Micro molding is in high demand in the medical device industry and molders are using all their skills and the newest equipment to reliably create incredibly small, complex features, even from sensitive materials.

This trend is largely driven by the demand for a growing variety of devices and tools for minimally invasive (MI) procedures. The increased functionality of these devices requires miniaturized features and components, many of which are made with micro molding. As innovation in medical devices grows at a rapid rate, “getting small” is a sought-after feature.

“We are in the midst of the largest boom the micro molding industry has ever seen, with 25% to 30% growth in the past two years,” said Donna Bibber, CEO of Isometric Micro Molding, a New Richmond, Wis.-based custom manufacturer of small to micro-sized injection molded components and ultra-precise automated assemblies. “This accelerated growth is largely attributed to the industry’s need for ultra-precision, tight tolerances, and thin-walled components.”

Miniaturization is often the key to making one-of-a-kind devices for MI procedures, improved therapy options using innovative devices, and developing less-expensive alternatives for existing products on the market. Micro molding is an essential technology that medical device companies count on for turning their next-generation designs into high-value, game-changing products.

“Device designers are always looking to do more in the same space or less,” said Aaron Johnson, vice president of marketing and customer strategy for Accumold, an Ankeny, Iowa-based provider of high-volume precision micro molding services to the medical device industry. “For example, a catheter-based device could provide a better patient outcome if the device were smaller, provided more accurate deployment, or offered more functionality—or in some cases, all three. Micro molding and other micro technologies can make this happen.”

Khristine Carroll, vice president of business development for Forum Plastics, a Waterbury, Conn.-based global contract manufacturer serving the medical device and life-science industries, agreed.

“As treatment options and innovations continue to leap-frog prior technologies, more core functionality is being required of smaller and smaller devices,” she said.

As exciting as innovation, complexity, and miniaturization can be, they do result in higher costs and longer lead times. Medical device manufacturers (MDMs) are eager to find partners that can improve speed to market by mitigating some of these costs and timelines. Increasingly, MDMs look for vertically integrated contract manufacturers (CMs) that can serve as single-source suppliers/partners to meet the multiple needs of their micro medical device clients, ranging from design, prototyping, and design for manufacturability through custom assembly and packaging.

“As OEMs prioritize consolidating their supplier lists, they are tasked to ensure the list contains specialty molders for their most complex/small designs that can support their immediate needs, as well as their high-volume production,” added Lindsay Mann, director of sales and marketing for MTD Micro Molding, a Charlton, Mass.-based provider of plastic injection molding and micro molding services to the medical device industry.

Latest Trends

As the medical device industry evolves, there is growing demand for even smaller injection-molded components; their tighter tolerances and complex geometries often push the limits of micro molding. “With parts getting so small, we also need to be thinking about how to measure the parts after molding,” said Maggie Beauregard, quality manager for MTD Micro Molding. “Non-contact vision systems or computerized tomography [CM] scanners allow hands-off inspection, which minimizes damage from handling.”

MDMs are also interested in determining which materials will allow them to “go smaller” and still deliver the precise tolerances they desire.

“There is a trend toward more exact material requirements—for example, the stability of the material—how stiff, how rigid, and how thin of a wall can be achieved,” said Scott Herbert, president of Rapidwerks, a Pleasanton, Calif.-based provider of precision micro injection molding and injection molding for the medical device industry.

Material selection (including bioresorbables and other process-sensitive materials) is a key step in designing combination and drug elution-based products, delivery mechanisms for bio-fabricated drug delivery and gene therapies, and electronics integration for wearable technologies—which often require greater levels of precision and lower spatial imposition than ever before.

Due to these high-precision requirements, consistency in processing, material flow rates, and inline-inspection for micro-molded parts are essential for meeting design specifications. “Many micro-molded targeted applications and products, given their diminutive size and finite dimensions, require the highest levels of precision, accuracy, and zero defects during the molding process,” said Carroll. “Materials that will best provide optimal dynamics for processing, functionality, and biocompatibility are critical early-stage considerations.”

