Dynamic Swelling Studies Research Articles

Evaluation of a statistical model for the formation of poly [acryloyl hydroxyethyl starch] microspheres.

To characterize the network structure of Poly(Acryloyl Hydroxyethyl Starch) (Ac-HES) microspheres and test the theoretical model and the hypothesis that the rate of swelling of microspheres is inversely related to the extent of crosslinking. Microspheres were prepared with varying degrees of derivatization (DD) and molar ratios (MR) and subjected to the characterization of matrix structure by dynamic and equilibrium swelling studies utilizing direct microscopic observation and the Flory-Rehner equation. The dependence of average molecular weight between crosslinking Mc, on DD and MR were compared to test the validity of the model. Study of the dependence of Mc on the microspheres preparation parameters, DD and MR, showed that at constant MR, the Mc decreased with DD, while at constant DD, the Mc initially decreased with MR to a minimum, and then increased with MR, complying with the model prediction. Dynamic swelling of microspheres showed a monotonical increase to equilibrium size featured by two time variables, Tp and Teq, that were dependent on Mc; this permitted a conceptual view of the general structure of the Ac-HES microspheres. The Mc, which was more accurately determined by the weight method (as opposed to volume method), was independent of the size of microspheres although there was evidence of variation among particles within a batch. The results validated the model in describing the polymerization/crosslinking reaction of the Ac-HES microsphere system and suggested that Mc is the principal factor in controlling release.

Equilibrium and dynamic swelling of polyacrylates

AbstractPolyacrylates were prepared by solution polymerization of partially neutralized acrylic acid at 37°C. The swelling behavior of the polyacrylates was examined using equilibrium and dynamic swelling studies. Equilibrium swelling studies in deionized water were used to determine the molecular weight between crosslinks using the Flory‐Rehner theory. The amount of crosslinking agent incorporated into the network was a function of the nominal crosslinking ratio. Dynamic swelling studies in saline solutions were used to investigate the initial swelling rate for the polyacrylates. Swelling studies of the polyacrylates in saline solutions under load were used to elucidate the degree of swelling under load, the compliance, and sample elasticity.

Transport of ionizable drugs and proteins in crosslinked poly(acrylic acid) and poly(acrylic acid-co-2-hydroxyethyl methacrylate) hydrogels. I. Polymer characterization

SYNOPSIS The purpose of this investigation was to define the polymer structure and elucidate the swelling behavior of ionizable hydrophilic polymers (hydrogels) in water and buffered media. Poly(acry1ic acid) (PAA) and poly(acry1ic acid-co-2-hydroxyethyl methacrylate) [P(AA-coHEMA)] hydrogels were synthesized with varying degrees of hydrophilicity and crosslinking and were designed as potential bioadhesive controlled-release dosage forms. The thermal initiation procedure employed during polymerization was optimized to eliminate unreacted residuals. Equilibrium and dynamic swelling studies were undertaken to determine the polymer mesh size and molecular weight between crosslinks of the hydrogels in the ionized and nonionized states. The PAA hydrogel mesh sizes ranged from 100 to 400 8, over pH values of 3-7, whereas the P(AA-co-HEMA) hydrogel mesh sizes were between 13 and 140 A. These results demonstrated the significance of the swelling medium pH on the hydrated state of the polymers relative to crosslinking or copolymerization composition. 0 1996 John Wiley & Sons, Inc.

5-FU loaded pHEMA drainage implants for glaucoma-filtering surgery: device design and in vitro release kinetics

Implantable monolithic and reservoir-like water-swellable drainage devices were developed for the subconjunctival sustained release of 5-fluorouracil (5-FU) in glaucoma-filtering surgery. A water-swellable matrix was formed of a copolymer of 2-hydroxyethyl methacrylate (HEMA) with different amounts of ethylene glycol dimethacrylate (EGDMA). Drug incorporation was done before polymerization and cross-linking. Briefly, to prepare the monolithic device the monomer-drug mixture is compression moulded into a 10 mm cylinder of 1 mm length. Furthermore, reservoir-like devices were obtained by coating the monolithic devices with a highly cross-linked polymer of HEMA (pHEMA) composition. The pHEMA devices containing 5-FU or not were well characterized by means of dynamic swelling studies, structural and thermal analysis. The release of 5-FU from these implants was studied in vitro. The rate of drug release was controlled by changing the drug loading (i.e. 10 mg or 20 mg 5-FU per device), cross-linking density of polymer matrix and type of implantable device, i.e. monolithic or reservoir-like device. While monolithic devices are releasing total releasable 5-FU during the first 10 h, reservoir-like devices prolong 5-FU release for up to 120 h. The 5-FU diffusion coefficient in swollen devices (Ds,s) is in the order of 10−8 cm2 s−1 (approximately 10 times smaller than Dw,g values) and it is dependent on the cross-linking density of polymeric matrix and device load. These preliminary results suggested that 20 mg 5-FU-loaded reservoir-like devices may be a potentially effective system to deliver 5-FU into the subconjunctiva.

