanning electron microscopy. The scanning electron micrographs of the polyelectrolyte complex, CP, showed the presence of rounded cells with raised nuclear regions, indicating delayed spreading; cells adhered on CPH were flattened with filopodia and showed good attachment and spreading, indicating better adhesion onto the HAP integrated composite. Comparing the MTT assay for quantitative evaluation of cell viability, CPH showed a higher percentage of metabolically active cells compared to CP.     

Effect of composition of interpenetrating polymer network hydrogels based on poly(acrylic acid) and gelatin on tissue response: a quantitative in vivo study

The local tissue response of the biomaterial is the most important criteria for determination of its biocompatibility. In the present study, full and semi-interpenetrating polymer networks (IPN) based on polyacrylic acid (AAc) and gelatin (Ge) crosslinked with 0.5 mol % N,N'-methylene bisacrylamide (BAm) and 4% glutaraldehyde (GA), respectively, were evaluated for tissue response in rats. IPNs with varying ratios of AAc and Ge were implanted subcutaneously in rats. Gentamicin sulfate (GS)-loaded IPN samples were also studied to evaluate the possible therapeutic use of these polymers. The site of implantation was biopsied and processed for light microscopy (LM) with image analysis for assessment of tissue reaction at 2-, 6-, and 12-week intervals. The tissue reaction was evaluated as a function of composition and time. The degree of neutrophil, lymphocyte and macrophage infiltration, fibrosis, granuloma formation, integration with extracellular matrix, vascular proliferation, and damage of adjacent structures were assessed. Polymers with >66% crosslinked Ge (Gx) showed persistence of acute inflammatory reaction till 3 months, with marked tissue injury and fibrosis. On the other hand, high crosslinked AAc (Ax) content showed chronic inflammatory reaction with high macrophage infiltration. Macrophages took active part in phagocytosis, degradation, and removal of polymers without granuloma formation or significant giant cell reaction. The IPNs with acrylic acid and gelatin in the ratio of 1:1 showed least tissue reaction and thus appeared to be most biocompatible. The majority of the polymers showed integration with extracellular matrix and growth of capillaries in and around the polymer. The heamogram, liver and renal function tests, and histology of vital organs were all normal. GS loading showed no additional local or systemic reaction suggesting the potential usefulness of the hydrogels as carrier for drugs such as GS.     

Multilayer assemblies of poly(4-vinylpyridine) bearing an osmium complex and poly(acrylic acid) via hydrogen bonding

Poly(4-vinylpyridine) bearing an osmium complex was alternately assembled with poly(acrylic acid) on a gold substrate via hydrogen bonding. UV-Vis spectra were used to monitor the assembling process. X-ray diffraction patterns and AFM images showed that the multilayer film is of high quality with low surface roughness. The properties of electrodes modified with such a film were characterized by means of cyclic voltammograms, which strongly depended on the architecture of the layered assembly.     

Efficient Synthesis and Copolymerization of Poly(acrylic acid) and Poly(acrylic ester) Macromonomers: Manipulation of Steric Factors

Summary: Macromonomers have been prepared by polymerization of acrylic acid (AA) and tert‐butyl acrylate (tBA) in the presence of the addition‐fragmentation chain transfer (AFCT) agents, ethyl α‐(bromomethyl)acrylate (EBMA) and tert‐butyl α‐(bromomethyl)acrylate (BBMA). Chain transfer constants of 1.25 (EBMA) and 1.14 (BBMA) in the AA polymerization, and 2.42 (EBMA) and 1.75 (BBMA) in the tBA polymerization were obtained. The reduction in molecular weight with increasing concentration of AFCT agent and efficient introduction of 2‐carbalkoxy‐2‐propenyl ω‐end group was indicative of macromonomer formation. Polymerizations were retarded with increasing concentrations of AFCT agent and increases in the absolute concentration of EBMA slowed down the polymerization of AA but not tBA. The difference between EBMA and BBMA was less significant with tBA; more efficient macromonomer synthesis was indicated by less retardation and greater double bond retention at higher conversions. Copolymerizations of poly(AA) and poly(tBA) macromonomers with styrene indicated that the former was more reactive towards the St propagating radical. The results are rationalized in terms of the steric hindrance imposed by the tert‐butyl group. Poly(tBA) macromonomer was successfully hydrolyzed to give an alternative route to the poly(AA) macromonomer.

Reaction mechanism for macromonomer synthesis using AFCT.     

