Vat Polymerization by Three-Dimensional Printing and Curing of Antibacterial Zinc Oxide Nanoparticles Embedded in Poly(ethylene glycol) Diacrylate for Biomedical Applications

Digital light processing (DLP) is a vat photopolymerization 3D printing technique with increasingly broad application prospects, particularly in personalized medicine, such as the creation of medical devices. Different resins and printing parameters affect the functionality of these devices. One of the many problems that biomedical implants encounter is inflammation and bacteria growth. For this reason, many studies turn to the addition of antibacterial agents to either the bulk material or as a coating. Zinc oxide nanoparticles (ZnO NPs) have shown desirable properties, including antibacterial activity with negligible toxicity to the human body, allowing their use in a wide range of applications. In this project, we developed a resin of poly(ethylene glycol) diacrylate (PEGDA), a cross-linker known for its excellent mechanical properties and high biocompatibility in a 4:1 weight ratio of monomers to water. The material's mechanical properties (Young's modulus, maximum elongation, and ultimate tensile strength) were found similar to those of human cartilage. Furthermore, the ZnO NPs embedding matrix showed strong antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S.A.). As the ZnO NPs ratio was changed, only a minor effect on the mechanical properties of the material was observed, whereas strong antibacterial properties against both bacteria were achieved in the case of 1.5 wt.% NPs.

3D bioprinting of nanoparticle-laden hydrogel scaffolds with enhanced antibacterial and imaging properties

Biomaterial-associated microbial contaminations in biologically conducive three-dimensional (3D) tissue-engineered constructs have significantly limited the clinical applications of scaffold systems. To prevent such infections, antimicrobial biomaterials are rapidly evolving. Yet, the use of such materials in bioprinting-based approaches of scaffold fabrication has not been examined. This study introduces a new generation of bacteriostatic gelatin methacryloyl (GelMA)-based bioinks, incorporated with varying doses of antibacterial superparamagnetic iron oxide nanoparticles (SPIONs). The SPION-laden GelMA scaffolds showed significant resistance against the Staphylococcus aureus growth, while providing a contrast in magnetic resonance imaging. We simulated the bacterial contamination of cellular 3D GelMA scaffolds in vitro and demonstrated the significant effect of functionalized scaffolds in inhibiting bacterial growth, while maintaining cell viability and growth. Together, these results present a new promising class of functionalized bioinks to 3D bioprint tissue-engineered scaffold with markedly enhanced properties for the use in a variety of in vitro and clinical applications.

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Functionalized bioinks with bacteriostatic properties are developed and thoroughly characterized

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The 200 μg/mL group yielded an optimal balance of printed scaffold properties

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Incorporating nanoparticle also enabled noninvasive imaging of the bioprinted scaffold

In Vivo Antibacterial Efficacy of Antimicrobial Peptides Modified Metallic Implants─Systematic Review and Meta-Analysis

Biomaterial-associated infection is difficult to detect and brings consequences that can lead to morbidity and mortality. Bacteria can adhere to the implant surface, grow, and form biofilms. Antimicrobial peptides (AMPs) can target and kill bacterial cells using a plethora of mechanisms of action such as rupturing the cell membrane by creating pores via depolarization with their cationic and amphipathic nature. AMPs can thus be coated onto metal implants to prevent microbial cell adhesion and growth. The aim of this systematic review was to determine the potential clinical applications of AMP-modified implants through in vivo induced infection models. Following a database search recently up to 22 January 2022 using PubMed, Web of Science and Cochrane databases, and abstract/title screening using the PRISMA framework, 24 studies remained, of which 18 were used in the random effects meta-analysis of standardized mean differences (SMD) to get effect sizes. Quality of studies was assessed using SYRCLE's risk of bias tool. The data from these 18 studies showed that AMPs carry antibacterial effects, and the meta-analysis confirmed the favorited antibacterial efficacy of AMP-coated groups over controls (SMD -1.74, 95%CI [-2.26, -1.26], p < 0.00001). Subgroup analysis showed that the differences in effect size are random, and high heterogeneity values suggested the same. HHC36 and vancomycin were the most common AMPs for surface modification and Staphylococcus aureus, the most tested bacterium in vivo. Covalent binding with polymer brush coating and physical layer-by-layer incorporation of AMPs were recognized as key methods of incorporation to achieve desired densities. The use of fusion peptides seemed admirable to incorporate additional benefits such as osteointegration and wound healing and possibly targeting more microbe strains. Further investigation into the incorporation methods, AMP activity against different bacterial strains, and the number of AMPs used for metal implant surface modification is needed to progress toward potential clinical application.

