Hua Fan, marketing intelligence officer, Veco
Constant developments in medical science mean that the medical industry sees tremendous growth opportunities as well as challenges. The demand for high precision and quality is becoming ever more critical. With the trend of miniaturisation, medical components are not only getting much smaller in size, but demanding more complex geometries, tighter tolerances and superior mechanical properties. Traditional manufacturing processes such as CNC milling, electrical discharge machining (EDM), stamping and water jetting often can no longer meet these requirements.
However, technologies such as electroforming, chemical etching and laser material processes are the next- generation solutions that will enable further innovation and development in medical applications. With these high techs, ultra-precise, burr-free and stress-free complex miniature components in bio-compatible materials can be produced from prototype to industrial volume in a matter of days.
Electroforming: innovation in additive manufacturing
Electroforming is an additive manufacturing (AM) process for the production of high-precision metal parts. It allows metal parts to be grown atom by atom, affording exceptional accuracy and high-aspect ratios. Electroforming is especially suitable for the creation of thin yet strong ultra-precise components in complex patterns. Miniature components with holes down to 2 μm and tolerances within ±1 μm are easily produced.
Depending on the way of the grow, there are two types of electroforming, namely plating defined electroforming (the overgrowth method) and photo defined electroforming (the thick resist method).
Plating defined electroforming, also referred to as overgrowth electroforming, uses a thin photoresist pattern to shield parts of the conductive substrate. A light-sensitive coating is applied to the conductive surface, which polymerises where exposed to ultraviolet (UV) light. Metal grows over the photoresist and the thickness of the product (T) exceeds the thickness of the photoresist (TR), hence why the process is also known as overgrowth. This process is mainly used to make small conical orifices for filtration or jetting. A special cross-section can be achieved during growth, with outer corners rounding off and inner corners staying sharp.
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A schematical cross-section of an overgrowth product (in blue) on a thin photoresist pattern (in orange).
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A unique cross-section of overgrowth electroforming.
Photo defined electroforming, also referred to as thick resist electroforming, uses a thick photoresist pattern during photo defined growth, such that the thickness of the product (T) does not exceed the thickness of the photoresist (TR). Aspect ratios (TR/WR) up to 1 can generally be achieved with ease. This process is applied when the objective is to make the product thicker or multi-layered.
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A schematical cross-section of a product (in blue) deposited between a thick photoresist pattern (in orange).
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A unique cross-section of thick resist electroforming.
Electroforming medical application case studyElectroforming, with its unique features and varieties, has enabled various medical application breakthroughs and can be of great benefit for next-generation medical product design.
Veco produced an electroformed nozzle plate (mesh) for a closed-system nebuliser designed to treat intensive care unit (ICU) ventilated patients non-invasively. The plate has a unique geometry that allows for the release of millions of micron-sized droplets per second, thus forming a perfect, fine mist for targeted drug delivery to the lung
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A microscopic photo showing the unique geometry of the microholes on Veco’s electroformed nozzle plate.
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A microscopic photo showing the unique geometry of the microholes on Veco’s electroformed nozzle plate.
The key to the closed-system nebuliser is the nozzle plate surrounded by a vibrational element. The plate is just 5 mm in diameter and features 1,000 precision tapered holes. It vibrates 128,000 times per second, creating a mini pump that produces a fine particle mist of uniform size droplets, each between 1 and 5 μm in diameter, an ideal size for deep lung penetration. This results in deposition rates far greater than those that can be achieved using conventional nebulisers and therefore could make circuit opening unnecessary. It not only helps patients by avoiding unnecessary pain, but protects caregivers from viral contamination. The nebuliser has therefore proved to be extremely useful in the treatment of contagious diseases such as COVID-19.
Chemical etching: high-precision subtractive manufacturing
Chemical etching is a subtractive manufacturing process that uses baths of temperature-regulated etching chemicals to selectively remove material, thus producing high-precision metal and alloy parts in any desired shape. It is also referred to as chemical milling, electrochemical etching, photo chemical etching, photo chemical machining (PCM), photo chemical milling and industrial etching.
Chemical etching is as precise as it is quick and economical. Complicated, multi-level, multi-featured high-precision parts from prototypes up to large-scale production can be achieved, minus the need for expensive tooling or machinery. Chemical etching is more cost-efficient, has shorter lead times and affords more design flexibility than traditional micromanufacturing techniques, plus there is no need for deburring.
