The forces involved in bioadhesion to flat surfaces and particles — Their determination and relative roles

Abstract

The non‐covalent forces involved in bioadhesion involving flat surfaces, small particles, cells and bio‐polymers are: Lifshitz‐van der Waals (LW), polar (electron‐acceptor‐electron‐donor) or Lewis acid‐base (AB) and electrostatic (EL) forces. LW and AB forces are determined by: (a) direct contact angle measurement with at least three liquids on flat surfaces, or (b) wicking, by capillary rise measurements of at least three liquids along glass plates coated with a thin layer of small particles. This approach yields the LW and AB components of the surface tension, as well as the electron‐acceptor and the electron donor parameters of its AB‐component. Together, these yield the total apolar + polar interfacial energies involved in bioadhesion. EL interaction energies must be obtained separately, by electrokinetic methods. In bioadhesion, the importance of these forces usually is: AB > > LW > EL. The electron‐donor properties of cells and biopolymers are dominant; their electron‐acceptor parameters are negligible or zero. The degree of hydrophilicity of most materials can be expressed fairly precisely, as the interfacial free energy of attraction between the material and water; it consists principally of LW interactions. The interfacial free energy of interaction between biomaterials and synthetic surfaces, immersed in water is, for the greatest part, due to AB forces. The surface properties of biopolymers and cells usually are such that a maximum of adhesion should occur onto synthetic polymer surfaces with a surface tension of approximately 30 mJ rn^‐2. The adhesion of cells to clay particles is also studied: few cells will adhere to moderately hydrophilic'clay particles (hectorite), but all cells will tend to adhere to hydrophobic clay particles (talc). A minimum of cell adhesion occurs where a maximum of protein adsorption has taken place.