(486d) Surface Science Studies on the Effects of Different Silanes and Metal Surface Treatments on the Binding of Chitosan, a Biopolymer

            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.

[1]  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

[2] 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.

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

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

[5] 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.

[6] 3-aminopropyltriethoxysilane, Material Safety Data
Sheet.  Alfa Aesar.  Retrieved April 27^th, 2006.  Last Edited March 28^th,
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

[8] J. Duchet, B. Chabert, J.P. Chapel, J.F. Gerard, J.M.
Chovelon, N. Jaffrezic-Renault. Langmuir, 13, 2271-2278, 1997.

[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.