Blood Compatibility of Stainless-Steel and Titanium Immobilized with Alginic Acid Layers
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Blood Compatibility of Stainless-Steel and Titanium Immobilized with Alginic Acid Layers Tomohiko Yoshioka, Kanji Tsuru, Satoshi Hayakawa, and Akiyoshi Osaka Biomaterials Laboratory, Faculty of Engineering, Okayama University Tsushima, Okayama, 700-8530, Japan. ABSTRACT γ-Aminopropyltriethoxysilane (γ-APS) was grafted on stainless-steel and titanium substrates, and subsequently alginic acid layer was immobilized on them. Their surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and contact angle measurement. Blood compatibility of thus obtained substrates was evaluated in terms of both the number of the adhered platelets and blood clotting factors for plasma contacted with the substrates such as active partial thromboplastin time (PTT), prothrombin time (PT), and amount of fibrinogen (Fib). The steel and titanium substrates with alginic acid layer did not affect blood clotting factors. In vitro platelet adhesion assay indicated that those substrates adhered less number of platelets than non-treated substrates. Hence the alginic acid immobilization leads to blood compatible surfaces. INTRODUCTION Stainless-steel and titanium are often used for biomedical devices such as coronary stent or artificial heart housing. These blood contacting materials are demanded for highly blood compatibility. Many efforts have been attempted to improve the blood compatibility of stainless-steel or titanium without using anticoagulant agents [1,2]. When artificial materials come into contact with blood, blood components immediately are adsorbed onto their surface, and finally thrombi are formed. To suppress the adsorption of blood components may lead to blood compatibility. In the present study, we immobilized alginic acid layer onto γ-aminopropyltriethoxysilane (γ-APS)-grafted stainless-steel and titanium substrates by covalent bonding. Since the alginic acid layer on the substrate surface prevent cell adhesion [3-6]. Their surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The blood compatibility was not only evaluated in terms of the number of the adhered platelets on their surfaces in platelet rich plasma (PRP) but also evaluated in terms of blood clotting factors of platelet poor plasma (PPP) contacted with the surfaces, such as active partial thromboplastin time (PTT), prothrombin time (PT), and amount of fibrinogen (Fib) [2]. EXPERIMENTAL Surface modification Surface modification was performed on 10x10x0.1 mm sheets of stainless-steel (SUS316L) or Ti. These substrates were ultrasonically cleaned in acetone for 5 min three times (denoted as
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NT). After heating at 500°C for 2 h in air, these substrates were silanized with γ-aminopropyltriethoxysilane (γ-APS) as they were soaked in a 1 vol% toluene solution of γ-APS for 1 h in air. After rinsed with toluene and ethanol, and ultrasonically rinsed in ethanol for 5 min, they were dried in air and then kept at 105°C for 10 min. The substrates heated at 500°C were denoted as HT, and the ones silaniz
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