I agree with the posts above that the inputs for the DID should be gotten directly from the end user or customer. In my company the marketing department is responsible for gathering VOC (voice of customer) inputs and using this feedback to compile the DID. The engineers are then responsible for translating the inputs into design specifications. This phase of the project is critical for its success, because it is extremely important that the right inputs are being gathered so that the resulting product that will be designed will meet the user needs and satisfy the majority of the customers. In my company we select surgeons to use as consultants on projects, but it is important that these surgeons are representative of the surgeon population that will be using the device.