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Tablet mechanics depend on nano and micro scale adhesion, lubrication and structure.

International journal of pharmaceutics (2015-04-07)
Maria Badal Tejedor, Niklas Nordgren, Michael Schuleit, Mark W Rutland, Anna Millqvist-Fureby
ABSTRACT

Tablets are the most convenient form for drug administration. However, despite the ease of manufacturing problems such as powder adhesion occur during the production process. This study presents surface and structural characterization of tablets formulated with commonly used excipients (microcrystalline cellulose (MCC), lactose, mannitol, magnesium (Mg) stearate) pressed under different compaction conditions. Tablet surface analyses were performed with scanning electron microscopy (SEM), profilometry and atomic force microscopy (AFM). The mechanical properties of the tablets were evaluated with a tablet hardness test. Local adhesion detected by AFM decreased when Mg stearate was present in the formulation. Moreover, the tablet strength of plastically deformable excipients such as MCC was significantly decreased after addition of Mg stearate. Combined these facts indicate that Mg stearate affects the particle-particle bonding and thus elastic recovery. The MCC excipient also displayed the highest hardness which is characteristic for a highly cohesive material. This is discussed in the view of the relatively high adhesion found between MCC and a hydrophilic probe at the nanoscale using AFM. In contrast, the tablet strength of brittle materials like lactose and mannitol is unaffected by Mg stearate. Thus fracture occurs within the excipient particles and not at particle boundaries, creating new surfaces not previously exposed to Mg stearate. Such uncoated surfaces may well promote adhesive interactions with tools during manufacture.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
D-Mannitol, ≥98%
Sigma-Aldrich
D-Mannitol, ACS reagent
Sigma-Aldrich
Magnesium stearate, technical grade
Sigma-Aldrich
D-Mannitol, meets EP, FCC, USP testing specifications
Sigma-Aldrich
D-Mannitol, suitable for plant cell culture
Sigma-Aldrich
D-Mannitol, BioXtra, ≥98% (HPLC)
Sigma-Aldrich
D-Mannitol, BioUltra, ≥99.0% (sum of enantiomers, HPLC)
Sigma-Aldrich
Magnesium stearate, puriss., meets analytical specification of Ph. Eur., BP, ≥90% stearic and palmitic acid basis, ≥40% stearic acid basis (GC), 4.0-5.0% Mg basis (calc on dry sub.)