Assembled gold nanorods for the photothermal killing of bacteria

Lipopolysaccharide targeting-peptide-capped chitosan gold nanoparticles for laser-induced antibacterial activity

Aim: We present the synthesis of anti-bacterial gold nanoparticles using chitosan as a dual-functional agent. The resulting ChAuNPs were further modified with a lipopolysaccharide-targeting antibacterial peptide to aid in biocompatibility and specificity.Materials & methods: The nanoparticles' antibacterial activity against Escherichia coli was tested in the presence of a 450 nm laser.Results: Our data suggested that the peptide and laser emissions had a synergistic impact on the gold nanoparticles, resulting in strong antibacterial effects. The study shows that advanced nanomaterials, including chitosan, gold nanoparticles and lipopolysaccharide targeting peptides, can boost antibacterial functions at a low concentration of 250 μg/ml.Conclusion: The findings highlight ChAuNPs' potential as strong antibacterial agents, with targeted alterations critical for maximizing their utilization.

Nanomaterials for Photothermal Antimicrobial Surfaces

Microbial infection diseases are a major threat to human health and have become one of the main causes of mortality. The search for novel antimicrobial strategies is an important challenge for the scientific community, considering also the constant increase of antimicrobial resistance and the rise of new diseases. Among the new strategies to combat microbial infections, the photothermal effect seems to be one of the most promising. Hyperthermia is an effective and broad spectrum strategy for the removal of microbial infections. Among all of the strategies to reduce the diffusion of microbial infections, the preparation of antimicrobial surfaces seems of primary importance. In many cases, in fact, an infection can be diffused through surfaces just by touching them, or by inoculating microbes through an internalizable device, such as an implant, a prosthesis, or a catheter. In this review, we will summarize the recent advances in the preparation of photothermal antibacterial surfaces.

Smart stimuli-responsive strategies for titanium implant functionalization in bone regeneration and therapeutics

With the increasing and aging of global population, there is a dramatic rise in the demand for implants or substitutes to rehabilitate bone-related disorders which can considerably decrease quality of life and even endanger lives. Though titanium and its alloys have been applied as the mainstream material to fabricate implants for load-bearing bone defect restoration or temporary internal fixation devices for bone fractures, it is far from rare to encounter failed cases in clinical practice, particularly with pathological factors involved. In recent years, smart stimuli-responsive (SSR) strategies have been conducted to functionalize titanium implants to improve bone regeneration in pathological conditions, such as bacterial infection, chronic inflammation, tumor and diabetes mellitus, etc. SSR implants can exert on-demand therapeutic and/or pro-regenerative effects in response to externally applied stimuli (such as photostimulation, magnetic field, electrical and ultrasound stimulation) or internal pathology-related microenvironment changes (such as decreased pH value, specific enzyme secreted by bacterial and excessive production of reactive oxygen species). This review summarizes recent progress on the material design and fabrication, responsive mechanisms, and in vitro and in vivo evaluations for versatile clinical applications of SSR titanium implants. In addition, currently existing limitations and challenges and further prospective directions of these strategies are also discussed.

Plasmonic inhibition of bacterial adhesion on gold-decorated mesoporous zirconium oxide thin films

Preventing bacterial development on surfaces is essential to avoid problems caused by biofouling. Surfaces decorated with gold nanoparticles have been shown to thermally kill bacteria under high-intensity NIR illumination. In this study, we evaluated the colonization by E. coli of nanostructured surfaces composed of mesoporous zirconia thin films, both with and without gold nanoparticles embedded into the pores. We studied the effect of the nanostructure and of low intensity visible light excitation of the gold nanoparticles on the colonization process. We found that neither the zirconia, nor the presence of pores, or even gold nanoparticles affect bacterial adhesion compared to the bare glass substrate. Therefore, mesoporous zirconia thin films are biologically inert scaffolds that enable the construction of robust surfaces containing functional nanoparticles that can affect bacterial growth. When the gold containing surfaces are irradiated with light, bacterial adhesion shows a remarkable 96 ± 4% reduction. Our studies revealed that these surfaces affect early colonization steps, prior to biofilm formation, preventing bacterial adhesion without affecting its viability. In contrast to related systems where plasmonic excitation induces membrane damage due to strong local heating, the membrane integrity is preserved, showing that these surfaces have a different working principle.

