Thomas Nicholas Julian

Permeability characteristics of calcium alginate films

Abstract The permeability of acetaminophen in hydrated calcium alginate films was measured in side-byside glass diffusion cells. The films were prepared by ionically crosslinking dry sodium alginate films by immersion in aqueous solutions of calcium acetate (0.1 to 1.0 M ) for 1 to 15 minutes. Permeability of acetaminophen in hydrated calcium alginate films varied approximately 14.6-fold, depending upon calcium acetate concentration and immersion duration used in the cross-linking process. Permeability of acetaminophen in calcium alginate films prepared by immersion of dry sodium alginate in aqueous solutions of calcium acetate for 3 to 8 minutes reached a limiting value at all calcium acetate concentrations. However, the magnitude of the limiting value was dependent upon the concentration of calcium acetate used in the crosslinking procedure. The highest limiting permeability was observed in films prepared using the lowest concentration of calcium acetate, whereas the lowest limiting permeability was observed in films prepared using the highest concentration of calcium acetate. When calcium alginate films were prepared by immersion in calcium acetate solutions of greater concentration than 0.5 M and immersion times less than 10 minutes, permeability coefficients were higher for the higher calcium acetate concentrations. Only when immersion times were greater than 10 minutes did permeability decrease as calcium acetate concentration increased. It is suggested that this is a result of the rapid crosslinking of sodium alginate at the surface, which in turn slows the diffusion of calcium ions into the film. Because of the relatively short immersion time, a high degree of crosslinking is not attained and this results in a calcium alginate film that is more permeable.

Aqueous Stability of Human Epidermal Growth Factor 1-48

Human epidermal growth factor 1-48 (hEGF 1-48, Des(49-53)hEGF) is a single chain polypeptide (48 amino acids; 3 disulfide bonds; 5445 Da) possessing a broad spectrum of biologic activity including the stimulation of cell proliferation and tissue growth. In this study, three primary aqueous degradation products of hEGF 1-48 were isolated using isocratic, reverse phase/ion-pair HPLC. The degradation products were characterized using amino acid sequencing, electrospray ionization mass spectrometry, isoelectric focusing, and degradation kinetics. Results indicate that hEGF 1-48 degrades via oxidation (Met21), deamidation (Asn1), and succinimide formation (Asp11). The relative contribution of each degradation pathway to the overall stability of hEGF 1-48 changes as a function of solution pH and storage condition. Succinimide formation at Asp11 is favored at pH < 6 in which aspartic acid is present mostly in its protonated form. Deamidation of Asn1 is favored at pH > 6. The relative contribution of Met21 oxidation is increased with decreasing temperature, storage as a frozen solution (−20°C), and exposure to fluorescent light.

Ultrasonically mediated solute permeation through polymer barriers.

The effects of ultrasound on the permeation of benzoic acid through polydimethylsiloxane, and hydrocortisone through cellulose was investigated. Ultrasonic irradiation resulted in a 23% increase in the permeability coefficient of hydrocortisone in a cellulose film. A 14% increase in permeability coefficient was observed for benzoic acid in a polydimethylsiloxane film. The effects of ultrasound on stagnant aqueous diffusion layers, membrane‐solution interfacial temperature, membrane integrity, and diffusant stability were investigated. These factors were not responsible for the observed increases in permeability.

Mechanism for ultrasonically enhanced transmembrane solute permeation

Abstract The transmembrane permeation of benzoic acid in polydimethylsiloxane and hydrocortisone in cellulose was characterized under conditions of ultrasonic (20 kHz) perturbation. In all cases the measured partition coefficients were independent of both temperature and ultrasonic energy input. Diffusion coefficients were directly proportional to the applied ultrasonic energy (0–45 W) when the donor reservoir was sonicated; a decrease in the activation energy for diffusion of approximately 300 cal/mol was observed for both solute/membrane systems at 33 W ultrasonic energy input. Diffusion coefficients measured under conditions of receptor reservoir sonication and no ultrasonic perturbation were similar. The results were consistent with a mechanism in which the solution-membrane interfacial transfer rate was increased by ultrasonic energy.