Design validation is one of the most important aspects of the design and development process for medical devices. It is at this stage that the medical device manufacturer confirms that the device that was designed is the right product that meets the needs of the user. Successful design validation requires a thorough understanding of the user needs. Some of the questions that need to be answered during design validation are:
- Does the device work for the user?
- Does it meet the specified user needs?
- Does the device work in the user’s environment?
- Is the device’s usability easy, clear, obvious, and evident?
- Is the device safe and effective for both the user and the patient?
Design validation has been the number one citation in FDA warning letters for design controls from 2011 to 2015. Six common categories for the design validation warning letter citations are:
- Not conducting any design validations to ensure finished device meets the intended use and end-user needs.
- Not using production units, lots, batches, or their equivalents.
- Not conducting design validations under defined operating conditions, under simulated, or under actual use conditions.
- Not conducting design validations when changes were made to a device released for production, sale, and use.
- Not providing rationale for the decision not to perform design validation.
- Not selecting individuals who represent actual users.
What is Design Validation?
Design Validation is defined in 21 CFR Part 820 – Quality System Regulations as “establishing by objective evidence that device specifications conform with user needs and intended use(s).”1 Design validation can occur during the development process, before the device has been released for production, sale, and use and, when changes are made to a device that has been released for production, sale, and use.
Figure 1 illustrates where design validation is conducted in the design and development process. The design and development process starts with the identification of user needs. The user needs are translated into the design requirements (design inputs). The user needs and the design inputs are the foundation for developing the right design and subsequently verifying and validating the design. Incomplete, inadequate, or incorrect user needs and design inputs will result in the design of the wrong product, wasting enormous amounts of resources, time, and money.
Design validation is a requirement for design and development in the U.S. FDA regulation 21 CFR Part 820, and the global international standard ISO 13485:2003/ISO 13485:2016.1–3 In addition to design performance and functionality requirements, human factors and usability are critical in design validation studies. The risks associated with the design (hardware, software, userinterface, and usability) should be identified and managed to ensure safety and effectiveness. Risk management for medical devices is conducted using the international standard ISO 14971.4 Usability engineering requires the use of the standard IEC 62366.5 This standard points to several aspects of ISO 14971 regarding the management of userelated hazards and risks. ANSI/AAMI HE75, though not a voluntary standard, provides in-depth information on human factors engineering and design guidelines for medical devices.6
To Validate or Not to Validate?
Design validation is a key requirement when changes to a device are made after it has been released for production, sale, and use. According to 21 CFR Part 820.30 (i), ISO 13485:2003 Clause 7.3.1, and ISO 13485:2016 Clause 7.3.1, design changes shall be verified and validated as appropriate, and, reviewed and approved before implementation.1–3 Rationale should be provided when design validation is not conducted. Several companies have been cited for not conducting design validation on a change to an existing, marketed product. A common reason used is that design validations cost time, money, and resources and could affect sales and revenue.
Instructions for use (IFU) is a prime example where companies rationalize that a simple verification of the change in an IFU is sufficient. Not validating this change with the user (i.e., conducting a design validation ensuring that the updated and revised instructions are evident and effective) can lead to use errors and potential harm or injury to the patient. Not validating a simple change in a device component shape, color, or feel can result in user confusion and use errors. Changes to software in a device are especially prone to adverse events in the field if the software is not validated adequately.
The proper due diligence in evaluating whether or not design validation is required is critical to patient safety and device effectiveness.
Design Verification vs. Design Validation
Many companies use the term design V&V for design verification and design validation, intentionally implying that the two activities are equivalent and can be done together. Design verification and design validation are two distinctly different terms and have significantly different requirements. Table 1 illustrates the differences between the two activities.
Things to consider for design validation – Several reports over the years by regulatory bodies indicate that as many as one-third of medical device failures and adverse events that involve use of medical devices point to failures of device use rather than failure of the device itself. This has often resulted in suboptimal medical treatment, injuries, and even patient deaths. In many cases the redesign of the device-user interface improved usability and reduced patient harm and injury.
Usability is defined as the “characteristic of the user interface that facilitates use and thereby establishes effectiveness, efficiency, and user satisfaction in the intended use environment.” (IEC-62366).5 All aspects of usability can result in safe and effective use or can result in use error leading to an unsafe, ineffective device. Factors that influence the outcome of either correct use or use error include the use environment, the user, the device, its user interface, and the IFU and training associated with the device (see Figure 2).
Design Validation should consider the following nine criteria:
- User-friendly device designs and operations that are self-evident and mistake-proof.
- Device safety, effectiveness, functionality, and performance.
- The range of intended user population( s). These include the range of users that have different physical characteristics and capabilities (size, height, dexterity, flexibility, functional reach ranges, vision, hearing, tactile sensitivity, etc.), cultural backgrounds and languages, learning capabilities, and emotional and cognitive capabilities. The level of knowledge and experience and training can also influence how well a user is able to interact with a particular medical device.
- The intended patient population(s), some of which include neonates, children, young adults, adults, and the elderly.
- The use environments, which can range from operating rooms (ORs), emergency rooms (ERs), to standard hospital rooms, clinics, and homes. The clinical environment is a complex system of medical and support personnel and patients. They can house a large number of different medical devices and supporting equipment. The environments in a clinical setting are well controlled compared with the environment of home. Factors like temperature, humidity, noise, vibration, compatibility with other devices, lighting, space, electrical and electromagnetic interference, radiofrequency interference, and atmospheric pressure should be built into the design validation.
- Clear, understandable IFUs that can be easily followed and remembered when users return after a period of time to use the device again. Methods of instructions should be geared toward specific user populations. Electronic instructions (videos) might be more effective for a certain demographic of users versus physical user manuals. In addition, methods of writing the instructions — i.e. pictorial versus straight text — can also affect usability.
- Effectiveness of use, which can be measured by the number of steps done correctly divided by the total number of steps. This can point to use errors and the severity of those errors during use.
- Efficiency of use, which can be measured by the total time taken to complete the tasks versus a targeted goal.
- User satisfaction and acceptability of use for each task and the overall usability and operation of the device can be measured using questionnaires with a Likert-type scale and subsequently analyzing the data.