Biomaterial-associated infection: locating the finish line in the race for the surface

Charge-Switchable Polymeric Coating Kills Bacteria and Prevents Biofilm Formation in Vivo

Preventing bacterial biofilm formation on medical devices and implants in vivo still remains a daunting task. Current antibacterial coatings to combat implant-associated infections are generally composed of toxic metals or nondegradable polymers and involve multistep surface modifications. Here, we present a charge-switchable antibacterial and antibiofilm coating based on water-insoluble cationic hydrophobic polymers that are soluble in organic solvents and can be noncovalently coated onto different surfaces. Toward this, a library of quaternary polyethylenimine (QPEI) polymers with an amide or ester group in their pendant alkyl chain was developed. These QPEIs are shown to hydrolyze from active cationic to nontoxic zwitterionic polymers under acidic or enzymatic conditions. Notably, polymers with both zwitterionic and cationic groups, obtained upon partial hydrolysis of QPEIs, are shown to retain their antibacterial activity with much lower toxicity toward mammalian cells. Furthermore, the zwitterionic polymer, a fully hydrolyzed product of the QPEIs, is shown to be nontoxic to mammalian cells in vitro as well as in vivo. The QPEIs, when coated onto surfaces, kill bacteria and prevent formation of biofilms. In an in vivo mice model, the QPEI-coated medical grade catheter is shown to reduce methicillin-resistant Staphylococcus aureus contamination both on the catheter surface and in the adjacent tissues (99.99% reduction compared to a noncoated catheter). Additionally, biofilm formation is inhibited on the catheter surface with negligible inflammation in the adjacent tissue. The above results thus highlight the importance of these polymers to be used as effective antibacterial coatings in biomedical applications.

Enantiomeric glycosylated cationic block co-beta-peptides eradicate Staphylococcus aureus biofilms and antibiotic-tolerant persisters

The treatment of bacterial infections is hindered by the presence of biofilms and metabolically inactive persisters. Here, we report the synthesis of an enantiomeric block co-beta-peptide, poly(amido-D-glucose)-block-poly(beta-L-lysine), with high yield and purity by one-shot one-pot anionic-ring opening (co)polymerization. The co-beta-peptide is bactericidal against methicillin-resistant Staphylococcus aureus (MRSA), including replicating, biofilm and persister bacterial cells, and also disperses biofilm biomass. It is active towards community-acquired and hospital-associated MRSA strains which are resistant to multiple drugs including vancomycin and daptomycin. Its antibacterial activity is superior to that of vancomycin in MRSA mouse and human ex vivo skin infection models, with no acute in vivo toxicity in repeated dosing in mice at above therapeutic levels. The copolymer displays bacteria-activated surfactant-like properties, resulting from contact with the bacterial envelope. Our results indicate that this class of non-toxic molecule, effective against different bacterial sub-populations, has promising potential for the treatment of S. aureus infections.

The authors report the synthesis of an enantiomeric block co-beta-peptide that kills methicillin-resistant Staphylococcus aureus, including biofilm and persister bacterial cells, and disperses biofilms. The copolymer displays antibacterial activity in human ex vivo and mouse in vivo infection models without toxicity.

Enzyme responsive titanium substrates with antibacterial property and osteo/angio-genic differentiation potentials

After implantation into a host, titanium (Ti) orthopaedic materials are facing two major clinical challenges: bacterial infection and aseptic loosening, which directly determine the long-term survival of the implant. To endow Ti implant with self-defensive antibacterial properties and desirable osteo/angio-genic differentiation potentials, hyaluronic acid (HA)-gentamicin (Gen) conjugates (HA-Gen) and chitosan (Chi) polyelectrolyte multilayers were constructed on deferoxamine (DFO) loaded titania nanotubes (TNT) substrates via layer-by-layer (LBL) assembly technique, termed as TNT/DFO/HA-Gen. The HA-Gen conjugate was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR). The physicochemical properties of the substrates were characterized by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The on-demand DFO release was associated with the degradation of multilayers triggered by exogenous hyaluronidase, which indicated enzymatic and bacterial responsiveness. The TNT/DFO/HA-Gen substrates displayed effective antifouling and antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), while were favourable for the adhesion, proliferation and osteo/angio-genic differentiation of mesenchymal stem cells (MSCs). The multifaceted drug-device combination (DDC) strategy showed potential applications in orthopaedic fields.

Protein adsorption dynamics to polymer surfaces revisited-A multisystems approach

Performance and safety of materials in contact with living matter are determined by sequential and competitive protein adsorption. However, cause and consequences of these processes remain hard to be generalized and predicted. In a new attempt to address that challenge, the authors compared and analyzed the protein adsorption and displacement on various thoroughly characterized polymer substrates using a combination of surface-sensitive techniques. A multiple linear regression approach was applied to model the dependence of protein adsorption, desorption, and exchange dynamics on protein and surface characteristics. While the analysis confirmed that protein properties primarily govern the observed adsorption and retention phenomena and hydrophobicity as well as surface charge are the most relevant polymer surface properties, the authors have identified several protein-surface combinations that deviate from these patterns and deserve further investigation.

Keratinocytes protect soft-tissue integration of dental implant materials against bacterial challenges in a 3D-tissue infection model

The soft-tissue seal around dental implants protects the osseo-integrated screw against bacterial challenges. Surface properties of the implant material are crucial for implant survival against bacterial challenges, but there is no adequate in vitro model mimicking the soft-tissue seal around dental implants. Here, we set up a 3D-tissue model of the soft-tissue seal, in order to establish the roles of oral keratinocytes, gingival fibroblasts and materials surface properties in the protective seal. To this end, keratinocytes were grown on membrane filters in a transwell system, while fibroblasts were adhering to TiO₂ surfaces underneath the membrane. In absence of keratinocytes on the membrane, fibroblasts growing on the TiO₂ surface could not withstand challenges by commensal streptococci or pathogenic staphylococci. Keratinocytes growing on the membrane filters could withstand bacterial challenges, but tight junctions widened to allow invasion of bacteria to the underlying fibroblast layer in lower numbers than in absence of keratinocytes. The challenge of this bacterial invasion to the fibroblast layer on the TiO₂ surface negatively affected tissue integration of the surface, demonstrating the protective barrier role of keratinocytes. Streptococci caused less damage to fibroblasts than staphylococci. Importantly, the protection offered by the soft-tissue seal appeared sensitive to surface properties of the implant material. Integration by fibroblasts of a hydrophobic silicone rubber surface was affected more upon bacterial challenges than integration of more hydrophilic hydroxyapatite or TiO₂ surfaces. This differential response to different surface-chemistries makes the 3D-tissue infection model presented a useful tool in the development of new infection-resistant dental implant materials. STATEMENT OF SIGNIFICANCE: Failure rates of dental implants due to infection are surprisingly low, considering their functioning in the highly un-sterile oral cavity. This is attributed to the soft-tissue seal, protecting the osseo-integrated implant part against bacterial invasion. The seal consists of a layer of keratinocytes covering gingival fibroblasts, integrating the implant. Implant failure involves high patient discomfort and costs of replacing an infected implant, which necessitates development of improved, infection-resistant dental implant materials. New materials are often evaluated in mono-culture, examining bacterial adhesion or tissue interactions separately and neglecting the 3D-structure of the tissue seal. A 3D-tissue model allows to study new materials in a more relevant way, in which interactions between keratinocytes, gingival fibroblast, bacteria and materials surfaces are accounted for.

