Foundation of Product Development: Design Input Requirements – Part 2

As mentioned in part 1 of this series, design input requirements are the foundation of medical device product development efforts. A set of poor requirements will make product development efforts difficult and challenging. Establishing a good foundation of solid, objective, and comprehensive design input requirements takes time and effort of a cross-functional team. Device safety and efficacy are the primary focus of product development. Design input requirements are the key to achieving this focus.

Prior to developing design input requirements, there should be a need. The “need” includes user needs and details regarding intended use(s). The need will likely be somewhat vague and ambiguous. Often times, a need is expressed in the form of a prototype. While the prototype appears to be close to a finished solution, realize that it is critical to take a few steps back in order to define and fully understand the need. The prototype should not be accepted as the solution. This can present difficult situations, however, because of the pride and ownership one attaches with a prototype design. Regardless, before establishing detailed, objective design input requirements, the user needs, intended uses, and the use environment must be understood.

Design input requirements should be comprehensive. All aspects of the medical device should be captured and defined within the list of design inputs. All aspects–including packaging, labeling, and instructions for use. I draw attention to packaging, labeling, and instructions because these aspects are often forgotten or saved until late in the product development process.

Design input requirements need to address intended uses. However, medical devices are sometimes used “off-label” and/or incorrectly. The design inputs should reflect off-label and incorrect usage of a device. Design input requirements should consider:

  • regualtions
  • industry standards
  • interactions with other devices and equipment
  • use environment
  • storage and shipping
  • end user (i.e. physician, home care)
  • similar devices
  • feedback and input from a cross-functional team
  • feedback and input from end users
  • patents
  • prototypes
  • manufacturability

FDA regulations and ISO requirements state that design input requirements must not be ambiguous, incomplete, or conflicting. These terms often cause confusion for product developers. Simply put, a design input requirement must be measurable, verifiable, and objective. Here is an example of an ambiguous and incomplete design input requirement:

The device must deliver adequate fluid for treatment of the disease.

Stay away from using words like adequate, sufficient, approximately, and similarly. Design input requirements using these terms are likely to be ambiguous and incomplete. To improve up the above example, consider this:

The device must deliver fluid at 300 cc/min at 50 psi for 30 minutes for treatment of the disease.

These improvements reduce ambiguity and allow the design input requirement to be verified.

Be sure a design input requirment does not conflict with another or even with itself. I was once asked by a team member to make a flexible stiffener. This should help illustrate an example of a conflicting design input requirement.

A suggestion for making design input requirements unambiguous, complete, and non-conflicting is to consider how the requirements will be verified. Design verification is a design control element and the details will be covered in a future post. Design verification methods include testing, inspection, and/or analysis to prove that design outputs meet design input requirements. When defining design inputs, think about how the requirement will be tested, inspected, or analyzed downstream during design verification. Again, objectivity is critical.

The responsibility for developing design input requirements should not lie with a single individual. Product developers (often engineering personnel) have primary responsibility for design input requirements. However, marketing, sales, regulatory affairs, quality, manufacturing, and end users should all be included during establishment of design input requirements.

Developing design input requirements is time consuming. I’ve worked on many product development projects where there was pressure to move forward. Company management will often push a team to move forward with ambiguous, incomplete, and conflicting requirements. Moving forward with poor design inputs is false progress. Design input requirements that are ambiguous cannot be objectively verified. It may be a battle to convince management the importance of fully defining clear and complete design input requirements. As stated earlier, design inputs represent the foundation of product development.

Future posts will address design input requirements and other design control issues. Creo Quality has the experience and ability to help with your challenges with design input requirements. Contact for questions and comments.

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