The current status of stimuli-responsive nanotechnologies on orthopedic titanium implant surfaces

With the continuous innovation and breakthrough of nanomedical technology, stimuli-responsive nanotechnology has been gradually applied to the surface modification of titanium implants to achieve brilliant antibacterial activity and promoted osteogenesis. Regarding to the different physiological and pathological microenvironment around implants before and after surgery, these surface nanomodifications are designed to respond to different stimuli and environmental changes in a timely, efficient, and specific way/manner. Here, we focus on the materials related to stimuli-responsive nanotechnology on titanium implant surface modification, including metals and their compounds, polymer materials and other materials. In addition, the mechanism of different response types is introduced according to different activation stimuli, including magnetic, electrical, photic, radio frequency and ultrasonic stimuli, pH and enzymatic stimuli (the internal stimuli). Meanwhile, the associated functions, potential applications and developing prospect were discussion.

Photothermal/Photoacoustic Therapy Combined with Metal-Based Nanomaterials for the Treatment of Microbial Infections

The increased spread and persistence of bacterial drug-resistant phenotypes remains a public health concern and has contributed significantly to the challenge of combating antibiotic resistance. Nanotechnology is considered an encouraging strategy in the fight against antibiotic-resistant bacterial infections; this new strategy should improve therapeutic efficacy and minimize side effects. Evidence has shown that various nanomaterials with antibacterial performance, such as metal-based nanoparticles (i.e., silver, gold, copper, and zinc oxide) have intrinsic antibacterial properties. These antibacterial agents, such as those made of metal oxides, carbon nanomaterials, and polymers, have been used not only to improve antibacterial efficacy but also to reduce bacterial drug resistance due to their interaction with bacteria and their photophysical properties. These nanostructures have been used as effective agents for photothermal therapy (PTT) and photodynamic therapy (PDT) to kill bacteria locally by heating or the controlled production of reactive oxygen species. Additionally, PTT or PDT therapies have also been combined with photoacoustic (PA) imaging to simultaneously improve treatment efficacy, safety, and accuracy. In this present review, we present, on the one hand, a summary of research highlighting the use of PTT-sensitive metallic nanomaterials for the treatment of bacterial and fungal infections, and, on the other hand, an overview of studies showing the PA-mediated theranostic functionality of metal-based nanomaterials.

Niobium carbide–mediated photothermal therapy for infected wound treatment

Bacterial infections of the wounds on the skin surface significantly reduce the rate of wound healing, potentially leading to serious systemic infections. Antibiotics are the first-line drugs for the treatment of these infections. However, the misuse and overuse of antibiotics have led to the emergence of bacterial resistance. Therefore, a new antimicrobial strategy is urgently needed. Photothermal therapy (PTT) is a novel efficient therapeutic technique that can produce irreversible cell damage to induce death of bacteria, possessing a great potential in infected wound healing. This work describes the use of a new photothermal agent (PTA) such as niobium carbide (NbC) nanoparticles with outstanding near-infrared (NIR) absorption property. NbC nanoparticles converted NIR laser irradiation energy into localized heat for photothermal treatment. In vitro antimicrobial experiments have revealed that NbC nanoparticles exert excellent antimicrobial effects against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Moreover, NbC nanoparticles accelerated E. coli–infected wound healing process, reduced inflammatory response, and showed good biosafety in vivo. Altogether, NbC nanoparticles represent an efficient PTA for antimicrobial treatment and are a bio-safe material with low toxicity in vivo.

Antibacterial Properties of Gold Nanoparticles in the Modification of Medical Implants: A Systematic Review

The widespread occurrence of bacterial infections and their increased resistance to antibiotics has led to the development of antimicrobial coatings for multiple medical implants. Owing to their desirable properties, gold nanoparticles (AuNPs) have been developed as antibacterial agents. This systematic investigation sought to analyze the antibacterial effects of implant material surfaces modified with AuNPs. The data from 27 relevant studies were summed up. The included articles were collected from September 2011 to September 2021. According to the retrieved literature, we found that medical implants modified by AuNPs have good antibacterial effects against gram-positive and gram-negative bacteria, and the antibacterial effects would be improved by near-infrared (NIR) radiation.

