Surface-tethered polymers to influence protein adsorption and microbial adhesion

In various applications it is desired that biological cells or protein molecules are immobilized at surfaces. Examples are enzymes or cells in bioreactors and biosensors, immuno-proteins in solid-state diagnostics and proteinaceous farmacons in drug delivery systems. In order to retain biological activity, the structural integrity of the immobilized bio-compounds should be preserved. In other cases immobilization of cells and proteins should be avoided. Adsorption of proteins from biofluids is considered to be the first event in the biofouling process. Subsequently, bacterial and/or other biological cells (e.g., blood platelets, erythrocytes) deposit on the adsorbed protein layer and a biofilm is formed. This causes great problems in areas as diverse as biomedicine, food processing and the marine environment. A generic approach to influence the magnitude of the interaction between a particle (e.g., a cell or a globular protein molecule) and a sorbent material is to manipulate both the long- and short-range interaction forces by grafting soluble polymers or oligomers onto the sorbent surface. Application of oligomers of ethylene oxide (EO) prevents the particles from making intimate contact with the surface. Thus, adsorbed enzymes may retain their native structure and, hence, their enzymatic activity. Another interesting example is the steering effect of pre-adsorbed polymers of EO (PEO) on the orientation of subsequently depositing anisotropic particles. For instance, IgG molecules may be forced in the right orientation and conformation in the interstitial spaces between the PEO chains, therewith doubling the specific antigen binding capacity. By far the greatest part of recent research on modifying surfaces by grafting soluble polymers (usually PEO) aims at the prevention of protein adsorption and/or adhesion of biological cells. Suppression of particle deposition depends primarily on two characteristics of the polymer layer: (a) the grafting density, and (b) the extension of the polymer layer into the solution. The efficacy of grafted PEO layers to reduce protein adsorption and microbial adhesion is illustrated for blood plasma proteins, saliva proteins and a number of bacterial and yeast cells.