Practical Preparation of Infection-Resistant Biomedical Surfaces from Antimicrobial β-Peptide Polymers

AMP-Mimetic Antimicrobial Polymer-Involved Synergic Therapy with Various Coagents for Improved Efficiency

The misuse of antibiotics contributes to the emergence of multidrug-resistant (MDR) bacteria. Infections caused by MDR bacteria are rapidly evolving into a significant threat to global healthcare due to the lack of effective and safe treatments. Antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity kill bacteria generally through a membrane disruption mechanism; hence, they tend not to induce resistance readily. However, AMPs exhibit disadvantages, such as high cost and susceptibility to proteolytic degradation, which limit their clinical application. AMP-mimetic antimicrobial polymers, with low cost, stability to proteolysis, broad-spectrum antimicrobial activity, negligible antimicrobial resistance, and rapid bactericidal effect, have received extensive attention as a new type of antibacterial drugs. Lately, AMP-mimetic polymer-involved synergic therapy provides a superior alternative to combat MDR bacteria by distinct mechanisms. In this Review, we summarize the AMP-mimetic antimicrobial polymers involved in synergic therapy, particularly focusing on the different combinations between the polymers with commercially available antimicrobials, organic small molecule photosensitizers, inorganic nanomaterials, and nitric oxide.

Antimicrobial peptide immobilization on catechol-functionalized PCL/alginate wet-spun fibers to combat surgical site infection

Surgical site infection (SSI) caused by pathogenic bacteria leads to delayed wound healing and extended hospitalization. Inappropriate uses of antibiotics have caused a surge in SSI and common antibiotics are proving to be ineffective against SSI. Antimicrobial peptides (AMPs) can be a potential solution to prevent SSI because of their broad spectrum of antimicrobial activities. In this study, naturally sourced AMPs were studied along with microfibers, fabricated by a novel wet-spinning method using sodium alginate and polycaprolactone. Afterward, fibers were functionalized by the catechol groups of dopamine immobilizing nucleophilic AMPs on the surface. Conjugation between PCL and alginate resulted in fibers with smooth surfaces improving their mechanical strength via hydrogen bonds. Having an average diameter of 220 μm, the mechanical properties of the fiber complied with USP standards for suture size 3-0. Engineered microfibers were able to hinder the growth of Proteus spp., a pathogenic bacterium for at least 60 hours whereas antibiotic ceftazidime failed. When subjected to a linear incisional wound model study, accelerated healing was observed when the wound was closed using the engineered fiber compared to Vicryl. The microfibers promoted faster re-epithelialization compared to Vicryl proving their higher wound healing capacity.

Mussel-Inspired Antimicrobial and Antifouling Coating Constructed by the Combination of Zwitterionic Copolymers and Silver Nanoparticles

Biofouling and bacterial infections are significant challenges in biomedical devices. In this study, a biocompatible dual-functional coating with antimicrobial and antifouling properties is developed by co-depositing the zwitterionic copolymer and silver nanoparticles via a dopamine-assisted strategy. Inspired by mussel adhesion, the coating exhibits substrate-independent adhesion as a result of the formation of irreversible covalent bonds. The zwitterionic copolymer in the dual coating plays a crucial role in improving surface wettability and reducing protein adsorption and platelet and bacterial adhesion, thereby improving its antifouling property significantly. The silver nanoparticles reduced by self-polymerized polydopamine without the addition of any chemical reductants can effectively improve the antimicrobial activity. Furthermore, as the zwitterion content in the zwitterion polymer increases, the antibacterial and antifouling properties of the coating can be further advanced. The simple and effective approach presented here provides a promising pathway for constructing potent antibacterial and antifouling surfaces, demonstrating great potential for clinical applications in implanted materials.

Facile Construction of Antimicrobial Surface via One-Step Co-Deposition of Peptide Polymer and Dopamine

The infections associated with implantable medical devices can greatly affect the therapeutic effect and impose a heavy financial burden. Therefore, it is of great significance to develop antimicrobial biomaterials for the prevention and mitigation of healthcare-associated infections. Here, a facile construction of antimicrobial surface via one-step co-deposition of peptide polymer and dopamine is reported. The co-deposition of antimicrobial peptide polymer DLL60 BLG40 with dopamine (DA) on the surface of thermoplastic polyurethane (TPU) provides peptide polymer-modified TPU surface (TPU-DLL60 BLG40 ). The antimicrobial test shows that the TPU-DLL60 BLG40 surfaces of the sheet and the catheter both exhibit potent killing of 99.9% of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). In addition, the TPU-DLL60 BLG40 surface also exhibits excellent biocompatibility. This one-step antimicrobial modification method is fast and efficient, implies promising application in surface antimicrobial modification of implantable biomaterials and medical devices.

