Lysostaphin and BMP-2 co-delivery reduces S. aureus infection and regenerates critical-sized segmental bone defects

Injectable Hydrogel Technologies for Bone Disease Treatment

Injectable hydrogels represent a highly promising approach for localized drug delivery systems (DDSs) in the management of bone-related conditions such as osteoporosis, osteonecrosis, osteoarthritis, osteomyelitis, and osteosarcoma. Their appeal lies in their biocompatibility, adjustable mechanical properties, and capacity to respond to external stimuli, including pH, temperature, light, redox potential, ionic strength, and enzymatic activity. These features enable enhanced targeted delivery of bioactive agents. This mini-review evaluates the synthesis of injectable hydrogels as well as recent advancements for treating a range of bone disorders, focusing on their mechanisms as localized and sustained DDSs for delivering drugs, nanoparticles, growth factors, and cells (e.g., stem cells). Moreover, it highlights their clinical studies for bone disease treatment. Additionally, it emphasizes the potential synergy between injectable hydrogels and hydrogel-based point-of-care technologies, which are anticipated to play a pivotal role in the future of bone disease therapies. Injectable hydrogels have the potential to transform bone disease treatment by facilitating precise, sustained, and minimally invasive therapeutic delivery. Nevertheless, significant challenges, including long-term biocompatibility, scalability, reproducibility, and precise regulation of drug release kinetics, must be addressed to unlock their clinical potential fully. Addressing these challenges will not only advance bone disease therapy but also open new avenues in regenerative medicine and personalized healthcare.

Unconventional Therapies in Periprosthetic Joint Infections: Prevention and Treatment: A Narrative Review

BACKGROUND

as the demand for total joint arthroplasty continues to grow each year, the healthcare burden is expected to increase due to periprosthetic joint infection (PJI). This review article aims to highlight the significance of biofilms in the pathogenesis of PJI and introduce alternative therapies that prevent bacterial adhesion to implants or enhance their eradication when infection occurs.

SEARCH STRATEGY

we conducted a bibliographic search in PubMed using the following MeSH terms as follows: "no antibiotic treatment of PJI", "bacterial biofilm eradication agents", and "unconventional prevention of PJI", among others. Most important results: after an initial analysis of the literature, we selected the most significant topics on novel PJI treatment methods and prevention strategies. A second PubMed search highlighted the following therapeutic modalities: the application of hydrogels on implant surfaces, the use of phage therapy, lysostaphin and antimicrobial peptides, the implementation of two-stage debridement, irrigation, implant retention and antibiotic therapy (DAIR), the intra-articular antibiotic infusion, and the use of methylene blue for biofilm eradication.

CONCLUSIONS

the use of new cement spacers with xylitol, ammonium compounds, or silver nanoparticles is another promising technique to increase the eradication rate in two-stage revision. It is important for professionals to deeply understand the pathogenesis of PJI and the role of biofilms in its development in order to become familiar with these novel techniques that could reduce the burdens on healthcare systems.

Bioactive hydrogel formulations for regeneration of pathological bone defects

Bone defects caused by osteoporosis, infection, diabetes, post-tumor resection, and nonunion often cause severe pain and markedly increase morbidity and mortality, which remain a significant challenge for orthopedic surgeons. The precise local treatments for these pathological complications are essential to avoid poor or failed bone repair. Hydrogel formulations serve as injectable innovative platforms that overcome microenvironmental obstacles and as delivery systems for controlled release of various bioactive substances to bone defects in a targeted manner. Additionally, hydrogel formulations can be tailored for specific mechanical strengths and degradation profiles by adjusting their physical and chemical properties, which are crucial for prolonged drug retention and effective bone repair. This review summarizes recent advances in bioactive hydrogel formulations as three-dimensional scaffolds that support cell proliferation and differentiation. It also highlights their role as smart drug-delivery systems with capable of continuously releasing antibacterial agents, anti-inflammatory drugs, chemotherapeutic agents, and osteogenesis-related factors to enhance bone regeneration in pathological areas. Furthermore, the limitations of hydrogel formulations in pathological bone repair are discussed, and future development directions are proposed, which is expected to pave the way for the repair of pathological bone defects.

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.

Multifunctional hydrogel scaffolds based on polysaccharides and polymer matrices promote bone repair: A review

With the advancement of medical technology, the utilization of bioactive materials to promote bone repair has emerged as a significant research area. Hydrogels, as biomaterials, play a crucial role in bone tissue engineering. These hydrogels exhibit high biocompatibility, providing in vivo ecological conditions conducive to cell survival, and offer substantial advantages in facilitating bone repair. Different matrices of hydrogels serve distinct functions. In recent years, numerous researchers have developed a variety of novel hydrogel materials utilizing diverse matrices. These materials not only enhance the osteogenic induction capacity of hydrogels but also improve their efficacy as scaffolds in the treatment of complex bone defects, such as those resulting from trauma, tumor resection, or large bone defects due to infection. This article primarily analyzes the role of hydrogels that utilize polysaccharides and polymers as matrices in bone tissue repair, focusing on the creation of an optimal microenvironment to promote bone regeneration. These investigations deepen the understanding of the mechanisms underlying the action of hydrogels and establish a foundation for future advancements in the biomedical field.

Ultrasound-Controllable Release of Carbon Monoxide in Multifunctional Polymer Coating for Synergetic Treatment of Catheter-Related Infections

Medical catheters are susceptible to biological contamination and pathogen invasion, leading to infection and inflammatory complications. The development of antimicrobial coatings for medical devices has emerged as a promising strategy. However, limited biological functionality and the incompatibility between bactericidal properties and biosafety remain great challenges. Herein, a multifunctional polymer coating (CPB-Ac) is created, incorporating an ultrasonic-responsive carbon monoxide release unit (CORM-Ac) and antifouling unit to treat catheter-related complications. As-synthesized CPB-Ac polymer can be stably anchored to various medical devices with arbitrary shapes and compositions via facile UV treatment. Both in vivo and vitro experiments demonstrated that this multi-functional coating exhibits anti-fouling, anti-inflammatory, and broad-spectrum antibacterial activities as well as good biosafety. During the initial implantation phase, the antifouling units of CPB-Ac coating effectively inhibit the attachment of biological contaminants, significantly reducing the risk of thrombosis and bacterial infection. Once bacterial infection occurs, ultrasonic irradiation can activate CPB-Ac coating to release CO with a much higher amount of 55.3 µm than non-ultrasound controls, therefore rapidly eliminating bacteria and alleviating inflammatory response. It is believed that the work may provide an effective method for the development of next-generation intelligent medical coatings against catheter-related complications.

Dual release scaffolds as a promising strategy for enhancing bone regeneration: an updated review

Advancements in tissue regeneration, particularly bone regeneration is key area of research due to potential of novel therapeutic approaches. Efforts to reduce reliance on autologous and allogeneic bone grafts have led to the development of biomaterials that promote synchronized and controlled bone healing. However, the use of growth factors is limited by their short half-life, slow tissue penetration, large molecular size and potential toxicity. These factors suggest that traditional delivery methods may be inadequate hence, to address these challenges, new strategies are being explored. These novel approaches include the use of bioactive substances within advanced delivery systems that enable precise spatiotemporal control. Dual-release composite scaffolds offer a promising solution by reducing the need for multiple surgical interventions and simplifying the treatment process. These scaffolds allow for sustained and controlled drug release, enhancing bone repair while minimizing the drawbacks of conventional methods. This review explores various dual-drug release systems, discussing their modes of action, types of drugs used and release mechanisms to improve bone regeneration.

