In general, a medical device is defined as follows: a medical device is an implant and equipment to be used either to achieve disease diagnosis, medical treatment, or disease prevention for human and animals, or to influence the physical structure and function of human and animals. Medical devices for humans may also be classified based on whether and how long the device is in contact with tissue or cells and on the degree of disjunction induced by the device when in a disabling situation. The term covers various categories, such as scissors and tweezers, with small risk to human function, to central venous catheters, artificial dialysis (human kidney), and pacemakers, with high risk to human function.
The ISO (International Standards Organization) standard (ISO 13485 ) for medical devices, Quality Assurance System for Medical Devices, has been implemented globally. GMPs are clearly required for the manufacture of medical devices, including process control, quality control, and appropriate facilities and equipment. GMP also plays a role in maintaining the quality of medical devices. Performing only a specification test of the final product for release may not guarantee high quality of the device; design qualification/verification in the development step must be done in detail and process control by scientific parameters is important to assure quality. Because the term medical device covers a variety of categories, it may be difficult to establish a simple quality control system. To achieve appropriate quality control status, medical devices may be categorized under design, manufacturing method, assembly method, and quality control testing, as shown in Table 1.
The medical devices in category 1 in Table 1 are controlled during in-
Table 1 Categories of Medical Devices Based on Their Design, Manufacturing
Method, Assembly Method, and Quality Control Testing
Category 1: Medical devices that are controlled by in-process tests, with critical specifications designed for both individual products and a group, but not implemented in human and animals.
Category 2: Medical devices that are composed in batches and are tested with representatives in a batch.
Category 3: Medical devices that are controlled with each component (part) for assembly in the manufacturing process, and constituted (assembled) and maintained at the user site. Of course, the function of the medical device after assembly must be tested before release.
Category 4: Medical devices that are controlled by in-process tests, with critical specifications designed for both individual products or a group, and are implemented in human and animals for the long term.
process testing with critical specifications designed either for individual products or a group of products. Qualification of equipment to test critical product specifications and validation of test methods should be key factors. In this category, scissors, tweezers, and a pair of glasses are involved.
The medical devices for category 2 in Table 1 are composed in batch. Process validation should be a key factor in manufacturing uniform products. In this category, sterile products, such as central venous catheters and ophthalmic viscosurgical solution without pharmacological and metabolic action, are involved. In vitro diagnostic products are also involved in this category.
The medical devices for category 3 in Table 1 are constituted (assembled) at the user site. Method verification for constitution should be one of the key factors, as well as qualification and validation in the manufacture of components (parts). Nuclear magnetic resonance spectroscopy (NMR) is included in this category.
The medical devices in category 4 of Table 1 are controlled in-process testing with critical specifications designed for individual products or a group of products and are implanted. The compatibility of product materials with tissue and cells, the stability of product in the implanted site, and the sterility of product should be key factors to assure the product safety. Intraocular lenses and pacemakers are included in this category.
Because a qualified method for the manufacture and implementation of medical devices may be more variable in comparison to pharmaceutical dosage forms, it may be necessary to make clear what is (are) critical factor(s) for each device during the validation of the manufacturing process. The validation method for the medical device in each category will thus be described later.
Since the definition of validation seems to vary from nation to nation, we will include all activities from design to final product, as well as individual validation, such as process validation  (product qualification in ISO).
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