Rheological behavior of needle-like hydroxyapatite nano-particle suspensions

We describe here the preparation and rheological behavior of stable suspensions of needle-like hydroxyapatite nanoparticles dispersed in organic media, including methylethylketone (MEK), polycaprolactone (PCL) solutions in MEK, and PCL melt. These suspensions are the main ingredients in preparing certain biodegradable orthopedic materials that have some advantages over traditional implants. Rheological properties were experimentally determined at shear rates approaching those used in the processing methods such as roll coating, extrusion, and pultrusion. Analysis of the flow behavior suggests possible shear alignment at high Pe number (Pe ≈ 6,000). The linear viscoelastic properties and the paste-like behavior suggest the formation of a network as the particle content increases. These results are critical in designing a process for making composite materials containing highly oriented anisotropic particles.