Impaired platelet adhesion to lysed fibrin, whereas neutrophil adhesion remains intact under conditions of flow

Thrombogenicity of biomaterials depends on hemodynamic shear rate

BACKGROUND

While it is well recognized that different biomaterials induce thrombosis at low shear rates, the effect of high shear rates may be quite different. We hypothesize that the amount of thrombus formation on a given material can be greatly influenced by the local shear rate.

METHODS

We tested this hypothesis with two different whole blood perfusion loop assays to quantify biomaterial thrombogenicity as a function of shear stress. One assay uses obstructive posts (pins) of material positioned centrally in a tube perfused at high shear rate of >5000/s for 24 h. A second assay uses a parallel plate chamber to perfuse low (<150/s), medium (~500/s), and high shear rates over 96 h. We evaluated the thrombogenicity of seven different biomaterials including stainless steel, acrylic, ceramic, Dacron, polytetrafluoroethylene (PTFE), silicone, and polyvinyl chloride (PVC).

RESULTS

For the pin assay, thrombus mass was significantly greater for stainless steel than either zirconia ceramic or acrylic (p < 0.001). Similarly, the parallel plate chamber at high shear showed that steel and PTFE (p < 0.02) occluded the chamber faster than acrylic. In contrast, a low shear parallel plate chamber revealed that stainless steel and PTFE were least thrombogenic, while silicone, Dacron, and other plastics such as acrylic were most thrombogenic. Histology revealed that high shear thrombi had a large proportion of platelets not seen in the low shear fibrin-rich thrombi.

CONCLUSION

This differential thrombogenicity based on shear rate conditions may be important in the selection of biomaterials for blood-contacting devices.

Thrombin production and human neutrophil elastase sequestration by modified cellulosic dressings and their electrokinetic analysis

Wound healing is a complex series of biochemical and cellular events. Optimally, functional material design addresses the overlapping acute and inflammatory stages of wound healing based on molecular, cellular, and bio-compatibility issues. In this paper the issues addressed are uncontrolled hemostasis and inflammation which can interfere with the orderly flow of wound healing. In this regard, we review the serine proteases thrombin and elastase relative to dressing functionality that improves wound healing and examine the effects of charge in cotton/cellulosic dressing design on thrombin production and elastase sequestration (uptake by the wound dressing). Thrombin is central to the initiation and propagation of coagulation, and elastase is released from neutrophils that can function detrimentally in a stalled inflammatory phase characteristic of chronic wounds. Electrokinetic fiber surface properties of the biomaterials of this study were determined to correlate material charge and polarity with function relative to thrombin production and elastase sequestration. Human neutrophil elastase sequestration was assessed with an assay representative of chronic wound concentration with cotton gauze cross-linked with three types of polycarboxylic acids and one phosphorylation finish; thrombin production, which was assessed in a plasma-based assay via a fluorogenic peptide substrate, was determined for cotton, cotton-grafted chitosan, chitosan, rayon/polyester, and two kaolin-treated materials including a commercial hemorrhage control dressing (QuickClot Combat Gauze). A correlation in thrombin production to zeta potential was found. Two polycarboxylic acid cross linked and a phosphorylated cotton dressing gave high elastase sequestration.

Biological and pharmacological aspects of perioperative hemorrhagic complications associated with oral platelet-directed antithrombotic agents. Focus on isolated coronary artery bypass grafting and oral irreversible P2Y(12) receptor antagonists

Coronary arterial bypass grafting (CABG)-the most common heart surgery performed worldwide-is an effective procedure for treating patients with advanced, obstructive atherothrombotic coronary artery disease, prolonging survival in selected high-risk patients. However, CABG is also associated with hemorrhagic complications, which can impact outcome measures such as perioperative morbidity, mortality, length of hospital stay, and health care expenditures. Recent observations have expanded our understanding of the complex process of hemostasis, fostering a more informed view of CABG-associated bleeding complications. Additional research is warranted to determine whether new antithrombotic drug treatment options, such as reversible P2Y12 receptor antagonists among patients with acute coronary syndromes, will favorably impact these clinically relevant complications.