Control of Pore Size of the Bubble-Template Porous Carbonated Hydroxyapatite Microsphere by Adjustable Pressure

Flowerlike porous B-type carbonated hydroxyapatite (CHAp) microspheres have been synthesized by a novel bubble-template route. Their pore sizes can be well regulated in a wide range from microscale to nanoscale by smartly constructing a kind of CO2 bubble as a template and precisely adjusting the system pressure. We studied the formation of a porous structure of CHAp microspheres and the effect of the system pressure on their morphologies. Most of all, the control of the pressure over the pore sizes of bubble-template porous CHAp microspheres was investigated. The results suggested that the gathering and growth of the CO2 bubbles generated the formation of the porous structure of CHAp microspheres, and along with the increase of system pressure, the surface of the microsphere got denser and the flakes, which assembled the porous structure, became smaller. In addition, with the increased pressure, the average pore sizes of bubble-template CHAp microspheres gradually decreased from microscale to nanoscale. Furthermore, the relation between the pressure P and the pore size r was derived from the Laplace equation, the Kelvin equation, and the Clapyeron equation.