More MDMs are also looking at ways to push the boundaries of how small a component can be when biocompatible, medical-friendly resins are used. With the constant challenge of miniaturization, micro-device technologies require that the material behave the same way, with the same integrity, at the micro and nano scales, as it does on a larger scale. “This is for specific performance reasons within the medical application and therefore typically not something that can be compromised,” said Patrick Haney, R&D engineer for MTD Micro Molding. “Therefore, as medical micro molders, we constantly face the challenge of coercing material into features that most would consider impossible.”

To make these products as cost-effectively and expeditiously as possible, during product design more MDMs are turning to the knowledge and expertise inherent in their supply chains. For example, CMs are increasingly involved with new product development project teams early in the design stage to determine the manufacturability of their products. “A major benefit to this is the reduction in lead time between the prototype and production stages,” said Alex Maroon, project manager for MTD Micro Molding. “We have seen an uptick in requests for molding with custom materials—most likely a push towards lighter and stronger materials that enhance certain polymer properties required for part performance.”

Molding trends have always been to “move the decimal point” in terms of feature size and tolerance. However, this should not be the only focus—customer value can also be delivered through efficient platform programs built on customer intellectual property. “These platforms come about from extremely thin-walled vessels, micron tolerance assembly stack-up Cpk [process capability index] requirements, and the ‘real-estate’-challenged tight space demands needed for minimally invasive surgery and drug delivery devices,” said Bibber.

What OEMs Want

Although capability, scalability, and sustainability are high on the list, speed to market is still the top priority for MDMs. “Even with everything that’s said about the importance of materials and size and the ability to fabricate a tool and meet drawing specifications, it’s still about speed to market,” said Herbert. “Being able to design a tool, fabricate production tools, and create first shots in a short period of time are critical for most customers.”

The faster the first shots are achieved, the sooner MDMs can make fast, cost-effective prototypes for their micro-sized designs, preferably in the material of their choice.

“When most OEMs think of prototypes, they think of 3D-printed parts,” said Mann. “However, most OEMs working on micro medical designs need more options to meet their needs and goals. In response, we have developed multiple prototyping services to iterate and innovate quickly, ultimately getting their products to market faster, including an option to receive fast prototypes in their material choice, including bioabsorbable materials.”

MDMs are increasingly reluctant to deal with aggravating supply chain issues, preferring to outsource their production work—ideally to a single supplier that can expertly mold their micro parts, but also provide other services and capabilities. This significantly shortens the supply chain, speeds up production and communications, and shortens time to market.

When a molded part has miniature details, the other features in that part become much more visible and prominent. For example, a standard parting line can appear huge on a micro-molded part. If tool precision is not good enough to achieve an acceptable level of parting line flash, then secondary processes like cryo-deflashing might be required. Silicone is a popular material used for a variety of medical applications.
“However, when it comes to parting line visibility and flash, silicone is a very challenging material to process due to the very low viscosity, so absolute precision when manufacturing the tool is a must,” said Lars Gerding, vice president of technology for Freudenberg Medical, a Beverly, Mass.-based global partner for the design, development, and manufacture of medical devices and components, including micro-molded components.

Ultimately, MDMs count on their micro molders to help solve their greatest design challenges, which often involve the enabling components in these devices. These components and assemblies are usually identified as high risk to their programs and are increasingly entrusted to advance micro molding technologies. “It’s this culture, focus, and diligence that allows us to achieve sub-micron tolerances, stringent PFMEAs [process failure mode and effects analysis], and CT-scanned STL [stereolithography] files that OEMs can use for their clinical submissions,” said Bibber.

Advanced Tools and Technologies

The fabrication of tools overall has not changed greatly in recent years. To achieve the design details and functionality their MDMs want, molders must get creative with existing materials and equipment, such as combining different methods to achieve innovative parts and tolerances.

For example, the most advanced electrical discharge machines and wire technologies are key for creating micro-sized cavities—especially the methods available now for fabricating electrodes and the types of materials used. “Creating longer-lasting electrodes will create a better-quality burn, providing sharper and crisper detail,” said Herbert.

