Nano-Surface Modification on Titanium Implants for Drug Delivery
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Nano-Surface Modification on Titanium Implants for Drug Delivery Chang Yao, and Thomas J Webster BROWN UNIVERSITY, PROVIDENCE, RI, 02912 ABSTRACT The surface layer of titanium implants, i.e. titanium dioxide, is responsible for the inertness of titanium-based implants within the human body. However, their cytocompatibility properties and long-term efficacy are limited without further surface engineering since the average functional lifetime of an orthopedic implant is only 10 to 15 years. In this study, an electrochemical method known as anodization was used to create titania nanotubular structures on titanium implant surfaces. These nanotubes were about 60 nm wide (inner diameter) and 200 nm deep. In vitro studies found that anodized surfaces consisting of titania nanotube arrays were favored by bone-forming cells (osteoblasts) compared to unanodized surfaces. These titania nano-tubular structures were utilized here as novel drug release delivery systems. It is proposed that the system designed here can have multi-functional drug release to inhibit infection and wound inflammation while increasing new bone formation. For this purpose, antibiotic drugs (penicillin and streptomycin) were loaded into these nanotubular structures by physical adsorption. To mediate interactions between drug molecules and nanotube walls, anodized titanium nanotubes were modified by silanization to possess amine or methyl groups on their surface instead of -OH groups. Results showed increased hydrophobicity of chemically modified titania nanotubes (methyl > amine > hydroxyl terminated surface). These drug loaded substrates were soaked in phosphate buffered solution in a simulated body environment to determine drug release behavior. Buffer solutions were collected and replaced every day. The eluted drug amounts were measured spectroscopically. Results showed more antibiotic penicillin and streptomycin released from chemically modified nanotubes compared to unanodized titanium substrates; specifically, titania anodized nanotubes functionalized with –OH groups did quite well. In this manner, this study advances titanium currently used in orthopedics to possess drug release behavior which can improve orthopedic implant efficacy. INTRODUCTION It is well known that current metal-based orthopedic implants (stainless steel, cobaltchromium alloys, and titanium alloys) clinically fail due to either biomechanical or biological reasons under physiological loading conditions. Statistics shows that the average functional lifetime of an orthopedic implant is only 10 to 15 years [1]. There is a high demand to extend the longevity of orthopedic implants considering that patients receiving implants are younger today than several decades ago. Obviously, the best solution to this problem is to develop a novel material (metal, composite, etc.) that satisfies all of the requirements for an orthopedic prosthesis, e.g., bone-like bulk properties and a highly active surface to promote cell growth.
Not surprisingly, today surface modification has b
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