Facile synthesis of black phosphorus-zinc oxide nanohybrids for antibacterial coating of titanium surface

Bacterial infection is a major complication associated with bioimplant materials, including titanium (Ti) based orthopedic joints and dental implants. Thus, the fabrication of Ti surfaces with antibacterial activity is highly important. Black phosphorus (BP) is a recently discovered promising two-dimensional semiconductor for various biomedical applications due to its tunable bandgap and physicochemical properties. The present study aimed to synthesize zinc oxide (ZnO) laden BP nanohybrids (NH) and their coatings on a Ti bioimplant surface for improving the antibacterial activities against pathogenic bacteria with and without near-infrared (NIR) light irradiation. Nanohybrids were produced with the slightly oxidized BP NF and electrostatically laden ZnO NP. The produced BP-ZnO NH was a NIR active nanomaterial (up to ∼1000 nm), demonstrating a photothermal effect against bacterial infection and showing improved activity by damaging the cell membrane towards S. aureus in comparison to E. coli. Ti surface coated with BP-ZnO NH embedded chitosan (CS) demonstrated better antibacterial activity than BP NF, especially with NIR light treatment. Additionally, the produced BP nanoflakes and BP-ZnO NH, and their coatings over the Ti surface were found to be toxic at a negligible level. Electrochemical studies revealed the high corrosion resistance of the Ti surface coated with the synthesized antibacterial agents without altering its characteristic passive behavior. Owing to the interactions between the charged groups between chitosan and cell surfaces, a slight increase in antibacterial activities was noticed. Chitosan-based coating matrix embedded with nanoagents has adhered well over the Ti surface due to its inherent film-forming and high adhesion properties.

Gold nanocrystals: optical properties, fine-tuning of the shape, and biomedical applications

Noble metal nanomaterials with special physical and chemical properties have attracted considerable attention in the past decades. In particular, Au nanocrystals (NCs), which possess high chemical inertness and unique surface plasmon resonance (SPR), have attracted extensive research interest. In this study, we review the properties and preparation of Au NCs with different morphologies as well as their important applications in biological detection. The preparation of Au NCs with different shapes by many methods such as seed-mediated growth method, seedless synthesis, polyol process, ultrasonic method, and hydrothermal treatment has already been introduced. In the seed-mediated growth method, the influence factors in determining the final shape of Au NCs are discussed. Au NCs, which show significant size-dependent color differences are proposed for preparing biological probes to detect biomacromolecules such as DNA and protein, while probe conjugate molecules serves as unique coupling agents with a target. Particularly, Au nanorods (NRs) have some unique advantages in the application of biological probes and photothermal cancer therapy compared to Au nanoparticles (NPs).

Light activation of gold nanorods but not gold nanospheres enhance antibacterial effect through photodynamic and photothermal mechanisms

Plasmonic nanomaterials of gold and silver have been reported to have antibacterial effect. In this study, three gold nanomaterials (NMs) of different aspect rations (Gold nanospheres (AuNSs, aspect ratio 1), and two gold nanorods (AuNRs636, aspect ratio 2.79; AuNRs772, aspect ratio 3.42)) and silver nanoparticles (AgNPs) were synthesized, characterized and the effect of incandescent light on their antibacterial properties were examined. Bacterial inactivation during photoinactivation of nanomaterials and antibacterial mechanisms (biotic ROS, membrane potential, membrane damage) were investigated using Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Salmonella enterica serovar Typhimurium, and methicillin-resistant S. aureus. The results indicated that AuNSs had no antibacterial activity in the tested concentration (0.49-250 μg/mL), while AuNR636 and AuNRs772 showed significant bactericidal effect on all tested bacteria. Notably, AuNRs636 presented higher antibacterial effect than AuNRs772, which could result from higher surface reactivity of AuNRs636 owing to higher dangling bonds. Further studies showed that AuNRs but not AuNSs generated hydroxyl radicals (·OH) (photodynamic effect) and photothermal effect when exposed to incandescent light. The combined photodynamic and photothermal effect resulted in bacterial inactivation through cell membrane damage, lowering of cell membrane potential and DNA degradation. In summary, this investigation showed that Au NRs but not Au NSs exhibit photodynamic and photothermal effects suggesting the potential of fabricating material surfaces with Au NRs for photoactivated bacterial inactivation.

