Albert Tsang looks at how photo-etching on titanium is opening up an array of possibilities for medical device OEMs
The metals industry and the medical industry are inextricably linked, and development and innovation in metal supply stimulates much product development in the medical device sector. Improvements in metal supply, and the development of new alloys drives the safe-use application of internal and external devices. For many years, stainless steel was the ‘go to’ metal for numerous medical applications, being low cost and exhibiting corrosion resistance. However, titanium is growing in popularity especially for implantable devices, but it is an expensive metal (meaning waste in production must be minimised) and it is also notoriously difficult to work.
In its pure form, titanium exhibits low density and very high strength characteristics, and crucially for medical applications (especially internal medical applications) is corrosion resistant. Certain titanium alloys (particularly Ti-6Al-4V and Ti-6Al-4V ELI) are especially non-reactive with bodily fluids, and greatly negate the risk of implant rejection. When properly treated, titanium also bonds well with human bone, meaning that fixation of implants is extremely secure.
Common medical uses of titanium are for orthopaedic devices such as hip, spinal, facial, shoulder, elbow, and knee replacements. In addition, some heart valves use titanium housings, and it is also used in the manufacture of pegs to attach prosthetic eyes and ears, as well as being the standard shield material for pacemakers and defibrillator cases, due to its resistance to attack by body fluids, its strength, and low modulus.
Finally, titanium is the perfect choice for surgical instruments, such as drills, forceps, retractors, scissors, needle holders, and eye surgery equipment. The metal is also compatible with MRIs or CT scans as it is non-ferromagnetic.
Developments in titanium manufacturing
The key limiting characteristic of titanium is its cost, which is significantly higher than aluminium and steel alloys, and therefore titanium usage requires a compelling justification in all applications. Elevated cost is a product of the difficulty inherent in extracting titanium from its ores, and the fact that carbon cannot be used as the reducing agent as it produces a carbide when heated with titanium. Instead, costly reducing agents such as sodium and magnesium have to be used which ensure production of the pure metal.
The cost implication of titanium use means that any manufacturing technology utilised with the metal must minimise wastage. But wastage issues in the processing of titanium is only one draw back when it is used as a material for manufacturing. The other is a product of its strength characteristics, which makes traditional machining technologies high cost and anything from 10 – 100 times slower than machining of aluminium alloys. Cost implications of using titanium, therefore, demand that any manufacturing technology minimises waste and is speedy.
Recent developments at Precision Micro Ltd are heralding the dawn of new possibilities in the practical and economic use of titanium in various medical applications. Precision Micro is expert in the art of photo-etching, a technology that has a history going back to the 1960s, and is a development of processes used in the printed circuit board industry. Over the decades since then, Precision Micro has been at the forefront of developing the technology that is now used on a variety of materials to fabricate sheet metal components using a photo-resist and etchants to corrosively machine away selected areas.
For complex or feature rich parts, or for parts where the retention of material properties is important, photo etching has been proved to be much more accurate and cost-effective than many traditional industry alternatives such as stamping, pressing, punching, or laser and water-jet cutting.
It is a technology that produces burr free parts with clean profiles and no heat-affected zones, and stress free parts with metal properties remaining unaffected. As the process relies on digital tooling (meaning that tooling costs are measured in the hundreds of pounds not the thousands of pounds), it allows for multiple design iterations quickly and at low cost, with no effect on product time-to-market.
The process itself is fast and economical with lead times in days not weeks, and is precise down to the most exacting micro levels, accuracy even on the most complex of parts being a key attribute.
In 2012, Precision Micro was purchased by the leading aerospace, defence and energy giant Meggitt plc, and is now an autonomous entity within the company. The purchase has opened up new possibilities for the company, not least due to the scale of investment in new processes and opportunities that is now taking place. One such is in the development of the photo-etching process for the volume production of parts from titanium, perhaps the Holy Grail for the sector in Europe. Precision Micro is now able to announce that it is able to provide this service for its customers.
Photo etching of titanium
Issues associated with the manipulation of metals via machining, stamping, punching, and pressing are exacerbated when manufacturing with titanium due to its strength and resilience. Applying photo etching to titanium eliminates stress and burr related problems associated with alternative manufacturing technologies, and opens up an array of possibilities in the areas of medical implants which require a combination of light-weight, strong, and corrosion resistance characteristics.
Key characteristics of photo etched titanium parts are the smoothness of surface and channels, and elimination of burrs and surface irregularities. The process is highly repeatable and economic, with an image of the parts to be manufactured effectively being printed on the sheet metal, and all of the parts etched at the same time. The digital “photo”-tooling used to print the image of the parts ensures that parts produced now are identical to parts produced a decade later.
