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Our lab has established a technical framework for the development and deployment of digital health applications that operate across mobile and web platforms. Applications are built using the Flutter/Dart framework, which supports cross-platform development for iOS, Android, and web, allowing us to maintain efficiency in code management while deploying to multiple environments. Separate codebases are implemented for patient-facing applications and provider or research team dashboards to ensure that functionality is optimized for each user group.

Flowchart of technical framework of devices and platforms.
The backend architecture is hosted on Google Cloud Platform and makes extensive use of Firebase services. Firebase Authentication provides secure identity management, Firestore enables real-time storage of pseudonymized data, and Firebase Hosting supports rapid deployment of front-end interfaces. Cloud Functions are used to manage backend logic, including data validation, automated triggers, and just-in-time adaptive intervention delivery. BigQuery is employed as the centralized data warehouse for aggregation and large-scale analysis, while Cloud Scheduler and Firebase Cloud Messaging support task orchestration and participant reminders.
Protected Health Information is stored exclusively within REDCap, which functions as the system of record under institutional governance. REDCap also integrates with external modules such as Twilio for secure messaging. All cloud resources are provisioned within the Weill Cornell Medicine enterprise environment, where system monitoring, patching, and compliance are managed centrally to meet HIPAA and IRB standards.
Wearable devices such as Fitbit Sense 2 are integrated through the Fitbit API, with server-to-server data transfer into BigQuery. This provides a continuous stream of passive activity and physiological measures, which can be combined with active ecological momentary assessments delivered via the mobile applications.
