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Determination of Interfacial Amorphicity in Functional Powders
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.ORCID iD: 0000-0001-5894-7123
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2017 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 4, p. 920-926Article in journal (Refereed) Published
Abstract [en]

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 2 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 alpha-lactose monohydrate and completely amorphous spray dried lactose particles were compared to a partially amorphized alpha-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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017. Vol. 33, no 4, p. 920-926
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-203167DOI: 10.1021/acs.langmuir.6b03969ISI: 000393269700010Scopus ID: 2-s2.0-85011117083OAI: oai:DiVA.org:kth-203167DiVA, id: diva2:1081296
Note

QC 20170313

Available from: 2017-03-13 Created: 2017-03-13 Last updated: 2017-12-19Bibliographically approved
In thesis
1. Interfacial and material aspects of powders with relevance to pharmaceutical tableting performance
Open this publication in new window or tab >>Interfacial and material aspects of powders with relevance to pharmaceutical tableting performance
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tablets are the most common forms of drug administration. They are convenient to administer and easy to manufacture. However, problems associated with the adhesion of the powders to the tableting tools are common. This phenomenon is known as sticking and even though it has been well documented and studied, it remains poorly understood. The many factors that contribute to good performance of the powders make the sticking problem difficult to solve.

The goal of this study is to establish a relationship between the properties measured at the nanoscale to the overall tablet mechanical properties, tablet performance and powder pre-processing induced modifications. By using atomic force microscopy (AFM) we aim to develop an analytical method to characterize the mechanical and adhesive properties of the pharmaceutical powders at the nanoscale. Other methodologies such as scanning electron microscopy (SEM), thermal analyses (DSC, TGA) and tablet strength test were also used. The materials used in this study are commonly used excipients, a sticky drug and magnesium stearate (MgSt). Two different approaches offered by AFM were employed: sharp tip imaging and colloidal probe force measurements. Nano-mechanical properties of the materials were evaluated with a sharp tip cantilever showing that higher adhesion correlates with higher tablet cohesion and that both are significantly affected by the presence of MgSt. AFM characterization of the particle surface mechanical properties at the nanoscale was also used to detect the crystallinity and amorphicity levels of the materials. New approaches to presenting such data considering the particle heterogeneity and to track the dynamics of surface recrystallization are revealed. Adhesive interactions between a steel sphere and sticky and non-sticky powders were performed with the colloidal probe technique. Sticky materials presented a higher adhesion against the steel surface, and reveal the mechanism of stickiness.

This work thus contributes to the provision of predictability of the performance of formulations at an early stage of the development process.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 92
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:14
Keyword
atomic force microscopy, excipients, surface characterization, tableting, milling, amorphisation
National Category
Materials Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-203125 (URN)978-91-7729-293-7 (ISBN)
Public defence
2017-03-24, F3, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170315

Available from: 2017-03-15 Created: 2017-03-13 Last updated: 2017-12-18Bibliographically approved

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