Evaluation of pharmaceutical beam bending tests using double-exposure holographic interferometry

Abstract

Cantilever, three- and four-point bending methods used in the determination of intrinsic elasticity of pharmaceutical powders were evaluated with double-exposure holographic interferometry. Microcrystalline cellulose, dicalcium phosphate dihydrate and α-lactose monohydrate were compressed to rectangular beams and the bending measurements of samples captured on holographic images, which were evaluated by calculating the Young's modulus values for both the upper and lower surfaces of the samples. Several methods were used in the moduli calculations. It was found that the four-point bending method seemed to be best for determining results of the elasticity of soft pharmaceutical powders. The superiority of this method was due to the fact that it resulted in the most homogeneous bending along the beams. The results of the three-point bending method were, however, in good agreement with those of the four-point bending method. On the other hand, the cantilever method was observed to be unsuitable for pharmaceutical powders. Inspection of the holograms revealed that the integrity of α-lactose sample beams was inadequate for moduli evaluation. This would not have been noticed with conventional displacement measurements.