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Biomedical subjects

E Ruckenstein

Publications and source records attributed to E Ruckenstein.

35 records · Page 2Linked to original sources
PubMed1997

Drainage and Coalescence in Standing Foams

A theoretical model is presented for the drainage, collapse, and coalescence in standing foams. The foam is assumed to consist of pentagonal dodecahedra and coalescence is assumed to occur due to a variation in the sizes of the films which constitute the faces of these polyhedra. Even in a monodispersed foam containing bubbles having the same volume, the film areas are not identical, but are distributed randomly about a mean. This leads to a nonuniformity of film-drainage rates and hence of film thicknesses within any volume element in the foam. Smaller films drain faster and rupture earlier, causing the bubbles containing them to coalesce. The evolution of coalescence is monitored via the mean bubble volume which varies in the vertical direction. The model is also able to predict the evolution of the surfactant concentration profile as it changes due to coalescence and collapse. Simulations are performed to examine the effect of various parameters, such as the apparent diffusion coefficient of the surfactant, the distribution of film sizes, and the concentrations of surfactant and salt in the foaming solution on the drainage and collapse behavior of the foam.

Journal Article↗
PubMed1986

Preparation and characterization of thin film surface coatings for biological environments.

An approach to the problem of selecting synthetic materials for use in biological media is presented. Firstly, a surface energetic criterion of biocompatibility of foreign surfaces is suggested. This criterion, which is based on an analysis of the surface interactions between a typical biological fluid (i.e. blood) and synthetic surfaces, is founded on the premise that a sufficiently low (but not very low) solid-biological fluid interfacial free energy of the order of 1-3 dyne/cm, is necessary in order to fulfil the dual requirements of maintaining a low thermodynamic driving force for the adsorption of fluid components on the solid surface as well as a mechanically stable solid-fluid interface. In the second part of this investigation, an experimental approach involving the radio frequency (rf) sputter deposition of thin solid films of tightly adhering polymeric compounds on materials with the desired bulk characteristics, is shown to be a promising method of tailoring the surface properties of many types of synthetic materials for use in biological environments. The preparation and surface characterization of thin, solid films of oxidized fluorocarbon coatings (from a Teflon FEP target) by rf sputtering is illustrated. The deposited polymer films were characterized for their surface morphology, thickness, elemental surface chemical composition and their wetting properties in a biological environment, by the techniques of scanning electron microscopy (SEM), ellipsometry, electron spectroscopy for chemical analysis (ESCA) and contact angle measurements, respectively. Based on the ESCA and contact angle results, it emerges that the surfaces of such polymeric coatings possess sufficient mobility to considerably alter their structures between different environments (such as air and water) and thereby present different wetting characters to these environments. The contact angle procedure developed in this investigation permitted the estimation of the relevant wetting properties of such mobile surfaces in an aqueous environment (which is the environment encountered in most biological fluids). In the final part of this investigation, the possibility of effecting a drastic reduction in the solid-water interfacial free energy of the sputtered polymer surfaces by physical and or chemical modification of their surfaces and thereby improving their biocompatibility is illustrated.

Biocompatible Materials↗
PubMed1985

Mechanism of tear film rupture and its implications for contact lens tolerance.

A mechanism for the rupture of the tear film is identified. The key step in the process of tear film breakup is the instability and eventual rupture of the mucous layer of 0.02 to 0.04 micron thickness, which covers the epithelium. The rupture is caused by the van der Waals dispersion forces acting on the mucous layer. The aqueous part of the tear film then ruptures because it comes into contact with the exposed hydrophobic epithelium. The time of rupture derived from the proposed mechanism is consistent with the range of observed breakup times (BUT's) and other clinically observed characteristics of rupture. The proposed mechanism has implications in understanding the cause of adhesion of the contact lens to cornea and in the rapid buildup of deposits on the lens surface, both of which are attributed to the mucous deficiency. It also suggests various possibilities for diagnosis and treatment of pathological conditions of a dry eye, and lends support to existing ones.

Biocompatible Materials↗
PubMed1976

Sedimentation and adhesion of platelets onto a horizontal glass surface.

An experimental method for measuring platelet adhesion to a glass surface and platelet sedimentation rate is described. Anticoagulated platelet-rich plasma is placed on a horizontal glass slide for various contact periods. The number of platelets adhering to the slide per unit area is recorded as a function of time. The experimental results are used to verify theoretical predictions which account for the effect of the slow sedimentation rate of the platelets and for their escape over the potential barrier between them and the solid surface. By a least-squares fit of the theoretical equation to the experimental data, both the platelet adhesiveness, in terms of P the probability to overcome the potential barrier, and the platelet sedimentation rate V are evaluated. A range of values of P and V for healthy humans is presented.

Blood Platelets↗
PubMed1976

Physico-chemical explanation of blood cell adhesion in thrombus formation.

A model is suggested which assumes that the rate of deposition of cells is determined both by hydrodynamic factors and by Brownian motion over the potential barrier caused by London and double-layer forces in the immediate vicinity of the deposition surface. The height of the barrier in the potential energy of interaction between blood cells and various surfaces is analyzed in relation to the physical properties of the cells, surfaces, and solutions. Based on this analysis, the adhesion of platelets to injured blood vessel walls and to non-biologic materials, the lack of adhesion of red blood cells under the same conditions, the mechanism of ADP induced aggregation and the interaction with blood flow are explained. The qualitative predictions of the model are substantiated by available experimental information. Quantitative results are presented in terms of a time constant, which typifies a period of contact with a surface, during which appreciable deposition occurs.

Adenosine Diphosphate↗
PubMedDate not supplied

Preparation of porous polyurethane particles and their use in enzyme immobilization.

Porous polyurethane particles were prepared as follows: (1) Two low molecular weight polymers, namely, poly[methylene(polyphenyl isocyanate)] and poly(propylene glycol) were mixed with stirring at room temperature and allowed to react. (2) The reacted mixture was dispersed with stirring in mineral oil containing small amounts of water, the catalyst dibutyltin dilaurate, and CaCO3 powder. In the presence of the catalyst, the reaction between the two polymers proceeded to completion. Small particles of polyurethane are thus formed which contain mineral oil and CaCO3 as porogens. The particles obtained, separated by filtration, were treated with a solution of HCl in order to generate additional pores, extracted with benzene to eliminate the mineral oil present in the pores, and finally subjected to drying and sieving. The particles were investigated by scanning electron microscopy (SEM), infrared (IR) spectroscopy, and specific surface area measurements. Lipase from Candida rugosa was immobilized by adsorption on the porous polyurethane particles and cross-linked with glutaraldehyde to enhance the stability of the immobilization. The biocatalytic particles were used for the hydrolysis of triacylglycerides. The high activity of the immobilized enzyme, which per enzyme molecule can be higher than that of the free enzyme, reveals that the porous polyurethane particles constitute excellent supports for lipase.

Emulsions↗
PubMedDate not supplied

Membrane chromatography: preparation and applications to protein separation.

As a result of the convective flow of solutes through porous membranes, membrane chromatography has a higher capture efficiency and a higher productivity than column chromatography and shows most promising industrial applications for the recovery, isolation, and purification of proteins and enzymes. This paper presents a comprehensive review of the methods for preparation of adsorptive membranes (such as surface modification, in situ copolymerization, direct formation from hydrophilic materials, and functionalized particulate-entrapped membranes) and deals particularly with novel macroporous chitin and chitosan membranes for protein separations developed by the authors.

Carbohydrate Sequence↗