Interaction and destabilization of a monoclonal antibody and albumin to surfaces of varying functionality and hydrophobicity

Protein products come into contact with many surfaces of differing wettability during bioprocessing, formulation and delivery, but corresponding data for the adsorbed conformations and the associated force of adhesion (F _ad) is sparse. Here we have generated a series of hydrophilic and hydrophobic surfaces through silanization of silica with various terminal groups, characterizing the surface energies and droplet contact angles. F _ad measured by atomic force microscopy for oriented monolayers of a human monoclonal antibody (mAb-1) clearly distinguished hydrophobic surfaces (low F_ad values) from hydrophilic surfaces (high F_ad values). High F_ad for a methoxy capped polyethylene glycol (1000 MW) surface supports the interaction of mAb-1 with buried ethylene oxide groups, consistent with mAb-1 compression into a distorted brush border. Solid state circular dichroism showed that mAb-1 (β-sheet) or albumin (α-helical) adsorbed to bare silica beads largely retained their secondary structures. However, the extent of structural loss upon protein adsorption to functionalized silica beads could not be simply correlated to hydrophilic/hydrophobic surface interaction as seen for the F_ad measurements. For example, of the hydrophilic surfaces mAb-1 unfolded notably more when adsorbed to the aminopropyl surface, and of the hydrophobic surfaces both mAb-1 and albumin retained most secondary structure when adsorbed to the perfluorooctyl surface (consistent with the lipophobic perfluorinated moiety limiting exposure of the protein hydrophobic core). The data show that F_ad values are not necessarily predictive of the subsequent extent of structural relaxation, and that significant structural loss is evident for proteins adsorbed to both hydrophilic and hydrophobic surfaces.