Preparation and characterization of a gallium-loaded antimicrobial artificial dermal scaffold

Artificial dermal scaffolds, which are made of natural or synthetic materials, can improve new blood vessel formation, cell migration and cell proliferation after being implanted into wounds, and they degrade slowly, playing an important role in dermal reconstruction and scar inhibition, finally achieving the goal of wound healing and functional reconstruction. Although these scaffolds have been widely used in clinical applications, biomaterial-associated infection is a deficiency or even a life-threatening problem that must be addressed, as it greatly affects the survival of the scaffolds. The gallium ion (Ga³⁺) is a novel metallic antimicrobial whose broad-spectrum antimicrobial properties against most bacteria encountered in burn wound infections have been confirmed, and it has been proposed as a promising candidate to prevent implant-associated infections. In this study, a gallium-loaded antimicrobial artificial dermal scaffold was successfully prepared by gallium ions and a collagen solution. The characterization results showed a porous structure with pore sizes ranging from 50 to 150 μm and a large porosity value of 97.4%. The enzymatic degradation rate in vitro was 19 and 28% after 12 and 24 h, respectively. In vitro antimicrobial testing revealed that the 1 h antibacterial rate against Staphylococcus aureus and Pseudomonas aeruginosa was close to 90%, which indicated its great antimicrobial activity. The results of the cytological evaluation showed slight effect on cell proliferation, with a relative growth rate (RGR) value of 80% and great cytocompatibility with cultured cells according to laser scanning confocal microscopy (LSCM) and scanning electron microscope (SEM). Furthermore, the successful prevention of wound infections in SD rats was confirmed with an in vivo antimicrobial evaluation, and the artificial dermal scaffolds also demonstrated great biocompatibility. This gallium-loaded antimicrobial artificial dermal scaffold exerted excellent antimicrobial activity and great biosafety, warranting further research for future clinical applications.

The Role of Orientation of Surface Bound Dihydropyrrol-2-ones (DHP) on Biological Activity

Quorum sensing (QS) signaling system is important for bacterial growth, adhesion, and biofilm formation resulting in numerous infectious diseases. Dihydropyrrol-2-ones (DHPs) represent a novel class of antimicrobial agents that inhibit QS, and are less prone to develop bacterial resistance due to their non-growth inhibition mechanism of action which does not cause survival pressure on bacteria. DHPs can prevent bacterial colonization and quorum sensing when covalently bound to substrates. In this study, the role of orientation of DHP compounds was investigated after covalent attachment by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) coupling reaction to amine-functionalized glass surfaces via various positions of the DHP scaffold. The functionalized glass surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements and tested for their in vitro biological activity against S. aureus and P. aeruginosa. DHPs attached via the N-1 position resulted in the highest antibacterial activities against S. aureus, while no difference was observed for DHPs attached either via the N-1 position or the C-4 phenyl ring against P. aeruginosa.

Chronic Implant-Related Bone Infections-Can Immune Modulation be a Therapeutic Strategy?

Chronic implant-related bone infections are a major problem in orthopedic and trauma-related surgery with severe consequences for the affected patients. As antibiotic resistance increases in general and because most antibiotics have poor effectiveness against biofilm-embedded bacteria in particular, there is a need for alternative and innovative treatment approaches. Recently, the immune system has moved into focus as the key player in infection defense and bone homeostasis, and the targeted modulation of the host response is becoming an emerging field of interest. The aim of this review was to summarize the current knowledge of impaired endogenous defense mechanisms that are unable to prevent chronicity of bone infections associated with a prosthetic or osteosynthetic device. The presence of foreign material adversely affects the immune system by generating a local immune-compromised environment where spontaneous clearance of planktonic bacteria does not take place. Furthermore, the surface structure of the implant facilitates the transition of bacteria from the planktonic to the biofilm stage. Biofilm formation on the implant surface is closely linked to the development of a chronic infection, and a misled adaption of the immune system makes it impossible to effectively eliminate biofilm infections. The interaction between the immune system and bone cells, especially osteoclasts, is extensively studied in the field of osteoimmunology and this crosstalk further aggravates the course of bone infection by shifting bone homeostasis in favor of bone resorption. T cells play a major role in various chronic diseases and in this review a special focus was therefore set on what is known about an ineffective T cell response. Myeloid-derived suppressor cells (MDSCs), anti-inflammatory macrophages, regulatory T cells (T_regs) as well as osteoclasts all suppress immune defense mechanisms and negatively regulate T cell-mediated immunity. Thus, these cells are considered to be potential targets for immune therapy. The success of immune checkpoint inhibition in cancer treatment encourages the transfer of such immunological approaches into treatment strategies of other chronic diseases. Here, we discuss whether immune modulation can be a therapeutic tool for the treatment of chronic implant-related bone infections.

Bioactive Silk Coatings Reduce the Adhesion of Staphylococcus aureus while Supporting Growth of Osteoblast-like Cells

Orthopedic and dental implants are associated with a substantial risk of failure due to biomaterial-associated infections and poor osseointegration. To prevent such outcomes, a coating can be applied on the implant to ideally both reduce the risk of bacterial adhesion and support establishment of osteoblasts. We present a strategy to construct dual-functional silk coatings with such properties. Silk coatings were made from a recombinant partial spider silk protein either alone (silk_wt) or fused with a cell-binding motif derived from fibronectin (FN-silk). The biofilm-dispersal enzyme Dispersin B (DspB) and two peptidoglycan degrading endolysins, PlySs2 and SAL-1, were produced recombinantly. A sortase recognition tag (SrtTag) was included to allow site-specific conjugation of each enzyme onto silk_wt and FN-silk coatings using an engineered variant of the transpeptidase Sortase A (SrtA*). To evaluate bacterial adhesion on the samples, Staphylococcus aureus was incubated on the coatings and subsequently subjected to live/dead staining. Fluorescence microscopy revealed a reduced number of bacteria on all silk coatings containing enzymes. Moreover, the bacteria were mobile to a higher degree, indicating a negative influence on the bacterial adhesion. The capability to support mammalian cell interactions was assessed by cultivation of the osteosarcoma cell line U-2 OS on dual-functional surfaces, prepared by conjugating the enzymes onto FN-silk coatings. U-2 OS cells could adhere to silk coatings with enzymes and showed high spreading and viability, demonstrating good cell compatibility.