Antibiotic-eluting scaffolds with responsive dual-release kinetics facilitate bone healing and eliminate S. aureus infection

Osteomyelitis (OM) is a progressive, inflammatory infection of bone caused predominately by Staphylococcus aureus. Herein, we engineered an antibiotic-eluting collagen-hydroxyapatite scaffold capable of eliminating infection and facilitating bone healing. An iterative freeze-drying and chemical crosslinking approach was leveraged to modify antibiotic release kinetics, resulting in a layered dual-release system whereby an initial rapid release of antibiotic to clear infection was followed by a sustained controlled release to prevent reoccurrence of infection. We observed that the presence of microbial collagenase accelerated antibiotic release from the crosslinked layer of the scaffold, indicating that the material is responsive to microbial activity. As exemplar drugs, vancomycin and gentamicin-eluting scaffolds were demonstrated to be bactericidal, and supported osteogenesis in vitro. In a pilot murine model of OM, vancomycin-eluting scaffolds were observed to reduce S. aureus infection within the tibia. Finally, in a rabbit model of chronic OM, gentamicin-eluting scaffolds both facilitated radial bone defect healing and eliminated S. aureus infection. These results show that antibiotic-eluting collagen-hydroxyapatite scaffolds are a one-stage therapy for OM, which when implanted into infected bone defects simultaneously eradicate infection and facilitate bone tissue healing.

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.

Progress in Designing Therapeutic Antimicrobial Hydrogels Targeting Implant-associated Infections: Paving the Way for a Sustainable Platform Applied to Biomedical Devices

Implantable biomedical devices have found widespread use in restoring lost functions or structures within the human body, but they face a significant challenge from microbial-related infections, which often lead to implant failure. In this context, antimicrobial hydrogels emerge as a promising strategy for treating implant-associated infections owing to their tunable physicochemical properties. However, the literature lacks a comprehensive analysis of antimicrobial hydrogels, encompassing their development, mechanisms, and effect on implant-associated infections, mainly in light of existing in vitro, in vivo, and clinical evidence. Thus, this review addresses the strategies employed by existing studies to tailor hydrogel properties to meet the specific needs of each application. Furthermore, this comprehensive review critically appraises the development of antimicrobial hydrogels, with a particular focus on solving infections related to metallic orthopedic or dental implants. Then, preclinical and clinical studies centering on providing quantitative microbiological results associated with the application of antimicrobial hydrogels are systematically summarized. Overall, antimicrobial hydrogels benefit from the tunable properties of polymers and hold promise as an effective strategy for the local treatment of implant-associated infections. However, future clinical investigations, grounded on robust evidence from in vitro and preclinical studies, are required to explore and validate new antimicrobial hydrogels for clinical use.

Dual-Functional Implant Based on Gellan-Xanthan Hydrogel with Diopside, BMP-2 and Lysostaphin for Bone Defect Repair and Control of Staphylococcal Infection

A new dual-functional implant based on gellan-xanthan hydrogel with calcium-magnesium silicate ceramic diopside and recombinant lysostaphin and bone morphogenetic protein 2 (BMP-2)-ray is developed. In this composite, BMP-2 is immobilized on microparticles of diopside while lysostaphin is mixed directly into the hydrogel, providing sustained release of BMP-2 to allow gradual bone formation and rapid release of lysostaphin to eliminate infection immediately after implantation. Introduction of diopside of up to 3% (w/v) has a negligible effect on the mechanical properties of the hydrogel but provides a high sorption capacity for BMP-2. The hydrogels show good biocompatibility and antibacterial activity. Lysostaphin released from the implants over a 3 h period efficiently kills planktonic cells and completely destroys 24 h pre-formed biofilms of Staphylococcus aureus. Furthermore, in vivo experiments in a mouse model of critically-sized cranial defects infected with S. aureus show a complete lack of osteogenesis when implants contain only BMP-2, whereas, in the presence of lysostaphin, complete closure of the defect with newly formed mineralized bone tissue is observed. Thus, the new implantable gellan-xanthan hydrogel with diopside and recombinant lysostaphin and BMP-2 shows both osteogenic and antibacterial properties and represents a promising material for the treatment and/or prevention of osteomyelitis after bone trauma.

A multifunctional self-reinforced injectable hydrogel for enhancing repair of infected bone defects by simultaneously targeting macrophages, bacteria, and bone marrow stromal cells

Injectable hydrogels (IHs) have demonstrated huge potential in promoting repair of infected bone defects (IBDs), but how to endow them with desired anti-bacterial, immunoregulatory, and osteo-inductive properties as well as avoid mechanical failure during their manipulation are challenging. In this regard, we developed a multifunctional AOHA-RA/Lap nanocomposite IH for IBDs repair, which was constructed mainly through two kinds of reversible cross-links: (i) the laponite (Lap) crystals mediated electrostatic interactions; (ii) the phenylboronic acid easter bonds between the 4-aminobenzeneboronic acid grafted oxidized hyaluronic acid (AOHA) and rosmarinic acid (RA). Due to the specific structural composition, the AOHA-RA/Lap IH demonstrated superior injectability, self-recoverability, spatial adaptation, and self-reinforced mechanical properties after being injected to the bone defect site. In addition, the RA molecules could be locally released from the hydrogel following a Weibull model for over 10 days. Systematic in vitro/vivo assays proved the strong anti-bacterial activity of the hydrogel against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Moreover, its capability of inducing M2 polarization of macrophages (Mφ) and osteogenic differentiation of bone marrow stromal cells (BMSCs) was verified either, and the mechanism of the former was identified to be related to the JAK1-STAT1 and PI3K-AKT signaling pathways and that of the latter was identified to be related to the calcium signaling pathway, extracellular matrix (ECM) receptor interaction and TGF-β signaling pathway. After being implanted to a S. aureus infected rat skull defect model, the AOHA-RA/Lap IH significantly accelerated repair of IBDs without causing significant systemic toxicity. STATEMENT OF SIGNIFICANCE: Rosmarinic acid and laponite were utilized to develop an injectable hydrogel, promising for accelerating repair of infected bone defects in clinic. The gelation of the hydrogel was completely driven by two kinds of reversible cross-links, which endow the hydrogel superior spatial adaption, self-recoverability, and structural stability. The as-prepared hydrogel demonstrated superior anti-bacterial/anti-biofilm activity and could induce M2 polarization of macrophages and osteogenic differentiation of BMSCs. The mechanism behind macrophages polarization was identified to be related to the JAK1-STAT1 and PI3K-AKT signaling pathways. The mechanism behind osteogenic differentiation of BMSCs was identified to be related to the ECM receptor interaction and calcium signaling/TGF-β signaling pathways.

Exploring the potential of naturally occurring antimicrobials for managing orthopedic-device-related infections

Orthopedic-device-related infections (ODRIs) are challenging clinical complications that are often exacerbated by antibiotic resistance and biofilm formation. This review explores the efficacy of naturally occurring antimicrobials - including agents sourced from bacteria, fungi, viruses, animals, plants and minerals - against pathogens common in ODRIs. The limitations of traditional antibiotic agents are presented, and innovative naturally occurring antimicrobials, such as bacteriophage therapy and antimicrobial peptides, are evaluated with respect to their interaction with conventional antibiotics and antibiofilm efficacy. The integration of these natural agents into clinical practice could revolutionize ODRI treatment strategies, offering effective alternatives to conventional antibiotics and mitigating resistance development. However, the translation of these compounds from research into the clinic may require the substantial investment of intellectual and financial resources.

