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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 CaCO3 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.

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.

Silica nanoparticles have received great interest in biomedicine due to their high biocompatibility. In this study, we report the preparation of rare-earth ions integrated silica nanoparticles using rice husk biomass through a rapid and simple microwave-assisted combustion technique for making cost-effective bioimaging contrast agents. X-ray diffraction, energy-dispersive X-ray spectroscopy, and transmission electron microscope studies indicated that rare earth (europium/gadolinium) ions were strongly integrated with silica matrix via electrostatic interaction with environmental oxygen atoms. Europium-integrated silica nanoparticles showed a strong red fluorescence imaging capability that was attributed to 5D0→7F1 and 5D0→7F2 transitions of europium ions in the silica host matrix whereas gadolinium-integrated silica nanoparticles showed paramagnetism with T1-weighted magnetic resonance (MR) imaging capability that was ascribed to magnetic moment originated from a spin-orbit coupling of partially filled 4f electrons of gadolinium in the silica host matrix. In vivo toxicity evaluation using zebrafish embryos indicated that the rare-earth ions integrated silica nanoparticles are non-toxic. In view of these results, the prepared rare-earth ions integrated silica nanoparticles may be considered as potential materials in developing new bioimaging contrast agents at low cost.

We report the apatite forming ability, biocompatibility, drug adsorption/desorption behavior, antibacterial activity and photoluminescence property of flower-like hydroxyapatite (HA) nanostructure which was obtained from eggshell biowaste via a simple and rapid microwave conversion process. The obtained results from the above studies indicate that the prepared flower-like hydroxyapatite nanostructure can be a potential material for the development of drug delivery carriers, bone substitutes and bioprobes.