Adsorption of serum alpha-1-microglobulin onto biomaterials

The adsorption of alpha-1-microglobulin (alpha-1-m) from serum to the surface of polymers with different physicochemical properties was investigated. Enzyme-linked immunosorbent assay showed binding of this protein to the surface of polystyrene (PS), polyvinyl chloride (PVC) and a polyurethane, Chronoflex, after water washing, but only trace levels could be detected on two polymethacrylate derivatives, polymethyl methacrylate and poly(2-hydroxyethyl methacrylate). alpha-1-m was selectively desorbed from the five materials by sequential washes of serum-conditioned surfaces with isopropanol solutions at increasing concentrations. The presence of alpha-1-m in the washing supernatants was detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The relative binding strength of alpha-1-m to each surface was evaluated as the isopropanol (IsoPOH) concentration required to desorb the protein from that surface. Analysis of bound proteins by SDS-PAGE conclusively demonstrated the binding of a range of serum proteins, including alpha-1-m, to all polymer systems, but with varying binding strengths. The majority of protein was removed by water washing for the polymethacrylate polymers, while varying concentrations of IsoPOH were required to desorb proteins from PS, PVC and Chronoflex. There was a correlation between the hydrophobic nature of the material, determined by water contact angle measurements, and adsorption of alpha-1-m. Immunoblotting of isopropanol-eluted proteins by alpha-1-m antibodies showed the positive staining of a 29 kDa protein as well as selected bands within a molecular weight range of 40 200 kDa, suggesting the adsorption of this protein as both free and complexed forms. The ability of alpha-1-m to adsorb on to material surfaces and to participate in events relevant to the biocompatibility of a polymer, such as bacterial infection or inflammation control, suggests the need for further characterization of the properties of this protein.