A review on the promising antibacterial agents in bone cement-From past to current insights

Antibacterial bone cements (ABCs), such as antibiotic-loaded bone cements (ALBCs), have been widely utilized in clinical treatments. Currently, bone cements loaded with vancomycin, gentamicin, tobramycin, or clindamycin are approved by the US Food and Drug Administration. However, traditional ALBCs exhibit drawbacks like burst release and bacterial resistance. Therefore, there is a demand for the development of antibacterial bone cements containing novel agents to address these defects. In this review, we provide an overview and prospect of the new antibacterial agents that can be used or have the potential to be applied in bone cement, including metallic antibacterial agents, pH-switchable antibacterial agents, cationic polymers, N-halamines, non-leaching acrylic monomers, antimicrobial peptides and enzymes. Additionally, we have conducted a preliminary assessment of the feasibility of bone cement containing N-halamine, which has demonstrated good antibacterial activities. The conclusion of this review is that the research and utilization of bone cement containing novel antibacterial agents contribute to addressing the limitations of ALBCs. Therefore, it is necessary to continue expanding the research and use of bone cement incorporating novel antibacterial agents. This review offers a novel perspectives for designing ABCs and treating bone infections.

Storage stability of lysostaphin solution and its pulmonary delivery

Methicillin-resistant Staphylococcus aureus (MRSA) has become a leading causative pathogen of nosocomial pneumonia with an alarming in-hospital mortality rate of 30%. Last resort antibiotic, vancomycin, has been increasingly used to treat MRSA infections, but the rapid emergence of vancomycin-resistant strains urges the development of alternative treatment strategies against MRSA-associated pneumonia. The bacteriolytic enzyme, lysostaphin, targeting the cell wall peptidoglycan of S. aureus, has been considered as a promising alternative for MRSA infections. Its proteinaceous nature is likely benefit from direct delivery to the lungs, but the challenges for successful pulmonary delivery of lysostaphin lying on a suitable inhalation device and a formulation with sufficient storage stability. In this study, the applicability of a vibrating mesh nebulizer (Aerogen Solo®) and a soft mist inhaler (Respimat®) was investigated. Both devices were capable of aerosolizing lysostaphin solution into inhalable droplets and caused minimum antibacterial activity loss. In addition, lysostaphin stabilized with phosphate-buffered saline and 0.1% Tween 80 was proved to have acceptable stability for at least 12 months when stored at 4 °C. These promising data encourage further clinical development of lysostaphin for management of MRSA-associated lung infections.

Bioinspired Hybrid Nanostructured PEEK Implant with Enhanced Antibacterial and Anti-inflammatory Synergy

Implant-associated infections and excessive immune responses are two major postsurgical issues for successful implantation. However, conventional strategies including antibiotic treatment and inflammatory regulation are always compromised due to the comodification of various biochemical agents and instances of functional interference. It is imperative to provide implant surfaces with satisfactory antibacterial and anti-inflammatory properties. Here, a dual-effect nanostructured polyetheretherketone (PEEK) surface (NP@PDA/Zn) with bionic mechano-bactericidal nanopillars and immobilized immunomodulatory Zn2+ is designed. The constructed hybrid nanopillars display remarkable antibacterial performance against Gram-negative and Gram-positive strains through the synergy of physical and chemical bactericidal effects imposed by nanopillars and Zn2+. Meanwhile, the immunoregulatory property is evaluated through the investigation of macrophage polarization both in vitro and in vivo, and the results reveal that NP@PDA/Zn could downregulate the expression of M1-related cytokines and decrease the M1 macrophage recruitment to lower the inflammatory response. Notably, the surface exhibited exceptional biocompatibility with discerning biocidal activity between bacterial and mammalian cells and antioxidant performance that effectively scavenges ROS, minimizing potential cytotoxicity. Taken together, NP@PDA/Zn presents a convenient and promising strategy of combining synergistic bactericidal activity and inflammatory regulation without any mutual interference, which can support the development of multifunctional implant-associated materials.

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

PLGA nanoparticle-encapsulated lysostaphin for the treatment of Staphylococcus aureus infections

Staphylococcus aureus possesses the ability to become pathogenic, leading to severe and life-threatening infections. Its methicillin-resistant variant MRSA has garnered high-priority status due to its increased morbidity and associated mortality. This emphasizes the urgency for novel anti-staphylococcal agents. The bacteriocin lysostaphin stands out for its remarkable bactericidal activity against S. aureus, including MRSA, outperforming conventional antibiotics. However, the clinical application of lysostaphin faces challenges, including enzymatic activity loss under physiological conditions and potential immunogenicity. This study introduces a novel approach by encapsulating lysostaphin within polylactic-co-glycolic acid (PLGA) nanoparticles, a biodegradable copolymer known for its biocompatibility and sustained drug release ability. The study assesses the antimicrobial activity of lysostaphin-loaded PLGA nanoparticles against different S. aureus strains, and we also used GFP-expressing S. aureus for facilitating its traceability in planktonic, biofilm, and intracellular infection models. The results showed the significant reduction in bacteria viability both in planktonic and biofilm states. The in vitro intracellular infection model demonstrated the significantly enhanced efficiency of the developed nanoparticles compared to the treatment with the free bacteriocin. This research presents lysostaphin encapsulation within PLGA nanoparticles and offers promising avenues for enhancing lysostaphin's therapeutic efficacy against S. aureus infections.

Efficacy of lysostaphin-coated titanium plates on implant-associated MRSA osteitis in minipigs

PURPOSE

The growing incidence of implant-associated infections (IAIs) caused by biofilm-forming Staphylococcus aureus in combination with an increasing resistance to antibiotics requires new therapeutic strategies. Lysostaphin has been shown to eliminate this biofilm. Own studies confirm the effectiveness in a murine model. The current study characterizes the effects of lysostaphin-coated plates in an IAI minipig model.

METHODS

The femur of 30 minipigs was stabilized with a five-hole plate, a bone defect was created, and in 20 cases methicillin-resistant Staphylococcus aureus was applied. Ten animals served as control group. After 14 days, local debridement, lavage, and plate exchange (seven-hole plate) were performed. Ten of the infected minipigs received an uncoated plate and 10 a lysostaphin-coated plate. On day 84, the minipigs were again lavaged, followed by euthanasia. Bacterial load was quantified by colony-forming units (CFU). Immunological response was determined by neutrophils, as well as interleukins. Fracture healing was assessed radiologically.

RESULTS

CFU showed significant difference between infected minipigs with an uncoated plate and minipigs with a lysostaphin-coated plate (p = 0.0411). The infection-related excessive callus formation and calcification was significantly greater in the infected animals with an uncoated plate than in animals with a lysostaphin-coated plate (p = 0.0164/p = 0.0033). The analysis of polymorphonuclear neutrophils and interleukins did not reveal any pioneering findings.

CONCLUSION

This study confirms the minipig model for examining IAI. Furthermore, coating of plates using lysostaphin could be a promising tool in the therapeutic strategies of IAI. Future studies should focus on coating technology of implants and on translation into a clinical model.

Hydrogels in Gene Delivery Techniques for Regenerative Medicine and Tissue Engineering

Hydrogels are 3D networks swollen with water. They are biocompatible, strong, and moldable and are emerging as a promising biomedical material for regenerative medicine and tissue engineering to deliver therapeutic genes. The excellent natural extracellular matrix simulation properties of hydrogels enable them to be co-cultured with cells or enhance the expression of viral or non-viral vectors. Its biocompatibility, high strength, and degradation performance also make the action process of carriers in tissues more ideal, making it an ideal biomedical material. It has been shown that hydrogel-based gene delivery technologies have the potential to play therapy-relevant roles in organs such as bone, cartilage, nerve, skin, reproductive organs, and liver in animal experiments and preclinical trials. This paper reviews recent articles on hydrogels in gene delivery and explains the manufacture, applications, developmental timeline, limitations, and future directions of hydrogel-based gene delivery techniques.

