Cell adhesion adsorbed protein layer

Fibronectin, vitronectin, and type 1 collagen are some of the most representative ECM proteins involved in cell adhesion processes, therefore adsorption studies with these proteins and the PLA/G5 composite material have been performed. Preliminary studies have shown that all proteins adhere better to the G5 (the most hydrophilic material) than to the other materials. Vitronectin presented the best adhesion with PLA (the most hydrophobic material), and the PLA/glass composite presented an intermediate behavior. Further experiments are being conducted to evaluate the direct impHcation of the main proteins present in ECM to regulate cell proliferation and differentiation in the studied materials, and to obtain information on how the quality of the surface (physicochemical and topographical) influences the adsorbed protein layer. 

Polymer Adsorption. A review of the theory and measurement of polymer adsorption points out succinctly the distinquishing features of the behavior of macromolecules at solid - liquid interfaces (118). Polymer adsoiption and desorption kinetics are more complex than those of small molecules, mainly because of the lower diffusion rates of polymer chains in solution and the "rearrangement" of adsorbed chains on a solid surface, characterized by slowly formed, multi-point attachments. The latter point is one which is of special interest in protein adsoiption from aqueous solutions. In the case of proteins, initial adsoiption kinetics may be quite rapid. However, the slow rearrangement step may be much more important in terms of the function of the adsorbed layer in natural processes, such as thrombogenesis or biocorrosion / biofouling caused by cell adhesion. 

Some of the areas where interfacial protein layers dominate the boundary chemistry are reviewed, and we introduce some nondestructive armlytical methods which can be used simultaneously and/or sequentially to detect and characterize the microscopic amounts of matter at protein or other substrates which spontaneously acquire protein conditioning films. Examples include collagen and gelatin, synthetic polypeptides, nylons, and the biomedically important surfaces of vessel grafts, skin, tissue, and blood. The importance of prerequisite adsorbed films of proteins during thrombus formation, cell adhesion, use of intrauterine contraceptives, development of dental adhesives, and prevention of maritime fouling is discussed. Specifics of protein adsorption at solid/liquid and gas/liquid interfaces are compared. 

Bioadhesion is very complicated from a physical-chemical point of view. Interfacial tensions, wetting, and electrical properties of the surfaces are prominently involved. Because the (aqueous) medium from which the cells adhere usually contains surface-active molecules, notably proteins, the cells adhere as anile onto an adsorbed proteinaceous layer. The preformed adsorbed layer will therefore largely determine the subsequent cell adhesion process. Furthermore, biological cells often carry polymeric substances at their surfaces. These components may influence the interaction with a substratum surface in various ways, as is explained in Section 16.3. Understanding bioadhesion therefore requires a thorough knowledge of various aspects of colloid and interface science. 

In this study, the adsorption of polyelectrolytes, such as the class of PLL-g-PEG graft copolymers on metal oxide surfaces, was found to be consistent with the related observations from previous studies. In previous characterizations of the adsorption behavior of polyeleotrolytes on such metal oxide surfaces, polycations in particular, such as PLL, were found to form stable adsorbed layers on negatively charged oxides such as silicon dioxide and titanium dioxide. However, the class of PLL-g-PEG-based copolymers thus far had been evaluated only in the contexts of drug delivery and the reduction of cell adhesion without a thorough characterization of the related modified surfaces and their reduction of protein adsorption. 

After a biomaterial is implanted in the body, it takes seconds to minutes for proteins to adsorb and cover its surface, forming the so-called conditioning film [11], Therefore, instead of the original surface of the implanted material, the cells will recognize and interact with this protein layer. It is fair to assume that the adhesion proteins are responsible for converting the biomaterials into biologically recognizable materials. The adsorption of these adhesion proteins is the basis for all the reactions that may further occur in the body [33]. 

The surface properties of the biomaterials will determine the type, amount and conformation of the adsorbed proteins [2]. The composition of this protein layer can be different, depending on the fluid composition and adsorption time [25], Besides the composition of the protein layer, the conformation and the orientation of the protein can also change with time [8]. This conditioning protein layer will increase the cell adhesiveness, since the cells have receptors in their membranes that specifically bind to the adhesion proteins. Moreover, the protein layer also increases the cell spreading at the biomaterial surface [6,10]. 

The thermodynamic model is, like the DLVO theory, only applicable for the adhesion in vitro. Both models are based upon non-specific interactions occurring between particles (cells) and solid surfaces. In vivOr or under in vivo like conditions, specific interactions also have to be taken into account. Such specific interactions have been shown to mediate adhesion between bacteria and natural substrata, such as adhesion of streptococci to dental enamel,29 y adhesion of E. coli to uroepithelial cells.30 Although not clearly demonstrated for the bacterial adhesion to synthetic polymers, it is highly possible that specific interactions, e.g. between bacterial surface proteins and protein layers adsorbed on the polymer surface, play an important role as well. 

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. 

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