SP Chemistry, Materials and Surfaces, SP Technical Research Institute of Sweden , Box 5607, SE-114 86 Stockholm, Sweden.
Division of Surface and Corrosion Science, KTH Royal Institute of Technology , Drottning Kristinas väg 51, SE-100 44 Stockholm, Sweden.
Langmuir. 2017 Jan 31;33(4):920-926. doi: 10.1021/acs.langmuir.6b03969. Epub 2017 Jan 13.
The nature of the surfaces of particles of pharmaceutical ingredients, food powders, and polymers is a determining factor for their performance in for example tableting, powder handling, or mixing. Changes on the surface structure of the material will impact the flow properties, dissolution rate, and tabletability of the powder blend. For crystalline materials, surface amorphization is a phenomenon which is known to impact performance. Since it is important to measure and control the level of amorphicity, several characterization techniques are available to determine the bulk amorphous content of a processed material. The possibility of characterizing the degree of amorphicity at the surface, for example by studying the mechanical properties of the particles' surface at the nanoscale, is currently only offered by atomic force microscopy (AFM). The AFM PeakForce QNM technique has been used to measure the variation in energy dissipation (eV) at the surface of the particles which sheds light on the mechanical changes occurring as a result of amorphization or recrystallization events. Two novel approaches for the characterization of amorphicity are presented here. First, since particles are heterogeneous, we present a methodology to present the results of extensive QNM analysis of multiple particles in a coherent and easily interpreted manner, by studying cumulative distributions of dissipation data with respect to a threshold value which can be used to distinguish the crystalline and amorphous states. To exemplify the approach, which is generally applicable to any material, reference materials of purely crystalline α-lactose monohydrate and completely amorphous spray dried lactose particles were compared to a partially amorphized α-lactose monohydrate sample. Dissipation data are compared to evaluations of the lactose samples with conventional AFM and SEM showing significant topographical differences. Finally, the recrystallization of the surface amorphous regions in response to humidity was followed by studying the dissipation response of a well-defined surface region over time, which confirms both that dissipation measurement is a useful measure of surface amorphicity and that significant recrystallization occurs at the surface in response to humidity.
药物成分、食品粉末和聚合物颗粒的表面性质是决定它们在例如片剂、粉末处理或混合性能的决定性因素。材料表面结构的变化将影响粉末混合物的流动性能、溶解速率和可压性。对于结晶材料，表面非晶化是一种已知会影响性能的现象。由于测量和控制非晶度水平很重要，因此有几种表征技术可用于确定加工材料的整体非晶含量。目前，只有原子力显微镜 (AFM) 可以对表面的非晶度程度进行特征描述，例如通过研究颗粒表面的纳米级机械性能。AFM PeakForce QNM 技术已用于测量颗粒表面能量耗散 (eV) 的变化，这揭示了由于非晶化或再结晶事件而发生的机械变化。这里介绍了两种用于非晶度表征的新方法。首先，由于颗粒是不均匀的，我们提出了一种方法，通过研究相对于可用于区分晶态和非晶态的阈值的耗散数据累积分布，以连贯且易于解释的方式呈现对多个颗粒进行广泛 QNM 分析的结果。为了举例说明该方法，该方法通常适用于任何材料，我们将纯晶态 α-乳糖一水合物和完全非晶态喷雾干燥乳糖颗粒的参考材料与部分非晶化的 α-乳糖一水合物样品进行了比较。耗散数据与常规 AFM 和 SEM 对乳糖样品的评估进行了比较，显示出显著的形貌差异。最后，通过研究一段时间内定义明确的表面区域的耗散响应，跟踪了表面非晶区域对湿度的再结晶情况，这证实了耗散测量是表面非晶度的有用度量，并且在湿度作用下表面确实会发生明显的再结晶。