Electrochemical technique to develop surface-controlled polyaniline nano-tulips (PANINTs) on PCL-reinforced chitosan functionalized (CS-f-Fe2O3) scaffolds for stimulating osteoporotic bone regeneration

Bone defects pose significant challenges in orthopedic surgery, often leading to suboptimal outcomes and complications. Addressing these challenges, we employed a three-electrode electrochemical system to fabricate surface-controlled polyaniline nano-tulips (PANINTs) decorated polycaprolactone (PCL) reinforced chitosan functionalized iron oxide nanoparticles (CS-f-Fe2O3) scaffolds. These structures were designed to emulate the natural extracellular matrix (ECM) and promote enhanced osseointegration by establishing a continuous interface between host bone and graft, thereby improving both biological processes and mechanical stability. In vitro experiments demonstrated that PANINTs-PCL/CS-f-Fe2O3 substrates significantly promoted the proliferation, differentiation, and spontaneous outgrowth and extension of MC3T3-E1 cell activity. The nanomaterials exhibited increased cell viability and osteogenic differentiation, as evidenced by elevated expression of bone-related markers such as ALP, ARS, COL-I, RUNX2, and SPP-I, as determined by qRT-PCR. Our findings underscore the regenerative potential of in situ cell culture systems for bone defects, emphasizing the targeted stimulation of essential cell subpopulations to facilitate rapid bone tissue regeneration.

An osteoinductive surface by adhesive bone morphogenetic protein-2 prepared using the bioorthogonal approach for tight binding of titanium with bone

Inorganic biomaterials are used in various orthopedic and dental implants. Nevertheless, they cause clinical issues such as loosening of implants and patient morbidity. Therefore, inspired by mussel adhesive proteins, we aimed to design an adhesive and dimer-forming highly active bone morphogenetic protein-2 (BMP-2) using bioorthogonal chemistry, in which recombinant DNA technology was combined with enzymatic modifications, to achieve long-term osseointegration with titanium. The prepared BMP-2 exhibited substantially higher binding activity than wild-type BMP-2, while the adhered BMP-2 was more active than soluble BMP-2. Therefore, the adhesive BMP-2 was immobilized onto titanium wires and screws and implanted into rat bones, and long-term osteogenesis was evaluated. Adhesive BMP-2 promoted the mechanical binding of titanium to bones, enabling efficient bone regeneration and effective stabilization of implants. Thus, such adhesive biosignaling proteins can be used in regenerative medicine.

Injective Programmable Proanthocyanidin-Coordinated Zinc-Based Composite Hydrogel for Infected Bone Repair

Effectively integrating infection control and osteogenesis to promote infected bone repair is challenging. Herein, injective programmable proanthocyanidin (PC)-coordinated zinc-based composite hydrogels (ipPZCHs) are developed by compositing antimicrobial and antioxidant PC-coordinated zinc oxide (ZnO) microspheres with thioether-grafted sodium alginate (TSA), followed by calcium chloride (CaCl2 ) crosslinking. Responsive to the high endogenous reactive oxygen species (ROS) microenvironment in infected bone defects, the hydrophilicity of TSA can be significantly improved, to trigger the disintegration of ipPZCHs and the fast release of PC-coordinated ZnOs. This together with the easily dissociable PC-Zn2+ coordination induced fast release of antimicrobial zinc (Zn2+ ) with/without silver (Ag+ ) ions from PC-coordinated ZnOs (for Zn2+ , > 100 times that of pure ZnO) guarantees the strong antimicrobial activity of ipPZCHs. The exogenous ROS generated by ZnO and silver nanoparticles during the antimicrobial process further speeds up the disintegration of ipPZCHs, augmenting the antimicrobial efficacy. At the same time, ROS-responsive degradation/disintegration of ipPZCHs vacates space for bone ingrowth. The concurrently released strong antioxidant PC scavenges excess ROS thus enhances the immunomodulatory (in promoting the anti-inflammatory phenotype (M2) polarization of macrophages) and osteoinductive properties of Zn2+ , thus the infected bone repair is effectively promoted via the aforementioned programmable and self-adaptive processes.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

Toward Clinical Applications: Transforming Nonantibiotic Antibacterials into Effective Next-Generation Supramolecular Therapeutics

Antibiotic resistance is a major driver of morbidity and mortality worldwide, necessitating alternatives. Due to their mechanism of action, bacteriophages, endolysins, and antimicrobial peptides (coined herein as nonantibiotic antibacterials, NAA) have risen to tackle this problem and led to paradigms in treating antibiotic-resistant bacterial infections. However, their clinical applications remain challenging and have been seriously hampered by cytotoxicity, instability, weak bioactivity, low on-target bioavailability, high pro-inflammatory responses, shorter half-life, and circulatory properties. Hence, to transit preclinical phases and beyond, it has become imperative to radically engineer these alternatives into innovative and revolutionary therapeutics to overcome recalcitrant infections. This perspective highlights the promise of these agents, their limitations, promising designs, nanotechnology, and delivery approaches that can be harnessed to transform these agents. Finally, I provide an outlook on the remaining challenges that need to be tackled for their widespread clinical administration.

An injectable carboxymethyl chitosan hydrogel scaffold formed via coordination bond for antibacterial and osteogenesis in osteomyelitis

The intricate, hostile, and diverse nature of osteomyelitis (OM) poses a challenge for complete bacterial eradication and osteogenesis promotion via conventional treatment. Recently, functional hydrogels exhibiting antibacterial and osteogenic properties emerge as a promising avenue for OM wound healing in clinical practice. However, the preparation procedures and associated costs on cytokine and cell therapies for certain functional hydrogels can be complex and prohibitively expensive. In our research, a hybrid hydrogel dressing has been formulated utilizing carboxymethyl chitosan (CMCS) as the base material, and designed with inherent antibacterial, adhesion, proliferation, and differentiation characteristics, showing promise as a candidate for eradicating infection and promoting bone regeneration. The hybrid hydrogel is composed of interconnected networks of Fe3+-induced self-assembled CMCS and the antibacterial drug ciprofloxacin (CIP), resulting in excellent injectability and moldability. Notably, the CMCS/Fe3+/CIP hybrid hydrogel is capable of regulating antibacterial responses and stimulating osteogenesis in infected microenvironments without additional additives. This injectable antibacterial and osteogenic-promoting hydrogel establish a high-potential platform for low-cost, safe and effective treatment of OM by expediting the initial stages of infected bone wound repair.

Designing Hydrogels for Immunomodulation in Cancer Therapy and Regenerative Medicine

The immune system not only acts as a defense against pathogen and cancer cells, but also plays an important role in homeostasis and tissue regeneration. Targeting immune systems is a promising strategy for efficient cancer treatment and regenerative medicine. Current systemic immunomodulation therapies are usually associated with low persistence time, poor targeting to action sites, and severe side effects. Due to their extracellular matrix-mimetic nature, tunable properties and diverse bioactivities, hydrogels are intriguing platforms to locally deliver immunomodulatory agents and cells, as well as provide an immunomodulatory microenvironment to recruit, activate, and expand host immune cells. In this review, the design considerations, including polymer backbones, crosslinking mechanisms, physicochemical nature, and immunomodulation-related components, of the hydrogel platforms, are focused on. The immunomodulatory effects and therapeutic outcomes in cancer therapy and tissue regeneration of different hydrogel systems are emphasized, including hydrogel depots for delivery of immunomodulatory agents, hydrogel scaffolds for cell delivery, and immunomodulatory hydrogels depending on the intrinsic properties of materials. Finally, the remained challenges in current systems and future development of immunomodulatory hydrogels are discussed.

