Co-designing MESA-Bot: Enhancing Accessibility, Privacy, Security, and Trust in a Mental Health Chatbot for Older Adults

Older adults are increasingly turning to chatbot-based mental health support, yet adoption remains limited by barriers in accessibility, privacy, security, and trust. We present a two-phase study on the co-design of MESA-Bot (Mental and Emotional Support Assistant for Older Adults), a non-diagnostic chatbot tailored to later-life needs. In Phase I, we analyzed ten leading mental health chatbots and conducted co-design sessions with N1 = 10 older adults to identify challenges and inform an accessible, privacy-aware prototype. In Phase II, we evaluated MESA-Bot with N2 = 28 older adults using semi-structured interviews and structured technical assessments. Participants emphasized transparent consent, supportive tone, and fine-grained data control. Features such as revocable consent, role-based access control, customizable data visibility, and simplified dialogue flows increased trust and usability; 86% found MESA-Bot easy to use. We offer design insights for inclusive, trustworthy mental health technologies that integrate accessibility with verifiable privacy and security protections.