Breakage behaviour of different materials—construction of a mastercurve for the breakage probability

Effect of crystallisation conditions and feedstock morphology on the aerosolization performance of micronised salbutamol sulphate

Salbutamol sulphate (SS) used in dry powder inhalers requires drug particles in the respirable size range of 1-5 μm to achieve a suitable therapeutic effect. The aim of this study was therefore to determine strategies for controlling drug substance characteristics pre and post-crystallisation to facilitate the production of micronised SS with desirable particle attributes for optimal delivery as an inhaled aerosol. SS batches were crystallised using an antisolvent method to produce a range of crystal morphologies. Air jet milling was then used to reduce the size of crystallised SS particles. Starting materials and micronised batches of SS were characterised in the solid state using a range of techniques with subsequent assessment of aerosol properties. Assessment of the aerodynamic characteristics of micronised SS delivered by DPI (without any carrier) indicated that fine particle fraction and emitted dose as a percentage of the total recovered dose were dependent on the quality attributes of the micronised SS, which were directly linked to the degree of imperfections and the morphology of the crystalline feedstock used in micronisation. Aerosolization performance of micronised SS can be optimised by manipulation of feedstock characteristics through crystal engineering and through definition of optimal processing conditions for micronisation.

Comminution of carbohydrate and protein microparticles on firing in a ballistic powder injector

The comminution of various powders produced by either spray-freeze-drying (SFD) or spray-drying (SD) on firing in a Ballistic powder injector could be evaluated quantitatively using light microscopic particle imaging. SFD lactose was damaged much less than SFD mannitol and was caused by greater mechanical strength and lower acceleration. SD lactose or mannitol showed much reduced comminution because of their low porosity. SFD lactose/mannitol/dextran 10 kDa formulations also showed less low comminution. The inclusion of catalase further reduced damage on firing. The extent of comminution on firing was found to be related to microparticle surface structure and porosity which influences both mechanical strength and acceleration.

Development of a novel approach towards predicting the milling behaviour of pharmaceutical powders

A novel approach has been developed for evaluating the milling behaviour of pharmaceutical powders based on their material and mechanical properties obtained by single particle impact testing. Milling behaviour of two widely used pharmaceutical excipients, namely microcrystalline cellulose and alpha-lactose monohydrate has been analysed in an oscillatory single ball mill. It is found that the milling behaviour of these two powders can be described by analogy with a first-order rate process except for alphaLM at 18Hz of milling frequency. At the same time, single particle impact testing has been used to infer the material properties that are related to breakage. The milling rate of these powders is found to correlate well with the parameter representing the material properties including the particle size, density, hardness and critical stress intensity factor. This provides the basis for a novel approach towards analyzing the milling behaviour of a material based on a simple and reliable approach.

Particle adhesion force distributions on rough surfaces

The effect of roughness on adhesion force distribution was studied in the gas phase. Spherical gold particles with diameters between 5 and 20 microm were generated in a flame process and glued onto atomic force microscope (AFM) cantilevers directly after. Nanostructured substrates with defined roughness were produced by a dip-coating process. The geometry of the adhering partners was determined by AFM imaging, and the adhesion force was measured with the AFM. Depending on the roughness of the particles and the substrates, three types of distribution functions can be identified; two of them can be explained with a simple model. The obtained adhesion force distributions not only agree with those experimentally recorded in previous studies of commercially important powders (e.g., alumina, toner, and gold on different substrates) but also agree with distributions reported in the literature.