Molders are taking existing technologies and finding new ways to use or manipulate it to get different results. “For example, we take existing machining technology and develop new ways to fixture and handle parts for machining to make it a good fit for our prototyping services,” said Gary Hulecki, CEO of MTD Micro Molding.

Isometric Micro Molding can make features smaller than 10 microns, sharp micro needles and barbs, and walls as thin as 25 microns. It now has the ability to down-select geometry and mimic the scalability of micro-molded components in the exact thermoplastic and FDA predicate materials in as little as two days. Nano dispensing and bonding substrates, including those from silicon wafers, are now scalable and automated to 1.33 Cpk or better. “Isometric’s in-house automation team designs, builds, and validates systems that allow for minimal handling of parts by retaining the datum structure right from the micro mold end-of-arm-tool directly to automation on the back side of the molding machine,” said Bibber. “This single-fixture handling allows for other larger and less-critical components to be married to assembly and reduces set-up errors, loose particulates, and bioburden.”

Molders are also exploring how additive manufacturing/3D printing (AM/3DP) can enhance their micro molding prototyping processes to get products to market faster.

In the past, engineers had to cut hard steel to make tooling for early stage designs. Now, however, engineers can produce prototypes faster and more economically with AM methods such DLP (digital light processing) or two-photon laser 3D printing systems.

For example, the higher-quality output of some of the latest 3D printing technologies has helped engineers with early-stage designs at a level that typically required tooling before. Some AM systems can provide very accurate micro parts, with micro features. Although AM/3DP cannot always replicate the same exactness of a molded part, these advancements in precision printing do help designers iterate faster and get to production more quickly.

“The accuracies of these AM systems have also allowed us to explore micro digital tooling,” said Johnson. “By printing micro inserts for an injection-mold tool, actual molded components can be produced—not for every part with every material, but the process is coming along quickly and has proven to be successful for many micro projects. For us, micro AM is a long-needed tool in the design and manufacturing process for micro components.”

How Small Can Micro Go?

How small can micro go these days? It depends on several factors, including material and volume production.

In many cases, parts can be extremely small—for example, with some engineered materials, wall thicknesses can be less than 0.004 inches. “However,” said Herbert, “when I am asked this question, I tend to respond with, ‘How many components are you trying to make? And with what material? Is the size realistic regarding volume production?’ These are very important factors that must be considered to determine size.”

“It is not really how small you can go, but doing it consistently,” added Gerding. “You can mold a small part, with a small cavity, but have a huge runner system to accommodate the shot size. In fact, we have seen parts from competitors where 95% of the shot size is the runner system—this is neither sustainable nor can it be controlled very well in the long run.”

“Everyone always wants to know how small you can go,” said Johnson. “The simple answer is we haven’t hit the bottom yet. At Accumold, we’ve been asked to produce commercial parts under 1.0 mm in total length. We’ve also produced features under 1 micron in size. That said, there is a dimension that is too small. At some point your design will collide with the material itself. In one project, the customer had to switch to a mineral-filled resin because the original glass filler was getting in the way—the micro shards of glass were too big for the part we were producing. Regardless, we always recommend that design engineers start with their ideal in mind—then we walk through the design for micro molding [DfMM] process together and see where innovation can lead us.”

Overall, there is no theoretical limit to how small a molded part can be; however, there is a practical limit that is driven by the manufacturing equipment’s ability to avoid material degradation, induce manageable stresses, and incite flow into a mold cavity with repeatability. “This limit can change drastically given the complexity of the part geometry, application of the device, and the type of polymer material,” said Kyle Kolb, tooling supervisor for MTD Micro Molding. “Different materials respond differently to factors such as pressure loss, compressibility, and even thermal conductivity, which can influence how quickly a flow front cools and how drastically the viscosity increases as flow continues.”

