Bacterial keratitis is a leading cause of corneal blindness, yet current antibiotic therapies suffer from poor ocular bioavailability and rising drug resistance. Effective treatment requires not only bacterial eradication but also coordinated anti-inflammation and wound repair. In this paper, we present a "two birds with one stone" strategy for bacterial keratitis treatment based on an ultrasound-activated cascade responsive core-shell microneedle. Upon corneal insertion and ultrasound stimulation, piezoelectric nanoparticles embedded in the microneedle shell generate reactive oxygen species (ROS) to eliminate bacteria. The elevated ROS levels subsequently trigger the degradation of an ROS-responsive hydrogel core, enabling sustained release of mesenchymal stem cell derived exosomes (MSC-Exos) that neutralize residual oxidative stress, promote macrophage M1 to M2 polarization, and facilitate epithelial barrier restoration. Our proposed formulation demonstrated enhanced therapeutic efficacy in a rat keratitis model, outperforming conventional antibiotic eye drops in bacterial clearance, inflammation resolution, and corneal repair. These findings establish the cascade-responsive core-shell microneedles as a clinically promising strategy for treating bacterial keratitis and other infectious ocular diseases.

The development of implantable bioelectronics is driven by emerging applications including continuous health monitoring and human-machine interfacing. The mechanical mismatch between implanted bioelectronics and tissues not only compromises device accuracy, but also causes interference with tissues undesirably. To address this issue, it is necessary to develop ultrasoft and biocompatible fiber strain sensor with proper stretchability and sensitivity. Here, we fabricate a bacterial cellulose-based sensing fiber which possesses the stretchability and elastic modulus (~ 102 kPa) close to those of soft tissues. In addition, such fiber has high sensitivity to tiny tensile force/strain (8.8 × 10⁻³ N/2.5%) and low cell cytotoxicity. These excellent properties make the bacterial cellulose (BC)-based sensing fiber an excellent candidate of implantable bioelectric devices for monitoring subtle motions of organs. We demonstrate this by applying it for continuous monitoring of human pulse and bullfrog heartbeats. The (BC/oxBC)@PANI (ox = oxidized and PANI = polyaniline) fibers can further be woven into an array sensor and serve more complex sensing functions, such as multipoint force perception and shape recognition as demonstrated.