Platelets Adsorption

Polyethylene glycols are well known as protein-compatible molecules when coated or grafted onto surfaces. Both protein and platelet adsorptions to polyethylene glycol (PEG)-modified surfaces were shown to be reduced by PEG chains when attached to surfaces at one end of a molecule. Adsorption and platelet attachment were shown to be inversely proportional to the length of the PEG chain 100 monomer units provided minimal adsorption and adherence.- ... 

This chapter deals with a specific test of blood-surface interaction in vitro platelet retention in a column of beads (due to platelet adhesion and aggregation). Protein adsorption precedes platelet adsorption, and thus the in vitro platelet retention test involves competitive and sequential adsorption of proteins, the outcome of which produces surfaces having widely varying degrees of platelet retention. Except in the case of thrombin (3), plasma protein absorption on these surfaces has not been studied. 

Parallel tests show that thrombin adsorption is minimal on well-prepared polyurethanes containing amorphous PEO, greater on PTMO, and very high on analogues of the hard segment (diisocyanate-diamine copolymers), thus paralleling the trends in platelet retention index p. This result is consistent with the postulate that protein adsorption must precede platelet adsorption. 

E.W.Salzman, E.W.Merrill, Polyether-polyurethanes surfaces Thrombin adsorption, platelet adsorption, and ESCA scanning, J, Colloid Interface Sci. 76 594 (1980)... 

Phosphorylcholine Dip-coating Fibrinogen and platelet adsorption, coagnlation time Static, in vitro Human PPP and PRP Contact angle decreased with PC, accordingly less platelets and longer PRT [65]... 

Rather hydrophobic hoUow-fiber membranes are produced by melt spinning from blends of isotactic and atactic PMMA starting from the pure MMA monomers, or copolymerized with small amounts of p-styrene sodium sulfonate, dissolved in dimethylsulfoxide. Symmetric, almost homogeneous, PMMA membranes for HD, HF and TA are commercially available that are all sterilized by "y-ray irradiation. Their adsorptive properties have been reported to cause platelet adsorption with fibrin formation, possibly leading to high residual blood volumes in the filter (LocateUi et al., 2000) and one reported case of anaphylactic reaction (Hoenich, 1998). 

The emphasis in the study of protein adsorption has been the composition of the adsorbed layer, rate of adsorption, and possible changes, such as denaturation of the proteins effected by the adsorption process. Such studies, in relation to surface character, surface thrombogenicity, and platelet adsorption, have primarily... 

The effects of foreign surfaces on platelets has been intensively studied because of the place of platelets in thrombotic processes and because the visible deposition of platelets is evidence of some surface-platelet interaction. This latter is not strictly true because protein adsorption precedes platelet adsorption so that in reality it is a platelet-protein adsorbate reaction in which the nature of the adsorbate reflects the nature of the underlying surface. In vitro studies, primarily using platelet-rich plasma, have involved measurement of the adsorption rate, number adsorbed, morphological changes, and more recently, the release reaction. 

Thus reduction in platelet adsorption in itself did not reduce thrombogenesis as measured by FPA production. Leukocyte release, however, has been shown to include thromboplastins. 

Platelet protective agents have also been bonded in an effort to reduce platelet adsorption. Covalent bonding of PGE has been shown effective (38) and more recently Ditazole and dipyridamole have been bonded to polymers with a consequent reduction of platelet adsorption (39). 

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