Novel printing tools and methods deliver the cure.

There’s no debating that the medical market is huge. According to Prismark Partners, spending on non-IT medical electronics was $53 billion in 2006, with this figure expected to grow to $66 billion by 2010.¹ As the population ages and people take on more responsibility for self-monitoring and self-administration of treatment, medical device manufacturing volumes will reach new levels. But, like the majority of products today, manufacturing these diagnostic tools at the lowest cost per unit is essential for OEM competitiveness. Not only do medical manufacturers need high-volume production speeds, but as these products become smaller, accuracy also becomes tantamount. These two requirements – speed and precision – are forcing medical device companies to seek alternatives to traditional production methods.

As has been the case with so many other applications, printing is again emerging as the most cost-effective and precise method by which to achieve yields and volumes required for medical device production, more specifically for biosensors. These small – and often disposable – products provide instant data on everything from pregnancy to blood sugar levels and are produced by depositing layers of live enzymes onto a very thin substrate that is usually some porous material such as paper or cardboard. Historically, because of the product size and deposit volumes, print accuracy hasn’t been a major concern. However, as these devices become smaller and the materials to be deposited become more expensive and challenging, medical firms now require a process capable of delivering a deposit thickness that fits within a Six Sigma envelope. The nominal thickness of deposit required depends on the application and can range from 25 to 50 µm. Alignment accuracy, fast cycle times and deposition control are, of course, where printing lends its expertise.

I’ve addressed printing platform speed and accuracy discussions in previous columns, and won’t go into great detail here about the capabilities and benefits of many of today’s high-end systems. What I will review, though, is the importance of screen production, substrate handling, and material management in relation to screen-printing biosensors, as these elements are just as critical as machine speed and accuracy. The accuracy and precision of the screens used in medical manufacturing is mission-critical – literally. With traditional electronics manufacturing, the worst that might happen if a manufacturing defect occurs is that your cellphone won’t work. But a wrong reading from a biosensor designed to diagnose a particular medical issue could spell tragedy. Keeping this in mind, it is essential that the accuracy of the screens is spot on; there can be no pinpricks, no room for errors. The choice of the mesh used, the way it is stretched, the emulsion selection and application – all are vital for precision medical screen production.

In addition to the screen technology, material management and substrate handling are other challenging components of biosensor printing processes. The materials printed are live enzymes suspended in a printable vehicle and, in most cases, are printed in layers. As you can imagine, these materials are very difficult to print because they are live products, so they must be handled with extreme care and control. They don’t like a dry environment; it will actually kill the enzyme. When these materials are stored en masse within a closed container at high humidity, they’re fine. But take them out, print them thinly onto a substrate and expose them to air, and the enzymes will die. So, the environmental conditions must be optimized for this type of production.

One of the most difficult aspects of biosensor printing, though, may be handling and printing of the substrates at high volume. Medical manufacturers produce millions of these things – so many, in fact, that they can wear out a mesh screen in a day. The beat rate is phenomenal: One big sheet of substrate cardboard and in one pass, a thousand biosensors are printed with an enzyme layer.

What our company has discovered is that a reel-to-reel system is the most cost-effective way to achieve speed, accuracy and substrate control (Figure 1). Remember these substrates are a little weird and wonderful. Cardboard and paper are porous materials, so moving them into the printer, enabling printing stability within the system during material deposition, and then moving the substrate out – all without tearing them – takes ingenuity and inventiveness. Also, because the enzymes are layered one on top of the other, this process happens inline – usually with several printing systems. The substrate is unrolled and travels all the way down the line through each material deposition process before getting re-rolled onto the cylinder at the end of the line. This is a delicate operation, to say the least.


As I’ve said, the possibilities for high-accuracy printing applications are endless. With biosensor manufacturing, just as with countless other applications, it’s just a matter of understanding what the end-product has to be and using the right screen printing equipment and know-how to develop novel ways of facilitating the process. As for medical manufacturing, the prognosis for robust high-volume manufacturing is excellent!

Reference

1. A. Primavera, R. Roberts and R. Subrahmanyan, “Medical Electronics Pose Unique Challenges,” Global SMT and Packaging, July 2007.

Clive Ashmore is global applied process engineering manager at DEK (dek.com); cashmore@dek.com. His column appears bimonthly.