The Seven Cardinal Principles Of Medical Device Design, by H. Kent Craig

The Seven Cardinal Principles Of Medical Device Design

by
H. Kent Craig

Whether you are engaged in medical device and product design on Class I, II, or III levels for patient use, or whether you design accouterments and implements for physicians, or whether you design diagnostic equipment for technicians, at the heart of your efforts lie a set of base principles which govern the production of all excellent design work.

1: You are not the template for humanity, or, it's the ergonomics, stupid!: Just because a manually-controlled widget fits your palm and finger-gap spacings comfortably, doesn't mean it will on anyone else. Just because a display is readable by your 20/40 corrected eyesight doesn't mean that someone with lesser vision will be able to accurately read the information in anything less than perfect lighting conditions. Just because the angle of depth for knees is okay for you, doesn't mean it will deep enough for anyone over 3'6" in height.

On a fixed budget, it's sometimes hard to come up with cash for software libraries of standard ergonomic models if you don't have them already and they do have limitations over live humans anyway, let alone paying for a live-body sampling of subjects to come to your lab and actually try things out for size, and in some cases it's obviously impossible to ergonomically parametize a device which might place a subject or patient at risk, IDE's (investigational device exemptions) aside. Where you can design at least some user-flexibility and customization features into a device, doing so will increase end-user satisfaction, decrease device returns, and solidify company goodwill assets. Even when ergonomically counterpointing means increased design costs by low double digits and increased manufacturing costs by low single digits, the results should result in higher bottom-line profits via increased unit sales from greater market penetration.

Beyond common sense, think old, and think young. Think how an older person, with arthritic hands, or an aged body chemistry, or with poorer eyesight, or with limited ranges of motion, would interact with your device. Think how a younger person, or someone of shorter physical stature, or someone with small adhesive and grip areas on their hands, or someone with shorter reach, with shorter fingers would interact with it.
2: While you may know your device's limitations inside and out, never assume others will as well.: Does your device function fine on the American grid, but when the power supplies are switched over for the European market the clock-cycles get a little dirty which slightly affects accuracy? Does effective pre-cleaning of your reusable device help preserve its cosmetic appearance after autoclaving? Did you notice strange happenings about your device the day your A/C went out for four hours, but you didn't bother to document that, since you assumed that wherever your device would be used would be within standard hospital or lab climate-controlled conditions? Did you notice any effects from random, transient EMF waves in your design lab on your device, but didn't bother to investigate and do a re-design because it's not required under FDA regs?

While management can be a lard-butt in regards to "enhancing" product limitation disclosures to either the FDA or your end-users from fears of increased liability windows, it's never the less important to incorporate knowledge of your device's limitations into its alpha design, even if you can't disclose fully those limitations to those outside of your company's NDA-bound-circle of employees.
3: Take pity on the poor SOB (Sweet Ol' Bobsledder) who has to service your device after-market.: For that matter, take even more pity on your in-house service guys, since they're the ones that will be dealing with your beta-level mistakes that escaped from your design lab. If your device is a manual surgical accouterment, if it's reusable, it's going to have to be serviced too, if that service is nothing more than sharpening, polishing, or cleaning. Why use an open pivot design when a lap-and-cover pivot would minimize potential organic contamination of said pivot? Why use a four tiny little screws for access to a device's innards when it would increase the unit price cost less than $.02 to go to the next-largest size screw, and would make access a whole lot easier for the technician having to get inside.

And why cram all the electronic components on a PCB (printed circuit board) that doesn't take half the available footprint space available inside a device, just because the layout looks so neat, so pretty in its visual impact, when increasing the board's dimensions by a factor of .5 would have resulted in less thermal lifecycle failure because of better air circulation between the discrete components, would have resulted in a net discount from your contract manufacturer because their insertion machines would have higher tolerances to play with, and most importantly, would have resulted in your factory floor service guys thanking you for actually giving them room to wiggle and waggle their desoldering and other tools around and on the PCB with?

It doesn't, it shouldn't, cost a dime to be nice to post-market service people, if they're your own or third-party. It actually saves a few dimes in the long run from increased efficiencies of turnaround times and better, longer-lasting repairs made. And it saves your end-users, your customers money too, because devices which have a reputation of being initially high-quality yes but also having an ease of service will have cheaper life-cycle costs associated with them than those that don't.
4: Know and accept your materials' limitations.: Don't try to push your precision machining subcontractor to give you a +/-.0003" tolerance for threads on a phenolic screw blank when you and they know that unless the material in question is just the perfect specimen ever made, all that can be realistically expected is a +/-.0025" tolerance. Don't expect then wish like hell for a 12 microgausss/cm² EM capture from shielding, when the manufacturer clearly states that the most you can expect, even with brand-new material installed correctly within a tight thermal and humidity operational range, that the most you can expect according to their tables is a 9 microgausss/cm² EM capture. Don't expect your silicone tubing vendor to guarantee life-cycle non-failure of their 3/8" tubing when bent on a 360-degree plus radius on a base of less than .5", when their technical department clearly covers their rears by faxing you their opinion of such after you make the appropriate inquiry.

Working around the limitations is how you make a substantial part of your cheque every couple of weeks. Using your skills and knowledge-base to work around seemingly insurmountable design obstacles is how you impress your bosses, impress your spouse, and if lucky wind up with the occasional patent.
5: Allow downtime for the creative process to do its thing.: While most supervisors you'll have in your career understand this, you might run across some that don't. And you, yourself, might ignore it from time to time as scheduling and product-design-cycle times become shorter and shorter.

