Skeletal infections: microbial pathogenesis, immunity and clinical management

Sequential construction of vascularized and mineralized bone organoids using engineered ECM-DNA-CPO-based bionic matrix for efficient bone regeneration

Given the limitations of allogeneic and artificial bone grafts, bone organoids have attracted extensive attention for their physiological properties that closely resemble natural bone, offering great potential to bone reconstruction for critical-sized bone defects. Although early-stage bone organoids such as osteo-callus organoids and woven bone organoids have been reported, functional bone organoids with vascularization and mineralization are currently unavailable due to the lack of bone-mimicking matrix and dynamic culture systems suitable for the long-term cultivation of mature bone organoids. Herein, a novel engineered bionic matrix hydrogels with multifunctional components and double network structure are developed by incorporating calcium phosphate oligomers (CPO) into a combination of bone-derived decellularized extracellular matrix (ECM) and salmon-derived deoxyribonucleic acid (DNA) via photo-crosslinking and dynamic self-assembly strategies. This kind of bionic matrix hydrogels facilitate recruitment, proliferation, osteogenesis and angiogenesis of bone marrow mesenchymal stromal cells (BMSCs). More importantly, vascularized and mineralized bone organoids are sequentially constructed using BMSCs-loaded engineered bionic matrix hydrogels via in vitro dynamic culture and in vivo heterotopic ossification. Meanwhile, this kind of engineered bionic matrix are capable of achieving efficient bone repair for cranial defect. These findings suggest that engineered bionic matrix hydrogels combined with such dynamic culture system, providing a promising strategy for functional bone organoids construction.

Synergistic photothermal-sonodynamic therapy for antibacterial and immune reprogramming in chronic osteomyelitis

The development of antibiotic resistance and inadequate immune response in chronic inflammation pose significant challenges in treating chronic osteomyelitis. As accepted non-antibiotic antimicrobial therapies, sonodynamic therapy (SDT) and photothermal therapy (PTT) are recognized for their effectiveness in eliminating bacteria and promoting tissue repair, rendering them promising therapeutic strategies for treating bacterial infections and preventing the emergence of drug-resistant bacteria. However, the antimicrobial action and efficacy in promoting tissue repair depend on the activation status of the host immune system. In this study, by encapsulating horseradish peroxidase (HRP)-loaded gold/polydopamine (PDA) nanoparticles within DOTAP/DOPE cationic liposomes (DLPs), a novel multifunctional nanocatalyst, Au/PDA/HRP@DLP (APH@DLP), was developed to achieve antimicrobial effects and immunological reprogramming of chronic osteomyelitis through synergistic SDT and PTT. The impact on immune activation was investigated by assessing the anti-infective and healing effects in osteomyelitis rat models. The release of bacterial-associated antigens during treatment serves as an in situ vaccine, activating antigen-presenting cells and further stimulating adaptive immunity, while also inducing immune memory that significantly reduces the risk of recurrence. Additionally, macrophage phenotypic transformation during SDT and PTT facilitates tissue repair. This study highlights the role of immune activation in SDT/PTT-based antimicrobial therapy and suggests new strategies for treating chronic osteomyelitis.

"Disguise strategy" to bacteria: A multifunctional hydrogel with bacteria-targeting and photothermal conversion properties for the repair of infectious bone defects

Addressing the challenge of eliminating bacteria and stimulating osteogenesis in infectious bone defects, where cells and bacteria coexist within the microenvironment, presents a significant hurdle. In this study, a strategy of targeting bacteria is proposed to address this challenge. For this purpose, a methacrylated gelatin composite hydrogel containing zinc ion and D-type cysteine-modified polydopamine nanoparticles (PZC) is developed. The D-cysteine, involved in the metabolism of the bacterial peptidoglycan chain, allows PZC to specifically target bacteria, exhibiting a form of "disguise strategy". Through the targeting effect, this composite hydrogel can selectively kill bacteria and promote osteogenesis combing photothermal therapy with Zn2+ release, which showcases spatial controllability. Moreover, the antibacterial ability will be further improved after Near-infrared light irradiation. The multifunctional hydrogel containing Zn2+ modified nanoparticles can also promote osteogenic differentiation of bone marrow stem cells. Animal studies have revealed that the multifunctional hydrogel can inhibit bacteria growth and promote repair of infectious bone defects in rats. Findings from this study imply that endowing the nanoparticles with bacteria-targeting function can precisely control the events in cells and bacteria in the complex microenvironment, which can provide insights for the treatment of complex diseases with antibacterial requirements.

Cecropin A-Derived Peptide for the Treatment of Osteomyelitis by Inhibiting the Growth of Multidrug-Resistant Bacteria and Eliminating Inflammation

Osteomyelitis poses substantial therapeutic challenges due to the prevalence of multidrug-resistant bacterial infections and associated inflammation. Current treatment regimens often rely on a combination of corticosteroids and antibiotics, which can lead to complications and impede effective bacterial clearance. In this study, we present CADP-10, a Cecropin A-derived peptide, designed to target methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Escherichia coli (MRE), while simultaneously addressing inflammatory responses. CADP-10 self-assembles into nanobacterial net (NBacN) that selectively identify and bind to bacterial endotoxins (LPS and LTA), disrupting membrane integrity and depolarizing membrane potential, which culminates in bacterial death. Importantly, these NBacN are bound to LPS and LTA from dead bacteria, preventing their engagement with TLR receptors and effectively blocking downstream inflammatory pathways. Our assessments of CADP-10 demonstrate good biosafety in both in vitro and in vivo models. Notably, in a rabbit osteomyelitis model, CADP-10 eliminated MRSA-induced bone infections, mitigated inflammation, and promoted bone tissue regeneration. This research highlights the potential of CADP-10 as a multifunctional antimicrobial agent for the management of infectious inflammatory diseases.

Animal Models of Orthopedic Implant-Associated Infections and Revisions

Orthopedic implant-associated infections such as prosthetic joint infections (PJIs) lead to devastating complications for patients and impose significant financial burdens on the healthcare systems. Although the primary orthopedic implant associated infection rate is relatively low (0.3-9%), the reinfection rate after implant revisions can be as high as 20% to 40%. To evaluate novel therapeutic strategies for preventing and treating infections associated with primary and revision implants, it is essential to develop appropriate animal models that closely emulate clinical realities. Here we discuss existing animal models developed for orthopedic implant revision surgeries including small animal models in rats and mice, and larger animal models in rabbits, sheep, and mini-pigs. While larger animal models offer the advantage of more closely mimicking human surgical procedures, implant dimensions, and infection treatment protocols, rodent models are more cost-effective and better suited for screening experimental prophylaxes and therapeutics. Existing animal revision models have focused on primary infections established by Staphylococcal aureus (S. aureus) and revisions involving both one-stage and two-stage procedures. Further development of smaller animal implant revision models that implement more clinically relevant surgical procedures and recapitulate polymicrobial infections could facilitate the discovery and more rigorous evaluation of novel implant coating prophylaxes and therapeutics for reducing reinfection rates following implant revisions.

PaAP-Activatable NIR Probe for Diagnosing, Imaging, and Discovering Small-Molecule Therapeutics against Implant-Associated Biofilm Infections

Biofilm formation on medical implants causes implant-associated infections (IAIs), leading to high morbidity and mortality. Developing molecular tools for precise biofilm detection, along with novel strategies and agents to target biofilm-related IAIs, is crucial for improving treatment options and patient outcomes. Pseudomonas aeruginosa aminopeptidase (PaAP), a key biofilm-associated virulence factor, is a promising target for combating infections. Here, we developed a PaAP-activatable near-infrared (NIR) fluorescent probe, Hcy-NEO-Leu, for real-time, specific, and sensitive detection of PaAP activity. This probe enables noninvasive imaging of the P. aeruginosa biofilm in vitro and in vivo. The probe also identified LY-58, a lycorine derivative that disrupts biofilm formation without affecting bacterial growth or mammalian cell viability, enhancing tobramycin penetration and overcoming antibiotic resistance. This study introduces LY-58 as a promising adjunctive therapy. In conclusion, the PaAP-activatable NIR imaging probe, combined with LY-58, offers innovative tools for the early diagnosis and effective treatment of IAIs.

Ultrasound-responsive smart biomaterials for bone tissue engineering

Bone defects resulting from trauma, tumors, or other injuries significantly impact human health and quality of life. However, current treatments for bone defects are constrained by donor shortages and immune rejection. Bone tissue engineering has partially alleviated the limitations of traditional bone repair methods. The development of smart biomaterials that can respond to external stimuli to modulate the biofunctions has become a prominent area of research. Ultrasound technology is regarded as an optimal "remote controller" and "trigger" for bone repair biomaterials. This review reports the comprehensive and systematic overview of ultrasound-responsive bone repair smart biomaterials. It presents the fundamental theories of bone repair, the definition of ultrasound, and its applications. Furthermore, the review summarizes the ultrasound effect mechanisms of biomaterials and their roles in bone repair, including detailed studies on anti-inflammation, immunomodulation, and cell therapy. Finally, the advantages of ultrasound-responsive smart biomaterials and their future prospects in this field are discussed.