Fabrication of Oleophilic Polypeptide Nanoparticle from Complexing of Cross-Linked Epsilon-poly-l-lysine with Docusate Sodium for Preparation of Bactericidal Thermoplastic Polyurethanes

Thermoplastic polyurethanes (TPUs) are extensively utilized in the biomedical field due to their exceptional mechanical properties and biocompatibility. However, the lack of antibacterial activity limits their application ranges. Nanoscopic particle-based additives with inherent antibacterial characteristics are regarded as promising strategies to prevent biomaterials-associated infection. Herein, a novel polymeric nanoparticle is prepared, which integrates chemically cross-linked epsilon-poly-l-lysine (CPL) and anionic surfactant-docusate sodium (DS). The cross-linked epsilon-poly-l-lysine/docusate sodium (CPL/DS) nanoparticle can be well dispersed in organic solvent and a polymer matrix, which is beneficial to endowing TPUs with synergistic miscibility and antibacterial properties. An antibacterial test showed that the CPL/DS nanoparticles have strong antibacterial activity against S. aureus. Moreover, the results of antibacterial experiments in vitro revealed that almost 100% of S. aureus could be killed by CPL/DS nanoparticle-embedded TPU film with a content of 0.5 wt %. In addition, all of the CPL/DS modified TPU films showed good cytocompatibility in vitro. Consequently, this kind of CPL/DS nanoplatform has great potential to serve as a safe and high-efficient bactericidal agent for endowing biomedical devices with bactericidal property.

Regulation of Hydrophobic Structures of Antibacterial Guanidinium-Based Amphiphilic Polymers for Subcutaneous Implant Applications

Antimicrobial peptide mimics have been used to kill bacteria and construct antibacterial materials. Precise design and construction of chemical structure are essential for easy access to highly effective antimicrobial peptide mimics. Herein, cationic guanidinium-based polymers (PGXs) with varying hydrophobic structures were synthesized to explore the structure and antibacterial activity relationship of antimicrobial peptide mimics and to construct antibacterial implants. The effect of the hydrophobic chemical structure, including carbon chain length and configuration, on the antimicrobial activities against both Escherichia coli and Staphylococcus aureus was investigated. The antibacterial activities of PGXs improved with increasing alkyl chain length, and PGXs with a straight-chain hydrophobic structure exhibited better bactericidal activities than those with cyclic alkane and aromatic hydrocarbon. Furthermore, PGXs grafted with poly(dimethylsiloxane) (PDMS-PGXs) showed a similar bactericidal change tendency of PGXs in solution. Additionally, the PDMS-PGXs showed potent antibiofilm performance in vitro, which can inhibit bacterial infection in vivo as subcutaneous implants. This study may propose a basis for the precise design and construction of antibacterial materials and provide a promising way of designing biomedical devices and implants with bacterial infection-combating activities.

Activities of a broad-spectrum antimicrobial peptide analogue SAMP-A4-C8 and its combat against pneumonia in Staphylococcus aureus-infected mice

Antimicrobial peptides and their analogues have become substitutes for antibiotics in recent years. The antimicrobial peptide analogue SAMP-A4-C8 (n-octanoic-VRLLRRRI) with high antimicrobial activity was found in our lab. We speculate that it may kill pathogens by some lethal mechanism of action. In the present investigation, the microbicidal activities of SAMP-A4-C8 and its mechanism of action were investigated. The results demonstrated that SAMP-A4-C8 had lethal activities against Staphylococcus aureus and Candida albicans by cell disruption. Based on its microbicidal activities, we believe that it is worth further research for its potential as drug candidate. The results showed that SAMP-A4-C8, with low propensity to induce the resistance of S. aureus and C. albicans, could kill the persister cells of S. aureus and C. albicans, exhibited biofilm forming inhibition activity and preformed biofilm eradication ability against S. aureus and C. albicans, and displayed therapeutic potential on pneumonia in S. aureus-infected mice by reducing lung inflammation. The present study provided a promising drug candidate in the war against multidrug resistance.

Gut-targeted nanoparticles deliver specifically targeted antimicrobial peptides against Clostridium perfringens infections

Specifically targeted antimicrobial peptides (STAMPs) are novel alternatives to antibiotics, whereas the development of STAMPs for colonic infections is hindered by limited de novo design efficiency and colonic bioavailability. In this study, we report an efficient de novo STAMP design strategy that combines a traversal design, machine learning model, and phage display technology to identify STAMPs against Clostridium perfringens. STAMPs could physically damage C. perfringens, eliminate biofilms, and self-assemble into nanoparticles to entrap pathogens. Further, a gut-targeted engineering particle vaccine (EPV) was used for STAMPs delivery. In vivo studies showed that both STAMP and EPV@STAMP effectively limited C. perfringens infections and then reduced inflammatory response. Notably, EPV@STAMP exhibited stronger protection against colonic infections than STAMPs alone. Moreover, 16S ribosomal RNA sequencing showed that both STAMPs and EPV@STAMP facilitated the recovery of disturbed gut microflora. Collectively, our work may accelerate the development of the discovery and delivery of precise antimicrobials.

A low-fouling electrochemical biosensor for biomarker detection in serum based on designed α/β-peptides with anti-enzymolysis and antifouling capabilities

The zwitterionic peptides, especially those composed of glutamic (E) and lysine (K) groups have drawn enormous attention as antifouling biomaterials owing to their strong hydration capability and biocompatibility. However, the susceptibility of α-amino acid K to the proteolytic enzymes in human serum limited the broad application of such peptides in biological media. Herein, a new multifunctional peptide with favorable stability in human serum was designed, and it was composed of three sections with immobilizing, recognizing and antifouling capabilities, respectively. The antifouling section was composed of alternating E and K amino acids, but the enzymolysis-susceptive amino acid α-K was replaced by the unnatural β-K. Compared with the conventional peptide composed of all α-amino acids, the α/β-peptide exhibited significantly enhanced stability and longer antifouling performance in human serum and blood. The electrochemical biosensor based on the α/β-peptide showed a favorable sensitivity to its target IgG, with a quite wide linear range from 100 pg mL^-1 to 10 μg mL^-1 and a low detection limit (33.7 pg mL^-1, S/N = 3), and it was promising for the detection of IgG in complex human serum. The tactic of designing antifouling α/β-peptides offered an efficient way to develop low-fouling biosensors with robust operation in complex body fluids.

