CHAPTER13 Biomaterials and Thrombosis 13-1 Introduction: Overview of Hemostasis Blood-Biomaterials Interaction via protein coats ---- blood coagulation control Injury ---- Hemostatic mechanism vascular constriction / platelet plug / blood coagulation (thrombosis) 13-2 Role of Platelets Platelet Characteristics and Functions Non-nucleated fragment of megakaryocyte (no proliferation) Mitochondria, ER, Golgi  -granule: platelet factors, b-thromboglobulin, fibrinogen, factor V and VIII Dense granule: ADP, Calcium, serotonin Lysosomal granules: hydrolytic enzymes Platelet plug formation / activation of blood coagulation cascade

Platelet Activation (1)Means of activation collagen, von Willerbrand factor (vWF), proteins on biomaterials (2) Sequelae shape change --- contraction of cytoskeletons --- granule release (ADP/thrombin/thromboxane A2) activated platelets ---- ECM adhesion --- platelet stimulation and coagulation platelet aggregation with fibrinogen (GPIIb/IIIa) platelet plug formation --- localized blood coagulation PL memb. of platelet --- factor X activation --- thrombin activation

Platelet Activation

13-3 Coagulation Cascade intrinsic pathway HMWK, prekallikrein, factor XI (proteolysis by factor XII) positive feedback extrinsic pathway tissue factor from macrophage and endothelial cells common pathway thrombus (attached through fibronectin)  -carboxyglutamate with vit. K

13-4 Means of Limiting Clot Formation (1) Physiologic factors normal blood flow surface (membrane) by activated platelets or platelet fragments (2) Soluble and insoluble biochemical factors a) heparin/antithrombin III (ATIII) complex b)  2-macroglobulin c) thrombomodulin on the endothelial surface thrombin sequestration --- protein C activation --- V & VIII inactivation d) clot dissolution process (fibrinolysis) plasmin tissue plasminogen activator (t-PA)  2-plasmin inhibitor

13-5 Role of the Endothelium Endothelium --- glycocalyx / integrin and other receptors (1) Anticogaulatory properties heparin sulfate / thrombomodulin / prostaglandin I 2 / tPA (2) Composition of the endothelium protective glycocalyx / exposure of endothelial ECM molecules decrease in thrombomodulin and release of TF vWF secretion for platelet aggregation inflammation and thrombosis

13-6 Tests for Hemocompatibility thrombosis, coagulation, platelets, hematology + immunology General Testing Concerns (1) Hemocompatibility test local effects systemic effects a. thrombus embolization (stroke) b. soluble products (inflammation) c. implants (reduced blood coagulation response) (2) Causes (biomaterials) blood characteristics 혈액종류, 항응고제, blood pumping flow regime transport of platelets and plasma proteins / low FR (thrombus formation) material surface characteristics (plasma protein adsorption and physicochemical properties) In Vitro Assessment a. coagulation timeb. amount of adhered platelets c. mass of adherent thrombus d. amount of platelet granule release (PF-4 and  -thromboglobulin) limits: use of anticoagulants and control materials

In Vivo Assessment - Choice of animals / length of study and choice of time points / control materials (1) Histology at the end of the experiments (2) Biochemical Assay (3) Blood flow conditions in animal models and tissue trauma during implantation procedure Shunt test (Ex vivo) blood flow control / native blood / long-term response no evaluation due to the trauma of surgery Final application of biomaterials