Mechanical properties, such as strength, weight, and durability, are major factors in determining the metals chosen for use as implants.  Titanium is commonly used as an implant material because of its mechanical properties and because it is easily passivated, meaning it does not react with the physiological fluids surrounding the implant.  However, implants in general do not possess the ability to promote bone cell attachment and growth, which prevent the integration of the implant into the bone.  Bioactive materials attached to the implant surface can improve osseointegration [1].  Several bioactive materials are currently being examined [2-6]. 

            Chitin is the second most abundant form of polymerized carbon in nature and is found in the exoskeletons of shellfish and insects [7,8].  The de-acetylated form of chitin, known as chitosan, is currently being investigated as an implantable material.  Chitosan is cationic and has been shown to encourage the attachment and growth of bone cells [9].  Also, chitosan encourages proper bone formation because bone cells retain their desired cell shape, which influences cell-specific functions [10].  Chitosan is also being examined because it is non-toxic and the by-products of degradation are non-toxic [8,11]. 

            At Mississippi State University, four treatment combinations have been designed to attach chitosan to implant quality titanium.  These four treatment combinations consist of a surface treatment, either passivation or piranha, and a silane treatment, either aminopropyltriethoxysilane (APTES) or triethoxsilylbutyraldehyde (TESBA) [12,13].  The titanium treated with APTES is then treated with gluteraldehyde before bonding chitosan, resulting in a three step process [12].  A two step process occurs when chitosan is bonded to the titanium treated with TESBA [13].  X-Ray Photoelectron Spectroscopy (XPS) was run during each reaction step, which showed that more silane was deposited on the piranha treated titanium as compared to the passivated titanium [12,13].  XPS was also used on the final films, which demonstrated no significant differences between the films produced using the four treatment combinations [14].  The bulk properties, including hardness and elastic modulus, were unaffected by the treatment combinations [14].  Tensile testing was performed, which demonstrated that there was no statistical difference between the four treatment combinations, but did show that the bond strengths were significantly higher than previous results [7,14].

            Before any biological testing can be performed, sterilization of the coating must be performed [15,16].  Sterilization of chitosan has been shown to change some bulk properties, affecting the tensile strength of the chitosan film and contact angle [15,16].  However, these studies were only performed on free chitosan films, not attached to a titanium surface using APTES and TESBA [15,16].  Hardness and elastic modulus, two bulk properties that deal with how the polymer absorbs stress, have not been examined.  The research presented will cover the effects of hardness, elastic modulus, and contact angle of chitosan bonded to titanium, following the deposition of the chitosan coating, neutralization of the chitosan coating using sodium hydroxide, and sterilization of the chitosan coating using ethylene oxide.  This research will also present bond strength data which will be used to determine if the neutralization and/or the sterilization of the coating affected the silane linker molecules.

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[8]  G. Haipeng, Z. Yinghui, L. Jianchun, G. Yandao, Z. Nanming, Z. Xiufang.  Journal of Biomedical Materials Research, 52, 285-295, 2000.

[9]  C. Jarry, C. Chaput, A. Chenite, M.A. Renaud, M. Buschmann, J.C. Leroux.  Journal of Biomedical Materials Research (Applied Biomaterials), 58, 127-135, 2001.

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[12]  H.J. Martin, K.H. Schulz, J.D. Bumgardner, K.B. Walters.  Langmuir, 23, 6645-6651, 2007.

[13]  H.J. Martin, K.H. Schulz, J.D. Bumgardner, K.B. Walters.  Applied Surface Science, 254, 4599-4605, 2008.

[14]  H.J. Martin, K.H. Schulz, J.D. Bumgardner, J.A Schneider.  Thin Solid Films, 2008, In Press.

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[16]  P.R. Marreco, P.d.L. Moreira, S.C. Genari, A.M. Moraes.  Journal of Biomedical Materials Research Part B: Applied Biomaterials, 71B, 268-277, 2004.