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Design Input Specifications

Kickstart your DIS: 6 Approaches to Generate Design Inputs

April 3, 2018

A Design Input Specification (DIS) plays a critical role in any product design process.

  • The product DIS contains all the characteristics of a device that are used as a basis for product design
  • The level of detail that your design inputs cover can be a deciding factor that makes or breaks a smooth run to market.
Who cares about DIS?

Investors and the FDA do for sure.

Investors want as little technical uncertainty as possible, and the FDA wants proof that your product will do the job as intended. On a serious note, the FDA will review EVERYTHING as it is a mandatory regulatory condition in our world for medical device development.

Detailed design input specifications make your design team's job easier -- which makes YOUR job easier.

Your DIS is a living document that will shift and move as you journey along the path to commercialization.

Far from a rigid, frozen document, the DIS is a tool that needs to be used by teams to foster innovation and should lead to greater confidence in the final deliverables.

Here are six approaches you can use to generate inputs.  Following afterward is a real example of how these approaches look in practice.

Six Approaches to Generate Design Inputs
Generate Design Inputs
1. Define the intended use, and provide as much detail as you can about who will use it.

This activity will vary greatly depend on whether this is an incremental improvement to an existing product, or a brand new direction.

As a team, consider where it will be used, how it will be used, and who is expected to use it.

Consider if it needs to be sterile, single use, needs to conform to a specific procedure, etc.

2. Review similar products or product families.

If you are looking to compete directly against a known competitor, this can be fairly straightforward.  Often, you can find published instructions for use; which will contain basic specifications.

Leverage the work of others to gather inputs on mandatory items. Learn what trade-offs other teams have made.

Depending on your goals, you can learn what your team must achieve to be an equivalent medical device or what they must strive for if you are introducing the next best device.

If you are working on something truly innovative, you may still get some good ideas from the design elements of existing complementary products that are used in the same environment.

3. Talk to end users, patients, buyers, etc., to determine their needs.

If possible, observe the procedure or interactions of your proposed device's environment. This can be a challenging and expensive task, but arguably the most influential.

These interactions can range from informal to formal.

You are looking to reduce uncertainty and build confidence to foster the creativity required in the ideation phase of design, which will follow.

Make a list of the needs in clear and simple language.

4. Identify the international standards and regulatory rules that apply to your product.

As a team, review the general, collateral, and specific standards that apply to your product, and extract the requirements needed to achieve conformance.

5. Perform a risk assessment and use the outputs as design requirements.

I recommend using the FDA's Manufacturer and User Facility Device Experience database (MAUDE) to review common failures associated with the product class within which you are designing. 

This can also be useful for detecting trends in similar devices. These trends can become inputs for your design team to consider.

6. Choose your markets and learn their regulatory standards.

Once you have selected your markets, you can start to classify your device in each of them. The USA, Europe, and Canada share similarities, but each will have some unique requirements.

Knowing your market locations and their regulatory standards ahead of time will affect the level of detail required for your DIS.

Defining design input specifications doesn't have to be a drag.  Come up with creative ways to get the team brainstorming and gain maximum benefit from this important design tool.

One big tip I cannot stress enough is: Make your DIS usable!  The level of detail should match the level of complexity and risk. You'll thank yourself later.

Keep reading to see how these six approaches to generating DIS look in practice.

In practice, your DIS generation may look like the following excerpt from the DIS of a stent for the superficial femoral artery.

1. Define the intended use, and provide as much detail as you can about who will use it.

Based on defining use, we generated these possible design inputs:

  • This product is likely to be used in the interventional radiology lab by a radiologist or a vascular surgeon.
  • It will be used inside the sterile field and will be handled with a gloved hand.
  • It will need to be sterile and is a single-use product.
  • It is intended to be used to place a metal scaffold via a delivery catheter into the superficial femoral artery to maintain the lumen.
2. Review similar products or product families

Reviewing currently marketed products can allow you to quickly determine the range of stent sizes available for this artery.

Based on reviews, it was determined that common stent lengths range from 20mm to 200mm. Therefore, depending on our goals, a design input will specify that the stent length must be as good as or better than competitors.

3. Talk to end users, patients, buyers, etc., and determine their needs.

While observing a stent placement procedure it was determined that backlash during stent deployment can negatively impact correct placement.

An input for establishing limits for unwanted movement during deployment will increase user satisfaction and improve patient outcomes.

4. Identify international standards and regulatory rules that apply to your product.

A review of the ISO standard ISO 25539-2:2012 Cardiovascular implants - Endovascular devices - Part 2: Vascular stents would be required. We use this information to generate more inputs.

5. Perform a risk assessment and use the outputs as design requirements.

A search of the FDA's MAUDE database reveals that for 'Product Code: NIP' and 'Event Type: Malfunction' reveals that a fairly common occurrence within the last 5 years is incomplete stent delivery or partial stent deployment.

Based on this information, an input should be developed to address primary deployment system failure, like having a secondary deployment system as a backup.

6. Markets & regulatory standards

If your selected market is the USA only, you would be required to conform to the FDA's 21 CFR Part 820. The device class for a stent, Superficial Femoral Artery is class 3, which becomes one of our design inputs.

Want more information on a particular topic?

As a medical device consultant, I offer up a wealth of knowledge and guidance, especially in Design Input Specification development.

I invite you to connect with me for a discussion. I am also available to hear any concerns you may have or to review your DIS if you want an outside perspective.

My name is Ian Maclean, let me be your expert. Click here to contact me.
Ian Maclean, Professional Engineer