Harvesting Light To Produce Heat: Photothermal Nanoparticles for Technological Applications and Biomedical Devices

The photothermal properties of nanoparticles (NPs), that is, their ability to convert absorbed light into heat, have been studied since the end of the last century, mainly on gold NPs. In the new millennium, these studies have developed into a burst of research dedicated to the photothermal ablation of tumors. However, beside this strictly medical theme, research has also flourished in the connected areas of photothermal antibacterial surface coatings, gels and polymers, of photothermal surfaces for cell stimulation, as well as in purely technological areas that do not involve medical biotechnology. These include the direct conversion of solar light into heat, a more efficient sun-powered generation of steam and the use of inkjet-printed patterns of photothermal NPs for anticounterfeit printing based on temperature reading, to cite but a few. After an analysis of the photothermal effect (PTE) and its mechanism, this minireview briefly considers the antitumor-therapy theme and takes an in-depth look at all the other technological and biomedical applications of the PTE, paying particular attention to photothermal materials whose NPs have joined those based on Au.

Surface Design for Antibacterial Materials: From Fundamentals to Advanced Strategies

Healthcare-acquired infections as well as increasing antimicrobial resistance have become an urgent global challenge, thus smart alternative solutions are needed to tackle bacterial infections. Antibacterial materials in biomedical applications and hospital hygiene have attracted great interest, in particular, the emergence of surface design strategies offer an effective alternative to antibiotics, thereby preventing the possible development of bacterial resistance. In this review, recent progress on advanced surface modifications to prevent bacterial infections are addressed comprehensively, starting with the key factors against bacterial adhesion, followed by varying strategies that can inhibit biofilm formation effectively. Furthermore, "super antibacterial systems" through pre-treatment defense and targeted bactericidal system, are proposed with increasing evidence of clinical potential. Finally, the advantages and future challenges of surface strategies to resist healthcare-associated infections are discussed, with promising prospects of developing novel antimicrobial materials.

Gold Nanostars with Reduced Fouling Facilitate Small Molecule Detection in the Presence of Protein

Gold nanoparticles have the potential to be used in biomedical applications from diagnostics to drug delivery. However, interactions of gold nanoparticles with different biomolecules in the cellular environment result in the formation of a “protein corona”—a layer of protein formed around a nanoparticle, which induces changes in the properties of nanoparticles. In this work we developed methods to reproducibly synthesize spheroidal and star-shaped gold nanoparticles, and carried out a physico-chemical characterization of synthesized anionic gold nanospheroids and gold nanostars through transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential (ZP), nanoparticles tracking analysis (NTA), ultraviolet-visible (UV–Vis) spectroscopy and estimates of surface-enhanced Raman spectroscopy (SERS) signal enhancement ability. We analyzed how they interact with proteins after pre-incubation with bovine serum albumin (BSA) via UV–Vis, DLS, ZP, NTA, SERS, cryogenic TEM (cryo-TEM) and circular dichroism (CD) spectroscopy. The tests demonstrated that the protein adsorption on the particles’ surfaces was different for spheroidal and star shaped particles. In our experiments, star shaped particles limited the protein corona formation at SERS “hot spots”. This benefits the small-molecule sensing of nanostars in biological media. This work adds more understanding about protein corona formation on gold nanoparticles of different shapes in biological media, and therefore guides design of particles for studies in vitro and in vivo.

