Spatiotemporally Adaptive and Stage-Matched Tissue-Engineered Constructs for MRSA Osteomyelitis: Pathogenesis-Informed Design

<b>Objective</b>: Osteomyelitis, particularly caused by methicillin-resistant <i>Staphylococcus aureus</i> (MRSA), often leads to significant infected bone defects and poses substantial challenges for functional reconstruction. Conventional one-stage interventions frequently fail due to the complex spatiotemporal pathogenesis. This study aims to delineate the spatiotemporal progression of MRSA-induced osteomyelitis to inform the rational design of staged, tissue-engineered constructs. <b>Methods</b>: A clinically relevant MRSA-induced osteomyelitis model was established in the tibiae of Sprague-Dawley rats using sodium morrhuate to simulate vascular occlusion and chronicity. The infection progression and bone repair were systematically evaluated at postoperative days 1, 4, 7, and 14 using longitudinal microbiological analysis, hematological profiling, Micro-CT, and histopathological staining. <b>Results</b>: The spatiotemporal analysis identified postoperative day 7 as a critical transition point, characterized by peak bacterial load (CFU), rampant cortical bone destruction (58.2% decrease in BMD), severe neutrophil infiltration (HE score of 3), and the onset of aberrant repair. Micro-CT and histology revealed a compartment-specific pathology, originating from the bone window and propagating to the medullary cavity and subchondral bone, culminating in sequestrum formation by day 14. This precise mapping underscores the limitation of debridement alone and the necessity for stage- and anatomy-specific intervention. <b>Conclusions</b>: The elucidated pathogenesis provides a critical roadmap for designing staged tissue engineering strategies. We propose a precision intervention framework: early phase (before day 7) constructs should prioritize antibiofilm and antimicrobial functions to prevent chronicity, while chronic-phase (after day 7) constructs must combine sustained antimicrobial activity with robust osteogenic capacity to address established infection and promote functional reconstruction in infected bone defects.