Advance in the Polymerization Strategy for the Synthesis of β-Peptides and β-Peptoids

Peptide mimics, possessing excellent biocompatibility and protease stability, have attracted broad attention and research in the biomedical field. β-Peptides and β-peptoids, as two types of vital peptide mimics, have demonstrated great potential in the field of foldamers, antimicrobials and protein binding, etc. Currently, the main synthetic strategies for β-peptides and β-peptoids include solid-phase synthesis and polymerization. Among them, polymerization in one-pot can minimize the repeated separation and purification used in solid-phase synthesis, and has the advantages of high efficiency and low cost, and can synthesize β-peptides and β-peptoids with high molecular weight. This review summarizes the polymerization methods for β-peptides and β-peptoids. Moreover, future developments of the polymerization method for the synthesis of β-peptides and β-peptoids will be discussed.

Surface antimicrobial functionalization with polymers: fabrication, mechanisms and applications

Undesirable adhesion of microbes such as bacteria, fungi and viruses onto surfaces affects many industries such as marine, food, textile, and healthcare. In particular in healthcare and food packaging, the effects of unwanted microbial contamination can be life-threatening. With the current global COVID-19 pandemic, interest in the development of surfaces with superior anti-viral and anti-bacterial activities has multiplied. Polymers carrying anti-microbial properties are extensively used to functionalize material surfaces to inactivate infection-causing and biocide-resistant microbes including COVID-19. This review aims to introduce the fabrication of polymer-based antimicrobial surfaces through physical and chemical modifications, followed by the discussion of the inactivation mechanisms of conventional biocidal agents and new-generation antimicrobial macromolecules in polymer-modified antimicrobial surfaces. The advanced applications of polymer-based antimicrobial surfaces on personal protective equipment against COVID-19, food packaging materials, biomedical devices, marine vessels and textiles are also summarized to express the research trend in academia and industry.

Fluorination of Polyethylenimines for Augmentation of Antibacterial Potency via Structural Damage and Potential Dissipation of Bacterial Membranes

The rise of drug-resistant bacteria (e.g., methicillin-resistant Staphylococcus aureus, MRSA) has continued, making the ″super-bugs″ a formidable threat to global health. Herein, we synthesize a series of fluoroalkylated polyethylenimines (PEI-F) with different grafting degrees of fluoroalkyls via a simple ring-opening reaction and demonstrate for the first time that fluoroalkylated PEIs are able to exert potent antibacterial activity to Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Among the fluoroalkylated polymers, PEI-F_3.0 shows the strongest antibacterial activity, with a minimum inhibitory concentration (MIC) of 64 μg mL^-1, against both E. coli and S. aureus. More importantly, we find that PEI-F_3.0 is able to kill over 99.8% of S. aureus within 1 min, which is extremely desirable for the treatment of acute and severe bacterial infections that require quick disinfection. We also demonstrate that the fluoroalkylated PEIs are able to kill bacteria via structural damage of the outer membrane (OM) and cytoplasmic membrane (CM), potential dissipation of CM, and generation of intracellular reactive oxygen species (ROS). The in vivo antibacterial test suggests that commercial Vaseline blended with 6.25 wt % of PEI-F_3.0 (VL/PEI-F_3.0) is able to efficaciously eradicate MRSA infection on a bacterial infected wound model and promote the healing procedure of the wound site. Therefore, the fluoroalkylated PEIs provide a promising strategy to cope with the major challenges of drug-resistant infections.

A Polymeric Strategy Empowering Vascular Cell Selectivity and Potential Application Superior to Extracellular Matrix Peptides

Endothelialization of vascular implants plays a vital role in maintaining the long-term vascular patency. In situ endothelialization and re-endothelialization is generally achieved by selectively promoting endothelial cell (EC) adhesion and, meanwhile, suppressing smooth muscle cell (SMC) adhesion. Currently, such EC versus SMC selectivity is achieved and extensively used in vascular-related biomaterials utilizing extracellular-matrix-derived EC-selective peptides, dominantly REDV and YIGSR. Nevertheless, the application of EC-selective peptides is limited due to their easy proteolysis, time-consuming synthesis, and expensiveness. To address these limitations, a polymeric strategy in designing and finding EC-selective biomaterials using amphiphilic β-peptide polymers by tuning serum protein adsorption is reported. The optimal β-peptide polymer displays EC versus SMC selectivity even superior to EC-selective REDV peptide regarding cell adhesion, proliferation, and migration of ECs versus SMCs. Study of the mechanism indicates that surface adsorption of bovine serum albumin, an abundant and anti-adhesive serum protein, plays a critical role in the ECs versus SMCs selectivity of β-peptide polymer. In addition, surface modification of the optimal β-peptide polymer effectively promotes the endothelialization of vascular implants and inhibits intimal hyperplasia. This study provides an alternative strategy in designing and finding EC-selective biomaterials, implying great potential in the vascular-related biomaterial study and application.