Approaches to inhibit biofilm formation applying natural and artificial silk-based materials

The discovery of penicillin started a new era of health care since it allowed the effective treatment of formerly deadly infections. As a drawback, its overuse led to a growing number of multi-drug resistant pathogens. Challenging this arising threat, material research focuses on the development of microbe-killing or microbe repellent agents implementing such functions directly into materials. Due to their biocompatibility, non-immunogenicity and mechanical strength, silk-based materials are attractive candidates for applications in the biomedical field. Furthermore, it has been observed that silks display high persistency in their natural environment giving reason to suspect that they might be attractive candidates to prevent microbial infestation. The current review describes the process of biofilm formation on medical devices and the most common strategies to prevent it, divided into effects of surface topography, material modification and integrated additives. In this context, recent state of the art developments in the field of natural and artificial silk-based materials with microbe-repellant or antimicrobial properties are addressed. These silk properties are controversially discussed and conclusions are drawn as to which parameters will be decisive for the successful design of new bio-functional materials based on the blueprint of silk proteins.

3D Bioprinted Bacteriostatic Hyperelastic Bone Scaffold for Damage-Specific Bone Regeneration

Current strategies for regeneration of large bone fractures yield limited clinical success mainly due to poor integration and healing. Multidisciplinary approaches in design and development of functional tissue engineered scaffolds are required to overcome these translational challenges. Here, a new generation of hyperelastic bone (HB) implants, loaded with superparamagnetic iron oxide nanoparticles (SPIONs), are 3D bioprinted and their regenerative effect on large non-healing bone fractures is studied. Scaffolds are bioprinted with the geometry that closely correspond to that of the bone defect, using an osteoconductive, highly elastic, surgically friendly bioink mainly composed of hydroxyapatite. Incorporation of SPIONs into HB bioink results in enhanced bacteriostatic properties of bone grafts while exhibiting no cytotoxicity. In vitro culture of mouse embryonic cells and human osteoblast-like cells remain viable and functional up to 14 days on printed HB scaffolds. Implantation of damage-specific bioprinted constructs into a rat model of femoral bone defect demonstrates significant regenerative effect over the 2-week time course. While no infection, immune rejection, or fibrotic encapsulation is observed, HB grafts show rapid integration with host tissue, ossification, and growth of new bone. These results suggest a great translational potential for 3D bioprinted HB scaffolds, laden with functional nanoparticles, for hard tissue engineering applications.

High concentrations of calcium suppress osteogenic differentiation of human periodontal ligament stem cells in vitro

Background/purpose

Periodontal ligament stem cells (PDLSCs)-based regeneration therapy has received attention for its potential alternative applications in hard tissue and tooth. However, the environmental diversity of oral cavity that regulates PDLSCs differentiation has made it difficult to develop. Therefore, we investigated how high calcium concentrations in the oral environment influence osteogenic differentiation of human PDLSCs (hPDLSCs).

Materials and methods

hPDLSCs collected from human molars were isolated and cultured with CaCl₂. First, multi lineage differentiation potentials to osteogenic, chondrogenic, and adipogenic cells were investigated. Then, the effects of CaCl₂ on both alkaline phosphatase (ALP) activity and bone mineralization were analyzed and the expression of mRNA and protein for osteogenic marker was explored. Further, luciferase assay was performed to evaluate CaCl₂ could regulate the transcriptional activity on osteogenic differentiation in hPDLSCs

Results

CaCl₂ treatment at normal to high concentrations showed similar suppression of ALP activity, while mineralized nodule formation was decreased by CaCl₂ treatment dose-dependently without affecting proliferation or cytotoxicity in hPDLSCs. We also observed that CaCl₂ treatment repressed the mRNA expression and protein abundance of osteogenic genes and transcriptional factors. Notably, repression of the Runx2 level was significant, and CaCl₂ treatment inhibited Runx2-mediated transcriptional activity on the osteoblast-specific element (OSE) and ALP promoters.

