(118c) Surface Science Studies on the Effects of Triethoxsilylbutyraldehyde and Two Metal Treatments to Bond Chitosan

            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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of Oral Implantology, 29, 6, 270-277, 2003.

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