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22 September 2019 Tablets & Capsules mented to obtain the benefits of a single-station R&D tablet press. Figure 1a shows a tabletability profile gener- ated by data from an instrumented single-station tablet press and compaction emulator. The profile compares the tensile strength of the tablets produced as a function of compaction pressure for a formulation containing varying percentages of API. Rotary tablet presses. The next step in the develop- ment process is to transfer the product to an instru- mented small-scale rotary tablet press. These machines are scaled-down versions of production-scale rotary tab- let presses, so they require just a few hundred grams of material to provide data. This allows researchers to evalu- ate a formulation's behavior through the complete rotary press cycle and generate data such as compaction profiles and strain-rate scalability studies, as shown in Figure 1. The instrumentation on an R&D rotary tablet press includes pre- and main compression forces, ejection force, and take-off sticking force. The pre- and main compression readings play a signifi- cant role when analyzing the consolidation and compac- tion phase, where entrapped air is removed from the for- mulation, particles are deformed, and interparticle bonding occurs. At this stage, it is critical to understand the product's failure limits with respect to tablet strength, capping and lamination, friability, disintegration, and dis- solution time. After the compression and decompression stages, the tablet is ejected from the die. The ejection force is a prod- uct of the residual radial die-wall force and the coefficient of friction between the compacted tablet and the die wall. High ejection forces can cause premature wear to the punches or press cams as well as tablet quality issues. The most common remedy for high ejection forces is increas- ing the amount of powdered lubricant (typically magne- sium stearate) in the blend. The amount of lubricant should be optimized, as too much lubricant can cause tab- let capping and friability and increase disintegration times. inherent lubricating properties. On the other hand, if the lower punch is not receiving a high percentage of the force applied to the upper punch, the formulation may require a lubricant or other excipient with lubricating properties. The single-ended compression system is a valuable tool during the formulation process but is not desirable in a manufacturing environment, as dou- ble-ended compression provides a more uniform tablet density and, ultimately, a more robust tablet. A single-station tablet press allows the use of dis- placement sensors to measure the movements of the upper and lower punches in real time. With proper cali- bration and machine compliance correction factors, the scientist can evaluate force displacement profiles or work curves. With a very limited amount of material, the press can provide data on the material's elastic nature. Materials that exhibit high elasticity often result in insuf- ficient tablet hardness or even capping and lamination problems. Displacement measures can also provide Heckel and Kawakita plots, which also characterize a material's deformation properties, including elasticity, plasticity, and brittleness. All of this information can be evaluated and proactively implemented during formula- tion, resulting in a shorter R&D phase and more efficient tablet production. Another instrument that can be easily installed on a single-station tablet press is a radial die-wall sensor. This sensor measures the radial force on the die wall resulting from the axial force applied to the formulation by the punches as well as the residual radial force remaining after the upper punch is released from the compaction event but prior to ejection of the tablet. Die-wall moni- toring is a valuable tool for characterizing compaction materials and detecting die-wall friction phenomena. Compaction emulators. A compaction emulator can also be used during a tablet's R&D phase. A compaction emulator is designed to match the compression times of a high-speed production rotary tablet press but is instru- Photo 3: An instrumented R&D rotary tablet press such as the NP-RD30 shown here allows researchers to evaluate a formulation's behavior through the complete rotary press cycle. Photo 2: A compaction emulator such as the Presster shown here mimics the compression times of a high-speed production rotary tablet press but is instrumented to provide the same data as a single-station R&D tablet press.