Design validation means that the right device was designed for its intended use, such as users requirements.

1) A diagnostic microscope slide that determines the presence of certain stem cell markers.
With Respect to the diagnostic microscope, it would not need a clinical trial because the microscope itself can not determine the presence of stem cell markers, but methods for prepping slides would enhance the microscopes imaging ability, but in the end the user has the diagnostic responsibility.

2) An implantable bone plate
yes, implantable bone plats are a class III medical device and require clinical trials to evaluate safety and effectiveness.

3) An antimicrobial suture
Yes, antimicrocobial sutures do need clinical trials, since they support wound closure and release a drug that prevent infection, it would be considered a combination device, that needs to be evaluated for effectiveness and safety.

4) An ergonomic knee brace
No because the brace is used as a support and does not have a high nor moderate risk to the user and most importantly they are non-invasive.