The output of the contextual inquiry and the value specification serves as the blueprint for the actual eHealth technology, which is developed in the design phase. This phase consists of the sub phases develop lo-fi and hi-fi prototypes, conduct usability tests, and add persuasive elements. A good design is also closely related to implementation, since a technology that fits the wishes and needs from the stakeholders will – in most cases – be used more and longer than a technology that doesn’t. That is why, during the design phase, the development team constantly has to keep the contextual inquiry and value specification in mind.
It is important that the final technology should not be developed at once, since chances are that, if that happens, a lot of important issues can be missed and arise just after its been implemented in practice. That is why multiple prototypes of the technology have to be developed to visualize and elaborate on initial ideas. A prototype is a visual representation of an idea about the eHealth technology, a simplified version of a final end-product. To make sure that issues are identified and that a technology fits with the needs and preferences of the users and other stakeholders, the prototypes have to be tested with them. This enables the development team to remove any critical issues and to add elements that are missed by the target group, and adapt the design accordingly. This is an iterative process, since constant changes to the idea and prototype of the technology can and should be made [1, 2].
Besides ensuring that the design and content of a technology appeal to the user, the development team should also ensure that the technology influences cognitions or behaviours of users that should be adapted in order to reach the value of the technology. This can be achieved by using theory to add elements to the technology, for example from the Persuasive System Design (PSD) model, and by using Behaviour Change Techniques (BCTs). This ensures that a technology is persuasive: it is compelling without being coercive , and consequently increases adherence and behaviour change.
The design phase is an extremely dynamic, iterative and collaborative phase, during which the development team actively collaborates with stakeholders like designers, psychologists, users, content experts and funders. Not just by testing and perhaps even developing the prototypes, but also by ideating, creating, and discussing ideas together.
The design phase has several main objectives:
- Both low-fidelity (lo-fi) and high-fidelity (hi-f) prototypes of the technology have to be developed.
- Usability tests of the prototypes have to be conducted with end-users, experts and possibly other stakeholders
- Persuasive elements and/or Behaviour Change Techniques have to be added to the design.
The main outcome of the design phase is the first version of the eHealth technology that will actually be used in practice by the stakeholders. Consequently, the output of the contextual inquiry and value specification has to be used in the design to make sure that there still is a fit between context, technology and people: the technology has to address the issue identified in the contextual inquiry, it has to incorporate the requirements and aim to reach the values that were identified in the value specification. Furthermore, the constant usability testing and the adding of persuasive elements assists in ensuring that the user will actually start and keep on using the technology. It is important to note that a design is never really finished: in most cases, adaptations or improvements are required.
 Beerlage-de Jong, N. Eikelenboom-Boskamp, A., Voss, A., Sanderman, R., & van Gemert-Pijnen, L. (2014). Combining user-centered design with the persuasive systems design model: The development process of a web-based registration and monitoring system for healthcare-associated infections in nursing homes. International Journal on Advances in Life Sciences, 6(3-4), 262-271.
 Wentzel, J., van Velsen, L., van Limburg, M., de Jong, N., Karreman, J., & Hendrix, R. (2014). Participatory eHealth development to support nurses in antimicrobial stewardship. BMC MedicalIinformatics and Decision Making, 14(1), 45.
 Fogg, B. J. (2009). A behavior model for persuasive design. In S. Chatterjee & P. Dev (Eds.), Proceedings of the 4th international Conference on Persuasive Technology (Article No. 40). New York, NY: ACM.