Value of metagenomic next-generation sequencing in the diagnosis of native pyogenic spinal infections: a multicenter, retrospective observational study

BACKGROUND CONTEXT

The etiological diagnosis of pyogenic spinal infection is crucial for its precise antibiotic treatment. Traditional methods of detection are often slow and ineffective. In recent times, metagenomic next-generation sequencing (mNGS) has revolutionized pathogen detection, offering a more effective approach to disease management.

PURPOSE

Comparing mNGS with microbial culture to comprehensively explore the diagnostic value of mNGS in pyogenic spinal infections.

DESIGN

A multicenter, retrospective observational study.

PATIENT SAMPLE

In a multicenter retrospective observational study, we analyzed the data from 301 patients admitted in four selected hospitals with pyogenic spinal infections from December 2019 to February 2024.

OUTCOME MEASURES

Identification of pathogenic bacteria in patients.

METHODS

Obtain blood and lesion tissue or pus samples from the enrolled patients for microbial culture, serological and hematological laboratory tests, pathological examination, and mNGS analysis, followed by a comparative analysis of the results.

RESULTS

In our cohort of 301 cases of clinically diagnosed pyogenic spinal infections, 242 yielded etiological evidence. The most common gram-positive bacterium was Staphylococcus aureus, and the most common gram-negative bacterium was Escherichia coli. mNGS showed a significantly higher rate of detection (77.9%) compared with microbial culture (27.2%) with a notable difference (X² = 140.17, P<.001). In culture-negative samples, mNGS could detect pathogens in 73.1% of cases, and in culture-positive samples, it could detect pathogens in 91.5% of cases with 94.7% genus-level concordance. mNGS provided faster results (24-48 h) compared with the culture method (2-7 days).

CONCLUSIONS

mNGS serves as a valuable supplement to the culture method and shows potential in identifying the causative pathogen in native pyogenic spinal infections.

Adhesive micro-liquid for efficient removal of bacterial biofilm infection

Bacteria are common infectious pathogens that can cause invasive and potentially life-threatening infections. Ionic liquids have emerged as a novel class of alternatives to antibiotics, however their inherent hydrophobicity and immiscible in water exhibits poor adhesion to bacteria and diminishes its utilization and bioavailability for infection control. Herein, an adhesive metal phenolic encapsulated ionic liquid choline and geranate (CAGE@MPN) microcapsules is designed to address the aforementioned challenges and remove bacterial biofilm infections. The CAGE@MPN microcapsules are prepared through self-assembly of quercetin and ferrous ions on the interface of CAGE and water via metal-phenolic coordination. The MPN interface can stabilize the micro liquid and effectively adhere to bacterial surfaces. The microcapsules can disrupt bacterial cell walls to facilitate the release of cellular contents and destruct the biofilm, thereby exerting a pronounced bactericidal effect. The in vivo bactericidal effect of CAGE@MPN microcapsules is demonstrated in a murine model of Staphylococcus aureus (S. aureus) skin infection. The proposed adhesive micro-liquid system offers a promising strategy for noninvasive and efficient removal of bacterial biofilm infection.

Hybrid Outer Membrane Vesicles with Genetically Engineering for Treatment of Implant-Associated Infections and Relapse Prevention Through Host Immunomodulation

Implant-associated infections (IAIs) are refractory to elimination, and the local immunosuppressive microenvironment (IME) exacerbates therapeutic difficulties, ultimately causing persistence and relapse. Therefore, exploring immunostrengthening treatments holds great promise for reversing IME and thoroughly eradicating chronic or repetitive infections. Bacterial outer membrane vesicles (OMVs) have emerged as potential immunostimulatory candidates; however, they lack active targeting capabilities and cause non-specific inflammatory side effects. In this study, bone marrow-derived mesenchymal stem cells (BMSCs) are genetically engineered to overexpress CXCR4 and isolated cell membranes (mBMSCCXCR4) for hybridization with OMVs derived from Escherichia coli (E. coli) to produce nanovesicles (mBMSCCXCR4@OMV). The resulting mBMSCCXCR4@OMV nanovesicles demonstrate excellent bone marrow targeting capability and are effectively taken up by bone marrow-derived macrophages, triggering the efficient transition to pro-inflammatory M1 status through TLR/NF-κB pathway. This alteration promotes innate bactericidal capacity and antigen presentation. Subsequent activation of T and B cells and inhibition of myeloid-derived suppressor cells (MDSCs) facilitated in vivo adaptive immunity in mouse models. Additionally, mBMSCCXCR4@OMV boosted memory B cell and bacteria-specific antibody responses. Together, these data highlight the potential of mBMSCCXCR4@OMV to eradicate complicated IAIs and provide whole-stage protection against postsurgical relapse, thus marking a significant immunotherapeutic advancement in the post-antibiotic era.

Addressing the challenges of infectious bone defects: a review of recent advances in bifunctional biomaterials

Infectious bone defects present a substantial clinical challenge due to the complex interplay between infection control and bone regeneration. These defects often result from trauma, autoimmune diseases, infections, or tumors, requiring a nuanced approach that simultaneously addresses infection and promotes tissue repair. Recent advances in tissue engineering and materials science, particularly in nanomaterials and nano-drug formulations, have led to the development of bifunctional biomaterials with combined osteogenic and antibacterial properties. These materials offer an alternative to traditional bone grafts, minimizing complications such as multiple surgeries, high antibiotic dosages, and lengthy recovery periods. This review examines the repair mechanisms in the infectious microenvironment and highlights various bifunctional biomaterials that foster both anti-infective and osteogenic processes. Emerging design strategies are also discussed to provide a forward-looking perspective on treating infectious bone defects with clinically significant outcomes.

Wear-resistant antibacterial UHMWPE-based implant materials obtained by radiation crosslinking

The crosslinking of ultrahigh molecular weight polyethylenes (UHMWPEs) by irradiation has been employed for decades to enhance the wear resistance of these materials when used as a load-bearing implant component for joint arthroplasty. This surgical procedure can restore the mobility of patients affected by severe arthritis by the implantation of an artificial joint made of an articulating pair and a bearing component. While the surgery is usually successful, one of the most severe complications is peri-prosthetic joint infection (PJI), which can be extremely difficult to treat and eradicate. The use of UHMWPEs as a platform for the local delivery of antibiotics in addition to their structural function could be extremely beneficial for the improvement in the outcome of PJIs. In this study, we investigated whether irradiation can be used to sterilize and crosslink antibiotic-loaded UHMWPEs, and its effect on the drug eluting and antibacterial properties of these materials. We found that the antibiotics gentamicin sulfate and vancomycin hydrochloride were stable in irradiated UHMWPEs and did not hinder crosslinking of the UHMWPE matrix. Effective crosslinking led to optimal wear resistance, which was comparable to that of clinically available UHMWPEs. Sustained drug release was observed for an extended duration (up to six months) and both the drug eluents and eluted material surfaces showed antibacterial activity against Staphylococcus aureus, the most common causative bacterium for PJIs.

Antimicrobial Phenolic Materials: From Assembly to Function

Infectious diseases pose considerable challenges to public health, particularly with the rise of multidrug-resistant pathogens that globally cause high mortality rates. These pathogens can persist on surfaces and spread in public and healthcare settings. Advances have been made in developing antimicrobial materials to reduce the transmission of pathogens, including materials composed of naturally sourced polyphenols and their derivatives, which exhibit antimicrobial potency, broad-spectrum activity, and a lower likelihood of promoting resistance. This review provides an overview of recent advances in the fabrication of antimicrobial phenolic biomaterials, where natural phenolic compounds act as active antimicrobial agents or encapsulate other antimicrobial agents (e.g., metal ions, antimicrobial peptides, natural biopolymers). Various forms of phenolic biomaterials synthesized through these two strategies, including antimicrobial particles, capsules, hydrogels, and coatings, are summarized, with a focus on their application in wound healing, bone repair and regeneration, oral health, and antimicrobial coatings for medical devices. The potential of these advanced phenolic biomaterials provides a promising therapeutic approach for combating antimicrobial-resistant infections and reducing microbial transmission.

Single-atom Zr doped heterojunction enhanced piezocatalysis for implant infection therapy through synergistic metal immunotherapy with sonodynamic and physical puncture

Recent common clinical treatments for implant bacterial infections involve replacing inert implants and using antibiotics. However, these methods remain limited in their effectiveness for pathogen clearance, immune regulation, and osteogenesis. In this study, we developed a Zr-doped heterointerface of SrTiO3 and Hap (SrTiZrO3/Hap) heterojunction coating with single-atom Zr doping and heterogeneous interfaces designed for ultrasound-responsive antimicrobial activity and bone formation. Under ultrasound, the mechanical force exerted by SrTiZrO3/Hap enhances its physical puncture and sonodynamic activity, synergizing with the metalloimmunotherapy effect of Zr4+ for efficient antimicrobial activity. The primary mechanism enhancing sonodynamic activity involves local interfacial polarization from single-atom Zr doping, achieving piezoelectric catalysis in conjunction with electronic polarization from the built-in electric field. SrTiZrO3/Hap achieved a 99.3% antibacterial rate against S. aureus and 99.7% against E. coli under ultrasound. Additionally, SrTiZrO3/Hap promoted osteogenic differentiation after ultrasound irradiation by activating the PI3K/Akt pathway via its piezoelectric, needle-like topological surface and the release of functional ions, thus accelerating bone repair.

