Direct Methods for Measurements of Bulk and Surface Properties of Materials and Products


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Preamble Properties considered in this section include: component distribution, compressibility, consolidation, electrostatic characteristics, wettability, adhesion, cohesion, rheological (single or multiphase flow), particle size and morphology distribution, surface roughness, coating thickness, permeation, etc. Current State

• Some bulk properties are related to surrogate measurements (i.e., wettability, compressibility, various measurements of excipient/dosage form functionality, etc.).

• Particle size and particle size distribution analysis methods are available; however, none are particularly well tuned for pharmaceutically relevant systems Future Desired State

• Availability of reliable direct methods for measurement of material and product bulk and surface properties

• Properties measured should be both efficient and capable of being used to predict relevant behavior of the material Barriers

• In general each of these properties is difficult to define and measure in terms of fundamental properties. Some analytical techniques are borrowed from parallel materials industries without the benefit of specific development for pharmaceutically relevant materials.

• Particle interactions and process history confound measurements in mixtures and products

• Inferences made from surrogate measurements are dependent upon the accuracy of the models used and not necessarily grounded in performance attribute. In many cases users are unaware of the limitations of the methods themselves…

• Measurements pertaining to excipient function within a drug product are limited by numerous, inter-related phenomena, none of which have direct methods for measurement

• Many analytical techniques work well in idealized cases, but fail to provide useful quantities in real systems (i.e. shear cells for flow, Faraday cages for electrostatic characteristics). The fundamental properties that affect product quality attributes are, in general, unknown

• The magnitudes of values measured by current techniques seldom reflect the differences manifest as material behavior, making batch-to-batch, lot-to-lot, and supplier-to-supplier variability difficult to evaluate

• Indicators of compressibility (elastic moduli, fracture toughness) are very difficult to predict from crystallographic structure owing to the anisotropy of pharmaceutically relevant solids, and made more difficult as the complexity of mixing and processing is increased Page 11 of 76 Pharmaceutical Technology & Education Roadmap Revision 0

• Estimates of electrostatic character (triboelectrification potential) are often ill-defined owing to limited understanding about the origins and dissipation of electrostatic charge on organic solid particles. Techniques for measuring electrostatics are borrowed from other industries without any ability to modify for use with pharmaceutically relevant materials.

• Wettability, cohesion, and adhesion all rely on measurements of solid interfacial energies, which are difficult to obtain for real (non-ideal) samples. Measurements made on porous compacts, powders, polycrystals, etc. have limited meaning

• Disparate techniques for particle size analysis do not provide absolute/universal measurements. Morphological measurements are restricted to image analysis, which can be time consuming.

• Analytical methods for characterizing nano-particulate systems are limited. Distinguishing between amorphous systems and nano-crystals is difficult; rapid particle size analysis at the nano-scale is unavailable. Current methods may work, but only under idealized circumstances Research Needs

• Develop alternatives to Faraday Cage/Pail instrumentation for measurements of triboelectric properties (LONG-TERM/LOW PRIORITY)

• Develop relationships between mechanical properties and desired product quality attributes to better establish “real systems” (MID-TERM/HIGH PRIORITY)

• Better methodology and instrumentation for measurements of compaction/tableting indices (i.e. Hiestand Indices), compressibility and modes of consolidation (SHORTTERM/LOW PRIORITY)

• Replacements/advancements of existing particle sizing technologies that would span the enormous range of pharmaceutically relevant materials (nano through coarse particulate systems). Development of methodologies based on the needs of organic systems is needed (VERY LONG-TERM/MED PRIORITY)

• Advanced methodology for characterization of particle size, morphology and microstructure of dosage forms and process intermediates.(LONG-TERM/MED PRIORITY)

• Determining useful correlations between surface measurements and processability for porous and non-porous samples…some improvement of contact angle (LONGTERM/LOW PRIORITY)

• Investigate measurements of surface roughness that have relevance, meaning and usefulness (MID-TERM/LOW PRIORITY)

• Adaptation of coating thickness and adhesion measurements to pharmaceutical applications from parallel industries (SHORT-TERM/MED PRIORITY)

• “Mapping” or imaging composition and uniformity of mixtures and finished products (SHORT-TERM/HIGH PRIORITY) Resources

• A partnering strategy with equipment technology developers to facilitate development of instrumentation (enabling technologies) more appropriately designed for pharmaceutically relevant materials. For example the recent purchase of Fisher Page 12 of 76 Pharmaceutical Technology & Education Roadmap Revision 0 Scientific by Thermo could provide the opportunity to develop such a partnering arrangement.

• A formal program to identify instrumentation needs should be established to facilitate NIPTE’s lobby with instrument groups to produce appropriate instrumentation for measurements of mechanical properties.

• Allow NIPTE sponsored programs for instrument development (open grant process using NSF model); specifically adaptation of measurement techniques for pharmaceutically relevant materials. NIPTE could enable initial funding for instrumentation to be leveraged with other funding programs

• Partner with NIST to establish a useful, readily accessible database of critical mechanical properties and standard techniques for their measurement. Utilize data to become change agents for USP monographs and specifications (this last sentence may be more appropriate elsewhere – education?)

• Establish a NIPTE centre for instrumentation and expertise in sizing over the nanothrough coarse ranges for use by NIPTE institutions. The centre would ultimately provide both measurement services while developing research methodologies


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