Preventing Implant-Associated Infections by Silver Coating

Evaluating antimicrobial efficacy in medical devices: The critical role of simulating in use test conditions

Biofilm infections represent the greatest risk associated with medical devices and implants, constituting 65 %-70 % of all device associated infections. Efforts to develop antimicrobial technologies for biomedical applications aim to reduce infection rates, antibiotic use, and the induction of antimicrobial resistance. However, standard laboratory test conditions often overestimate efficacy, highlighting the need for experimental designs that simulate real-world settings. To this end, we evaluated four commercially available antimicrobial materials containing silver (AG1, AG2, AG3) or zinc (ZN1) to assess their ability to mitigate microbial proliferation in for longer duration or multi-use medical devices. The materials' homogeneity and surface topography were characterized through Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) and Atomic Force Microscopy (AFM). Antimicrobial efficacy was tested using a modified ISO 22196 protocol under clinically relevant conditions and a dry contact test developed to mimic in-use conditions for many extracorporeal medical devices. Results revealed homogeneous elemental distributions in AG1, AG2, and ZN1, and heterogeneous clusters for AG3. Surface roughness was highest for AG2 (170.1 nm), followed by TPE control (155.3 nm), ZN1 (83.51 nm) and silicone control (66.74 nm). All test materials demonstrated antimicrobial efficacies against S. aureus and E. coli, but not against C. albicans. In the dry contact assay, only AG2 proved effective against E. coli, and P. aeruginosa, underlining the role of humidity in antimicrobial action. Results were further corroborated by measurement of ion release by the materials at various temperatures, revealing greater release at higher temperatures. These outcomes emphasize the importance of testing antimicrobial materials under in use conditions to minimize discrepancies between laboratory results and clinical outcomes. Our findings provide a valuable framework for testing and integrating these materials into next-generation multi-use medical devices.

From adhesion to biofilms formation and resilience: Exploring the impact of silver nanoparticles-based biomaterials on Pseudomonas aeruginosa

Colonization of medical devices by microorganisms, often progressing to the formation of resilient biofilms, presents a common clinical issue. To address this challenge, there is growing interest in developing novel biomaterials with antimicrobial/antibiofilm properties as a promising preventive measure. This study explores nanocomposite biomaterials based on silver nanoparticles (AgNPs) deposited on thin silica (SiO2) layers for their potential effect on the adhesion, detachment, viability and biofilm formation of the opportunistic Pseudomonas aeruginosa. The AgNPs-based biointerface effect on biofilm development is investigated on the PAO1-Tn7-gfp strain by combining experiments under static and dynamic conditions. For the latter, a shear-stress flow chamber is used to mimic conditions encountered around certain medical devices. The findings reveal a rapid bactericidal effect of the AgNPs, noticeable within 30 min of exposure. Moreover, a delay in surface colonization is observed with a thin and unstructured biofilm, even after 72h of dynamic culture. A considerable fragility and sensitivity to hydrodynamic stresses is noticed for this loosely attached bacterial monolayer when compared with the thick and resilient biofilm formed on SiO2 surface. This study underlines the potential of AgNPs-based biomaterials in the conception of novel antimicrobial/antibiofilm surfaces with controlled release of the biocidal agent.

Emerging Strategies to Prevent Bacterial Infections on Titanium-Based Implants

Titanium and titanium alloys remain the gold standard for dental and orthopedic implants. These materials are heavily used because of their bioinert nature, robust mechanical properties, and seamless integration with bone. However, implant-associated infections (IAIs) remain one of the leading causes of implant failure. Eradicating an IAI can be difficult since bacteria can form biofilms on the medical implant, protecting the bacterial cells against systemic antibiotics and the host's immune system. If the infection is not treated promptly and aggressively, device failure is inevitable, leading to costly multi-step revision surgeries. To circumvent this dire situation, scientists and engineers continue to develop novel strategies to protect the surface of medical implants from bacteria. In this review, details on emerging strategies to prevent infection in titanium implants are reported. These strategies include anti-adhesion properties provided by polymers, superhydrophobic, superhydrophilic, and liquid-infused surface coatings, as well as strategies and coatings employed to lyse the bacteria. Additionally, commercially available technologies and those under preclinical trials are examined while discussing current and future trends.

Antimicrobial resistance: Biofilms, small colony variants, and intracellular bacteria

Soft tissue and bone infections continue to be a serious complication in orthopedic and trauma surgery. Both can lead to a high burden for the patients and the healthcare system. Musculoskeletal infections can be induced by intraoperative contamination, bacterial contamination of open wounds or hematogenous bacterial spread. During the recent decades, advances were achieved in the understanding of pathogenesis and antibiotic resistance. Despite some progress in the diagnosis and advancing of therapeutic concepts, groundbreaking successful improvement of treatment concepts is still missing. Current therapy concepts are based on the two pillars consisting of surgical debridement with joint or bone reconstruction as well as prolonged antibiotic therapy. An improved understanding of both host and pathogen-related factors leading to treatment failure is essential in musculoskeletal infections. Therefore, this review aims to give an overview of pathogen-related pathophysiology in musculoskeletal infections. It describes defense strategies of pathogens such as (1) biofilm, its development, characteristics, and treatment options. In addition, (2) characteristics of small colony variants and (3) intracellular bacteria are highlighted. Lastly (4) an outlook for potential and promising future therapeutic strategies is provided.

Antimicrobial Effects of Metal Coatings or Physical, Chemical Modifications of Titanium Dental Implant Surfaces for Prevention of Peri-Implantitis: A Systematic Review of In Vivo Studies

Introduction: Peri-implantitis poses a significant challenge for implant dentistry due to its association with bacterial colonization on implant surfaces and the complexity of its management. This systematic review aims to assess evidence from in vivo studies regarding the antimicrobial efficacy of titanium (Ti) dental implant surfaces following physical/chemical modifications or the application of various metal element coatings in preventing bacterial growth associated with peri-implantitis. Materials and Methods: A literature review was conducted across four scientific databases (PubMed, Embase, Scopus, Web of Science), encompassing in vivo studies published between 2013 and 2024, and 18 reports were included in the systematic review. Results: The findings suggest that titanium dental implant surfaces, following physical/chemical modifications and metal element coatings, exhibit antimicrobial effects against bacteria associated with peri-implantitis in humans and various animal models. Conclusions: The reviewed studies indicated a reduction in bacterial colonization, diminished biofilm formation, and decreased signs of inflammation in the peri-implant tissues, which provides evidence that physical/chemical alterations on titanium dental implant surfaces or metal element coatings, like silver (Ag), zinc (Zn), magnesium (Mg), and copper (Cu), demonstrate antimicrobial properties in in vivo studies. However, caution is warranted when translating findings to clinical practice due to methodological disparities and high bias risks. Further larger-scale clinical trials are imperative to assess their long-term efficacy and validate their clinical applicability.

Use of a silver-coated plate to treat a postoperative infection after high tibial osteotomy - a case report

Unilateral osteoarthritis of the knee can be treated by osteotomy. In case of postoperative infection after high tibial osteotomy, treatment can be challenging and often requires implant removal with the risk of loss of reduction. In the presented case, a 47-year old patient suffered postoperative infection after high tibial osteotomy using an angular stable plate with the need for multiple revision surgeries and anti-infective therapy. Implant exchange to a silver-coated angular plate led to infection control with undisturbed wound healing and further bone consolidation. Full bone consolidation could be achieved radiographically 12 months after the last revision surgery. One-step implant exchange using silver-coated implants could be a promising approach to address postoperative infections after high tibial osteotomy.

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.