Dual-Loaded Chitosan-Based Nanoparticles: A Novel approach for treating polymicrobial osteomyelitis

Developing innovative approaches to target osteomyelitis caused by polymicrobial infections remains a significant therapeutic challenge. In this study, monodispersed chitosan nanoparticles co-loaded with antibacterial (minocycline) and antifungal (voriconazole) agents were successfully prepared. Minocycline presented higher encapsulation efficiency as compared to voriconazole. Thermostability analysis suggested interactions between the co-loaded drugs within the dual-delivery system, potentially limiting voriconazole release. The dual-loaded chitosan nanoparticles exhibited significant in vitro anti-biofilm activity, achieving up to a 90% reduction in polymicrobial biofilms of S. aureus and C. albicans. Additionally, the nanoparticles showed cytocompatibility with a human osteoblast cell line. These findings highlight the potential of this dual-delivery chitosan-based nanoparticle system to address a critical gap in osteomyelitis treatment by targeting both bacterial and fungal pathogens.

Antimicrobial photodynamic therapy with 5-aminolevulinic acid plus antibiotics: a promising treatment for tibial osteomyelitis caused by drug-resistant bacteria

Osteomyelitis is a severely destructive bone disease caused by microbial infections, and currently, no available treatment effectively controls the infection. 5-Aminolevulinic acid is a second-generation endogenous photosensitizer. This study investigated the efficacy of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) in combination with antibiotics in the treatment of tibial osteomyelitis in rabbits. The results illustrated that ALA-PDT alone and in combination of antibiotics displayed significant efficacy in treating osteomyelitis. Animals in the photodynamic antimicrobial chemotherapy (PACT) + antibiotics group exhibited a higher survival rate, an improved overall mental status, a lower localized infection rate, and reduced Tang Hui and Norden scores (P < 0.05), indicating less severe bone destruction. Histologically, more strips of lamellar new bone formation and more pronounced periosteal hyperplasia were noted in the PACT + antibiotics group. Micro-computed tomography illustrated that the structural integrity of cortical bone and cancellous bone structure had better continuity and clearer display in the PACT + antibiotics group than in the other groups, and the periosteal reaction in the modeling area was the most obvious. Bone parameter analysis indicated that trabecular thickness, bone volume, and trabeculae volume were significantly higher in the PACT + antibiotics group than in the model and antibiotics groups (P < 0.05). Additionally, trabecular separation was significantly lower in the PACT + antibiotic group than in the other groups (P < 0.05). These findings suggest that the combination of ALA-PDT and antibiotics has a sensitizing therapeutic effect, offering a promising strategy for the clinical treatment of osteomyelitis.

Application of Antimicrobial Peptides (AMPs) in Treatment of Osteomyelitis in Human and Veterinary Orthopedics

Osteomyelitis, a severe bone infection, poses a significant therapeutic challenge in both human and veterinary medicine, especially due to the increasing prevalence of antibiotic-resistant pathogens like methicillin-resistant Staphylococcus aureus (MRSA). Conventional treatments, including surgical debridement and systemic antibiotics, often prove inadequate due to the ability of bacteria to form biofilms and evade host immune responses. Antimicrobial peptides (AMPs), such as LL-37 and β-defensins, have emerged as a promising alternative therapeutic strategy. AMPs exhibit broad-spectrum antimicrobial activity, including efficacy against resistant strains, and possess immunomodulatory properties that can promote bone regeneration. This article comprehensively reviews AMP applications in treating osteomyelitis across both human and veterinary medicine. We discuss diverse therapeutic approaches, including free AMPs, their conjugation with biomaterials such as collagen and chitosan to enhance delivery and stability, and the development of AMP-based nanoparticles. Furthermore, we analyze preclinical and clinical findings, highlighting the efficacy and safety of AMPs in combating osteomyelitis in both human and animal patients. Finally, we explore future perspectives and challenges, such as optimizing delivery, stability, and efficacy, while minimizing cytotoxicity, and in translating AMP-based therapies into clinical practice to effectively manage this debilitating disease.

Suppressive antibiotic treatment (SAT) in the era of MDRO infections: a narrative review

INTRODUCTION

Antibiotics were originally developed to treat acute bacterial infections, and research studies focus their efforts on safety and efficacy in the short term; however, prolonged course of antibiotics has been documented in multiple clinical settings. The aim of this narrative review is to provide a new perspective on SAT and to discuss new therapeuticpossibilities.

AREAS COVERED

We discuss new clinical scenarios in which SAT could be considered. We provided a broad discussion about long-acting agents and new or repurposed oral agents as well as the use of OPAT with elastomeric pumps and an overview of the pipeline of new antifungals. Limitations of SAT are presented in this review and especially patients' adherence issues, possible spread of MDROs, possible rising of the incidence of Clostridioides difficile infections, drug-to-drug interactions and drug-related problems, cost-effectiveness evaluation issues.

EXPERT OPINION

Many research gaps are evident and further studies are needed. Above all, the efficacy and safety of SAT in the different clinical scenarios. Discovery of new molecules against MDROs and ongoing research on PK/PD variables as well as a better understanding of the relationship between SAT and the emergence of resistance could improve SAT usage and reduce the impact of DRPs.

Accelerating repair of infected bone defects through post-reinforced injectable hydrogel mediated antibacterial/immunoregulatory microenvironment at bone-hydrogel interface

Functional injectable hydrogel (IH) is promising for infected bone defects (IBDs) repair, but how to endow it with desired antibacterial/immunoregulatory functions as well as avoid mechanical failures during its manipulation has posed as main challenges. Herein, rosmarinic acid (RosA), a natural product with antibacterial/immunoregulatory activities, was utilized to develop a FCR IH through forming phenylboronic acid ester bonds with 4-formylphenyl phenylboronic acid (4-FPBA) grafted chitosan (CS) (FC). After being applied to the IBD site, the FCR IH was then injected with tobramycin (Tob) solution, another alkaline antibacterial drug, to induce in situ crystallization of the FC, endowing the resultant FCRT hydrogel with adaptively enhanced mechanical strength and structural stability. Owing to the specific structural composition, the FCRT hydrogel could sustainedly release Tob and RosA molecules at the IBD interface, effectively eliminating in situ bacterial infection. In addition, the released RosA molecules also induced the M2 polarization of in situ macrophages (Mφ), which was identified to be related to the NF-κB and PI3K-AKT pathways, therefore promoting the osteogenic differentiation of in situ bone marrow stromal cells (BMSCs). Due to the simultaneous antibacterial/osteo-immunoregulatory microenvironment at the IBD interface, the repair of IBDs was proved to be greatly accelerated by the FCRT hydrogel.

A Fused Membrane-Camouflaged Biomimetic Nanosystem for Dual-Targeted Therapy of Septic Arthritis

Due to the inherent aseptic and enclosed characteristics of joint cavity, septic arthritis (SA) almost inevitably leads to intractable infections and rapidly progressing complex pathological environments. Presently, SA faces not only the deficient effectiveness of the gold-standard systemic antibiotic therapy but also the scarcity of effective localized targeted approaches and standardized animal models. Herein, an ingenious multifunctional nanosystem is designed, which involves the methylation of hyaluronic acid (HA), copolymerization with DEGDA, loading with vancomycin (VAN), and then coating with fused macrophage-platelet membrane (denoted as FM@HA@VAN). Upon intra-articular administration, FM@HA@VAN nanoparticles exhibit sustained retention and selectively targeting to infected sites, leveraging macrophage-mediated inflammation homing and platelet-directed bacteria targeting. The acidic microenvironment triggers responsive release of vancomycin, leading to potent bactericidal effects. Subsequently, the exposed HA@VAN nanoparticles are efficiently internalized by activated macrophages, releasing HA to alleviate oxidative stress and achieve chondroprotection by inhibiting pro-inflammatory cytokines, neutralizing ROS and upregulating macrophage M2 polarization. In vivo model and experiments confirm the efficacy of this dual-targeting antibacterial approach, demonstrating its precision in eradicating bacterial infections and alleviating associated pathological processes, including synovial hyperplasia and cartilage erosion. The dual-targeting therapeutic nanosystem, coordinated with fused-membranes, holds promise for enhancing the treatment efficacy of SA.

