Physicochemical principles of tissue material interactions.

Biocompatibility of a material has to be adapted to the specific properties of the locus of application that are the type of tissue and the composition of extracellular fluid or the blood being in contact with the surface. The biocompatibility is beyond that greatly influenced by the design of the medical device which has to be planned close to the material's properties and the function within the body. Physical chemical reactions at and physical properties of the surface which influence the adsorption behavior for biomacromolecules. Conformational or functional changes of f.i. proteins due to physical forces originating from the surface could be the communication messages to the immunological system. The immersion of a material into an aqueous electrolyte leads generally to a space charge layer on both sides of the interface forming the electrical double layer, physically described by the isoelectric point of the materials surface. A numerical example hints on the importance of the double layer structure for the 'communication' between an implant and the surrounding extracellular fluid including beside ions complex structured proteins as biomacromolecules. Biocompatibility depends on the physical structure of the material and physicochemical properties of the interface to the biosystem. The conductivity of the surface film control reactions across the interface with biomacromolecules of the biological environment. Conformational unchanged macromolecules are the prior condition for biocompatibility and controls the attachment and probably also the degree of attachment via adhesion proteins. Later on, when the cells develop tension through the cytoskeleton on these attachment sites, the strength of the integrin adhesion protein-matrix protein interaction might probably prove decisive in differentiation state of the cell. It has been proved by molecular biological methods that an undestroyed oxide layer of anatase on titanium through passivation leaves for instance albumin conformational unchanged.