I. PURPOSE
This guidance is intended to assist manufacturers in understanding quality system requirements concerning design controls. Assistance is provided by interpreting the language of the quality systems requirements and explaining the underlying concepts in practical terms.
Design controls are an interrelated set of practices and procedures that are incorporated into the design and development process, i.e., a system of checks and balances. Design controls make systematic assessment of the design an integral part of development. As a result, deficiencies in design input requirements, and discrepancies between the proposed designs and requirements, are made evident and corrected earlier in the development process. Design controls increase the likelihood that the design transferred to production will translate into a device that is appropriate for its intended use.
In practice, design controls provide managers and designers with improved visibility of the design process. With improved visibility, managers are empowered to more effectively direct the design process-that is, to recognize problems earlier, make corrections, and adjust resource allocations. Designers benefit both by enhanced understanding of the degree of conformance of a design to user and patient needs, and by improved communications and coordination among all participants in the process.
The medical device industry encompasses a wide range of technologies and applications, ranging from simple hand tools to complex computer-controlled surgical machines, from implantable screws to artificial organs, from blood-glucose test strips to diagnostic imaging systems and laboratory test equipment. These devices are manufactured by companies varying in size and structure, methods of design and development, and methods of management. These factors significantly influence how design controls are actually applied. Given this diversity, this guidance does not suggest particular methods of implementation, and therefore, must not be used to assess compliance with the quality system requirements. Rather, the intent is to expand upon the distilled language of the quality system requirements with practical explanations and examples of design control principles. Armed with this basic knowledge, manufacturers can and should seek out technology-specific guidance on applying design controls to their particular situation.
When using this guidance, there could be a tendency to focus only on the time and effort required in developing and incorporating the controls into the design process. However, readers should keep in mind the intrinsic value of design controls as well. It is a well-established fact that the cost to correct design errors is lower when errors are detected early in the design and development process. Large and small companies that have achieved quality systems certification under ISO 9001 cite improvements in productivity, product quality, customer satisfaction, and company competitiveness. Additional benefits are described in comments received from a quality assurance manager of a medical device firm regarding the value of a properly documented design control system:
"...there are benefits to an organization and the quality improvement of an organization by having a written design control system. By defining this system on paper, a corporation allows all its employees to understand the requirements, the process, and expectations of design and how the quality of design is assured and perceived by the system. It also provides a baseline to review the system periodically for further improvements based on history, problems, and failures of the system (not the product)."
II. SCOPE
The guidance applies to the design of medical devices as well as the design of the associated manufacturing processes. The guidance is applicable to new designs as well as modifications or improvements to existing device designs. The guidance discusses subjects in the order in which they appear in FDA's Quality System regulation and is cross-referenced to International Organization for Standards (ISO) 9001:1994, Quality SystemsModel for Quality Assurance in Design, Development, Production, Installation, and Servicing, and the ISO draft international standard ISO/DIS 13485, Quality SystemsMedical DevicesParticular Requirements for the Application of ISO 9001, dated April 1996.
Design controls are a component of a comprehensive quality system that covers the life of a device. The assurance process is a total systems approach that extends from the development of device requirements through design, production, distribution, use, maintenance, and eventually, obsolescence. Design control begins with development and approval of design inputs, and includes the design of a device and the associated manufacturing processes.
Design control does not end with the transfer of a design to production. Design control applies to all changes to the device or manufacturing process design, including those occurring long after a device has been introduced to the market. This includes evolutionary changes such as performance enhancements as well as revolutionary changes such as corrective actions resulting from the analysis of failed product. The changes are part of a continuous, ongoing effort to design and develop a device that meets the needs of the user and/or patient. Thus, the design control process is revisited many times during the life of a product.
Some tools and techniques are described in the guidance. Although aspects of their utility are sometimes described, they are included in the guidance for illustrative purposes only. Including them does not mean that they are preferred. There may be alternative ways that are better suited to a particular manufacturer and design activity. The literature contains an abundance of information on tools and techniques. Such topics as project management, design review, process capability, and many others referred to in this guidance are available in textbooks, periodicals, and journals. As a manufacturer applies design controls to a particular task, the appropriate tools and techniques used by competent personnel should be applied to meet the needs of the unique product or process for that manufacturer.
III. APPLICATION OF DESIGN CONTROLS
Design controls may be applied to any product development process. The simple example shown in Figure 1 illustrates the influence of design controls on a design process.
Figure 1 - Application of Design Controls to Waterfall Design Process (figure used with permission of Medical Devices Bureau, Health Canada)
The development process depicted in the example is a traditional waterfall model. The design proceeds in a logical sequence of phases or stages. Basically, requirements are developed, and a device is designed to meet those requirements. The design is then evaluated, transferred to production, and the device is manufactured. In practice, feedback paths would be required between each phase of the process and previous phases, representing the iterative nature of product development. However, this detail has been omitted from the figure to make the influence of the design controls on the design process more distinct.