Piezoelectric Biomaterial with Advanced Design for Tissue Infection Repair

Bacterial infection has become the most dangerous factor in tissue repair, which strongly affects the tissue regeneration efficiency and wellness of patients. Piezoelectric materials exhibit the outstanding advantage of producing electrons without external power supply. The ability of electron enrichment and reactive oxygen species generation through noninvasive stimulations enables piezoelectric materials the potential applications of antibacterial. Many studies have proved the feasibility of piezoelectric materials as a functional addition in antibacterial biomaterial. In fact, numerous piezoelectric materials with ingenious designs are reported to be effective in antibacterial processes. This review summarizes the antibacterial mechanisms of piezoelectric, illuminating their potential in combating bacteria. Recent advancement in the design and construction of piezoelectric biomaterial including defect engineering, heterojunction, synergy with metal and the composite scaffold configuration are thoroughly reviewed. Moreover, the applications and therapeutic effects of piezoelectric materials in common tissues with antibacterial requirements are introduced, such as orthopedics, dental, and wound healing. Finally, the development prospects and points deserving further exploration are listed. This review is expected to provide valuable insight into the relationship between antibacterial processes and piezoelectric materials, further inspiring constructive development in this emerging scientific discipline.

Directional Freeze-Casting Cryogel Loaded with Quaternized Chitosan Modified Gallium Metal-Organic Frameworks to Capture and Eradicate the Resistant Bacteria for Guided Regeneration in Infected Bone Defects

Antimicrobial resistance and impaired bone regeneration are the great challenges in treating infected bone defects. Its recurrent and resistant nature, high incidence rate, long-term hospitalization, and high medical costs have driven the efforts of the scientific community to develop new therapies to improve the situation. Considering the complex microenvironment and persistent mechanisms mediated by resistant bacteria, it is crucial to develop an implant with enhanced osseointegration and sustained and effective infection clearance effects. Here, a positively charged quaternized chitosan (QCS) coated gallium-based metal-organic framework (GaMOF) is designed, to capture the antibiotic-resistant bacteria (Methicillin-resistant Staphylococcus aureus, MRSA) as a "captor", and rejuvenate Methicillin (Me) via disturbing the tricarboxylic acid (TCA) cycle. Then, a radially oriented porous cryogel loaded with the Me and QCSGaMOF is fabricated by the directional freeze-casting method. The oriented porous structure has an enhanced osseointegration effect by guiding the ingrowth of osteogenic cells. In vitro and in vivo experiments prove the advantages of as-prepared Me/QCSGa-MOF@Cryogel in combating resistant bacteria and guiding bone regeneration in infected bone defects.

Directional Mushroom-Derived Scaffold for Microenvironment Regulation in Infected Bone Defects

Infected bone defects are a common clinical condition, but conventional treatments often fail to achieve the desired outcomes, including addressing antibiotic resistance and preventing nonunion complications. In the presented study, a functionalized decellularized mushroom stem scaffold is developed composed of its naturally aligned channels, Zn2+/curcumin MOFs, hydroxyapatite minerals, and icariin. In vitro, It is found that functionalized acellular mushroom stem scaffold can control bacterial infections through Zn2+/curcumin MOFs. The naturally aligned channels guide bone mesenchymal stem cells (BMSCs) migration, and the components adsorbed on the acellular substrate further promote the migration of BMSCs. Moreover, these functional components further accelerated the polarization of M2 macrophage and osteogenic differentiation of BMSCs. In vivo, the functionalized decellularized mushroom stem scaffold cleared infected bacteria within 3 days, induced extracellular matrix secretion and alignment, and promoted new bone formation to cover defects within 8 weeks. The functionalized decellularized mushroom stem scaffold provides a promising strategy for treating infectious bone defects.

Long-term follow-up of chronic osteomyelitis after bone tumor resection

The standard treatment for chronic osteomyelitis after trauma is affected bone resection and bone and soft tissue defect reconstruction. However, few reports exist regarding chronic osteomyelitis after bone tumor surgery. We retrospectively reviewed five cases of chronic infection after bone tumor surgery, including their treatment strategy and clinical course. We reviewed three cases of giant cell tumors of bone and two cases of osteosarcoma. Reconstruction was performed after tumor resection in all cases. Despite careful management, fistula formation and chronic infection occurred. Two patients underwent radical surgery for chronic infection. After the infection subsided, reconstruction was performed again. However, in one case, the infection recurred, and consequently, amputation was performed. When radical surgery is performed, implant replacement is essential due to biofilm formation. Controlling soft tissue infection, besides bone and implant infection, is important. In some cases, however, radical surgery is undesirable, and patients choose to live with the chronic infection instead. Even when methicillin-resistant S. aureus (MRSA) was detected, anti-MRSA drugs were used only in the early stages, after which the infection was managed by switching to oral antibiotics, such as minocycline and sulfamethoxazole-trimethoprim combination drugs. Careful follow-up is necessary due to the risk of fistula cancer in conservative management.

Targeting ClpP: Unlocking a novel therapeutic approach of isochlorogenic acid A for methicillin-resistant Staphylococcus aureus-infected osteomyelitis

A medical predicament has led to extensive drug resistance in methicillin-resistant Staphylococcus aureus (MRSA), and the complexity of treatment has increased exponentially with the induction of osteomyelitis. In view of the severe situation and the potential of bacterial antivirulence strategies, this study focused on the key virulence factor caseinolytic protease (ClpP) of S. aureus to identify new strategies against MRSA-induced osteomyelitis. As the main protein "quality control" system of S. aureus, ClpP is indispensable for coordinating drug resistance, regulating adhesion, and acting on numerous virulence targets. Through fluorescence resonance energy transfer (FRET), we successfully identified isochlorogenic acid A (I-A), a polyphenol derivative, as an efficient inhibitor of ClpP, with an IC50 value of 24.89 μg/mL. Further analysis revealed that I-A can effectively inhibit the expression of virulence factors of MRSA and significantly reduce its adhesion to fibrinogen. Molecular docking revealed the potential binding sites of ClpP and I-A, namely, ILE-81, LYS-109, GLU-156, ARG-157, and GLY-184. At the cellular level, I-A can alleviate the death and increased secretion of inflammatory factors caused by MRSA USA300 in MC3T3-E1 cells. Moreover, it downregulates the activity of ClpP and reduces the response of bacteria to environmental stress. In vivo experiments have confirmed that I-A shows significant efficacy in both rat osteomyelitis models and Galleria mellonella infection models. This study provides new insights into the field of treatment strategies targeting virulence and provides a solid foundation for further exploration of the potential of I-A in combating drug-resistant S. aureus.

Infections in sickle cell disease

Sickle cell disease (SCD) is one of the commonest severe inherited disorders in the world. Infection accounts for a significant amount of the morbidity and mortality, particularly in sub-Saharan Africa, but is relatively poorly studied and characterized. Patients with SCD have significant immunodeficiency and are more likely to suffer severe and life-threatening complications of infection, and additionally infections can trigger complications of SCD itself. Those with more severe forms of SCD have functional asplenia from a very early age, which accounts for much of the morbidity in young children, particularly invasive infections from encapsulated bacteria including Streptococcus pneumoniae, Haemophilus influenzae, Salmonella typhi and meningococcal disease. Additionally, there are other defects in immune function in SCD, associated with anemia, tissue infarction and impaired adaptive immunity. Complications of infections in SCD include acute chest syndrome, acute painful episodes, osteomyelitis, meningitis, urinary tract infections, overwhelming sepsis and death. Viral infections cause significant morbidity, particularly severe anemia associated with parvovirus, and to a lesser extent other infections such as influenza and coronavirus disease 2019. The relationship between malaria and SCD is complicated and discussed in this review. Unlike many of the genetic risk factors for poor outcomes in SCD, it is theoretically possible to modify the risks associated with infections with established public health measures. These include the provision of vaccination, prophylactic antibiotics and access to clean water and mosquito avoidance, although current financial restraints and political priorities have made this difficult.

Comparative study of the inhibitory effects of different antibiotic administration routes on bone healing in a rat tibial infection model

Objective

This study aimed to evaluate the effectiveness of intravenous versus oral antibiotic treatments in managing bone infections, particularly osteomyelitis, using a rat tibial infection model.

Methods

A tibial bone infection model was established in twelve-week-old Wistar rats via injection of Staphylococcus aureus at a cortical defect site. After six weeks, rats were treated with vancomycin (intravenous), cefazolin (intravenous), ciprofloxacin (oral), or ciprofloxacin combined with rifampin (oral). Microbial analysis, blood analysis for pro-inflammatory cytokines, micro-computed tomography (μCT), histological analysis, and osteoclast activity were used to assess the efficacy of each treatment.

Results

Blood analysis showed significant reductions in white blood cell count and pro-inflammatory cytokines in the intravenous treatment groups, especially with vancomycin. μCT imaging revealed better preservation of bone structure in intravenous treatment groups, while oral treatments resulted in more pronounced structural deterioration. Microbial analysis confirmed a lower bacterial load in the intravenous groups, particularly vancomycin, compared to oral treatments. Histological analysis revealed reduced inflammation, lower fibrosis, and minimal bacterial presence in intravenous groups. Osteoclast activity was notably reduced in the vancomycin and cefazolin groups, indicating better control of bone resorption.