Implantable antimicrobial biomaterials for local drug delivery in bone infection models

Increased use of implantable biomedical devices demonstrates their potential in treating a wide variety of ailments and disorders in bone trauma and orthopaedic, reconstructive, and craniofacial applications. However, the number of cases involving implant failure or malfunction due to bacterial infection have also increased in recent years. Implanted devices can facilitate the growth of bacteria as these micro-organisms have the potential to adhere to the implant and grow and develop to form biofilms. In an effort to better understand and mitigate these occurrences, biomaterials containing antimicrobial agents that can be released or presented within the local microenvironment have become an important area of research. In this review, we discuss critical factors that regulate antimicrobial therapy to sites of bone infection, such as key biomolecular considerations and platforms for delivery, as well as current in vivo models and current advances in the field. STATEMENT OF SIGNIFICANCE: This review outlines the important factors that are taken into consideration for the development of biomaterials for local delivery of therapeutics to the site of bone infections. An overview of important criteria for development of this model (such as type of bone defect, antimicrobial therapeutic, and delivery vehicle) are provided, along with current research that utilizes these considerations. Additionally, this review highlights recent clinical trials that have utilized antimicrobial therapeutics for treatment of osteomyelitis.

In Vitro Performance of Bioinspired Phenolic Nanocoatings for Endosseous Implant Applications

In the quest for finding new strategies to enhance tissue integration and to reduce the risk of bacterial colonization around endosseous implants, we report the application of auto-oxidative phenolic coatings made of tannic acid and pyrogallol to titanium surfaces. The functionalized surfaces were screened for their biological performance using cultures of primary human osteoblasts and biofilm-forming bioluminescent staphylococci S. epidermidis Xen43 and S. aureus Xen29. No toxic effect of the coatings on osteoblasts was detected. While tannic acid coatings seemed to induce a delay in osteoblast maturation, they revealed anti-inflammatory potential. Similar effects were observed for pyrogallol coatings deposited for 24 h. Thin pyrogallol coatings deposited for 2 h seemed to promote osteoblast maturation and revealed increased calcium deposition. The effects on osteoblast were found to be related to the release of phenolic compounds from the surfaces. While the phenolic coatings could not inhibit staphylococcal biofilm formation on the titanium surfaces, released phenolic compounds had an inhibitory effect the growth of planktonic bacteria. In conclusion, the assessed coating systems represent a versatile functionalization method which exhibit promising effects for endosseous implant applications.

Drug-loaded/grafted peptide-modified porous PEEK to promote bone tissue repair and eliminate bacteria

Bone restoration and related infection in bone defect repair remain thorny problems in clinical practice. Herein, a drug-loaded (chlorogenic acid, CGA)/grafted peptide (BFP) hydrogel system supported on a sulfonated polyetheretherketone (SPEEK) surface is constructed to address the problem of large-scale defects and related infections in clinical bone implantation. Briefly, the encapsulated chlorogenic acid is released during hydrogel degradation and can inhibit the growth of bacteria and provide a bacteria-free environment for new bone formation. In vitro experiments and cell adhesion/proliferation evaluation reveal that the chlorogenic acid-sodium alginate-peptide bridging system shows better bioaffinity than the control groups due to the BFP peptide on the surface of the hydrogel. In addition, bacterial experiments suggest that the released chlorogenic acid has excellent antibacterial activity against gram-negative and gram-positive bacteria. Therefore, the hydrogel bridging system has a prospective application in clinical applications for bone repair.

Design of an Antifungal Surface Embedding Liposomal Amphotericin B Through a Mussel Adhesive-Inspired Coating Strategy

Microbial colonization of urinary catheters remains a serious problem for medicine as it often leads to biofilm formation and infection. Among the approaches reported to deal with this problem, surfaces functionalization to render them with antimicrobial characteristics, comprises the most promising one. Most of these strategies, however, are designed to target bacterial biofilms, while fungal biofilms are much less taken into account. In real-life settings, fungi will be inevitably found in consortium with bacteria, especially in the field of biomaterials. The development of antifungal coating strategies to be combined with antibacterial approaches will be pivotal for the fight of biomaterial-associated infections. The main goal of the present study was, therefore, to engineer an effective strategy for the immobilization of liposomal amphotericin B (LAmB) on polydimethylsiloxane (PDMS) surfaces to prevent Candida albicans colonization. Immobilization was performed using a two-step mussel-inspired coating strategy, in which PDMS is first immersed in dopamine solution. Its polymerization results in the deposition of a thin adherent film, called polydopamine (pDA), which allowed the incorporation of LAmB, afterwards. Different concentrations of LAmB were screened in order to obtain a contact-killing surface with no release of LAmB. Surface characterization confirmed the polymerization of dopamine and further functionalization with LAmB yielded surfaces with less roughness and more hydrophilic features. The proposed coating strategy rendered the surfaces of PDMS with the ability to prevent the attachment of C. albicans and kill the adherent cells, without toxicity toward mammalian cells. Overall results showed that LAmB immobilization on a surface retained its antifungal activity and reduced toxicity, holding therefore a great potential to be applied for the design of urinary catheters. Since the sessile communities commonly found associated to these devices exhibit a polymicrobial nature, the next challenge will be to co-immobilize LAmB with antibacterial agents to prevent the establishment of catheter-associated urinary tract infections (CAUTI).

Designing Nanostructured Ti6Al4V Bioactive Interfaces with Directed Irradiation Synthesis toward Cell Stimulation to Promote Host-Tissue-Implant Integration

A new generation of biomaterials are evolving from being biologically inert toward bioactive surfaces, which can further interact with biological components at the nanoscale. Here, we present directed irradiation synthesis (DIS) as a novel technology to selectively apply plasma ions to bombard any type of biomaterial and tailor the nanofeatures needed for in vitro growth stimulation. In this work, we demonstrate for the first time, the influence of physiochemical cues (e.g., self-organized topography at nanoscale) of medical grade Ti₆Al₄V results in control of cell shape, adhesion, and proliferation of human aortic smooth muscle stem cells. The control of surface nanostructures was found to be correlated to ion-beam incidence angle linked to a surface diffusive regime during irradiation synthesis with argon ions at energies below 1 keV and a fluence of 2.5 × 10¹⁷ cm^-2. Cell viability and cytoskeleton morphology were evaluated at 24 h, observing an advance cell attachment state on post-DIS surfaces. These modified surfaces showed 84% of cell biocompatibility and an increase in cytoplasmatic protusions ensuring a higher cell adhesion state. Filopodia density was promoted by a 3-fold change for oblique incidence angle DIS treatment compared to controls (e.g., no patterning) and lamellipodia structures were increased more than a factor of 2, which are indicators of cell attachment stimulation due to DIS modification. In addition, the morphology of the nanofeatures were tailored, with high fidelity control of the main DIS parameters that control diffusive and erosive regimes of self-organization. We have correlated the morphology and the influence in cell behavior, where nanoripple formation is the most active morphology for cell stimulation.

