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Tablets & Capsules September 2019 23 You can optimize the lubricant amount by conducting a compaction profile study in which you make a number of tablets using incrementally increasing compression forces and record the ejection forces for each. To ensure accurate data, the ejection transducer must be a "full- travel" design, especially if the press is one on which you change the tablet thickness and compression force by adjusting the lower compression roller. A full-travel ejec- tion design will provide an accurate millivolt signal across the full range of the ejection sensor. Some press manufac- turers use a button load cell that only captures the data in one small area, which will report inaccurate data for a compaction profile study. The last phase of the tableting cycle is the tablet take- off or removal from the lower punch face. Take-off is the phase where tablet sticking or picking may occur. An instrumented take-off bar will measure the force required to release the tablet from the lower punch face and detect early signs of sticking. The force required is normally in the range of a few newtons, so this requires a very sensi- tive sensor, typically manufactured with a material that exhibits a very low elastic modulus (such as aluminum). Additionally, a semiconductor strain gauge allows more than 20 times the sensitivity output of a standard foil strain gauge. Conclusion While they may appear simple, tablets are complex drug delivery systems. Underestimating the importance of their design, formulation, and manufacture invites sig- nificant production difficulties at some stage of develop- ment or product life. Instrumented R&D tablet presses and data-collecting software packages are critical for the success of a tablet manufacturing process. T&C Robert Sedlock is director of technical training and develop- ment at Natoli Scientific, Telford, PA, a division of Natoli Engineering (636 926 8900, www.natoli.com). Natoli Scien- tific provides regularly scheduled solid dosage training semi- nars, contract research and development, AIM Data Acquisi- tion & Analysis software, and calibration services. Figure 1 In-process data generated by R&D tablet press instrumentation c. Strain rate profile (Rotary tablet press) Tensile strength (millipascals) 1.5 1.3 1.1 0.9 0.7 0.5 Dwell time (milliseconds) 39.70 26.47 19.85 15.88 13.23 Wet granulation a. Tabletability profile Tensile strength (millipascals) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Compaction pressure (millipascals) 0 50 100 150 200 250 Lactose/MCC (3:1 ratio) 3:1 ratio + 20% APAP 3:1 ratio + 10% APAP 0 50 100 150 200 250 b. Compressibility profile Solid fraction 0.74 0.72 0.70 0.68 0.66 0.64 0.62 0.60 Compaction pressure (millipascals) Lactose/MCC (3:1 ratio) 3:1 ratio + 20% APAP 3:1 ratio + 10% APAP Subscribe today www.tabletscapsules.com