Multifunctional Gold Nanorod for Therapeutic Applications and Pharmaceutical Delivery Considering Cellular Metabolic Responses, Oxidative Stress and Cellular Longevity

Multifunctional gold nanorods (GNR) have drawn growing interest in biomedical fields because of their excellent biocompatibility, ease of alteration, and special optical properties. The great advantage of using GNR in medicine is their application to Photothermal therapy (PPTT), which is possible thanks to their ability to turn luminous energy into heat to cause cellular hyperthermia. For this purpose, the relevant articles between 1988 and 2020 were searched in databases such as John Wiley, Free paper, Scopus, Science Direct, and Springer to obtain the latest findings on multifunctional gold nanorods for therapeutic applications and pharmaceutical delivery. In this article, we review recent progress in diagnostic and therapeutic applications of multifunctional GNR, highlighting new information about their toxicity to various cellular categories, oxidative stress, cellular longevity, and their metabolic effects, such as the effect on the energy cycles and genetic structures. The methods for the synthesis and functionalization of GNR were surveyed. This review includes new information about GNR toxicity to various cellular categories and their metabolic effects.

Toward Bactericidal Enhancement of Additively Manufactured Titanium Implants

Implant-associated infections (IAIs) are among the most intractable and costly complications in implant surgery. They can lead to surgery failure, a high economic burden, and a decrease in patient quality of life. This manuscript is devoted to introducing current antimicrobial strategies for additively manufactured (AM) titanium (Ti) implants and fostering a better understanding in order to pave the way for potential modern high-throughput technologies. Most bactericidal strategies rely on implant structure design and surface modification. By means of rational structural design, the performance of AM Ti implants can be improved by maintaining a favorable balance between the mechanical, osteogenic, and antibacterial properties. This subject becomes even more important when working with complex geometries; therefore, it is necessary to select appropriate surface modification techniques, including both topological and chemical modification. Antibacterial active metal and antibiotic coatings are among the most commonly used chemical modifications in AM Ti implants. These surface modifications can successfully inhibit bacterial adhesion and biofilm formation, and bacterial apoptosis, leading to improved antibacterial properties. As a result of certain issues such as drug resistance and cytotoxicity, the development of novel and alternative antimicrobial strategies is urgently required. In this regard, the present review paper provides insights into the enhancement of bactericidal properties in AM Ti implants.

Nanoparticles as therapeutic options for treating multidrug-resistant bacteria: research progress, challenges, and prospects

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.

Gold Nanomaterials as a Promising Integrated Tool for Diagnosis and Treatment of Pathogenic Infections-A Review

This review summarizes research on functionalized gold nanomaterials as pathogen detection sensors and pathogen elimination integrated tools. After presenting the challenge of current severe threat from pathogenic bacteria and the increasingly serious growth rate of drug resistance, the first section mainly introduces the conspectus of gold nanostructures from synthesis, characterization, physicochemical properties and applications of gold nanomaterials. The next section deals with gold nanomaterials-based pathogen detection sensors such as colorimetric sensors, fluorescence sensors and Surface-Enhanced Raman Scattering sensors. We then discuss strategies based on gold nanomaterials for eliminating pathogenic infections, such as the dual sterilization strategy for grafting gold nanomaterials with antibacterial substances, photothermal antibacterial and photodynamic antibacterial methods. The fourth part briefly introduces the comprehensive strategy for diagnosis and sterilization of pathogen infection based on gold nanomaterials, such as the diagnosis and treatment strategy for pathogen infection using Roman signals real-time monitoring and photothermal sterilization. A concluding section that summarizes the current status and challenges of the novel diagnosis and treatment integrated strategy for pathogenic infections, gives an outlook on potential future perspectives.

Antibacterial activity of an NIR-induced Zn ion release film

Photothermal therapy originated from using gold nanorods (GNRs) and near-infrared (NIR) irradiation has been widely used in the antibacterial field. Zn element exhibits antimicrobial activity against various bacterial and fungal strains. In this study, a bilayer film, consisting of GNRs as the inner layer and a polydopamine layer containing Zn element (PDA@Zn) as the outer layer, was deposited on the Ti surface. The results testified that all the GNR-modified surfaces had the same photothermal conversion efficiency. The Ti surface modified with GNR and PDA@Zn layers had better antibacterial activity against E. coli and S. aureus due to the GNR-induced photothermal effect and the antibacterial Zn element. Moreover, the accelerated release of Zn ions from the PDA@Zn layer was attributed to the GNR-induced high temperature under the NIR irradiation, which caused the concentration of Zn ions to be high enough to kill the surrounding bacteria. This study illustrates that a composite surface possessing both the contact and heat-responsive antibacterial property was constructed on titanium for potential clinical applications.