Conclusion

High concentrations of calcium negatively regulate osteogenic differentiation of hPDLSCs, by repressing osteogenic gene expressions and transcriptional activity. Therefore, these conditions may be applicable to determine the physiologically appropriate concentration of calcium.

Lactoferrin Functionalized Biomaterials: Tools for Prevention of Implant-Associated Infections

Tissue engineering is one of the most important biotechnologies in the biomedical field. It requires the application of the principles of scientific engineering in order to design and build natural or synthetic biomaterials feasible for the maintenance of tissues and organs. Depending on the specific applications, the selection of the proper material remains a significant clinical concern. Implant-associated infection is one of the most severe complications in orthopedic implant surgeries. The treatment of these infections is difficult because the surface of the implant serves not only as a substrate for the formation of the biofilm, but also for the selection of multidrug-resistant bacterial strains. Therefore, a promising new approach for prevention of implant-related infection involves development of new implantable, non-antibiotic-based biomaterials. This review provides a brief overview of antimicrobial peptide-based biomaterials-especially those coated with lactoferrin.

Encapsulated bacteriophages in alginate-nanohydroxyapatite hydrogel as a novel delivery system to prevent orthopedic implant-associated infections

An innovative delivery system based on bacteriophages-loaded alginate-nanohydroxyapatite hydrogel was developed as a multifunctional approach for local tissue regeneration and infection prevention and control. Bacteriophages were efficiently encapsulated, without jeopardizing phage viability and functionality, nor affecting hydrogel morphology and chemical composition. Bacteriophage delivery occurred by swelling-disintegration-degradation process of the alginate structure and was influenced by environmental pH. Good tissue response was observed following the implantation of bacteriophages-loaded hydrogels, sustaining their biosafety profile. Bacteriophages-loaded hydrogels did not affect osteoblastic cells' proliferation and morphology. A strong osteogenic and mineralization response was promoted through the implantation of hydrogels system with nanohydroxyapatite. Lastly, bacteriophages-loaded hydrogel showed excellent antimicrobial activity inhibiting the attachment and colonization of multidrug-resistant E. faecalis surrounding and within femoral tissues. This new local delivery approach could be a promising approach to prevent and control bacterial contamination during implantation and bone integration.

Periodicities in the roughness and biofilm growth on glass substrate with etching time: Hydrofluoric acid etchant

Adherence of the microorganism to submerged solid surfaces leads to biofilm formation. Biofilm formation modifies the surfaces in favor of bacteria facilitating the survival of the bacteria under different stressed conditions. On the other hand, the formation of biofilm has a direct adverse economic impact in various industries and more importantly in medical practices. This adherence is the reason for the failure of many indwelling medical devices. Surface biofilm adhesion is the key to biofilm growth and stability. Hence this adhesion needs to be substantially lowered to inhibit biofilm stability. Both chemical and physical properties of the surface influence biofilm formation and modulating these properties can control this formation. In this study, we have investigated the effect of Hydrofluoric acid (HF), at a specific concentration as an etchant, on the surface morphology of substrates and the growth of biofilms of Pseudomonas aeruginosa. and Staphylococcus aureus. We find that the bacterial counts on the etched surfaces undergo a periodic increase and decrease. This, on one hand, shows the close correlation between the biofilm growth and the particular roughness scale, and on the other hand, explains the existing contradictory results regarding the effects of etching on substrate roughness and biofilm growth. We propose a simple model of a sequence of hole formation, hole expansion and etching away of the hole walls to form a new, comparatively smooth surface, coupled with the preferential accumulation of bacteria at the hole edges, to explain these periodicities.

