Rob Blanchard
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Earlier this year, I Holland and the UK's University of Nottingham launched a two-year Tabletting Science Anti-stick Research
project. One particular issue that will be investigated is what makes formulations stick to tablet tooling surfaces, including
why certain coatings resist sticking, whereas others do not. With sticking being an important issue facing tablet manufacturers,
Pharmaceutical Technology Europe spoke to Rob Blanchard, Research and Development Manager at I Holland, and Clive Roberts, Chair of Pharmaceutical Nanotechnology
at the UK's University of Nottingham and Director at the Nottingham Nanotechnology and Nanoscience Centre at the University
of Nottingham, to find out more about the collaboration.
Q: What issues can tablet sticking cause during pharmaceutical manufacturing, and how well understood is this problem?
Clive Roberts
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Sticking is a complex phenomenon created by different parameters such as Van der Waals forces, capillary action, electrostatics
and the surface roughness of the tablet tooling, to name but a few. Sticking can reduce yields, double compression (causing
damage to tablet press and tooling), and cause poor tablet appearance, inconsistent tablet dosage and inconsistent tablet
hardness, as well as other production issues. Sticking should not be confused with picking, which can look very similar to
sticking, but which can commonly be resolved by changing tablet design. In recent years, I Holland has seen increasing requests
for assistance in solving sticking from both generics and pharmaceutical companies alike.
Q: How do manufacturers currently address the problem of tablet sticking? Has the issue influenced the development of any
new tools and technologies?
A common way of reducing sticking is to slow the tablet press down, thus increasing the dwell time. However, this solution
is unpopular with tablet manufacturers because it reduces productivity of the tablet press. As a consequence, tablet press
manufacturers and tablet tooling manufacturers have introduced solutions to help the end-user reduce sticking issues in production.
For instance, I Holland has developed a range of antistick coatings that have been successful in solving sticking, but the
coating used should always be matched to the specific formulation. In the past we have worked in partnership with our customers
to carry out trials using all the antistick coating solutions in order to match the correct coating with the formulation and
environmental conditions. A potential issue with this method is the associated cost incurred in time and expense to find the
correct solution.
Q: With a variety of ingredients used in manufacturing, it must be difficult to systematically benchmark sticking behaviour
for each ingredient. Can you talk about how the new collaboration between I Holland and the University of Nottingham aims
to tackle this issue?
This is an important question and is in fact also complicated by orientation effects because the same material (if crystalline)
can present quite different surface properties (chemical and mechanical) depending on preferential orientation effects. However,
whilst building a library of data will take time, the range of excipients used in most formulations is not actually so extensive
with the same materials (albeit in slightly different forms) often being used, particularly, with the high percentage content
of solid dosage forms. Of course, APIs will be different and we will deal with the ones known to cause the most problems first
and attempt to cluster compounds that have similar properties. Ultimately, the intention is to have a model that can predict
sticking to various punch surfaces not based upon complex analytical measurements, but on a limited set of parameters that
may largely already be known.
