Structure and rheology of cetomacrogol creams: the influence of alcohol chain length and homologue composition

API-polymer interactions in Sepineo P600 based topical gel formulation- impact on rheology

In the present study, topical gel and emulsion gel were formulated using Acrylamide/ Sodium Acryloyldimethyl taurate copolymer (Sepineo P600) as a gelling agent, and their rheological attributes and physical stability were evaluated upon incorporation of API. Lidocaine, a free base drug (pK_a 7.92) was used as a model drug in all formulations. Medium- chain Triglycerides (MCT) was used as a dispersed phase to prepare the emulgel. Results show that the rheological properties of both gel and emulgel such as viscosity, elastic moduli and yield stress were significantly influenced by the pH of the topical formulations and API concentration. A lower pH (pH < pKa) leads to the increase in number of cationic species of lidocaine, which results in the weakening of the structure of the gel matrix by charge screening of polymer-polymer repulsions. Interactions between API and polymer chains through electrostatic attraction may play a major role in altering the rheology, which could potentially impact the physical stability against phase separation of the internal phase in emulsion gel samples. This study provides valuable insights into rheological behaviors of Sepineo P600 gel and emulgel which can be modified or tuned though the interplay of the API properties and critical formulation parameters such as pH. The tunable rheological properties with simpler manufacturing process make Sepineo P600 gel and emulsion gel very suitable systems for use in semisolid topical formulations.

Influence of Solvent Evaporation Technique Parameters on Diameter of Submicron Lamivudine-Poly-ε-Caprolactone Conjugate Particles

The size of active pharmaceutical ingredient carrier is one of the key properties considered during design of submicron drug delivery systems. Particle diameter may determine drug biodistribution, cellular uptake, and elimination path. Solvent evaporation technique is a flexible method of particle preparation, in which various macromolecules and drugs may be employed. Parameters of emulsion obtained as first step of particle preparation are crucial in terms of particle size, drug loading, and morphology. The aim of the study was to investigate the influence of emulsion preparation parameters on diameter of resulting particles. Impact of surfactant type and concentration, homogenization time, homogenization rate, phase ratio, and conjugate concentration were evaluated. Model drug lamivudine was covalently bound to polymer and applied in solvent evaporation method in order to overcome issues related to drug loading and provide method-independent incorporation. Synthesized drug-polymer conjugate and obtained particles were evaluated via dynamic light scattering, chromatography, scanning electron microscopy, and spectroscopic methods. Covalent bonding between drug and polymeric chain was confirmed, estimated drug content per milligram of conjugate was 19 μg. Among employed colloid stabilizer, poly(vinyl alcohol) was proven to be most effective. Homogenization rate and surfactant concentration were identified as crucial parameters in terms of particle diameter control.

Application of emulsion theory to complex and real systems

Synopsis Theories of emulsion stability are discussed in relation to dilute, concentrated and semisolid emulsions. It is shown that whilst a unified theory cannot be applied quantitatively to emulsion systems, a better understanding of the various mechanisms of stabilization and breakdown is emerging. Established concepts, eg, the HLB concept, are now given a less empirical gloss. The application of colloid stability theory, even to very dilute emulsions, is difficult. This is because of the polydispersity of the systems and because surfactant and stabilizers may be free to move on the globule surfaces, as well as dissolve in the dispersed or continuous phases. Further difficulties arise because flocculation is not necessarily a sign of emulsion instability in the practical sense, as creamed or flocculated emulsions often may be redispersed by shaking. Crucial to emulsion stability is the prevention of coalescence, and this is governed by the nature of the adsorbed emulsifier film. The flocculation and coalescence that can be understood in dilute emulsions from the DVLO theory and the metastability of thin films against rupture do not address themselves to flocculation and coalescence in concentrated, structured or semi-solid emulsions. These may possess surfactant multilayers rather than monolayers at the oil/water interfaces and the bulk phases are frequently structured. Some emulsions invert at critical temperatures. In semi-solid emulsions, stability is controlled by the phase behaviour of the emulsifier components, rather than by the forces governing stability in dilute colloids and thin films. Stability is usually considered to be product stability during storage. The stability of an emulsion in use, eg, during and after application to the skin, is a topic of equal importance but little documented. This related problem is also discussed.

