[An integrated electrical stimulation-drug iontophoresis-monitoring system for tendon injury repair]

To develop an integrated system for tendon injury repair that combines electrical stimulation, drug iontophoresis, and electromyography (EMG) monitoring, and validate it in a rat Achilles tendon injury model.

A flexible 16-channel acquisition and stimulation system was constructed based on field programmable gate array. The system had a sampling rate ranging from 250 SPS to 16 kSPS with a resolution of 5 μV, and the stimulation current was 2.55 mA with a resolution of 10 nA, enabling synchronous and stable stimulation and signal monitoring. Fifteen Sprague-Dawley rats with induced Achilles tendon injuries were randomly allocated to three groups ( n=5): blank control, electrical stimulation, and drug iontophoresis groups. The Achilles tendon injury model was established by injecting typeⅠcollagenase solution into the Achilles tendon of right hind limb. At 3 days after modeling, the electrical stimulation group and drug iontophoresis group received corresponding interventions with the self-developed system for 2 consecutive weeks, and aspirin was delivered via iontophoresis in the latter group. No treatment was performed in the blank control group. The survival status and limb motor function of rats were observed, and EMG signals were recorded throughout the intervention. Gross observation and histological examination (HE staining and Sirius red staining) of Achilles tendons were performed at 2 and 4 weeks since the initiation of intervention to evaluate the repair effect.

All rats survived until the scheduled experimental time point. All animals presented postoperative limping, which recovered spontaneously within 2 weeks without obvious intergroup difference. EMG results demonstrated that all groups underwent a consistent three-stage recovery process, namely compensatory activation, collagen remodeling, and functional recovery. The electrical stimulation group exhibited the mildest EMG fluctuations, whereas the drug iontophoresis group showed the most significant early muscular compensatory activation. Obvious differences in EMG characteristics between the injured and contralateral healthy sides were observed in the early stage, which gradually diminished and finally achieved synchronization with the progression of tendon repair. The support vector machine (SVM) achieved a classification accuracy of 85.8% for recovery stage identification. Gross observation and histological examination revealed that both intervention groups displayed milder peritendinous adhesion and better tendon luster compared with the blank control group, and achieved superior tendon repair outcomes.

The integrated system proves to be effective for both the assessment and intervention of tendon injury repair. EMG signals can reliably distinguish between different stages of Achilles tendon recovery. Furthermore, both electrical stimulation and iontophoretic drug delivery promote repair by effectively regulating collagen remodeling and modulating compensatory muscle activation patterns.