Spray drying has been used in the production of fine powders from emulsions for many years, but it is not a process in which most people associate the production of microspheres.? This journal article shows how the authors were able to produce highly spherical microspheres in the 2-10um range by controlling the levels of Chitosan and crosslinking agents used.
The quality of the microspheres that were produced, as seen the the attached SEM micrograph.
How the process variables did not affect the zeta potential of the microspheres produced (Table 4 below), and how the size can be varied by varying the concentrations of Chitosan or the Molecular weight (MW).
During some research on PLGA microspheres we found this interesting article published in European Cells and Materials Vol 7 Suppl 2. 2004 (pages 11-12).?? They were able to achieve a significant change in the zeta potential of their microspheres just by increasing the dosage of Chitosan.?? The authors conclusions and a graph of their data follow.
Discussion and Conclusions by the authors:
The increase in zeta potential from ?70.8 mV (chitosan-free PLGA particles) to +20.5 mV with increasing chitosan concentrations in the W2-phase used for particle preparation strongly suggests that the polycationic chitosan was firmly adsorbed to the particle surface. This finding was confirmed by X-ray photoelectron spectroscopy (data not shown). The coupling of biotin via a NHS-PEGlinker showed that the amino groups of? chitosan represent suitable sites for covalent bioconjugation of different ligands. The process allows the production of particles with a mean diameter between 1 and 10 um, a useful size range for the phagocytosis by? phagocytes like dendritic cells or macrophages.