Since announcing its ability to photo-etch titanium, Precision Micro has received massive uptake from medical OEMs throughout Europe, especially manufacturers of implantable products. A reliable European-based titanium photo-etch capability like that now offered by Precision Micro means that companies do not have to suffer exposure to currency fluctuations or delivery costs which occur when relying on supply from outside of Europe, and can take advantage of shorter lead times. Precision Micro is able and willing to offer short runs with no minimum batch sizes as well as volume manufacture, and recommends engagement with OEMs early in the design cycle to allow input on product development.
Titanium’s biocompatibility — as previously mentioned — fits perfectly with the production of technical medical applications like implantable reconstructive meshes. Titanium mesh cranioplasty is now the preferred treatment for an array of cranial defects, and photo etching provides a quick and efficient means of manufacture. Titanium’s corrosion resistance, strength, and biocompatibility are all hugely advantageous for cranial meshes, and the burr-free and stress-free nature of the process, and the fact that chemical processing causes no hardening or thermal distortion, all serve to produce uniform products.
The loss of complex or extensive bone structures due to an accident or tumour creates significant physical and emotional stress for patients. It also represents a great challenge for the physician pondering the question of how the defect can be covered in the best possible way. In such cases, patient-specific implants can be an effective means of mastering these difficulties and keeping the resulting uncertainties under control, representing a more efficient and satisfactory treatment than standard sized implants.
For one leading cranial mesh manufacturer, Precision Micro makes pre-contoured titanium mesh implants and templates using photo-etching. Mesh sizes and shapes are created using a compilation of adult CT scans to develop the best possible “average” fit in titanium, which is rigid, but can also be modified slightly to adjust to precise patient anatomy. One unique characteristic of photo-etching is the fact that with digital tooling, the tools for these cranial meshes are the same for prototyping and full production, and as they are digital and no steel is cut, they are low cost, easy, and quick to make, and can be adapted and changed with little expense.
Such cranial meshes are extremely feature dense, and demand burr free edges which alternative manufacturing and machining technologies find difficult to achieve. In addition, as well as manufacturing the meshes, the photo-etch process can also depth etch the counter sinks for the screws to sit in in one single process, overcoming the need (as was previously the case) to laser cut the mesh and then machine the sink holes.
Photo etching is also an extremely clean process, tightly controlled chemistry selectively removing metal atom by atom with micron accuracy imparting no stress on the base material and avoiding undesirable features such as recast layers.
Another medical device OEM that works with Precision Micro manufactures implantable cardiac defibrillators which are used to treat patients suffering from ventricular fibrillation, a chaotic heart rhythm that can quickly result in death if not corrected. In operation, the defibrillator device continuously monitors the electrical activity of the heart of the patient, detects ventricular fibrillation, and in response to that detection, delivers appropriate shocks to restore a normal heart rhythm. Shocks as large as 30-35 joules may be needed.
Shocks are delivered from capacitors which need to be charged with the required amount of energy in only a few seconds. The power source, therefore must be highly reliable and provide urgently needed therapy whenever necessary. In addition, as cardiac defibrillators are implanted, the battery must be able to supply energy from a very small footprint.
Precision Micro manufactures very fine, sub 80 micron thick titanium anode and cathode battery current collector grids used in the lithium batteries contained in the implantable defibrillator. These intricate grids, less than 300mm wide, are photo-etched from titanium because it is vital that stray metal pieces are eliminated from the current collectors as they could poke through the separator material and short the battery. Traditional machining and processing technologies cannot guarantee that no waste metal would be present.
The use of titanium in product design has been held back due to its inherent cost and the difficulty in manufacturing via traditional machining, stamping, and punching processes. However, through the use of photo-etching, a proven volume manufacturing technology used on various metals (recently including titanium), Precision Micro is offering a cost-effective and efficient route to the production of titanium parts that is unique in Europe.
Photo-etching has many inherent advantages as a manufacturing technology that have been detailed above, and these advantages can now be applied to the serial manufacture of titanium parts. While the cost of design iterations are dramatically reduced using photo-etching — with its low digital tooling costs —product designers and OEMs looking to take advantage of this new process are encouraged to engage Precision Micro early in the development stage of the product life-cycle to ensure DfM, and maximum cost efficiency.
Albert Tsang is the Technical Manager at Precision Micro, Birmingham, UK, and has been at the company for 13 years. For over 50 years, Precision Micro has pioneered photo chemical etching, a manufacturing technology.