Antimicrobial polymer modifications to reduce microbial bioburden on endotracheal tubes and ventilator associated pneumonia

Hospital associated infections (HAIs), infections acquired by patients during care in a hospital, remain a prevalent issue in the healthcare field. These infections often occur with the use of indwelling medical devices, such as endotracheal tubes (ETTs), that can result in ventilator-associated pneumonia (VAP). When examining the various routes of infection, VAP is associated with the highest incidence, rate of morbidity, and economic burden. Although ETTs are essential for the survival of patients requiring mechanical ventilation, their use comes with complications. The presence of an ETT in the airway impairs physiological host defense mechanisms for clearance of pathogens and provides a platform for oropharynx microorganism transport to the sterile tracheobronchial network. Antibiotics are administered to treat lower respiratory infections; however, they are not always effective and consequently can result in increased antibiotic resistance. Prophylactic approaches by altering the surface of ETTs to prevent the establishment and growth of bacteria have exhibited promising results. In addition, passive surface modifications that prevent bacterial establishment and growth, or active coatings that possess a bactericidal effect have also proven effective. In this review we aim to highlight the importance of preventing biofilm establishment on indwelling medical devices, focusing on ETTs. We will investigate successful antimicrobial modifications to ETTs and the future avenues that will ultimately decrease HAIs and improve patient care. STATEMENT OF SIGNIFICANCE: Infections that occur with indwelling medicals devices remain a constant concern in the medical field and can result in hospital-acquired infections. Specifically, ventilator associated pneumonia (VAP) occurs with the use of an endotracheal tube (ETT). Infections often require use of antibiotics and can result in patient mortality. Our review includes a summary of the recent collective work of antimicrobial ETT modifications and potential avenues for further investigations in an effort to reduce VAP associated with ETTs. Polymer modifications with antibacterial nature have been developed and tested; however, a focus on ETTs is lacking and clinical availability of new antimicrobial ETT devices is limited. Our collective work shows the successful and prospective applications to the surfaces of ETTs that can support researchers and physicians to create safer medical devices.

Biomaterial surfaces self-defensive against bacteria by contact transfer of antimicrobials

Despite extensive engineering of tissue-contacting biomedical devices to control healing, these devices remain susceptible to bacterial colonization, biofilm formation, and chronic infection. The threat of selecting for resistance genes largely precludes sustained antimicrobial elution as a wide-spread clinical solution. In response, self-defensive surfaces have been developed where antimicrobial is released only when and where there is a bacterial challenge. We explore a new self-defensive approach using anionic microgels into which small-molecule cationic antimicrobials are loaded by complexation. We identify conditions where antimicrobial remains sequestered within the microgels for periods as long as weeks. However, bacterial contact triggers release and leads to local bacterial killing. We speculate that the close proximity of bacteria alters the local thermodynamic environment and interferes with the microgel-antimicrobial complexation. The contact-transfer approach does not require bacterial metabolism but instead appears to be driven by differences between the microgels and the bacterial cell envelope where there is a high concentration of negative charge and hydrophobicity. Contact with metabolizing macrophages or osteoblasts is, however, insufficient to trigger antimicrobial release, indicating that contact transfer can be specific to bacteria and suggesting an avenue to biomedical device surfaces that can simultaneously promote healing and resist infection.

Effects of Programmed Local Delivery from a Micro/Nano-Hierarchical Surface on Titanium Implant on Infection Clearance and Osteogenic Induction in an Infected Bone Defect

The two major causes for implant failure are postoperative infection and poor osteogenesis. Initial period of osteointegration is regulated by immunocytes and osteogenic-related cells resulting in inflammatory response and tissue healing. The healing phase can be influenced by various environmental factors and biological cascade effect. To synthetically orchestrate bone-promoting factors on biomaterial surface, built is a dual delivery system coated on a titanium surface (abbreviated as AH-Sr-AgNPs). The results show that this programmed delivery system can release Ag⁺ and Sr²⁺ in a temporal-spatial manner to clear pathogens and activate preosteoblast differentiation partially through manipulating the polarization of macrophages. Both in vitro and in vivo assays show that AH-Sr-AgNPs-modified surface renders a microenvironment adverse for bacterial survival and favorable for macrophage polarization (M2), which further promotes the differentiation of preosteoblasts. Infected New Zealand rabbit femoral metaphysis defect model is used to confirm the osteogenic property of AH-Sr-AgNPs implants through micro-CT, histological, and histomorphometric analyses. These findings demonstrate that the programmed surface with dual delivery of Sr²⁺ and Ag⁺ has the potential of achieving an enhanced osteogenic outcome through favorable immunoregulation.

A roadmap for promoting endogenous in situ tissue restoration using inductive bioscaffolds after acute brain injury

The regeneration of brain tissue remains one of the greatest unsolved challenges in medicine and by many is considered unfeasible. Indeed, the adult mammalian brain does not regenerate tissue, but there is ongoing endogenous neurogenesis, which is upregulated after injury and contributes to tissue repair. This endogenous repair response is a conditio sine que non for tissue regeneration. However, scarring around the lesion core and cavitation provide unfavorable conditions for tissue regeneration in the brain. Based on the success of using extracellular matrix (ECM)-based bioscaffolds in peripheral soft tissue regeneration, it is plausible that the provision of an inductive ECM-based hydrogel inside the volumetric tissue loss can attract neural cells and create a de novo viable tissue. Following perturbation theory of these successes in peripheral tissues, we here propose 9 perturbation parts (i.e. requirements) that can be solved independently to create an integrated series to build a functional and integrated de novo neural tissue. Necessities for tissue formation, anatomical and functional connectivity are further discussed to provide a new substrate to support the improvement of behavioral impairments after acute brain injury. We also consider potential parallel developments of this tissue engineering effort that can support therapeutic benefits in the absence of de novo tissue formation (e.g. structural support to veterate brain tissue). It is envisaged that eventually top-down inductive "natural" bioscaffolds composed of decellularized tissues (i.e. ECM) will be replaced by bottom-up synthetic designer hydrogels that will provide very defined structural and signaling properties, potentially even opening up opportunities we currently do not envisage using natural materials.

Triple-functional polyetheretherketone surface with enhanced bacteriostasis and anti-inflammatory and osseointegrative properties for implant application

Polyetheretherketone (PEEK) is considered a potential orthopedic/dental material because of its excellent mechanical and chemical properties (e.g., similar elastic modulus to that of human bone). However, the poor bacteriostasis and anti-inflammatory and osseointegrative properties of bioinert PEEK impede its clinical application. We previously developed a facile and versatile surface modification method using dexamethasone plus minocycline-loaded liposomes (Dex/Mino liposomes) bonded by a mussel-inspired polydopamine coating, which effectively modulated cell inflammatory response and discouraged bacterial colonization in vitro. Herein, we report the application of this multifunctional surface modification method to improve bioinert PEEK, aimed at further studying the in vitro osteogenesis and in vivo properties of Dex/Mino liposome-modified PEEK to prevent bacterial contamination, attenuate the inflammatory response, and enhance ossification for physiologic osseointegration. Our study established that the Dex/Mino liposome-modified PEEK surface presented favorable stability and cytocompatibility. Compared with bare PEEK, improved osteogenic differentiation of human mesenchymal stem cells under both osteoinductive and osteoconductive conditions was found on the functionalized surface due to the liposomal Dex releasing. In vivo bacteriostasis assay confirmed that Mino released from the functionalized surface provided an effective antibacterial effect. Moreover, the subcutaneous foreign body reaction and beagle femur implantation models corroborated the enhanced anti-inflammatory and osteointegrative properties of the functionalized PEEK. Our findings indicate that the developed Dex/Mino liposome-modified PEEK with enhanced antibacterial, anti-inflammatory, and osseointegrative capacity has great potential as an orthopedic/dental implant material for clinical application.