Conclusion

Intravenous administration of vancomycin demonstrated superior efficacy in controlling bone infection, reducing inflammation, and preserving bone structure compared to oral treatments. While ciprofloxacin and the ciprofloxacin-rifampin combination showed some efficacy, they were less effective than intravenous vancomycin, likely due to lower bioavailability and insufficient drug penetration in bone tissue.

Calcium phosphate-based anti-infective bone cements: recent trends and future perspectives

Bone infection remains a challenging condition to fully eradicate due to its intricate nature. Traditional treatment strategies, involving long-term and high-dose systemic antibiotic administration, often encounter difficulties in achieving therapeutic drug concentrations locally and may lead to antibiotic resistance. Bone cement, serving as a local drug delivery matrix, has emerged as an effective anti-infective approach validated in clinical settings. Calcium phosphate cements (CPCs) have garnered widespread attention and application in the local management of bone infections due to their injectable properties, biocompatibility, and degradability. The interconnected porous structure of calcium phosphate particles, not only promotes osteoconductivity and osteoinductivity, but also serves as an ideal carrier for antibacterial agents. Various antimicrobial agents, including polymeric compounds, antibiotics, antimicrobial peptides, therapeutic inorganic ions (TIIs) (and their nanoparticles), graphene, and iodine, have been integrated into CPC matrices in numerous studies aimed at treating bone infections in diverse applications such as defect filling, preparation of metal implant surface coatings, and coating of implant surfaces. Additionally, for bone defects and nonunions resulting from chronic bone infections, the utilization of calcium phosphate-calcium sulfate composite multifunctional cement loaded with antibacterial agents serves to efficiently deal with infection, stimulate new bone formation, and attain an optimal degradation rate of the bone cement matrix. This review briefly delves into various antibacterial strategies based on calcium phosphate cement for the prevention and treatment of bone infections, while also discussing the application of calcium phosphate-calcium sulfate composites in the development of multifunctional bone cement against bone infections.

Multifunctional metal-phenolic nanoparticles with antibacterial and anti-inflammatory effects for osteomyelitis management

Osteomyelitis is a serious inflammatory disease mostly caused by bacterial infections. It is necessary to simultaneously eradicate bacterial cells and inhibit inflammation in treating osteomyelitis. Herein, we design an innovative zinc ion (Zn2+)-based nano delivery system for the management of osteomyelitis. Taking advantage of the coordination self-assembly of Zn2+, quercetin (QU), and ε-poly-L-lysine (EPL), Zn2+-containing nanoparticles (denoted as ZQE NPs) are prepared. ZQE NPs are spherical nanoparticles with amorphous structures. They are stable in the physiological neutral environment but can be dissociated in an acidic microenvironment of infection sites. Since Zn2+ is encapsulated into ZQE NPs by coordination interaction, the deactivation of Zn2+ by proteins can be effectively avoided. Therefore, ZQE NPs can maintain excellent bactericidal activity in a protein-rich environment, while dissociative Zn2+ doesn't exhibit obvious bactericidal ability. Meanwhile, ZQE NPs are highly effective at scavenging intracellular reactive oxygen species (ROS) and inhibiting pro-inflammatory cytokines, due to the strong anti-inflammatory effects of QU and Zn2+. The in vivo therapeutic efficacy of ZQE NPs is assessed using a rat model of methicillin-resistant Staphylococcus aureus (MRSA)-induced osteomyelitis. Results demonstrate that ZQE NPs effectively eradicate bacterial cells and reduce inflammation in vivo, thereby promoting osteogenesis and recovery of osteomyelitis.

Engineered Nanovesicles for the Precise and Noninvasive Treatment of Deep Osteomyelitis Caused by MRSA Infection with Enhanced Immune Response

The clinical treatment of hospital-acquired persistent osteomyelitis caused by methicillin-resistant Staphylococcus aureus (MRSA) presents two major challenges: ineffective drug delivery into deep tissues and counteracting the rapid establishment of an immunosuppressive microenvironment. Indeed, MRSA can evade immunosurveillance and undermine both innate and adaptive immune responses. Herein, the engineered nanovesicles, functioning by combining sonodynamic therapy (SDT) with immune modulation, were constructed for the precise and noninvasive removal of MRSA in deep tissue and activation of the antimicrobial immune response using a newly engineered nanovesicle. Macrophage-derived M1 phenotypic microvesicles (M1-MW) internalized vancomycin-cross-linked micelles with the acoustic sensitizer indocyanine green (ICG) (VCG micelles). The vesicles of M1-MW were grafted with PEGylated mannose, allowing for targeted accumulation at the infection site. The VCG micelles were responsive to the highly reducing environment and released ICG to generate ROS after exposure to ultrasounds. This effect was combined with the presence of vancomycin to kill MRSA. In an osteomyelitis infection model, we observed an improved survival rate and reprogramming of macrophages to a pro-inflammatory M1 phenotype. The latter promoted T-cell activation and immune defense against MRSA-camouflaged homologous cell-transferred infections. Thus, our study presents a noninvasive and efficient treatment (VCG@MMW) for deep osteomyelitis with improved bacterial clearance and reduced risk of recurrence with enhanced immune response.

In Situ Application of Berberine-Loaded Liposomes on the Treatment of Osteomyelitis

Osteomyelitis is a major challenge in global healthcare, as it requires the simultaneous management of bone defects and bacterial infections, which poses considerable difficulties for orthopedic clinicians. In this study, we developed berberine liposome-modified bone cement specifically aimed at treating osteomyelitis induced by Staphylococcus aureus. We characterized the physical properties of this modified bone cement, conducted in vitro antibacterial assays to evaluate its efficacy in eradicating Staphylococcus aureus biofilm, established an in vivo rat model of osteomyelitis, and performed histopathological assessments alongside micro-CT analysis of bone parameters. The results indicated that the berberine liposome-modified bone cement exhibited favorable biodegradability and sustained-release characteristics, with a drug release rate of more than 90% within 14 days, while effectively eliminating bacterial biofilm with a biofilm eradication rate of up to 80% and facilitating bone repair with a bone volume fraction of 80%. This innovative treatment demonstrated both safety and efficacy in addressing tibial osteomyelitis in rats, thereby offering novel insights and methodologies for clinical interventions against osteomyelitis.

Staphylococcus aureus in Inflammation and Pain: Update on Pathologic Mechanisms

Staphylococcus aureus (S. aureus) is a Gram-positive bacterium of significant clinical importance, known for its versatility and ability to cause a wide array of infections, such as osteoarticular, pulmonary, cardiovascular, device-related, and hospital-acquired infections. This review describes the most recent evidence of the pathogenic potential of S. aureus, which is commonly part of the human microbiota but can lead to severe infections. The prevalence of pathogenic S. aureus in hospital and community settings contributes to substantial morbidity and mortality, particularly in individuals with compromised immune systems. The immunopathogenesis of S. aureus infections involves intricate interactions with the host immune and non-immune cells, characterized by various virulence factors that facilitate adherence, invasion, and evasion of the host's defenses. This review highlights the complexity of S. aureus infections, ranging from mild to life-threatening conditions, and underscores the growing public health concern posed by multidrug-resistant strains, including methicillin-resistant S. aureus (MRSA). This article aims to provide an updated perspective on S. aureus-related infections, highlighting the main diseases linked to this pathogen, how the different cell types, virulence factors, and signaling molecules are involved in the immunopathogenesis, and the future perspectives to overcome the current challenges to treat the affected individuals.

Metal Ion and Antibiotic Co-loaded Nanoparticles for Combating Methicillin-Rresistant Staphylococcus aureus-Induced Osteomyelitis

Methicillin-resistant Staphylococcus aureus (MRSA) causes osteomyelitis (OM), which seriously threatens public health due to its antimicrobial resistance. To increase the sensitivity of antibiotics and eradicate intracellular bacteria, a Zn2+ and vancomycin (Van) codelivered nanotherapeutic (named Man-Zn2+/Van NPs) was fabricated and characterized via mannose (Man) modification. Man-Zn2+/Van NPs exhibit significant inhibitory activity against extra- and intracellular MRSA and obviously decrease the minimum inhibitory concentration of Van. Man-Zn2+/Van NPs can be easily internalized by MRSA-infected macrophages and significantly accumulated in infected bone via Man-mediated targeting. In vivo experiments in a mouse OM model verified that Man-Zn2+/Van NPs significantly reduce the extra- and intracellular MRSA burden, improve gait patterns, increase bone mass, and decrease inflammatory cytokine expression. The antibacterial mechanism of Man-Zn2+/Van NPs includes destruction of the MRSA membrane, degeneration of intracellular proteins and DNA, inhibition of MRSA glycolysis, and intervention in the energy metabolism of bacteria. Overall, this metal-antibiotic nanotherapeutics strategy provides new insight for combating extra- and intracellular infections caused by MRSA-induced OM.