Three lines of defense: A multifunctional coating with anti-adhesion, bacteria-killing and anti-quorum sensing properties for preventing biofilm formation of Pseudomonas aeruginosa

Surfaces of synthetic materials are highly susceptible to pathogenic bacteria colonization and further biofilm formation, leading to device failure in both biomedical and industrial applications. Complete elimination of the mature biofilms formed on the surfaces, however, remains a great challenge due to the complexity of chemical composition and physical structure. Therefore, prevention of biofilm formation becomes a preferred strategy for solving the biofilm-associated problems. Herein, a multifunctional coating showing three lines of defense to prevent biofilm formation of Pseudomonas aeruginosa is fabricated by a simple and versatile method. This coating is composed of multilayers of quaternized chitosan with bactericidal property and acylase with anti-quorum sensing property and a topmost layer of hyaluronic acid with anti-adhesion property. The substrate deposited with this coating could suppress initial adhesion of a majority of bacteria, and then kill the attached bacteria and interfere with their quorum sensing systems related to biofilm formation. The results of short-term antibacterial experiments show that our coating reduced 98 ± 2% of attached live bacteria. In long-term antibiofilm experiments, this "three lines of defense" design endows the coating with enhanced antibiofilm property against the biofilm formation for at least 3 days by reducing 98 ± 1% of bacterial proliferation and 71 ± 2% of biomass production. Benefiting from the natural building blocks with good biocompatibility and the versatile and environmentally friendly preparation method, this coating shows negligible cytotoxicity and broad applicability, providing great potential for a variety of biomedical applications. STATEMENT OF SIGNIFICANCE: Pathogenic biofilms formed on the surfaces of medical devices and materials pose an urgent problem, and it remains challenging to treat and eradicate the established biofilms. Herein, we developed an antibiofilm coating showing three lines of defense to prevent biofilm formation, which could be deposited on diverse substrates via a simple and versatile method. This coating was based on three natural materials with anti-adhesive, bactericidal, and anti-quorum sensing properties and showed different function in a self-adaptive way to target the sequential stages of biofilm formation by preventing initial bacterial adhesion, killing attached bacteria and interfering with their quorum sensing system to inhibit bacterial proliferation and biofilm maturation. This coating with improved antibiofilm performance might provide a simple and reliable solution to the problems associated with biofilm on surfaces.

Preparation of a Novel Type of Zwitterionic Polymer and the Antifouling PDMS Coating

As awareness of environmental protection increases, environmentally friendly coatings have been receiving great interest. Zwitterionic polymers are considered promising candidates due to their biocompatibility and excellent antifouling properties. In this paper, a type of polypeptoid containing zwitterions on the side chain was synthesized via ring-opening polymerization (ROP) and post-modification. This obtained polypeptoid was subsequently grafted onto the surface of polydimethylsiloxane (PDMS) via plasma and UV-induced surface polymerization. Surface morphology and protein adsorption tests of the resulting coating were systematically carried out. The results show that the modified coating has excellent antifouling properties and thus has great potential for environmentally friendly coating applications.

Titanium carbide MXene-based hybrid hydrogel for chemo-photothermal combinational treatment of localized bacterial infection

With the increased emergence and threat of multi-drug resistant microorganisms, MXenes have become not only an emerging class of two-dimensional functional nanomaterials, but also potential nanomedicines (i.e., antimicrobial agents) that deserve further exploration. Very recently, Ti₃C₂ MXene was observed to offer a unique membrane-disruption effect and superior light-to-heat conversion efficiency, but its antibacterial property remains unsatisfactory due to poor MXene-bacteria interactions, low photothermal therapy efficiency, and occurrence of bacterial rebound in vivo. Herein, the cationic antibiotic ciprofloxacin (Cip) is combined with Ti₃C₂ MXene, and a hybrid hydrogel was constructed by incorporating Cip-Ti₃C₂ nanocomposites into the network structure of a Cip-loaded hydrogels to effectively trap and kill bacteria. We found that the Cip-Ti₃C₂ nanocomposites achieved an impressive in vitro bactericidal efficiency of >99.99999% (7.03 log₁₀) for the inhibition of methicillin-resistant Staphylococcus aureus (MRSA) by combining chemotherapy with photothermal therapy. In an MRSA-induced murine abscess model, the hybrid hydrogel simultaneously achieved high-efficiency sterilization and long-term inhibition effects, avoiding the rebound of bacteria after photothermal therapy, and thus maximized the in vivo therapeutic efficacy of Ti₃C₂ MXene-based systems. Overall, this work provides a strategy for efficiently combating localized bacterial infection by rationally designing MXene-based hybrid hydrogels. STATEMENT OF SIGNIFICANCE: Two-dimensional Ti₃C₂ MXene was recently regarded as a promising functional nanomaterial, however, its antibacterial applications are limited by the poor MXene-bacteria interactions, low photothermal therapy efficiency, and the occurrence of bacterial rebound in vivo. This work aims to construct a Ti₃C₂ MXene-based hybrid hydrogel for chemo-photothermal therapy and enhance the antimicrobial performance via a combination of the high-efficiency sterilization of ciprofloxacin-Ti₃C₂ nanocomposites with the long-term inhibition effect of ciprofloxacin hydrogel. The present study provides an example of efficient MXene-based antimicrobials to treat localized bacterial infection such as methicillin-resistant Staphylococcus aureus (MRSA)-induced skin abscess.

