Search

Purpose. To evaluate N-trimethyl chitosan chloride (TMC) of highdegrees of substitution as intestinal permeation enhancers for thepeptide drug buserelin in vitro using Caco-2 cell monolayers, and toinvestigate TMCs as enhancers of the intestinal absorption of buserelin in vivo, in rats. Methods. TMCs were tested on Caco-2 cells for their efficiency toincrease the paracellular permeability of the peptide buserelin. For the in vivo studies male Wistar rats were used and buserelin wasadministered with or without the polymers intraduodenally. Both types ofexperiments were performed at pH 7.2. Results. Transport studies with Caco-2 cell monolayers confirmed thatthe increase in buserelin permeation is dependent on the degree oftrimethylation of TMC. In agreement with the in vitro results, in vivodata revealed highly increased bioavailability of buserelin followingintraduodenal co-administration with 1.0% (w/v) TMCs.Intraduodenally applied buserelin resulted in 0.8% absolute bioavailability,whereas co-administrations with TMCs resulted in mean bioavailabilityvalues between 6 and 13 %. Chitosan HCl (1.0% pH = 7.2) did notsignificantly increase the intestinal absorption of buserelin. Conclusions. Both the in vitro and in vivo results indicate that TMCsare potent mucosal permeation enhancers of the peptide drug buserelinat neutral pH values. [ABSTRACT FROM AUTHOR]

The thermal behaviour of human stratum corneum (SC) with various hydration levels was studied using differential thermal analysis DSC within the temperature range of −130 to 120°C. SC containing 20% water, resembling the intact condition, shows thermal transitions at around −20°C (representing water in skin), −10, 40, 70°C (representing skin lipids), 85°C (representing protein-associated lipids) and 100°C (representing skin protein). Dehydration of SC causes the transitions at −20 and 100°C to be invisible. Lipid extraction followed by dehydration eliminates all transitions. Further hydration produces a transition of water at around 0°C with a huge change in enthalpy. The perturbation effects of penetration enhancers fatty acids (FA) and propylene glycol (PG) were studied using DTA on SC after pretreatment with PG alone and FA/PG. The application of PG alone shifted the transitions at 70 and 85°C to lower temperatures. Additionally, the application to dehydrated stratum corneum removes the transitions at −10°C. Saturated fatty acids, e.g. nonanoic and decanoic acids, exert barely noticeable effects on the thermal behaviour of SC suggesting that they easily mix with the skin lipids. Thermal analysis also revealed that the cis-9- and 13-isomers of octadecenoic acid (monounsaturated fatty acids) form a separate domain containing mostly the pure fatty acids within the SC lipids and suppress the lipid transitions at 70/80°C. Polyunsaturated fatty acids linoleic and α-linolenic acids — form separate domains but do not completely suppress the SC lipid transitions at 70/80°C as monounsaturated acids do. This study suggests different ways of perturbation by various fatty acids. [ABSTRACT FROM AUTHOR]

As part of a study polyoxyethylene alkyl ethers (CEO), water and decane, the phase diagram and the structures of the mesophases of pure CEO and technical grade CEO were compared. The constructed phase diagrams of the two systems show a great resemblance except for one difference: the viscous isotropic phase is only present in the CEO phase diagram. The swelling behavior of the lamellar and hexagonal phases was studied with smallangle x-ray scattering. Both the lamellar and hexagonal phases showed an ideal swelling behavior and no differences between the lamellar and hexagonal phases of the two systems were detected. With freeze-fracture electron microscopy the hexagonal and lamellar phases were visualized. No differences in the textures of the lamellar phases were found, however, the micrographs of the hexagonal phases of the two systems clearly showed different textures. While in the hexagonal phase of the CEO system only infinite long rods were visualized, short interrupted rods were found in the hexagonal phase of the CEO system. [ABSTRACT FROM AUTHOR]