Chemical etching is suited to an extensive range of materials; the most commonly used include brass, bronze, copper, nickel, stainless steel and non- or low-alloy steel. Many other metals such as aluminium, gold, hastelloy, silver and titanium as well as special alloys such as nitinol and vitrovac can be etched under appropriate conditions. Furthermore, various profile geometries can be achieved depending on the demands of the application.
Chemical etching medical application case study
Chemical etching has long been applied in a broad range of industries typically requiring a combination of small size, excellent corrosion resistance, high-precision tolerances, exceptional mechanical strength and, in the case of medical applications, material biocompatibility.
Microneedling is a method of skin treatment that involves using a tool—referred to as a dermapen, dermaroller or rejuvapen—that has numerous, super-tiny needles to penetrate the stratum cornea, or the superficial layer of skin. The treatment is advantageous because the skin naturally builds up collagen and grows back healthier from the micro-punctures.
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A microneedle at the current industry level.
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A chemically etched microneedle produced by Tecan.
Tecan has used chemical etching to produce bio-compatible microneedles that afford ultra-smooth and sharp edges. They are superior in quality to those produced via other industry standard processes, resulting in less skin invasion and contamination.
Laser material processing: accurate material ablation at the (sub)micron level
Laser material processing encompasses various processes, namely laser cutting, laser drilling, laser engraving, laser micromachining and laser welding. Laser cutting is the most widely known process, with applications in a variety of industries including medical. It affords numerous advantages over traditional mechanical cutting and plasma cutting. Moreover, there are more materials that can be cut with a laser than with other technologies.
Laser micromachining is the latest laser process for precise removal of material, enabled by the use of ultrashort pulse (USP) laser ablation with picosecond and femtosecond lasers. Almost any material can be machined with these highly accurate machines. Through accurate ablation, the heat affected zone (HAZ) is considerably less than that with traditional laser processes. Laser micromachining allows layers of a few microns to be ablated, depending on the material.
A medical stent produced by Reith Laser.
Laser material processing medical application case study
Laser material processing is relied on in the medical industry to produce instruments, diagnostic equipment components, implants, stents and more. The stent is one application in particular that has benefited from advances in laser technology.
A stent is a small, narrow and expandable mesh tube used to expand coronary arteries that become too narrow. First, a catheter that has a balloon surrounded by the stent on the end is threaded through the blood vessel and into the narrowed section of the artery. The balloon is then inflated to expand the stent, causing it to lock in place, compress the plague and prop the artery open. Finally, the balloon is deflated and the catheter is withdrawn, leaving the stent in place.
A stent plays a crucial role, reducing chest pain and helping to treat heart attacks. The technology has evolved over the past 20 years and today’s stents are of much higher quality. They are getting smaller and smaller for minimally invasive procedures. Moreover, adding a controlled surface texture or geometry is preferred to improve biocompatibility, for example, to reduce risk of restenosis. Many traditional manufacturing procedures may have reached their limits in being able to meet these demands.
Reith Laser uses USP (picosecond and femtosecond) laser micromachining systems to address the increasing demand for miniature stents that have very thin walls and extremely complex shapes. USP lasers enable laser micromachining to offer a number of advantages over traditional laser cutting, including remarkably clean and burr-free microscale features, and reduced occurrence of material recast, melting and HAZ for increased controllability of surface texture. Not only are these capabilities beneficial for the manufacture of medical stents, but many other medical products following the miniaturisation trend.
Precision technologies comparison
High-precision manufacturing procedures vary according to different processes and applications. In determining the right tool to do the job, most medical product engineers consider the following factors: runtime, precision level, tooling costs and surface quality (stress, burrs, etc.).
Runtime
If the goal is prototyping/sampling, then the best choice of tool based on runtime, precision level and surface quality is laser micromachining, followed by laser cutting and then microstamping. All three processes take an extremely short amount of time. However, in the case of production, these processes are not so advantageous in terms of runtime, and other processes such as electroforming may be a better option.
Precision level
If precision level is the primary concern, electroforming and laser micromachining are both at micron level and able to achieve perfectly clean, stress-free and burr-free surfaces. Electroforming allows for the formation of special conical shaped holes that have rounded outer corners. Laser micromachining, on the other hand, can be used on a wider range of materials.
Tooling costs
Aside from CNC machining and microstamping, most other precision manufacturing technologies are cost-effective, quick to start and do not require much if anything in the way of hard tooling. Electroforming, chemical etching and laser material processing also offer higher design flexibility.
Surface quality
Demand for medical components that are of an exceptional quality is extremely high. Ultra-smooth, clean surfaces that are burr- and stress-free is of crucial importance. Electroforming, chemical etching and laser micromachining are the preferred manufacturing technologies for such high-precision components.
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