Showing papers by "Nicholas A. Peppas published in 1995"
TL;DR: The dynamic and equilibrium swelling properties of dry glassy poly(2-hydroxyethyl methacrylate-co-methacrylic acid) and polymeric networks were studied as a function of pH, ionic strength, nature of the counterion and buffer composition.
407 citations
TL;DR: In this article, random copolymer hydrogels of methacrylic acid (MAA) and N-isopropylacrylamide (NIPAAm) were synthesized by free-radical polymerization in the presence of a cross-linking agent.
Abstract: Random copolymer hydrogels of methacrylic acid (MAA) and N-isopropylacrylamide (NIPAAm) were synthesized by free-radical polymerization in the presence of a cross-linking agent. The gels were characterized for their temperature- and pH-responsive behavior by equilibrium swelling experiments, differential scanning calorimetry, and thermal mechanical analysis. Depending upon composition, the gels showed sharp swelling transitions with small changes in temperature or pH, with initial time-dependent response reaching equilibrium on a time scale of hours.
307 citations
TL;DR: It was shown that as drug solubility increased, the undissolved drug gel layer thickness decreased, again showing the importance of the movement of the diffusion front in controlling the overall release.
227 citations
TL;DR: In this paper, a volume-based crystalline fraction of PVA on a wet basis varied from 0.052 to 0.116 and was a function of the degree of crystallinity.
212 citations
TL;DR: This work begins with an introduction to the structural characteristics and behavior of hydrogel membranes followed by a discussion of the types of environmentally responsive behavior seen with hydrogels.
Abstract: Biomedical applications of hydrogel membranes require understanding of their structural characteristics and diffusive behavior. Thus, the subject of this review is the analysis of the response of such biomembranes to their surrounding environment. This responsive behavior may be due to the presence of certain functional groups along the polymer chains or specific interactions between polymer chains (complexation). This behavior is particularly important in the use of these physiologically responsive materials in membrane applications. We begin with an introduction to the structural characteristics and behavior of hydrogel membranes followed by a discussion of the types of environmentally responsive behavior seen with hydrogels. The subject of interpolymer complexation is then treated with emphasis on complexation due to hydrogen bonding and how this type of behavior may be used to produce responsive membranes. Finally, the theories of transport in membranes are reviewed.
188 citations
TL;DR: In this paper, the average molecular weight between cross-links, Mc, and mesh size of polyvinyl alcohol and poly(acrylic acid) networks was determined and equilibrium swelling studies were conducted.
Abstract: Hydrogels with varying cross-linking ratio and ionic content were prepared from interpenetrating networks of poly(vinyl alcohol) and poly(acrylic acid). Equilibrium swelling studies were conducted and the average molecular weight between cross-links, Mc, and mesh size were determined. Hydrogels with large Mc, values were found to swell to a greater extent than those with small Mc values. It was also observed that an increase in Mc yielded faster swelling and deswelling rates, as the rates for membranes with Mc = 18,000 were about twice as fast as were the rates for membranes with Mc = 34,000. Oscillatory swelling behavior was investigated in response to changes in the pH and ionic strength of the swelling medium. A change in pH from 3 to 6 caused an ionization of the hydrogels and an increase in the weight swelling ratio, with a greater increase exhibited by IPNs with a higher ionic content. Increase in pH also caused an increase in the average mesh size. © 1995 John Wiley & Sons, Inc.
178 citations
TL;DR: In this paper, 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 materials, including acrylic acid and 2-hydroxyethyl methacrylate.
162 citations
TL;DR: In this paper, the authors used an interpenetrating networks of poly(vinyl alcohol) and poly(acrylic acid) with varying degree of crosslinking and ionic content to determine the average molecular weight between crosslinks, crosslink density and mesh size.
152 citations
TL;DR: In this paper, the swelling behavior of and solute transport in ionic copolymers of 2-hydroxyethyl methacrylate and methacrylic acid was studied for a wide range of copolymer compositions.
108 citations
TL;DR: In this paper, the authors studied the mucoadhesive capacity of poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres in contact with Sprague-Dawley rat jejunum atpH = 6 and at 22°C.