The influence of the addition of liquid paraffin ( LP) on the structure of the lamellar ( L) and hexagonal (H) mesophases formed in mixtures of water ( W) and BRIJ 96 ( B) was studied. Mesophases were identified using polarization microscopy and small angle x-ray diffraction (SAXD). Repeat spacings were also determined with SAXD. Depending on the W/B ratio, addtion of LP to L gives a large, almost linear one-dimensional swelling or an initial swelling followed by a gradual transition to H. L with a high LP-content gives a diffraction pattern showing only the first order diffraction maximum, possibly a result of undulations of the layers. The lamellar structure, however, was confirmed using freeze fracture electron microscopy (FFEM). Addition of LP to H gives an initial swelling followed by a transition to a transparent, highly viscous, isotropic phase, called the gel-phase ( G). The diffraction pattern obtained from G yields little information on its structure. A large swelling of G with LP was observed. From the degree of swelling as a function of hydrocarbon content it was inferred that this phase consists of spherical aggregates forming a close-packed structure. Using FFEM, textures were visualized resembling those obtained from the isotropic mesophase (I) in water-surfactant mixtures. Finally, geometrical factors are discussed that may play a role in the formation of the gel-phase. [ABSTRACT FROM AUTHOR]

Lamellar ( L) and hexagonal ( H) mesophases, formed in mixtures of water and polyethylene oxide (PEO) oleylethers (average EO-numbers 5 (a), 8.5 (b) and 14 (c)) and pure hexaoxyethylene dodecylether (d), were investigated with small-angle X-ray diffraction. Analysis of repeat spacings shows a deviation from linear one- and two-dimensional swelling of L and H, respectively, when a transition to a mesophase with a larger curvature of the interface is approached. With regard to L, in this respect similar behaviour is observed for a pure surfactant (d) and a surfactant with an EO-length distribution (b). It is proposed that, through the formation of aggregates of limited extent, water filled pores in the mesophases arise. This is confirmed by analysis of the intensity ratio of diffraction maxima of first and second order in L. Models for finite aggregates are introduced. These consist of (1) lamellae, infinite in one direction and with variable length L in a direction perpendicular to the first, with cylindrical edges and (2) cylinders with variable length L bounded by spherical caps. According to these models, under certain conditions, finite aggregates may be formed without an increase of the interfacial area per surfactant molecule. Applying the models to the regions where non-linear swelling is observed, reasonable values for L are found, which decrease progressively when the phase transition is approached. [ABSTRACT FROM AUTHOR]

Mixtures of polyoxyethyleneoleylether, with an average of 14 oxyethylene units per molecule, and water, were investigated at between 20‡ and 100‡C using polarization microscopy. A lamellar ( L), hexagonal ( H), viscous isotropic ( V) and cubic ( I) mesophase were found and an outline of the pseudo binary phase diagram was constructed. The mesophases were investigated with freeze-fracture electron microscopy and micrographs of characteristic textures are presented. L and H displayed well known features, the repeat distances observed were in good agreement with findings from X-ray diffraction. H showed fracture planes with and without a ribbed pattern. Using specific decoration with ice crystals, fracture planes with the ribbed pattern were found to be more hydrophilic. V showed regular patterns, in some places forming a square lattice, in other places resembling a network of short rods with two-dimensional hexagonal symmetry. The repeat spacing observed in the textures was about 11 nm. I showed foremost fractured layers with a fine texture of spherical units in a two-dimensional hexagonal array. The centre-to-centre distance between these units was about 8-9 nm. [ABSTRACT FROM AUTHOR]

The time dependent changes of the lamellar gel structure in a nonionic O/W cream were studied. It appeared that the changes were connected with alterations in the hydrophilic layers of this lamellar gel structure. The structure of the hydrocarbon layers did not change. The alterations were induced by an increasing hydration of the surfactant molecules on cooling from the preparation temperature to room temperature. Ageing of the cream involves a decrease of the thickness of the hydrophilic layers and a change of the distribution of the surfactant molecules, resulting in, among other things, a decrease of the release rate of a hydrophilic drug. Ageing of the cream can be prevented by using the appropriate amount of starting materials or by the use of polymerizable surfactants. In the former case a cream, from which a drug is slowly released, is obtained. On the other hand, creams containing polymerized surfactants can release drugs at a relatively high rate. [ABSTRACT FROM AUTHOR]

The structure of a nonionic O/W cream and its separate components were investigated by X-ray diffraction and microscopic methods. The results presented in this paper are combined with the results obtained with DSC in order to elucidate these structures. The very important role of water with respect to the formation of the colloidal structures is discussed. The influence of water on the polymorphic behaviour of cetylstearylalcohol is attributed to a good structural fit of its α-modification and water. Hydration induces a tilt of the alkyl chains of poly(oxyethylene)glycerylmonostearate (PGM). For this surfactant an antiparallel arrangement of the molecules is proposed. The lamellar structures present in mixtures of cetylstearylalcohol, PGM and water are discussed extensively. [ABSTRACT FROM AUTHOR]

