Implants are commonly made from commercially pure titanium and from different types of metal alloys, which include titanium combined with aluminum and vanadium and cobalt-chromium. These metals are chosen for their strength, weight, and formation of oxide layers to prevent interaction between the implant surface and the bone cells surrounding these implants. However, interactions do occur, in the form of leeching of metal ions and necrosis of the surrounding tissue due to friction. One method to prevent this leeching and necrosis is to bond a biocompatible coating onto the surface of the implant material. Currently, several different coatings are being used to improve the metal surface-bone interface, which include calcium phosphate [1] and biological molecules, such as proteins [2] and enzymes [3,4].
One major technique to bond a biologically compatible material to metal is the use of silanes, most commonly 3-aminopropyltriethoxysilane. A linker molecule, commonly gluteraldehyde, is used to create a different terminal group if needed [2-5]. Poor quality films can be produced using an aqueous solution, as the use of water has been shown to cause the release of the terminal group in the form of nitrogen oxides [6] and the formation of polysiloxanes [7, 8]. To prevent the removal of the terminal group and polysiloxane formation, toluene was used as the solvent, instead of water.
At Mississippi State University, we are investigating methods to bind chitosan to the surface of commercially pure titanium, grade 4. Chitosan, a de-acetylated form of chitin, is biologically produced and is a cationic copolymer of glucosamine and N-acetylglucosamine [9]. It is considered biocompatible and is being tested for use as wound dressings, bone implants, and drug delivery systems [9]. To improve the adhesion of the chitosan to titanium, passivation as guided by ASTM F86 and a piranha treatment to increase the Ti-OH groups present were investigated. Two silane molecules were also chosen, 3-aminopropyltriethoxysilane and triethoxsilylbutyraldehyde,to further test the ability to adhere chitosan to the surface.
The treatment combinations were then examined using X-Ray Photoelectron Spectroscopy (XPS) to investigate the chemical properties. Preliminary results suggest that the silane bonds more frequently with the piranha treated metal as compared with the passivated metal, demonstrated by a smaller titanium elemental peak. This preliminary finding indicates that the piranha treatment converts the oxide layer from the Ti2O3 present on the passivated metal to TiOH on the piranha treated metal, thereby providing more binding sites for the silane molecules, irregardless of the silane compound. Further results from the XPS studies will also be discussed.
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[6] 3-aminopropyltriethoxysilane, Material Safety Data Sheet. Alfa Aesar. Retrieved April 27th, 2006. Last Edited March 28th, 2001. Retrieved from http://www.setonresourcecenter.com/MSDS/Alfa/Docs/wcd0004e/wcd04ebf.pdf
[7] P.A. Heiney, K. Gruneburg, J. Fang. Langmuir, 16, 2651-2657, 2000
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