Immobilizing bacitracin on titanium for prophylaxis of infections and for improving osteoinductivity: An in vivo study

Bacitracin immobilized on the titanium (Ti) surface significantly improves anti-bacterial activity and biocompatibility in vitro. In the current study, we investigated the biologic performance (bactericidal effect and bone-implant integration) of bacitracin-modified Ti in vivo. A rat osteomyelitis model with femoral medullary cavity placement of Ti rods was employed to analyze the prophylactic effect of bacitracin-modified Ti (Ti-BC). Thirty-six female Sprague Dawley (SD) rats were used to establish the Ti implant-associated infection. The Ti and Ti-BC rods were incubated with and without Staphylococcus aureus to mimic the contaminated Ti rod and were implanted into the medullary cavity of the left femur, and sterile Ti rods were used as the blank control. After 3 weeks, the bone pathology was evaluated using X-ray and micro-computed tomography (micro-CT) analysis. For the investigation of the Ti-BC implant osseointegration in vivo, fifteen SD rats were divided into three groups (N=5), namely Ti, Ti-dopamine immobilized (Ti-DOPA), and Ti-BC. Ti rods were implanted into the left femoral cavity and micro-CT and histological evaluation was conducted after 12 weeks. The in vivo study indicated that Ti-immobilized bacitracin owned the prophylaxis potential for the infection associated with the Ti implants and allowed for the osseointegration. Thus, the multiple biofunctionalized Ti implants could be realized via immobilization of bacitracin, making them promising candidates for preventing the Ti implant-associated infections while retaining the osseointegration effects.

PROGRESS ON ANTIMICROBIAL SURGICAL GLOVES: A REVIEW

Surgical gloves provide a protective blockade for patients and members of the surgical team. Glove integrity is critical in an era of blood-borne pathogens. Therefore, the need for improved means for prevention and also gloving and appropriate hand hygiene in a hospital setting is ostensible. This perspective highlights the progress on antimicrobial surgical gloves in deducting the microbial passage after a glove puncture in a model of wound contamination. Moreover, traditional methods to avoid microbes in the hospital and various antimicrobial agents, such as metal ions and antiseptic dyes, are reviewed.

A Smart Antibacterial Surface for the On-Demand Killing and Releasing of Bacteria

For various human healthcare and industrial applications, endowing surfaces with the capability to not only efficiently kill bacteria but also release dead bacteria in a rapid and repeatable fashion is a promising but challenging effort. In this work, the synergistic effects of combining stimuli-responsive polymers and nanomaterials with unique topographies to achieve smart antibacterial surfaces with on-demand switchable functionalities are explored. Silicon nanowire arrays are modified with a pH-responsive polymer, poly(methacrylic acid), which serves as both a dynamic reservoir for the controllable loading and release of a natural antimicrobial lysozyme and a self-cleaning platform for the release of dead bacteria and the reloading of new lysozyme for repeatable applications. The functionality of the surface can be simply switched via step-wise modification of the environmental pH and can be effectively maintained after several kill-release cycles. These results offer a new methodology for the engineering of surfaces with switchable functionalities for a variety of practical applications in the biomedical and biotechnology fields.

Preparation of Extracellular Matrix Developed Using Porcine Articular Cartilage and In Vitro Feasibility Study of Porcine Articular Cartilage as an Anti-Adhesive Film

In this study, we examined whether porcine articular cartilage (PAC) is a suitable and effective anti-adhesive material. PAC, which contained no non-collagenous tissue components, was collected by mechanical manipulation and decellularization of porcine knee cartilage. The PAC film for use as an anti-adhesive barrier was easily shaped into various sizes using homemade silicone molds. The PAC film was cross-linked to study the usefulness of the anti-adhesive barrier shape. The cross-linked PAC (Cx-PAC) film showed more stable physical properties over extended periods compared to uncross-linked PAC (UnCx-PAC) film. To control the mechanical properties, Cx-PAC film was thermally treated at 45 °C or 65 °C followed by incubation at room temperature. The Cx-PAC films exhibited varying enthalpies, ultimate tensile strength values, and contact angles before and after thermal treatment and after incubation at room temperature. Next, to examine the anti-adhesive properties, human umbilical vein endothelial cells (HUVECs) were cultured on Cx-PAC and thermal-treated Cx-PAC films. Scanning electron microscopy, fluorescence, and MTT assays showed that HUVECs were well adhered to the surface of the plate and proliferated, indicating no inhibition of the attachment and proliferation of HUVECs. In contrast, Cx-PAC and thermal-treated Cx-PAC exhibited little and/or no cell attachment and proliferation because of the inhibition effect on HUVECs. In conclusion, we successfully developed a Cx-PAC film with controllable mechanical properties that can be used as an anti-adhesive barrier.