Ascorbate-loaded MgFe layered double hydroxide for osteomyelitis treatment

Bacterial infections evoke considerable apprehension in orthopedics. Traditional antibiotic treatments exhibit cytotoxic effects and foster bacterial resistance, thereby presenting an ongoing and formidable obstacle in the realm of therapeutic interventions. Achieving bacterial eradication and osteogenesis are critical requirements for bone infection treatment. Herein, we design and fabricate a nanoenzyme-mimicking drug through the co-precipitation process, integrating MgFe layered double hydroxide with ascorbic acid (AA@LDH), to facilitate the simultaneous presence of these two unique functionalities. Within a bacterial acidic milieu, the degradation of the AA@LDH nanosystem prompts ascorbic acid to undergo a pro-oxidative transformation, generating an abundance of reactive oxygen species (ROS). These ROS overwhelm bacterial cellular processes, including nucleic acid replication, cell wall construction, virulence factor production, biosynthetic pathways, and energy generation. This disruption culminates in substantial bacterial mortality, as substantiated by RNA sequencing data. Hence, the AA@LDH nano system exhibits an in vitro antibacterial rate of approximately 100 % and 99 %, against S.aureus and E. coli, respectivaly. Additionally, the AA@LDH could directly accelerate osteogenic differentiation in vitro, evidenced by a 50 % increase in alkaline phosphatase activity and a 270 % improvement in extracellular matrix mineralization capability. Moreover, it enhances osteointegration process in vivo by favorably reshaping the osteogenic immune microenvironment. This innovative nanosystem for delivery offers new strategies that concurrently combat bacterial infections, mitigate inflammation, and induce tissue regeneration, marking a significant advancement in the realm of advanced materials and its applications.

Clinical and epidemiological differences in staphylococcal osteoarticular infections: insights for developing hospital-based infection control interventions

PURPOSE

Osteoarticular infections (OAI) are serious clinical conditions with Staphylococcus aureus and Coagulase-negative Staphylococcus (CoNS) responsible for up to two-thirds of cases. This work aimed to compare the epidemiological, clinical, and microbiological characteristics of OAI caused by S. aureus versus CoNS to aid in clinical management and infection control strategies.

METHODS

A single-centre retrospective study was performed at the Centro Hospitalar e Universitário de Coimbra for the period of January 2011 to December 2021. A total of 458 cases of OAI were gathered. Data was retrieved from medical records and statistical analysis was performed with SPSS.

RESULTS

S. aureus accounted for 60.7% of infections, followed by S. epidermidis (29.9%). Independent risk factors for S. aureus infections included being male (p < 0.001; OR = 0.47) and a history of osteomyelitis (p < 0.001; OR = 0.18). In contrast, CoNS infections were associated with older age (p = 0.018), carrying a prosthetic device (p < 0.001; OR = 2.92), and a prior periprosthetic infection (p = 0.023; OR = 1.86). Both groups exhibited significant antimicrobial resistance, with CoNS showing greater resistance to gentamicin, linezolid, teicoplanin and trimethoprim-sulfamethoxazole, while S. aureus was more commonly resistant to clindamycin.

CONCLUSION

Our findings show the distinct characteristics of OAI caused by S. aureus and CoNS, highlighting the need for targeted risk factor management and tailored empiric antibiotic therapy to reduce incidence and improve outcomes.

Staphylococcus aureus induces mitophagy via the HDAC11/IL10 pathway to sustain intracellular survival

BACKGROUND

The immune evasion and prolonged survival of Staphylococcus aureus (S. aureus) within macrophages are key factors contributing to the difficulty in curing osteomyelitis. Although macrophages play a vital role as innate immune cells, the mechanisms by which S. aureus survives within them and suppresses host immune functions remain incompletely understood.

METHODS

This study employed confocal microscopy, flow cytometry, ELISA, and siRNA technology to assess the survival capacity of S. aureus within macrophages and the impact of inflammatory cytokines on its persistence. Proteomics was used to investigate the potential mechanisms and differential proteins involved in S. aureus intracellular survival. Additionally, confocal microscopy, flow cytometry, Mdivi-1 intervention, and Western blot were utilized to validate the role of mitophagy in supporting S. aureus survival. The study further explored how the HDAC11/IL10 axis enhances mitophagy to promote intracellular S. aureus survival by using HDAC11 overexpression, siRNA, and rapamycin intervention combined with confocal microscopy and flow cytometry.

RESULTS

The findings demonstrated that IL10 promotes mitophagy to clear mitochondrial reactive oxygen species (mtROS), thereby enhancing the intracellular survival of S. aureus within macrophages. Additionally, we discovered that the transcriptional repressor of IL10, HDAC11, was significantly downregulated during S. aureus infection. Overexpression of HDAC11 and the use of the autophagy activator rapamycin further validated that the HDAC11/IL10 axis regulates mitophagy via the mTOR pathway, which is essential for supporting S. aureus intracellular survival.

CONCLUSION

This study reveals that S. aureus enhances IL10 production by inhibiting HDAC11, thereby promoting mitophagy and mtROS clearance, which supports its survival within macrophages. These findings offer new insights into the intracellular survival mechanisms of S. aureus and provide potential therapeutic approaches for the clinical management of osteomyelitis.

Synthetic nanointerfacial bioengineering of Ti implants: on-demand regulation of implant-bone interactions for enhancing osseointegration

Titanium and its alloys are the most commonly used biometals for developing orthopedic implants to treat various forms of bone fractures and defects, but their clinical performance is still challenged by the unfavorable mechanical and biological interactions at the implant-tissue interface, which substantially impede bone healing at the defects and reduce the quality of regenerated bones. Moreover, the impaired osteogenesis capacity of patients under certain pathological conditions such as diabetes and osteoporosis may further impair the osseointegration of Ti-based implants and increase the risk of treatment failure. To address these issues, various modification strategies have been developed to regulate the implant-bone interactions for improving bone growth and remodeling in situ. In this review, we provide a comprehensive analysis on the state-of-the-art synthetic nanointerfacial bioengineering strategies for designing Ti-based biofunctional orthopedic implants, with special emphasis on the contributions to (1) promotion of new bone formation and binding at the implant-bone interface, (2) bacterial elimination for preventing peri-implant infection and (3) overcoming osseointegration resistance induced by degenerative bone diseases. Furthermore, a perspective is included to discuss the challenges and potential opportunities for the interfacial engineering of Ti implants in a translational perspective. Overall, it is envisioned that the insights in this review may guide future research in the area of biometallic orthopedic implants for improving bone repair with enhanced efficacy and safety.

Exosomes derived from bone marrow mesenchymal stem cells induce the proliferation and osteogenic differentiation and regulate the inflammatory state in osteomyelitis in vitro model

Chronic osteomyelitis is a chronic bone infection characterized by progressive osteonecrosis and dead bone formation, which is closely related to persistent infection and chronic inflammation. Exosomes derived from bone marrow-derived mesenchymal stem cells (BMSC) play an important role in bone tissue regeneration and the modulation of inflammatory processes. However, their role and mechanism of action in osteomyelitis have not been reported so far. This paper explores the potential effect of BMSC-derived exosomes on osteomyelitis in vitro model with the aim of providing a theoretical basis for the treatment of osteomyelitis in the future. In this study, exosomes were isolated and extracted from BMSCs and identified. MC3T3-E1 cells were treated with Staphylococcal protein A (SPA) to establish an in vitro model of osteomyelitis. Next, the effects of BMSC-derived exosomes on cell proliferation, apoptosis, angiogenesis, and autophagy in MC3T3-E1 cells treated with SPA were evaluated. Results showed that the proliferation ability of MC3T3-E1 cells increased after co-culture with BMSC-derived exosomes. Moreover, exosomes induced autophagy and osteogenic differentiation in MC3T3-E1 cells. The mRNA and protein levels of factors related to proliferation, differentiation, apoptosis, autophagy, and angiogenesis including β-Catenin, Runx2, Bcl-2, VEGFA, and Beclin-1 upregulated in SPA-treated MC3T3-E1 cells, whereas the levels of inflammatory cytokines including TNF-α, IL-1β, and IL-6 decreased in the supernatant. The results showed that exosomes derived from BMSCs may participate in the attenuation of osteomyelitis by inducing proliferation and osteogenic differentiation and regulating the inflammatory state in bone cells.

Dual-Energy Computed Tomography Iodine Maps: Application in the Diagnosis of Periprosthetic Joint Infection in Total Hip Arthroplasty

BACKGROUND

The challenge of early and rapid diagnosis of periprosthetic joint infection (PJI) remains important. This study aimed to assess the efficacy of dual-energy computed tomography (DECT) iodine maps for diagnosing PJI in total hip arthroplasty.