90 citations
TL;DR: In this paper, a model was developed for interdiffusion at interfaces of polymers with dissimilar physical properties based on the assumption that the monomeric friction coefficients of the two polymers are identical but a strong function of the matrix composition.
TL;DR: In this article, a photopolymerization of poly(ethylene glycol (400)) diacrylate was performed using 2,2-dimethoxy-2-phenylacetophenone as the initiator at a light intensity of 2 mW cm−2.
TL;DR: In this paper, the swelling force of interpolymer complexes formed by graft polymerization of poly (ethylene glycol) monomethacylate on poly(methacrylic acid) was measured as a function of time in various pH buffered solutions.
21 Jun 1995
TL;DR: Two approaches are presented: model-based control algorithms for use in implantable insulin pumps, and a novel polymeric device which releases insulin at desirable levels.
Abstract: The complications of diabetes are thought to arise from poor control of blood glucose concentration because of inadequate secretion of insulin by the pancreas. This has motivated the undertaking of novel therapeutic approaches to improve insulin delivery. In this paper, two approaches are presented: model-based control algorithms for use in implantable insulin pumps, and a novel polymeric device which releases insulin at desirable levels.
TL;DR: In this paper, real-time attenuated total reflectance-Fourier transform infrared spectroscopy was used to follow the conversion during acrylate polymerizations by measuring the presence of functional groups at finite depths from the crystal surface.
Abstract: Real-time attenuated total reflectance-Fourier transform infrared spectroscopy was used to follow the conversion during acrylate polymerizations by measuring the presence of functional groups at finite depths from the crystal surface By varying the film thickness, the reactivity of multiacrylates could be spatially resolved These results were compared to results from differential photocalorimetric studies
TL;DR: In this article, a stochastic simulation technique was developed to describe the kinetic behavior of bulk multifunctional photopolymerizations and the structural evolution of the polymer networks, and a specific reaction pathway was chosen from knowledge of the reaction probability density function.
Abstract: A stochastic simulation technique was developed to describe the kinetic behavior of bulk multifunctional photopolymerizations and the structural evolution of the polymer networks. Rate equations were written for each of the reacting species. In cross-linking polymerizations, the initiator efficiency, f, and the propagation and termination rate constants, k p and k t , are diffusion-dependent from the onset of the reaction. We were able to calculate f, k p , and k t throughout the simulation using previously developed models. From a waiting time distribution, the time between two consecutive reactions was computed. A specific reaction pathway was chosen from knowledge of the reaction probability density function. Corresponding changes were made in the molecular distribution. With such an approach, we were able to obtain kinetic as well as structural information. The results presented here simulate the bulk polymerization of diethylene glycol diacrylate containing 1% 2,2-dimethoxy-2-phenylacetophenone as the photoinitiator. The simulation was able to predict experimentally observed reaction trends.
TL;DR: In this article, Bioadhesives for Optimization of Drug Delivery are used to optimize the drug delivery in the context of target-based drug delivery, where the authors use BioAdhesives as an optimization technique.
Abstract: (1995). Bioadhesives for Optimization of Drug Delivery. Journal of Drug Targeting: Vol. 3, No. 3, pp. 183-184.
TL;DR: The data demonstrated that it is possible to evaluate the polymer/solute interactions by using FTIR microscopy and indicated that the model solute, oxprenolol HC1, was evenly distributed throughout the bulk and surface of the hydrogel samples.
Abstract: Purpose. The purpose of this work was to study solute (drug and protein)/polymer interactions that affect solute diffusion in and subsequent release from swellable dosage forms based on environmentally responsive, pH-sensitive polymer networks.
TL;DR: In this article, the effect of polystyrene matrix relaxation on interdiffusion at a PS and polyvinyl methyl ether (PVME) interface was investigated with attenuated total internal reflectance infrared spectroscopy (ATR-FTIR) at 105 and 85 °C, corresponding to 5 °C above and 15 °C below the T g of PS, respectively.
