Gerd Hüffmann reveals how a compaction simulator can deliver a realistic tableting scale up
When turning pharmaceutical powder into a tablet by means of a tablet press, there are many challenges. The challenge becomes even greater when tablet parameters established during R&D should become the basis for a successful commercial scale production.
The master challenge is to establish (in R&D) the most important tablet qualities and to transfer them all successfully to a production scale machine. Tablet weight is the first quality to consider. The contents of API are defined by the tablet weight, which is the most critical parameter for the pharmacist! Tablet hardness is next on the list. The disintegration and dissolution time is the next critical parameter for the pharmacist. The third quality is tablet thickness. The total height can be a critical issue for the packaging of the final tablet.
To provide this transfer or scale-up capability, the R&D tablet press in question must provide the following features and function:
* To be able to handle all common tablet shapes and sizes
* To be able to compress not only single layer tablets, but multi-layer, ring tablets and core in core (tab in tab) tablets as well
* It has to be able to work with all common tool standards and sizes (EU, TSM, B, D, D-441, etc)
* Last but not least, it has to replicate the working sequence of a modern rotary press with a driven (forced) feed system, a regulated powder dosing and the application of pre- and main compression forces as well as ejection force measurement
Rotary tablet press
Commonly a (smaller) rotary press is being used successfully for the R&D portion of the task. This finds its limitations once serious scale-up becomes part of the equation, simply for one common reason: the pitch circle diameter of these presses typically ranges from approximately 150 to 280mm, while large-scale production presses typically have a PCD ranging from 550 to 800mm. Therefore the actual punch speed of an R&D rotary press is always considerably slower than that of the rotary press later used in production.
As an example, the dwell time of a rotary R&D press with a pitch circle diameter of 180mm running with EU-B type punches at 70rpm is around 12,8ms. A production press with a PCD of, for instance, 700mm, would only have a dwell of 3,689 ms available at the same rotation speed. This means that the very important tableting parameter of dwell time cannot be adequately simulated, leaving to chance if it will be possible to obtain the required tablet hardness and to avoid capping of tablets at speed.
The answer to all scale-up challenges and the ultimate scale-up tool is a compaction simulator such as the Styl’One Evolution from Romaco Kilian. This is a flexible, single-stroke tablet press that can assist with the development of single to five layer tablets, as well as core tablets (tab in tab).
To fulfil all tableting requirements this simulator is fully instrumented to measure compaction forces (tamping force, pre- and main compaction force), as well as ejection forces and punch displacement.
Compaction cycles can either be force- or displacement controlled to replicate all commercially available control systems.
It can operate with gravity feed for pure R&D applications and with force-feed fill shoes when up-scaling to a rotary press is required.
Most important is the ability to replicate the compaction cycle of a rotary press at a given operational speed. For this purpose, unrestricted compaction profiles can be created, as the press is fully programmable.
Working principle
The Styl‘One Evolution compaction simulator has a compression system made up of two pistons on which the punches are fixed (Euro, TSM formats). The lower and upper punches are linked to a planetary roller screw, driven by brushless engines, allowing a great positioning precision and great displacement speeds (up to 350mm/s).
During the compression phase, the upper punch will enter the die, while the lower punch will go up, performing the compression movement. All three cycle phases (filling, compression and ejection) are performed by the lower punch and its numerical engine. The whole cycle is fully configurable (times, forces, displacements) thanks to the acquisition and control software Analis in R&D mode.
Thus it is possible to achieve compaction speeds far beyond eccentric presses, for instance, and equivalent to a standard high-speed rotary press and replicating the desired compaction cycle in a 1:1 relation, offering full scale-up potential.
For more information, visit www.scientistlive.com/eurolab
Gerd Hüffmann is with Kilian Tableting.