METHODS

We prospectively enrolled 68 patients who had postoperative joint pain after hip arthroplasty. All patients underwent preoperative DECT iodine imaging to quantify iodine concentration (IC) in periprosthetic tissues during arterial and venous phases. The diagnostic efficacy of DECT iodine maps was evaluated by constructing receiver operating characteristic curves according to the Musculoskeletal Infection Society criteria.

RESULTS

Compared with erythrocyte sedimentation rate (area under the curve [AUC] = 0.837), polymorphonuclear cell percentage (AUC = 0.703), and C-reactive protein (AUC = 0.837), periprosthetic tissue venous-phase IC (AUC = 0.970) and arterial-phase IC (AUC = 0.964) exhibited outstanding discriminative capability between PJI and aseptic failure. The PJI cut-off point was venous IC = 1.225 mg/mL, with a sensitivity of 92.31% and specificity of 90.48%; for arterial IC = 1.065 mg/mL, the sensitivity was 96.15% and specificity was 90.70%.

CONCLUSIONS

This study demonstrates the great potential of DECT iodine maps for the diagnosis of PJI around hip arthroplasty, which helps to differentiate between periprosthetic infection and aseptic failure after hip arthroplasty.

Development of an ex vivo model to study Staphylococcus aureus invasion of the osteocyte lacuno-canalicular network

Staphylococcus aureus has multiple mechanisms to evade the host's immune system and antibiotic treatment. One such mechanism is the invasion of the osteocyte lacuno-canalicular network (OLCN), which may be particularly important in recurrence of infection after debridement and antibiotic therapy. The aim of this study was to develop an ex vivo model to facilitate further study of S. aureus invasion of the OLCN and early-stage testing of antibacterial strategies against bacteria in this niche. The diameter of the canaliculi of non-infected human, sheep, and mouse bones was measured microscopically on Schmorl's picrothionin stained sections, showing a large overlap in canalicular diameter. S. aureus successfully invaded the OLCN in all species in vitro as revealed by presence in osteocyte lacunae in Brown and Brenn-stained sections and by scanning electron microscopy. Murine bones were then selected for further experiments, and titanium pins with either a wild-type or ΔPBP4 mutant S. aureus USA300 were placed trans-cortically and incubated for 2 weeks in tryptic soy broth. Wild-type S. aureus readily invaded the osteocyte lacunae in mouse bones while the ΔPBP4 showed a significantly lower invasion of the OLCN (p = 0.0005). Bone specimens were then treated with gentamicin, sitafloxacin, R14 bacteriophages, or left untreated. Gentamicin (p = 0.0027) and sitafloxacin (p = 0.0280) significantly reduced the proportion of S. aureus-occupied lacunae, whilst bacteriophage treatment had no effect. This study shows that S. aureus is able to invade the OLCN in an ex vivo model. This ex vivo model can be used for future early-stage studies before proceeding to in vivo studies.

Piezoelectric-Enhanced Nanocatalysts Trigger Neutrophil N1 Polarization against Bacterial Biofilm by Disrupting Redox Homeostasis

Strategies of manipulating redox signaling molecules to inhibit or activate immune signals have revolutionized therapeutics involving reactive oxygen species (ROS). However, certain diseases with dual resistance barriers to the attacks by both ROS and immune cells, such as bacterial biofilm infections of medical implants, are difficult to eradicate by a single exogenous oxidative stimulus due to the diversity and complexity of the redox species involved. Here, this work demonstrates that metal-organic framework (MOF) nanoparticles capable of disrupting the bacterial ROS-defense system can dismantle bacterial redox resistance and induce potent antimicrobial immune responses in a mouse model of surgical implant infection by simultaneously modulating redox homeostasis and initiating neutrophil N1 polarization in the infection microenvironment. Mechanistically, the piezoelectrically enhanced MOF triggers ROS production by tilting the band structure and acts synergistically with the aurintricarboxylic acid loaded within the MOF, which inhibits the activity of the cystathionine γ-cleaving enzyme. This leads to biofilm structure disruption and antigen exposure through homeostatic imbalance and synergistic activation of neutrophil N1 polarization signals. Thus, this study provides an alternative but promising strategy for the treatment of antibiotic-resistant biofilm infections.

Borosilicate bioactive glass synergizing low-dose antibiotic loaded implants to combat bacteria through ATP disruption and oxidative stress to sequentially achieve osseointegration

Bone infection is a catastrophe in clinical orthopedics. Despite being the standard therapy for osteomyelitis, antibiotic-loaded polymethyl methacrylate (PMMA) cement has low efficiency against bacteria in biofilms. Furthermore, high-dose antibiotic-loaded implants carry risks of bacterial resistance, tissue toxicity, and impairment of local tissue healing. By incorporating borosilicate bioactive glass (BSG) into low-dose gentamicin sulfate (GS)-loaded PMMA cement, an intelligent strategy that synergistically eradicates bacteria and sequentially promotes osseointegration, was devised. Results showed that BSG did not compromises the handling properties of the cement, but actually endowed it with an ionic and alkaline microenvironment, thereby damaging the integrity of bacterial cell walls and membranes, inhibiting ATP synthesis by disrupting the respiratory chain in cell membranes and glycogen metabolism, and elevating reactive oxygen species (ROS) levels by weakening antioxidant components (peroxisomes and carotenoids). These antibacterial characteristics of BSG synergistically reinforced the effectiveness of GS, which was far below the actual clinical dosage, achieving efficient bacterial killing and biofilm clearance by binding to the 30S subunit of ribosomes. Furthermore, the released GS and the ionic and alkaline microenvironment from the implants fostered the osteogenic activity of hBMSCs in vitro and coordinately enhanced osseointegration in vivo. Collectively, this study underscores that BSG incorporation offers a promising strategy for reducing antibiotic dosage while simultaneously enhancing the antibacterial activity and osteogenesis of implants. This approach holds potential for resolving the conflict between bacterial resistance and bone infection.

Resensitizing β-Lactams by Reprogramming Purine Metabolism in Small Colony Variant for Osteomyelitis Treatment

Small colony variant (SCV) is strongly linked to antibiotic resistance and the persistence of osteomyelitis. However, the intrinsic phenotypic instability of SCV has hindered a thorough investigation of its pathogenic mechanisms. In this study, phenotypically stable SCV strains are successfully recovered from clinical specimens, characterized by elevated drug resistance and reduced immunogenicity. Multi-omics analysis revealed that the acquired high drug resistance is associated with altered flux in the purine metabolism pathway, attributable to mutations in the hypoxanthine phosphoribosyltransferase (hpt) gene. Furthermore, this study innovatively discovered that lonidamine, an inhibitor of cellular energy metabolism, can effectively mitigate SCV resistance to β-lactam antibiotics, thereby facilitating its eradication. The underlying mechanism involves the reprogramming of purine metabolism. Therefore, a co-delivery system for lonidamine and oxacillin is constructed with amino-modified dendritic mesoporous silica as a carrier, which showed high efficacy and safety in combating SCV both in vitro and in vivo experiments. Overall, this study elucidated the pathogenic mechanisms of a class of clinically isolated SCV isolates with hpt mutations and provided a paradigm for treating SCV-associated osteomyelitis by reprogramming purine metabolism.

pH-responsive and nanoenzyme-loaded artificial nanocells relieved osteomyelitis efficiently by synergistic chemodynamic and cuproptosis therapy

Osteomyelitis is an osseous infectious disease that primarily affects children and the elderly with high morbidity and recurrence. The conventional treatments of osteomyelitis contain long-term and high-dose systemic antibiotics with debridements, which are not effective and lead to antibiotic resistance with serious side/adverse effects in many cases. Hence, developing novel antibiotic-free interventions against osteomyelitis (especially antibiotic-resistant bacterial infection) is urgent and anticipated. Here, a bone mesenchymal stem cell membrane-constructed nanocell (CFE@CM) was fabricated against osteomyelitis with the characteristics of acid-responsiveness, hydrogen peroxide self-supplying, enhanced chemodynamic therapeutic efficacy, bone marrow targeting and cuproptosis induction. Notably, mRNA sequencing was applied to unveil the underlying biological mechanisms and found that the biological processes related to copper ion binding, oxidative phosphorylation, peptide biosynthesis and metabolism, etc., were disturbed by CFE@CM in bacteria. This work provided an innovative antibiotic-free strategy against osteomyelitis through copper-enhanced Fenton reaction and distinct cuproptosis, promising to complement the current insufficient therapeutic regimen in clinic.

Could a Reduced Dose of 8 g of Continuous Infusion Fosfomycin Be Considered as Effective as and Safer than a Standard 16 g Dose When Combined with High-Dose Daptomycin in the Treatment of Staphylococcal osteoarticular Infections?

