Micro-Extrusion, Done Right
It’s not hard to produce a small extrusion. It is possible to produce a micro-sized thermoplastic extrusion using oversized extrusion equipment and high melt strength raw materials. The ability to produce extrusions in micro-sizes is just the beginning. Micro-extrusion is a science in itself.
Precision: Microcatheter device design capabilities are compromised when standard industrial tolerances are applied to microcatheter extrusions. Scientific micro-extrusion requires a right-sized, well-engineered system that controls the output and delivers essential precision. Precision must be controlled within the process and cannot reliably be delivered through processes of secondary inspections and sorting. All elements of every microcatheter device system must be tightly controlled for optimum performance in critical medical procedures, and for navigation through small and fragile vessels of the vascular system, dimensional consistency is key.
Tolerancing: Our industry has seen a steady shift towards tighter tolerances as issues of variation have become better understood. Variation invariably causes challenges to design engineers, waste in medical device assembly, increases to order cycle times and device performance risks in the field. For micro-extrusions, tolerancing is especially critical considering diameters can be well below .010”, and wall thicknesses can be .001” and less. One of our customers said it well.
“…There is a significant need for true micro-catheters, on the order of 0.020” (500 microns) OD or less. While there are a fair number of firms that are able to extrude small diameter tubing, with ID’s as small as 0.004” or so, the tolerances quoted are usually on the order of +/- 0.001”. A 0.001” tolerance on a 0.004” ID is, obviously, 25% of the diameter. With the continued miniaturization of medical devices, the need for very tight tolerances becomes paramount.”
Measurement: Micro-extrusion measurement requires precision in-line measurement as an element of the extrusion control process, and as a tool for characterization of the product. Analysis of micro-extrusion cross sections relies on high magnification measuring microscopy, in order to confirm measurements in tens of thousandths of an inch. In addition to measurement at magnification, the quality of cross-section cut represents a critical element of measurement precision.
Microstructure and Mechanical Properties: Any process that thermally or mechanically degrades the material compromises the ultimate physical properties of micro-extrusions. Over-sized extruders and working channels that are too large for production of micro-extrusions hold materials too long at in the molten state. Gear pumps used to smooth instability and variation only add to risk for mechanical and thermal degradation. Micro-extrusion technology is designed to preserve critical properties, controlling dimensional variation at the extruder, and keeping the thermal and mechanical energy below the degradation threshold. Surface quality, smooth and free from score lines is also essential to downstream assembly processes and device design.
Micro-extrusion technology manages control and quality at the micro-level. It is its own science, addressing the unique needs of the microcatheter market.