Magnetic Drug Targeting as New Therapeutic Option for the Treatment of Biomaterial Infections

Implant-associated infections are a challenging problem in surgery. Bacteria in biofilms are difficult to treat as they are less susceptible to antibiotics or antiseptics which require high drug concentrations at the site of infection. We present a novel strategy to concentrate high antibiotic doses systemically at the target site using newly developed antibiotic-functionalized nanoparticles directed by a magnetic drug-targeting system. The important and effective antibiotic gentamicin served as antimicrobial substance and was ionically or covalently attached to magnetic nanoparticles. Subsequently, the particles were characterized thoroughly. Anti-infective properties with regard to Staphylococcus aureus and the degree of cytotoxicity concerning human umbilical vein endothelial cells were determined. The enrichment of the magnetic nanoparticles at the surface of model tubes in circulatory experiments was investigated. We describe a promising technique for the loading of magnetic nanoparticles to treat systemic infections. Gentamicin-coated magnetic nanoparticles reduced bacterial growth even beyond pathologically relevant concentrations within 24 h. Excellent concentration independent biocompatibility was found for the nanoparticles themselves and we demonstrate that the magnetic nanoparticles can be navigated and concentrated on surfaces of model implants using a permanent magnetic field.

Titanium Oxide Antibacterial Surfaces in Biomedical Devices

Titanium oxide is a heterogeneous catalyst whose efficient photoinduced activity, related to some of its allotropic forms, paved the way for its widespread technological use. Here, we offer a comparative analysis of the use of titanium oxide as coating for materials in biomedical devices. First, we introduce the photoinduced catalytic mechanisms of TiO2 and their action on biological environment and bacteria. Second, we overview the main physical and chemical technologies for structuring suitable TiO2 coatings on biomedical devices. We then present the approaches for in vitro characterization of these surfaces. Finally, we discuss the main aspects of TiO2 photoactivated antimicrobial activity on medical devices and limitations for these types of applications.

Mesoporous titanium dioxide coating for metallic implants

A bioactive mesoporous titanium dioxide (MT) coating for surface drug delivery has been investigated to develop a multifunctional implant coating, offering quick bone bonding and biological stability. An evaporation induced self-assembly (EISA) method was used to prepare a mesoporous titanium dioxide coating of the anatase phase with BET surface area of 172 m(2)/g and average pore diameter of 4.3 nm. Adhesion tests using the scratch method and an in situ screw-in/screw-out technique confirm that the MT coating bonds tightly with the metallic substrate, even after removal from bone. Because of its high surface area, the bioactivity of the MT coating is much better than that of a dense TiO(2) coating of the same composition. Quick formation of hydroxyapatite (HA) in vitro can be related to enhance bonding with bone. The uptake of antibiotics by the MT coating reached 13.4 mg/cm(3) within a 24 h loading process. A sustained release behavior has been obtained with a weak initial burst. By using Cephalothin as a model drug, drug loaded MT coating exhibits a sufficient antibacterial effect on the material surface, and within millimeters from material surface, against E.coli. Additionally, the coated and drug loaded surfaces showed no cytotoxic effect on cell cultures of the osteoblastic cell line MG-63. In conclusion, this study describes a novel, biocompatiblemesoporous implant coating, which has the ability to induce HA formation and could be used as a surface drug-delivery system.

