When foreign materials of medical device come into contact with blood, most of them will adsorb various plasma proteins from the blood, thereby activating the human coagulation system and platelets, and finally forming a thrombus (Figure 1). The thrombus will occlude the device lumen, block the device, even lead to thrombosis and endanger the patient's life.
Figure 1. Schematic diagram of the thrombus formation without any antithrombotic coatings.
Antithrombotic coatings include active antithrombotic and passive antithrombotics.
Active antithrombotics include Heparin, Hirudin, etc., which can be chemically bonded to or released from the coatings. Heparin inhibits the activity of prothrombin, reduces the conversion of prothrombin to thrombin, which in turn reduces platelet activation and aggregation, reduces superficial thrombus formation ultimately (Figure 2). The activity of heparin should be maintained during the bonding process; while a slow and uniform release rate is the key to success of the release type coating. Heparin is currently the only antithrombotic substance approved by the FDA for use in the United States, while hirudin is a synthetic chemical antithrombotic agent with low molecular weight and relatively stable properties. Compared with heparin, it is not only could be used in small doses, but also not cause bleeding, not is dependent on endogenous cofactors.
Figure 2. Effect comparison diagram between uncoated (left) and coated(right)
Passive antithrombotics include amphiphilic ionic materials such as phosphorylcholine (MPC) and betaine (carboxybetaine, phosphobetaine), which mimic the structure of cell membranes and reduce protein adsorption.
There are also some hydrophilic materials, such as polyvinyl alcohol (PEO), which can play the role of hydrophilic anti-fouling and reduce the probability of thrombosis to a certain extent.
Antithrombotic coatings are especially suitable for consumables that come into contact with blood, including:
Figure 3. Applications examples that usually need antithrombotic coatings
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1. Li C. et al., Thrombolytic Agents: Thrombosis-Responsive Thrombolytic Coating Based on Thrombin-Degradable Tissue Plasminogen Activator (t-PA) Nanocapsules. Adv. Funct. Mater. 2017, 27(45), 1703934