The structure of a simple O/W cream and its separate components were investigated by differential scanning calorimetry. The results obtained for cetylstearylalcohol agree with those cited in literature. The thermal behaviour of the component poly(oxyethylene) glycerolmonostearate (= PGM) was also investigated. It is pointed out that the thermal history of the PGM batch may play an important role in a study concerning the structure of this surfactant. To both components water was added to study the effects of hydration. Hydration affected the transition temperatures of either component. The melting enthalpy per unit mass of cetylstearylalcohol was not influenced, in contrast with the melting enthalpy of the hydrocarbon fraction in PGM/water mixtures. It is supposed that hydration induces a tilt of the hydrocarbon chains with respect to the lattice plane in lamellar PGM/water mixtures. Cooling experiments indicated that, in samples containing sufficient water, 2 water molecules were tightly bound to the polyoxyethylene chains of the surfactant. The properties of simple creams containing cetylstearylalcohol, PGM and water can be explained regarding their structure and considering the behaviour of the separate components. [ABSTRACT FROM AUTHOR]

As a part of a study of the colloidal structures present in nonionic ointments, the interaction between polyoxyethylene and water is investigated. A series of mixtures of polyoxyethylene 1550 and water is studied using differential scanning calorimetry. Heating as well as cooling experiments are performed. The effects of the heat of mixing, supercooling and melting point depression on the measured enthalpy changes are discussed. From the non-freezing water fraction it is concluded that 2 water molecules per oxyethylene unit are tightly bound to the polymer chain. The observed differences between the cooling and the heating curves lead to a possible explanation for the alterations in the samples occurring at low temperatures. A hydrate structure of polyoxyethylene at low temperatures is proposed. Finally, comment is made on the phase diagram of the system polyoxyethylene/water. [ABSTRACT FROM AUTHOR]

The structure of systems containing equal weights of cetylalcohol, stearylalcohol and the nonionic surfactant poly(oxyethylene)-glycerolmonostearate is studied as a function of the water concentration. In this paper mainly results are presented obtained by small angle X-ray-diffraction. Up to ± 22% (w/w) water several coexisting phases were observed. From ± 22% to ± 55% water a lamellar structure is found. This structure consists of lipophilic bilayers formed by the hydrocarbon tails of cetylalcohol, stearylalcohol and the surfactant, alternated by hydrophilic layers formed by the polyoxyethylene glycerol chains, the hydroxyl groups of cetylalcohol and stearylalcohol and water. From the swelling behaviour the density of the gel structure (0.9 g/cm) and the cross sectional area of the molecules in the bilayers (0.19 nm) have been calculated. It is concluded that the hydrocarbon chains are in a crystalline, state and are placed perpendicular to the lattice plane. Upwards of ± 55% water the lamellar phase disperses in the excess of water. [ABSTRACT FROM AUTHOR]

This study deals with effects of electrical (current density, frequency and duty cycle) and chemical (buffer pH and ionic strength) conditions on the flux of the octapeptide, 9-desglycinamide, 8-arginine-vasopressin (DGAVP), through dermatomed human skin. A pulsed constant current was applied during iontophoresis. The anode faced the anatomical surface of the skin samples inside the diffusion cells. The resistive and capacitative components of the equivalent electrical circuit of human skin could be calculated by fitting the voltage response to a bi-exponential equation. The skin resistance prior to iontophoresis varied between 20 and 60 k Ω.cm. During iontophoresis a decrease of skin resistance and an increase of the series capacitances was observed, which were most pronounced during the first hour of iontophoresis; thereafter both quantities gradually levelled off to an apparent steady state value. The reduction of the resistance during iontophoresis increased non-linearly with increasing current density between 0.013-0.64 mA.cm. The steady state resistance and capacitances did not vary significantly with frequency and duty cycle of the current pulse. There was no pH dependence of skin resistance at steady state. Between pH 4 and 10, the steady state peptide flux had a bell-shaped pH-dependence with a maximum of 0.17 nmol.cm.h at pH 7.4, which is close to the I.E.P. of the peptide. Lowering the ionic strength from 0.15 to 0.015 M NaCl increased the steady state flux at pH 5 and pH 8 by a factor 5 to 0.28 ± 0.21 and 0.48 ± 0.37 nmol.cm.h, respectively. Together these observations suggested that DGAVP is transported predominately by volume flow. At pH 6, at which 65% of the peptide carried a net single positive charge, the steady state flux increased with increasing current density (0.013-0.64 mA.cm) from 0.11 ± 0.03 to 0.19 ± 0.04 nmol.cm.h. Skin permeability during passive diffusion preceding iontophoresis at pH 6.0 was 2.9 ± 0.6 * 10 cm.h. In accordance with theoretical predictions based on the Nernst-Planck equation, to which a volume flow term was added, the flux was proportional to the mean voltage across the skin between 0.013 and 0.32 mA.cm.h. Variation of frequency or duty cycle did not result in significantly different peptide transport rates. From these studies it is concluded that DGAVP can be transported iontophoretically through human skin. The pH- and ionic strength-dependence of the iontophoretic peptide flux suggests that transport of DGAVP mainly occurs by volume flow. Furthermore, the flux of DGAVP appears to be controlled by the applied voltage rather than by the current density, as predicted by the Nernst-Planck equation. [ABSTRACT FROM AUTHOR]

