Showing papers by "Nicholas A. Peppas published in 1988"
TL;DR: Methods of studying bioadhesion are described as well as the existing bioadhesive dosage forms, which include polycarbophil a Carbopol 934, and low chemical bonds.
Abstract: Bioadhesion could lead to the solution of bioavailability problems resulting from a too short stay of the pharmaceutical dosage form at the absorption or activity level of the active ingredient. Bioadhesion stages are: intimate contact resulting from a good wetting of the bioadhesion surface and the swelling of the bioadhesive polymer, then penetration of the bioadhesive into the crevice of the tissue surface or interpenetration of bioadhesive chains with those of the mucus, and finally low chemical bonds. date, the most important bioadhesive polymers are polycarbophil a Carbopol 934. Methods of studying bioadhesion are described as well as the existing bioadhesive dosage forms.
359 citations
TL;DR: The swelling and dissolution behavior of pharmaceutical systems containing a drug and a polymer can be analyzed by a mathematical model which predicts the drug released and the gel layer thickness as a function of time.
Abstract: The swelling and dissolution behavior of pharmaceutical systems containing a drug and a polymer can be analyzed by a mathematical model which predicts the drug released and the gel layer thickness as a function of time It is possible to approximate the values of several of the physicochemical parameters of this model in order to obtain an order-of-magnitude analysis of the tablet dissolution process Selected experimental results of tablet dissolution and drug release are analyzed and conclusions are made about the importance of the drug and polymer content and solubility in the release behavior
264 citations
TL;DR: In this article, a scaling law for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium-swollen hydrogels was developed.
Abstract: A scaling law was developed for the diffusion coefficient of spheroidal and ellipsoidal solutes in nonporous, equilibrium-swollen hydrogels. The law relates the solute diffusion coefficient to the solute size, the gel mesh size, and the gel equilibrium volume degree of swelling. The law was verified by appropriate data of low and high molecular weight solute diffusion through hydrogels such as swollen networks of poly(vinyl alcohol), poly(2-hydroxyethyl methacrylate), cellulose, and others. An additional scaling law was developed which relates the rate of release of a small or large molecule from an equilibrium swollen hydrogel with time and with morphological characteristics of the polymeric network.
246 citations
TL;DR: In this paper, a new model was developed to account for the kinetics of drug release from porous, non-swellable polymeric microparticles in the case where both drug dissolution and diffusion mechanisms control the overall release process.
91 citations
TL;DR: In this paper, a stochastic model is presented to predict the molecular weight dependence of the polymer fracture energy and strength for polymers with molecular weights higher than the critical value corresponding to the onset of entanglements.
Abstract: A stochastic model is presented to predict the molecular weight dependence of the polymer fracture energy and strength for polymers with molecular weights higher than the critical value corresponding to the onset of entanglements. A chain scission criterion is invoked for the polymer chain segments crossing the fracture plane and being entangled about it. The presence of dangling ends is shown to be responsible for the change of the fracture properties with molecular weight. The predictions of the model agree with experimental data of the fracture energy and strength of poly(methyl methacrylate) and polystyrene.
68 citations
60 citations
TL;DR: A new method is proposed here to estimate theCopolymer-water Flory interaction parameter, chi, for biomaterials, based on the pairwise thermodynamic interactions of copolymer segments and solvent molecules.
44 citations
TL;DR: In this article, a physical analysis of the disintegration of compressed tablets is presented, using an equation which expresses the normalized disintegration force, F F ∞, as a function of time.
36 citations
TL;DR: A new model was developed to accurately describe the swelling behavior of charged polymeric networks that incorporates elastic, mixing and ionic contributions to the chemical potential.
Abstract: A new model was developed to accurately describe the swelling behavior of charged polymeric networks. The model incorporates elastic, mixing and ionic contributions to the chemical potential. Changes in the equilibrium degree of swelling as a function of pH can be predicted.
32 citations
TL;DR: In this article, a thorough analysis of the diffusional problems associated with iodide and albumin transport in the hydrogels during adsorption and the methods that can be used to correct for this phenomenon are presented.
27 citations
TL;DR: In this article, the authors modeled penetration-activated solute release in polymers undergoing case-II penetrant uptake and showed that swelling of a polymer slab can have a significant effect on release behavior.
TL;DR: In this paper, the authors reported the presence of cell-type patterns on the surface of poly(2-hydroxyethyl methacrylate-co-methacrylic acid) during planar swelling in a buffered solution of pH = 10 at 27.5° C.
TL;DR: In this article, the authors investigated the transport of liquid cyclohexane through well characterised, initially glassy, crosslinked polystyrene slabs at 20, 30, 40, and 50°C.
