Contaminated open fracture and crush injury: a murine model

Implants coating strategies for antibacterial treatment in fracture and defect models: A systematic review of animal studies

Objective

Fracture-related infection (FRI) remains a major concern in orthopaedic trauma. Functionalizing implants with antibacterial coatings are a promising strategy in mitigating FRI. Numerous implant coatings have been reported but the preventive and therapeutic effects vary. This systematic review aimed to provide a comprehensive overview of current implant coating strategies to prevent and treat FRI in animal fracture and bone defect models.

Methods

A literature search was performed in three databases: PubMed, Web of Science and Embase, with predetermined keywords and criteria up to 28 February 2023. Preclinical studies on implant coatings in animal fracture or defect models that assessed antibacterial and bone healing effects were included.

Results

A total of 14 studies were included in this systematic review, seven of which used fracture models and seven used defect models. Passive coatings with bacteria adhesion resistance were investigated in two studies. Active coatings with bactericidal effects were investigated in 12 studies, four of which used metal ions including Ag+ and Cu2+; five studies used antibiotics including chlorhexidine, tigecycline, vancomycin, and gentamicin sulfate; and the other three studies used natural antibacterial materials including chitosan, antimicrobial peptides, and lysostaphin. Overall, these implant coatings exhibited promising efficacy in antibacterial effects and bone formation.

Conclusion

Antibacterial coating strategies reduced bacterial infections in animal models and favored bone healing in vivo. Future studies of implant coatings should focus on optimal biocompatibility, antibacterial effects against multi-drug resistant bacteria and polymicrobial infections, and osseointegration and osteogenesis promotion especially in osteoporotic bone by constructing multi-functional coatings for FRI therapy.

The translational potential of this paper

The clinical treatment of FRI is complex and challenging. This review summarizes novel orthopaedic implant coating strategies applied to FRI in preclinical studies, and offers a perspective on the future development of orthopaedic implant coatings, which can potentially contribute to alternative strategies in clinical practice.

Palladium(II) Metal Complex Fabricated Titanium Implant Mitigates Dual-Species Biofilms in Artificial Synovial Fluid

Metallodrugs have a potent application in various medical fields. In the current study, we used a novel Palladium(II) thiazolinyl picolinamide complex that was directly fabricated over the titanium implant to examine its potency in inhibiting dual-species biofilms and exopolysaccharides. Additionally, inhibition of mono- and dual-species biofilms by coated titanium plates in an in vitro joint microcosm was performed. The study was carried out for 7 days by cultivating mono- and dual-species biofilms on titanium plates placed in both growth media and artificial synovial fluid (ASF). By qPCR analysis, the interaction of co-cultured biofilms in ASF and the alteration in gene expression of co-cultured biofilms were studied. Remarkable alleviation of biofilm accumulation and EPS secretion was observed on the coated titanium plates. The effective impairment of biofilms and EPS matrix of biofilms on Pd(II)-E-coated titanium plates were visualized by Scanning Electron Microscopy. Moreover, coated titanium plates improved the adhesion of osteoblast cells, which is crucial for a bone biomaterial. The potential bioactivity of coated plates was also confirmed at the molecular level using qPCR analysis. The stability of coated plates in ASF for 7 days was examined with FESEM-EDAX analysis. Collectively, the present study provided an excellent anti-infective effect on Pd(II)-E-coated titanium plates without affecting their biocompatibility with bone cells.

Temporal Pattern of micro-CT Angiography Vascular Parameters and VEGF mRNA Expression in Fracture Healing: a Radiograph and Molecular Comparison

Angiogenesis plays an important role in fracture healing with vascular endothelial growth factor (VEGF) as the main protein involved. Micro-computed tomography (CT) angiography may be used to analyze this revascularization with several parameters such as number of branches, total volume, and diameter. This systematic review is aimed to assess available studies on the temporal pattern of vascular imaging on micro-CT angiographs, especially in terms of the number of branches, total volume, and diameter as well as the temporal pattern of VEGF mRNA expression as the molecular comparison during bone fracture healing. This review was conducted according to the PRISMA guidelines. Electronic database searches were performed using PubMed, ProQuest, ScienceDirect, EBSCOhost, Taylor & Francis Online, and hand searching. The search strategy and keywords were adjusted to each database using the Boolean operators and other available limit functions to identify most relevant articles based on our inclusion and exclusion criteria. Screening and filtration were done in several stages by removing the duplicates and analyzing each title, abstract, and full-text in all included entries. Data extraction was done for syntheses to summarize the temporal pattern of each parameter. A total of 28 articles were eligible and met all criteria, 11 articles were synthesized in its angiograph's analysis, 16 articles were synthesized in its VEGF mRNA expression analysis, and 1 article had both parameters analyzed. The overall temporal pattern of both three micro-CT angiographic parameters and VEGF mRNA expression was in line qualitatively. The number of branches, total volume, and diameter of the blood vessels in micro-CT angiography showed an exponential rise at week 2 and decline at week 3 of fracture healing, with the VEGF mRNA expression concurrently showing a consistent pattern in the phase.

