## 2 Materials and Methods
### Interview Procedure  
This study was conducted across three locations within the VA Health Care System in the United States; Seattle, WA; Louisville, KY; and Nashville, TN. Three research coordinators, one located at each of the three sites, conducted interviews at their respective locations. The interviewers had clinical backgrounds in dialysis practice and trained as research coordinators with interview training. The interviewers distributed a pre-interview survey and followed an interview guide that was developed and subsequently reviewed and revised by the authors of this paper. The interviews were conducted over a four-month period during the summer of 2019. Prior to conducting the interviews, the three research coordinators at each of the three VA study sites met in an online virtual meeting room and refined the flow of the interview questions, and established interview protocols to ensure interview consistency among the three study sites. The interview guide was nearly identical for the patients and the care partners. The main difference was that some questions asked the care partners to reflect on their patient partners' experiences instead of their own.  
Patients and care partners were all individually interviewed in two stages that occurred during two different interview sessions. First, the research coordinators administered a paper-based pre-interview survey to the participant during one of their visits to the dialysis center. The survey included demographic and background questions, as well as open-ended questions about participants' experiences with dialysis, familiarity with mobile medical devices, and a question asking the participants to describe the designs of the most ideal mobile dialysis device. The reason for having a pre-interview survey prior to the in-person interview is twofold. First, the survey was intended to limit the risk of interview fatigue during the interview [60]. Second, as there are currently no mobile hemodialysis devices on the market, we aimed to encourage the participants to begin thinking about the most ideal design for a mobile dialysis device prior to the interview.  
The second interview stage included an in-person interview where the participant was asked rating questions and in-depth open-ended questions. Each participant was given a choice of where to conduct the interview: at their home, at their respective VA research location, or at the dialysis clinic where they were recruited (provided privacy could be ensured at the clinic). All patients and care partners chose to be interviewed at their respective dialysis centers. The participants were asked to reflect on current and prior dialysis procedures. They were asked about any physical signs indicating the need for dialysis treatment or the successful removal of excess water, solutes, and toxins from the blood. We asked the participants the following questions: \"How do you know if you (or your patient partner) need(s) to receive dialysis?\" (Section 3.1.1) and \"How do you know when dialysis was performed well?\" (Section 3.1.2).  
The combined duration of a participant's pre-interview survey along with the in-person interview was approximately 80 min on average. All interviews were audio-recorded by the research coordinator and labeled using participants' study identification (ID) numbers to ensure anonymity. After the completion of each interview, the research coordinator uploaded the recording to a secure online database where it was later accessed by a research team member and sent to Verbal-Ink, an online transcription service. Figure 1 displays the detailed interview process. This study was approved by the Institutional Review Board at the University of Washington.