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Understanding DFM and Risk Mitigation of Micro-Sized Implantable Devices

OEM medical and drug-delivery companies need to cover all the bases in mitigating risk when designing and manufacturing micro-sized devices, said Donna Bibber, vice president of business development at Isometric Micro Molding Inc. MD+DI spoke with Bibber about her upcoming talk at MD&M West.

Image by mohamed Hassan from Pixabay

Image by mohamed Hassan from Pixabay 

Sensors, guidewire assemblies, glaucoma implants, bioresorbable polymer anchors, screws, tacks, and slow-release point-of-use drug-delivery devices are just some examples of micro-sized implantable products that have special design and manufacturing needs. OEMs designing these innovative devices might assume that they can just go to their usual component suppliers for smaller versions of what they would use for a larger device. This can be a determinant to success, Donna Bibber, vice president of business development at Isometric Micro Molding Inc., told MD+DI, because tiny parts require the day-in and day-out attention to micro details to achieve single-micron stack-up tolerances.

Bibber’s session at MD&M West 2020, “Risk Mitigation Strategies for Designing & Manufacturing Micro-Sized Implantable Devices,” will focus on risk mitigation in designing and manufacturing these tiny devices. She will describe various design challenges, materials and testing, and scalability, among other design attributes.

“Much of the risk in micro molding and micro automated assembly is in the mold and machining. Robust parting line shut-offs, extremely accurate vent channels, and gate diameters of 125 microns are all inputs to a well-defined PFMEA [Process Failure Mode Effects Analysis],” she said. Tool fabrication inserts and a sound maintenance plan is another focus area to consider, she noted, especially when designing things like hair-sized core pins with 3-micron steel tolerances. Risk can also be mitigated in micro molding processes, and materials selection and processing, she said.

Bibber explained that a contract manufacturer should place a significant emphasis on developing a PFMEA, which it develops using the OEM’s DFMEA. “The PFMEA is done in the tool design review, before we even cut a piece of steel that is going to be used to mold piece of plastic inside of it,” she said. “It's very detailed so that we can understand what those risks are and mitigate them along the way. It's not uncommon for us to have tolerances that are eight microns on a part, forcing the process design to develop risk mitigation tools to find single microns for 1.33 Cpk compliance.”

“If you're looking at a bell curve, and I'm looking at that plus or minus eight microns, it better be tightly in the middle of that bell curve so then it can have a little wiggle room,” she continued, stressing that the PFMEA must be very detailed.

Metrology is also important in risk mitigation. Bibber’s company, Isometric Micro Molding Inc., uses in-house, high-resolution CT to scan parts. This enables detection of deviations in the actual molded or assembled part against original 3D CAD design data down to 0.1 micron in all axes. It provides a full CAD model of the part in less than 10 minutes, which can be more helpful to the process engineer than lists of numbers on a page. The 3D images exported from the CT scanner are MRI-like in quality and can depict an internal wall thickness view of the parts or assemblies that could not otherwise be obtained during validation or production.

Bibber said that she hopes that attendees to her session will take away a clear understanding of the specific design and manufacturing needs that micro-sized devices have and the ways in which failure risks can be reduced or eliminated. “This is just really near and dear to a lot of companies because they want to mitigate risks as much as possible during the development phase of a micro-molded or ultra-precision sub assembly,” she concluded.

Bibber will present “Risk Mitigation Strategies for Designing & Manufacturing Micro-Sized Implantable Devices,” during the MD&M West conference on Wednesday, February 12, from 2:05 to 3:00 p.m., in Room 210C. Isometric Micro Molding Inc. will be exhibiting at Booth #1187 February 11-13. The company will also be participating in the Booth Bar Crawl during the “Networking Reception" from 4-5pm on Wednesday, Feb. 12.

Bibber spoke last year during a BIOMEDevice Boston 2019 panel discussion and offered tips for developing miniaturized medical devices.

Susan Shepard

Susan Shepard

Susan Shepard is a freelance contributor to MD + DI.

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