Chelation properties of polymer complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide)

The metal-complexing properties of intermolecular complexes of poly(acrylic acid) with poly(acrylamide), and poly(acrylic acid) with poly(N,N-dimethylacrylamide) were studied by means of the liquid-phase polymer based retention (LPR) technique. The metal ion retention ability at pH 5 for 400 μg of Cu(II), Cd(II), Co(II), Cr(III), Hg(II), Ni(II), Pb(II), and Zn(II) was investigated due to their environmental and analytical interest in the presence of 1.1 M of carboxylic acid units and variable amounts of amide groups. The retention profiles of the intermolecular complexes were compared with those of the correspondent homopolymers and copolymers. The retention capacity of poly(acrylic acid) is 100% for all metal ions except for Co(II), Ni(II), and Zn(II) whose values were about 90%, while poly(acrylamide) does not retain any of the metal ion studied. The presence of poly(acrylamide) decreases the retention capacity down to 60% for Co(II) and Ni(II) and to 70% for Zn(II). The decrease on the retention values is dependent on the polymer ratio. A smaller effect is observed by the addition of poly(N,N-dimethylacrylamide) which also decreases the retention capacity down to 80% for Co(II) and Ni(II) for a ratio poly(acrylic acid)/poly(N,N-dimethylacrylamide) = 1/2. The metal ion binding behavior of the interpolymer complexes is very close to that of the copolymers.     

Synthesis and characterization of chitosan-poly(acrylic acid) nanoparticles

Chitosan (CS)-poly(acrylic acid) (PAA) complex nanoparticles, which are well dispersed and stable in aqueous solution, have been prepared by template polymerization of acrylic acid (AA) in chitosan solution. The physicochemical properties of nanoparticles were investigated by using size exclusion chromatography, FT-IR, dynamic light scattering, transmission electron microscope and zeta potential. It was found that the molecular weight of PAA in nanoparticles increased with the increase of molecular weight of CS, indicating that the polymerization of acrylic acid in the chitosan solution was a template polymerization. It was also found that the prepared nanoparticles carried a positive charge and showed the size in the range from 50 to 400 nm. The surface structure and zeta potential of nanoparticles can be controlled by different preparation processes. The experiment of in vitro silk peptide (SP) release showed that these nanoparticles provided a continuous release of the entrapped SP for 10 days, and the release behavior was influenced by the pH value of the medium.     

Interaction of water-soluble collagen with poly(acrylic acid)

Interactions between poly(acrylic acid) labeled with pyrene (PAA-Py) and succinylated calfskin collagen (type I) (SCSC) were studied by fluorescence spectroscopy. PAA-Py exhibits a strong emission from pyrene monomer (intensity, I(M)) when it exists in an extended conformation. It exhibits another broad emission from pyrene excimer (intensity, I(E)) when it adopts a collapsed globule conformation. At pH 3, a value that is lower than the isoelectric point of SCSC, the ratio I(E)/I(M) value decreased cooperatively with increasing concentration of SCSC at constant PAA-Py concentration, under salt-free condition. On the other hand, this effect was not observed in the presence of 0.1 M NaCl. At pH 7, a value higher than the isoelectric point of SCSC, the ratio I(E)/I(M) was not affected by the presence of SCSC in the absence and presence of salt. From electrophoretic light scattering experiments, it was found that at pH 3 PAA-Py was negatively charged, while SCSC had a positive charge. Thus it is strongly suggested that the two polymers interact by electrostatic attraction at low pH where they are oppositely charged, and that PAA-Py adopts an extended conformation in the complex formed with SCSC. Similar interactions are believed to occur between dentinal collagen and the polycarboxylate component of glass-ionomer cements.     

Synthesis of radiolabeled congeners of the carbomers: (14)C-labeled poly(acrylic acid)s

A general method for the synthesis of (14)C-acrylic acid is described in detail. The material is used for the synthesis of a range of radiolabeled poly(acrylic acid)s in which the (14)C-label forms an integral part of the polymer backbone. The chemical structure of the synthesized polymers is examined in the light of spectroscopic data, molecular weight determinations, and rheological studies.     

Formation‐destruction conditions of an interpolymer complex between a poly(acrylic acid) gel and linear poly(ethylene glycol) in methanol

The contraction of a poly(acrylic acid) gel (GPAAc) ( 1 ) induced by complexation with linear poly‐(ethylene glycol) (PEG) ( 2 ) in methanol media proceeds in a similar manner to that in aqueous solution. It was found that both the concentration and molecular mass of the PEG have a strong effect on the complexation with GPAAc. The existence of a stable interpolymer complex between components under consideration takes place in the range of lower and upper critical values of molecular mass (CMM) of the linear polymer. Outside of these CMM values of PEG no perfect complexation occurred due to thermodynamic and kinetic reasons. The structure of the interpolymer complex formed due to the hydrogen bonding is destabilized as a result of ionization and the changing of the thermodynamic characteristics of the solvent under addition of dimethylsulfoxide to methanol.     