Hematoma-like dynamic hydrogelation through natural glycopeptide molecular recognition for infected bone fracture repair

Infected bone fractures remain a major clinical challenge for orthopedic surgeons. From a tissue regeneration perspective, biomaterial scaffolds with antibacterial and osteoinductive activities are highly desired, while advanced materials capable of mimicking the pathological microenvironment during the healing process of infected tissues remain an area deserving more research. Hematoma, the gel-like blood coagulum, plays an essential role in bone fracture repair because of its ability to serve as a dynamic and temporary scaffold with cytokines for both pathogen elimination and tissue healing. In light of this, we designed a dynamic hydrogel with hematoma-like antimicrobial or reparative performance for infected bone fracture repair in this study. The proposed dynamic hydrogel network was based on the reversible recognition of a natural glycopeptide antibiotic vancomycin (Van) and its target dipeptide D-Ala-D-Ala (AA), which could serve as a hematoma-like scaffold for obliterating bacteria in the fracture region and promoting bone repair by introducing an endogenous osteogenic peptide (OGP). In vivo experiments demonstrated that the hydrogel could rapidly eradicate bacteria, improve bone regeneration and restore the local inflammatory microenvironment. Together, findings from this study imply that the use of hematoma-like dynamic hydrogel could lead to a biomimetic revolution in surgical strategies against susceptible bone fractures.

Parathyroid hormone therapy improves MRSA-infected fracture healing in a murine diabetic model

Introduction

Diabetes mellitus (DM) impairs fracture healing and is associated with susceptibility to infection, which further inhibits fracture healing. While intermittent parathyroid hormone (1-34) (iPTH) effectively improves fracture healing, it is unknown whether infection-associated impaired fracture healing can be rescued with PTH (teriparatide).

Methods

A chronic diet-induced type 2 diabetic mouse model was used to yield mice with decreased glucose tolerance and increased blood glucose levels compared to lean-fed controls. Methicillin-resistant Staphylococcus aureus (MRSA) was inoculated in a surgical tibia fracture model to simulate infected fracture, after which mice were treated with a combination of antibiotics and adjunctive teriparatide treatment. Fracture healing was assessed by Radiographic Union Scale in Tibial Fractures (RUST), micro-computed tomography (μCT), biomechanical testing, and histology.

Results

RUST score was significantly poorer in diabetic mice compared to their lean nondiabetic counterparts. There were concomitant reductions in micro-computed tomography (μCT) parameters of callus architecture including bone volume/total volume, trabecular thickness, and total mineral density in type 2 diabetes mellitus (T2DM) mice. Biomechanicaltesting of fractured femora demonstrated diminished torsional rigidity, stiffness, and toughness to max torque. Adjuvant teriparatide treatment with systemic antibiotic therapy improved numerous parameters of bone microarchitecture bone volume, increased connectivity density, and increased trabecular number in both the lean and T2DM group. Despite the observation that poor fracture healing in T2DM mice was further impaired by MRSA infection, adjuvant iPTH treatment significantly improved fracture healing compared to antibiotic treatment alone in infected T2DM fractures.

Discussion

Our results suggest that teriparatide may constitute a viable adjuvant therapeutic agent to improve bony union and bone microarchitecture to prevent the development of septic nonunion under diabetic conditions.

Conserved loop residues-Tyr270 and Asn372 near the catalytic site of the lysostaphin endopeptidase are essential for staphylolytic activity toward pentaglycine binding and catalysis

Lysostaphin endopeptidase cleaves pentaglycine cross-bridges found in staphylococcal cell-wall peptidoglycans and proves very effective in combatting methicillin-resistant Staphylococcus aureus. Here, we revealed the functional importance of two loop residues, Tyr270 in loop 1 and Asn372 in loop 4, which are highly conserved among the M23 endopeptidase family and are found close to the Zn2+-coordinating active site. Detailed analyses of the binding groove architecture together with protein-ligand docking showed that these two loop residues potentially interact with the docked ligand-pentaglycine. Ala-substituted mutants (Y270A and N372A) were generated and over-expressed in Escherichia coli as a soluble form at levels comparable to the wild type. A drastic decrease in staphylolytic activity against S. aureus was observed for both mutants, suggesting an essential role of the two loop residues in lysostaphin function. Further substitutions with an uncharged polar Gln side-chain revealed that only the Y270Q mutation caused a dramatic reduction in bioactivity. In silico predicting the effect of binding site mutations revealed that all mutations displayed a large ΔΔGbind value, signifying requirements of the two loop residues for efficient binding to pentaglycine. Additionally, MD simulations revealed that Y270A and Y270Q mutations induced large flexibility of the loop 1 region, showing markedly increased RMSF values. Further structural analysis suggested that Tyr270 conceivably participated in the oxyanion stabilization of the enzyme catalysis. Altogether, our present study disclosed that two highly conserved loop residues, loop 1-Tyr270 and loop 4-Asn372, located near the lysostaphin active site are crucially involved in staphylolytic activity toward binding and catalysis of pentaglycine cross-links.

Zinc-Based Tannin-Modified Composite Microparticulate Scaffolds with Balanced Antimicrobial Activity and Osteogenesis for Infected Bone Defect Repair

Treatment of infected bone defects is a major clinical challenge; bioactive materials combining sufficient antimicrobial activity and favorable osteogenic ability are urgently needed. In this study, through a facile one-pot hydrothermal reaction of zinc acetate in the presence of tannic acid (TA), with or without silver nitrate (AgNO3 ), is used to synthesize a TA or TA and silver nanoparticles (Ag NPs) bulk-modified zinc oxide (ZnO) (ZnO-TA or ZnO-TA-Ag), which is further composited with zein to fabricate porous microparticulate scaffolds for infected bone defect repair. Bulk TA modification significantly improves the release rate of antibacterial metal ions (Zn2+ release rate is >100 times that of ZnO). Fast and long-lasting (>35 d) Zn2+ and Ag+ release guaranteed sufficient antibacterial capability and excellent osteogenic properties in promoting the osteogenic differentiation of bone marrow mesenchymal stem cells and endogenous citric acid production and mineralization and providing considerable immunomodulatory activity in promoting M2 polarization of macrophages. At the same time, synchronously-released TA could scavenge endogenous reactive oxygen species (ROS) and ROS produced by antibacterial metal ions, effectively balancing antibacterial activity and osteogenesis to sufficiently control infection while protecting the surrounding tissue from damage, thus effectively promoting infected bone defect repair.

