Platelets adhesion and activation

For pH sensors used in in-vivo applications, especially those in continuous pH monitor or implantable applications, hemocompatibility is a key area of importance [150], The interaction of plasma proteins with sensor surface will affect sensor functions. Thrombus formation on the device surface due to accelerated coagulation, promoted by protein adsorption, provided platelet adhesion and activation. In addition, variation in the blood flow rate due to vasoconstriction (constriction of a blood vessel) and sensor attachment to vessel walls, known as wall effect , can cause significant errors during blood pH monitoring [50, 126],... 

In practice, some anticoagulation agents such as heparin or antiplatelet agents, e.g. nitric oxide (NO) are delivered to sensor sites in order to reduce the risk of thrombus formation. Nitric oxide (NO), which is a potent inhibitor of platelet adhesion and activation as well as a promoter of wound healing in tissue, has been incorporated in various polymer metrics including PVC (poly(vinyl-chloride)), PDMS (poly-dimethyl-siloxane) and PU (poly-urethanes). Those NO release polymers have been tested in animals as outer protection coatings and have shown promising effects for the analytical response characteristics of the sensor devices [137],... 

A partially or completely occlusive clot forms on top of the raptured plaque. Exposure of collagen and tissue factor induce platelet adhesion and activation, which promote release of adenosine diphosphate and thromboxane A2 from platelets. These produce vasoconstriction and potentiate platelet activation. A change in the conformation of the glycoprotein (GP) Ilb/IIIa surface receptors of platelets occurs that cross-links platelets to each... 

The result was that albumin passivation came into vogue for sometime. In fact, artificial kidneys and blood oxygenators were often treated with albumin solutions prior to clinical use 118,119). There is considerable evidence that such pre-treatment did indeed result in decreased platelet adhesion and activation for short periods, perhaps up to several hours, but that the effect was relatively short-lived. 

Dr. David Calverley is a hematologist with a research interest in the molecular mechanisms of platelet adhesion and activation. His clinical interest lies in the area ofplatelet and hemostatic disorders. In addition to research, clinical, and teaching activities, he is Associate Director of the University of Southern Califomia/Nonis Cancer Hospital Qinical Coagulation Laboratoiy. Dr. Gerald Roth is a hematologist with interests in both research and clinical aspects of platelets. He has studied molecular aspects of aspirin s effect on platelets and observed the acetylation reaction between aspirin and platelet cyclo-oxygenase. 

EFE-immobilized surface may minimize platelet adhesion and activation by preventing fibrinogen from adsorption or by altering the conformation of adsorbed fibrinogen at an early stage of blood contact. The antithrombogenicity increases hydrophilicity of surface on behalf of MAMEC for implantation. Clinical applications of this material to artificial organs could be expected to develop in the near future. 

One possible objection to the comparison of protein adsorption on flat surfaces with platelet adhesion and activation in polymer-coated bead columns is raised by the work of Vroman et al. (28) who showed that protein adsorption onto surfaces from plasma in narrow... 

PEG-phenylazide and photoinduced grafting onto DDS-glass is shown in Figure 4. Platelet adhesion and activation was prevent on PEG-gr ted DDS-glass. 

Before proceeding to the advanced technology area of biosensors, brief consideration goes to coatings of medical devices to improve performance and to prevent such adverse reactions as adhesion of the medical device to the tissues, bacterial adhesion, platelet adhesion and activation, and adverse tissue reaction of host to device from the standpoint of protecting both the host and the function of the device. 

In the platelet adhesion assay, Af,0-snlfated chitosan with cationic NH3+ groups was shown to reduce platelet adhesion and activation by ionic interactions between the platelets membrane surface and the cationic groups on the modified chitosan manbrane. 

Ti, TiN, TiO and DLC modified PU Pulsed laser deposition Combination of materials Platelet adhesion and activation, GPIIb/IIIa Dynamic, in vitro Human blood Overall best results on DLC-TiN and TiN [72]... 

Fluorinated PU Two-step Bulk polymerization Fluorine content Platelet adhesion and activation Static, in vitro Human PRP Increasing content of fluorine = increasing contact angle, decreasing platelet adhesion and shape change [74]... 

Au and Pt nanoparticles in PU Pulsed laser ablation in liquid wt% of Au resp. Pt Cell proliferation and platelet adhesion Dynamic cell culture static in vitro Endothelial cells forming cells, human PRP Best cell proliferation on 0.1 wt% Au and <0.25 wt% Pt additionally no platelet adhesion and activation [73]... 

PU Grooves, varying width Width 1.8 im, 3.4 pm, 90 pm Platelet adhesion and activation Dynamic, in vitro Porcine whole blood Reduced on groove widths smaller than 3 pm [12]... 

PU Pillars, varying interspacing d=25pm =100pm Z=20pm, 50 pm, 100 pm Platelet adhesion and activation Dynamic, ex vivo Bovine PRP At shear stress <3.3 dyn/cm better for /=700nm [14]... 

PU Nano tubes Protrusions h 40nm rf=lOOnm Ridges /t = 100nm w = 500nm Platelet adhesion and activation Dynamic, in vitro Human PRP Structured surfaces with higher contact angle few platelets, no shape change [99]... 

Ding Y, Leng Y, Huang N, Yang P, Lu X, Ge X, et al. Effects of microtopographic patterns on platelet adhesion and activation on titanium oxide surfaces. J Biomed Mater Res A March 2013 101(3) 622-32. 

Park KD, Suzuki K, Lee WK, et al. Platelet adhesion and activation on polyethylene glycol modified polyurethane surfaces. Measurement of cytoplasmic calcium. ASAIO J September 1996 42(5) M876-81. 

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