Poly(acrylic acid)-grafted Poly(N-isopropyl acrylamide) Networks: Preparation,Characterization and Hydrogel Behavior

Poly(acrylic acid)-grafted poly(N-isopropylacrylamide) co-polymer networks (PNIPAAm-g-PAA) were prepared via the reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropyl- acrylamide (NIPAAm) with trithiocarbonate-terminated PAA as a macromolecular chain-transfer agent in the presence of N,N-methylenebisacrylamide. The PNIPAAm-g-PAA co-polymer networks were characterized by means of Fourier transform infrared spectroscopy, differential scanning calorimetry and small-angle X-ray scattering. It is found that the PNIPAAm-g-PAA co-polymer networks were microphase-separated, in which the microdomains of PNIPAAm-PAA interpolymer complexes were dispersed into the PNIPAAm matrix. The PNIPAAm-g-PAA hydrogels displayed a dual response to temperature and pH values. The thermoresponsive properties of PNIPAAm-g-PAA networks were investigated. Below the volume phase transition temperatures, the PNIPAAm-g-PAA hydrogels possessed much higher swelling ratios than control PNIPAAm hydrogel. In terms of swelling, deswelling and reswelling tests, it is judged that the PNIPAAm-g-PAA hydrogels displayed faster response to the external temperature changes than control PNIPAAm hydrogel. The improved thermoresponsive properties of hydrogels are ascribed to the formation of PAA-grafted PNIPAAm networks, in which the water-soluble PAA chains behave as the hydrophiphilic tunnels and allow water molecules to go through and, thus, to accelerate the diffusion of water molecules.     

Vinylpyrrolidone-co-(meth)acrylic acid inserts for ocular drug delivery: synthesis and evaluation

Copolymeric hydrogels constituting of vinylpyrrolidone and methacrylic or acrylic acid repeat units have been prepared and investigated for their ability to act as controlled release vehicles in ophthalmic drug delivery. The materials were synthesized by radical-induced polymerization in the presence of N,N'-methylenebisacrylamide crosslinker, and the influences of network composition and drug solubility upon the swelling properties, adhesion behavior, and drug release characteristics were studied. In vitro release experiments showed that some of these materials could be useful vehicles for the delivery of drugs such as pilocarpine or chloramphenicol, while in vivo studies, using the rabbit model, confirmed their high potential for the controlled ocular delivery of pilocarpine hydrochloride.     

Studies on biodegradation and release of gentamicin sulphate from interpenetrating network hydrogels based on poly(acrylic acid) and gelatin: in vitro and in vivo

Interpenetrating network hydrogels (IPNs) based on poly(acrylic acid) and gelatin (Ge) were evaluated for in vitro and in vivo biodegradation and in vivo release of gentamicin sulphate. In vitro and in vivo degradation studies demonstrated that with the increase of acrylic acid content in the polymer, the rate of degradation decreases, and a reverse phenomenon was observed with increasing Ge content in the hydrogel. The rate of in vivo degradation was much lower than in vitro degradation. Incorporation of gentamicin sulphate in hydrogel further reduces their degradation. In vitro and in vivo drug release profile showed a burst effect, followed by controlled release. Drug concentration was measured in the local skin tissue, blood serum, kidney, liver and spleen. The local skin tissue concentration of 50% and 100% gentamicin sulphate, loaded full IPNs (i.e., Ax-1 and Ax-2), was found to be higher (20+/-2mug/g) than the minimum bactericidal concentration for Staphylococcus aureus (1.2mug/g) and Pseudomonas aeruginosa (10mug/g), respectively, for a study time of 60 days.     

Release of amoxicillin from polyionic complexes of chitosan and poly(acrylic acid). Study of polymer/polymer and polymer/drug interactions within the network structure

Polyionic complexes of chitosan (CS) and poly(acrylic acid) (PAA) were prepared in a wide range of copolymer composition and with two kind of drugs. Release of amoxicillin trihydrate and amoxicillin sodium from these different complexes were studied. The swelling behavior of and solute transport in swellable hydrogels were investigated to check the effect of polymer/polymer and polymer/drugs interactions. The electrostatic polymer/polymer interactions take place between the cationic groups from CS and the anionic ones from PAA. The diffusion of amoxicillin trihydrate was controlled only by the swelling/eroding ratio of the polyionic complexes. The swelling degree of amoxicillin sodium hydrogels was more extensive when compared to the swelling degree of amoxicillin trihydrate formulations. It was concluded that the water uptake was mainly governed by the degree of ionization. Restriction of amoxicillin sodium diffusion could be achieved by polymer/ionized-drug interaction that retards the drug release. Freeze-dried polyionic complexes could serve as suitable candidates for amoxicillin site-specific delivery in the stomach.