Enhanced bone regeneration via local low-dose delivery of PTH1-34 in a composite hydrogel

Introducing bone regeneration-promoting factors into scaffold materials to improve the bone induction property is crucial in the fields of bone tissue engineering and regenerative medicine. This study aimed to develop a Sr-HA/PTH_1-34-loaded composite hydrogel system with high biocompatibility. Teriparatide (PTH_1-34) capable of promoting bone regeneration was selected as the bioactive factor. Strontium-substituted hydroxyapatite (Sr-HA) was introduced into the system to absorb PTH_1-34 to promote the bioactivity and delay the release cycle. PTH_1-34-loaded Sr-HA was then mixed with the precursor solution of the hydrogel to prepare the composite hydrogel as bone-repairing material with good biocompatibility and high mechanical strength. The experiments showed that Sr-HA absorbed PTH_1-34 and achieved the slow and effective release of PTH_1-34. In vitro biological experiments showed that the Sr-HA/PTH_1-34-loaded hydrogel system had high biocompatibility, allowing the good growth of cells on the surface. The measurement of alkaline phosphatase activity and osteogenesis gene expression demonstrated that this composite system could promote the differentiation of MC3T3-E1 cells into osteoblasts. In addition, the in vivo cranial bone defect repair experiment confirmed that this composite hydrogel could promote the regeneration of new bones. In summary, Sr-HA/PTH_1-34 composite hydrogel is a highly promising bone repair material.

Poly Ethylene Glycol (PEG)-Based Hydrogels for Drug Delivery in Cancer Therapy: A Comprehensive Review

Hydrogel-based drug delivery systems (DDSs) can leverage therapeutically beneficial outcomes in cancer therapy. In this domain, polyethylene glycol (PEG) has become increasingly popular as a biomedical polymer and has found clinical use. Owing to their excellent biocompatibility, facile modifiability, and high drug encapsulation rate, PEG hydrogels have shown great promise as drug delivery platforms. Here, the progress in emerging novel designs of PEG-hydrogels as DDSs for anti-cancer therapy is reviewed and discussed, focusing on underpinning multiscale release mechanisms categorized under stimuli-responsive and non-responsive drug release. The responsive drug delivery approaches are discussed, and the underpinning release mechanisms are elucidated, covering the systems functioning based on either exogenous stimuli-response, such as photo- and magnetic-sensitive PEG hydrogels, or endogenous stimuli-response, such as enzyme-, pH-, reduction-, and temperature-sensitive PEG hydrogels. Special attention is paid to the commercial potential of PEG-based hydrogels in cancer therapy, highlighting the limitations that need to be addressed in future research for their clinical translation.

Detrimental alteration of mesenchymal stem cells by an articular inflammatory microenvironment results in deterioration of osteoarthritis

BACKGROUND

Articular injection of mesenchymal stem cells (MSCs) has been applied to treat knee osteoarthritis (kOA), but its clinical outcomes are controversial. This study investigated whether an articular inflammatory microenvironment (AIM) impacts MSC-based therapy in a rat model of kOA.

METHODS

The biological change of MSCs and the functional change of MSCs on chondrocytes were evaluated under AIM. The key mediator and mechanism for the AIM impact on MSC therapy were explored via gain- and loss-of-function approaches.

RESULTS

The results showed that MSCs exerted potent anti-kOA effects in vivo and in vitro, but that this therapy become chondrodestructive if a chronic AIM was present. Mechanistically, the overexpression of MMP13 in the injected MSCs via a MAPKs-AP1 signaling axis was revealed as the underlying mechanism for the detriment outcome.

CONCLUSIONS

This study thus clarifies recent clinical findings while also suggesting a means to overcome any detrimental effects of MSC-based therapy while improving its efficacy.

Transformation of arginine into zero-dimensional nanomaterial endows the material with antibacterial and osteoinductive activity

Implant-associated infection is a major threat affecting the success of orthopedic surgeries. Although various materials scavenge bacteria by generating reactive oxygen species (ROS), the intrinsic inability of ROS to distinguish bacteria from cells notably limits the therapeutic effects. Here, we found that the arginine carbon dots (Arg-CDs) that were transformed from arginine exhibited supreme antibacterial and osteoinductive activity. We further designed the Schiff base bond between Arg-CDs and aldehyde hyaluronic acid/gelatin methacryloyl (HG) hydrogel to release Arg-CDs in response to the acidic bone injury microenvironment. The free Arg-CDs could selectively kill bacteria by generating excessive ROS. Furthermore, the Arg-CD-loaded HG composite hydrogel showed excellent osteoinductive activity through inducing the M2 polarization of macrophages by up-regulating interleukin-10 (Il10) expression. Together, our findings revealed that transformation of the arginine into zero-dimensional Arg-CDs could endow the material with exceptional antibacterial and osteoinductive activity, favoring the regeneration of infectious bone.

Flourishing Antibacterial Strategies for Osteomyelitis Therapy

Osteomyelitis is a destructive disease of bone tissue caused by infection with pathogenic microorganisms. Because of the complex and long-term abnormal conditions, osteomyelitis is one of the refractory diseases in orthopedics. Currently, anti-infective therapy is the primary modality for osteomyelitis therapy in addition to thorough surgical debridement. However, bacterial resistance has gradually reduced the benefits of traditional antibiotics, and the development of advanced antibacterial agents has received growing attention. This review introduces the main targets of antibacterial agents for treating osteomyelitis, including bacterial cell wall, cell membrane, intracellular macromolecules, and bacterial energy metabolism, focuses on their mechanisms, and predicts prospects for clinical applications.

Drug delivery systems based on polyethylene glycol hydrogels for enhanced bone regeneration

Drug delivery systems composed of osteogenic substances and biological materials are of great significance in enhancing bone regeneration, and appropriate biological carriers are the cornerstone for their construction. Polyethylene glycol (PEG) is favored in bone tissue engineering due to its good biocompatibility and hydrophilicity. When combined with other substances, the physicochemical properties of PEG-based hydrogels fully meet the requirements of drug delivery carriers. Therefore, this paper reviews the application of PEG-based hydrogels in the treatment of bone defects. The advantages and disadvantages of PEG as a carrier are analyzed, and various modification methods of PEG hydrogels are summarized. On this basis, the application of PEG-based hydrogel drug delivery systems in promoting bone regeneration in recent years is summarized. Finally, the shortcomings and future developments of PEG-based hydrogel drug delivery systems are discussed. This review provides a theoretical basis and fabrication strategy for the application of PEG-based composite drug delivery systems in local bone defects.

Antibacterial and Anti-Biofilm Properties of Diopside Powder Loaded with Lysostaphin

BACKGROUND

Diopside-based ceramic is a perspective biocompatible material with numerous potential applications in the field of bone prosthetics. Implantable devices and materials are often prone to colonization and biofilm formation by pathogens such as Staphylococcus aureus, which in the case of bone grafting leads to osteomyelitis, an infectious bone and bone marrow injury. To lower the risk of bacterial colonization, implanted materials can be impregnated with antimicrobials. In this work, we loaded the antibacterial enzyme lysostaphin on diopside powder and studied the antibacterial and antibiofilm properties of such material to probe the utility of this approach for diopside-based prosthetic materials.

METHODS

Diopside powder was synthesized by the solid-state method, lysostaphin was loaded on diopside by adsorption, the release of lysostaphin from diopside was monitored by ELISA, and antibacterial and anti-biofilm activity was assessed by standard microbiological procedures.

RESULTS AND CONCLUSIONS

Lysostaphin released from diopside powder showed high antibacterial activity against planktonic bacteria and effectively destroyed 24-h staphylococcal biofilms. Diopside-based materials possess a potential for the development of antibacterial bone grafting materials.