Abstract: The effect of polystyrene (PS) matrix relaxation on interdiffusion at a PS and poly(vinyl methyl ether) (PVME) interface was investigated with attenuated total internal reflectance infrared spectroscopy (ATR-FTIR) at 105 and 85 °C, corresponding to 5 °C above and 15 °C below the T g of PS, respectively. Monodisperse PS samples with M w of 3.0 x 10 6 and 1.05 x 10 5 were used to simulate relaxation in the PS matrix corresponding to chain reptation and constrained-release mechanisms, respectively. A binary blend of monodisperse PS samples consisting of short chains with M w of 3.0 x 10 4 and long chains with M w of 3.0 x 10 6 was used to simulate relaxation in the PS matrix by tube dilation. In the binary PS blend, the short chains were deuterated in order to monitor the concentration of each component independently. Non-Fickian diffusion was observed above and below the T g of the PS matrix. Above the T g of PS, interdiffusion was enhanced as the matrix relaxation mechanism changed from chain reptation to tube dilation to constrained release, consistent with the predicted relaxation time of these matrices. Below the T g of PS, interdiffusion was controlled by the rate of swelling of PS by PVME and interdiffusion was faster in the binary PS blend due to the reduced entanglement density between the long chains.
Journal Article•
TL;DR: In this article, a number of potentially muco-adhesive hydrophilic polymer microparticles with rat intestinal mucosa were investigated using the falling liquid film technique, and it was found that the mucoadhesive capacity was independent of the degree of polymer crosslinking and increased with increasing amount of the ionic component in the copolymers.
TL;DR: In this article, the swelling behavior of disintegrating agents produced from microparticles of crosslinked, hydrophilic polymers was investigated as a function of time by using a swelling force measurement apparatus.
TL;DR: In this article, the effect of poly-polymer compatibility on interdiffusion at polymer interfaces with dissimilar mobilities was investigated by attenuated total internal reflectance infrared spectroscopy.
Abstract: The effect of polymer-polymer compatibility on interdiffusion at polymer interfaces with dissimilar mobilities was investigated by attenuated total internal reflectance infrared spectroscopy. The polymer pair consisting of polystyrene and poly(vinyl methyl ether) was used to study interdiffusion at the interface of compatible polymers. The polymer pair consisting of polystyrene and poly(isobutyl vinyl ether) was used to study interdiffusion at the interface of incompatible polymers. Results indicate that the extent of interdiffusion is controlled by the polymer-polymer compatibility parameter, irrespectively of the differences in the mobility of the polymers.
TL;DR: In this paper, transmission electron microscopy and energy dispersive spectroscopy (TEM/EDS) were used to map the concentration profile at the interface of a poly(vinyl chloride) and poly(methyl methacrylate) bilayer.
Abstract: Transmission electron microscopy and energy dispersive spectroscopy (TEM/EDS) were used to map the concentration profile at the interface of a poly(vinyl chloride) and poly(methyl methacrylate) bilayer. Thin sections in the order of 800 A were cut using an ultramicrotome, examined with TEM, and the concentration profile was mapped with EDS. The intensity of fluorescence X-rays was adjusted for sample thickness variation by measuring the relative thickness across the interface with electron energy-loss spectroscopy (EELS). The interfacial thickness of the bilayer after 6 h at 120°C was 1.5 μm, whereas the interdiffusion coefficient was determined as 8.0 X 10 -14 cm 2 /s. © 1995 John Wiley & Sons, Inc.
TL;DR: The volume shrinkage during photopolymerization was observed using a dilatometric technique as discussed by the authors, which was affected by the comonomer ratio and the nature of the poly(ethylene glycol)dimethacrylate comonomers.
Abstract: Polymer samples that could be used as wound adhesives were prepared from poly(ethylene glycol)dimethacrylate (PEGDMA) and 2-hydroxyethyl methacrylate (HEMA) copolymers in concentrations from 0 to 50 mol %. The UV copolymerization was initiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA) and ultraviolet light intensities ranged from 0.1 to 0.5 m W/cm. The volume shrinkage during photopolymerization was observed using a dilatometric technique. The overall volume shrinkage was affected by the comonomer ratio and the nature of the PEGDMA comonomer. The rate of volume shrinkage was higher at higher ultraviolet light intensities. PEG(400)DMA-based copolymers exhibited lower glass transition temperatures than those of PEG(200)-based copolymers. The introduction of HEMA to the copolymers reduced both their glass transition and degradation temperatures. The equilibrium water-swelling ratio increased with increasing PEGDMA molecular weight and HEMA content. © 1995 John Wiley & Sons, Inc.