Tailoring the self-assembly of a tripeptide for the formation of antimicrobial surfaces

The accumulation of bacteria on surfaces is currently one of the greatest concerns for the management of proper healthcare systems, water and energy. Here, we describe the mechanism by which a single peptide forms two pH-dependent supramolecular particles that resist bacterial contamination. By using NMR and molecular dynamics (MD), we determined the structures of the peptide monomers and showed the forces directing the self-assembly of each structure under different conditions. These peptide assemblies change the characteristics of bare glass and confer it with the ability to prevent biofilm formation. Furthermore, they can adsorb and release active compounds as demonstrated with an anticancer drug, antibiotic and enzyme. This synergism and the detailed understanding of the processes are necessary for developing new sterile surfaces for healthcare systems, water purification devices, food packaging or any environment that suffers from biocontamination.

Microbiome on the Bone-Anchored Hearing System: A Prospective Study

The bone-anchored hearing system (BAHS) has evolved to a common treatment option for various types of hearing revalidation. The BAHS consists of an implant in the skull that breeches the skin. Soft tissue reactions are a common complication associated with BAHS and are generally poorly understood. This study aims to investigate the influence of BAHS and associated skin reactions around the implant. A total of 45 patients were prospectively followed from implantation up to at least 1 year. Swabs were obtained at baseline, 12 weeks follow-up and during cases of inflammation (Holgers score ≥2). The microbiota was assessed using IS-pro^TM, a bacterial profiling method based on the interspace region between the 16S–23S rRNA genes. Detection of operational taxonomic units, the Shannon Diversity Index, sample similarity analyses and Partial Least Squares Discriminant Analysis (PLS-DA) were employed. Staphylococcus epidermidis, Streptococcus pneumoniae/mitis, Propionibacterium acnes, Staphylococcus capitis, Staphylococcus hominis, Bifidobacterium longum, Haemophilus parainfluenzae, Lactobacillus rhamnosus, Bordetella spp., Streptococcus sanguinis, Peptostreptococcus anaerobius, Staphylococcus aureus, Lactococcus lactis, Enterobacter cloacae, and Citrobacter koseri were the most commonly found bacterial species. S. pneumoniae/mitis was significantly more often observed after implantation, whereas P. acnes was significantly less observed after implantation compared with baseline. The relative abundance of S. epidermidis (17%) and S. aureus (19.4%) was the highest for the group of patients with inflammation. The Shannon Diversity Index was significantly increased after implantation compared with pre-surgical swabs for Firmicutes, Actinobacteria, Fusobacteria, Verrucomicrobia (FAFV), but not for other phyla. When combining all phyla, there was no significant increase in the Shannon Diversity Index. The diversity index was similar post-surgically for patients experiencing inflammation and for patients without inflammation. With a supervised classifier (PLS-DA), patients prone to inflammation could be identified at baseline with an accuracy of 91.7%. In addition, PLS-DA could classify post-surgical abutments as non-inflamed or inflamed with an accuracy of 97.7%. This study shows the potential of using IS-pro^TM to describe and quantify the microbiota associated with the percutaneous BAHS. Furthermore, the results indicate the possibility of an early identification of patients susceptible to adverse skin reaction following implantation. Both S. aureus and S. epidermidis should be considered as relevant bacteria for BAHS-associated inflammation.

Biofunctionalization of TiO2 Surfaces with Self-Assembling Layers of Oligopeptides Covalently Grafted to Chitosan

In the field of tissue engineering, a promising approach to obtain a bioactive, biomimetic, and antibiotic implant is the functionalization of a "classical" biocompatible material, for example, titanium, with appropriate biomolecules. For this purpose, we propose preparing self-assembling films of multiple components, allowing the mixing of different biofunctionalities "on demand". Self-assembling peptides (SAPs) are synthetic materials characterized by the ability to self-organize in nanostructures both in aqueous solution and as thin or thick films. Moreover, ordered layers of SAPs adhere on titanium surface as a scaffold coating to mimic the extracellular matrix. Chitosan is a versatile hydrophilic polysaccharide derived from chitin, with a broad antimicrobial spectrum to which Gram-negative and Gram-positive bacteria and fungi are highly susceptible, and is already known in the literature for the ability of its derivatives to firmly graft titanium alloys and show protective effects against some bacterial species, either alone or in combination with other antimicrobial substances such as antibiotics or antimicrobial peptides. In this context, we functionalized titanium surfaces with chitosan grafted to EAK16-II (a SAP), obtaining layer-by-layer structures of different degrees of order, depending on the preparative stoichiometry and path. The chemical composition, molecular structure, and arrangement of the obtained biofunctionalized surfaces were investigated by surface-sensitive techniques such as reflection-absorption infrared spectroscopy (RAIRS) and state-of-the-art synchrotron radiation-induced spectroscopies as X-ray photoemission spectroscopy (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS). Furthermore, was demonstrated that surfaces coated with EAK and Chit-EAK can support hNPs cell attachment and growth.

Advanced antibacterial activity of biocompatible tantalum nanofilm via enhanced local innate immunity

Tantalum (Ta) has been shown to enhance osseointegration in clinical practice, yet little is known about whether Ta nanofilms can be used as antimicrobial coatings in vivo. A highly biocompatible Ta nanofilm was developed using magnetron sputtering technology to further study the mechanism of its antibacterial effects in vivo and elucidate its potential for clinical translation. The Ta nanofilms exhibited effective antimicrobial activity against soft tissue infections but did not show an intrinsic antimicrobial effect in vitro. This inconsistency between the in vivo and in vitro antimicrobial effects was further investigated using ex vivo models. The Ta nanofilms could enhance the phagocytosis of bacteria by polymorphonuclear neutrophils (PMNs, neutrophils), reduce the lysis of neutrophils and enhance the proinflammatory cytokine release of macrophages. This accumulative enhancement of the local host defenses contributed to the favorable antibacterial effect in vivo. The alleviated osteolysis observed in the presence of the Ta nanofilms in the osteomyelitis model further proved the practicality of this antibacterial strategy in the orthopedic field. In summary, Ta nanofilms show excellent biocompatibility and in vivo antimicrobial activity mediated by the enhancement of local innate immunity and are promising for clinical application. STATEMENT OF SIGNIFICANCE: In this study, Ta nanofilms were deposited on titanium substrate by magnetron sputtering. Ta nanofilms exhibited excellent in vivo and in vitro biocompatibility. In vivo antimicrobial effects of Ta nanofilms were revealed by soft tissue infection and osteomyelitis models, while no direct antibacterial activity was observed in vitro. Comprehensive ex vivo models revealed that Ta nanofilms could enhance the phagocytosis of bacteria by neutrophils, reduce the lysis of neutrophils and promote the release of proinflammatory cytokines from macrophages. This immunomodulatory effect helps host to eliminate bacteria. In contrast to traditional antimicrobial nanocoatings which apply toxic materials to kill bacteria, this work proposes a safe, practical and effective Ta nanofilm immunomodulatory antimicrobial strategy with clinical translational prospect.

