Nanomedicine, Volume IIA: Biocompatibility
© 2003 Robert A. Freitas Jr. All Rights Reserved.
Robert A. Freitas Jr., Nanomedicine, Volume IIA: Biocompatibility, Landes Bioscience, Georgetown, TX, 2003
220.127.116.11 Protein Adsorption on Teflon Surfaces
Teflon is very hydrophobic  but has protein-binding capacity . Despite Teflon’s reputation as a non-stick material, serum proteins bind almost instantly to its surface, principally via hydrophobic interactions . Hydrophobic fluorocarbon films also show high protein retention [1113, 1114]. Higher protein deposition has been observed on fluoroethylenpropylene than on tetrafluoroethylene surfaces , and on Teflon surfaces modified by exposure to nitrogen or oxygen plasmas than on unmodified Teflon . Protein adsorption is slightly higher to Teflon than to siliconized glass despite its slightly lower surface tension . Fungal hyphae can firmly attach to Teflon surface, mediated by SC3p hydrophobin protein . (Teflon surface hydrophobicity changes upon adsorption of fungal protein, probably as a bilayer .) The human plasma proteins fibrinogen, albumin and fibronectin influence bacterial adherence to Teflon .
Adsorption of cell adhesive proteins with known thrombogenic activity such as fibrinogen, fibronectin, and vitronectin on Teflon surface has been studied [1207-1209]. Platelet adhesive proteins such as von Willebrand factor are also adsorbed, with less than 1% of the surface covered by fibrin . Teflon exposed to human blood preferentially adsorbs fibrinogen . In one canine experiment, luminal fibrinogen adherence to Teflon vascular graft surface was 320 mg/m2 (570,000 molecules/micron2) after 4 weeks and 124 mg/m2 (220,000 molecules/micron2) after 12 weeks  in vivo. This implies multiple layers of deposition. Glow-discharge-treated Teflon surfaces have lower surface free energy and retain a larger fraction of adsorbed fibrinogen (e.g., lower elutability) than ordinary untreated Teflon surfaces [1327, 1328].
Glow-discharge-treated Teflon surfaces also exhibit tenacious adsorption (e.g., tight binding, low elutability) of albumin . This is believed to contribute to the thromboresistant character of these surfaces including resistance to thrombus deposition, embolization, and thrombotic occlusion . The strong binding of albumin to such surfaces “may be exploited clinically to enhance the retention of albumin preadsorbed to blood-contacting surfaces to render them thromboresistant” . However, nondenatured albumin adsorbed on ordinary Teflon maintains weak protein-polymer and protein-protein bonds, whereas fibrinogen adsorbates are fostered by strong protein-protein interactions .
Protein deposits have been observed microscopically on Teflon surfaces . For instance, TEM images of protein adsorption on Teflon  show albumin deposits that are irregular in shape, unconnected and with low surface coverage, with deposits following surface structural details to a scale of 400 nm. In contrast, fibrinogen deposits are reticulated, connected, and have high surface coverage not reflecting the details of surface structure.
The three-dimensional structure of Teflon-bound proteins is significantly perturbed by the adsorption interaction . For example, fibrinogen undergoes biologically significant conformational changes upon adsorption. This may contribute to the hemocompatibility of the polymer following implantation in the body . Fibrinogen unfolds and spreads on Teflon to minimize interfacial free energy in water and to maximize the protein-surface interaction . Adsorbed fibrinogen assumes a state which prevents its recognition and binding by platelet receptors. This improves thromboresistance because fibrinogen must be loosely held by an artificial surface to facilitate maximum interaction with platelet receptors .
Major structural changes have been observed in other Teflon-adsorbed proteins. For instance, changes in the secondary structure of beta-casein upon adsorption at the Teflon-water interface (as a function of pH) have been reported . The proteolytic enzyme alpha-chymotrypsin, once adsorbed from aqueous solution onto hydrophobic Teflon surface, assumes a remarkably stable helical structure . Conversely, adsorption of the lipolytic enzyme cutinase reduces the protein’s helical structure . Adsorption-induced denaturation of immunoglobulin G (IgG) doesn’t lead to complete unfolding into an extended polypeptide chain, but leaves a significant part of the IgG molecule in a globular or corpuscular form and enhances the formation of alpha-helices and random coils while reducing the beta-sheet content .
In many cases, adhesion of enzymes to hydrophobic surfaces results in large conformational changes with significant loss of enzymatic activity . For example, adsorption of xanthine oxidase onto Teflon distorts protein structure to the extent that all biologic activity is eliminated . As another example, the proteolytic enzyme savinase (the inhibited form of subtilisin) alters its conformation (e.g., increased alpha-helix content) when it adsorbs on Teflon at low surface coverage, although at full monolayer coverage the protein retains its original structure . Savinase adsorption on the surface of hydrophobic Teflon particles deactivates the enzyme with a half-life of 0.7 hours . Interestingly, modification of enzymes by adding a large number of fluorocarbon residues forms a hydrophobic envelope around the protein, which can help to prevent enzyme deactivation upon adsorption .
Lipids are rapidly adsorbed onto Teflon surfaces, influenced by their strong affinity for the highly hydrophobic polymer .
Last updated on 30 April 2004