Covalent surface immobilization on metal implants: Key aspects on post-synthesis characterization

A variety of methodologies have been applied for characterizing covalent immobilizations of biomolecules and other compounds on metal implant surfaces, due to the positive impact of functionalization and the enhancement of biomimetic signaling at covalently immobilized biomaterial surfaces. However, current challenges should be addressed, as both physically adsorbed and covalently immobilized molecules usually coexist on functionalized surfaces and covalent immobilization efficiencies greatly vary among works, in which the immobilized biomolecule size seems a determinant parameter of the efficiency.Discrimination of the irreversible-bound covalent fraction should be assessed and advanced techniques for surface characterization must be conducted, such as quartz crystal microbalance or photon induced spectroscopy, as evaluation criteria. Verification of biomolecule activity once it is covalently immobilized on metal substrates is also required. Long-term stability and degradation resistances studies are also highly recommended for obtention of long-lasting, biomimetic-active surfaces upon covalent functionalization of metal biomaterials for medical applications.