Showing papers by "Nicholas A. Peppas published in 1989"
TL;DR: In this paper, a coupled diffusion/relaxation model is presented for general analysis of the release behavior of controlled release systems using a coupled diffusional and relaxation model, and the general form of this equation's exponent is related to the geometric shape of the releasing device through its aspect ratio.
1,385 citations
TL;DR: Experimental results with hydrogels of poly(vinyl alcohol) and poly(2-hydroxy ethyl methacrylate) are used to verify the new scaling laws.
Abstract: A correlation is established between the mesh size of a swollen cross-linked network and its equilibrium polymer volume fraction, for hydrogels isothermally swollen up to semidilute, dilute, or concentrated conditions. The exponent of this correlation decreases as the water concentration of the hydrogel decreases. Experimental results with hydrogels of poly(vinyl alcohol) and poly(2-hydroxy ethyl methacrylate) are used to verify the new scaling laws.
610 citations
TL;DR: In this article, copolymers were prepared by bulk polymerization of 2-hydroxyethyl methacrylate (HEMA) with either methacrylic acid or maleic anhydride.
227 citations
TL;DR: Three types of poly(vinyl alcohol) were cross-linked by glutaraldehyde to form water-swellable materials possessing a three-dimensional, molecular network, characterized by equilibrium swelling measurements which allowed the determination of the average distance between two cross-links and, hence, the macromolecular mesh size.
Abstract: Three types of poly(vinyl alcohol) were cross-linked by glutaraldehyde to form water-swellable materials possessing a three-dimensional, molecular network. Proxyphylline and theophylline were incorporated into the polymer networks during the cross-linking reaction. The firm hydrogels formed were dried and reduced to a particle size of 400-630 microns. The molecular structure of the gels was characterized by equilibrium swelling measurements which allowed the determination of the average distance between two cross-links and, hence, the macromolecular mesh size. The sulfate and glutaraldehyde residues contained in the purified and nonpurified cross-linked polymers were analyzed, and methods for their elimination and inactivation were developed. Drug release from the highly cross-linked gels could be controlled over more than 12 hr, as the diffusion process in these very dense macromolecular networks is rather slow. The extent of branching and entanglement of the polymeric chains appeared to have an important effect. In addition, the release rate was influenced greatly by the amount and, to a lesser extent, by the type of drug in the network.
81 citations
TL;DR: In this article, a model is developed to express the solute diffusion coefficient through semicrystalline polymeric networks, where the crystallites create impermeable diffusional barriers around the amorphous regions.
Abstract: A model is developed to express the solute diffusion coefficient through semicrystalline polymeric networks. The crystallites create impermeable diffusional barriers around the amorphous regions. Solute diffusion is determined by applying a transport model to the amorphous phase and incorporating the crosslinked polymer structure characteristics. This model is tested with theophylline and vitamin B12 permeation experiments through semicrystalline poly(vinyl alcohol) membranes prepared by annealing of amorphous PVA membranes. The degree of crystallinity varies between 23.1 % and 40.5 % on a dry basis. The solute diffusion coefficients correlate well with various parameters of the model.
57 citations
TL;DR: In this paper, a bioadhesive tablet of metronidazole has been developed for oral or vaginal administration, and the influence of the test medium was investigated in order to determine the adhesion of the tablet during routine use by the various routes.
Abstract: A bioadhesive tablet of metronidazole has been developed for oral or vaginal administration. The bioadhesive component is poly(acrylic acid) (Carbopol 934), and the matrix component is hydroxypropyl methylcellulose (HPMC K4M). The influence of the test medium was investigated in order to determine the adhesion of the tablet during routine use by the various routes. The parameter retained to evaluate adhesion was the adhesion work on a biological tissue. The factors whose influence was investigated were pH, ionic force and nature of cations, and type of biological substrate
56 citations
TL;DR: In this paper, a copolymerisation radicalaire en suspension, apres gonflement dans l'eau, les particules ont un diametre compris entre 10 and 60 μm and sont stables entre pH 4,75 and 7,4.
Abstract: Preparation par copolymerisation radicalaire en suspension; apres gonflement dans l'eau, les particules ont un diametre compris entre 10 et 60 μm et sont stables entre pH 4,75 et 7,4. L'augmentation de la concentration en agent de surface (PDMS-CO-PEO) entraine une distribution plus etroite des dimensions
53 citations
TL;DR: In this article, the surface tension of various mucin solutions at constant or varying pH was measured using the pendent drop method, independent of added electrolyte concentration, pH and mucin concentration.
42 citations
TL;DR: In this paper, the development of disintegration forces in porous pharmaceutical compacts consisting of drugs, various disintegrants and other excipients is analyzed as a coupled phenomenon of water penetration in the porous structure of the compact, and disintegrant swelling leading to exertion of additional stresses on the overall systems.
