I have synthesized nano-hydroxyapatite particles via wet chemistry precipitation of a Ca-PO4 solution. In water and PBS, these crystals tend to clump together in aggrigates up to 20-30 microns. The only way that I can get them to disperse is to sonicate them in either Hexafluoro-2-propanol or Dimethylformamide. I have also tried adding acid groups to the surfaces of the particles, such as 12 aminododecanoic acid and dodecanedioic acid, but so far all of my attempts have been unsuccessful. Are there any simple methods to get a well dispersed solution of nano-hydroxyapatite in water or PBS? I was thinking I would continue to try adding other molecules to the surface of the crystals, but I am unsure which direction to go in. Any insight would be appreciated.