Polymer Surfaces plasma protein adsorption

These studies indicate that heparin directly affixed to a surface does not provide optimal, solution-like, anticoagulant behavior. The immobilization of heparin directly to the polymer surface resulted in alterations of the surface properties relative to control surfaces, which greatly influenced the plasma protein adsorption characteristics, a controlling factor in platelet adhesion and overall blood compatibility (12). 

Surface modification with hydrophilic polymers, such as poly(ethylene oxide) (PEO), has been beneficial in improving the blo( compatibility of polymeric biomaterials. Surface-bound PEO is expected to prevent plasma protein adsoiption, platelet adhesion, and bacterial adhesion by the steric repulsion mechanism. PEO-rich surfaces have been prepared either by physical adsorption, or by covalent grafting to the surface. Physically adsorbed PEO homopolymers and copolymers are not very effective since they can be easily displaced from the surface by plasma proteins and cells. Covalent grafting, on the other hand, provides a permanent layer of PEO on the surface. Various methods of PEO grafting to the surface and their effect on plasma protein adsorption, platelet adhesion, and bacterial adhesion is discussed. 

A wide variety of natural and synthetic materials have been used for biomedical applications. These include polymers, ceramics, metals, carbons, natural tissues, and composite materials (1). Of these materials, polymers remain the most widely used biomaterials. Polymeric materials have several advantages which make them very attractive as biomaterials (2). They include their versatility, physical properties, ability to be fabricated into various shapes and structures, and ease in surface modification. The long-term use of polymeric biomaterials in blood is limited by surface-induced thrombosis and biomaterial-associated infections (3,4). Thrombus formation on biomaterial surface is initiated by plasma protein adsorption followed by adhesion and activation of platelets (5,6). Biomaterial-associated infections occur as a result of the adhesion of bacteria onto the surface (7). The biomaterial surface provides a site for bacterial attachment and proliferation. Adherent bacteria are covered by a biofilm which supports bacterial growth while protecting them from antibodies, phagocytes, and antibiotics (8). Infections of vascular grafts, for instance, are usually associated with Pseudomonas aeruginosa Escherichia coli. Staphylococcus aureus, and Staphyloccocus epidermidis (9). 

The formation of surface pores, the changes in the polar component of the surface free energy, and the disruption and formation of centers of specific adsorption in the course of ion bombardment considerably affect the cell adhesion at the ion-implanted polymers, which opens up new possibilities for controlling the biocompatibility of polymer materials [76,77]. Thus the changes in the dynamics of plasma protein adsorption at silicon rubber upon implantation with 150-keV, ... 

S. Sant, S. Poulin, and P Hildgen, Effect of polymer architecture on surface properties, plasma protein adsorption, and cellular interactions of pegylated nanoparticles, / Biomed. Mater. Res. Part A, 87,885-895,2008. 

Fundamentals of Native Plasma Protein Adsorption on Polymer Surfaces... 

The amount of phospholipids adsorbed from plasma on the MPC polymers increased with increasing amounts of MPC. In the case of hydrophobic poly( -butyl methacrylate (BMA)) and hydrophilic poly(2-hydroxyethyl methacrylate (HEMA)), the amount of adsorbed phospholipids was the same level (about 0.5 pg/cm ). This means that the MPC moiety in the poly(MPC-co-BMA) played an important role to increase adsorption. To clarify the state of phospholipids adsorbed on the polymer surface, the phospholipid liposomal suspension was put in contact with these polymers. Phospholipids were adsorbed on every polymer surface, however, the adsorption state of the phospholipids was different on each polymer. On the surface of the MPC polymer, the adsorbed phospholipids maintained a liposomal structure, like a biomembrane this was confirmed by a differential scanning calorimetry. X-ray photoelectron spectroscopy (XPS), quarts crystal microbalance, and atomic force microscope. The phospholipids adsorbed on the poly(BMA) and poly(HEMA) did have any organized form. It was concluded that the MPC polymers stabilized the adsorption layer of phospholipids on the surface. Small amounts of plasma proteins were adsorbed on the MPC polymer surface pretreated with phospholipid... 

The adsorption experiments were carried out by quantifying each of proteins adsorbed on the material from mono-component protein solutions, from four-component protein solutions, and from plasma and diluted plasma. Adsorption profiles of protein were largely different, depending on the aforementioned experimental conditions. For instance, the behavior of any particular protein from diluted plasma varied in response to the extent of plasma dilution. Cooper s results are illustrated in Fig. 3, on fibrinogen adsorption onto five polymer surfaces. It is seen that the adsorption profiles are different one another, being influenced by the different nature of the polymer surfaces. The surface concentrations of adsorbed protein are mostly time-dependent, and maxima in the adsorption profiles were observed. This is interpreted in terms of replacement of adsorbed fibrinogen molecules by other proteins later in time (Vroman effect). Corresponding profiles were also presented for FN and VN. 

Protein adsorption onto intrinsically repellent materials is enhanced by a brief plasma treatment that chemically and physically alters the surface properties. Stencil-assisted plasma oxidation of inherently hydrophobic polymers (e.g., PDMS... 

Lassen and Malmsten have performed ellipsometrically determined in situ protein adsorption measurements on the above plasma polymer surfaces with human serum albumin (HSA). human immunoglobulin (IgG), and human fib-... 

Other materials have also been studied for their ability to reduce protein adsorption onto surfaces. Because many cell membranes are based on phospholipids, polymers containing phospholipid-type head groups have been utilized for this purpose. Poly(2-methacroylethyl phosphoryl choline) could be plasma deposited onto silicone rubber and the adhesion of albumin reduced by factors of up to 80 (Fig. 

The adsorption of plasma proteins to polymers precedes the interaction of blood cells with the surfaces, and therefore, is likely to be an important initial event in the response of blood to polymers (25, 29). At present, however, little is known about the adsorbed protein layer, even though it has been studied in some detail in recent years (30-36). Because protein adsorption from blood plasma is a competitive process, differences in the adsorbed layer on different polymer substrates could be a primary cause of differences in thrombogenicity. Previous studies of the composition of the adsorbed protein layer have employed 12oI-labeled protein added to plasma (37-39), antibody binding (34) to detect individual proteins, or electrophoretic analysis of detergent-elutable proteins (17, 33, 35). The procedure used in this study does not require the large surface areas used in previous work (35), nor does it rely on incorporation of radiolabels (36) into adsorbed protein. Instead, a staining method at least 100-fold more sensitive than these other techniques has been used. 

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. 

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