You get paid for solving problems, not for creating them. You get paid for what you know and what you can do with that knowledge, not for any work which is the end-result of that. You get paid for making your company money by creating excellent designs, not from manufacturing those products made from your designs, not for installing them in patients or in labs or hospitals, and not for servicing them after-market.

Without the freedom and flexibility just to chill out more or less when and how and where you feel like doing so at work within limitations of deadlines and such, without the ability to surf the Internet just for the fun of it at work to momentarily purposely distract your brain from pressing tasks at hand, without the financial and work schedule support from management to help enable you to attend continuing education classes and maybe go for your Master's or Doctorate, without the understanding from your supervisors that if you hump five 16-hour days in a row to churn out the last alpha print for a PMA (premarket approval) design submission that you really should be given a comp-Monday off as an earned reward just to hang at home and rest an extra day, then it really will be hard for you to be the creative genius you really need to be to do your job with professionalism and aplomb.
6: Do your homework!: What helped drive the great bursts of creativeness among the different artists in the Impressionist School? What helped drive the great competitions between Ford, GM, and Chrysler? What helped Gandhi drive the British out of India?

Knowing their competition, studying exactly what their competition was doing and how they were doing it, and then adapting what their competition was doing to their own means and ends, within their own self-selected precepts and concepts.

Even in a business so arcane as ours, often driven more by FDA and governmental regulations and whims than by the more typical market forces which govern the rest of the world's sub-economies, certain marketing principles still apply. End-users for medical devices are like end-users for any other product, except even more so. They like next-generation advances in technology, but not quantum leaps of two or three generations ahead at one fell-swoop, which scares them a little and gets them thinking more about the "what-ifs" of potential liabilities than any potential short or long-term benefits to either themselves or their end-users/patients. They like ease of use, but also familiarity of design, taking comfort in the facts that if a given design has become an industry standard for such, it's that way for a reason, maybe not the "right" reason, maybe not for the reason you like, but for a reason. And they like believing that they are they ones doing the actual driving of all your design efforts, because in many ways, they are, since if you consistently turn out designs which they don't like and won't accept for whatever reasons, your company won't get orders and eventually you'll design your way out of your job.

How do you determine the paradigms of industry-accepted design practices and limitations? Since you're in the industry and read trade publications and attend industry conferences and such, you're all the time busily gathering intelligence on your competition whether you realize it or not, and that industry knowledge, that trade intelligence, is of course how you develop a core vision of what is and isn't accepted in the industry. Every time you surf the Net or peruse a Usenet group related to the industry and read an opinion from someone like me no matter how silly it may seem at the time, you're busily reforming your own projections of your trade, of what end-users like and don't like, of what might potentially sell and why and what won't.

That energy, that drive that comes from our more-or-less free market competition system is what makes you slog through half a dozen trade publications at home when you'd rather just mellow out and watch ESPN, is what makes you attend a trade conference a thousand miles away when you'd rather fly home to see your folks that same weekend, is what makes you attend an AutoCADŽ V.978.4 class at the local community college for three nights a week for a solid month when you'd rather be attending your son's little league games, is what doing your homework to improve your job skill and asset-set to improve your job performance to enhance your company's market position and help assure your continuing employment is all about.
7: Don't re-invent the wheel, or, sometimes borderline plagiarism is the sincerest form of not just flattery, but also product-cycle-developmental-time efficiency.: To design and manufacture a new refrigerator, you don't need to invent a new kind of compressor, a new kind of gaseous refrigerant, a new kind of thermal evaporator, or even a new kind of contact-less, pressure-less switch to turn the inside light on once the door is open. To design a new medical device, you (usually) don't need to design a new kind of PLD, a new kind of shielding material, a new kind of neutral intracavity contact material, or a new kind of venous shunt.

This is where CAE (computer-aided engineering) and CAD software has really made a significant impact in our industry. By either buying or creating libraries of standard design templates and assemblies, a medical device designer can plug-and-play greater and greater parts of a device's completed design. CAE software isn't going to be at the oft-predicted "connect the dots" stage of A/E (artificial intelligence) supremacy tomorrow or the next day, though that day does loom closer and closer. When that day comes, manufacturers will still need medical device designers, because some one has to sit down and pull the initial concepts for the theta designs from someone's rear, usually their own, and actually think this stuff up from somewhere. Even if A/E ever does mature into a bullet-proof alpha stage, it will never replace the medical device designer, because it will always be, it can only be, reactive, not pro-active, and certainly not creative.

Management still being tolerant of older fogies who haven't bothered to learn CAD and still do much of their designs on drafting boards because they make their bosses money in the end, using "cookbooks" and such, or not, is still a matter of how much time you want to spend actually having fun and being creative and how much time you want to spend re-inventing the too many little wheels and gears which will grind away in the belly of your designs. I've never understood designers who come up with simply elegant solutions to a particular problem in a design concept, and then never attempt to re-use that solution in any other of their subsequent designs that follow. Myself, once I nail down an electrical, mechanical, optical, or any combination or hybrid of those three of more solution to a given problem, then that baby becomes a workhorse assembly, and is used when and wherever I can, even if I have to fit in the design with the proverbial crowbar, because that bullet-proof subassembly always make me look good in the end.

Most world-class designers I know always have their own "cookbook" stashed back somewhere, even if they never admit to owning it let alone using it. Between design help you can get from vendors, what's available in software libraries, and what tidbits of inspirational design you author yourself, over the years you should be able to fill out a thick volume of alchemic knowledge about our trade of medical device design, a necronomicon of design spells and incantations which, in the end, will increase your job performance and offer you the odd lifeline when you're backed into a corner and have no where else to turn, always finding inspiration for answers if not the answers themselves in your bound hardcopy of accumulated wisdom.

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