BACKGROUND: Muscle strains are one of the most common injuries treated by physicians. Standard conservative therapy for acute muscle strains usually involves short-term rest, ice, and non-steroidal anti-inflammatory medications, but there is no clear consensus regarding treatments to accelerate recovery. Recently, clinical use of platelet-rich plasma (PRP) has gained momentum as an option for therapy and is appealing for many reasons, most notably because it provides growth factors in physiological proportions and it is autologous, safe, easily accessible, and potentially beneficial. Local delivery of patients' PRP to injured muscles can hasten recovery of function. However, specific targeting of PRP to sites of tissue damage in vivo is a major challenge that can limit its efficacy. HYPOTHESIS: Location of PRP delivery can be monitored and controlled in vivo with non-invasive tools. STUDY DESIGN: Controlled laboratory study using rats. METHODS: Superparamagnetic iron oxide nanoparticles (SPIONs) can be visualized by both MRI (in vivo) and fluorescence microscopy (after tissue harvesting). We labeled PRP with SPIONs and administered intramuscular injections of SPION-containing platelets. MRI was used to monitor the ability to manipulate and retain the location of PRP in vivo by placement of an external magnet. Platelets were isolated from whole blood and incubated with SPIONs. Following SPION incubation with PRP, a magnetic field was used to manipulate platelet location in culture dishes. In vivo, the tibialis anterior muscles (TAs) of anesthetized Sprague-Dawley rats were injected with SPION-containing platelets and MRI was used to track platelet position with and without a magnet worn over the TAs for 4 days. RESULTS: The method used to isolate PRP yielded a high concentration (almost 4-fold increase) of platelets. In vitro experiments show that the platelets successfully took up SPIONs and then rapidly responded to an applied magnetic field. Platelets without SPIONs did not respond to the magnetic field. In vivo experiments show that the SPION-containing platelets can be non-invasively maintained at a specific site with the application of a magnetic field. CONCLUSION: PRP may be a useful product in clinical treatment of muscle injuries, but one problem with using PRP as a therapeutic tool, is retaining PRP at the site of injury. We propose a potential solution with our findings that support this method at the cell, whole muscle, and in vivo levels. Controlling the location of PRP will allow the clustering of PRP to enrich the target area with growth factors and will prevent loss of the platelets over time at the site of injury.