Physicochemical regulation of biofilm formation

This article reviews the physical and chemical constraints of environments on biofilm formation. We provide a perspective on how materials science and engineering can address fundamental questions and unmet technological challenges in this area of microbiology, such as biofilm prevention. Specifically, we discuss three factors that impact the development and organization of bacterial communities. (1) Physical properties of surfaces regulate cell attachment and physiology and affect early stages of biofilm formation. (2) Chemical properties influence the adhesion of cells to surfaces and their development into biofilms and communities. (3) Chemical communication between cells attenuates growth and influences the organization of communities. Mechanisms of spatial and temporal confinement control the dimensions of communities and the diffusion path length for chemical communication between biofilms, which, in turn, influences biofilm phenotypes. Armed with a detailed understanding of biofilm formation, researchers are applying the tools and techniques of materials science and engineering to revolutionize the study and control of bacterial communities growing at interfaces.

Current requirements for polymeric biomaterials in otolaryngology

In recent years otolaryngology was strongly influenced by newly developed implants which are based on both, innovative biomaterials and novel implant technologies. Since the biomaterials are integrated into biological systems they have to fulfill all technical requirements and accommodate biological interactions. Technical functionality relating to implant specific mechanical properties, a sufficiently high stability in terms of physiological conditions, and good biocompatibility are the demands with regard to suitability of biomaterials. The goal in applying biomaterials for implants is to maintain biofunctionality over extended periods of time. These general demands to biomaterials are equally valid for use in otolaryngology. Different classes of materials can be utilized as biomaterials. Metals belong to the oldest biomaterials. In addition, alloys, ceramics, inorganic glasses and composites have been tested successfully. Furthermore, natural and synthetic polymers are widely used materials, which will be in the focus of the current article with regard to their properties and usage as cochlear implants, osteosynthesis implants, stents, and matrices for tissue engineering. Due to their application as permanent or temporary implants materials are differentiated into biostable and biodegradable polymers. The here identified general and up to date requirements for biomaterials and the illustrated applications in otolaryngology emphasize ongoing research efforts in this area and at the same time demonstrate the high significance of interdisciplinary cooperation between natural sciences, engineering, and medical sciences.

Ciprofloxacin-modified electrosynthesized hydrogel coatings to prevent titanium-implant-associated infections

New promising and versatile materials for the development of in situ sustained release systems consisting of thin films of either poly(2-hydroxyethyl methacrylate) or a copolymer based on poly(ethylene-glycol diacrylate) and acrylic acid were investigated. These polymers were electrosynthesized directly on titanium substrates and loaded with ciprofloxacin (CIP) either during or after the synthesis step. X-ray photoelectron spectroscopy was used to check the CIP entrapment efficiency as well as its surface availability in the hydrogel films, while high-performance liquid chromatography was employed to assess the release property of the films and to quantify the amount of CIP released by the coatings. These systems were then tested to evaluate the in vitro inhibition of methicillin-resistant Staphylococcus aureus (MRSA) growth. Moreover, a model equation is proposed which can easily correlate the diameter of the inhibition haloes with the amount of antibiotic released. Finally, MG63 human osteoblast-like cells were employed to assess the biocompatibility of CIP-modified hydrogel coatings.

Multifunctional implant coatings providing possibilities for fast antibiotics loading with subsequent slow release

