Biomedical subjects

C J Radke

Publications and source records attributed to C J Radke.

21 records · Page 2Linked to original sources

PubMed1999

Protein adsorption at the oil/water interface: characterization of adsorption kinetics by dynamic interfacial tension measurements.

The dynamics of protein adsorption at an oil/water interface are examined over time scales ranging from seconds to several hours. The pendant drop technique is used to determine the dynamic interfacial tension of several proteins at the heptane/aqueous buffer interface. The kinetics of adsorption of these proteins are interpreted from tension/log time plots, which often display three distinct regimes. (I) Diffusion and protein interfacial affinity determine the duration of an initial induction period of minimal tension reduction. A comparison of surface pressure profiles at the oil/water and air/water interface reveals the role of interfacial conformational changes in the early stages of adsorption. (II) Continued rearrangement defines the second regime, where the resulting number of interfacial contacts per protein molecule causes a steep tension decline. (III) The final regime occurs upon monolayer coverage, and is attributed to continued relaxation of the adsorbed layer and possible build-up of multilayers. Denaturation of proteins by urea in the bulk phase is shown to affect early regimes.

Adsorption↗

PubMed1998

Adsorption dynamics of L-glutamic acid copolymers at a heptane/water interface.

Random copolymers of glutamic acid (glu-ala, glu-leu, glu-phe, glu-tyr) were employed to investigate the relationship between side chain structure and peptide charge on adsorption behavior at an oil/water boundary. Adsorption of a series of glutamate copolymers at a heptane/water interface was examined by the dynamic pendant-drop method to determine interfacial tension. Incorporation of leucine or phenylalanine into a glutamate copolymer results in greater tension reduction than incorporation of alanine or tyrosine. These effects are amplified at pH values near the isoelectric point of glutamate, where macroscopic adsorbed films of glu-leu and glu-phe exhibit gel-like properties in response to interfacial area compression. Differences in interfacial tension behavior of glu-tyr and glu-phe indicate the importance of the tyrosine p-hydroxyl group on adsorption and aggregation at the oil/water interface.

Adsorption↗

PubMed1998

In vivo tear-film thickness determination and implications for tear-film stability.

PURPOSE: Previous measurements of tear-film thickness in vivo are limited and cannot be easily applied in a clinical setting. A novel technique to measure tear-film thickness indirectly is introduced here, requiring only a slit lamp, video camera, and computer. A recent fluid mechanical theory relates tear-film thickness h, to the tear meniscus radius R, tear surface tension or, tear viscosity mu, and upper lid velocity U. This theory yields the result that h/R = 2.12 (microU/sigma)2/3. All parameters except h/R are taken as known physical constants, and R was measured for each subject, allowing the above equation to establish h. Tear-film breakup was also evaluated and correlated with tear-film thickness. METHODS: A clinical study was performed in which aqueous tear-film thickness was determined for 45 subjects, including 24 non-lens subjects, 15 hydrogel contact lens wearers, and 6 RGP lens wearers. R was measured by instilling fluorescein dye in the form of an eyedrop and videotaping the tear meniscus in profile. Tear-film breakup was videotaped through the ocular port of the slit lamp and evaluated based on a severity scale. RESULTS: Aqueous tear-film measurements are in the same range as literature values, with most measured values falling between 6 and 12 microm. Average tear-film thicknesses for non-lens, hydrogel, and RGP subjects are 10.4, 6.5, and 5.8 microm, respectively. Tear-film breakup is most severe in subjects with thin tear films, especially in contact-lens wearers. CONCLUSIONS: Tear-film thickness is an important parameter that varies among individuals. These variations correlate with differences in tear-film stability.

Adult↗