Low-Molecular-Weight Polylysines with Excellent Antibacterial Properties and Low Hemolysis

The steady development of bacterial resistance has become a global public health issue, and new antibacterial agents that are active against drug-resistant bacteria and less susceptible to bacterial resistance are urgently needed. Here, a series of low-molecular-weight cationic polylysines (C_x-PLL_n) with different hydrophobic end groups (C_x) and degrees of polymerization (PLL_n) was synthesized and used in antibacterial applications. All the obtained C_x-PLL_n have antibacterial activity. Among them, C₆-PLL₁₃ displays the best antibacterial effect for Gram-positive bacteria, that is, Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA), and highest selectivity against Gram-positive bacteria. A mechanistic study revealed that the C₆-PLL₁₃ destroys the integrity of the bacterial cell membrane and causes effective bacterial death. Owing to this membrane-disrupting property, C₆-PLL₁₃ showed rapid bacterial killing kinetics and was not likely to develop resistance after repeat treatment (up to 13 generations). Moreover, C₆-PLL₁₃ demonstrated a significant therapeutic effect on an MRSA infection mouse model, which further proved that this synthetic polymer could be used as an effective weapon against bacterial infections.

Biomaterial-based delivery of antimicrobial therapies for the treatment of bacterial infections

The rise in antibiotic-resistant bacteria, including strains that are resistant to last-resort antibiotics, and the limited ability of antibiotics to eradicate biofilms, have necessitated the development of alternative antibacterial therapeutics. Antibacterial biomaterials, such as polycationic polymers, and biomaterial-assisted delivery of non-antibiotic therapeutics, such as bacteriophages, antimicrobial peptides and antimicrobial enzymes, have improved our ability to treat antibiotic-resistant and recurring infections. Biomaterials not only allow targeted delivery of multiple agents, but also sustained release at the infection site, thereby reducing potential systemic adverse effects. In this Review, we discuss biomaterial-based non-antibiotic antibacterial therapies for the treatment of community- and hospital-acquired infectious diseases, with a focus in in vivo results. We highlight the translational potential of different biomaterial-based strategies, and provide a perspective on the challenges associated with their clinical translation. Finally, we discuss the future scope of biomaterial-assisted antibacterial therapies.

WEB SUMMARY

The development of antibiotic tolerance and resistance has demanded the search for alternative antibacterial therapies. This Review discusses antibacterial biomaterials and biomaterial-assisted delivery of non-antibiotic therapeutics for the treatment of bacterial infectious diseases, with a focus on clinical translation.

A Novel Antibacterial Gold Nanoparticles Layer with Self-Cleaning Ability by the Production of Oxygen Bubbles

Bacterial contamination of medical devices not only constitutes a serious threat to the health of patients, but also promotes the evolution of bacterial drug-resistance. Here, a new strategy to fabricate...

Layer-by-layer construction of zwitterionic/biguanide polymers on silicone rubber as antifouling/bactericidal coating

Biofilm formation on biomedical devices is the major cause of devices associated infections. Traditional antibiotics treatments on biofilm associated infections is increasing the risk of multidrug resistance. Thus, developing antibiotics-free...

Versatile antibacterial surface with amphiphilic quaternized chitin-based derivatives for catheter associated infection prevention

Microbial colonization of catheter surfaces is responsible for most healthcare-associated infections. Quaternized chitin and chitosan have excellent antimicrobial and biocompatible properties and can be used to provide safe and prolonged protection for biomedical catheters. Herein, we prepared quaternized β-chitin derivative (QC)- and quaternized chitosan derivative (QCS)-based antimicrobial surfaces. The quaternized polysaccharides modified TPU surfaces exhibited hydrophilicity, good biocompatibility. Among these, QCS2-modified TPU exhibited excellent antibacterial properties against Gram-positive and Gram-negative bacteria, and prevented the adherence of bacteria compared with pristine TPU. The antibacterial activity of QCS2-modified surfaces maintained for 8 weeks under the condition of immersion in serum. An in vivo subcutaneous implantation experiment revealed 99.87% reduction of bacteria and reduced expression of inflammation-related factors in the surrounding tissue five days after implantation with QCS2-modified TPU. Therefore, quaternized polysaccharide-modified surfaces have promising potential in preventing medical catheter-associated infections.

Tug-of-War between Covalent Binding and Electrostatic Interaction Effectively Killing E. coli without Detectable Resistance

Antimicrobial resistance in Gram-negative bacteria has become one of the leading causes of morbidity and mortality and a serious worldwide public health concern due to the fact that Gram-negative bacteria have an additional outer membrane protecting them from an unwanted compound invading. It is still very difficult for antimicrobials to reach intracellular targets and very challenging to treat Gram-negative bacteria with the current strategies. Here, we found that (o-(bromomethyl)phenyl)boronic acid was incorporated into poly((2-N,N-diethyl)aminoethyl acrylate) (PDEA), forming a copolymer (poly(o-B_n-DEA)) having both phenylboronic acid (B) and ((2-N,N-diethyl)amino) (DEA) units. Poly(o-B_n-DEA) exhibits very strong intramolecular B-N coordination, which could highly promote the covalent binding of phenylboronic acid with lipopolysaccharide (LPS) on the outer membrane of E. coli and lodge poly(o-B_n-DEA) on the LPS layer on the surface of E. coli. Meanwhile, the strong electrostatic interaction between poly(o-B_n-DEA) and the negatively charged lipid preferred tugging the poly(o-B_n-DEA) into the lipid bilayer of E. coli. The combating interactions between covalent binding and electrostatic interaction form a tug-of-war action, which could trigger the lysis of the outer membrane, thereby killing Gram-negative E. coli effectively without detectable resistance.

