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Biomedical subjects

R D Bagnall

Publications and source records attributed to R D Bagnall.

At least 19 recordsLinked to original sources
PubMed1992

A problem with modern dental materials.

It may come as a surprise to learn that there is more than one discipline in medicine dealing with artificial organs. The obvious one is bio-engineering, which is largely concerned with fashioning existing biologically acceptable materials into useful spare parts such as hip or knee joints. The materials themselves hardly change, and the difference between rival prostheses lies more in design than novel chemistry. This is the world of titanium or cobalt-chromium joint designs, bone screws and plates, orthotic limbs, supports and wheelchairs, and futuristic ideas such as miniature video cameras for artificial eyes.

Biocompatible Materials↗
PubMed1986

Cranio-maxillary fixation using supra-orbital pins.

This paper compares the forces which external frames, used for cranio-maxillary fixation, can resist. Clinically, several frames using supra-orbital pins have been proven satisfactory. By quantifying the resistance forces, a more objective assessment of their effectiveness is made. The resistance to backward displacement of the maxilla is measured and compared for 3 frames. Two frames are used for comparison of resistance to occlusal forces.

Biomechanical Phenomena↗
PubMed1980

Adsorption of plasma proteins on hydrophobic surfaces. IV. Contact angle studies on implanted polymers.

Contact angle studies have been carried out on plasma protein layers adsorbed on selected polymer surfaces under buffered saline at 37 degrees, in an attempt to demonstrate directly a recent suggestion that the interfacial free energy between such protein layers and surrounding liquid phase should be zero at equilibrium. Although an initial contact angle of 180 degrees was always obtained, the angle decayed slowly to a stationary value which varied for any one drop on each polymer surface. The stationary values could be reasonably correlated with the reversible work of adhesion predicted for each polymer/protein combination, suggesting that protein desorption from the solid surface is a dominant event in the contact angle decay process. It is concluded that the data bear more relevance to the protein layer/polymer interface than to the protein layer/solution interface, and that the contact angle technique is not a suitable technique for studying the latter on biomaterials.

Adsorption↗
PubMed1978

Adsorption of plasma proteins on hydrophobic surfaces. II. Fibrinogen and fibrinogen-containing protein mixtures.

The adsorption of fibrinogen from single solution and from mixed solution with albumin and gamma-globulin has been followed at the air-buffer, isooctane-buffer, and methylene iodide-buffer interfaces by the pendant drop technique. Fibrinogen is shown to form substantial coherent films on isooctane and methylene iodide, suggesting considerable unfolding and lateral association. From this, a novel hypothesis has been proposed to account for the dominance of fibrinogen adsorption from mixed solutions on certain hydrophobic surfaces, in which the spreading pressure of rapidly unfolding fibrinogen molecules is sufficient to desorb other plasma proteins.

Adsorption↗
PubMed1978

A novel technique for studying the adsorption of plasma proteins on hydrophobic surfaces.

A method is shown for deducing the surface area of a pendant drop from the same profile photograph as is normally used to determine interfacial tension. Manipulation of such drops by a micrometer syringe then enables the pendant drop to be used as a surface balance for studying adsorption from bulk solutions. Results are given for the compression of films from solutions of albumin, gamma-globulin, fibrinogen, albumin-gamma-globulin mixture and albumin-gamma-globulin-fibrinogen mixture, and from serum, plasma, and blood at the isooctane-buffer interface. It is suggested that gamma-globulin and fibrinogen films are unfolded at the interface but that albumin films are different in that they consist of an inner, unfolded layer and an outer, globular layer. A film from serum resembles that from gamma-globulin alone, and not that from albumin-gamma-globulin mixture, whereas a film from plasma resembles that of fibrinogen at low compression and that of albumin-gamma-globulin-fibrinogen mixture at high compression. A film from blood is shown to resemble that from plasma.

Adsorption↗
PubMed1978

Adsorption of plasma proteins on hydrophobic surfaces. III. Serum, plasma, and blood.

Liquid-air and liquid-liquid interfaces were used as models for the liquid-solid system of plasma proteins and hydrophobic surfaces in the study of adsorption of serum, plasma, and blood onto these surfaces. The interfacial tension is determined for three phases: air, methylene iodide, and isooctane. Curves of interfacial tension versus time for the various systems are given from which a triple-intersection point, where the protein solution is in equilibrium with each surface, is found. It is shown that albumin, gamma-globulin, and a mixed solution of these at in vivo concentrations behave in characteristic and constant manners at the three interfaces of air, methylene iodide, and isooctane. A range of synthetic surfaces which have constant behavior at equilibrium is deduced and it is concluded that any soft tissue response differences between such surfaces could not be the result of albumin or gamma-globulin.

Adsorption↗
PubMed1978

Adsorption of collagen on model hydrophobic surfaces.

The change in interfacial tension with time for rat-tail tendon collagen adsorbing at the air, methylene iodide and isooctane interfaces has been followed by the pendant drop technique as a model for hydrophobic biomaterials. It is shown that the surface activity of tropocollagen at these three interfaces is less than that of albumin, gamma-globulin, serum of plasma, so that displacement of a preadsorbed plasma protein layer by tropocollagen molecules is energetically unfavourable and unlikely to occur. It is proposed that this may be one reason for the lack of interaction between hydrophobic soft tissue implants and their tissue capsules. It is then speculated that such interaction may require the development of biomaterials with a specific affinity for connective tissue components.

Adsorption↗
PubMed1977

An approach to the soft tissue/synthetic material interface.

It is argued that chemical modification of soft tissue implants in the hope of obtaining an associated tissue response is unlikely to succeed as a method for studying the fundamentals of implant/tissue interactions. An alternative approach is proposed which places greater emphasis on the interfacial interactions (such as protein adsorption) which occur after implantation, in a manner paralleling current advances in knowledge of the blood/material interface. From simple arguments, it is proposed that the observed similarities in soft tissue response of hydrophobic materials may result from irreversible protein adsorption, and that if unusual tissue responses are possible they are likely to be found only with hydrophilic implants. The possiblity of a critical hydrophilic/hydrophobic character which an implant must possess for essentially irreversible protein adsorption is also discussessed.

Animals↗
PubMed1977

Adsorption of plasma proteins on hydrophobic surfaces. I. Albumin and gamma-globulin.

The adsorption of albumin and gamma-globulin from solution at the liquid/air and liquid/liquid interfaces has been studied by the pendant drop technique as a model for the solid-liquid system. It is concluded that each protein adsorbs in a constant manner at the air, isooctane, and methylene iodide interfaces at equilibrium (1 hr), and the surface tension components of the protein layer presented to the hydrophobic phase have been found. The range of hydrophobic surfaces for which such constant behavior might be expected has been deduced, and it is shown that most common polymers lie within this range. A new model for protein adsorption is proposed, and the implications for biomaterials are discussed.

Adsorption↗
PubMed1977

Double contrast preparations: an in vitro study of some antifoaming agents.

An apparatus is described for the study of foam formation in double contrast preparations in vitro. Antifoaming agents are shown to be of considerable benefit to the double contrast technique, silicone and silicone-free antifoamers being equally effective. Silicone antifoamers are preferred because of their wide clinical acceptability. Antifoamer formulation and concentration are found to be critical factors in determining efficacy of foam suppression, and may lead to erroneous results in the clinic.

Antifoaming Agents↗