Guest Column | April 27, 2015

The Art Of Medical Device Design Inputs

By Jon Speer, founder & VP of QA/RA,

Design inputs are the foundation of medical device development. And without a strong foundation, bringing a new product to market can be problematic.

Call them what you want (design inputs, design requirements, design and development inputs, etc.), getting your design inputs right is the most important thing you can do to make sure your device is developed correctly.

I know it’s tempting to rush through device development. Once you have a great idea and you have a prototype that works, you just want to get the product to market as quickly as possible.

But, there are several steps along the way where it’s good to slow down. Design inputs is one of those times.

According to the FDA’s design controls guidance, design inputs can take up as much as 30% of the project timeline for complex designs. This means that if your timeline is 12 months, design inputs should take at least three months to define.

That’s a good thing to remember. Taking a deep breath, slowing down, and getting design inputs right the first time will only help the rest of development.

Defining Design Inputs
In a nutshell, design inputs define all the performance criteria, requirements, and features of your product. Primarily, you should pull from your user needs to define the design inputs.

However, there is a key difference between user needs and design inputs.

User needs are abstract, using words like “easy,” “better,” and “simple.” This is a good way to state user needs, because it keeps things broad enough to tweak during the process.

Yet, sometimes we either trivialize or do not invest much time defining user needs. Keep in mind that these user needs are a precursor to the design inputs. User needs are a starting point for building the foundation of your medical device.

With design inputs, it’s time to get concrete. They should be objective and measurable, not abstract.

My advice is to make a first pass at defining all the design inputs for your medical device. While words like “easy”, “better”, and “simple” are too subjective and cannot be measured, your first version of a design input may include one of these types of words.

Keep in mind defining Design Inputs is often iterative. The first iteration is likely to be ambiguous and vague. It is your job to figure out how to define these so that all are clear and objective.

A good practice is to make a prototype and to do some informal bench testing to help make design inputs clear and objective.

There are a few goals to consider while approaching Design Inputs:

  • Capture all functional, performance, safety, and regulatory requirements
  • Build upon user needs and intended use
  • Make them clear and objective
  • State them in a way that allows you to prove or disprove them

Defining great design inputs is an art form. You may recognize great design inputs when you see them, but it will take time to train yourself to produce them.

Remember to give yourself and your project plenty of time during this phase.

Sources For Design Inputs
The user needs you’e already defined should be the primary source for your design inputs, but they can’t be the only one.

And no one person on the team should have the sole responsibility for design inputs. When a team is involved, you get everyone’s experience and opinions, which will make the effort stronger.

Besides user needs and the team, there are several more sources you should consider while defining design inputs:

  • Industry standards
  • Regulations
  • Previous projects or products
  • Competitor products
  • End users
  • Prototypes

This list isn’t exhaustive, but it’s a good start.

Your list of design inputs needs to be comprehensive. You need to consider all aspects of the medical device you are designing and ensure that you have defined all design inputs. This means capturing everything — all criteria about your product — what’s important, how the device should perform, and so on.

Remember, some claim design inputs should take almost a third of a project’s timeline.

Think of your design inputs as a contract of sorts. This “contract” lays the groundwork for medical device product developers. The engineers and designers responsible for developing the medical device use the design inputs as the criteria.

Becoming A Design Input Artist
Remember that everything you establish during your design input phase will have to be proven during design verification.

Design verification proves you designed your medical device correctly. You should always consider this step during design inputs, and write your inputs in a way that makes them easy to verify (or at least as easy as possible) when the time comes.

Defining a comprehensive list of design inputs is one thing.

Defining a comprehensive list of design inputs which can be easily proven as part of design verification is a whole different thing. Having the ability to establish design inputs with design verification in mind is definitely an art.

Let me elaborate.

Earlier, I shared that it is a good idea to do some informal testing to help define clear and objective design inputs. In addition to helping you with design inputs, the informal testing can also help you establish test methods for design verification purposes.

Just one word of caution about design verification and testing.

Remember that design verification methods include testing, inspection, and analysis. Sometimes a design input can be verified by means other than just testing.

Including Acceptance Criteria
You need to define criteria for features of your medical device so that you know the product performs as expected. This is referred to as acceptance criteria. Regulations mention the need to define acceptance criteria (usually as part of design outputs).

It is my opinion that when you define clear and objective design inputs and keep design verification in mind while doing so, you will instinctively include acceptance criteria as part of this process. And including this as part of design inputs is perfectly fine.

Design inputs will make or break your project, and mastering the art of writing good ones will take some time.

But doing it right will set you up for a very successful product development.

About The Author
Jon Speer is the cofounder and VP of QA/RA at, a software company that produces beautifully simple quality management software exclusively for medical device companies. He is also the founder of Creo Quality, a consultancy that specializes in assisting startup medical device companies with product development, quality systems, regulatory compliance, and project management. You can follow him on twitter @creoquality and read all his latest blog posts here, including the comprehensive 13-part series The Ultimate Guide To Design Controls For Medical Device Startups