Calorimetric measurements have been carried out to determine to which extent water interacts with p-HEMA gels and with p-(HEMA+MAA) gels. It appeared, that 0.14 g water/g dry p-HEMA and 0.23 g water/g dry p-(HEMA+MAA) show strong negative enthalpy changes on sorption in the polymer, the enthalpy changes being −180 J/g and −360 J/g water respectively. [ABSTRACT FROM AUTHOR]

Hydrogels are widely studied materials for the preparation of sustained release drug dosage forms. Their soft, tissue-like consistency and their high biocompatibility in a number of applications make them promising candidates for this purpose. The water and the polymer in the gel form intricate structures and much research has been devoted to the elucidation of these structures, and of the interactions involved in their formation. Simple, drug-loaded hydrogels normally give a matrix-type delivery profile, in which the release rate is proportional to the square root of time; a number of approaches has been used to change this profile to other types of delivery, for instance to zero-order release. A number of in vivo tests using hydrogel delivery systems has given favourable results. [ABSTRACT FROM AUTHOR]

Within the Center for Bio-Pharmaceutical Sciences the release characteristics of drugs form the major research object of the Division of Pharmaceutical Technology. Transdermal systems are being developed that can supply a drug during several days. Irritation of the skin may be avoided by using hydrogels. To enable long-term transdermal application also the colloidal structure of creams and ointments is investigated. As most drugs are to be taken orally, however, a research project was also started to make cheap and easy to produce controlled release tablets. The results with a microporous polypropylene polymer are promising. [ABSTRACT FROM AUTHOR]

O/W creams with crystalline gel structures (Water Containing Hydrophilic Ointment DAB 8, Non-ionic Hydrophilic Ointment DAC and a stearate cream) were investigated by means of small angle X-ray diffraction, differential scanning calorimetry, thermogravimetry and freeze fracture technique in combination with Transmission Electron Microscopy (TEM). It was found that these bases are building up two different colloidal gel structures, a hydrophilic gel phase and a lipophilic gel phase, each of them forming a coherent network. The hydrophilic gel phase is characterized by an interlamellar water layer; this interlamellarly fixed water is in a dynamic equilibrium with the bulk water phase. The lipophilic gel phase immobilizes mainly the inner (dispersed) phase. So the O/W creams presented here are supposed to be four-phase systems. The ratio of interlamellarly fixed water and bulk water, which may be determined easily by means of thermogravimetry, is found to be an important quality criterion for these O/W creams. The desired properties of water release of such a cream may be chosen by shifting the ratio of interlamellarly fixed water and bulk water. [ABSTRACT FROM AUTHOR]

A simple model is described, in which the influence of two parallel Brillouin zone faces on the electron phonon coupling parameter λ can be studied. In this model it is observed that λ, considered as a function of the Fermi energy E, has a peculiar structure when the Fermi body just passes through the two Bragg planes. Both an enhancement as well as a reduction of the more familiar density of states effect on λ and therefore on the critical temperature T of superconductors appears to be possible. In this respect approaching a Brillouin zone face turns out to be very favourable. The structure in λ is due to a combination of Umklapp, wave function mixing, and density of states effects. The calculations indicate that it is worthwhile to study these effects in detail in actual systems. [ABSTRACT FROM AUTHOR]