With some products, post-market surveillance includes reclaiming and testing units from users. These tests reveal early information
about potential reliability problems that could have been missed in laboratory trials. Post-market surveillance is not a required
part of design validation, but it reduces commercial risks and engineering costs.
The Development Process
Product development can be conceived of in stages: concept feasibility, prototype development, pre-production, and pilot production.
The time and relative effort expended at each stage depends on the type of product, but the design proceeds in parallel with
the development of the manufacturing processes. In particular, some components, such as plastic injection moldings, often
force the alignment of product, process, and validation schedules. Table 1 shows how design and process validation fit together.
Development trials may be part of the design validation, especially for reliability and when defining certain aspects of the
performance specification. This is the time to finish writing the validation master plan and to perform the FMEA.
Development samples are used to check performance and set up assembly processes. These differ from the previous prototypes
in that molded components are available and allow more realistic trials to be performed.
A pre-production batch is assembled from "final" components by operators under the guidance of engineers. Verification tests
at this stage include the effects of natural variation from component tolerances and differences between operators. The batch
is also used to complete design validation tests. After testing, the units often are used as demonstration samples, but they
should not be used by customers as they were not produced using a fully validated process.
Later pre-production and pilot production batches can be sold and used by customers. Design validation is complete by this
stage, but process validation is still underway. Final release tests may be needed if the units go to customers.
Components and Parameters
The various types of components and manufacturing processes must be treated differently at each stage of development.
Different numbers of units are needed at each stage for a typical, assembled product. A simpler product like a skin patch
could have many more samples at each stage. During early development there will be many components and sub-assemblies but
often only one complete unit.
It typically takes several months before injection-molded parts are available in volume from a validated process. Hand-crafted
samples or computer-made prototypes can be used in the beginning, followed by initial samples from a tool.
Mechanical parts include the clips, springs, and fixtures that are either custom built or standard, off-the-shelf items. Many
of them do not change during design and development, and the initial parts are "substantially equivalent" to the final design.
Most electronic designs have standard components on a printed circuit board. As with mechanical parts, the initial design
is often similar to the final version.
Software embedded in a product may be simple to change, but verification tests are long and need to be repeated each time,
since changes to complex logic paths can have unexpected consequences.
Engineers who assemble the first prototypes know what they are doing, but the variation that arises from operators following
their instructions can contribute to poor performance and must be considered in the design validation.
In the early stages, the product is tested by engineers using laboratory equipment. Units used in design verification trials
should be tested using production equipment, especially if the equipment is used to adjust or calibrate the product and can
affect performance. The equipment itself does not need to be validated at this stage. Typically, process engineers will not
validate the tests until the design is complete and they have sufficient units to test.
Final release tests are needed if there is insufficient data to show that the standard production tests can guarantee the
performance of the product. This occurs when the standard tests measure a feature of the product, such as a running speed,
pressure, or force, that predicts the amount of drug delivered, the delivery time, or other important factors. Development
trials may have demonstrated a strong relationship, but variation in the product or the test may weaken the link. These tests
show the form of the relationship and protect customers who receive early production units. As with production tests, this
is not part of design validation, but it does show how design and process cannot always be cleanly separated.
George R Bandurek, Ph.D., is principal of GRB Solutions Ltd, 9 Cissbury Road, Worthing, West Sussex BN14 9LD, England, 44.1903.215175, firstname.lastname@example.org