Mechanical Properties and Corrosion Rate of ZnAg3 as a Novel Bioabsorbable Material for Osteosynthesis

Osteosynthesis in fracture treatment typically uses hardware that remains in the patient's body, which brings a permanent risk of negative side effects such as foreign body reactions or chronic inflammation. Bioabsorbable materials, however, can degrade and slowly be replaced by autologous bone tissue. A suitable material is requested to offer great biocompatibility alongside excellent mechanical properties and a reasonable corrosion rate. Zinc-silver alloys provide these characteristics, which makes them a promising candidate for research. This study investigated the aptitude as a bioabsorbable implant of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3). Here, the tensile strength as well as the corrosion rate in PBS solution (phosphate buffered solution) of ZnAg3 were assessed. Furthermore, shear tests, including fatigue and quasi-static testing, were conducted with ZnAg3 and magnesium pins (MAGNEZIX®, Syntellix AG, Hannover, Germany), which are already in clinical use. The detected corrosion rate of 0.10 mm/year for ZnAg3 was within the proposed range for bioabsorbable implants. With a tensile strength of 237.5 ± 2.12 MPa and a shear strength of 144.8 ± 13.2 N, ZnAg3 satisfied the mechanical requirements for bioabsorbable implants. The fatigue testing did not show any significant difference between ZnAg3 and magnesium pins, whereas both materials withstood the cyclic loading. Thus, the results support the assumption that ZnAg3 is qualified for further investigation.

Antibiofilm Effect of Nitric Acid-Functionalized Carbon Nanotube-Based Surfaces against E. coli and S. aureus

Chemically modified carbon nanotubes are recognized as effective materials for tackling bacterial infections. In this study, pristine multi-walled carbon nanotubes (p-MWCNTs) were functionalized with nitric acid (f-MWCNTs), followed by thermal treatment at 600 °C, and incorporated into a poly(dimethylsiloxane) (PDMS) matrix. The materials' textural properties were evaluated, and the roughness and morphology of MWCNT/PDMS composites were assessed using optical profilometry and scanning electron microscopy, respectively. The antibiofilm activity of MWCNT/PDMS surfaces was determined by quantifying culturable Escherichia coli and Staphylococcus aureus after 24 h of biofilm formation. Additionally, the antibacterial mechanisms of MWCNT materials were identified by flow cytometry, and the cytotoxicity of MWCNT/PDMS composites was tested against human kidney (HK-2) cells. The results revealed that the antimicrobial activity of MWCNTs incorporated into a PDMS matrix can be efficiently tailored through nitric acid functionalization, and it can be increased by up to 49% in the absence of surface carboxylic groups in f-MWCNT samples heated at 600 °C and the presence of redox activity of carbonyl groups. MWCNT materials changed the membrane permeability of both Gram-negative and Gram-positive bacteria, while they only induced the production of ROS in Gram-positive bacteria. Furthermore, the synthesized composites did not impact HK-2 cell viability, confirming the biocompatibility of MWCNT composites.

In Vivo Prevention of Implant-Associated Infections Caused by Antibiotic-Resistant Bacteria through Biofunctionalization of Additively Manufactured Porous Titanium

Additively manufactured (AM) porous titanium implants may have an increased risk of implant-associated infection (IAI) due to their huge internal surfaces. However, the same surface, when biofunctionalized, can be used to prevent IAI. Here, we used a rat implant infection model to evaluate the biocompatibility and infection prevention performance of AM porous titanium against bioluminescent methicillin-resistant Staphylococcus aureus (MRSA). The specimens were biofunctionalized with Ag nanoparticles (NPs) using plasma electrolytic oxidation (PEO). Infection was initiated using either intramedullary injection in vivo or with in vitro inoculation of the implant prior to implantation. Nontreated (NT) implants were compared with PEO-treated implants with Ag NPs (PT-Ag), without Ag NPs (PT) and infection without an implant. After 7 days, the bacterial load and bone morphological changes were evaluated. When infection was initiated through in vivo injection, the presence of the implant did not enhance the infection, indicating that this technique may not assess the prevention but rather the treatment of IAIs. Following in vitro inoculation, the bacterial load on the implant and in the peri-implant bony tissue was reduced by over 90% for the PT-Ag implants compared to the PT and NT implants. All infected groups had enhanced osteomyelitis scores compared to the noninfected controls.

Mechanism of regulating macrophages/osteoclasts in attenuating wear particle-induced aseptic osteolysis

Joint replacement surgery is the most effective treatment for end-stage arthritis. Aseptic loosening caused by periprosthetic osteolysis is a common complication after joint replacement. Inflammation induced by wear particles derived from prosthetic biomaterials is a major cause of osteolysis. We emphasize that bone marrow-derived macrophages and their fusion-derived osteoclasts play a key role in this pathological process. Researchers have developed multiple intervention approaches to regulate macrophage/osteoclast activation. Aiming at wear particle-induced periprosthetic aseptic osteolysis, this review separately discusses the molecular mechanism of regulation of ROS formation and inflammatory response through intervention of macrophage/osteoclast RANKL-MAPKs-NF-κB pathway. These molecular mechanisms regulate osteoclast activation in different ways, but they are not isolated from each other. There is also a lot of crosstalk among the different mechanisms. In addition, other bone and joint diseases related to osteoclast activation are also briefly introduced. Therefore, we discuss these new findings in the context of existing work with a view to developing new strategies for wear particle-associated osteolysis based on the regulation of macrophages/osteoclasts.

A randomized, single-blind, multi-center clinical observational study of a new super lubricath coating catheter latex catheters using in urethral catheterization

Polymer polyvinylpyrrolidone (PVP) can be described as the main coating. After heating and curing, it is able to build a strong adhesion to the latex catheter for creating a durable and effective hydrophilic coating. In this study, we aim to explore the advantages and disadvantages of the new super lubricath latex catheter PVP coating compared with the common latex catheter. 148 patients who participated in the study were completely randomly divided into two groups, the observation group and the control group. When the urinary catheter was incubated, indwelling in subjects' body, and removed from the subjects, the researchers accordingly recorded the subjects' comfort feedback, device safety evaluation and the patient's vital signs, relevant blood and urine examination index, electrocardiogram (ECG) changes and recorded various adverse events. PVP super lubricath coating latex catheter offered better comfort, less damage to the urethra, and no significant disadvantage in safety compared to regular latex catheters, improving quality of care and patient satisfaction compared to regular latex urinary catheters.

Deploying a Novel Approach to Prepare Silver Nanoparticle Bellamya bengalensis Extract Conjugate Coating on Orthopedic Implant Biomaterial Discs to Prevent Potential Biofilm Formation

This study is based on the premise of investigating antibacterial activity through a novel conjugate of silver nanoparticles (AgNPs) and antimicrobial peptides (AMPs) in line with a green synthesis approach by developing antimicrobial-coated implants to prevent bacterial resistance. The AMPs were obtained from Bellamya Bengalensis (BB), a freshwater snail, to prepare the nanocomposite conjugate, e.g., AgNPs@BB extract, by making use of UV-Visible spectroscopy. The antimicrobial assessment of AgNPs@BB extract conjugate was performed using the Resazurin Microtiter Assay Method (REMA), followed by the use of three biocompatible implant materials (titanium alloys, Ti 6AL-4V stainless steel 316L, and polyethylene). Finally, the coating was analyzed under confocal microscopy. The results revealed a significant reduction of biofilm formation on the surfaces of implants coated with conjugate (AgNPs@BB extract) in comparison to uncoated implants. For the MTT assay, no significant changes were recorded for the cells grown on the AgNPs/AMP++ sample in high concentrations. Staphylococcus epidermidis, however, showed more prominent growth on all implants in comparison to Staphylococcus aureus. It is evident from the results that Staphylococcus epidermidis is more susceptible to AgNPs@BB extract, while the minimum inhibitory concentration (MIC) value of AgNPs@BB extract conjugates and biosynthesized AgNPs was also on the higher side. This study indicates that AgNPs@BB extract carries antibacterial activity, and concludes that an excessive concentration of AgNPs@BB extract may affect the improved biocompatibility. This study recommends using robust, retentive, and antimicrobial coatings of AgNPs@BB extract for implantable biocompatible materials in accordance with the novel strategy of biomaterial applications.

