Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs

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1063-OO05-04

Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs Steven Fox, Inessa Stanishevskaya, Shafiul Chowdhury, Shane Catledge, and Andrei Stanishevsky University of Alabama at Birmingham, Birmingham, AL, 35294 ABSTRACT Composite materials based on crystalline hydroxyapatite (HA) nanoparticles and biopolymers offer potential advantages in the fabrication of artificial scaffolds for bone tissue regeneration. This article presents the results of the ongoing study on the structure/mechanical property relationships in hydroxyapatite nanoparticle/gelatin-based composite materials prepared by the electrospinning and freeze-drying techniques. Maximum values of the Young’s modulus and hardness of such composites were obtained for 40% - 60% HA content in polymer by weight, whereas the maximum bending modulus was achieved for 20% HA. The observed trends of the mechanical behavior of the composites and their dependence on the material composition, microarchitecture, and environment are discussed and compared with those of HA/collagen composites. INTRODUCTION The growing need for resorbable bone substitutes and scaffolds require the development of materials that are both resorbable and bioactive, while structurally and mechanically similar to bone and stable for certain periods of time. Natural bone consists of up to 70% of mostly nanocrystalline hydroxyapatite (HA), while the rest is mostly collagen [1], and one can suggest that synthetic nanoHA/collagen composites could potentially be chemically and structurally the closest materials to resemble a low level of the bone microarchitecture. As the result, a large number of studies have been conducted to prepare HA/collagen composites and to analyze the resulting structures [2,3]. However, the data on the mechanical properties and property/structure relationships of HA/collagen composites remain scarce, in particular, because of the high cost of collagen and a need for relatively large samples for specific tests. Gelatin is prepared by the denaturation of collagen, it has similar properties, but it is much cheaper than collagen. It can also be used as a possible substitute for collagen in tissue engineering scaffolds [4,5]. In this study, we report the results of an investigation of the structure, surface morphology, and elastic properties of the nanoparticle loaded HA/gelatin composites prepared by freeze-drying and electrospinning techniques with 20% to 80 % (35% for the electrospun samples) HA nanoparticle loading, and compare the results with those of similar HA/collagen composites. EXPERIMENT HA nanoparticles were prepared by using the chemical reaction between Ca(OH)2 and H3PO4 in the presence of ammonia to maintain the solution pH at ~10. The resulting colloidal HA nanoparticles were washed in deionized (DI) water and methanol, and finally redispersed in DI water (for HA/gelatin freeze-dried composites), and in trifluoroethanol (TFE) or hexafluoropropanol (HFP) (for HA/gelatin or HA/collagen, respectively). The HA dispersions were mixed with cor

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