(613a) Comparing the Mechanical Properties of Chitosan Films Bound to Titanium Following Deposition, Neutralization, and Sterilization | AIChE

(613a) Comparing the Mechanical Properties of Chitosan Films Bound to Titanium Following Deposition, Neutralization, and Sterilization

Authors 

Martin, H. J. - Presenter, Center for Advanced Vehicular Systems, Mississippi State University
Schulz, K. H. - Presenter, Mississippi State University
Bumgardner, J. D. - Presenter, Herff College of Engineering, University of Memphis

            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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