The Effect of Carbon Nanotube Surface Energy on the Adhesion of Macrophages
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The Effect of Carbon Nanotube Surface Energy on the Adhesion of Macrophages Young Wook Chun and Thomas J. Webster Division of Engineering, Brown University, 184 Hope Street, Providence, RI 02912 U.S.A.
ABSTRACT Purified carbon nanotubes (with toxic catalytic particles removed) have been considered as improved drug delivery and artificial organ materials due to their unique biologically inspired nanometer surface features. The surface chemistry of carbon nanotubes has been modified through various functionalization strategies to increase biocompatibility. Importantly, modulating the intrinsic material surface energy of carbon nanotubes (without functionalization, thus, establishing permanent, non degradable chemical, and physical surface properties) can potentially reduce an immune response mediated by macrophages. Herein, we report macrophage responses on different surface energy carbon nanotubes while maintaining their desirable nanoscale surface roughness. Specifically, in vitro interactions of ultra hydrophobic (hydrocarbon coated) and hydrophilic (stripped of hydrocarbons and oxidized outlayer on surface) carbon nanotubes with macrophages were investigated. It was observed that macrophage density on both carbon nanotubes were lower than on traditional materials such as titanium. In particular, the amount of the cytokine, TNF-α, released from macrophages cultured on hydrophilic carbon nanotube scaffolds was much smaller than on hydrophobic carbon nanotubes. All results suggested that tailoring the surface energy of carbon nanotubes mediates macrophage cell responses. . INTRODUCTION Carbon nanotubes (CNTs) have attracted considerable attention due to their remarkable structural, electrical, and mechanical properties [1]. CNTs have been used to fabricate nanoscale drug delivery materials and sensors for the detection of proteins [2]. Individual CNTs as well as groups of CNTs have been used to change the surface energy of materials such as polymers [3]. Such CNTs offer great opportunities for studying the interaction between cells and materials at the nanoscale level due to their intrinsic surface energy that has been related with cell functions such as adhesion, migration and proliferation [4]. According to a recent report [3], the increased surface energy of CNTs mixed with polymers promoted fibronectin adsorption which is a key protein related to the functions of numerous cells. Based on this fact, the oxidized surface of CNTs may be controlled to reduce immune responses by macrophages to promote implant efficacy by tailoring such CNFs to manipulate protein adsorption. In this study, different macrophage responses on different surface energy CNTs were investigated. To determine the initial functions of macrophages on CNTs, the adhesion of macrophages was observed after a 4 hour seeding on both hydrophobic and hydrophilic CNTs.
EXPERIMENT Hydrophobic (PR-1AG) and hydrophilic CNTs (PR-24PS) (each 5 mg) were purchased from Pyrograf Inc. and dissolved in chloroform (20 ml) and ethanol (15 ml), respect
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