Substrate-Independent Coating with Persistent and Stable Antifouling and Antibacterial Activities to Reduce Bacterial Infection for Various Implants

Implantation of biomedical devices accompanying infections has caused severe problems to public health that require feasible solutions. In this study, a simple approach is reported to fabricate a antimicrobial and antifouling dual-functional coating. This coating consists of a substrate-independent layer-by-layer (LBL) film formed by poly (diallyldimethylammonium) (PDDA) and poly (styrenesulfonate) (PSS), where parts of PSS and PDDA are physically substituted by hetero-bifunctional polyethylene glycol (PEG) ending with a carboxyl group and antimicrobial peptide (ε-Poly-l-lysine, ε-PL). This design (ε-PL-PEG-(PDDA/PSS)9 coating) exhibits not only potent antimicrobial activity against Gram-positive/negative bacteria but also superior antifouling activity on various substrates, including glass and plastic. Moreover, the antifouling and antibacterial performance can be maintained for a longer period of time under physiological environments even after physical damage of the surface due to the homogeneous interspersion and free migration of ε-PL-PEG-COOH in the LBL film. This allows the supplement of these molecules to the surface against molecule loss during usage. Both in vitro and in vivo (rodent subcutaneous infection model) studies show obvious reduction of the bacteria on the coated substrate and in the surrounding tissues with up to 3.2-log reduction, even after repeated usage. The inflammation around the implantation area is also significantly inhibited.

Evaluating Efficacy of Antimicrobial and Antifouling Materials for Urinary Tract Medical Devices: Challenges and Recommendations

In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient-days. Of these cases, catheter-associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health-care costs of £1-2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary-tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device-associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.

Surface Structuring Combined with Chemical Surface Functionalization: An Effective Tool to Manipulate Cell Adhesion

In this study, we investigate how a surface structure underneath a surface-attached polymer coating affects the bioactivity of the resulting material. To that end, structured surfaces were fabricated using colloidal lithography (lateral dimensions: 200 nm to 1 µm, height ~15 to 50 nm). The surface structures were further functionalized either with antimicrobial, cell-adhesive polycations or with protein-repellent polyzwitterions. The materials thus obtained were compared to non-functionalized structured surfaces and unstructured polymer monolayers. Their physical properties were studied by contact-angle measurements and atomic force microscopy (AFM). Protein adhesion was studied by surface plasmon resonance spectroscopy, and the antimicrobial activity against Escherichia coli bacteria was tested. The growth of human mucosal gingiva keratinocytes on the materials was analyzed using the Alamar blue assay, optical microscopy, and live-dead staining. The data shows that the underlying surface structure itself reduced protein adhesion and also bacterial adhesion, as evidenced by increased antimicrobial activity. It also enhanced cell adhesion to the surfaces. Particularly in combination with the adhesive polycations, the surfaces increased the cell growth compared to the unstructured reference materials. Thus, functionalizing structured surfaces with adhesive polymer could be a valuable tool for improved tissue integration.

Recommendations for design and conduct of preclinical in vivo studies of orthopedic device-related infection

Orthopedic device-related infection (ODRI), including both fracture-related infection (FRI) and periprosthetic joint infection (PJI), remain among the most challenging complications in orthopedic and musculoskeletal trauma surgery. ODRI has been convincingly shown to delay healing, worsen functional outcome and incur significant socio-economic costs. To address this clinical problem, ever more sophisticated technologies targeting the prevention and/or treatment of ODRI are being developed and tested in vitro and in vivo. Among the most commonly described innovations are antimicrobial-coated orthopedic devices, antimicrobial-loaded bone cements and void fillers, and dual osteo-inductive/antimicrobial biomaterials. Unfortunately, translation of these technologies to the clinic has been limited, at least partially due to the challenging and still evolving regulatory environment for antimicrobial drug-device combination products, and a lack of clarity in the burden of proof required in preclinical studies. Preclinical in vivo testing (i.e. animal studies) represents a critical phase of the multidisciplinary effort to design, produce and reliably test both safety and efficacy of any new antimicrobial device. Nonetheless, current in vivo testing protocols, procedures, models, and assessments are highly disparate, irregularly conducted and reported, and without standardization and validation. The purpose of the present opinion piece is to discuss best practices in preclinical in vivo testing of antimicrobial interventions targeting ODRI. By sharing these experience-driven views, we aim to aid others in conducting such studies both for fundamental biomedical research, but also for regulatory and clinical evaluation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:271-287, 2019.

Poly(dopamine) and Ag nanoparticle-loaded TiO2 nanotubes with optimized antibacterial and ROS-scavenging bioactivities

AIM

To create polydopamine (PDA) and Ag nanoparticle-loaded TiO₂ nanotubes coating on titanium (Ti) alloy.

MATERIALS & METHODS

TiO₂-PDA-Ag coating was fabricated on Ti implants by electrochemical anodization. The in vitro and in vivo bactericidal and antibiofilm activities were tested. Intracellular reactive oxygen species (ROS) and antioxidative capability were measured, and cell proliferation, adhesion and cell morphology were characterized.

RESULTS

TiO₂-PDA-Ag coating showed satisfactory bactericidal and antibiofilm activities in vitro and in vivo, improved Ag release pattern, evident ROS scavenging properties and enhanced cell adhesion and proliferation.

CONCLUSION

Our study successfully fabricated a PDA and Ag nanoparticle-loaded TiO₂ nanotubes coating on Ti alloy. The improved Ag release kinetics and ROS-scavenging properties achieve an optimal balance between antibacterial ability and biocompatibility.

Three-Dimensional Printing of Drug-Loaded Scaffolds for Antibacterial and Analgesic Applications

Pneumatic extrusion-based three-dimensional (3D) printing can be used to fabricate custom-made scaffolds to restore irregular bone defects. During the 3D printing process, therapeutic agents can be added to the scaffolds. This study aimed to develop a polycaprolactone (PCL) scaffold loaded with Ag₃PO₄ to prevent infections and lidocaine for pain relief by one-step 3D printing. We hypothesized that the drug release could be controlled by varying the filament diameter of the 3D printed scaffolds. To this end, PCL slurry mixed with different amounts of silver phosphate and lidocaine was printed via differently sized nozzles. The obtained cylindric scaffolds displayed a porous interconnected microstructure with high fidelity. The Ag₃PO₄ and lidocaine were distributed homogeneously. The lidocaine release could be controlled by adjusting the filament diameter while the silver release is correlated with the Ag₃PO₄ loading amount. The released medium from silver-loaded scaffolds exhibited an obvious inhibition zone against Staphylococcus aureus and Escherichia coli upon loading with 1% Ag₃PO₄ for up to 6 days and with 3% Ag₃PO₄ for at least 7 days. Cytotoxicity of all scaffolds was screened by cell assay. In conclusion, the pneumatic extrusion-based 3D printing provides a practical technique to fabricate drug-loaded scaffolds. The Ag₃PO₄ and lidocaine loaded PCL scaffolds showed the potential for infection prevention and pain relief.

