The Evolution of a Prototype

A visual guide to my experience taking an invention from concept to working prototype for a new medical device.

View of working prototype installed on stethoscope with extra connector.

The concept for my stethoscope adapter device struck me in November of 2018. This was after our regional paper, The Houston Chronicle published an article featuring my wife standing at the bedside working as a nurse.

At the time my wife Megan was working as a neo-natal intensive care unit nurse (NICU). Years before she had contracted a viral inner ear infection after using a shared stethoscope at the bedside. This resulted in permanent hearing loss. In the photo a stethoscope can be seen dangling through an opening in the isolete bed. That is when the idea struck, design a stethoscope that can separate. This allows ease of use in NICU and other ICU settings and can replace disposable stethoscopes that have terrible sound quality and generate waste.

What began as a specialty device for the ICU expanded into a concept for entire healthcare systems. Now at the working prototype phase, the following is a visual history of the process.

Megan Matula bedside Texas Women’s Hospital — Houston Chronicle 2018


The concept sketched out. My first design only included an embedded magnetic design. The actual first prototype was two ring magnets hot glued to the stethoscope tubing. It worked and led me to believe there was something to this concept.

Other connectors

Initially I devised three different connection types. When I filed my patent application I submitted these three designs. At the time the intent was to make my “claim” as all encompassing as possible for the current and any future technology.

One for all and all for one

While the patent includes multiple adapters it quickly became clear that a single, simple way to connect the device was needed. A magnetic connection works great and can even be used hands free. The problem was that it required a specialized embedding production process for the stethoscope.

Based on my experience in healthcare working in EMS, I was familiar with the connectors used by medical equipment suppliers. The most common being IV tubing and syringe / needle connections. These all use a “luer-slip” type connection. This design is comprised of a “male” and “female” type connector secured by a couple of threads. This seemed by far the best option. A connector that was already known by healthcare staff and would be easy to produce.

My first prototype was made from disassembled syringes and cut up stethoscope parts.

I decided to have a “working” prototype made by 3D Printing. The technology is widely accessible in my area and can allow for flexible design and rapid production without the need for casting or molding.

3D design and print

Despite a global pandemic which this device hopes to help combat, designing and have the connector made was quite simple thanks to digital communication.

In a matter of weeks I had bids with multiple vendors in the area and designs were being drawn up.

Trial and error

This is one of the most exciting parts of the invention process. As an inventor or in this case more “innovator” I was able to see my idea come to fruition.

Once I had the first version in hand the decision to go with the “luer-slip” design was validated. While the material used for the print was very weak and I broke half of the adapters, it proved the proof of concept.

Working prototype in hand

Now that I had a digitally drafted adapter and print in hand, it was time to zero in on the design. Obviously a much stronger material was needed, this was easy to accomplish.

The difficult part proved to be designing the adapter in a way to work for all brands of stethoscopes. While the tubing used for stethoscopes is fairly standard in outside diameter, the internal diameter can vary greatly. This is largely due to differences in production quality by various manufactures. If they sell a version with a thinner tube wall they save on production costs. The downside is that these versions tend to lack in sound quality for the user and would prove difficult to match all sizes.

This would also prove challenging in determining a proper tolerance for all types. Initially I had the “teeth” of the barb widened, for more grip, but this proved to be too much. The current version is slightly larger in diameter and the barb length has been increased. This allowed for a tight fit for both thick and thin tubes and still allowed for easy instillation and removal.

My advice

While far from finished, this process has reinforced my experience and taught me some new lessons as well.

First and foremost, listen to the people you hire and keep around. Hopefully you have realized by now that if you are doing something like this you do not know everything.

At every step of the process from patent attorneys and design engineers to copy writers and colleagues, listen to what they have to say.

All of these individuals contributed greatly and this design would not be what it is today without them.

Allow room for change. What I have in hand now is nothing like I envisioned when I first had my eureka moment and is now better than ever.

Next Steps

Now that I have a functioning prototype I am currently in the process of establishing a clinical study with a hospital system. In addition I have sent off prototypes to several colleagues in the industry for feedback.

If you have any questions about this invention, the patent process or 3D printing feel free to contact me. Visit the device home page for more information.

I would like to thank my brother and bio-medical engineer Frank Matula, the staff at Madan Law and 3D Print Texas for all the help.



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Sean Matula

Sean Matula

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Owner of SBCSM. Small Business Consulting Strategic Marketing. Providing small business owners with solutions to grow their business and reach more customers.