Universal Antifouling and Photothermal Antibacterial Surfaces Based on Multifunctional Metal-Phenolic Networks for Prevention of Biofilm Formation

Biofilms formed from the pathogenic bacteria that attach to the surfaces of biomedical devices and implantable materials result in various persistent and chronic bacterial infections, posing serious threats to human health. Compared to the elimination of matured biofilms, prevention of the formation of biofilms is expected to be a more effective way for the treatment of biofilm-associated infections. Herein, we develop a facile method for endowing diverse substrates with long-term antibiofilm property by deposition of a hybrid film composed of tannic acid/Cu ion (TA/Cu) complex and poly(ethylene glycol) (PEG). In this system, the TA/Cu complex acts as a multifunctional building block with three different roles: (i) as a versatile "glue" with universal adherent property for substrate modification, (ii) as a photothermal biocidal agent for bacterial elimination under irradiation of near-infrared (NIR) laser, and (iii) as a potent linker for immobilization of PEG with inherent antifouling property to inhibit adhesion and accumulation of bacteria. The resulted hybrid film shows negligible cytotoxicity and good histocompatibility and could prevent biofilm formation for at least 15 days in vitro and suppress bacterial infection in vivo, showing great potential for practical applications to solve the biofilm-associated problems of biomedical materials and devices.

Trends in Bactericidal Nanostructured Surfaces: An Analytical Perspective

Since the discovery of the bactericidal properties of cicada wing surfaces, there has been a surge in the number of studies involving antibacterial nanostructured surfaces (NSS). Studies show that there are many parameters (and thus, thousands of parameter combinations) that influence the bactericidal efficiency (BE) of these surfaces. Researchers attempted to correlate these parameters to BE but have so far been unsuccessful. This paper presents a meta-analysis and perspective on bactericidal NSS, aiming to identify trends and gaps in the literature and to provide insights for future research. We have attempted to synthesize data from a wide range of published studies and establish trends in the literature on bactericidal NSS. Numerous research gaps and findings based on correlations of various parameters are presented here, which will assist in the design of efficient bactericidal NSS and shape future research. Traditionally, it is accepted that BE of NSS depends on the bacterial Gram-stain type. However, this review found that factors beyond Gram-stain type are also influential. Furthermore, it is found that despite their higher BE, hydrophobic NSS are less commonly studied for their bactericidal effect. Interestingly, the impacts of surface hydrophobicity and roughness on the bactericidal effect were found to be influenced by a Gram-stain type of the tested bacteria. In addition, cell motility and shape influence BE, but research attention into these factors is lacking. It was found that hydrophobic NSS demonstrate more promising results than their hydrophilic counterparts; however, these surfaces have been overlooked. Confirming the common belief of the influence of nanofeature diameter on bactericidal property, this analysis shows the feature aspect ratio is also decisive. NSS fabricated on silicon substrates perform better than their titanium counterparts, and the success of these silicon structures maybe attributed to the fabrication processes. These insights benefit engineers and scientists alike in developing next-generation NSS.

Dual-Functional Surfaces Based on an Antifouling Polymer and a Natural Antibiofilm Molecule: Prevention of Biofilm Formation without Using Biocides

Pathogenic biofilms formed on the surfaces of implantable medical devices and materials pose an urgent global healthcare problem. Although conventional antibacterial surfaces based on bacteria-repelling or bacteria-killing strategies can delay biofilm formation to some extent, they usually fail in long-term applications, and it remains challenging to eradicate recalcitrant biofilms once they are established and mature. From the viewpoint of microbiology, a promising strategy may be to target the middle stage of biofilm formation including the main biological processes involved in biofilm development. In this work, a dual-functional antibiofilm surface is developed based on copolymer brushes of 2-hydroxyethyl methacrylate (HEMA) and 3-(acrylamido)phenylboronic acid (APBA), with quercetin (Qe, a natural antibiofilm molecule) incorporated via acid-responsive boronate ester bonds. Due to the antifouling properties of the hydrophilic poly(HEMA) component, the resulting surface is able to suppress bacterial adhesion and aggregation in the early stages of contact. A few bacteria are eventually able to break through the protection of the anti-adhesion layer leading to bacterial colonization. In response to the resulting decrease in the pH of the microenvironment, the surface could then release Qe to interfere with the microbiological processes related to biofilm formation. Compared to bactericidal and anti-adhesive surfaces, this dual-functional surface showed significantly improved antibiofilm performance to prevent biofilm formation involving both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus for up to 3 days. In addition, both the copolymer and Qe are negligibly cytotoxic, thereby avoiding possible harmful effects on adjacent normal cells and the risk of bacterial resistance. This dual-functional design approach addresses the different stages of biofilm formation, and (in accordance with the growth process of the biofilm) allows sequential activation of the functions without compromising the viability of adjacent normal cells. A simple and reliable solution may thus be provided to the problems associated with biofilms on surfaces in various biomedical applications.

PVC grafted zinc oxide nanoparticles as an inhospitable surface to microbes

Antimicrobial Polyvinyl chloride (PVC) was obtained by covalent bonding of zinc oxide nanoparticles, which have gained important achievements in antimicrobial fields because of their auspicious properties. This was achieved by grafting mercaptopropyltrimethoxysilane onto PVC, followed by the growth of zinc oxide nanoparticles covalently bonded on the polymer surface. In this study, the relationship between the physicochemical features of modified-surface PVC and antimicrobial activity on Staphylococcus aureus and Candida albicans was investigated. Zinc oxide with controllable morphologies (rods, rod flowers, and petal flowers) was synthesized on the polymer surface by tuning merely base-type and concentration using a hydrothermal process. The antimicrobial activity was more pronounced for rod flower morphology, because of their differences in microscopic parameters such as specific Zn-polar planes. This work provides an important hint for the safe use of PVC for biomedical devices by the structure surface tuning without injuring polymer bulk properties and a reduced risk of the covalently bonded nanoparticle dispersion in the host and the environment.