Plasmonically Modulated Gold Nanostructures for Photothermal Ablation of Bacteria

With the wide utilization of antibiotics, antibiotic-resistant bacteria have been often developed more frequently to cause potential global catastrophic consequences. Emerging photothermal ablation has been attracting extensive research interest for quick/effective eradication of pathogenic bacteria from contaminated surroundings and infected body. In this field, anisotropic gold nanostructures with tunable size/morphologies have been demonstrated to exhibit their outstanding photothermal performance through strong plasmonic absorption of near-infrared (NIR) light, efficient light to heat conversion, and easy surface modification for targeting bacteria. To this end, this review first introduces thermal treatment of infectious diseases followed by photothermal therapy via heat generation on NIR-absorbing gold nanostructures. Then, the usual synthesis and spectral features of diversified gold nanostructures and composites are systematically overviewed with the emphasis on the importance of size, shape, and composition to achieve strong plasmonic absorption in NIR region. Further, the innovated photothermal applications of gold nanostructures are comprehensively demonstrated to combat against bacterial infections, and some constructive suggestions are also discussed to improve photothermal technologies for practical applications.

Photothermal bactericidal surfaces: killing bacteria using light instead of biocides

Recent developments of photothermal bactericidal surfaces based on immobilized photothermal agents to kill bacteria through hyperthermia effects are reviewed.

A facile and universal strategy to endow implant materials with antibacterial ability via alkalinity disturbing bacterial respiration

Multifarious strategies have been proposed to enhance the antibacterial ability of implant surfaces for preventing bacterial infection, however, developing facile and universal modification methods still remains extremely elusive. Herein, inspired by the fact that the electron transfer respiratory chain of bacteria is embedded in the membrane, we proposed a novel strategy of local alkalinity disturbing bacterial respiration to endow implant materials with antibacterial ability. As a demonstration, MgO was deposited on biomedical titanium via magnetron sputtering to regulate surface alkalinity. With the thickness of MgO films increasing, they exhibited an excellent antibacterial rate against both Gram-negative and positive bacteria. The antibacterial mechanism confirmed that the alkaline surface can disturb the bacterial respiration action via weakening the transmembrane proton concentration gradient, resulting in the blockage of energy metabolism and the increase of oxidative stress of bacteria. Cell experiments indicated that MgO films not only have no obvious cytotoxicity to osteoblast cells, but can also selectively kill bacteria and promote cell proliferation in the presence of both bacteria and cells. More importantly, the by-product of MgO was only the biocompatible Mg2+, reducing any concerns about potential toxic effects. Furthermore, sputtering alkaline MgO films was confirmed to work well on polyetheretherketone polymer and zirconia ceramic implants, which indicates that this strategy has broad prospects of clinical application for preventing implant-associated bacterial infection.

Nano-Modified Titanium Implant Materials: A Way Toward Improved Antibacterial Properties

Titanium and its alloys have superb biocompatibility, low elastic modulus, and favorable corrosion resistance. These exceptional properties lead to its wide use as a medical implant material. Titanium itself does not have antibacterial properties, so bacteria can gather and adhere to its surface resulting in infection issues. The infection is among the main reasons for implant failure in orthopedic surgeries. Nano-modification, as one of the good options, has the potential to induce different degrees of antibacterial effect on the surface of implant materials. At the same time, the nano-modification procedure and the produced nanostructures should not adversely affect the osteogenic activity, and it should simultaneously lead to favorable antibacterial properties on the surface of the implant. This article scrutinizes and deals with the surface nano-modification of titanium implant materials from three aspects: nanostructures formation procedures, nanomaterials loading, and nano-morphology. In this regard, the research progress on the antibacterial properties of various surface nano-modification of titanium implant materials and the related procedures are introduced, and the new trends will be discussed in order to improve the related materials and methods.

