163ah The Effects of Different Silanes and Metal Surface Treatments on the Binding of Chitosan as Investigated by Mechanical and Biological Testing

Holly J. Martin, Mississippi State University, 330 Swalm President's Circle, Mississippi State, MS 39740, Keisha Walters, Dave C. Swalm School of Chemical Engineering, Mississippi State University, 330 Swalm Chemical Engineering Building, P.O. Box 9595, Mississippi State, MS 39762, Kirk H. Schulz, Bagley College of Engineering, Mississippi State University, Mississippi State, MS 39762, Joel D. Bumgardner, Biomedical Engineering Department, Herff College of Engineering, University of Memphis, Memphis, TN 38152, and Judith A. Schneider, Department of Mechanical Engineering, Mississippi State University, Mississippi State, MS 39740.

            Implants are commonly made from strong, light, durable metals, such as commercially pure titanium and titanium alloys.  These metals are usually chosen based on the lack of interaction between the body and the surface because of the formation of a passive oxide layer.  However, interactions do occur between the implant surface and the bone cells surrounding the implant.  These interactions include the necrosis, or death, of the surrounding tissue and the leeching of metal ions, both grouped in a broad category of biocorrosion.  One way to prevent biocorrosion is bond a biocompatible material onto the surface of the metal implant before the implant is placed in the body.  Currently, coatings of several different variations are being investigated, including calcium phosphate [1], hydroxyapatite [2], and biological molecules such as proteins and enzymes [3-5].

            Two of the most biologically compatible materials, calcium phosphate and hydroxyapatite, which are precursors to bone formation, have been investigated as possible coatings.  However, these materials are considered ceramics.  By their nature, these materials are very brittle and are easily sheared or flaked off when the implant is placed into bones within the human body [6].  This shearing and flaking will ultimately result in pitting and crevice corrosion, leading to the complete and catastrophic failure of these implants [7]. 

            One method to prevent the flaking and shearing of the coating is to use a biologically compatible polymer, which can withstand the stresses incurred during implantation.  The material being investigated at Mississippi State University is chitosan, a de-acetylated form of chitin, which is produced in biological systems.  Chitin is the second most abundant form of polymerized carbon in nature [8] and is primarily found in the exoskeletons of arthropods [9] and fungi [10].  Chitosan is a cationic copolymer of glucosamine and N-acetylglucosamine [11] and is considered biocompatible because specific enzymes can degrade it [9].  Currently, chitosan is being investigated for use as implant material coatings, wound dressings, drug delivery systems, and bone implants [11]. 

            At Mississippi State University, we have been investigating four different treatment combinations to bind chitosan to commercially pure titanium, grade 4.  The chemical, mechanical, and biological features of these combinations were investigated to determine the highest quality film produced.  Atomic Force Microscopy was used to determine the roughness and thickness of the chitosan films.  Nanoindentation was used to determine the hardness of the films, while Scratch-Testing was performed to determine the resistance to shearing of the different treatment combinations.  In-Vitro biological testing was performed to determine the interaction of cells to the different films and chemicals used.  

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