Bacterial Biofilm Formation on Biomaterials and Approaches to Its Treatment and Prevention

Bacterial biofilms can cause widespread infection. In addition to causing urinary tract infections and pulmonary infections in patients with cystic fibrosis, biofilms can help microorganisms adhere to the surfaces of various medical devices, causing biofilm-associated infections on the surfaces of biomaterials such as venous ducts, joint prostheses, mechanical heart valves, and catheters. Biofilms provide a protective barrier for bacteria and provide resistance to antimicrobial agents, which increases the morbidity and mortality of patients. This review summarizes biofilm formation processes and resistance mechanisms, as well as the main features of clinically persistent infections caused by biofilms. Considering the various infections caused by clinical medical devices, we introduce two main methods to prevent and treat biomaterial-related biofilm infection: antibacterial coatings and the surface modification of biomaterials. Antibacterial coatings depend on the covalent immobilization of antimicrobial agents on the coating surface and drug release to prevent and combat infection, while the surface modification of biomaterials affects the adhesion behavior of cells on the surfaces of implants and the subsequent biofilm formation process by altering the physical and chemical properties of the implant material surface. The advantages of each strategy in terms of their antibacterial effect, biocompatibility, limitations, and application prospects are analyzed, providing ideas and research directions for the development of novel biofilm infection strategies related to therapeutic materials.

Antibacterial and biocompatible polyaniline-doped titanium oxide layers

Titanium anodization has been shown to produce crystalline oxides exhibiting photocatalytic reactions that form reactive oxygen species (ROS) when exposed to UV light. The ROS subsequently attack bacteria cells, and thus reduce bacteria attachment on titanium implant surfaces. Polyaniline (PANI) is a conductive polymer that has shown antibacterial properties when electropolymerized onto titanium. Our research group hypothesized the addition of PANI to crystalline titanium oxide surfaces would increase the available free electrons and thus increase photocatalytic activity (PCA). This research led to the development of a novel single-step anodization approach for PANI doping crystalline titanium oxide layers. The objective of the present study was to determine the proper aniline electrolyte concentration needed to maximize the PCA and reduce bacterial attachment on the formed oxides. Aniline concentrations up to 1 M were added into a 1 M sulfuric acid electrolyte. The formed oxides exhibited increased PANI surface coverage but decreased anatase and rutile crystalline titanium oxide phase formation with increasing aniline electrolyte concentrations. Despite exhibiting the lowest levels of anatase and rutile formation, the 0.75 M and 1 M aniline oxides with the greatest PANI surface coverage also exhibited the highest PCA levels. 1 M aniline oxides showed significantly higher PCA under UVA irradiation compared to oxides formed from aniline concentrations up to 0.5 M (p < 0.001). 0.75 M aniline oxides exhibited significant reductions in Staphylococcus aureus attachment with or without UVA irradiation compared to control oxides without PANI. MTT and live/dead assays confirmed cytocompatibility and nearly 100% cell viability for the PANI doped oxides.

Inhibition of Cancer Cell Proliferation and Bacterial Growth by Silver(I) Complexes Bearing a CH3-Substituted Thiadiazole-Based Thioamide

Ag(I) coordination compounds have recently attracted much attention as antiproliferative and antibacterial agents against a wide range of cancer cell lines and pathogens. The bioactivity potential of these complexes depends on their structural characteristics and the nature of their ligands. Herein, we present a series of four Ag(I) coordination compounds bearing as ligands the CH₃-substituted thiadiazole-based thioamide 5-methyl-1,3,4-thiadiazole-2-thiol (mtdztH) and phosphines, i.e., [AgCl(mtdztH)(PPh₃)₂] (1), [Ag(mtdzt)(PPh₃)₃] (2), [AgCl(mtdztH)(xantphos)] (3), and [AgmtdztH)(dppe)(NO₃)]_n (4), where xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene and dppe = 1,2-bis(diphenylphosphino)ethane, and the assessment of their in vitro antibacterial and anti-cancer efficiency. Among them, diphosphine-containing compounds 3 and 4 were found to exhibit broad-spectrum antibacterial activity characteristics against both Gram-(+) and Gram-(-) bacterial strains, showing high in vitro bioactivity with IC₅₀ values as low as 4.6 μΜ. In vitro cytotoxicity studies against human ovarian, pancreatic, lung, and prostate cancer cell lines revealed the strong cytotoxic potential of 2 and 4, with IC₅₀ values in the range of 3.1-24.0 μΜ, while 3 and 4 maintained the normal fibroblast cells' viability at relatively higher levels. Assessment of these results, in combination with those obtained for analogous Ag(I) complexes bearing similar heterocyclic thioamides, suggest the pivotal role of the substituent groups of the thioamide heterocyclic ring in the antibacterial and anti-cancer efficacy of the respective Ag(I) complexes. Compounds 1-4 exhibited moderate in vitro antioxidant capacity for free radicals scavenging, as well as reasonably strong ability to interact with calf-thymus DNA, suggesting the likely implication of these properties in their bioactivity mechanisms. Complementary insights into the possible mechanism of their anti-cancer activity were provided by molecular docking calculations, exploring their ability to bind to the overexpressed fibroblast growth factor receptor 1 (FGFR1), affecting cancer cells' functionalities.

Antibacterial and Antibiofilm Activity of Nanostructured Copper Films Prepared by Ionized Jet Deposition

Metal coatings represent good strategies to functionalize surfaces/devices and limit bacterial contamination/colonization thanks to their pleiotropic activity and their ability to prevent the biofilm formation. Here, we investigated the antibacterial and antibiofilm capacity of copper coatings deposited through the Ionized Jet Deposition (IJD) on the Calgary Biofilm Device (CBD) against the growth of two gram-negative and two gram-positive pathogenic strains. Three areas (i.e., (+)Cu, (++)Cu, and (+++)Cu based on the metal amount) on the CBD were obtained, presenting nanostructured coatings with high surface homogeneity and increasing dimensions of aggregates from the CBD periphery to the centre. The coatings in (++)Cu and (+++)Cu were efficient against the planktonic growth of the four pathogens. This antibacterial effect decreased in (+)Cu but was still significant for most of the pathogens. The antibiofilm efficacy was significant for all the strains and on both coated and uncoated surfaces in (+++)Cu, whereas in (++)Cu the only biofilms forming on the coated surfaces were inhibited, suggesting that the decrease of the metal on the coatings was associated to a reduced metal ion release. In conclusion, this work demonstrates that Cu coatings deposited by IJD have antibacterial and antibiofilm activity against a broad range of pathogens indicating their possible application to functionalize biomedical devices.

Mutagenesis and Resistance Development of Bacteria Challenged by Silver Nanoparticles

Because of their extremely broad spectrum and strong biocidal power, nanoparticles of metals, especially silver (AgNPs), have been widely applied as effective antimicrobial agents against bacteria, fungi, and so on. However, the mutagenic effects of AgNPs and resistance mechanisms of target cells remain controversial. In this study, we discover that AgNPs do not speed up resistance mutation generation by accelerating genome-wide mutation rate of the target bacterium Escherichia coli. AgNPs-treated bacteria also show decreased expression in quorum sensing (QS), one of the major mechanisms leading to population-level drug resistance in microbes. Nonetheless, these nanomaterials are not immune to resistance development by bacteria. Gene expression analysis, experimental evolution in response to sublethal or bactericidal AgNPs treatments, and gene editing reveal that bacteria acquire resistance mainly through two-component regulatory systems, especially those involved in metal detoxification, osmoregulation, and energy metabolism. Although these findings imply low mutagenic risks of nanomaterial-based antimicrobial agents, they also highlight the capacity for bacteria to evolve resistance.