27 citations
TL;DR: In this paper, the influence of chain entanglement on the autohesion of linear polymers was investigated using a stochastic model and the fracture energy of a polymer interface was expressed in terms of the total number of effective crossings, which was in turn related to the molecular weight distribution and the contact time.
25 citations
TL;DR: In this article, the disintegration force of tablets prepared from calcium diphosphate dihydrate and containing various swellable disintegrants is analyzed using an Arrhenius-type expression.
TL;DR: In continuite avec la theorie developpee par les auteurs relative a l'energie de rupture fragile de polymeres, calcul de la resistance critique a la rupture τ FO and du taux d'etirage des segments de chaines.
Abstract: En continuite avec la theorie developpee par les auteurs relative a l'energie de rupture fragile de polymeres, calcul de la resistance critique a la rupture τ FO et du taux d'etirage des segments de chaines a la rupture de polymeres de masse moleculaire M superieure a 2Me, Me etant la masse moleculaire des chaines entre les enchevetrements
TL;DR: The idea of accessibility factors or parameters is introduced to describe the ability of a planar or spherical controlled-release system to deliver a specific drug within a desired period of time.
01 Jan 1989
TL;DR: In the early days of the development of this field, industrial chemistry was the most “acceptable” method of education of students as mentioned in this paper. But this was not the case in the early 1970s.
Abstract: Chemical Engineering started as a discipline concerned with the education of engineers who would work in chemical plants. Yet, in the early days of the development of this field, industrial chemistry was the most “acceptable” method of education of students.
Journal Article•
01 Jan 1989
TL;DR: The academic genealogical tree of Justus von Liebig (1803-1873) is probably the most well-known one, and can be admired at the Liebig Museum in Giessen, Federal Republic of Germany as mentioned in this paper.
Abstract: The preparation of academic genealogical charts has been a natural way to crown the retirement celebrations for a distinguished scientist, especially a university professor. It appeared for the first time in Germany during the second half of the 19th century. The academic genealogical tree of Justus von Liebig (1803–1873), the famous German chemist who was professor at the University of Giessen from 1824 to 1852 and then at the University of Munich from 1852 to 1873, is probably the most well-known one, and can be admired at the Liebig Museum in Giessen, Federal Republic of Germany.
Journal Article•
TL;DR: In this paper, the diffusional release of small and large molecular weight peptides from polymeric matrices is described using the solution of the Fickian diffusion equation with a peptide diffusion coefficient that depends on the structural (polymeric) charcteristics of the semicrystalline network.
Abstract: The diffusional release of small and large molecular weight peptides from polymeric matrices is described using the solution of the Fickian diffusion equation with a peptide diffusion coefficient that depends on the structural (polymeric) charcteristics of the semicrystalline network. It is shown that such release is a strong function of the volumetric fraction of amorphous polymer and other network parameters
01 Jan 1989
TL;DR: In the open fields of Indiana, roughly equidistant between Gary and Indianapolis and built on the then navigable Wabash river, lay in the middle 19th century a small town of 4,000 inhabitants, the town of Lafayette as mentioned in this paper.
Abstract: In the open fields of Indiana, roughly equidistant between Gary and Indianapolis and built on the then navigable Wabash river, lay in the middle 19th century a small town of 4,000 inhabitants, the town of Lafayette. A trade center for northwest Indiana, the town was inhabited mostly by German and Anglosaxon farmers and traders. As a result of the 1862 Morrill Act, the General Assembly of Indiana voted in 1865 to establish a land-grant university (1). The fierce competition between various towns continued for four years with Monroe, Marion and Tippecanoe counties becoming the three finalists. Finally, the balance tilted in favor of Lafayette, mainly because of the then generous contribution of $150,000 by John Purdue, $50,000 by the Tippecanoe County and 100 acres of land from local residents. Thus, in the fourth and final ballot in the Indiana House, Tippecanoe county received 52 votes, with 17 voting for Monroe and 8 for Marion county. In the Senate questions arose and the representatives of Bloomington (Monroe county) and Indianapolis (Marion county) “stigmatized as selfish vanity for Mr. Purdue to ask that the institution be named Purdue University (1).” On May 4, 1869 Purdue’s offer was accepted with 32 to 10 votes in the Senate and 76 to 19 in the House.
01 Jan 1989
TL;DR: The origins of chemical engineering can be linked to the industrial revolution of the 18th and 19th century in Europe and the United States (1, 4) and the sociopolitical changes following the 1848 revolution in France and Germany (5, 6) as discussed by the authors.
Abstract: The origins of chemical engineering can be linked to the industrial revolution of the 18th and 19th century in Europe and the United States (1–4) and the sociopolitical changes following the 1848 revolution in France and Germany (5–6). No doubt one can claim that chemical engineering was practiced even by the ancient Greeks and Romans when they were making soap or wine, or treating ores in Lavrion or Sicily.