CHALLENGES IN MICRO MOLDING WITH BIO-RESORBABLES
11/12/12: Micro Molding in bio-resorbable PLA and PGA materials creates challenges with small gate sizes for these highly shear sensitive and highly moisture sensitive materials, such as shear stress through small gates, humidity control for extremely small shot sizes, and integrating macro to micro technologies to produce near micron level geometry in precision, micro molded bio-resorbable components.
The first challenge encountered by processors of bio-resorbables is material handling, which is the single largest area for error. PLA/PGA materials are highly susceptible to moisture and heat. They must be stored properly at a specified temperature in nitrogen-sealed foil pouches. They must then be used according to the processing run quantities needed and material drying cycle. The material usage must be matched with the injection screw and shot size in an injection molding machine so that the material is not sitting in an improperly sized machine where over-drying and over-heating can occur due to the prolonged temperature and drying exposure.
A mold design with a properly sized gate and a very small runner and sprue (if any) is critical to product quality and cost.
Mold venting is also important as clogged vents will also degrade the polymer prematurely and cause burning of the implant during processing.
Lastly, micro molding machines are a key component to processing resorbable polymers. Because they are highly shear and heat sensitive, proper fit of the shot size to the screw and barrel is critical. The residence time (time the polymer sits in the barrel) can affect the IV of the material.
You can see some of the components we have worked on here.
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