Race for Applicable Antimicrobial Dental Implant Surfaces to Fight Biofilm-Related Disease: Advancing in Laboratorial Studies vs Stagnation in Clinical Application

Across years, potential strategies to fight peri-implantitis have been notoriously explored through the antimicrobial coating implant surfaces capable of interfering with the bacterial adhesion process. However, although experimental studies have significantly advanced, no product has been marketed so far. For science to reach the society, the commercialization of research outcomes is necessary to provide real advancement in the biomedical field. Therefore, the aim of this study was to investigate the challenges involved in the development of antimicrobial dental implant surfaces to fight peri-implantitis, through a systematic search. Research articles reporting antimicrobial dental implant surfaces were identified by searching PubMed, Scopus, Web of Science, The Cochrane Library, Embase, and System of Information on Grey Literature in Europe, between 2008 and 2020. A total of 1778 studies were included for quality assessment and the review. An impressive number of 1655 articles (93,1%) comprised in vitro studies, whereas 123 articles refer to in vivo investigations. From those 123, 102 refer to animal studies and only 21 articles were published on the clinical performance of antibacterial dental implant surfaces. The purpose of animal studies is to test how safe and effective new treatments are before they are tested in people. Therefore, the discrepancy between the number of published studies clearly reveals that preclinical investigations still come up against several challenges to overcome before moving forward to a clinical setting. Additionally, researchers need to recognize that the complex journey from lab to market requires more than a great idea and resources to develop a commercial invention; research teams must possess the skills necessary to commercialize an invention.

Surface coating of orthopedic implant to enhance the osseointegration and reduction of bacterial colonization: a review

The use of orthopedic implants in surgical technology has fostered restoration of physiological functions. Along with successful treatment, orthopedic implants suffer from various complications and fail to offer functions correspondent to native physiology. The major problems include aseptic and septic loosening due to bone nonunion and implant site infection due to bacterial colonization. Crucial advances in material selection in the design and development of coating matrixes an opportunity for the prevention of implant failure. However, many coating materials are limited in in-vitro testing and few of them thrive in clinical tests. The rate of implant failure has surged with the increasing rates of revision surgery creating physical and sensitive discomfort as well as economic burdens. To overcome critical pathogenic activities several systematic coating techniques have been developed offering excellent results that combat infection and enhance bone integration. This review article includes some more common implant coating matrixes with excellent in vitro and in vivo results focusing on infection rates, causes, complications, coating materials, host immune responses and significant research gaps. This study provides a comprehensive overview of potential coating technology, with functional combination coatings which are focused on ultimate clinical practice with substantial improvement on in-vivo tests. This includes the development of rapidly growing hydrogel coating techniques with the potential to generate several accurate and precise coating procedures.

Injectable bone cement containing carboxymethyl cellulose microparticles as a silver delivery system able to reduce implant-associated infection risk

In the challenging quest for a solution to reduce the risk of implant-associated infections in bone substitution surgery, the use of silver ions is promising regarding its broad spectrum on planktonic, sessile as well as multiresistant bacteria. In view of controlling its delivery in situ at the desired dose, we investigated its encapsulation in carboxymethyl cellulose (CMC) microparticles by spray-drying and included the latter in the formulation of a self-setting calcium phosphate bone cement. We implemented an original step-by-step methodology starting from the in vitro study of the antibacterial properties and cytotoxicity of two silver salts of different solubility in aqueous medium and then in the cement to determine the range of silver loading able to confer anti-biofilm and non-cytotoxic properties to the biomaterial. A dose-dependent efficiency of silver was demonstrated on the main species involved in bone-implant infection (S. aureus and S. epidermidis). Loading silver in microspheres instead of loading it directly inside the cement permitted to avoid undesired silver-cement interactions during setting and led to a faster release of silver, i.e. to a higher dose released within the first days combining anti-biofilm activity and preserved cytocompatibility. In addition, a combined interest of the introduction of about 10% (w/w) silver-loaded CMC microspheres in the cement formulation was demonstrated leading to a fully injectable and highly porous (77%) cement, showing a compressive strength analogous to cancellous bone. This injectable silver-loaded biomimetic composite cement formulation constitutes a versatile bone substitute material with tunable drug delivery properties, able to fight against bone implant associated infection. STATEMENT OF SIGNIFICANCE: This study is based on two innovative scientific aspects regarding the literature: i) Choice of silver ions as antibacterial agent combined with their way of incorporation: Carboxymethylcellulose has never been tested into bone cement to control its drug loading and release properties. ii) Methodology to formulate an antibacterial and injectable bone cement: original and multidisciplinary step-by-step methodology to first define, through (micro)biological tests on two silver salts with different solubilities, the targeted range of silver dose to include in carboxymethylcellulose microspheres and, then optimization of silver-loaded microparticles processing to fulfill requirements (encapsulation efficiency and size). The obtained fully injectable composite controls the early delivery of active dose of silver (from 3 h and over 2 weeks) able to fight against bone implant-associated infections.

Comparative Analysis of the Mechanism of Resistance to Silver Nanoparticles and the Biocide 2,2-Dibromo-3-Nitrilopropionamide

Antimicrobials such as nanoparticles and biocides are used to control microbial growth. We used Escherichia coli to study the process of acquired resistance to silver nanoparticles (Ag-NP) and the industrial biocide DBNPA when grown in sub-MICs. We determined the MICs of these two antimicrobials against E. coli. We then performed an experimental evolution study where E. coli was grown in subinhibitory concentrations of the antimicrobials and transferred 10 times. We then tracked the changes in growth characteristics, lactate dehydrogenase (LDH) activity, reactive oxidative species (ROS) production, and the role of efflux pumps in conferring resistance. We also performed genome sequencing to determine the genetic basis for acquired resistance. Our results showed that E. coli could rapidly develop resistance to Ag-NP and DBNPA after growth in low concentrations of the antimicrobials. The expression of efflux pumps plays a vital role in both Ag-NP and DBNPA resistance. Multiple mutations occurred in the adapted strains that may confer resistance to both Ag-NP and DBNPA. Our study provides insights into mechanisms of adaptation and resistance to antimicrobials. Our results suggest that there are some shared mechanisms to resist nanoparticles and biocides as well as some key differences. The mechanism of resistance to Ag-NP might be related to flagellin production, while efflux pumps seem to be associated with resistance to DBNPA. This work provides a comparative study of the mechanisms of acquired resistance to these two types of antimicrobials.

Prodigiosin-Loaded Poly(lactic acid) to Combat the Biofilm-Associated Infections

Poly(lactic acid) (PLA) is an emerging biobased implant material. Despite its biocompatibility and the aseptic procedures followed during orthopedic surgery, bacterial infection remains an obstacle to implementing PLA-based implants. To tackle this issue, prodigiosin-incorporated PLA has been developed, which possesses improved hydrophobicity with a contact angle of 111 ± 1.5°. The degradation temperature of the prodigiosin is 215 °C, which is more than the melting temperature of PLA, which supports the processability and sterilization of the PLA-based implants without any toxic gases. Further, prodigiosin improves the transparency of PLA and acts as a nucleation site. The spherulite density increases three times compared to that of neat PLA. The inherent methoxy group of prodigiosin is an active site responsible for the inhibition of bacterial attack and biofilm formation. The in vitro study on biofilm formation shows excellent inhibition activity against implant-associated pathogens such as Klebsiella aerogenes and Staphylococcus aureus.

Mapping Bacterial Biofilm on Features of Orthopedic Implants In Vitro

Implant-associated infection is a major complication of orthopedic surgery. One of the most common organisms identified in periprosthetic joint infections is Staphylococcus aureus, a biofilm-forming pathogen. Orthopedic implants are composed of a variety of materials, such as titanium, polyethylene and stainless steel, which are at risk for colonization by bacterial biofilms. Little is known about how larger surface features of orthopedic hardware (such as ridges, holes, edges, etc.) influence biofilm formation and attachment. To study how biofilms might form on actual components, we submerged multiple orthopedic implants of various shapes, sizes, roughness and material type in brain heart infusion broth inoculated with Staphylococcus aureus SAP231, a bioluminescent USA300 strain. Implants were incubated for 72 h with daily media exchanges. After incubation, implants were imaged using an in vitro imaging system (IVIS) and the metabolic signal produced by biofilms was quantified by image analysis. Scanning electron microscopy was then used to image different areas of the implants to complement the IVIS imaging. Rough surfaces had the greatest luminescence compared to edges or smooth surfaces on a single implant and across all implants when the images were merged. The luminescence of edges was also significantly greater than smooth surfaces. These data suggest implant roughness, as well as large-scale surface features, may be at greater risk of biofilm colonization.

