A Theranostic Implant Platform for In Vivo Infection Monitoring and Light-Based Therapy

Periprosthetic joint infection (PJI) remains a major limitation of joint arthroplasty, driven by the absence of localized, continuous diagnostics and controllable in vivo therapy during the spacer interval. Here, we introduce a theranostic implant platform that integrates sensing, communication, and light-based intervention within a temporary joint spacer. The SmartSpacer enables real-time intra-articular monitoring, combining high-resolution temperature sensing (± 0.1 °C), optical imaging, and spectral detection of bacterial activity down to ~10³ CFU ml⁻¹. We establish a translation-oriented framework that maps wavelength-dependent antimicrobial effects onto implant-level constraints. Within this framework, visible blue light provides continuous suppression of bacterial growth, while ultraviolet radiation enables rapid bactericidal action via pulsed, spatially confined exposure. These modalities operate within implant-compatible energy budgets and without measurable thermal load, enabling sustained and repeatable intervention. Continuous multimodal sensing enables longitudinal tracking of infection dynamics, transforming diagnostics from static assessment to predictive monitoring. By linking localized sensing with controllable therapy, the SmartSpacer converts the spacer interval from a passive waiting phase into an active treatment window. This work defines a system-level strategy for implant-based infection control and establishes a foundation for future feedback-driven, closed-loop therapeutic systems.