TL;DR: In this paper, the first results of an off-lattice Monte Carlo simulation of network formation by chain polymerization of divinyl liquid-crystalline monomer are presented.
Abstract: The first results of an off-lattice Monte Carlo simulation of network formation by chain polymerization of divinyl liquid-crystalline monomer are presented. Snapshots show the spatial inhomogeneity typical of chain reaction processes. In the present simulations the order in the nematic and smectic B phases decreases only slowly during polymerization. Due to the limited number of particles in the simulation, the radical concentation is necessarily higher than in most experiments. This expiains the small number of trapped radicals and the slow increase of the cross-link fraction as a function of conversion. The cross-link fraction is constant in the moderate-conversion region, in qualitative agreement with experiment.
01 Jan 1995
TL;DR: In this article, the authors studied the mucoadhesive capacity of poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres in contact with Sprague-Dawley rat jejunum at pH = 6 and at 22°C.
Abstract: The mucoadhesive capacity of poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres was studied in contact with Sprague-Dawley rat jejunum at pH = 6 and at 22°C. Dry PHEMA microparticles exhibited adequate mucoadhesive capacity, which was independent of nominal crosslinking ratio. When PHEMA microparticles were loaded with linear PEO chains of molecular weight 1000, the mucoadhesive capacity increased significantly, almost doubling. This behavior was attributed to a significant increase of the PEO chains penetrating across the mucosal tissue. However, very long pendant chains could have a detrimental effect on interpenetration, was shown with PHEMA microparticles loaded with PEO chains of molecular weight 100 000 which exhibited only a limited mucoadhesive capacity. This was the result of extensive entanglements by the long PEO chains and impediment of chain mobility across the PHEMA/mucosal interface.
TL;DR: In this article, in-situ penetrant transport in coals of various cross linking densities and at various temperatures was carried out and the penetrant front velocity was determined and correlated to experimental variables.
Abstract: Microscopic studies of in-situ penetrant transport in coals of various cross linking densities and at various temperatures were carried out. The penetrant front velocity was determined and correlated to experimental variables. The velocity increased with increasing temperature and average molecular weight between crosslinks, Mc c, of the coal network structure. Penetrant front velocity could be employed to characterize the penetrant/coal compatibility.
TL;DR: A model is presented to describe drug absorption and administration from the nasal and ocular routes that considers several physiological processes occurring in the ocular and nasal cavities and that it can incorporate information about the permeability of the nasal mucosa and tissue.
Journal Article•
TL;DR: In this paper, a combination of transmission electron microscopy and energy dispersive spectroscopy (TEMIEDS) is used to map the concentration profile at the interface of a poly (vinyl chloride) and poly (methyl methacrylate) bllayer.
Abstract: The interfacial thickness of polymer-poymer bilayers is determined by the concentration profile of the two polymers across the interface. After intimate contact is established between two polymer films, adhesion takes place by interdiffusion of polymer chains across the Interface . The combination of transmission electron microscopy and energy dispersive spectroscopy (TEMIEDS) is used to map the concentration profile at the interface of a poly (vinyl chloride) and poly (methyl methacrylate) bllayer . Thin sections in the order of 800 A are cut using an uftramkxotome, examinedwith TEM, and the concentration profile is mapped with EDS . The intensity of x-ray fluorescence is adjusted for variation in sample thickness by measuring the relative thickness across the interface with electron energy-loss spectroscopy (EELS). The interfacial thickness of the bilayer after 6 hours at 120-C was 1.5 rum. The concentration profile is fitted to the Ficklen diffusion equation and an average interdiffusion coefficient of 8 .0 x io-t4 cm2Js is obtained in good agreement with values reported in the literature.
TL;DR: A modified analysis with which one can calculate drug reflection coefficients in polymer membranes used in transdermal delivery using a potential barrier model that can be used to analyze various solute transport situations.