Opa1-knocked out EMSC-derived EV-Mito and LL37-loaded PEEK scaffolds combat drug-resistant bone infection

Treating drug-resistant bone infections, particularly those involving biofilm formation on implants, presents a significant clinical challenge. Standard antibiotic therapies often fail to completely eradicate these infections, leading to persistent inflammation and impaired bone healing. Current strategies, such as two-stage revision surgery with antibiotic-loaded bone cement, offer local drug delivery but may not fully address the complex interplay between infection and the inflammatory microenvironment that hinders osteogenesis. There's a critical need for combined approaches that simultaneously provide potent antimicrobial action and actively promote tissue regeneration, especially in the face of resistant pathogens like MRSA.

Researchers engineered a sulfonated-PEEK scaffold, termed SPMiL, designed to deliver two therapeutic agents: the human antimicrobial peptide LL37 and mitochondria-rich extracellular vesicles (EV-Mito). These EV-Mito were derived from ectomesenchymal stem cells (EMSCs) in which the Opa1 gene, a key regulator of mitochondrial dynamics, was knocked out to substantially boost vesicle production. The SPMiL scaffold was then tested in a preclinical model of MRSA-infected rat calvarial defects. The study evaluated the scaffold's ability to continuously release LL37 for bacterial elimination and to transfer functional mitochondria into recipient cells, assessing its impact on osteogenic differentiation and osteoclast activity.

The engineered SPMiL scaffold demonstrated a dual therapeutic effect in MRSA-infected rat calvarial defects. It achieved continuous release of LL37, which effectively eliminated the resistant bacteria from the infection site. Simultaneously, the scaffold facilitated the transfer of functional mitochondria from the Opa1-knocked out EMSC-derived EV-Mito into host cells. This mitochondrial transfer led to significant regenerative outcomes: it promoted osteogenic differentiation and suppressed osteoclast activity. These beneficial effects were attributed to several cellular mechanisms, including metabolic reprogramming, enhanced antioxidant effects, and the restoration of mitochondrial membrane potential within the recipient cells. > This work demonstrates that combining antibacterial defense with mitochondrial transfer offers a viable approach for treating infected bone defects that resist conventional treatment.