Influence of Mineral -Polymer Interactions on Molecular Mechanics of Polymer in Composite Bone Biomaterials
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Influence of Mineral -Polymer Interactions on Molecular Mechanics of Polymer in Composite Bone Biomaterials Rahul Bhowmik, Kalpana S Katti, and Dinesh R Katti Civil Engineering, North Dakota State University, CIE201, Fargo, ND, 58105 ABSTRACT Nanocomposite bone materials of polymers and hydroxyapatite are widely investigated for bone replacement. The mechanical properties of the composites determine the use of these as implant materials. The molecular phenomenon at the interface between mineral and polymer is known to have significant contribution on overall mechanical response of composites. Understanding behavior of interfaces under applied load, and the load transfer mechanisms will lead to development of superior biomaterial composites with desired properties. We have performed Steered Molecular Dynamics (SMD) simulations on the composite system consisting of hydroxyapatite and polyacrylic acid. Our simulations describe the detailed molecular mechanisms responsible at the interface with applied load. Our SMD simulations also indicate that the polymer shows significant changes when it interacts with the mineral. The loaddeformation behavior of polymer has shown that the polymer is stiffer when it is interacting with mineral. The binding and unbinding events are also calculated during load transfer in polymer. This work describes specific molecular mechanism responsible for mechanical behavior in composites used as bone biomaterials.
INTRODUCTION Composite bone biomaterials are the synthetic materials consist of two or more phases. Composite biomaterials which consist of mineral (hard phase) and polymer (soft phase) have shown much promise for total bone replacement [1]. The minerals are rigid with high hardness whereas the polymers are flexible with high tensile strength. The mechanical properties of different components in composites are generally different from individual constituents when they are not in composites. It is observed from experimental observation that the interfaces between different components affect the overall mechanical response of composites. Therefore, understanding the interfaces between mineral and polymeric phases will lead to design new composite biomaterials with desired properties. It has been shown that Molecular Dynamics (MD) and Steered MD (SMD) simulations are useful techniques for studying the interfaces in composites [2]. In this present work, we have used the above mentioned techniques to study the interfaces between hydroxyapatite (mineral phase) and polyacrylic acid/polycaprolactone (polymeric phase). In order to perform the MD/SMD simulations, it is necessary to identify the potential function (force field) which provide different structural parameters, thermodynamic quantities, etc. of the modeled structures with reasonable accuracy. We have shown in our earlier studies that CHARMm force field provides better details of the interfaces between the components in composites [3]. We have used CHARMm force filed to study the interfaces between hydroxyapati
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