Tongue depressors, although a simple medical device, must also meet certain design specifications.  They must meet a certain size.  The standard wood tongue depressor is 6 inches long & almost 1 inch wide but can be manufactured in smaller sizes for juvenile patients. They can come sterile or non-sterile.  They can also come in grape, cherry, & strawberry flavors.  

An example of a product or products that would require a need for design specification would be syringes and needles. Considering that there are various sizes and types of needles and syringes, it would be necessary to ensure that each object have the proper size, since they vary in length and desired purpose Additionally, since there are various syringes and needles for different purposes, specification of each specific item must be required to ensure the effectiveness and safety of the product overall while it is being used.

Installed medical devices such as hip prosthetics was a thought that occurred to me. Within the design specification document for hip prosthesis devices, I would expect to see a self-maintenance kit and regular monthly check-in's as a mandatory follow up to prevent bacterial plaque and extracellular matrix build-up on the hip implemented device. I believe that instructions should be included such as not to swim in salt water, methodology for covering the hip installation from rainwater and other liquid material, and an emergency contact line in case of adverse events. Decontamination regularly should be documented and examined at every monthly check-up.

Q tips, however simple they may seem are classified as medical devices and their design specifications state they must fall within a certain range to avoid damage to the ear. One criteria is the cotton swap at the end must be ~9.5mm to generate a good spin. Anything larger than that will not move as freely and anything small could cause damage internally.

I haven't had any experience developing a medical device, but the logic still applies. I have worked in industries that have developed products with specifications. Before mass production can begin, specifications must be verified, and a sample must be approved. I currently work for a company that produces cell phone accessories like cases, earbuds, chargers, etc. It's very crital that specifications are well executed. It can result in a delay in the product or a loss of profit because it wasn't produced properly. The material to make the product is also wasted.

For my senior year capstone project, my group and I created a design specification document for our pediatric exoskeleton. We are definitely not professionals in the development of these documents, but our document consisted of the following sections: physical/mechanical, electrical, software & interfacing, operational, performance, and safety requirements. The physical/mechanical requirements include instructions on how the device should be put together, as well as the dimensions for every component, hole, etc. presented using drawings. The electrical requirements section provides the detailed electrical schematic of the exoskeleton and information on electrical components of the device. Software and interfacing requirements include instructions on how hardware should communicate with software. Operational, performance, and safety requirements sections include instructions on how the device should function while maintaining its safety. Each section consists of a detailed description of the specifications required to develop the device, and these specifications were later tested for verification.

Upon reading through responses from my peers, this seems like really fun thread to respond to. Another example of a medical device with important design specifications include drug eluting stents. Some generic specifications include material (considerations include biocompatibility, elasticity, and visibility with imaging such as Stainless Steel, Cobalt Chromium, Tantalum, and Nitinol), dimensions (such as length, diameter, and thickness depending on vessel and resistance), drug release rate, delivery system (i.e. balloon angioplasty and the necessary guide wire dimensions), and shelf life.

One example of a product that probably we have all seen before that would have a design specifications document is an otoscope. An otoscope is a tool that allows doctors to see inside the ear canal, to examine the eardum and the outer ear. The otoscope usually has a light to illuminate the inside of the ear canal, a handle which allows the doctor to rotate or adjust the otoscope, a lens to allow the doctor to magnify and visually inspect certain parts of the ear, and a disposable plastic speculum which is thrown out usually after every use. The otoscope must also be designed so that it allows for careful examination of the ear whilst also being comfortable for the patient being examined. 

As mentioned by my peer, capstone was a great introduction to what may go into a design specification document. My group worked on creating a microfluidic device that could hold stem cells in scaffolds, primarily used in research. Our design specifications included the different layers of the device itself -- the air chamber, the scaffold chambers, the fluid channels, and the reservoirs. Then the dimensions and the type of required connections were specified. This included silicone tubing for the air delivery system and electrical cables for the DC generator and breadboard. The voltage of the components used needed to be recorded as well. Our document also specified the materials we used and the environment that it could be used in. It is important to specify these as our device, for example, needed to be able to be placed in an incubator and also allow cell biocompatibility.