Megaprosthesis anti-bacterial coatings: A comprehensive translational review

Periprosthetic joint infections (PJI) are catastrophic complications for patients with implanted megaprostheses and pose significant challenges in the management of orthopaedic oncology patients. Despite various preventative strategies, with the increasing rate of implanted orthopaedic prostheses, the number of PJIs may be increasing. PJIs are associated with a high rate of amputation. Therefore, novel strategies to combat bacterial colonization and biofilm formation are required. A promising strategy is the utilization of anti-bacterial coatings on megaprosthetic implants. In this translational review, a brief overview of the mechanism of bacterial colonization of implants and biofilm formation will be provided, followed by a discussion and classification of major anti-bacterial coatings currently in use and development. In addition, current in vitro outcomes, clinical significance, economic importance, evolutionary perspectives, and future directions of anti-bacterial coatings will also be discussed. Megaprosthetic anti-bacterial coating strategies will help reduce infection rates following the implantation of megaprostheses and would positively impact sarcoma care. STATEMENT OF SIGNIFICANCE: This review highlights the clinical challenges and a multitude of potential solutions to combating peri-prosthetic join infections in megaprotheses using anti-bacterial coatings. Reducing infection rates following the implantation of megaprostheses would have a major impact on sarcoma care and major trauma surgeries that require reconstruction of large skeletal defects.

Antimicrobial coatings based on chitosan to prevent implant-associated infections: A systematic review

Despite the advancements in material science and surgical techniques, the incidence of implant-associated infections (IAIs) has increased significantly. IAIs are mainly caused by microbial adhesion and biofilm formation on implant surfaces. In this study, we aimed to evaluate and critically discuss the antimicrobial efficacy of chitosan-based coatings to prevent the occurrence of IAIs. For this purpose, a PRISMA-oriented systematic review was conducted based on predefined criteria and forty studies were selected for qualitative analysis. Results indicated that chitosan (CS) association with enzymes and antimicrobial peptides improves its antimicrobial activity and extends its use in a broad range of physiological conditions. Likewise, CS association with polymers resulted in enhanced antimicrobial and anti-adhesive coatings with desirable properties, such as biocompatibility and durability, for implantable medical devices (IMDs). These findings can assist researchers in the design of new CS coatings for application in IMDs.

Molybdenum trioxide enhances viability, osteogenic differentiation and extracellular matrix formation of human bone marrow-derived mesenchymal stromal cells

BACKGROUND

Metals and their ions allow specific modifications of the biological properties of bioactive materials that are intended for application in bone tissue engineering. While there is some evidence about the impact of particles derived from orthopedic Cobalt-Chromium-Molybdenum (Co-Cr-Mo) alloys on cells, there is only limited data regarding the influence of the essential trace element Mo and its ions on the viability, osteogenic differentiation as well as on the formation and maturation of the primitive extracellular matrix (ECM) of primary human bone marrow-derived stromal cells (BMSCs) available so far.

METHODS

In this study, the influence of a wide range of molybdenum (VI) trioxide (MoO₃), concentrations on BMSC viability was evaluated via measurement of fluorescein diacetate metabolization. Thereafter, the impact of three non-cytotoxic concentrations of MoO₃ on the cellular osteogenic differentiation as well as on ECM formation and maturation of BMSCs was assessed.

RESULTS

MoO₃ had no negative influence on BMSC viability in most tested concentrations, as viability was in fact even enhanced. Only the highest concentration (10 mM) of MoO₃ showed cytotoxic effects. Cellular osteogenic differentiation, measured via the marker enzyme alkaline phosphatase was enhanced by the presence of MoO₃ in a concentration-dependent manner. Furthermore, MoO₃ showed a positive influence on the expression of relevant marker genes for osteogenic differentiation (osteopontin, osteocalcin and type I collagen alpha 1) and on the formation and maturation of the primitive ECM, as measured by collagen deposition and ECM calcification.

CONCLUSION

MoO₃ is considered as an attractive candidate for supplementation in biomaterials and qualifies for further research.

Comparing the Antimicrobial Effect of Silver Ion-Coated Silicone and Gentamicin-Irrigated Silicone Sheets from Breast Implant Material

BACKGROUND

Post-operative infection is a significant complication of breast implant surgery that may require extensive use of antibiotics and surgical interventions. Here, we developed a biomaterial coating that is chemically bonded to silicone implants which delivers antimicrobial ions over time.

METHODS

After coating the silicone implants with a "mediator" polymer (γ-PGA), the implants were impregnated with silver (Ag) ions. Antimicrobial effects of these implants were assayed with modified Kirby-Bauer disk diffusion method. The silicone disks were transferred to a plate with fresh bacteria. Control was intended to simulate an intra-operative wash.

RESULTS

The Ag-γ-PGA coated silicone demonstrated antimicrobial effects against the most common etiological agents of breast implant infections, including Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Klebsiella pneumoniae. There was no effect of inhibition of bacterial growth around the control silicone or the silicone coated only with γ-PGA. The zone of inhibition was generally larger around the Ag-γ-PGA coated silicone as compared to the silicone irrigated with gentamicin, and continued antibacterial effect was also observed at 48 hours in the Ag-γ-PGA coated silicone for all bacteria groups with the exception of P. aeruginosa. Gentamicin-irrigated silicone did not inhibit bacterial growth at 48 hours.

CONCLUSION

The observed antibacterial performance of the Ag-γ-PGA coating as compared to simulated intra-operative antibiotic wash is promising and should be further evaluated to develop the next generation of implants with diminished risk for post-operative implant infections.

Microbial Biofilm Decontamination on Dental Implant Surfaces: A Mini Review

Introduction

After insertion into the bone, implants osseointegrate, which is required for their long-term success. However, inflammation and infection around the implants may lead to implant failure leading to peri-implantitis and loss of supporting bone, which may eventually lead to failure of implant. Surface chemistry of the implant and lack of cleanliness on the part of the patient are related to peri-implantitis. The only way to get rid of this infection is decontamination of dental implants.

Objective

This systematic review intended to study decontamination of microbial biofilm methods on titanium implant surfaces used in dentistry.

Methods

The electronic databases Springer Link, Science Direct, and PubMed were explored from their inception until December 2020 to identify relevant studies. Studies included had to evaluate the efficiency of new strategies either to prevent formation of biofilm or to treat matured biofilm on dental implant surfaces.

Results and Discussion

In this systematic review, 17 different groups of decontamination methods were summarized from 116 studies. The decontamination methods included coating materials, mechanical cleaning, laser treatment, photodynamic therapy, air polishing, anodizing treatment, radiation, sonication, thermal treatment, ultrasound treatment, chemical treatment, electrochemical treatment, antimicrobial drugs, argon treatment, and probiotics.

Conclusion

The findings suggest that most of the decontamination methods were effective in preventing the formation of biofilm and in decontaminating established biofilm on dental implants. This narrative review provides a summary of methods for future research in the development of new dental implants and decontamination techniques.

