Materials interface, blood

Blood/Material Interface Problems Confronting Artificial Heart Development... 

Heparin is lost from surface to create a heparin microenvironment at the blood/material interface. 

Of the many methods reported in the literature for improving the thrombogenicity of biomaterials, heparinization has been one of the more intriguing and sometimes controversial. lonically bound heparin was found to be released from the surface at biologically significant rates while early attempts at covalent immobilization led to inactivation of the heparin. This prompted early critics to conclude that heparinized materials could be effective only if enough heparin was released from the surface to create a microenvironment at the blood-material interface. 

Figure 4.9 Model of a blood/material interface. The liquid phase, i.e. static or flowing blood, contains water, ions, proteins and cells. The solid phase is characterised by structural parameters, i.e. size, surface area, rigidity, crystallinity and conformation, and by composition dependent parameters, i.e. types of chemical group, hydrophilicity/hydrophobidty, charge and homogeneity of distribution.

One of the initial events occuring as blood comes in contact with a polymer is the adsorption of a protein layer at the blood-material interface 1 . This layer modifies the original surface and has an important influence on subsequent phenomena such as platelet adhesion and blood coagulation... 

Partial or complete replacement of natural organs with prosthetic components will someday be commonplace. For instance, the design of the total artificial heart, which has had limited clinical success, involved an application of many fundamental principles already discussed as they relate to hemodynamics, biomaterials, and control. Most would agree, however, that the materials-blood-tissue interface is the nidus for some of the most serious problems preventing the development of a safe and reliable artificial heart. This reinforces the importance of investigating at the molecular level the complex interactions that occur between artificial surfaces and the physiological environment. 

The arrangement of molecular elements of a polymeric material at a blood-polymer interface generally is not known in detail x-ray photoelectron spectroscopy (XPS, also called ESCA) indicates that for block copolymers, polymers having large side groups of differing polarity and polyelectrolytes, the surface composition may be quite different from the bulk, stoichiometric composition (2). 

An understanding of protein adsorption behavior is applicable in numerous fields including blood-synthetic materials interfaces, macromolec-ular-rnembrane interactions, receptor interactions, enzyme engineering, adhesion, and protein separation on chromatographic supports. Many methods have evolved to study interfacial adsorption, but no single independent method seems adequate. The ideal technique should produce quantitative, real-time, in situ data concerning the amount, activity, and conformation of proteins adsorbed on well-characterized surfaces. All adsorption techniques are approximations to this optimum. 

Protein Adsorption at the Solid-Solution Interface in Relation to Blood-Material Interactions... 

HE CURRENT STATE OF KNOWLEDGE of proteins at interfaces is reflected in this book. Developed from a symposium that was one of a continuing series entitled Surface Chemistry in Biology, Dentistry, and Medicine, the book is organized around the subtopics of behavior, mechanisms, methods of study, blood-material interactions, and applications of proteins at solid-liquid, air-water, and oil-water interfaces. 

Liotta (12) constructed his artificial heart from a combination of different materials - Lucite, teflon, polyester urethane, and silk. It is difficult to evaluate the thrombogenic potential of this combination of materials because the longest survival was 13 hours in dogs. The principle cause of death in these animals was low cardiac output secondary to inadequate venous return. The following year in a different series of experiments Liotta (13) tried a different combination of materials. Here, although the experiments were acute in scope, thrombus formation at the blood-plastic interface was a major problem. The left ventricular assist device (LVAD) was a tube-type with the housing and valves constructed of Estane. The internal elastic tube was made of either natural rubber. Silastic, or natural rubber covered externally with Silastic. 

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