Abstract Spray drying is widely used in pharmaceutical manufacturing to produce microspheres from solutions or suspensions. The mechanical properties of the microspheres are reflected by the morphology formed in the drying process. In suspension drying, solids dissolved in the carrier liquid may form bridges between the suspended primary particles, producing a microsphere structure which is resistant against mechanical loads. Experiments with individual, acoustically levitated droplets were performed to simulate the drying of suspension droplets in a spray drying process. The suspensions studied consisted of a binary liquid mixture as the carrier liquid, and primary particles of suspended lactose material which is partially soluble in the liquid. The solubility of lactose was varied by the composition of the liquid mixture. The experiments revealed longer first and second drying stages for higher lactose solubility. Electron micrographs revealed the morphology of individual microspheres produced by drying in the levitator. Microspheres with only primary particles and no visible crust were obtained for low lactose solubility, whereas higher contents of dissolved lactose resulted in a more densely packed microsphere with crust formation. To quantify the hardness of individual microspheres, the maximum breaking force upon mechanical loading was measured for a range of varying suspension compositions. These measurements confirmed that densely packed structures with a thick crust reveal high mechanical strength. It was shown that, for primary lactose particles to be conserved in spray drying, the dissolved lactose mass loading Xd must be below 5.2%.

中文翻译：

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通过干燥声悬浮悬浮液滴产生的微球的机械强度

摘要 喷雾干燥广泛用于制药业，以从溶液或悬浮液中生产微球。微球的机械性能通过干燥过程中形成的形态来反映。在悬浮干燥中，溶解在载液中的固体可以在悬浮的初级颗粒之间形成桥，产生抗机械载荷的微球结构。对单个声悬浮液滴进行实验以模拟喷雾干燥过程中悬浮液滴的干燥。所研究的悬浮液由作为载液的二元液体混合物和部分可溶于液体的悬浮乳糖材料的初级颗粒组成。乳糖的溶解度因液体混合物的组成而异。实验揭示了更长的第一和第二干燥阶段以获得更高的乳糖溶解度。电子显微照片揭示了通过在悬浮器中干燥产生的单个微球的形态。由于乳糖溶解度低，获得了只有初级颗粒且没有可见外壳的微球，而溶解的乳糖含量越高，微球越密集，形成外壳。为了量化单个微球的硬度，对一系列不同的悬浮液组合物测量了机械负载时的最大断裂力。这些测量证实，具有厚壳的致密结构显示出高机械强度。结果表明，为了在喷雾干燥中保存初级乳糖颗粒，溶解的乳糖质量负载 Xd 必须低于 5.2%。