My father always said “you put garbage in, you get garbage out.” High quality, superior medical devices start with the highest quality materials and components. In the catheter tubing market quality is defined by a smooth surface, free of bumps, nibs, gels, foreign matter and/or contamination. Along with cosmetic issues, a superior compound also is easy to process, produces low start up scrap, lines out quickly and is consistent from lot to lot. Every lot of compound should be headache free and process similar if not the same as the previous lot.
The processing of the compound plays such an important role in a well dispersed compound which in turn yields excellent quality medical devices. The demands of today’s thin walled catheter device market begin to test the limits of current materials available. Many compounds are being used in sub 0.001 wall thickness. In medical compounds the resin and additives are scrutinized for the highest quality, quite often OEM’s are looking for USP Class VI certification on the chosen materials. By vetting these components the resulting compound should be of highest quality. However these ingredients still need to be compounded effectively to ensure consistent formulation, excellent dispersion of fillers and pigments, and a stable melt flow rate.
Good compounding starts by drying all components and keeping them dry throughout the process. At Compounding Solutions all of our feeders are kept under positive pressure with Nitrogen to keep water reabsorption to an absolute minimum. In the past all components were weighed and then mixed by hand in a bag tumbling process then transferred to a volumetric feeder. These feeders meter a consistent volume of material by a turning screw releasing a steady quantity of material over time, which provides an economical way to meter materials that have a consistent bulk density. If two components are of different particle sizes, say a plastic resin and a radiopaque filler, there is a chance for these components to separate in the feeder due to vibrations form the turning screw. This separation causes variability within the compounding process.
New technology in feeding systems are loss in weight gravimetric feeders. A loss in weight feeder is a gravimetric metering device that receives material from an upstream supply from a hopper and accurately doses the material into a process at a predetermined feed rate, typically through a turning screw(s). At the base of the feeder is a load cell that the feeder receives constant feedback from the sensitive weighing device, which ensures that the precise amount of material is delivered continuously. With the addition of a PLC driven controller the accuracy of the loss in weight feeder can be dialed in to autocorrect any potential variance.
Compounding Solutions has utilized loss in weight feeders over the past 14 years; we have worked hard to constantly improve the quality of our compounds to decrease surface defects, and gels, while increasing our customer yields. Not only from Lot to lot, but from every pellet that our customers have purchased. Along with using loss in weight feeding we keep components in their own feeders to ensure the correct amount is being supplied into the compound. The typical accuracy of these feeders is +/- 0.2%. Compounding Solutions also utilizes loss in weight micro feeders, which are similar to the above but can dose in small amount on the order of 0.2lbs per hour. This is beneficial when expensive additives such as tungsten, antimicrobials, etc… are within the compound. Compounding Solutions also upgraded their capabilities last year with the addition of a loss in weight liquid feeding system. Now the same accuracy that delivers powders and pellets can be used with liquids and pastes.