Eradicating Infecting Bacteria while Maintaining Tissue Integration on Photothermal Nanoparticle-Coated Titanium Surfaces

Photothermal nanoparticles locally release heat when irradiated by near-infrared (NIR). Clinical applications initially involved tumor treatment, but currently extend toward bacterial infection control. Applications toward much smaller, micrometer-sized bacterial infections, however, bear the risk of collateral damage by dissipating heat into tissues surrounding an infection site. This can become a complication when photothermal nanoparticle coatings are clinically applied on biomaterial surfaces requiring tissue integration, such as titanium-made, bone-anchored dental implants. Dental implants can fail due to infection in the pocket formed between the implant screw and the surrounding soft tissue ("peri-implantitis"). We address the hitherto neglected potential complication of collateral tissue damage by evaluating photothermal, polydopamine nanoparticle (PDA-NP) coatings on titanium surfaces in different coculture models. NIR irradiation of PDA-NP-coated (200 μg/cm2) titanium surfaces with adhering Staphylococcus aureus killed staphylococci within an irradiation time window of around 3 min. Alternatively, when covered with human gingival fibroblasts, this irradiation time window maintained surface coverage by fibroblasts. Contaminating staphylococci on PDA-NP-coated titanium surfaces, as can be per-operatively introduced, reduced surface coverage by fibroblasts, and this could be prevented by NIR irradiation for 5 min or longer prior to allowing fibroblasts to adhere and grow. Negative impacts of early postoperative staphylococcal challenges to an existing fibroblast layer covering a coated surface were maximally prevented by 3 min NIR irradiation. Longer irradiation times caused collateral fibroblast damage. Late postoperative staphylococcal challenges to a protective keratinocyte layer covering a fibroblast layer required 10 min NIR irradiation for adverting a staphylococcal challenge. This is longer than foreseen from monoculture studies because of additional heat uptake by the keratinocyte layer. Summarizing, photothermal treatment of biomaterial-associated infection requires precise timing of NIR irradiation to prevent collateral damage to tissues surrounding the infection site.

PDA/Cu Bioactive Hydrogel with "Hot Ions Effect" for Inhibition of Drug-Resistant Bacteria and Enhancement of Infectious Skin Wound Healing

Quick and effective sterilization of drug-resistant bacteria inevitably became an ever-growing global challenge. In this study, a multifunctional composite (PDA/Cu-CS) hydrogel mainly composed of polydopamine (PDA) and copper-doped calcium silicate ceramic (Cu-CS) was prepared. It was confirmed that PDA/copper (PDA/Cu) complexing in the composite hydrogel played a key role in enhancing the photothermal performance and antibacterial activity. Through a unique "hot ions effect", created by the heating of Cu ions through the photothermal effect of the composite hydrogel, the hydrogel showed high-efficiency, quick, and long-term inhibition of methicillin-resistant Staphylococcus aureus and Escherichia coli. In addition, the hydrogel possessed remarkable bioactivity to stimulate angiogenesis. The in vivo results confirmed that the "hot ions effect" of the composite hydrogel removed existing infection in the wound area efficiently and significantly promoted angiogenesis and collagen deposition during infectious skin wound healing. Our results suggested that the design of multifunctional hydrogels with "hot ions effect" may be an effective therapeutic approach for the treatment of infectious wounds.

Nanomaterials for the Photothermal Killing of Bacteria

An upsurge in the multidrug-resistant (MDR) bacterial pestilence is a global cause for concern in terms of human health. Lately, nanomaterials with photothermal effects have assisted in the efficient killing of MDR bacteria, attributable to their uncommon plasmonic, photocatalytic, and structural properties. Examinations of substantial amounts of photothermally enabled nanomaterials have shown bactericidal effects in an optimized time under near-infrared (NIR) light irradiation. In this review, we have compiled recent advances in photothermally enabled nanomaterials for antibacterial activities and their mechanisms. Photothermally enabled nanomaterials are classified into three groups, including metal-, carbon-, and polymer-based nanomaterials. Based on substantial accomplishments with photothermally enabled nanomaterials, we have inferred current trends and their prospective clinical applications.

Synthesis of Gold Nanoparticle: Peptide-Drug Conjugates for Targeted Drug Delivery

Peptide-drug conjugates (PDCs) are being developed for the targeted delivery of drugs to cancer cells. Several approaches are being followed to enhance their stability in biological solutions. Here we describe an effective method to easily couple PDCs to polyethylene-coated gold nanoparticles. We also outline analytical methods to validate the coupling and assays to measure the stability and cytotoxic efficacy of the conjugates.