Repeated exposure of nosocomial pathogens to silver does not select for silver resistance but does impact ciprofloxacin susceptibility

The rise of antimicrobial resistant bacteria coupled with a void in antibiotic development marks Antimicrobial Resistance as one of the biggest current threats to modern medicine. Antimicrobial metals are being developed and used as alternative anti-infectives, however, the existence of known resistance mechanisms and limited data regarding bacterial responses to long-term metal exposure are barriers to widespread implementation. In this study, a panel of reference and clinical strains of major nosocomial pathogens were subjected to serial dosage cycles of silver and ciprofloxacin. Populations exposed to silver initially showed no change in sensitivity, however, increasingly susceptibility was observed after the 25th cycle. A control experiment with ciprofloxacin revealed a selection for resistance over time, with silver treated bacteria showing faster adaptation. Morphological analysis revealed filamentation in Gram negative species suggesting membrane perturbation, while sequencing of isolated strains identified mutations in numerous genes. These included those encoding for efflux systems, chemosensory systems, stress responses, biofilm formation and respiratory chain processes, although no consistent locus was identified that correlated with silver sensitivity. These results suggest that de novo silver resistance is hard to select in a range of nosocomial pathogens, although silver exposure may detrimentally impact sensitivity to antibiotics in the long term. STATEMENT OF SIGNIFICANCE: The adaptability of microbial life continuously calls for the development of novel antibiotic molecules, however, the cost and risk associated with their discovery have led to a drying up in the pipeline, causing antimicrobial resistance (AMR) to be a major threat to healthcare. From all available strategies, antimicrobial metals and, more specifically, silver showcase large bactericidal spectrum and limited toxic effect which coupled with a large range of processes available for their delivery made these materials as a clear candidate to tackle AMR. Previous reports have shown the ability of this metal to enact a synergistic effect with other antimicrobial therapies, nevertheless, the discovery of Ag resistance mechanisms since the early 70s and limited knowledge on the long term influence of silver on AMR poses a threat to their applicability. The present study provides quantitative data on the influence of silver based therapies on AMR development for a panel of reference and clinical strains of major nosocomial pathogens, revealing that prolonged silver exposure may detrimentally impact sensitivity to antibiotics.

Aseptic and septic prosthetic joint loosening: Impact of biomaterial wear on immune cell function, inflammation, and infection

The success of total joint replacements has led to consistent growth in the use of arthroplasty in progressively younger patients. However, more than 10 percent of patients require revision surgeries due to implant failure caused by osteolytic loosening. These failures are classified as either aseptic or septic and are associated with the presence of particulate wear debris generated by mechanical action between implant components. Aseptic loosening results from chronic inflammation caused by activation of resident immune cells in contact with implant wear debris. In contrast, septic loosening is defined by the presence of chronic infection at the implant site. However, recent findings suggest that subclinical biofilms may be overlooked when evaluating the cause of implant failure, leading to a misdiagnosis of aseptic loosening. Many of the inflammatory pathways contributing to periprosthetic joint infections are also involved in bone remodeling and resorption. In particular, wear debris is increasingly implicated in the inhibition of the innate and adaptive immune response to resolve an infection or prevent hematogenous spread. This review examines the interconnectivity of wear particle- and infection-associated mechanisms of implant loosening, as well as biomaterials-based strategies to combat infection-related osteolysis.

Development of Chitosan-Based Surfaces to Prevent Single- and Dual-Species Biofilms of Staphylococcus aureus and Pseudomonas aeruginosa

Implantable medical devices (IMDs) are susceptible to microbial adhesion and biofilm formation, which lead to several clinical complications, including the occurrence of implant-associated infections. Polylactic acid (PLA) and its composites are currently used for the construction of IMDs. In addition, chitosan (CS) is a natural polymer that has been widely used in the medical field due to its antimicrobial and antibiofilm properties, which can be dependent on molecular weight (Mw). The present study aims to evaluate the performance of CS-based surfaces of different Mw to inhibit bacterial biofilm formation. For this purpose, CS-based surfaces were produced by dip-coating and the presence of CS and its derivatives onto PLA films, as well surface homogeneity were confirmed by contact angle measurements, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The antimicrobial activity of the functionalized surfaces was evaluated against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. Chitosan-based surfaces were able to inhibit the development of single- and dual-species biofilms by reducing the number of total, viable, culturable, and viable but nonculturable cells up to 79%, 90%, 81%, and 96%, respectively, being their activity dependent on chitosan Mw. The effect of CS-based surfaces on the inhibition of biofilm formation was corroborated by biofilm structure analysis using confocal laser scanning microscopy (CLSM), which revealed a decrease in the biovolume and thickness of the biofilm formed on CS-based surfaces compared to PLA. Overall, these results support the potential of low Mw CS for coating polymeric devices such as IMDs where the two bacteria tested are common colonizers and reduce their biofilm formation.

Can Copper Products and Surfaces Reduce the Spread of Infectious Microorganisms and Hospital-Acquired Infections?

Pathogen transfer and infection in the built environment are globally significant events, leading to the spread of disease and an increase in subsequent morbidity and mortality rates. There are numerous strategies followed in healthcare facilities to minimize pathogen transfer, but complete infection control has not, as yet, been achieved. However, based on traditional use in many cultures, the introduction of copper products and surfaces to significantly and positively retard pathogen transmission invites further investigation. For example, many microbes are rendered unviable upon contact exposure to copper or copper alloys, either immediately or within a short time. In addition, many disease-causing bacteria such as E. coli O157:H7, hospital superbugs, and several viruses (including SARS-CoV-2) are also susceptible to exposure to copper surfaces. It is thus suggested that replacing common touch surfaces in healthcare facilities, food industries, and public places (including public transport) with copper or alloys of copper may substantially contribute to limiting transmission. Subsequent hospital admissions and mortality rates will consequently be lowered, with a concomitant saving of lives and considerable levels of resources. This consideration is very significant in times of the COVID-19 pandemic and the upcoming epidemics, as it is becoming clear that all forms of possible infection control measures should be practiced in order to protect community well-being and promote healthy outcomes.

An Improved 2-Aminoimidazole Based Anti-Biofilm Coating for Orthopedic Implants: Activity, Stability, and in vivo Biocompatibility

Orthopedic device-related infections remain a serious challenge to treat. Central to these infections are bacterial biofilms that form on the orthopedic implant itself. These biofilms shield the bacteria from the host immune system and most common antibiotic drugs, which renders them essentially antibiotic-tolerant. There is an urgent clinical need for novel strategies to prevent these serious infections that do not involve conventional antibiotics. Recently, a novel antibiofilm coating for titanium surfaces was developed based on 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine as an active biofilm inhibitor. In the current study we present an optimized coating protocol that allowed for a 5-fold higher load of this active compound, whilst shortening the manufacturing process. When applied to titanium disks, the newly optimized coating was resilient to the most common sterilization procedures and it induced a 1 log reduction in biofilm cells of a clinical Staphylococcus aureus isolate (JAR060131) in vitro, without affecting the planktonic phase. Moreover, the antibiofilm effect of the coating in combination with the antibiotic cefuroxime was higher than cefuroxime treatment alone. Furthermore, the coating was successfully applied to a human-scale fracture fixation device resulting in a loading that was comparable to the titanium disk model. Finally, an in vivo biocompatibility and healing study in a rabbit osteotomy model indicated that these coated implants did not negatively affect fracture healing or osteointegration. These findings put our technology one step closer to clinical trials, confirming its potential in fighting orthopedic infections without compromising healing.

The selective cytotoxicity of silver thiosulfate, a silver complex, on MCF-7 breast cancer cells through ROS-induced cell death

BACKGROUND

Silver is a transition metal that is known to be less toxic than platinum. However, only few studies have reported the anticancer effects of some silver complexes and their possibility as an alternative to platinum complex. This study investigated the anticancer effects of the silver thiosulfate complex (STS), [Ag(S₂O₃)₂]^3-, consisting of silver and sodium thiosulfate.

METHODS

In vitro cytotoxic activity of STS was investigated comparatively in human cancer cell lines (K562 and MCF-7) and normal human cells (mesenchymal stem cells and mammary epithelial cells). For its anticancer effects, cell cycle, mode of cell death, morphological changes, and accumulation of intracellular ROS and GSH were evaluated in MCF-7 to provide mechanistic insights.