Risk factors for surgical site infection after malignant bone tumor resection and reconstruction

BACKGROUND

Use of an implant is one of the risk factors for surgical site infection (SSI) after malignant bone tumor resection. We developed a new technique of coating titanium implant surfaces with iodine to prevent infection. In this retrospective study, we investigated the risk factors for SSI after malignant bone tumor resection and to evaluate the efficacy of iodine-coated implants for preventing SSI.

METHODS

Data from 302 patients with malignant bone tumors who underwent malignant bone tumor resection and reconstruction were reviewed. Univariate analyses were performed, followed by multivariate analysis to identify risk factors for SSI based on the treatment and clinical characteristics.

RESULTS

The frequency of SSI was 10.9% (33/302 tumors). Pelvic bone tumor (OR: 4.8, 95% CI: 1.8-13.4) and an operative time ≥ 5 h (OR: 3.4, 95% CI: 1.2-9.6) were independent risk factors for SSI. An iodine-coated implant significantly decreased the risk of SSI (OR: 0.3, 95% CI: 0.1-0.9).

CONCLUSION

The present data indicate that pelvic bone tumor and long operative time are risk factors for SSI after malignant bone tumor resection and reconstruction, and that iodine coating may be a promising technique for preventing SSI.

Povidone-iodine-functionalized fluorinated copolymers with dual-functional antibacterial and antifouling activities

Povidone-iodine-functionalized fluorinated polymer coatings with dual-functional antibacterial and antifouling activities should be very promising in practical biomedical applications.

Bactericidal effects of nanopatterns: A systematic review

We systematically reviewed the currently available evidence on how the design parameters of surface nanopatterns (e.g. height, diameter, and interspacing) relate to their bactericidal behavior. The systematic search of the literature resulted in 46 studies that satisfied the inclusion criteria of examining the bactericidal behavior of nanopatterns with known design parameters in absence of antibacterial agents. Twelve of the included studies also assessed the cytocompatibility of the nanopatterns. Natural and synthetic nanopatterns with a wide range of design parameters were reported in the included studies to exhibit bactericidal behavior. However, most design parameters were in the following ranges: heights of 100-1000 nm, diameters of 10-300 nm, and interspacings of  <500 nm. The most commonly used type of nanopatterns were nanopillars, which could kill bacteria in the following range of design parameters: heights of 100-900 nm, diameters of 20-207 nm, and interspacings of 9-380 nm. The vast majority of the cytocompatibility studies (11 out of 12) showed no adverse effects of bactericidal nanopatterns with the only exception being nanopatterns with extremely high aspect ratios. The paper concludes with a discussion on the evidence available in the literature regarding the killing mechanisms of nanopatterns and the effects of other parameters including surface affinity of bacteria, cell size, and extracellular polymeric substance (EPS) on the killing efficiency. STATEMENT OF SIGNIFICANCE: The use of nanopatterns to kill bacteria without the need for antibiotics represents a rapidly growing area of research. However, the optimum design parameters to maximize the bactericidal behavior of such physical features need to be fully identified. The present manuscript provides a systematic review of the bactericidal nanopatterned surfaces. Identifying the effective range of dimensions in terms of height, diameter, and interspacings, as well as covering their impact on mammalian cells, has enabled a comprehensive discussion including the bactericidal mechanisms and the factors controlling the bactericidal efficiency. Overall, this review helps the readers have a better understanding of the state-of-the-art in the design of bactericidal nanopatterns, serving as a design guideline and contributing to the design of future experimental studies.

Nanotechnology-based antimicrobials and delivery systems for biofilm-infection control

Bacterial-infections are mostly due to bacteria in their biofilm-mode of growth. Nanotechnology-based antimicrobials possess excellent potential in biofilm-infection control, overcoming the biological barriers of biofilms.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

AMPs as Anti-biofilm Agents for Human Therapy and Prophylaxis

Microbial cells show a strong natural tendency to adhere to surfaces and to colonize them by forming complex communities called biofilms. In this growth mode, biofilm-forming cells encase themselves inside a dense matrix which efficiently protects them against antimicrobial agents and effectors of the immune system. Moreover, at the physiological level, biofilms contain a very heterogeneous cell population including metabolically inactive organisms and persisters, which are highly tolerant to antibiotics. The majority of human infectious diseases are caused by biofilm-forming microorganisms which are responsible for pathologies such as cystic fibrosis, infective endocarditis, pneumonia, wound infections, dental caries, infections of indwelling devices, etc. AMPs are well suited to combat biofilms because of their potent bactericidal activity of broad spectrum (including resting cells and persisters) and their ability to first penetrate and then to disorganize these structures. In addition, AMPs frequently synergize with antimicrobial compounds and were recently reported to repress the molecular pathways leading to biofilm formation. Finally, there is a very active research to develop AMP-containing coatings that can prevent biofilm formation by killing microbial cells on contact or by locally releasing their active principle. In this chapter we will describe these strategies and discuss the perspectives of the use of AMPs as anti-biofilm agents for human therapy and prophylaxis.

Polymer-Nanoparticle Interaction as a Design Principle in the Development of a Durable Ultrathin Universal Binary Antibiofilm Coating with Long-Term Activity

Bacterial attachment and biofilm formation pose major challenges to the optimal performance of indwelling devices. Current coating methods have significant deficiencies including the lack of long-term activity, easy of application, and adaptability to diverse materials. Here we describe a coating method that could potentially overcome such limitations and yield an ultrathin coating with long-term antibiofilm activity. We utilized the interaction between polydopamine (PDA) nanoaggregates/nanoparticles and ultrahigh molecular weight (uHMW) hydrophilic polymers to generate stable coatings with broad spectrum antibiofilm activity. We used a short-term bacterial adhesion assay as an initial screening method to identify coating compositions that give superior performance and found that only selected polymers (out of 13 different types) and molecular weights gave promising antifouling activity. Optimization of PDA self-assembly, polymer-PDA interaction, and deposition on the surface using uHMW poly( N,N-dimethylacrylamide) (PDMA) (∼795 kDa) resulted in a stable ultrathin coating (∼19 nm) with excellent antifouling and antibiofilm properties (>4 weeks) against diverse bacteria (∼10⁸ CFU/mL) in shaking and flow conditions. The ultrathin coating is effective on diverse substrates including metals and polymeric substrates. The uHMW PDMA is stabilized in the coating via supramolecular interactions with PDA and generated a surface that is highly enriched with PDMA in aqueous conditions. Based on the surface analyses data, we also propose a mechanism for the stable coating formation. The molecular weight of PDMA is a crucial factor, and only uHMW polymers generate this property. An attractive feature of the coating is that it does not contain any antimicrobial agents and has the potential to prevent biofilm formation for diverse applications both short- and long-term.