Virus-Sized Gold Nanorods: Plasmonic Particles for Biology

Plasmons, collective oscillations of conduction-band electrons in nanoscale metals, are well-known phenomena in colloidal gold and silver nanocrystals that produce brilliant visible colors in these materials that depend on the nanocrystal size and shape. Under illumination at or near the plasmon bands, gold and silver nanocrystals exhibit properties that enable fascinating biological applications: (i) the nanocrystals elastically scatter light, providing a straightforward way to image them in complex aqueous environments; (ii) the nanocrystals produce local electric fields that enable various surface-enhanced spectroscopies for sensing, molecular diagnostics, and boosting of bound fluorophore performance; (iii) the nanocrystals produce heat, which can lead to chemical transformations at or near the nanocrystal surface and can photothermally destroy nearby cells. While all the above-mentioned applications have already been well-demonstrated in the literature, this Account focuses on several other aspects of these nanomaterials, in particular gold nanorods that are approximately the size of viruses (diameters of ∼10 nm, lengths up to 100 nm). Absolute extinction, scattering, and absorption properties are compared for gold nanorods of various absolute dimensions, and references for how to synthesize gold nanorods with four different absolute dimensions are provided. Surface chemistry strategies for coating nanocrystals with smooth or rough shells are detailed; specific examples include mesoporous silica and metal-organic framework shells for porous (rough) coatings and polyelectrolyte layer-by-layer wrapping for "smooth" shells. For self-assembled-monolayer molecular coating ligands, the smoothest shells of all, a wide range of ligand densities have been reported from many experiments, yielding values from less than 1 to nearly 10 molecules/nm2 depending on the nanocrystal size and the nature of the ligand. Systematic studies of ligand density for one particular ligand with a bulky headgroup are highlighted, showing that the highest ligand density occurs for the smallest nanocrystals, even though these ligand headgroups are the most mobile as judged by NMR relaxation studies. Biomolecular coronas form around spherical and rod-shaped nanocrystals upon immersion into biological fluids; these proteins and lipids can be quantified, and their degree of adsorption depends on the nanocrystal surface chemistry as well as the biophysical characteristics of the adsorbing biomolecule. Photothermal adsorption and desorption of proteins on nanocrystals depend on the enthalpy of protein-nanocrystal surface interactions, leading to light-triggered alteration in protein concentrations near the nanocrystals. At the cellular scale, gold nanocrystals exert genetic changes at the mRNA level, with a variety of likely mechanisms that include alteration of local biomolecular concentration gradients, changes in mechanical properties of the extracellular matrix, and physical interruption of key cellular processes-even without plasmonic effects. Microbiomes, both organismal and environmental, are the likely first point of contact of nanomaterials with natural living systems; we see a major scientific frontier in understanding, predicting, and controlling microbe-nanocrystal interactions, which may be augmented by plasmonic effects.

Sesbania Gum-Supported Hydrophilic Electrospun Fibers Containing Nanosilver with Superior Antibacterial Activity

In this contribution, we report for the first time on a new strategy for developing sesbania gum-supported hydrophilic fibers containing nanosilver using electrospinning (SG-Ag/PAN electrospun fibers), which gives the fibers superior antibacterial activity. Employing a series of advanced technologies-scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, and contact angle testing-we characterized the as-synthesized SG-Ag/PAN electrospun fibers in terms of morphology, size, surface state, chemical composition, and hydrophilicity. By adjusting the synthesis conditions, in particular the feed ratio of sesbania gum (SG) and polyacrylonitrile (PAN) to Ag nanoparticles (NPs), we regulated the morphology and size of the as-electrospun fibers. The fibers' antibacterial properties were examined using the colony-counting method with two model bacteria: Escherichia coli (a Gram-negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium). Interestingly, compared to Ag/PAN and SG-PAN electrospun fibers, the final SG-Ag/PAN showed enhanced antibacterial activity towards both of the model bacteria due to the combination of antibacterial Ag NPs and hydrophilic SG, which enabled the fibers to have sufficient contact with the bacteria. We believe this strategy has great potential for applications in antibacterial-related fields.