As well as the ISO 9001 Standard, The ISO 13485 requires defining inputs required to execute the development. The inputs should be determined according to the design and the development activities.
Within the design and the development inputs requirements, the organization must refer to the next issues:

The main idea is that the inputs must relate to the medical device's requirements. How? The inputs shall be determined according to the medical device's functionality, quality requirements or safety requirements.   Let's split the atom…

Employees' requirements 
Engineers, scientists, programmers, lab technicians, etc. Any function performs any kind of activity of development. In addition (oppose to the ISO 9001 Standard) The ISO 13485 Standard requires the organization referring to safety requirements as well where applicable. For example which functions are required or what information is required in every step of the development process.

Documented requirements of any kind

Requirements may include standard or technical requirements or specifications, customer's requirements, marketing requirement, legal requirement, packaging requirements, etc. Any sort of information that must be referred to during development and might serve the development process. In any case these requirements are to be documented (remember chapter 7.2.1 where you required defining and documenting?). When designing and developing, these requirements are to be handed to the relevant parties in an appropriate method.

While reviewing the documentation that may serve as input, you are required to refer to any unpractical requirements, requirements that cannot be validated or verified, lack of required information regarding the user or the unintended use, and any documentation that is related to the design and the development and do not appear on the plan.

Outputs of applicable earlier developments

Where applicable, one should refer to prior similar or parallel developments performed in the organization (when one was performed). When the organization had already developed before, the outputs may be used throughout the new development. That might save time, resources or victims (depends on what you are developing).

Working tools or utilities of any kind

Computer software, glass tubes, supporting tools, rulers, etc. the idea is to define the development environment.

Safety requirements

The inputs for the design and the development are required according to the functional, performances and quality requirements of the medical device (according to the ISO 9001 Standard). The ISO 13485 Standard requires regards also safety requirements according to the intended use of the medical device. If the medical device consist materials that by using them may set a risk, the organization must refer to the matter.  Safety shall be regarded in two different ways:

• Risk analysis regarding the development processes - If the organization develops a medicine of some kind, it is required to set inputs regarding the development activities of the medicine; safety measures  of experiments, published researches, required safety data sheets of the materials in hand, etc. Now, The ISO 13485 Standard requires a risk management as one of the miles stones of the design and the development. Risk management has conclusions: what to do or not to do, where to take measures, "what if", etc.  These outputs are the design and development inputs.
• Risk analysis regarding the user of the medical device - If the organization develops a medical device that might risk its user by any chance or by any way when using the medical device, the organization must relate to the risks during the development stage. The reference shall appear as a risk analysis. The outputs of the risk analysis would be inputs to the development. Pay attention, this is not a recommendation but the ISO 13485 Standard requirement. If you organization develops a medical device that may cause any risk to its user, you are required to conduct a risk analysis and the result shall serve as the design and development inputs. And it's not over.  That is what so special about the ISO 13485 Standard, just when you think it is over, comes another requirements…

The organization must certify a responsible party that would review safety aspects of the development. This party would be considered as one of the development inputs and must be documented within the design and the development plan.  For example, if the development takes place in a laboratory and dangerous chemicals are involved, some function must be responsible for implementing the entire safety requirement such as MSDS. This requirement (for safety) must be defined as one of the development inputs and documented.

Inputs approval
The next requirement is to approve any input before introducing it o the development process. The ISO 9001 Standard requires reviewing the input before introducing them into the development process. The ISO 13485 Standard requires reviewing and approving. Naturally this approval must be documented.  Let's get back to the laboratory. Supposed the company wants to develop some kind of new chemical. This chemical is compounded of few other chemicals. Before the development, any chemical that would be involved in the development must be reviewed and approved by an authorized function. How to approve or how to supply evidences of approval? Well, unless you are very creative and ISO Standard talented, I would suggest to simply document it somewhere, somehow.

Records
In any case, no matter what are your design and development inputs, they are to be recorded and documented. Design and development inputs must be under the control of records a specified in paragraph 4.2.4 – control of records. This is not a recommendation but an ISO 13485 Standard requirement.