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Design Controls: Inputs and Outputs in Synergy

This is the third in a series of articles focused on the design controls process from a standpoint of business acumen as well as meeting customer requirements in the orthopaedic medical device market. Sometimes called the requirements phase, design inputs are the starting point of understanding the customer’s requirements, whether they be internal or external in nature. The requirements that form the design input establish a basis for performing subsequent design tasks and, ultimately, validating the entire device for its intended use. Therefore, development of a solid foundation of requirements is the single most important design control activity.

The design input defines device performance, safety and reliability characteristics, environmental limits, physical attributes, compatibility with other devices, applicable standards, regulatory requirements, packaging specifications and labeling. The intended use of the device must address needs of users and patients. This intended use must be unambiguous in its labeling claims and ultimate intended use. The final device specifications should cover all of these device characteristics.

Risk management activities commonly start during the design input stage, as the device’s intended use must be not only functionally accurate but also safe for use. Reviewing data from complaints, medical device reporting, competitor product issues, recall data, clinical literature and other post-manufacturing activities can assist in identifying certain hazards that must be mitigated by starting with inputs and determining how the risk priorities are ultimately addressed by robust design outcomes.

Design Inputs

Section 820.30(c), Design Input, requires that each manufacturer shall establish and maintain procedures to make certain that the design requirements relating to a device are appropriate and address the intended use of the device, including the needs of the user and patient. Also, a design requirement in 820.130 requires that each manufacturer shall make certain that device packaging and shipping containers are designed and constructed to protect the device from alteration or damage during the customary conditions of processing, storage, handling and distribution.

User needs are the basis for design inputs. User needs are not design inputs. Conceptually, these needs can be vague and sometimes confusing. For example, if your company spoke to customers concerning hand-held medical instruments and the end-user indicated that the devices must be comfortable, easy to handle and very maneuverable in tight spaces, your engineers would have to convert those requirements to measurable, requisite terminology such as ergonomically dimensional sizes, materials that are of a certain weight and mass, and cutting or clasping configurations to match body contours.

Another example of this conversion process could be best shown by using the terminology “must be portable.” In a concept document developed for a new defibrillator design, for instance, this could raise questions from product developers about size and weight limitations, resistance to shock and vibration, the need for protection from moisture and corrosion, the capability of operating over a wide temperature range and many other essential requirements. Thus, a concept document may be the starting point for development, but it does not fulfill the requirements of the design input phase.

The intent of the quality system requirements is that the product’s conceptual description be elaborated, expanded and transformed into a complete set of design input requirements that are written in sufficient detail to an acceptable engineering level. I’ll reiterate, this is an important concept to embrace for the continued successful control of the entire design process. The use of qualitative terms in a concept document is both appropriate and practical. This is not the case for a document that is to be used as a quantitative basis for design engineering.

After the concept of the new device design is established, the following basic design input questions regarding the device should be answered.

  • What is the real need for the new device?
  • Where will it be used?
  • Who will use it?
  • How will it be used?
  • With what devices will it be used?
  • How long will it be used?

Design input requirements usually fall into three categories. Almost every product will have requirements of all three types.

  • Functional requirements specify what the device does, focusing on operational capabilities and processing of inputs and resultant outputs.
  • Performance requirements specify how much or how well the device must perform, addressing speed, strength, response times, accuracy, limits of operation, etc.
  • Interface requirements specify characteristics critical to compatibility with external systems; specifically, those characteristics which are mandated by external systems and outside the control of the developers. An example is important in every case is the user and/or patient interface.

These design input requirements are the result of the first stage of the design control process.