Design Validation is the assurance that the product is able to meet the needs of the customer and is in accordance with expectations set by the engineers responsible for creating the product. It involves acceptance and approval from third parties (e.g. customers, external manufacturers, regulators, stakeholders, etc.).

1) Diagnostic slide: These slides wouldn’t really benefit from clinical trials and don’t really require them. These slides would be used for research and diagnostic purposes, so the work done on these slides would be completed in vitro. In the simplest scenario, the company designing these slides would attempt to create them using existing products on the market in order to have them classified as a class 1 medical device by the FDA. Unless there is something drastically different about the design of these diagnostic slides, they would not need clinical trials in my opinion.
2) Implantable Bone Plate: Without a doubt, a product as invasive as an implantable bone plate would need clinical trials. Like dag56 said above, this would be classified as a class III medical device and would need significant clinical data before commercialization. Even if its design is similar to another currently in the market, any small differences in mechanical and chemical properties can cause severe harm to the patient if tested improperly.
3) Antimicrobial Suture: Unless this suture is of a very similar design to another on the market, I would argue that it would need clinical trials for design validation. Sutures are neither truly invasive implants nor extracorporeal devices; they would likely be classified as class II medical devices. An antimicrobial suture would be used as a standard in surgery, so clinical data is very important to ensure proper performance of the suture’s ability to close a wound and safely assist the wound healing process without exacerbation.
4) Knee Brace: In 9/10 cases, I would say it does not need a clinical trial. An ergonomic knee brace is an extracorporeal device likely classified by the FDA as a class I medical device. The knee brace itself would most likely either be similar or an improvement on an already existing knee brace design. Specific situations may call for clinical trials; for example, to test a new material in the design on whether it causes an allergic reaction.

-Talha Chaudhry