Abstract: Transport of liquid cyclohexane through well characterised, initially glassy, crosslinked polystyrene slabs was Investigated at 20, 30, 40, and 50°C. The samples used were produced by bulk polymerization of styrene and divinyl benzene (DVB) at 90°C for 43 hr using benzoyl peroxide as an initiator. The samples tested had initial cross-linking ratios, X, between 5 and 25 × 10−3 mol DVB/mol styrene. The initial thickness of the samples tested varied from 0.25 mm to 1.80 mm, and the aspect ratio (length to thickness ratio) was maintained above 10;1 in order to analyze the results by one-dimensional transport equations. Cyclohexane uptake was followed as a function of time along with dimensional changes in the thickness and area of the samples. The results of penetrant uptake as a function of time were analyzed using a simplified exponential expression and employing all the data points from the beginning of the experiment until the time of observation of the maximum in uptake. Good correlations were established between the penetrant uptake and the transport temperature. These results were interpreted in terms of competitive relaxational and diffusional mechanisms.
TL;DR: In this paper, the crack formation in divinyl benzene (DVB)-crosslinked polystyrene samples swollen by cyclohexane was followed as a function of time, temperature, degree of crosslinking and initial sample thickness.
TL;DR: In this paper, the theory of branching processes is used to describe the polymer network formation resulting from the reaction of tetraepoxides with diamines using various initial compositions; however, intramolecular reactions in the pregel stage are neglected.
Abstract: The theory of branching processes is used to describe the polymer network formation resulting from the reaction of tetraepoxides with diamines using various initial compositions. Differences in reactivities of primary and secondary amine groups and the reaction between the epoxide groups and reaction-generated hydroxyl groups are taken into account; however, intramolecular reactions in the pregel stage are neglected. Expressions are derived for the critical epoxide conversion at the gel point, molecular weight in the pregel stage, changes in sol and gel fraction in the post-gel stage, and the concentration of elastically active network chains as a function of reaction conditions. The analysis of the simulation results shows that etherification reactions significantly raise the concentration of elastically active network chains of the mixture under stoichiometric excess of epoxide groups.
TL;DR: In this article, various multiethylene glycol dimethacrylates were polymerized by UV light in the presence of 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator.
Abstract: Various multiethylene glycol dimethacrylates were polymerized by UV light in the presence of 2,2-dimethoxy-2-phenyl-acetophenone as a photoinitiator. The ensuing highly crosslinked polydimethacrylates were characterized by thermomechanical analysis and swelling studies. The crosslinked structure was investigated and kinetic aspects of the reactions were analyzed.
TL;DR: In this paper, the authors developed new scaling expressions for the description of chain interpenetration and fracture at the gel-gel interface, and different scaling relationships were predicted depending on the fracture mechanism of the polymer chains crossing the interface.
Abstract: New scaling expressions are developed for the description of chain interpenetration and fracture at the gel-gel interface. Different scaling relationships are predicted depending on the fracture mechanism of the polymer chains crossing the interface. The fracture energy at contact time, t, smaller than the terminal relaxation time, ?r, scales to t1/2 for chain rupture and to t5/4 for chain pull-out.
Journal Article•
TL;DR: In this article, the complex sequence of the hydrolysis/polymerization reaction of certain types of alkoxysilanes is modelled using a novel approach based on the branching theory.
Abstract: The complex sequence of the hydrolysis/polymerization reaction of certain types of alkoxysilanes is modelled using a novel approach based on the branching theory. Network formation is described, resulting from the reaction of multifunctional oligomers. Expressions are derived for the critical silane conversion at the gel point, the molecular weight, and changes in the sol and gel fractions as a function of time.
01 Jan 1988
TL;DR: In this paper, a Raman microprobe spectroscopy was used to detect the abrupt change of the penetrant concentration at the rubbery/glassy interface during swelling of poly(2-hydroxyethyl methaerylate-co-N-vinyl-2-pyrrolidone) copolymers.
Abstract: Summary Methylene chloride transport in copolymers of .poly(2-hydroxyethyl methaerylate-co-N-vinyl-2-pyrrolidone) was studied at 25 C using Raman microprobe spectroscopy. It is shown that the abrupt change of the penetrant concentration at the rubbery/glassy interface during swelling can be detected and followed to obtain useful information about the penetrant transport mechanisms in these copolymers.
TL;DR: In this paper, a novel analysis is presented to explain mechanistic aspects of the fracture of low molecular weight polymers, where the fracture energy is calculated as a function of the mean interpenetration distance of a polymer chain which has been derived from the solution of the Fokker-Planck equation.
Abstract: A novel analysis is presented to explain mechanistic aspects of the fracture of low molecular weight polymers. The fracture energy is calculated as a function of the mean interpenetration distance of a polymer chain which has been derived from the solution of the Fokker-Planck equation. Experimental results with monodisperse polystyrene have been used to validate the theory.