The mechanisms responsible are just as varied and include hydrophobic, electrostatic animal study and van der Waals interactions as well as structural changes in the molecule, which may result in entropy or enthalpy changes, though hydrophobic ones are usually considered to be the most important.34 Adsorption is often considered to be a reversibel process, but this is only partially true and depends on the free energy of the adsorption: the higher this is, the less reversible the process will be. During the initial minutes the interaction between protein and surface is fast and indeed reversible, but then the surface induces conformational changes in the protein that increase the interaction and can lead to complete protein denaturation after unlimited adsorption time.
35 These conformational changes contribute to the free energy and thus reduce desorption, but as these changes are comparatively slow the desorption rate can be described as a function of the contact time. Molecules with very stable conformations can be expected to have only negligible changes with little contribution to the free energy, thus forming no strong adsorptive interactions. An exception are large, fibrillar proteins: due to their high surface to volume ratio they have a much higher number of potential binding sites than globular proteins of a comparable size, and they can interact with the surface via several segments. Although the adsorption free energy of each segment may be small as no structural changes take place to contribute, engagement of many segments will increase the total adsorption free energy until the molecule does not readily desorb anymore.
36 In this case there is no time dependency and adsorption is irreversible even after short times. For this reason collagen fibrils can be immobilized using this method with concentrations between 40 to 60 ��g/cm2, and are still stable against competitive adsorption of serum proteins.37 Solvents of a higher ionic strength tend to reduce immobilization by about 20%, which indicates the importance of electrostatic interactions. The effect is somewhat larger on collagen type III, but generally there are no significant differences to collagen I, and this may only be caused by the higher surface area resulting from the finer fibrils. Heterotypic fibrils again take intermediate positions.
12 Including non-collagenous components usually had no influence on the adsorbed amount, excepting very thin fibrils as seen for high decorin concentrations.3 The adsorption of all types of collagen-based aECM is thus determined by Drug_discovery the collagen part. Characterizing aECM Biochemical characteristics This includes the stability of the matrices against desorption, the release of individual components (especially for multi-component aECM that depend on physiological, non-covalent interactions), as well as the bioavailability and functionality of the components (a large issue for crosslinked matrices).