Influence of hydration state and homologue composition of magnesium stearate on the physical chemical properties of liquid paraffin lipogels

Lipogels were prepared by dispersing mixed (60:40 C(16)-C(18)) and pure (C(18)) homologue magnesium stearate (MgSt) in liquid paraffin, using three methods of preparation, i.e. addition of water at 95 °C during cooling cycle (method 1), homogenisation upon cooling (method 2) or cooling without addition of water or homogenisation (method 3). The systems were characterised by physical inspection, polarised, hot stage and scanning electron microscopy (SEM), differential scanning calorimetry (DSC), rheology, and X-ray diffraction (XRD). Systems formed stable semisolid lipogels (no syneresis), unstable solids showing syneresis or structured fluids, depending on the type of magnesium stearate used and the preparation technique. The stable semisolid lipogels containing mixed homologue MgSt (commercial-as received, anhydrous or dihydrate) prepared by methods 1 (∼ 1-2% water) and 2 contained α-crystalline lamellar structure. These were not present in the unstable solids formed with method 3 or in systems prepared from pure homologue MgSt which were generally structured fluids rather than semisolids. In addition, semisolid lipogels of pure homologue trihydrate MgSt prepared by method 3 showed plate-like crystals, implying pressure sensitivity. There is significantly more amorphous MgSt in the unstable solids compared to the stable semisolid lipogels, which are mainly crystalline (confirmed by XRD).

Quantification of the osmotic expansion in implants filled with polyethylene glycol

High reoperation rates continue to agonize the field of breast augmentation surgery. Patient dissatisfaction is a contributing factor for reoperations. This is often attributable to patients' desire to be larger after the augmentation. Polyethylene glycol (PEG) is a potential alternative breast implant filler under investigation. It has been shown to swell secondary to osmotic expansion when it is placed in vivo. We hypothesize that there is a finite expansion in this process. An experimental study was designed utilizing an in vitro model to quantify the rate and volume of the osmotic expansion of PEG-filled implants. Seventeen silicone elastomer shells were filled with various percent concentration and molecular weight PEG/saline solutions. These implants were kept in saline baths at varying temperatures to assess the effect of temperature on osmotic expansion. Daily weights were recorded to quantify the expansion and determine if a plateau was reached. Implant expansion was observed to plateau in all groups tested. Implants filled with 85% concentration PEG solutions demonstrated a uniform expansion at a rate of 0.032 to 0.037 g/d. Implants filled with 85% concentration PEG stored at human core temperature (37 degrees C) gained on average 6.2% to 7.6% of their original weight. Implants stored at 4 degrees C expanded to a higher volume than implants stored at 37 degrees C (P < 0.01). Implants filled with 50% concentration PEG solution gained only 2.7% of their original weight (P < 0.01). PEG-filled implants undergo controlled osmotic expansion to a final predictable weight in vitro. Higher concentration PEG induces greater volume expansion. A colder environment also induces greater volume expansion. PEG is biologically inert and may be an alternative filler for breast implants. The predictable expansion process may be beneficial in breast augmentation that may alleviate patient dissatisfaction about breast size once postoperative edema resolves.

Analysis of the acid–base reaction between solid indomethacin and sodium bicarbonate using infrared spectroscopy, X-ray powder diffraction, and solid-state nuclear magnetic resonance spectroscopy

Indomethacin was used as a model compound to investigate acid-base reactions of solid materials, a common type of drug-excipient interaction. In a typical experiment, 500 mg of pure alpha-form indomethacin were mixed with 500 mg of sodium bicarbonate. The mixture was kept at 40 degrees C and at several relative humidities. The reaction was monitored by IR spectroscopy, X-ray powder diffraction, and solid-state NMR. At 40 degrees C and 80% RH, the reaction is nearly complete after 300 h. As observed by IR spectroscopy, the characteristic peaks of alpha-indomethacin disappear during the course of the reaction with the appearance of the characteristic peaks of the salt product, sodium indomethacin trihydrate. Solid-state NMR spectra and X-ray powder diffraction patterns of the reaction mixtures confirm the transformation of the mixtures to sodium indomethacin trihydrate; the reduced peak intensities in the diffraction patterns of the product relative to the initial mixtures indicate the formation of a microcrystalline product. A change in the reaction rate of sodium bicarbonate with alpha-indomethacin is observed when the mixtures are stored at different relative humidities. At 40 degrees C and 66% RH, the reaction of sodium bicarbonate with alpha-indomethacin is about 86% complete after 500 h. No detectable reaction was observed for sodium bicarbonate with the alpha form of indomethacin at 40 degrees C and 11% RH after 15 months. The combination of these solid-state characterization techniques is demonstrated to be essential to detect and monitor acid-base reactions in solid materials, which are impossible to monitor using solution-chemistry methods. The reaction kinetics at 66% RH fits the Jander equation very well, which is consistent with a diffusion-controlled mechanism.