An Amphiphilic Carbonaceous/Nanosilver Composite-Incorporated Urinary Catheter for Long-Term Combating Bacteria and Biofilms

Biofilms formed on urinary catheters remain a major headache in the modern healthcare system. Among the various kinds of biocide-releasing urinary catheters that have been developed to prevent biofilm formation, Ag nanoparticles (AgNPs)-coated catheters are of great promising potential. However, the deposition of AgNPs on the surface of catheters suffers from several inherent shortcomings, such as damage to the urethral mucosa, uncontrollable Ag ion kinetics, and unexpected systematic toxicity. Here, AgNPs-decorated amphiphilic carbonaceous particles (ACPs@AgNPs) with commendable dispersity in solvents of different polarities and broad-spectrum antibacterial activity are first prepared. The resulting ACPs@AgNPs exert good compatibility with silicone rubber, which enables the easy fabrication of urinary catheters using a laboratory-made mold. Therefore, ACPs@AgNPs not only endow the urinary catheter with forceful biocidal activity but also improve its mechanical properties and surface wettability. Hence, the designed urinary catheter possesses excellent capacity to resist bacterial adhesion and biofilm formation both in vitro and in an in vivo rabbit model. Specifically, a long-term antibacterial study highlights its sustainable antibacterial activity. Of note, no obvious toxicity or inflammation in rabbits was triggered by the designed urinary catheter in vivo. Overall, the hybrid urinary catheter may serve as a promising biocide-releasing urinary catheter for antibacterial and antibiofilm applications.

Self-adhesive lubricated coating for enhanced bacterial resistance

Limited surface lubrication and bacterial biofilm formation pose great challenges to biomedical implants. Although hydrophilic lubricated coatings and bacterial resistance coatings have been reported, the harsh and tedious synthesis greatly compromises their application, and more importantly, the bacterial resistance property has seldom been investigated in combination with the lubrication property. In this study, bioinspired by the performances of mussel and articular cartilage, we successfully synthesized self-adhesive lubricated coating and simultaneously achieved optimal lubrication and bacterial resistance properties. Additionally, we reported the mechanism of bacterial resistance on the nanoscale by studying the adhesion interactions between biomimetic coating and hydrophilic/hydrophobic tip or living bacteria via atomic force microscopy. In summary, the self-adhesive lubricated coating can effectively enhance lubrication and bacterial resistance performances based on hydration lubrication and hydration repulsion, and represent a universal and facial strategy for surface functionalization of biomedical implants.

Alternatives to Conventional Antibiotic Therapy: Potential Therapeutic Strategies of Combating Antimicrobial-Resistance and Biofilm-Related Infections

Antibiotics have been denoted as the orthodox therapeutic agents for fighting bacteria-related infections in clinical practices for decades. Nevertheless, overuse of antibiotics has led to the upsurge of species with antimicrobial resistance (AMR) or multi-drug resistance. Bacteria can also grow into the biofilm, which accounts for at least two-thirds of infections. Distinct gene expression and self-produced heterogeneous hydrated extracellular polymeric substance matrix architecture of biofilm contribute to their tolerance and externally manifest as antibiotic resistance. In this review, the difficulties in combating biofilm formation and AMR are introduced, and novel alternatives to antibiotics such as metal nanoparticles and quaternary ammonium compounds, chitosan and its derivatives, antimicrobial peptides, stimuli-responsive materials, phage therapy and other therapeutic strategies, from compounds to hydrogel, from inorganic to biological, are discussed. We expect to provide useful information for the readers who are seeking for solutions to the problem of AMR and biofilm-related infections.

Poly(hexamethylene biguanide) (PHMB) as high-efficiency antibacterial coating for titanium substrates

Bacterial associated infection is a remaining urgent challenge in clinic application of metallic implants and devices. Here, we developed a new strategy to combat the bacterial associated infection of titanium alloy (TC4). Novel phosphonate/active ester block polymers (pDEMMP-b-pNHSMA) with identical phosphonate segments (DP = 29) as the metal anchorable ligand but varied active ester segments (DPs = 7, 29, and 64) as the conjugation site for poly(hexamethylene biguanide) (PHMB) were precisely prepared. Through a facile two-step process, the polymeric coating were successfully constructed on TC4 substrates as evidenced by water contact angle and XPS measurements. Through systematical in vitro antibacterial evaluations, robust relationship between the chemical structure of coating polymer and the antibacterial property endowed to the TC4 substrates has been established. Results showed that the block polymer, bearing an active ester segment of 64 repeat units, enabled dense packing of PHMB coating on the TC4 surface, which is able to kill 100% of both S. aureus and E. coli. that seeded without compromising the cytocompatibility of TC4 substrates. Furthermore, PHMB coating could significantly inhibit the colony of the bacteria and consequently reduce the bacterial associated inflammatory reaction as verified by a subcutaneous infection model on rat.

