“…Nowadays, one of the most promising approaches is hydroxyapatite synthesis from hen egg-shell sources due to the mimetic composition and structure of the carbonated apatite obtained compared with human bone [ 36 , 37 , 38 ]. Such carbonated apatite is prepared using several routes, including dry methods (solid state [ 39 ] and mechanochemical synthesis [ 40 ]), wet methods (precipitation [ 41 , 42 , 43 ], hydrolysis, sol–gel [ 44 ], emulsion [ 45 ], sonochemical [ 46 ], hydrothermal [ 47 , 48 ], and solvothermal [ 49 , 50 ]), or high-temperature methods (pyrolysis, combustion, and microwave heating [ 50 ]). Each of the abovementioned methods induces different morphologies of micro- and nano-size HA particles: rods [ 51 , 52 ], sheets [ 53 ], spheres [ 54 ], wires [ 55 ], fibers [ 56 ], flower, worm, hexagonal prism, platelet, lath, strip, dandelion, chrysanthemum, rosette, or spheres [ 20 ].…”