Influence of processing conditions in the manufacture of O/W creams: I. Effect on dispersion grade and rheological characteristics

Two series of O/W creams having the same general formulation were prepared in three different mechanical conditions (F with an hand blender; S with a turbomixer; T with a vacuum turbo emulsor) using two types of surfactants, polyoxyethylene-cetostearyl alcohols and polyglyceryl-3-methylglucose-distearate. By means of microscopic image analysis it was possible to point out the dispersion grade of the oil internal phase increasing with the energy applied under the conditions of manufacture (F < S < T). The level of dispersion influenced significantly on the rheological characteristics of the creams. With polyoxyethylene-cetostearyl alcohols, the viscosity of creams increased as the energy applied in manufacturing increased, with polyglyceryl-3-methylglucose-distearate on the contrary decreased. Moreover, indifferently to the manufacturing conditions, even in the same concentration of surfactant, the creams obtained with the last produced a much greater viscosity. At a parity of manufacturing conditions the differences between the batches of productions were not significant.

An investigation into the supramolecular structure of ternary gel systems using oscillatory rheometry, microscopy, and low frequency dielectric spectroscopy

A series of ternary gel systems based on cetostearyl alcohol (CSA) and cetomacrogol 1000 or sodium lauryl sulfate have been studied using oscillatory rheology, differential interference contrast (DIC) microscopy, cryoscanning electron microscopy (cryo-SEM), and low-frequency dielectric analysis in order to elucidate the nature of the lamellar structures formed in relation to composition. The effects of altering the concentration of CSA (0.25% to 8% w/w) for 1% and 2% w/v cetomacrogol 1000 and 0.5% and 1% w/v sodium lauryl sulfate systems have been investigated, with marked increases in the storage and loss moduli seen on increasing the concentration of CSA for both surfactants. DIC microscopy indicated that at low CSA concentrations, needlelike structures were seen which, on increasing the concentration, were observed to congregate into nuclei. At concentrations of 4% CSA and above, neospherical structures were also observed. Cryo-SEM revealed that the needlelike objects were sheet structures ascribed to lamellar gel phases, while the nuclei were folded "rosettes" formed by those sheets, with the spherical structures being ascribed to cetostearyl alcohol. It was also noted that the lamellae were more tightly folded at 8% w/w CSA, which may be associated with the higher rheological moduli for these systems. Low-frequency dielectric analysis was performed over a frequency range of 10(4) Hz to 10(-2) Hz. A decrease in both the dielectric loss and capacitance was observed as the concentration of cetostearyl alcohol was increased. The dielectric data were described in terms of an equivalent circuit model based on a modified Maxwell-Wagner response. A good correlation was found between the fitted and experimental data and the effect of altering the gel composition on specific features of the equivalent circuit are discussed.

An investigation into the use of low-frequency dielectric spectroscopy as a means of characterizing the structure of creams based on Aqueous Cream BP

A range of creams based on Aqueous Cream BP have been analyzed using low-frequency dielectric spectroscopy, with accompanying circuit modeling in combination with rheological and microscopic supportive techniques, to explore the use of the dielectric approach as a novel means of characterizing cream systems. Creams based on the formula for Aqueous Cream BP were produced by hand-mixing and mechanical mixing, with and without the inclusion of the preservative phenoxyethanol. Dielectric analysis was performed over a frequency range of 10(-2)-10(5) Hz. Cream samples were also examined using stress scan rheology and differential interference contrast microscopy. Dielectric analysis indicated that the presence of preservative decreased the capacitance and loss of the creams. The responses were modeled in terms of a dispersive capacitance in series with two RC circuits (series and parallel). Rheological studies indicated higher viscosities for the hand-mixed and unpreserved systems. Differential interference contrast microscopy showed marked differences in the distribution of the oil droplets, depending on the method of mixing. The study has demonstrated that dielectric spectroscopy, with accompanying circuit analysis, may be used as a means of modeling the structure of cream systems. The investigation has also shown that the formulation and preparation method of Aqueous Cream BP may have a profound effect on sample structure.