Injectable polylysine and dextran hydrogels with robust antibacterial and ROS-scavenging activity for wound healing

Cutaneous wound management remains a major concern due to uncontrolled inflammation and bacterial infection in clinical care. A desirable hydrogel dressing with antibacterial and antioxidative properties can drive wound healing by inhibiting infection and inflammation. Herein, a multifunctional hydrogel based on polylysine-graft-cysteine (EPL-SH)/oxidized dextran (ODex) was fabricated for promoting skin tissue regeneration. The engineered hydrogel possessed versatile properties including tunable gelation time (60-300 s), typical rheological behavior, suitable swelling and degradation progress, injectable and self-healing ability. The unique hydrogels also displayed promising tissue adhesiveness, high cell affinity, excellent antioxidant and antimicrobial activity. Furthermore, the in vivo full-thickness skin defect experiment demonstrated the simple-to-implement injectable hydrogels could significantly promoting wound healing by improving the collagen deposition and angiogenesis. The manufacture of our multifunctional hydrogels dressing affords a new strategy for improving efficacy of cutaneous wound treatment.

Oral administration of hepcidin and chitosan benefits growth, immunity, and gut microbiota in grass carp (Ctenopharyngodon idella)

Intensive high-density culture patterns are causing an increasing number of bacterial diseases in fish. Hepcidin links iron metabolism with innate immunity in the process of resisting bacterial infection. In this study, the antibacterial effect of the combination of hepcidin (Cihep) and chitosan (CS) against Flavobacterium columnare was investigated. The dosing regimen was also optimized by adopting a feeding schedule of every three days and every seven days. After 56 days of feeding experiment, grass carp growth, immunity, and gut microbiota were tested. In vitro experiments, Cihep and CS can regulate iron metabolism and antibacterial activity, and that the combination of Cihep and CS had the best protective effect. In vivo experiments, Cihep and CS can improve the growth index of grass carp. After challenge with Flavobacterium columnare, the highest survival rate was observed in the Cihep+CS-3d group. By serum biochemical indicators assay and Prussian blue staining, Cihep and CS can increase iron accumulation and decrease serum iron levels. The contents of lysozyme and superoxide dismutase in Cihep+CS-3d group increased significantly. Meanwhile, Cihep and CS can significantly reduce the pathological damage of gill tissue. The 16S rRNA sequencing results showed that Cihep and CS can significantly increase the abundance and diversity of grass carp gut microbiota. These results indicated that the protective effect of consecutive 3-day feeding followed by a 3-day interval was better than that of consecutive 7-day feeding followed by a 7-day interval, and that the protective effect of Cihep in combination with chitosan was better than that of Cihep alone. Our findings optimize the feeding pattern for better oral administration of Cihep in aquaculture.

Dual-functional composite scaffolds for inhibiting infection and promoting bone regeneration

The treatment of infected bone defects is an intractable problem in orthopedics. It comprises two critical parts, namely that of infection control and bone defect repair. According to these two core tasks during treatment, the ideal approach of simultaneously controlling infection and repairing bone defects is promising treatment strategy. Several engineered biomaterials and drug delivery systems with dual functions of anti-bacterial action and ostogenesis-promotion have been developed and demonstrated excellent therapeutic effects. Compared with the conventional treatment method, the dual-functional composite scaffold can provide one-stage treatment avoiding multiple surgeries, thereby remarkably simplifying the treatment process and reducing the treatment time, overcoming the disadvantages of conventional bone transplantation. In this review, the impaired bone repair ability and its specific mechanisms in the microenvironment of pathogen infection and excessive inflammation were analyzed, providing a theoretical basis for the treatment of infectious bone defects. Furthermore, we discussed the composite dual-functional scaffold composed of a combination of antibacterial and osteogenic material. Finally, a series of advanced drug delivery systems with antibacterial and bone-promoting capabilities were summarized and discussed. This review provides a comprehensive understanding for the microenvironment of infectious bone defects and leading-edge design strategies for the antibacterial and bone-promoting dual-function scaffold, thus providing clinically significant treatment methods for infectious bone defects.

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Antibacterial and bone-promoting dual-function scaffolds are ideal strategies for treatment of infectious bone defects.

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The effect of infection on bone repair was summarized in detail from four important aspects.

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A variety of dual-function scaffolds based on antibacterial and osteogenic materials were discussed.

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Dual-function drug delivery systems promoting repair of infectious bone defects by locally releasing functional agents.

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Leading-edge design strategies, challenges and prospects for dual-functional biomaterials were provided.

Fracture-related infection

Musculoskeletal trauma leading to broken and damaged bones and soft tissues can be a life-threating event. Modern orthopaedic trauma surgery, combined with innovation in medical devices, allows many severe injuries to be rapidly repaired and to eventually heal. Unfortunately, one of the persisting complications is fracture-related infection (FRI). In these cases, pathogenic bacteria enter the wound and divert the host responses from a bone-healing course to an inflammatory and antibacterial course that can prevent the bone from healing. FRI can lead to permanent disability, or long courses of therapy lasting from months to years. In the past 5 years, international consensus on a definition of these infections has focused greater attention on FRI, and new guidelines are available for prevention, diagnosis and treatment. Further improvements in understanding the role of perioperative antibiotic prophylaxis and the optimal treatment approach would be transformative for the field. Basic science and engineering innovations will be required to reduce infection rates, with interventions such as more efficient delivery of antibiotics, new antimicrobials, and optimizing host defences among the most likely to improve the care of patients with FRI.

Lysostaphin: Engineering and Potentiation toward Better Applications

Lysostaphin is a potent bacteriolytic enzyme with endopeptidase activity against the common pathogen Staphylococcus aureus. By digesting the pentaglycine crossbridge in the cell wall peptidoglycan of S. aureus including the methicillin-resistant strains, lysostaphin initiates rapid lysis of planktonic and sessile cells (biofilms) and has great potential for use in agriculture, food industries, and pharmaceutical industries. In the past few decades, there have been tremendous efforts in potentiating lysostaphin for better applications in these fields, including engineering of the enzyme for higher potency and lower immunogenicity with longer-lasting effects, formulation and immobilization of the enzyme for higher stability and better durability, and recombinant expression for low-cost industrial production and in situ biocontrol. These achievements are extensively reviewed in this article focusing on applications in disease control, food preservation, surface decontamination, and pathogen detection. In addition, some basic properties of lysostaphin that have been controversial and only elucidated recently are summarized, including the substrate-binding properties, the number of zinc-binding sites, the substrate range, and the cleavage site in the pentaglycine crossbridge. Resistance to lysostaphin is also highlighted with a focus on various mechanisms. This article is concluded with a discussion on the limitations and future perspectives for the actual applications of lysostaphin.

Bacterial Toxin-Triggered Release of Antibiotics from Capsosomes Protects a Fly Model from Lethal Methicillin-Resistant Staphylococcus aureus (MRSA) Infection

Antibiotic resistance is a severe global health threat and hence demands rapid action to develop novel therapies, including microscale drug delivery systems. Herein, a hierarchical microparticle system is developed to achieve bacteria-activated single- and dual-antibiotic drug delivery for preventing methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections. The designed system is based on a capsosome structure, which consists of a mesoporous silica microparticle coated in alternating layers of oppositely charged polymers and antibiotic-loaded liposomes. The capsosomes are engineered and shown to release their drug payloads in the presence of MRSA toxins controlled by the Agr quorum sensing system. MRSA-activated single drug delivery of vancomycin and synergistic dual delivery of vancomycin together with an antibacterial peptide successfully kills MRSA in vitro. The capability of capsosomes to selectively deliver their cargo in the presence of bacteria, producing a bactericidal effect to protect the host organism, is confirmed in vivo using a Drosophila melanogaster MRSA infection model. Thus, the capsosomes serve as a versatile multidrug, subcompartmentalized microparticle system for preventing antibiotic-resistant bacterial infections, with potential applications to protect wounds or medical device implants from infections.