Background: Daptomycin plus fosfomycin combination therapy is a valuable strategy for treating staphylococcal osteoarticular infections (OIs), but hypernatremia and hypokalemia due to sodium overload are important issues. The aim of this study was to assess the likelihood of attaining a pharmacokinetic/pharmacodynamic (PK/PD) target of AUC/MIC > 66.6 and/or of 70%t > MIC with continuous infusion (CI) fosfomycin at the recommended vs. reduced dose in patients with OIs receiving combination therapy with high-dose daptomycin. Adverse events were also evaluated. Methods: Patients with OIs treated with 8-10 mg/kg daily daptomycin plus CI fosfomycin, and who had a ≥1 TDM assessment of CI fosfomycin, were retrospectively included in the high-dose (16 g daily) or reduced-dose (<16 g daily) groups. The attainment of the PK/PD targets of 70%t > MIC and AUC/MIC > 66.6 up to an MIC of 32 mg/L was calculated. A CART analysis was used to identify a cut-off of fosfomycin AUC that indicated occurrence of hypernatremia and/or hypokalemia. Results: A total of 44 and 39 patients were included in the high- and reduced-dose groups, respectively. The two groups did not differ in terms of demographic characteristics, underlying infectious diseases and microbiological isolates. No differences between groups in attaining both PK/PD targets up to an MIC of 32 mg/L and in C-reactive protein reduction at the end of treatment were observed. Fosfomycin AUC > 8245 mg × h/L and >8326 mg × h/L were associated with hypernatremia and hypokalemia, respectively. Conclusions: CI fosfomycin at 8 g daily may reach optimal PK/PD target attainment with better safety than the recommended 16 g daily dose in patients with preserved renal function. Targeting fosfomycin AUC at 2131-8326 mg × h/L or steady-state concentration at 88.8-347 mg/L may be adequate for optimizing drug pharmacodynamics up to an MIC of 32 mg/L and minimizing the risk of hypernatremia and hypokalemia.

Supramolecular discrimination and diagnosis-guided treatment of intracellular bacteria

Pathogenic intracellular bacteria pose a significant threat to global public health due to the barriers presented by host cells hindering the timely detection of hidden bacteria and the effective delivery of therapeutic agents. To address these challenges, we propose a tandem diagnosis-guided treatment paradigm. A supramolecular sensor array is developed for simple, rapid, accurate, and high-throughput identification of intracellular bacteria. This diagnostic approach executes the significant guiding missions of screening a customized host-guest drug delivery system by disclosing the rationale behind the discrimination. We design eight azocalix[4]arenes with differential active targeting, cellular internalization, and hypoxia responsiveness to penetrate cells and interact with bacteria. Loaded with fluorescent indicators, these azocalix[4]arenes form a sensor array capable of discriminating eight intracellular bacterial species without cell lysis or separation. By fingerprinting specimens collected from bacteria-infected mice, the facilitated accurate diagnosis offers valuable guidance for selecting appropriate antibiotics. Moreover, mannose-modified azocalix[4]arene (ManAC4A) is screened as a drug carrier efficiently taken up by macrophages. Doxycycline loaded with ManAC4A exhibits improved efficacy against methicillin-resistant Staphylococcus aureus-infected peritonitis. This study introduces an emerging paradigm to intracellular bacterial diagnosis and treatment, offering broad potential in combating bacterial infectious diseases.

Structural characteristics, functions, and counteracting strategies of biofilms in Staphylococcus aureus

Background

Staphylococcus aureus (S. aureus) is a prevalent pathogen associated with a wide range of infections, exhibiting significant antibiotic resistance and posing therapeutic challenges in clinical settings. The formation of biofilms contributes to the emergence of resistant strains, further diminishing the efficacy of antibiotics. This, in turn, leads to chronic and recurrent infections, ultimately increasing the healthcare burden. Consequently, preventing and eliminating biofilms has become a critical focus in clinical management and research.

Aim of review

This review systematically examines the mechanisms underlying biofilm formation in S. aureus and its contribution to antibiotic resistance, emphasizing the essential roles biofilms play in maintaining structural integrity and enhancing resistance. It also analyses the protective mechanisms that fortify S. aureus biofilms against antimicrobial treatments. Furthermore, the review provides a comprehensive overview of recent therapeutic innovations, including enzymatic therapy, nanotechnology, gene editing, and phage therapy.

Key scientific concepts of review

Emerging therapeutic strategies present novel approaches to combat S. aureus biofilm-associated infections through various mechanisms. This review discusses recent advancements in these therapies, their practical challenges in clinical application, and provides an in-depth analysis of each strategy's mechanisms and therapeutic potential. By mapping future research directions, this review aims to refine anti-biofilm strategies to control infection progression and effectively mitigate recurrence.

Stimuli-responsive and targeted nanomaterials: Revolutionizing the treatment of bacterial infections

Bacterial infections have emerged as a major threat to global public health. The effectiveness of traditional antibiotic treatments is waning due to the increasing prevalence of antimicrobial resistance, leading to an urgent demand for alternative antibacterial technologies. In this context, antibacterial nanomaterials have proven to be powerful tools for treating antibiotic-resistant and recurring infections. Targeting nanomaterials not only enable the precise delivery of bactericidal agents but also ensure controlled release at the infection site, thereby reducing potential systemic side effects. This review collates and categorizes nanomaterial-based responsive and precision-targeted antibacterial strategies into three key types: exogenous stimuli-responsive (including light, ultrasound, magnetism), bacterial microenvironment-responsive (such as pH, enzymes, hypoxia), and targeted antibacterial action (involving electrostatic interaction, covalent bonding, receptor-ligand mechanisms). Furthermore, we discuss recent advances, potential mechanisms, and future prospects in responsive and targeted antimicrobial nanomaterials, aiming to provide a comprehensive overview of the field's development and inspire the formulation of novel, precision-targeted antimicrobial strategies.

Development and validation of a prognostic nomogram model for severe osteomyelitis patients

After severe infection in osteomyelitis patients in the Intensive Care Unit (ICU), there's a higher risk of mortality. However, limited research exists on predicting prognosis. Develop a predictive model for 1-year mortality risk in ICU-admitted osteomyelitis patients to inform clinical diagnosis and treatment. MIMIC IV database was used to retrieve ICU data for osteomyelitis patients. The data were randomly split into training and validation sets (7:3 ratio). Univariate and multiple logistic regression identified independent predictors of one-year mortality and constructed a risk prediction nomogram in the training set. Predictive value of the nomogram was assessed using C-indexes, ROC curves, DCA, CIC and calibration curves. This study included a total of 1153 osteomyelitis patients, with 137 deaths within one year. These patients were randomly divided into training (N = 807) and validation (N = 346) sets. In the training set, multiple features were identified as key predictors of one-year mortality in osteomyelitis patients in the ICU. These factors were incorporated into the nomogram model, demonstrating good identification performance, with AUCs of 0.872 and 0.826 for the training and validation sets, respectively. The calibration curve and ROC curve indicate excellent predictive accuracy. DCA suggests strong clinical utility and robust predictive efficiency. Further analysis through CIC illustrates the clinical effectiveness of this predictive model. We have developed a nomogram model to predict the 1-year mortality rate for osteomyelitis patients admitted to the ICU, providing valuable predictive information for clinical decision-making.

Functional antimicrobial peptide-loaded 3D scaffolds for infected bone defect treatment with AI and multidimensional printing

Infection is the most prevalent complication of fractures, particularly in open fractures, and often leads to severe consequences. The emergence of bacterial resistance has significantly exacerbated the burden of infection in clinical practice, making infection control a significant treatment challenge for infectious bone defects. The implantation of a structural stent is necessary to treat large bone defects despite the increased risk of infection. Therefore, there is a need for the development of novel antibacterial therapies. The advancement in antibacterial biomaterials and new antimicrobial drugs offers fresh perspectives on antibacterial treatment. Although antimicrobial 3D scaffolds are currently under intense research focus, relying solely on material properties or antibiotic action remains insufficient. Antimicrobial peptides (AMPs) are one of the most promising new antibacterial therapy approaches. This review discusses the underlying mechanisms behind infectious bone defects and presents research findings on antimicrobial peptides, specifically emphasizing their mechanisms and optimization strategies. We also explore the potential prospects of utilizing antimicrobial peptides in treating infectious bone defects. Furthermore, we propose that artificial intelligence (AI) algorithms can be utilized for predicting the pharmacokinetic properties of AMPs, including absorption, distribution, metabolism, and excretion, and by combining information from genomics, proteomics, metabolomics, and clinical studies with computational models driven by machine learning algorithms, scientists can gain a comprehensive understanding of AMPs' mechanisms of action, therapeutic potential, and optimizing treatment strategies tailored to individual patients, and through interdisciplinary collaborations between computer scientists, biologists, and clinicians, the full potential of AI in accelerating the discovery and development of novel AMPs will be realized. Besides, with the continuous advancements in 3D/4D/5D/6D technology and its integration into bone scaffold materials, we anticipate remarkable progress in the field of regenerative medicine. This review summarizes relevant research on the optimal future for the treatment of infectious bone defects, provides guidance for future novel treatment strategies combining multi-dimensional printing with new antimicrobial agents, and provides a novel and effective solution to the current challenges in the field of bone regeneration.