The importance of the design input and verification of design outputs is illustrated by this example. When the design input has been reviewed and the design input requirements are determined to be acceptable, an iterative process of translating those requirements into a device design begins. The first step is conversion of the requirements into system or high-level specifications. Thus, these specifications are a design output. Upon verification that the high-level specifications conform to the design input requirements, they become the design input for the next step in the design process, and so on.
This basic technique is used repeatedly throughout the design process. Each design input is converted into a new design output; each output is verified as conforming to its input; and it then becomes the design input for another step in the design process. In this manner, the design input requirements are translated into a device design conforming to those requirements.
The importance of design reviews is also illustrated by the example. The design reviews are conducted at strategic points in the design process. For example, a review is conducted to assure that the design input requirements are adequate before they are converted into the design specifications. Another is used to assure that the device design is adequate before prototypes are produced for simulated use testing and clinical evaluation. Another, a validation review, is conducted prior to transfer of the design to production. Generally, they are used to provide assurance that an activity or phase has been completed in an acceptable manner, and that the next activity or phase can begin.
As the figure illustrates, design validation encompasses verification and extends the assessment to address whether devices produced in accordance with the design actually satisfy user needs and intended uses.
An analogy to automobile design and development may help to clarify these concepts. Fuel efficiency is a common design requirement. This requirement might be expressed as the number of miles-per-gallon of a particular grade of gasoline for a specified set of driving conditions. As the design of the car proceeds, the requirements, including the one for fuel efficiency, are converted into the many layers of system and subsystem specifications needed for design. As these various systems and subsystems are designed, design verification methods are used to establish conformance of each design to its own specifications. Because several specifications directly affect fuel efficiency, many of the verification activities help to provide confirmation that the overall design will meet the fuel efficiency requirement. This might include simulated road testing of prototypes or actual road testing. This is establishing by objective evidence that the design output conforms to the fuel efficiency requirement. However, these verification activities alone are not sufficient to validate the design. The design may be validated when a representative sample of users have driven production vehicles under a specified range of driving conditions and judged the fuel efficiency to be adequate. This is providing objective evidence that the particular requirement for a specific intended use can be consistently fulfilled.
CONCURRENT ENGINEERING. Although the waterfall model is a useful tool for introducing design controls, its usefulness in practice is limited. The model does apply to the development of some simpler devices. However, for more complex devices, a concurrent engineering model is more representative of the design processes in use in the industry.
In a traditional waterfall development scenario, the engineering department completes the product design and formally transfers the design to production. Subsequently, other departments or organizations develop processes to manufacture and service the product. Historically, there has frequently been a divergence between the intent of the designer and the reality of the factory floor, resulting in such undesirable outcomes as low manufacturing yields, rework or redesign of the product, or unexpectedly high cost to service the product.
One benefit of concurrent engineering is the involvement of production and service personnel throughout the design process, assuring the mutual optimization of the characteristics of a device and its related processes. While the primary motivations of concurrent engineering are shorter development time and reduced production cost, the practical result is often improved product quality.
Concurrent engineering encompasses a range of practices and techniques. From a design control standpoint, it is sufficient to note that concurrent engineering may blur the line between development and production. On the one hand, the concurrent engineering model properly emphasizes that the development of production processes is a design rather than a manufacturing activity. On the other hand, various components of a design may enter production before the design as a whole has been approved. Thus, concurrent engineering and other more complex models of development usually require a comprehensive matrix of reviews and approvals to ensure that each component and process design is validated prior to entering production, and the product as a whole is validated prior to design release.
RISK MANAGEMENT AND DESIGN CONTROLS. Risk management is the systematic application of management policies, procedures, and practices to the tasks of identifying, analyzing, controlling, and monitoring risk. It is intended to be a framework within which experience, insight, and judgment are applied to successfully manage risk. It is included in this guidance because of its effect on the design process.
Risk management begins with the development of the design input requirements. As the design evolves, new risks may become evident. To systematically identify and, when necessary, reduce these risks, the risk management process is integrated into the design process. In this way, unacceptable risks can be identified and managed earlier in the design process when changes are easier to make and less costly.
An example of this is an exposure control system for a general purpose x-ray system. The control function was allocated to software. Late in the development process, risk analysis of the system uncovered several failure modes that could result in overexposure to the patient. Because the problem was not identified until the design was near completion, an expensive, independent, back-up timer had to be added to monitor exposure times.
THE QUALITY SYSTEM AND DESIGN CONTROLS. In addition to procedures and work instructions necessary for the implementation of design controls, policies and procedures may also be needed for other determinants of device quality that should be considered during the design process. The need for policies and procedures for these factors is dependent upon the types of devices manufactured by a company and the risks associated with their use. Management with executive responsibility has the responsibility for determining what is needed.
Example of topics for which policies and procedures may be appropriate are:
- risk management
- device reliability
- device durability
- device maintainability
- device serviceability
- human factors engineering
- software engineering
- use of standards
- configuration management
- compliance with regulatory requirements
- device evaluation (which may include third party product certification or approval)
- clinical evaluations
- document controls
- use of consultants
- use of subcontractors
- use of company historical data
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