The possibility to fast-load biomimetic hydroxyapatite coatings on surgical implant with the antibiotics Amoxicillin, Gentamicin sulfate, Tobramycin and Cephalothin has been investigated in order to develop a multifunctional implant device offering sustained local anti-bacterial treatment and giving the surgeon the possibility to choose which antibiotics to incorporate in the implant at the site of surgery. Physical vapor deposition was used to coat titanium surfaces with an adhesion enhancing gradient layer of titanium oxide having an amorphous oxygen poor composition at the interface and a crystalline bioactive anatase TiO(2) composition at the surface. Hydroxyapatite (HA) was biomimetically grown on the bioactive TiO(2) to serve as a combined bone in-growth promoter and drug delivery vehicle. The coating was characterized using scanning and transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The antibiotics were loaded into the HA coatings via soaking and the subsequent release and antibacterial effect were analyzed using UV spectroscopy and examination of inhibition zones in a Staphylococcus aureus containing agar. It was found that a short drug loading time of 15 min ensured antibacterial effects after 24 h for all antibiotics under study. It was further found that the release processes of Cephalothin and Amoxicillin consisted of an initial rapid drug release that varied unpredictably in amount followed by a reproducible and sustained release process with a release rate independent of the drug loading times under study. Thus, implants that have been fast-loaded with drugs could be stored for ~10 min in a simulated body fluid after loading to ensure reproducibility in the subsequent release process. Calculated release rates and measurements of drug amounts remaining in the samples after 22 h of release indicated that a therapeutically relevant dose could be achieved close to the implant surface for about 2 days. Concluding, the present study provides an outline for the development of a fast-loading slow-release surgical implant kit where the implant and the drug are separated when delivered to the surgeon, thus constituting a flexible solution for the surgeon by offering the choice of quick addition of antibiotics to the implant coating based on the patient need.

Polysorbate 80 inhibition of Pseudomonas aeruginosa biofilm formation and its cleavage by the secreted lipase LipA

Surface-associated bacterial communities known as biofilms are an important source of nosocomial infections. Microorganisms such as Pseudomonas aeruginosa can colonize the abiotic surfaces of medical implants, leading to chronic infections that are difficult to eradicate. Our study demonstrates that polysorbate 80 (PS80), a surfactant commonly added to food and medicines, is able to inhibit biofilm formation by P. aeruginosa on a variety of surfaces, including contact lenses. Many clinical isolates of P. aeruginosa, as well as gram-negative and gram-positive clinical isolates, were also inhibited in their ability to form biofilms in the presence of PS80. A P. aeruginosa mutant able to form biofilms in the presence of this surfactant was identified and characterized, and it was revealed that this mutant overexpresses a lipase, LipA. Surfactants such as PS80 can be cleaved by lipases, and we demonstrate that PS80 is cleaved by LipA at its ester bond. Finally, polyethoxylated(20) oleyl alcohol, a chemical with a structure that is similar to that of PS80 but that lacks the ester bond of PS80, can inhibit the biofilm formation of P. aeruginosa strains, including the mutant overexpressing LipA. Our results demonstrate that surfactants such as PS80 can inhibit bacterial biofilm formation on medically relevant materials at concentrations demonstrated to be safe in humans and suggest that the understanding of the mechanisms of bacterial resistance to such surfactants will be important in developing clinically effective derivatives.

Adhesion forces between Staphylococcus epidermidis and surfaces bearing self-assembled monolayers in the presence of model proteins

Self-assembled monolayers (SAMs) are being developed into coatings to reduce microbial biofilm formation on biomaterials. To test anti-adhesion properties, SAMs can be easily constructed on gold, and used to represent a coated biomaterial. However, coatings that prevent bacterial adhesion must also resist protein adsorption. We explored the competitive effects of bacteria and protein for adsorption to SAMs, choosing fetal bovine serum (FBS) to represent protein non-specific binding, and fibronectin (FN) to evaluate ligand/receptor binding. Staphylococcus epidermidis were immobilized on an atomic force microscope (AFM) tip and used as a force probe to detect the interaction forces between bacteria and gold-coated SAMs. The SAMs tested were alkanethiol molecules terminating in isophthalic acid (IPA) or isophthalic acid with silver (IAG). While S. epidermidis showed weak interactions with FBS, the bacteria showed strong adhesion with FN, due to ligand/receptor binding. Bacterial retention and viability experiments were correlated with the force measurements. S. epidermidis interacting with IAG SAMs showed a loss of viability, due to the mobility of silver ions. For most substrata, there was a link between high adhesion forces with bacteria and a high percentage of dead cells being retained on that substratum (even in the absence of a specific biocidal effect, such as silver). This may suggest that high adhesion forces can cause stress to the bacteria which contributed to their death. The relationship between highly adhesive SAMs and bacterial inactivation may be useful in future biomaterial design. When evaluating coatings for biomaterials, it is important to consider the interplay between bacteria, proteins, and the coating material.