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Design Controls: Design Verification and Validation

Design Evaluation vs. Specifications (Performance Standards)

The original design of devices and any subsequent changes should be verified by appropriate and formal laboratory, animal and in vitro testing. Risk analysis should be conducted to identify possible hazards associated with the design. Failure Mode Effects Analysis and Fault Tree Analysis are examples of risk analysis techniques. Verification testing can begin with prototypes (sometimes called breadboards), and may be repeated as design changes are realized and accounted for. Some examples of verification tests for orthopaedic devices could be:

  • Comparative testing with a predicate device or a legacy product type
  • Simulated-use testing with prototypes
  • Animal model testing
  • Biocompatibility
  • Compatibility with other devices
  • Reliability testing
  • Performance/functionality testing
  • Material compatibility
  • Environmental emissions

Once the design is translated into physical form, its safety, performance and reliability should be verified by testing under simulated use conditions. Such verification may include in vitro and in vivo testing. Appropriate laboratory and animal testing followed by analysis of the results should be carefully performed before clinical testing or commercial distribution of the devices. The manufacturer should be assured that the design is safe and effective to the extent that can be determined by various scientific tests and analysis before clinical testing on humans or use by humans. It should be noted at this juncture that design verification should ideally involve personnel other than those responsible for the design under review. Removing as much potential bias as possible will help to remove uncertainty and other subsequent aspects of risk.
 

Risk-Based Decisionmaking

A widely used risk-based evaluation technique is Failure Mode and Effects Analysis (FMEA), in which failures are assumed to occur. FMEA is useful for evaluating reliability, safety and general quality in which, for example, the evaluator assumes that:

  • Each component fails,
  • Each subsystem or subassembly fails,
  • The operator makes errors, and
  • The power source is interrupted and immediately restarted

The probability of each failure actually occurring and then the resulting effects are analyzed toward eventual mitigation. Then, where needed and feasible, hazards and faulty performance are designed out of the device or reduced, or are compensated or prevented/reduced by interlocks, warning signs, explicit instructions, alarms, etc. Risks, of course, cannot always be totally removed from medical devices, but they should be known and controlled to the extent feasible with cutting edge technology. Mitigation is sometimes the reduction of risks through compromise rather than elimination. The idea is not to promote one method above the other, because a reasonable amount of both actual testing and FMEA should be performed before a device is presented for design validation.

Aside from FMEA, there are other human factor and validation process techniques that can be used in developing an overall risk analysis. These techniques include timelines, workload analysis, failure analysis, alternative calculations, testing including animal testing, auditing the design output (including the DHF at prescribed intervals), design reviews, demonstrations and comparing a new design to a proven design, etc.

During design reviews, all evaluation results should be evaluated by a cross-functional team that will compare the tests and FMEA results with design specifications, including safety and performance standards, to make sure that the desired level of essential quality has been designed into the device. Also, the appropriate design of manufacturing processes, including validation, where appropriate, is needed to assure that production can achieve the level of quality designed into the device.
 

The Medical Device Directive (MDD) - The Essential Requirements and Design Control Impact

This is the most important section of the MDD, because the essential requirements are the legal requirements that must be met by the end of the original transition period. (June 1, 1998 –You may recall from an earlier article that this was the end of the one-year grace period that FDA gave industry to establish design controls, and to be formally judged by regulatory bodies for same.)

These requirements are divided into six general requirements and eight design and construction requirements. These design requirements are basically verified using testing and other evaluation techniques and, in some cases, require subsequent design validation to meet user needs and intended use.

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