University of Tasmania
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Synthesis methods for uniform particles of nano and micron sized apatite of various structures

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posted on 2023-05-27, 09:50 authored by Lawson, TS
Inherently brittle materials can be somewhat be toughened by changing the way they are constructed. However, the nanostructures seen in materials such as nacre and the toughness that derives from them have yet to be repeated in the laboratory with artificial materials. One obstacle to their construction was the limited availability of bulk amounts of regular anisometric carbonate or apatite particles. Therefore, the hypothesis of this work was to ask if it was feasible to make regular morphology nanoparticles of apatite in large amounts rapidly and at a low cost. This hypothesis was tested by undertaking three investigations. Investigations 1 and 2 utilised and extended the existing methods for making apatite, but did so in novel ways by combining the hydrothermal approach for producing regular particles with the precipitation approach for producing a high yield of particles. Investigation 3 then applied the insights gained from 1 and 2 to a method that used a domestic microwave to shorten the reaction time. Investigation 1 sought to test if the particles could be made which were regular and unidirectional in shape. This work found that adding citric acid to the reaction gel and then ramping the incubation temperature from room temperature to 85 !¬¨‚àûC increased the regularity of the crystals produced. It also found that regular particles could be produced, albeit at a lower level of regularity, without the addition of a chelate such as citric acid and this also substantially increased the yield. It was observed that mixing by shaking for a short time was simple to perform and yet still produced regular particles. The pH and temperature of the gel were also optimised in the method to maximise regularity. Investigation 2 tested if regular particles could be made in large quantities using precipitation. It was found that the hydrothermal method could be repeated with the same milder temperatures commonly used in the precipitation method and still produce particles with regularity. It was also possible to make regular particles of apatite without fluoride or a chelate added. Without the addition of these reagents, the yield was increased more than 10-fold. It was also found that heating the gel above 65 ¬¨‚àûC and cooling it for 10 minutes afterwards was the minimum required for crystals to form in the gel. Investigation 3 tested if regular particles of apatite could be made in less than one hour. It was found that adding reagents together by pouring was simpler and faster than adding with a burette. Some mixing was necessary, but stirring for long periods of time was not. It was also found that using a microwave could produce the same particles of apatite as conventional heating on a hot plate, but in 10 minutes rather than in 4 hours. With further optimisation, this turnaround time was reduced to 15 minutes for 8 mL of gel. Although this work was based on methods from the literature, it was uniquely focused on creating particles that were morphologically regular as well as tailorable. It sought to optimise fabrication of these particles by combining and applying aspects of the methods in the literature that were considered optimal, an approach not undertaken previously for making regular particles. Finally, it focused on the yield and turnaround time of the methods developed, which are aspects of apatite synthesis also rarely reported. Thus the aim of the thesis was to optimise the conditions necessary to prepare a large amount of apatite with particles whose shape and size were uniform. Towards this aim the Author achieved the following. A method was developed that was substantially shorter than that reported elsewhere; one that could completed in less than quarter of an hour; the method produced particles of low crystalline hydroxyapatite with a minimal variance in morphology at a yield higher than 80%; and the procedure to make this precipitate was performed with equipment that was readily accessible. It was found that the final microwave procedure developed was scalable; similar particles were produced when the reaction volume was increased 10-fold from 8 to 80 ml. This work has sought to refine and to shift the current research focus from making small amounts of apatite particles with di‚Äövú¬µerent shapes to making particles with tailored shapes in large quantities. It was hoped that some of the outcomes of this work will be of use in the construction of biocompatible monolithic materials for structural application within the body.


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