ABSTRACT
The simplest form of interaction between implant materials and the biological environment is the transfer of material across the material-tissue interface in the absence of reaction. If the substance — ions or fluid — moves from the tissue into the biomaterial, the result in a fully dense material will be swelling due to conservation of volume. Even in the absence of fluid uptake, the biomaterial may absorb some component or solute from the surrounding fluid phase. If the fluid moves into the tissue, or if one component of the biomaterial dissolves in the fluid phase of the tissue, the resulting material porosity is said to be due to leaching. Both of these effects have profound influences on the behavior of materials despite the absence of externally applied mechanical stresses and obvious shape changes. Swelling and leaching result from the process of diffusion. Before considering the effects on materials’ properties, the fundamentals of diffusion and the diffusion models appropriate to each situation will be examined.
