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Utilizing eggshells to synthesize a value added product like nanocrystalline hydroxyapatite (HA) has received a lot of attention from researchers since they are composed of CaCO 3 with biologically essential trace elements such as Mg, Si, etc. Different biomedical applications need HA with appropriate nanoscale characteristics like crystallinity, particle size, morphology, surface area, mesoporous nature, etc. The same can be achieved by tuning the reaction parameters, choosing a suitable mode of preparation and utilizing organic modifiers. Here, we report the rapid synthesis of eggshell derived HA in the presence different organic modifiers using a custom built microwave reactor employing the previously optimized parameters. The synthesis process is relatively rapid and gets completed in 5 min. The absence of an organic modifier yielded inhomogeneous size nanorods in the range of 40 – 600 nm. Ethylenediaminetetraacetic acid (EDTA) assisted synthesis resulted in a flower like 1.67 ± 0.12 μm sized HA. Whereas polyethylene glycol 6000 (PEG) and cetyltrimethylammonium bromide (CTAB) assisted synthesis produced aggregated nanorods of length 31 ± 8 and 68 ± 20 nm, respectively. While the synthesis with trisodium citrate dihydrate (TSC) resulted in needles of HA with typical length of 32 ± 8 nm. Presence of Na, Mg and Si trace elements are confirmed from the composition analysis. All the samples are found to be mesoporous in nature. The in vitro cell culture experiment carried out using fibroblast NIH 3T3 cell line clearly revealed equal or higher cell viability for the samples synthesized in presence of organic modifiers as compared to sample produced without organic modifier. Thus, from the present study we find that the synthesis of eggshell derived HA using different organic modifiers via a custom built microwave reactor can be a potential approach for the rapid preparation of precursor materials with suitable nanoscale characteristics for developing bone fillers, drug/protein delivery carriers, tissue engineering scaffolds, etc. [ABSTRACT FROM AUTHOR]

The high demand for synthetic hydroxyapatite for biomedical applications is on the rise day by day at the same time, there is a pressing need for producing hydroxyapatite (HA) at an economically viable cost to make the treatment affordable to everyone. In order to meet this objective, recycling of waste to value added products and cost effective methods suitable for scaling up the process are being attempted by researchers. In this report, an attempt has been made to optimize the parameters for the synthesis of nano HA from eggshell biowaste using well explored microwave method by employing a lab scale and pilot scale microwave reactors. Several parameters such as pH, organic modifier concentration and microwave power against volume of the reaction mixture has been studied from the view point of enhancing the yield of the product. The preliminary experiments done using lab scale reactor helped the optimization of pH and EDTA concentration. From the lab scale experiments, we found that the yield was directly proportional to the microwave power. The parameters optimized in the lab scale has been carried over to the pilot scale reactor. The results from pilot scale reactor revealed that although the microwave power from pilot scale reactor is considerably higher than that of the maximum power (900 W) of the lab scale reactor there is no significant difference in the yield of the product but the microwave irradiation time has reduced considerably which is almost in proportion to the power of the reactor. Parameters optimized from these batch processes will be useful for devising new scaling up process such as continuous flow methods. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the eggshell biowaste has been effectively utilized to produce flower-like hydroxyapatite nanostructure by using a simple and rapid microwave irradiation method with the help of ethylenediaminetetraacetic acid (EDTA) as a chelating agent. Conversion of eggshell into HA occurs via the formation of Ca–EDTA complex which subsequently reacted with phosphate under microwave irradiation. The obtained product is Mg containing b-type carbonated HA and it can be a potential material for biomedical applications. [Copyright &y& Elsevier]