Development of dry powder coating technique for pellets

Abstract

Dry powder coating is an innovative coating method utilizing only dry polymer powder without applying any liquid throughout the process. Objectives of this work were to study the feasibility of this dry powder coating technique and to investigate the parameters that affect polymer adhesion on core material (pellets). The parameter studied were polymer application rate, loading amount of polymer, pellet size, polymer size, surface roughness and moisture content of core pellets and the possibility of secondary layer coating. Propranolol hydrochloride core pellets were prepared by extrusion-spheronization technique and were coated with Eudragit® E polymer powder using the powder coating technique in a conventional coating pan. Eudragit® E polymer powder had low glass transition temperature (45-50 ℃) and good adhesion property. Physical characteristics and drug release characteristics of core and coated pellets were investigated. It was found that higher polymer loading could improve the smoothness of the coating surface. At a constant pellet size, smaller polymer particle size was proven to promote better adhesion, better heat dissipation and more uniform film distribution than larger particles. The results also showed that the more surface roughness the core pellets exhibited, the higher coating efficiency was observed. And higher moisture content on surface of core pellets might result in better polymer adhesion. It was possible to apply the secondary coating layer with an appreciable increase in film thickness. However, the process induced undesirable pellet aggregation due to thermosoftening of the primary coating material. The solid state characterization of core and coated pellets was also investigated by Fourier transform infrared spectroscopy (FTIR), x-ray powder diffractometry (XRPD) and differential scanning calorimetry (DSC). Solid state characteristics of every component remained unchanged. Also, the results indicated that incompatibility between the drug and polymer or other excipients in the formulation did not take place. Thus, with a minor process adjustment, this dry powder coating technique may be considered as an alternative method in the future for coating core materials without the use of water or environmentally hazardous organic solvents involved.