A Trans-Atlantic Perspective on Stagnation in Clinical Translation of Antimicrobial Strategies for the Control of Biomaterial-Implant-Associated Infection

Current regulatory requirements impede clinical translation and market introduction of many new antimicrobial combination implants and devices, causing unnecessary patient suffering, doctor frustration, and costs to healthcare payers. Regulatory requirements of antimicrobial combination implants and devices should be thoroughly revisited and their approval allowed based on enrichment of benefit demonstrations from high-risk patient groups and populations or device components to facilitate their clinical translation. Biomaterial implant and devices equipped with antimicrobial strategies and approved based on enrichment claims should be mandatorily enrolled in global registry studies supervised by regulatory agencies for a minimum five-year period or until statistically validated evidence for noninferiority or superiority of claims is demonstrated. With these recommendations, this trans-Atlantic consortium of academicians and clinicians takes its responsibility to actively seek to relieve the factors that stagnate downward clinical translation and availability of antimicrobial combination implants and devices. Improved dialogue between the various key players involved in the current translational blockade, which include patients, academicians and doctors, policymakers, regulatory agencies, manufacturers, and healthcare payers, is urgently needed.

Pentadecanal inspired molecules as new anti-biofilm agents against Staphylococcus epidermidis

Staphylococcus epidermidis, a harmless human skin colonizer, is a significant nosocomial pathogen in predisposed hosts because of its capability to form a biofilm on indwelling medical devices. In a recent paper, the purification and identification of the pentadecanal produced by the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125, able to impair S. epidermidis biofilm formation, were reported. Here the authors report on the chemical synthesis of pentadecanal derivatives, their anti-biofilm activity on S. epidermidis, and their action in combination with antibiotics. The results clearly indicate that the pentadecanal derivatives were able to prevent, to a different extent, biofilm formation and that pentadecanoic acid positively modulated the antimicrobial activity of the vancomycin. The cytotoxicity of these new anti-biofilm molecules was tested on two different immortalized eukaryotic cell lines in view of their potential applications.

Antibacterial Surface Coating for Bone Scaffolds Based on the Dark Catalytic Effect of Titanium Dioxide

Biomaterials which promote tissue integration and resist microbial colonisation are required in bone tissue engineering to prevent biomaterial-associated infections. Surface modification of established materials for bone tissue engineering, such as TiO₂, have emerged as promising anti-infective strategies. Interestingly, the antibacterial activity of TiO₂ in the form of particles can be enhanced by combining it with H₂O₂, even in the absence of irradiation. However, it remains unknown whether TiO₂ surfaces elicit a similar effect. In this study, the antibacterial effect of porous TiO₂ scaffolds generated by the catalytic decomposition of H₂O₂ in the absence of light (dark catalysis) was investigated. Porous ceramic foams were fabricated and sol-gel coated for high catalytic activity. Degradation of methylene blue in the presence of 3% H₂O₂ increased by 80% for the sol-gel-coated surfaces. The degradation kinetics indicate that intermediate free radicals that form at the liquid-TiO₂ interface are responsible for the oxidative behavior of the surface. TiO₂ surfaces were further pretreated with 30% H₂O₂ for prolonged oxidative behavior. The biological response toward such surfaces was assessed in vitro. S. epidermidis biofilms formed on modified surfaces showed reduced viability compared to nonmodified surfaces. Further, the same surface modification showed no cytotoxic effects on MC3T3 preosteoblasts. However, the results from the conducted genotoxicity assay were inconclusive, and further studies are needed to exclude ROS-mediated DNA damage. To conclude, this study provides evidence that a simple surface modification based on the dark catalytic effect of TiO₂ can be used to create antibacterial surface properties for ceramic bone scaffolds.

Simvastatin delivery on PEEK for bioactivity and osteogenesis enhancements

A strategy developed for obtaining positive cellular responses remains to be focused in the filed of functional biomimetics. In this study, a hydrogel covered simvastatin-loaded polyetheretherketone (PEEK) bio-composites was constructed with the purpose of bone tissue regeneration therapy. Briefly, a three-dimensional (3D) porous structure was fabricated on PEEK surface; then the substrate was functionalized with the poly(L-lactic acid)/simvastatin porous film and hyaluronic acid hydrogel subsequently. In vitro cell attachment, proliferation, and cytoskeletal observation experiments reveal that our scaffolds show better bio-affinity due to the layer of hyaluronic acid hydrogel compared with control. Furthermore, the alkaline phosphatase activity, calcium mineral deposition evaluation, and gene expression for osteogenic potential all exhibit that the superior osteogenic differentiation of MC3T3-E1 pre-osteoblasts on our scaffolds. Therefore, our PEEK samples loaded with simvastatin and covered with hyaluronic acid hydrogel hold great potential in clinical applications for bone repair.

Tissue repair in neonatal and paediatric surgery: Analysis of infection in surgical implantation of synthetic resorbable biomaterials

BACKGROUND

There has been increased interest in the use of biomaterials that resorb completely leaving only the patient's native tissue. Synthetic materials are advantageous for tissue repair because they are highly customisable. The infection rate of using resorbable natural materials in paediatric surgery has recently been outlined, but there has not yet been a review of the use of synthetic resorbable materials in paediatric surgery.

OBJECTIVES

This systematic review analyses the risk of infection after implantation of fully resorbable synthetic biomaterials in paediatric cases.

METHODS

The literature was searched from January 1970 to January 2018 (inclusive), specifically searching for paediatric cases (0-18 years old), use of synthetic resorbable materials and infection.

RESULTS

The infection rate in 3573 cases of synthetic resorbable material implantation was 1.1% (41 cases). A Chi-squared test for independence found infection rate to vary among materials. Of the many biomaterials identified in this review, the highest infection rates were seen in Suprathel's use in burns injuries (12.1%).

CONCLUSIONS

This review found a low infection rate in synthetic resorbable materials used in paediatric surgery, with particularly strong evidence for low infection risk in LactoSorb® use.

Preferential Colonization of Osteoblasts Over Co-cultured Bacteria on a Bifunctional Biomaterial Surface

Implant-related infection is a devastating complication in clinical trauma and orthopedics. The aim of this study is to use a bifunctional biomaterial surface in order to investigate the competitive colonization between osteoblasts and bacteria, which is the cause of implant-related infection. A bone-engineering material capable of simultaneously facilitating osteoblast adhesion and inhibiting the growth of Staphylococcus aureus (S. aureus) was prepared. Then, three different co-cultured systems were developed in order to investigate the competitive colonization between the two cohorts on the surface. The results suggested that while the pre-culturing of either cohort compromised the subsequent adhesion of the other according to the ‘race for the surface’ theory, the synergistic effect of preferential cell adhesion and antibacterial activity of the bifunctional surface led to the predominant colonization and survival of osteoblasts, effectively inhibiting the bacterial adhesion and biofilm formation of S. aureus in the co-culture systems with both cohorts. This research offers new insight into the investigation of competitive surface-colonization between osteoblasts and bacteria for implant-related infection.