Biomimetic calcium carbonate-gelatin composites as a model system for eggshell mineralization
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The composite nature of mineralized natural materials is achieved through both the microstructural inclusion of an organic component and an overall microstructure that is controlled by templating onto organic macromolecules. A modification of an existing laboratory technique is developed for the codeposition of a CaCO3–gelatin composite with a controllable organic content. First, calibration curves are developed to determine the organic content of a CaCO3–gelatin composite from infrared spectra. Second, a CaCO3–gelatin composite is deposited on either glass coverslips or demineralized eggshell membranes using an automated alternating soaking process. Electron microscopy images and use of the infrared spectra calibration curves show that by altering the amount of gelatin in the ionic growth solutions, the final organic component of the mineral can be regulated over the range of 1–10%, similar to that of natural eggshell.
I. INTRODUCTION
Biomineralized composites constitute the majority of the “hard” materials in nature. Different biomineralized composites exhibit different material properties using the same constituent materials, by influencing both the location and absolute amount of the organic components within the mineral while controlling the overall microstructure and local mineral polymorphs by templating onto organic macromolecules.1 It is this composite nature of included organic components and controlled microstructure that gives many biomineralized composites superior mechanical properties when compared with their constituent parts. Mollusks achieve a large fracture toughness2 of a calcium carbonate– organic composite (nacre) by depositing thin layers of chitin and protein between plates of aragonite giving a mineral of total organic content of less than 5%. Ascidians manipulate the tunic spicules of their skeleton by controlling the polymorphs of calcium carbonate deposited to have an amorphous calcium carbonate (ACC) core (stabilized using a protein content of less than 1%3) surrounded by a calcitic outer layer, which has a lower solubility in the seawater in which they live than the ACC core.3 In this way, organisms achieve the mechanical superiority of ceramic-like materials (on a per weight if not absolute basis) while being formed under ambient conditions from naturally abundant ingredients. The majority of work on replicating CaCO3 biomineralization has been conducted using either a vapor diffusion method4–6 or supersaturated solutions of Ca21 and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.379 J. Mater. Res., Vol. 27, No. 24, Dec 28, 2012
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CO2 3 ions for exploration of how a variety of proteins and other biological macromolecules affect crystal growth.7,8 Work by Munch et al.9 has focused on nacre replication by using preformed ceramic crystals and binding them with various polymeric or organic components to produce nacre-like microstructures. Yet, very little work has focused on the codeposi
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