Polyurethane protein adsorbates

Surface layer-MALDI-MS has been developed specifically to identify proteins adsorbed onto biomaterial surfaces. Although the experimental approach for this technique is analogous to traditional MALDI-ToF MS, surface layer-MALDI-MS does not require protein isolation from the biomaterial surface, because the protein-adsorbed surface is submerged directly in a matrix solvent for crystallization (Griesser et al., 2004). For example, surface-MALDI-MS can be used to identify which proteins from blood plasma adsorb onto a biomaterial surface directly off the original material surface, such as polyurethane, as shown in Fig. 5.14 (Oleschuk et al., 2000). The acquired spectra show clear peaks, indicating different proteins with a distinct mass. Each of these proteins can be identified by comparing the experimentally determined masses with those in the literature. 

We have shown that the morphology of the adsorbed individual molecule and the protein film is dependent upon the surface to which the protein is adsorbed and the wall shear rate at which the protein solution contacts the surface. We have studied the interaction of proteins with surfaces from two approaches the first involved observations of the tertiary structures of individual molecules, and the second involved the use of a flow cell and the exposure of test materials to flowing, dilute, purified human plasma protein solutions. On the hydrophobic surfaces of polystyrene and polycarbonate, albumin and fibrinogen films form networks. On the surface of the hard segment model polyurethane, the morphology of the adsorbed film is very similar to that formed on the hydrophobic polystyrene and polycarbonate surfaces. On the peu-2000, the lowest... 

As we and others continue this line of investigation it is becoming evident that the whole area of competitiveness of protein adsorption in the blood context, which at the moment seems hopelessly mired and anecdotal, may eventually reveal a rational, orderly nature. Vroman has postulated (50) that a rapid sequence of adsorption and displacement events occurs by which, over time, more abundant proteins are displaced by less abundant. The time frame of these events is such that albumin is adsorbed and replaced in a fraction of a second, thus accounting for the fact that it is not often observed on the surface after plasma contact. Clearly the time frame may be expected to vary with the surface so that in some cases the sequence will be relatively fast and in others relatively slow. Thus the apparent absence of a Vroman Effect for hydrophilic polyurethanes may reflect a very rapid sequence, such that a fibrinogen peak would be observed only at very short times or at low plasma concentrations (less than 0.05%). 

When each of the acrylate or methacrylate polymers was preincubated with whole plasma, the platelet reactivity of the surfaces upon subsequent exposure to whole blood decreased significantly (Fig. 3). On the other hand, with many other polymers this effect of plasma was not seen. Of 20 varieties of segmented polyurethanes examined, none showed this behavior (22), and platelet adhesion to polystyrene was also unaffected by plasma pretreatment ( ). The phenomenon of plasma-induced passivation of methacrylate and acrylate polymers presumably involves selective adsorption of specific plasma proteins by the surfaces and/or a particular alteration of the adsorbed protein once bound. 

Figure 5.14 MALDI-ToF MS of three different plasma standards bovine, canine, and human on polyurethane membrane, (a) Low-molecular weight region, (b) High-molecular weight region, (c) Identification of adsorbed proteins in mass spectra compared with the literature values of proteins.

Bacterial adhesion is the altical step in the pathogenesis of biomaterial-associated infection and is critically inflnenced by numerous variables including surface properties of biomaterials, the nature of the environment, and the bacterial cell surface. In addition, adsorbed proteins play an important role in bacteria-surface interactions. One strategy for the development of antibacterial polyurethanes has focused on... 

Wu Y, Simonovsky FI, Ratner BD, Horbett TA. The role of adsorbed fibrinogen in platelet adhesion to polyurethane surfaces a comparison of surface hydrophobicity, protein adsorption, monoclonal antibody binding, and platelet adhesion. J Biomed Mater Res A 2005 74(4) 722-38. 

In protective clothing, a layer of polyurethane, foam-entrapped, activated charcoal is embedded between several layers of polyester fabric. Polyurethanes are effective substrates for OP adsorption, and reports have documented that polyurethane foam particles can be used as adsorbent materials for pesticide vapors in farming fields. If proteins could be incorporated into polyurethanes, some interesting materials might emerge. 

Figure 8 shows a Phngn adsorption isotherm recorded on hydrophobic, methylene dianiline (MDA) polyurethane [2]. A radiolabeling technique using was used to measure the adsorbed mass of Phngn in these experiments. The isotherm experiments were carried out at pH 7.4, with protein dissolved in isotonic Tris buffer. Tables 10 and 11 show the relevant thermodynamic and regression data associated with the Phngn adsorption isotherm. 

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