Factors influencing drug and protein transport and release from ionic hydrogels

The effect of polymer structural parameters of ionic hydrogels on the transport of drugs and proteins has been studied for a number of anionic and cationic hydrogels. Crosslinked anionic hydrogels were composed of acrylic acid and 2-hydroxyethyl methacrylate, whereas cationic hydrogels were based on diethyl aminoethyl acrylate or diethyl aminoethyl methacrylate and 2-hydroxyethyl methacrylate. The hydrogel structure was investigated using dynamic swelling studies to deduce the variation of mesh size available for solute transport as a function of environmental parameters including the pH and ionic strength. For anionic hydrogels, the mesh size increased with increasing pH due to the ionization of the network. The reverse was true for cationic hydrogels. Ionizable drugs and proteins could interact with the ionizable hydrogels during the transport process. The solute size also affected the release behavior, causing additional hindrance and decreased mobility.

The volume shrinkage, thermal and sorption behaviour of polydiacrylates

Crosslinked polymers of ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate and poly(ethylene glycol (400)) diacrylate were prepared by photopolymerization using 2,2-dimethoxy-2-phenylacetophenone as the initiator at a light intensity of 2 mW cm −2. Volume shrinkage on polymerization was recorded. The most highly crosslinked networks exhibited the maximum volume shrinkage. Thermal stability was directly related to the high crosslinking density. The presence of heterogeneities in the network structure was ascertained using thermomechanical analysis. Dynamic and equilibrium swelling studies were used to study further the crosslinked structure of these polymers.

THE EFFECT OF TEMPERATURE TREATMENT ON PENETRANT TRANSPORT IN COAL

Abstract The macromolecular structure of coals thermally treated at 35°C, 100°C and 150°C was investigated by dynamic penetrant transport in thin coal sections. The effects of temperature, carbon content in coal, and penetrant type on the transport mechanism were investigated. Dynamic swelling studies showed that penetrant transport into coal is a function of the average molecular weight between crosslinks, Mc. The penetrant transport mechanism at low activity is Fickian diffusion. The transport mechanism deviates from Fickian diffusion to anomalous transport, when the carbon content in coal and penetrant activity increase. Variations of the diffusion coefficients and relaxation constants were determined using a diffusion/relaxation coupled model.

Controlled release by using poly(methacrylic acid-g-ethylene glycol) hydrogels

Graft copolymers of poly (ethylene glycol) with poly(methacrylic acid) were prepared by reaction of poly(ethylene glycol) methacrylate macromonomer with methacrylic acid in the presence of tetraethylene glycol dimethacrylate as a crosslinking agent. The materials were swollen in aqueous solutions with the pH ranging from 1.5 to 12.0. Dynamic swelling studies were performed. The swelling rates were lowest in copolymer networks with 1:1 ratios of ethylene oxide to methacrylic acid. These results were attributed to the combined effects of diffusion and complex dissociation during swelling. Solute release studies were carried out to investigate the effect of pH and swelling on the release behavior. Lowest solute release rates were observed in complex-forming networks, verifying the relationship between complexation, swelling and solute permeability.

Solute and penetrant diffusion in swellable polymers. IX. The mechanisms of drug release from ph-sensitive swelling-controlled systems

Copolymers were prepared by bulk polymerization of 2-hydroxyethyl methacrylate (HEMA) with either methacrylic acid or maleic anhydride. The reaction was initiated with benzoyl peroxide, the crosslinking agent was ethylene glycol dimethacrylate, and the temperature of the reaction varied from 40°C to 80°C and was increased in step intervals. Dynamic swelling and solute release studies were performed in buffered aqueous solutions of various pH values. It was shown that the relaxation-controlled mechanism of controlled release prevailed in alkaline solutions. Deborah and swelling interface numbers were used to analyze this diffusional release behavior.

Transport of penetrants in the macromolecular structure of coals. V. Anomalous transport in pretreated coal particles

Dynamic swelling studies were performed on well-characterized coal particles treated in various ways. Pyridine was the penetrant and all studies were performed at 35°C. The transport behavior was compared for untreated, pyridine-extracted, oxidized and alkylated samples. Data analysis using an exponential equation of the penetrant uptake as a function of time and a relaxation-controlled analysis showed that the pyridine transport mechanism was non-Fickian or Case-II transport, and that it was only slightly affected by the pretreatment of the coal samples.