Role of Animal Models to Advance Research of Bacterial Osteomyelitis

Osteomyelitis is an inflammatory bone disease typically caused by infectious microorganisms, often bacteria, which causes progressive bone destruction and loss. The most common bacteria associated with chronic osteomyelitis is Staphylococcus aureus. The incidence of osteomyelitis in the United States is estimated to be upwards of 50,000 cases annually and places a significant burden upon the healthcare system. There are three general categories of osteomyelitis: hematogenous; secondary to spread from a contiguous focus of infection, often from trauma or implanted medical devices and materials; and secondary to vascular disease, often a result of diabetic foot ulcers. Independent of the route of infection, osteomyelitis is often challenging to diagnose and treat, and the effect on the patient's quality of life is significant. Therapy for osteomyelitis varies based on category and clinical variables in each case. Therapeutic strategies are typically reliant upon protracted antimicrobial therapy and surgical interventions. Therapy is most successful when intensive and initiated early, although infection may recur months to years later. Also, treatment is accompanied by risks such as systemic toxicity, selection for antimicrobial drug resistance from prolonged antimicrobial use, and loss of form or function of the affected area due to radical surgical debridement or implant removal. The challenges of diagnosis and successful treatment, as well as the negative impacts on patient's quality of life, exemplify the need for improved strategies to combat bacterial osteomyelitis. There are many in vitro and in vivo investigations aimed toward better understanding of the pathophysiology of bacterial osteomyelitis, as well as improved diagnostic and therapeutic strategies. Here, we review the role of animal models utilized for the study of bacterial osteomyelitis and their critically important role in understanding and improving the management of bacterial osteomyelitis.

Recent Advances in Multifunctional Hydrogels for the Treatment of Osteomyelitis

Osteomyelitis (OM), a devastating disease caused by microbial infection of bones, remains a major challenge for orthopedic surgeons. Conventional approaches for prevention and treatment of OM are unsatisfactory. Various alternative strategies have been proposed, among which, hydrogel-based strategies have demonstrated potential due to their unique properties, including loadable, implantable, injectable, printable, degradable, and responsive to stimuli. Several protocols, including different hydrogel designs, selection of antimicrobial agent, co-administration of bone morphogenetic protein 2 (BMP 2), and nanoparticles, have been shown to improve the biological properties, including antimicrobial effects, osteo-induction, and controlled drug delivery. In this review, we describe the current and future directions for designing hydrogels and their applications to improve the biological response to OM in vivo.

Novel Techniques and Future Perspective for Investigating Critical-Size Bone Defects

A critical-size bone defect is a challenging clinical problem in which a gap between bone ends will not heal and will become a nonunion. The current treatment is to harvest and transplant an autologous bone graft to facilitate bone bridging. To develop less invasive but equally effective treatment options, one needs to first have a comprehensive understanding of the bone healing process. Therefore, it is imperative to leverage the most advanced technologies to elucidate the fundamental concepts of the bone healing process and develop innovative therapeutic strategies to bridge the nonunion gap. In this review, we first discuss the current animal models to study critical-size bone defects. Then, we focus on four novel analytic techniques and discuss their strengths and limitations. These four technologies are mass cytometry (CyTOF) for enhanced cellular analysis, imaging mass cytometry (IMC) for enhanced tissue special imaging, single-cell RNA sequencing (scRNA-seq) for detailed transcriptome analysis, and Luminex assays for comprehensive protein secretome analysis. With this new understanding of the healing of critical-size bone defects, novel methods of diagnosis and treatment will emerge.

The intersection of fracture healing and infection: Orthopaedics research society workshop 2021

Infection is a common cause of impaired fracture healing. In the clinical setting, definitive fracture treatment and infection are often treated separately and sequentially, by different clinical specialties. The ability to treat infection while promoting fracture healing will greatly reduce the cost, number of procedures, and patient morbidity associated with infected fractures. In order to develop new therapies, scientists and engineers must understand the clinical need, current standards of care, pathologic effects of infection on fractures, available preclinical models, and novel technologies. One of the main causes of poor fracture healing is infection; unfortunately, bone regeneration and infection research are typically approached independently and viewed as two separate disciplines. Here, we aim to bring these two groups together in an educational workshop to promote research into the basic and translational science that will address the clinical challenge of delayed fracture healing due to infection. Statement of clinical significance: Infection and nonunion are each feared outcomes in fracture care, and infection is a significant driver of nonunion. The impact of nonunions on patie[Q2]nt well-being is substantial. Outcome data suggests a long bone nonunion is as impactful on health-related quality of life measures as a diagnosis of type 1 diabetes and fracture-related infection has been shown to significantly l[Q3]ower a patient's quality of life for over 4 years.  Although they frequently are associated with one another, the treatment approaches for infections and nonunions are not always complimentary and cannot be performed simultaneously without accepting tradeoffs. Furthermore, different clinical specialties are often required to address the problem, the orthopedic surgeon treating the fracture and an infectious disease specialist addressing the sources of infection. A sequential approach that optimizes treatment parameters requires more time, more surgeries, and thus confers increased morbidity to the patient. The ability to solve fracture healing and infection clearance simultaneously in a contaminated defect would benefit both the patient and the health care system.

Fabrication and evaluation of a BMP-2/dexamethasone co-loaded gelatin sponge scaffold for rapid bone regeneration

Improving the osteogenic activity of BMP-2 in vivo has significant clinical application value. In this research, we use a clinical gelatin sponge scaffold loaded with BMP-2 and dexamethasone (Dex) to evaluate the osteogenic activity of dual drugs via ectopic osteogenesis in vivo. We also investigate the mechanism of osteogenesis induced by BMP-2 and Dex with C2C12, a multipotent muscle-derived progenitor cell. The results show that the gelatin scaffold with Dex and BMP-2 can significantly accelerate osteogenesis in vivo. It is indicated that compared with the BMP-2 or Dex alone, 100 nM of Dex can dramatically enhance the BMP-2-induced alkaline phosphatase activity (ALP), ALP mRNA expression and mineralization. Further studies show that 100 nM of Dex can maintain the secondary structure of BMP-2 and facilitate recognition of BMP-2 with its receptors on the surface of C2C12 cells. We also find that in C2C12, Dex has no obvious effect on the BMP-2-induced Smad1/5/8 protein expression and the STAT3-dependent pathway, but Runx2-dependent pathway is involved in the Dex-stimulated osteoblast differentiation of BMP-2 both in vitro and in vivo. Based on these results, a potential mechanism model about the synergistic osteoinductive effect of Dex and BMP-2 in C2C12 cells via Runx2 activation is proposed. This may provide a theoretical basis for the pre-clinical application of Dex and BMP-2 for bone regeneration.

Comparative Transcriptome Analysis Reveals Differentially Expressed Genes Related to Antimicrobial Properties of Lysostaphin in Staphylococcus aureus

Comparative transcriptome analysis and de novo short-read assembly of S. aureus Newman strains revealed significant transcriptional changes in response to the exposure to triple-acting staphylolytic peptidoglycan hydrolase (PGH) 1801. Most altered transcriptions were associated with the membrane, cell wall, and related genes, including amidase, peptidase, holin, and phospholipase D/transphosphatidylase. The differential expression of genes obtained from RNA-seq was confirmed by reverse transcription quantitative PCR. Moreover, some of these gene expression changes were consistent with the observed structural perturbations at the DNA and RNA levels. These structural changes in the genes encoding membrane/cell surface proteins and altered gene expressions are the candidates for resistance to these novel antimicrobials. The findings in this study could provide insight into the design of new antimicrobial agents.