RESULTS

STS showed a concentration-dependent cytotoxicity in MCF-7 cell, which was abolished by pretreatment with N-acetylcysteine, suggesting ROS accumulation by STS. Moreover, STS caused cell cycle arrest at the G1 phase, decrease in the GSH levels, and morphological changes in MCF-7. Direct measurement of ROS demonstrated the elevation of intracellular ROS accumulation in cancer cells treated with STS; however, neither cytotoxicity nor ROS accumulation was observed in normal human cells.

CONCLUSION

The results obtained here are the first evidence to show that STS exhibited an anticancer activity through ROS-induced mechanisms, and that its cytotoxicity is highly selective to cancer cells. The results of the present study warrant further investigation on the detailed mechanism of STS actions, as well as its in vivo effectiveness and safety for clinical application.

Antimicrobial stewardship of antiseptics that are pertinent to wounds: the need for a united approach

Long before the nature of infection was recognized, or the significance of biofilms in delayed healing was understood, antimicrobial agents were being used in wound care. In the last 70 years, antibiotics have provided an effective means to control wound infection, but the continued emergence of antibiotic-resistant strains and the documented antibiotic tolerance of biofilms has reduced their effectiveness. A range of wound dressings containing an antimicrobial (antibiotic or non-antibiotic compound) has been developed. Whereas standardized methods for determining the efficacy of non-antibiotic antimicrobials in bacterial suspension tests were developed in the early twentieth century, standardized ways of evaluating the efficacy of antimicrobial dressings against microbial suspensions and biofilms are not available. Resistance to non-antibiotic antimicrobials and cross-resistance with antibiotics has been reported, but consensus on breakpoints is absent and surveillance is impossible. Antimicrobial stewardship is therefore in jeopardy. This review highlights these difficulties and in particular the efficacy of current non-antibiotic antimicrobials used in dressings, their efficacy, and the challenges of translating in vitro efficacy data to the efficacy of dressings in patients. This review calls for a unified approach to developing standardized methods of evaluating antimicrobial dressings that will provide an improved basis for practitioners to make informed choices in wound care.

Antibacterial hydrogel coating in joint mega-prosthesis: results of a comparative series

PURPOSE

Joint mega-prosthesis after bone tumors, severe trauma or infection is associated with high rates of post-surgical septic complications. A fast-resorbable antibacterial hydrogel coating (DAC®, Defensive Antibacterial Coating) has previously been shown to be able to significantly reduce surgical site infection in various clinical settings. Aim of the present study was to evaluate the safety and efficacy of the DAC hydrogel coating to prevent early periprosthetic joint infection after joint mega-prosthesis.

METHODS

In this three-centers, case-control study, 43 patients, treated with an antibacterial hydrogel coated mega-prosthesis for oncological (N = 39) or non-oncological conditions (N = 4), were retrospectively compared with 43 matched controls, treated with mega-implants without the coating. Clinical, laboratory and radiographic examinations were performed to evaluate the occurrence of post-surgical infection, complications and adverse events.

RESULTS

At a mean follow-up of 2 years, no evidence of infection or adverse events were observed in the DAC-treated group, compared to six cases of post-surgical infection in the control group.

CONCLUSION

This matched case-control study shows that a fast-resorbable, antibiotic-loaded coating can be safely used to protect joint mega-prosthesis, providing a reduction of early surgical site infections with no side effects. Larger prospective trials with longer follow-ups are warranted to confirm this report.

TRIAL REGISTRATION

RS1229/19 (Regina Elena National Cancer Institute Experimental Registry Number).

Adjuvant antibiotic-loaded bone cement: Concerns with current use and research to make it work

Antibiotic-loaded bone cement (ALBC) is broadly used to treat orthopaedic infections based on the rationale that high-dose local delivery is essential to eradicate biofilm-associated bacteria. However, ALBC formulations are empirically based on drug susceptibility from routine laboratory testing, which is known to have limited clinical relevance for biofilms. There are also dosing concerns with nonstandardized, surgeon-directed, hand-mixed formulations, which have unknown release kinetics. On the basis of our knowledge of in vivo biofilms, pathogen virulence, safety issues with nonstandardized ALBC formulations, and questions about the cost-effectiveness of ALBC, there is a need to evaluate the evidence for this clinical practice. To this end, thought leaders in the field of musculoskeletal infection (MSKI) met on 1 August 2019 to review and debate published and anecdotal information, which highlighted four major concerns about current ALBC use: (a) substantial lack of level 1 evidence to demonstrate efficacy; (b) ALBC formulations become subtherapeutic following early release, which risks induction of antibiotic resistance, and exacerbated infection from microbial colonization of the carrier; (c) the absence of standardized formulation protocols, and Food and Drug Administration-approved high-dose ALBC products to use following resection in MSKI treatment; and (d) absence of a validated assay to determine the minimum biofilm eradication concentration to predict ALBC efficacy against patient specific micro-organisms. Here, we describe these concerns in detail, and propose areas in need of research.

Implant-Associated Infections: A Review of the Safety of Cardiac Implants

Cardiac implantations are among the most critical, and life-saving patient management procedures. Most cardiac implantations are performed to correct abnormalities in the conduction and the rhythm of the heart. Because the implants are intended for long-term use ranging from months to years, the failure of an implant is considered a major setback both in the patients as well as surgeons' perspectives. Implant failures can have multifactorial reasons, amongst which infectious causes need to be adequately addressed. This review attempts to evaluate the nature of implants, etiology, predisposing factors, infection control, and preventive strategies for cardiac implant-associated infections.

Biomedical nanomaterials: applications, toxicological concerns, and regulatory needs

Advances in cutting-edge technologies such as nano- and biotechnology have created an opportunity for re-engineering existing materials and generating new nano-scale products that can function beyond the limits of conventional ones. While the step change in the properties and functionalities of these new materials opens up new possibilities for a broad range of applications, it also calls for structural modifications to existing safety assessment processes that are primarily focused on bulk material properties. Decades after the need to modify existing risk management practices to include nano-specific behaviors and exposure pathways was recognized, relevant policies for evaluating, and controlling health risks of nano-enabled materials is still lacking. This review provides an overview of current progress in the field of nanobiotechnology rather than intentions and aspirations, summarizes long-recognized but still unresolved issues surrounding materials safety at the nanoscale, and discusses key barriers preventing generation and integration of reliable data in bio/nano-safety domain. Particular attention is given to nanostructured materials that are commonly used in biomedical applications.

Biofunctional Elements Incorporated Nano/Microstructured Coatings on Titanium Implants with Enhanced Osteogenic and Antibacterial Performance

Bone fracture is prevalent among athletes and senior citizens and may require surgical insertion of bone implants. Titanium (Ti) and its alloys are widely used in orthopedics due to its high corrosion resistance, good biocompatibility, and modulus compatible with natural bone tissues. However, bone repair and regrowth are impeded by the insufficient intrinsic osteogenetic capability of Ti and Ti alloys and potential bacterial infection. The physicochemical properties of the materials and nano/microstructures on the implant surface are crucial for clinical success and loading with biofunctional elements such as Sr, Zn, Cu, Si, and Ag into nano/microstructured TiO2 coating has been demonstrated to enhance bone repair/regeneration and bacterial resistance of Ti implants. In this review, recent advances in biofunctional element-incorporated nano/microstructured coatings on Ti and Ti alloy implants are described and the prospects and limitations are discussed.

