Purification of biomimetic apatite-based hybrid colloids intended for biomedical applications: A dialysis study

The field of nanobiotechnology has lately attracted much attention both from therapeutic and diagnosis viewpoints. Of particular relevance is the development of colloidal formulations of biocompatible nanoparticles capable of interacting with selected cells or tissues. In this context, the purification of such nanoparticle suspensions appears as a critical step as residues of unreacted species may jeopardize biological and medical outcomes, and sample purity is thus increasingly taken into account by regulatory committees. In the present work, we have investigated from a physico-chemical point of view the purification by dialysis of recently developed hybrid colloids based on biomimetic nanocrystalline apatites intended for interacting with cells. Both Eu-doped (2mol.% relative to Ca) and Eu-free suspensions were studied. The follow-up of the dialysis process was carried out by way of FTIR, TEM, XRD, pH and conductivity measurements. Mathematical modelling of conductivity data was reported. The effects of a change in temperature (25 and 45°C), dialysis medium, and starting colloid composition were evaluated and discussed. We show that the dialysis method is a well-adapted and cheap technique to purify such mineral-organic hybrid suspensions in view of biomedical applications, and we point out some of the characterization techniques that may prove helpful for following the evolution of the purification process with time.