Metal implants are composed of metals that are light-weight and strong, such as titanium or titanium alloys.  These metal implants, however, do not possess the ability to integrate into the surrounding bone.  This lack of osseointegration is a major issue with metal implants.  One way to encourage osseointegration is to use a bioactive material, or a material that has been shown to promote bone cell attachment and growth [1].  These bioactive materials can be made of ceramics, polymers, and biological molecules [2-6]. 

            One bioactive polymer currently being investigated as an implant coating is chitosan, a de-acetylated form of chitin [7].  Chitin is found in the exoskeletons of shellfish and insects, leading it to be the second most abundant form of polymerized carbon in nature [7,8].  Chitosan is valuable as an implant coating because it is non-toxic [9].  The degradation by-products of chitosan also resemble the by-products of normal cellular metabolism, making chitosan by-products non-toxic as well [8].  Chitosan has also been shown to be antibacterial and bacteriostatic [10,11].  Finally, chitosan is cationic and has been shown to encourage attachment and growth of bone cells, which promotes osseointegration [12].

            At Mississippi State University, we are investigating ways to bound chitosan to implant quality titanium.  Previous research used a three step reaction in an aqueous solution, which lead to poorly bound films.  In our research, two different reaction schemes were created, using toluene as the solvent instead of an aqueous solution [13,14].  A three step reaction scheme using 3-aminopropyltriethoxysilane (APTES) followed by gluteraldehyde was initially used to bond chitosan to titanium [13].  In order to reduce the number of steps necessary to bond chitosan, a two step reaction scheme was designed using triethoxsilylbutyraldehyde (TESBA) as the linker molecule [14]. 

            X-Ray Photoelectron Spectroscopy (XPS) was used to document the binding of triethoxsilylbutyraldehyde to passivated titanium and piranha treated titanium.  XPS was also used to demonstrate that the titanium treatment and the silane molecules did not affect the chitosan films.  By examining elements expected to change, including but not limited to silicon and titanium, it was demonstrated that more TESBA was bound to the piranha treated titanium surface as compared to the passivated titanium surface [14].  Silicon, in the form of Si-O-Si, demonstrated that a polysiloxane layer formed across the surface of the piranha treated titanium surface, binding adjacent TESBA molecules to one another [14].  However, more SiO₃ was seen on the surface of the passivated titanium surface, indicating that a bond between adjacent TESBA molecules to form a polysiloxane layer did not form as easily as on the piranha treated surface [14].  The titanium peak on the piranha treated surface was significantly less than on the passivated surface following the TESBA deposition, indicating that more TESBA was bound to the piranha treated surface as compared to the passivated surface [14].  XPS also demonstrated that there were no significant differences between the chitosan films on the four treatment combinations, indicating that the chitosan films were not affected by APTES, TESBA, passivated titanium, or passivated titanium [13,14].  Overall, XPS demonstrated that more TESBA was bound to the piranha treated titanium surface than the passivated titanium surface.

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[2]  Y. Yang, C.M. Agrawal, K.H. Kim, H. Martin, K. Schulz, J.D. Bumgardner, J.L. Ong.  Journal of Oral Implantology, 29, 6, 270-277, 2003.

[3] R.J. Friedman, T.W. Bauer, K. Garg, M. Jaing, Y.H. An, R.A. Draughn.  Journal of Applied Biomaterials.  6, 231-235, 1995.

[4] A. Nanci, J.D. Wuest, L. Peru, P. Brunet, V. Sharma, S. Zalzal, M.D. McKee.  Journal of Biomedical Materials Research, 40, 324-335, 1998.

[5] D. A. Puleo.  Journal of Biomedical Materials Research, 37, 222-228, 1997.

[6] D. A. Puleo.  Journal of Biomedical Materials Research, 29, 951-957, 1995.

[7]  J.D. Bumgardner, R. Wiser, P.D. Gerard, P. Bergin, B. Chestnutt, M. Marini, V. Ramsey, S.H. Elder, J.A. Gilbert.  Journal of Biomaterials Science: Polymer Edition, 14, 5, 423-438, 2003.

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

[9]  M. Prasitsilp, R. Jenwithisuk, K. Kongsuwan, N. Damrongchai, P. Watts. Journal of Materials Science: Materials in Medicine, 11, 773-778, 2000.

[10]  A.K. Singla, M. Chawla. Journal of Pharmacy and Pharmacology, 53, 1047-1067, 2001.

[11]  R.A.A. Muzzarelli, R. Tarsi, O. Filippini, E. Giovanetti, G. Biagini, P.E. Varaldo.  Antimicrobial Agents and Chemotherapy, 34, 2019-2023, 1990.

[12]  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.

[13]  H.J. Martin, K.H. Schulz, J.D. Bumgardner, K.B. Walters.  Langmuir, 2007, In Press.

[14]  H.J. Martin, K.H. Schulz, J.D. Bumgardner, K.B. Walters.  Langmuir, 2007, Under Review.