Fibrinogen Adsorption on Hydroxyapatite, Carbonate Apatite and Gold Surfaces In Situ Detected by Quartz Crystal Microbal
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Fibrinogen Adsorption on Hydroxyapatite, Carbonate Apatite and Gold Surfaces In Situ Detected by Quartz Crystal Microbalance with Resistance Technique Hiroshi Yonekura, Motohiro Tagaya, Tomohiko Yoshioka, Toshiyuki Ikoma and Junzo Tanaka Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8550, Japan ABSTRACT When a biomaterial is implanted into the body, blood proteins adsorb on its surface and subsequently cells adhere via the protein adlayer. Thus, the understanding of protein adsorption and conformational change on the biomaterial surfaces is of great importance to control the biocompatibility such as antithrombotic properties and cell adhesion behaviors. In this study, we synthesized hydroxyapatite (HAp) and carbonate apatite (CAp) by a wet method. Then we successfully fabricated the HAp and CAp sensors for QCM-R by an electrophoretic deposition method. Adsorption behavior of proteins on the bone substitute material can be monitored by using these apatite sensors. Bovine serum albumin and fibrinogen were employed for the model proteins, and monitored the adsorption behavior on the HAp, CAp and reference gold (Au) sensors by the QCM-R technique. As a result, we revealed that fibrinogen and bovine serum albumin adsorbs on the gold surface by hydrophobic interaction, and adsorbs on the HAp and CAp surfaces mainly by electrostatic force. Besides, we revealed that fibrinogen adsorbs on the Au surface more rigid than on the HAp and CAp surfaces while bovine serum albumin adsorbs on the HAp and CAp surface more rigidly than on the Au surface. INTRODUCTION Hydroxyapatite (HAp; Ca10(PO4)6(OH)2) is a typical bone substitute with excellent biocompatibility[1]. But apatite in human bone contains 4~8 wt% of carbonate ions substituted for phosphate ions; there are two substitution sites, i.e. one is PO4 site called B-type, and the other is OH site called A-type[2]. Then, B-type CAp has much attention for bone substitute material. Blood contains proteins such as albumin and fibrinogen (Fgn). The higher-order structure of albumin and Fgn are shown in figure 1. Albumin with the spherical shape in figure 1 (a) is a main component in blood with isoelectric point of 4.7, molecular weight of 69 kDa, and size of 9 nm, and plays a carrier of substances such as calcium and zinc, and a coordinator of osmotic pressure. On the other hand, Fgn, a structural glycoprotein in blood plasma with isoelectric point of 5.5, molecular weight of 340 kDa, and length of 45 nm, and is known as a blood coagulation factor, which occasionally can be a cause of thrombi. Fgn has an iron dumbbell like structure shown in figure 1. (b); a central hydrophobic E domain with negative charges under neutral pH condition is connected to two hydrophobic D domains by coiled-coil chain. The αC domains, with Arg and Lys residues, are charged positive and are substantially hydrophilic compared with the E domain and D domains.
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Figure 1. Schematic illustration of (a) albumin and (b) Fgn molecule.
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