F
irst, like any material-sparing
methods, mimicking the dry
granulation process on a single punch
press has some limitations. The
feeding system, de-aeration, pressure
gradient along the ribbon width, the
roll surface and shape are actually
not taken into account. That’s sounds
like a lot, but this method is actually
the only method to evaluate the dry
granulation process at early stages.
The dry granulation is a slow
symmetric compaction process. Many
formulators were using eccentric
presses trying to predict the powder
ability to be dried granulated
with more or less success, as this
compaction is asymmetric and
therefore does not fully mimic a roller
compactor.
More recently Sanofi published
research performed on a Medelpharm
rotary press simulator at very slow
speed with the benefit of symmetric
compaction. Their findings were
already much more satisfactory. [3]
With the new STYL’One Tableting
Instrument, this method was greatly
improved. This was achieved by
implementing a mathematical model
to compute, from the pressure
measured on the STYL’One, the
equivalent hydraulic pressure (or
specific compaction force) that should
be entered on a roller compactor to
reach the same solid fraction. This
method is called “hybrid modelling”,
since it uses a mathematical model
combined with real compacts made
on a single punch press. Recently, the
University of Düsseldorf published a
paper [2] using different excipients
(brittle, plastic). They've shown that
compacts, called ribblets (a neologism
created from ribbon + tablet) made
on a STYL'One and ribbons made on
a Gerteis roller compactor had similar
relative density.
Even with the limitations listed
earlier, this material-sparing method
remains the most effective method
available to assess dry granulation
with a small amount of material. It
has been adopted by pharmaceutical
companies across the globe as one
of their reference method to decide if
dry granulation is a feasible process
and to speed up their design of
experiments (DoE) when scaling-up to
a commercial-size roller compactor.