Influence of fines on the surface energy heterogeneity of lactose for pulmonary drug delivery

The effects of the blending of lactose fines to the overall adhesion property of coarse α-lactose monohydrate carrier particles were investigated. Five samples, three of them commercial samples from DOMO (Lactohale® LH100, LH210, and LH250) whilst the other two are blends of LH210 and LH250, were studied. Characterisation included particle sizing, SEM, PXRD and IGC. Dispersive surface energy γSVd was determined using a finite concentration IGC method to obtain a distribution profile. The γSVd distribution of lactose crystals was found to vary from 40 to 48 mJ/m2. The unmilled coarse crystalline lactose sample (LH100) γSVd was lowest and showed less heterogeneity than the milled sample (LH250). Fines (LH210) were found to have the highest γSVd value. The samples with loaded LH210 were found to have a higher energy than LH100. The amount of LH210 in Blend 1 was not able to decrease surface energy heterogeneity, whereas sample Blend 2 showed adequate loading of fines to obtain a relatively homogeneous surface. Addition of fines resulted in an increase in γSVd, suggesting that coarse lactose surfaces were replaced by surfaces of the fines. Increasing the loading of fines may result in a more homogeneous surface energy of lactose particles.