MICRO MOLDING NEEDLES AND SHARPS: THE SCIENCE OF COMPLIANCE
9/4/12: Micro molded Needles and Sharps are getting attention these days due to their many advantages including; disposability, recyclability, ease of use, and cost effectiveness. They are being used in applications such as cost-effective vaccine delivery, glucose monitoring and insulin delivery devices, transdermal wearable drug patches, and automatic blister or capsule drug puncturing just to name a few. They are designed and developed in many different forms; transdermal patches, staples, singular needle sites, anchors, forceps, and cannulas. They are manufactured and processed using several micro manufacturing methods; micro molding, micro milling, etching, laser machining, embossing, and forming.
Needle compliance is defined as a needle with the least amount of pain inflicted on the patient AND the ease of use of the device for both patient and surgeon. Compliance can also be taken to the microscopic level as seen in Figure 1.1 which shows the body’s reaction (in this case a cell) to foreign body (the needle) that has been inserted into it. The cell or even the skin will react to the puncture of needles by sending white blood cells to that area immediately as the army of protection comes to the aid of the skin or surrounding cells/organs. This phenomenon is baffling to glucose monitoring device engineers and researchers as these extremely fast responses are measured automatically and in some cases falsely administer insulin unnecessarily.
Figure 1.1 Cellular response of White Blood Cells to Needle Penetrating it (Foreign Body)
In order to provide the least amount of pain to the patient, micro molded needles must be designed and manufactured without a blunt tip which would “drag” the skin and cause pain and prolong puncturing. As is the case with any micro technology (thermoplastic, silicone, or metal), the tooling is THE most critical component to success.
The tooling (see Figure 1.2) for micro molded needles have features in the double digit micron range, there are several challenges that must be overcome to achieve tool to molded needle replication. It is one thing to make nice sharp corners and cavities in steel (less than 1 micron radii) but it quite another to FILL those tiny spaces with polymer. VENTING, VENTING, VENTING: Similar to the real estate sales mantra “location, location, location” it’s all about proper venting and cavity to core fits for the successful degassing of polymer during the ultra-fast injection phase. Proper venting is required. These tiny pockets of steel in the mold leading to atmosphere allow for the flow of polymer to get right to the bottom of the steel cavity thus creating a very sharp point in polymer.
Figure 1.2 Mold Insert and Molded Part on left and Micro Molded Needle Sites with <0.050” (1.3mm) tall needles with 0.002” (50 micron) lumens through each site.
Because needles and sharps can be dust speck in size and require micron level radii to achieve skin, tissue, or organ puncture forces, the tooling or micro mold is the true enabler to their success.
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