In the Risk Assessment you will Identify all the risks and measures to reduce risk.
Toxicity of materials and route of exposure.  Physical properties as well need to be assessed.  Human factors also play a role in the risk assessment.
Start with final finished form
Then establish the tissue contact of each component.  What additives, processes, processing aids, contaminants were used and what do they degrade into.  Physical properties such as wear debris, metal fatigue, foreign body reaction due to movement or friction.  Chemical changes caused from physical interactions such as; heat, pressure, cleaners, detergents, UV lights, electricity, transportation, aging.
Comparisons to products on the market requires knowing the manufacturing processes and formulations.  It is hard to say you are equivalent to a competitor if you do not know the processes utilized in the manufacture of their product.
Chemical characterization of the predicate product and chemical characterization of the new product must be conducted.
Geometry and rigidity are physical conditions that will affect biocompatibility.

​A new risk assessment must be performed when there is a design change on the device.  Changes of the device could alter the biological safety of the device.
Material changes do require re-evaluation.
Changes that require re-evaluation would be
                Changes in the manufacturing process or location
                Changes in the sources of the materials comprising the device
                Changes in material specification
                Changes in the formulation
                Changes in storage conditions, duration and transportation
                Changes in intended use