Identification of mesenchymal stromal cell survival responses to antimicrobial silver ion concentrations released from orthopaedic implants

Antimicrobial silver (Ag⁺) coatings on orthopaedic implants may reduce infection rates, but should not be to the detriment of regenerative cell populations, primarily mesenchymal stem/stromal cells (MSCs). We determined intramedullary silver release profiles in vivo, which were used to test relevant Ag⁺ concentrations on MSC function in vitro. We measured a rapid elution of Ag⁺ from intramedullary pins in a rat femoral implantation model, delivering a maximum potential concentration of 7.8 µM, which was below toxic levels determined for MSCs in vitro (EC₅₀, 33 µM). Additionally, we present in vitro data of the reduced colonisation of implants by Staphylococcus aureus. MSCs exposed to Ag⁺ prior to/during osteogenic differentiation were not statistically affected. Notably, at clonal density, the colony-forming capacity of MSCs was significantly reduced in the presence of 10 µM Ag⁺, suggesting that a subpopulation of clonal MSCs was sensitive to Ag⁺ exposure. At a molecular level, surviving colony-forming MSCs treated with Ag⁺ demonstrated a significant upregulation of components of the peroxiredoxin/thioredoxin pathway and processes involved in glutathione metabolism compared to untreated controls. Inhibition of glutathione synthesis using l-buthionine sulfoxamine eliminated MSC clonogenicity in the presence of Ag⁺, which was rescued by exogenous glutathione.

Protecting the skin-implant interface with transcutaneous silver-coated skin-and-bone-integrated pylon in pig and rabbit dorsum models

Implant-associated soft tissue infections at the skin-implant interface represent the most frequent complications in reconstructive surgery and lead to implant failures and revisions. Titanium implants with deep porosity, called skin-and-bone-integrated-pylons (SBIP), allow for skin ingrowth in the morphologically natural direction, thus restoring a reliable dermal barrier and reducing the risk of infection. Silver coating of the SBIP implant surface using physical vapor deposition technique offers the possibility of preventing biofilm formation and exerting a direct antimicrobial effect during the wound healing phase. In vivo studies employing pig and rabbit dorsum models for assessment of skin ingrowth into the pores of the pylon demonstrated the safety of transcutaneous implantation of the SBIP system. No postoperative complications were reported at the end of the follow-up period of 6 months. Histological analysis proved skin ingrowth in the minipig model without signs of silver toxicity. Analysis of silver release (using energy dispersive X-ray spectroscopy) in the model of intramedullary-inserted silver-coated SBIP in New Zealand rabbits demonstrated trace amounts of silver after 3 months of in-bone implantation. In conclusion, selected temporary silver coating of the SBIP implant surface is powerful at preventing the periprosthetic infections without imparing skin ingrowth and can be considered for clinical application.

Long acting anti-infection constructs on titanium

Peri-prosthetic joint infections (PJI) are a serious adverse event following joint replacement surgeries; antibiotics are usually added to bone cement to prevent infection offset. For uncemented prosthesis, alternative antimicrobial approaches are necessary in order to prevent PJI; however, despite elution of drug from the surface of the device being shown one of the most promising approach, no effective antimicrobial eluting uncemented device is currently available on the market. Consequently, there is a clinical need for non-antibiotic antimicrobial uncemented prosthesis as these devices present numerous benefits, particularly for young patients, over cemented artificial joints. Moreover, non-antibiotic approaches are driven by the need to address the growing threat posed by antibiotic resistance. We developed a multilayers functional coating on titanium surfaces releasing chlorhexidine, a well-known antimicrobial agent used in mouthwash products and antiseptic creams, embedding the drug between alginate and poly-beta-amino-esters. Chlorhexidine release was sustained for almost 2 months and the material efficacy and safety was proven both in vitro and in vivo. The coatings did not negatively impact osteoblast and fibroblast cells growth and were capable of reducing bacterial load and accelerating wound healing in an excisional wound model. As PJI can develop weeks and months after the initial surgery, these materials could provide a viable solution to prevent infections after arthroplasty in uncemented prosthetic devices and, simultaneously, help the fight against antibiotic resistance.

Antimicrobial Copper-Based Materials and Coatings: Potential Multifaceted Biomedical Applications

Surface contamination by microbes leads to several detrimental consequences like hospital- and device-associated infections. One measure to inhibit surface contamination is to confer the surfaces with antimicrobial properties. Copper's antimicrobial properties have been known since ancient times, and the recent resurgence in exploiting copper for application as antimicrobial materials or coatings is motivated by the growing concern about antibiotic resistance and the pressure to reduce antibiotic use. Copper, unlike silver, demonstrates rapid and high microbicidal efficacy against pathogens that are in close contact under ambient indoor conditions, which enhances its range of applicability. This review highlights the mechanisms behind copper's potent antimicrobial property, the design and fabrication of different copper-based antimicrobial materials and coatings comprising metallic copper/copper alloys, copper nanoparticles or ions, and their potential for practical applications. Finally, as the antimicrobial coatings market is expected to grow, we offer our perspectives on the implications of increased copper release into the environment and the potential ecotoxicity effects and possibility of development of resistant genes in pathogens.

Silver-Containing Titanium Dioxide Nanocapsules for Combating Multidrug-Resistant Bacteria

BACKGROUND

Joint arthroplasty has improved the quality of life of patients worldwide, but infections of the prosthesis are frequent and cause significant morbidity. Antimicrobial coatings for implants promise to prevent these infections.

METHODS

We have synthesized nanocapsules of titanium dioxide in amorphous or anatase form containing silver as antibacterial agent and tested their impact on bacterial growth. Furthermore, we explored the possible effect of the nanocapsules on the immune system. First, we studied their uptake into macrophages using a combination of electron microscopy and energy-dispersive spectroscopy. Second, we exposed immune cells to the nanocapsules and checked their activation state by flow cytometry and enzyme-linked immunosorbent assay.

RESULTS

Silver-containing titanium dioxide nanocapsules show strong antimicrobial activity against both E. coli and S. aureus and even against a multidrug-resistant strain of S. aureus. We could demonstrate the presence of the nanocapsules in macrophages, but, importantly, the nanocapsules did not affect cell viability and did not activate proinflammatory responses at doses up to 20 μg/mL.

CONCLUSION

Our bactericidal silver-containing titanium dioxide nanocapsules fulfill important prerequisites for biomedical use and represent a promising material for the coating of artificial implants.

Biomaterials for orthopedics: anti-biofilm activity of a new bioactive glass coating on titanium implants

This study evaluated adhesion and biofilm formation by Candida albicans, Pseudomonas aeruginosa and Staphylococcus epidermidis on surfaces of titanium (Ti) and titanium coated with F18 Bioactive Glass (BGF18). Biofilms were grown and the areas coated with biofilm were determined after 2, 4 and 8 h. Microscopy techniques were applied in order to visualize the structure of the mature biofilm and the extracellular matrix. On the BGF18 specimens, there was less biofilm formation by C. albicans and S. epidermidis after incubation for 8 h. For P. aeruginosa biofilm, a reduction was observed after incubation for 4 h, and it remained reduced after 8 h on BGF18 specimens. All biofilm matrices seemed to be thicker on BGF18 surface than on titanium surfaces. BGF18 showed significant anti-biofilm activity in comparison with Ti in the initial periods of biofilm formation; however, there was extensive biofilm after incubation for 48 h.

Enhanced antibacterial performance of ultrathin silver/platinum nanopatches by a sacrificial anode mechanism

The development of antibacterial implant surfaces is a challenging task in biomaterial research. We fabricated a highly antibacterial bimetallic platinum (Pt)/silver(Ag) nanopatch surface by short time sputtering of Pt and Ag on titanium. The sputter process led to a patch-like distribution with crystalline areas in the nanometer-size range (1.3-3.9 nm thickness, 3-60 nm extension). Structural analyses of Pt/Ag samples showed Ag- and Pt-rich areas containing nanoparticle-like Pt deposits of 1-2 nm. The adhesion and proliferation properties of S. aureus on the nanopatch samples were analyzed. Consecutively sputtered Ag/Pt nanopatches (Pt followed by Ag) induced enhanced antimicrobial activity compared to co-sputtered Pt/Ag samples or pure Ag patches of similar Ag amounts. The underlying sacrificial anode mechanism was proved by linear sweep voltammetry. The advantages of this nanopatch coating are the enhanced antimicrobial activity despite a reduced total amount of Ag/Pt and a self-limited effect due the rapid Ag dissolution.