Blood proteins onto polymer surfaces, adsorption

Adsorption of Blood Proteins onto Polymer Surfaces... 

Protein Adsorption. The development of medical implant polymers has stimulated interest in the use of ATR techniques for monitoring the kinetics of adsorption of proteins involved in thrombogenesis onto polymer surfaces. Such studies employ optical accessories in which an aqueous protein solution (93) or even ex - vivo whole blood (94-%) can be flowed over the surface of the internal reflection element (IRE), which may be coated with a thin layer of the experimental polymer. Modem FT-IR spectrometers are rapid - scanning devices, and hence spectra of the protein layer adsorbed onto the IRE can be computed from a series of inteiferograms recorded continuously in time, yielding ah effective time resolution of as little as 0.8 s early in the kinetic runs. Such capability is important because of the rapid changes in the composition of the adsorbed protein layers which can occur in the first several minutes (97). 

To attain this goal, we used ATR techniques which have been described previously (6). A liquid ATR cell can be used to circulate protein solutions (or blood) through the cell while spectrally monitoring the adsorption of proteins onto the surface of the ATR crystal. In addition, the ATR crystal can be coated with a thin layer of polymer, permitting us to follow the adsorption of pro-... 

Our studies (19) indicated that proteins were readily adsorbed from aqueous solution onto hydrophobic polymer surfaces with Langmuir type adsorption and that the rate of adsorption toward a plateau surface concentration depends on the polymer nature. In the study of competitive adsorption from a protein mixture solution (20), fibrinogen and y-globulin adsorb onto FEP very rapidly compared with PEUU and SR. Therefore, the FEP surface in contact with blood has more acceptor sites for platelet adhesion than does the PEUU or SR surface. 

To increase the residence time of drug carriers in the blood, the carriers are modified with hydrophilic synthetic polymers, such as PEG [62-64]. Coating nanoparticles with PEG sterically disrupts the interactions of blood components with the carrier surface and subsequently decreases the binding of plasma proteins. This minimizes opsonin adsorption onto the carrier and carrier uptake rates by the reticuloendothelial system (RES) [65-67]. Repulsive interactions [68] and poor permeability of proteins through PEG coating [69] may contribute to this observation. 

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). 

PLL(375)-g[5.6]-PEG(5) was also found to adsorb onto a preadsorhed layer of serum proteins. After a typical adsorption of serum protein (about 260 ng/cm ), subsequent exposure to a 1 mg/mL solution of PLL(375)-g[5.6]-PEG(5) led to an overlayer of polymer with a surface areal density of approximately 90 ng/cm. Earlier studies showed that the treatment of living red blood cells with PLL(375)-g[5.6]-PEG(5) prevented their subsequent agglutination. The observation of PLL(375)-g[5.6]-PEG(5) adsorption onto an adsorbed protein layer confirms the model proposed to explain this effect. 

For biomedical applications, inhibition of protein adsorption, as well as platelet activation and adhesion on the polymer surface, is critical to the efficiency of the material. For example, use of PHAs as artificial blood contacting devices such as arteries and anticoagulant films was limited by surface-induced thrombosis. The adsorption of plasma proteins and adherence of activated platelets onto the polymer surface resulted in their transformation to pseudopods and subsequent release of platelet biochemical content, which in turn activated other platelets leading to the... 

Very little of the research that has been done on these proteins has involved the use of electrochemical techniques. Instead, ellipsometry, FTIR/ATR spectroscopy, radioactive labeling, and photon correlation spectroscopy have been used. Many of the studies have been directed toward the development of biocompatible polymer surfaces. The first event that takes place after contact of blood or plasma with an artificial surface is the rapid adsorption of proteins from the blood onto the material surface. It is generally assumed that all subsequent events, such as platelet adhesion and surface activation of blood coagulation, are determined by the composition and structure of the initially adsorbed protein layer. It is known from in vitro experiments that the adhesion of platelets is promoted when fibrinogen has been adsorbed on a material surface and that platelet adhesion is reduced when preadsorbed albumin is present on the surface. In a study of the adsorption behavior of three of the more abundant... 

Figure 20 summarizes the result of BSA adsorption to the polymer films. We used BSA as model for protein because albumin is the protein that is most prominently present in human blood serum. The BSA adsorption onto regenerated cellulose, which had a highly hydrophilic surface, was extremely low. These data gave the same result reported in the previous study [70]. On the other hand, the adsorbed amounts of BSA onto aramid and nylon were high (0.5-0.6 p,g/cm ). For the PASs, the amount of BSA was almost half the amounts of those with aramid and nylon, but similar to that for SILASTIC 500-1, and more than that of the regenerated cellulose. There was no difference in the adsorbed amounts onto the three samples of PASs. In the previous work, PDMS blocks were condensed at the outermost surface of PAS [10]. The phenomenon of protein adsorption onto PAS seems to be due to the low surface free-energy of the PAS surface [71-73] caused by the condensation of PDMS blocks on the outermost surface of PAS. Therefore, the BSA was bound onto PAS surface as well as the surface of the silicone rubber [74,75]. 

Polymers can also be used to prevent the adsorption of proteins to surfaces. For example, polyvinylpyrrolidone can prevent protein adsorbing onto a variety of surfaces and it can also displace adsorbed protein [ 18]. This has led, for example, to its application in the coating of filtration membranes in order to reduce biofouling. Polymers are also used to inhibit the adhesion of bacteria or water-borne micro-organisms onto siufaces [19,20]. Bacteria are usually surrounded by exoceUular polysaccharides that can aid adhesion to clean surfaces. Thus prosthetic devices and vascular implants carrying blood suffer from the build up of biofilms, leading to blockages and infection. This build up can be markedly reduced... 

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