How small a feature can be depends greatly on the type of feature in question and the properties of the selected material, noted Haney. For example, lower-viscosity resins that have more linear polymer backbones tend to fill thinner features better, “where wall thicknesses as small as 0.0015 inches can be realistic,” he said. “In the case of high-viscosity materials, wall thicknesses around 0.009-0.005 inches might be more realistic.”

Isometric’s smallest molded component is over 1,000 parts per single plastic pellet of resin in size (0.00004 grams). “These dimensions are definitely not the norm, but should the need arise, OEMs can extrapolate and design components after seeing that these size parts are not only possible, but scalable and economical,” said Bibber.

On the opposite scale, micro molding can achieve parts as large as six inches in length, with micro features, tight tolerances, and/or long aspect ratios. “For example, the smallest microfluidic channel molded by Isometric is a mere three microns deep and wide,” said Bibber. “It is amazing that there is a steel core that creates this geometry and that these parts can be made in high volumes for specific applications.”

Making It Happen

MDMs often think a design or a process is impossible—but with some creativity, ingenuity, and DfMM—it can usually be made, and even more cost-effectively.

“The big challenge is bringing a product to life in the real world,” said Gerding. “In a CAD program, everything looks quite easy when looking at the design at 1:100 magnification. Customers should also be aware of the tolerances that can or cannot be achieved; most of the time, the nominal values are taken for granted as if the part would be made from steel. It is even more challenging for elastomeric materials.”

Molders are always looking to improve their processes. This includes investing in new machining techniques, combined equipment, laser treatments, or other non-traditional technologies that add to overall capabilities. In-house tooling and automation teams are focused on coming up with new ways to boost efficiency and speed, especially for prototyping options, such as freeform injection molded cavities.
A good business has a good business strategy, including micro molders that continue to spend a large percentage of their revenue on R&D. This includes new advances in AM, micro molding equipment and auxiliary equipment, attribute micro tensile bar testing, material analysis and testing, and the use of CT scanning. “These investments pay off immensely when projects arise with shear-sensitive bioresorbable polymers, high-heat PEEK [polyetheretherketone] implants, and the application of AM that significantly speed up the development process, including iterations completed within days instead of weeks or months,” said Bibber.

Accumold builds its own micro presses for constructing highly efficient micro production cells. These systems can include multiple injection units, automation, inspection, and packaging. “In one case, we built a custom system that could articulate a fabric mesh through the mold for a micro-filter application,” said Johnson. “We have also built what we believe is the first true two-shot micro molding system to produce a sealing gasket on a ridged carrier. This not only proved to be a very effective component, it saved our customer time and expense on the assembly line and failures in the field.”

MTD Micro Molding engineers constantly think outside the box to solve problems. Sometimes this includes getting creative with material selection or tool construction. For example, MTD had a customer whose parts where so small and delicate, they could not be safely extracted from the mold with typical retrieval methods. The staff developed a vacuum system with sensors to pull parts directly through the mold upon ejection, with the parts traveling through the tubing and past the sensor to confirm there was a part and then deposited into individual sealed vials. The part was never handled by robotics or exposed to the cleanroom environment. “On another project, we had to create a customized fixture for measurements in our CT scanner,” said Maroon. “We were struggling to find the right fixture material based on density and rigidity. We trialed about five to six fixture materials before discovering an unconventional material that worked best—balsa wood.”

Isometric engineers recently dubbed one of its micro-molded solutions as the “Michelangelo” because of the three slides, sharp barbs in multiple directions, and wall thicknesses of less than 0.005 inches in PEEK. “At first glance, these projects appear impossible, but with some ingenuity from our very experienced staff, these solutions are vetted out by multiple plastic, design, tooling, and process engineers to collaboratively find a solution that works,” said Bibber. “A technology company is only as good as its people and this is especially true for micro molding and precision assemblies.” 

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Mark Crawford is a full-time freelance business and marketing/communications writer based in Madison, Wis. His clients range from startups to global manufacturing leaders. He also writes a variety of feature articles for regional and national publications and is the author of five books.