Validation of the modified radiographic union score for tibia fractures (mRUST) in murine femoral fractures

Bony union is a primary predictor of outcome after surgical fixation of long bone fractures. Murine models offer many advantages in assessing bony healing due to their low costs and small size. However, current fracture recovery investigations in mice frequently rely on animal sacrifice and costly analyses. The modified Radiographic Union Score for Tibia fractures (mRUST) scoring system is a validated metric for evaluating bony healing in humans utilizing plain radiographs, which are relatively inexpensive and do not require animal sacrifice. However, its use has not been well established in murine models. The aim of this study was to characterize the longitudinal course of mRUST and compare mRUST to other conventional murine fracture analyses. 158 mice underwent surgically created midshaft femur fractures. Mice were evaluated after fracture creation and at 7, 10, 14, 17, 21, 24, 28, 35, and 42 days post-injury. mRUST scoring of plain radiographs was performed by three orthopaedic surgeons in a randomized, blinded fashion. Interrater correlations were calculated. Micro-computed tomography (μCT) was analyzed for tissue mineral density (TMD), total callus volume (TV), bone volume (BV), trabecular thickness, trabecular number, and trabecular separation. Histomorphometry measures of total callus area, cartilage area, fibrous tissue area, and bone area were performed in a blinded fashion. Ultimate torque, stiffness, toughness, and twist to failure were calculated from torque-twist curves. A sigmoidal log-logistic curve fit was generated for mRUST scores over time which shows mRUST scores of 4 to 6 at 7 days post-injury that improve to plateaus of 14 to 16 by 24 days post-injury. mRUST interrater correlations at each timepoint ranged from 0.51 to 0.86, indicating substantial agreement. mRUST scores correlated well with biomechanical, histomorphometry, and μCT parameters, such as ultimate torque (r=0.46, p<0.0001), manual stiffness (r=0.51, p<0.0001), bone percentage based on histomorphometry (r=0.86, p<0.0001), cartilage percentage (r=-0.87, p<0.0001), tissue mineral density (r=0.83, p<0.0001), BV/TV based on μCT (r=0.65, p<0.0001), and trabecular thickness (r=0.78, p<0.0001), among others. These data demonstrate that mRUST is reliable, trends temporally, and correlates to standard measures of murine fracture healing. Compared to other measures, mRUST is more cost-effective and non-terminal. The mRUST log-logistic curve could be used to characterize differences in fracture healing trajectory between experimental groups, enabling high-throughput analysis.

Transition metal complex laminated bioactive implant alleviates Methicillin Resistant Staphylococcus aureus virulence

Orthopedic implant infections cause a serious threat after implantation. The major source of implant infection is biofilms which are highly tolerant to antibiotics due to the presence of rigid biofilm matrix. Hence to overcome biofilm mediated implant infections, we developed a novel antibiofilm agent, palladium (II) thiazolinyl picolinamide complex (Pd(II)-E). From our study, it was found that Pd(II)-E have profound biofilm inhibition activity and also reduced various virulence factors of Methicillin resistant Staphylococcus aureus (MRSA) including slime synthesis, Phenol soluble modulin (PSM) mediated spreading, Exopolysaccharides production and staphyloxanthin synthesis. Further, Pd(II)-E was coated over the titanium plates which was confirmed using EDX (Energy Dispersive X-Ray) analysis. The Pd(II)-E coated plates were able to prevent the biofilm formation on them which was evident under a Scanning electron microscope (SEM) and several virulent genes were found to be downregulated in the biofilms on the coated titanium plates which confirmed by qPCR. From our findings, it was found that Pd(II)-E coated titanium implants would be an effective alternate approach for preventing biofilm mediated implant infections.

Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

Modern combat-related injuries are often associated with acute polytrauma. As a consequence of severe combat-related injuries, a dysregulated immune response results in serious infectious complications. The gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that often causes life-threatening bloodstream, lung, bone, urinary tract, and wound infections following combat-related injuries. The rise in the number of multidrug-resistant P. aeruginosa strains has elevated its importance to civilian clinicians and military medicine. Development of novel therapeutics and treatment options for P. aeruginosa infections is urgently needed. During the process of drug discovery and therapeutic testing, in vivo testing in animal models is a critical step in the bench-to-bedside approach, and required for Food and Drug Administration approval. Here, we review current and past literature with a focus on combat injury-relevant animal models often used to understand infection development, the interplay between P. aeruginosa and the host, and evaluation of novel treatments. Specifically, this review focuses on the following animal infection models: wound, burn, bone, lung, urinary tract, foreign body, and sepsis.

IGF-1 promotes angiogenesis in endothelial cells/adipose-derived stem cells co-culture system with activation of PI3K/Akt signal pathway

OBJECTIVES

The aim of this study was to investigate the role of insulin-like growth factor-1 (IGF-1) and crosstalk between endothelial cells (ECs) and adipose-derived stem cells (ASCs) in the process of angiogenesis.

METHODS

A three-dimensional collagen gel used to culture mouse ASCs and mouse ECs in vitro was established. The effects of angiogenesis after exposure to IGF-1 were observed by confocal laser scanning microscopy. Western blotting and qPCR were performed to elucidate the underlying mechanisms.

RESULTS

IGF-1 treatment promoted the formation of vessel-like structures and the recruitment of ASCs in the three-dimensional collagen gel. The angiogenic genes and proteins in ECs were up-regulated by IGF-1 and in co-culture. Similar changes in the genes and in the proteins were detected in ASCs after exposure to IGF-1 and co-culture. p-Akt expression levels were high in ECs and ASCs after exposure to IGF-1 and co-culture.

CONCLUSIONS

IGF-1 and co-culture between cells facilitate the process of angiogenesis via the PI3-kinase/Akt signalling pathway. In ECs, IGF-1 stimulates the expression of angiogenesis-related growth factors with the activation of the PI3-kinase/Akt signalling pathway. Co-cultured ECs exposed to excess VEGF-A and other angiogenesis-related growth factors para-secreted from ASCs exhibit high expression of angiogenesis-related genes and proteins. In ASCs, IGF-1 induces the recruitment and function of ASCs by up-regulating the expression of PDGFB, MMPs and α-SMA. Crosstalk with ECs further facilitates changes in ASCs.

The JAK/STAT3 signalling pathway regulated angiogenesis in an endothelial cell/adipose-derived stromal cell co-culture, 3D gel model

OBJECTIVES

The aim of the study was to investigate the role of the JAK/STAT3 signalling pathway in angiogenesis.

MATERIALS AND METHODS

The model established in vitro, involved a 3D collagen gel being implanted with endothelial cells (ECs) from red fluorescent protein-labelled mice, and adipose-derived stromal cells (ASCs) from green fluorescent protein-labelled mice. Phenomena of angiogenesis, after treatment by the inhibitor and the activator of JAK/STAT3 pathway respectively, were observed using confocal laser scanning microscopy. Transwell co-culture of ECs and ASCs was used to elucidate mechanisms.

RESULTS

Stattic, inhibitor of JAK/STAT3 pathway, attenuated angiogenesis in the model. In contrast, angiogenesis was promoted after treatment of Olanzapine, an activator. We found that protein levels of VEGFA and cyclin D1 were regulated by the JAK/STAT3 pathway, and flow cytometry further confirmed variations in cell cycle parameters of ECs and ASCs. Genes VEGFA/B, VEGFR2, MMP-2, MMP-9, IGF-1 and b-FGF were down-regulated by Stattic in ECs, while Olanzapine significantly up-regulated mRNA levels of these genes. As for ASCs, genes VEGFA, MMP-2, MMP-9, IGF-1 and b-FGF were modulated by the JAK/STAT3 pathway.

CONCLUSIONS

Angiogenesis in the 3D collagen gel was regulated by the JAK/STAT3 pathway which involved changes in vessel length, vessel diameter and sprout number. The underlying mechanism was that the JAK/STAT3 signalling pathway regulated angiogenesis by modulation of numbers of angiogenesis-related growth factors and by direct regulation of cell cycle.