Effective and biocompatible antibacterial surfaces via facile synthesis and surface modification of peptide polymers

It is an urgent need to tackle drug-resistance microbial infections that are associated with implantable biomedical devices. Host defense peptide-mimicking polymers have been actively explored in recent years to fight against drug-resistant microbes. Our recent report on lithium hexamethyldisilazide-initiated superfast polymerization on amino acid N-carboxyanhydrides enables the quick synthesis of host defense peptide-mimicking peptide polymers. Here we reported a facile and cost-effective thermoplastic polyurethane (TPU) surface modification of peptide polymer (DLL: BLG = 90 : 10) using plasma surface activation and substitution reaction between thiol and bromide groups. The peptide polymer-modified TPU surfaces exhibited board-spectrum antibacterial property as well as effective contact-killing ability in vitro. Furthermore, the peptide polymer-modified TPU surfaces showed excellent biocompatibility, displaying no hemolysis and cytotoxicity. In vivo study using methicillin-resistant Staphylococcus aureus (MRSA) for subcutaneous implantation infectious model showed that peptide polymer-modified TPU surfaces revealed obvious suppression of infection and great histocompatibility, compared to bare TPU surfaces. We further explored the antimicrobial mechanism of the peptide polymer-modified TPU surfaces, which revealed a surface contact-killing mechanism by disrupting the bacterial membrane. These results demonstrated great potential of the peptide-modified TPU surfaces for practical application to combat bacterial infections that are associated with implantable materials and devices.

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A convenient surface modification of peptide polymer 90 : 10 DLL : BLG to enable material surfaces antibacterial properties.

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The modified thermoplastic polyurethane (TPU) surfaces show board-spectrum antibacterial performance and excellent biocompatibility both in vitro and in vivo.

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The contact-killing surfaces demonstrate great potential for practical application to combat bacterial infections associated with implantable materials and devices.

Design of nanoengineered antibacterial polymers for biomedical applications

Pathogenic bacteria have become global threats to public health. Since the advent of antibiotics about 100 years ago, their use has been embraced with great enthusiasm because of their effective treatment of bacterial infections. However, the evolution of pathogenic bacteria with resistance to conventional antibiotics has resulted in an urgent need for the development of a new generation of antibiotics. The use of antimicrobial polymers offers the promise of enhancing the efficacy of antimicrobial agents. Of the various antibacterial polymers that effectively eradicate pathogenic bacteria, those that are nanoengineered have garnered significant research interest in their design and biomedical applications. Because of their high surface area and high reactivity, these polymers show greater antibacterial activity than conventional antibacterial agents, by inhibiting the growth or destroying the cell membrane of pathogenic bacteria. This review summarizes several strategies for designing nanoengineered antibacterial polymers, explores the factors that affect their antibacterial properties, and examines key features of their design. It then comments briefly on the future prospects for nanoengineered antibacterial polymers. This review thus provides a feasible guide to developing nanoengineered antibacterial polymers by presenting both broad and in-depth bench research, and it offers suggestions for their potential in biomedical applications.

Dimeric lipo-α/sulfono-γ-AA hybrid peptides as broad-spectrum antibiotic agents

There is an urgent need to develop novel antibiotic agents that can combat emerging drug resistance. Herein, we report the design and investigation of a class of short dimeric antimicrobial lipo-α/sulfono-γ-AA hybrid peptides. Some of these peptides exhibit potent and broad-spectrum antimicrobial activity toward both clinically related Gram-positive and Gram-negative bacteria. The TEM study suggests that these hybrid peptides can compromise bacterial membranes and lead to bacterial death. Membrane depolarization and fluorescence microscopy studies also indicate that the mechanism of action is analogous to host-defense peptides (HDPs). Furthermore, the lead compound shows the ability to effectively inhibit biofilms formed from MRSA and E. coli. Further development of the short dimeric lipo-α/sulfono-γ-AA hybrid peptides may lead to a new generation of antimicrobial biomaterials to combat drug resistance.

Advances of peptides for antibacterial applications

In the past few decades, peptide antibacterial products with unique antibacterial mechanisms have attracted widespread interest. They can effectively reduce the probability of drug resistance of bacteria and are biocompatible, so they possess tremendous development prospects. This review provides recent research and analysis on the basic types of antimicrobial peptides (including poly (amino acid)s, short AMPs, and lipopeptides) and factors to optimize antimicrobial effects. It also summarizes the two most important modes of action of antimicrobial peptides and the latest developments in the application of AMPs, including antimicrobial agent, wound healing, preservative, antibacterial coating and others. Finally, we discuss the remaining challenges to improve the antibacterial peptides and propose prospects in the field.

Recent Progress in Bile Acid-Based Antimicrobials

With the emergence of drug-resistant bacteria and the formation of biofilms by bacteria and fungi, microbial infections gradually threaten global health. Natural antimicrobial peptides (AMPs) have low susceptibility for developing resistance due to the membrane targeted mechanism, but instability and high manufacturing cost limit their applications in clinic. Bile acids, a group of steroids in the human body, with high stability, biocompatibility, and inherent facial amphiphilic structure similar to the characteristics of AMPs, have been applied to the biological field, such as drug delivery systems, self-healing hydrogels, antimicrobials, and so on. In this review, we mainly focus on the different classes of bile acid-based antimicrobials in recent years. Various designs and methods for the preparation of unimolecular antimicrobials with bile acid skeletons are first introduced, including coupling of primary amine, quaternary ammonium, and amino acid units with bile acid skeletons. Some representative oligomeric antimicrobials, including dimers of bile acids, are summarized. Finally, macromolecular antimicrobials bearing some positive charges at the main chain or side chain and interaction mechanisms of these bile acid-based antimicrobials are discussed.

Beyond Amphiphilic Balance: Changing Subunit Stereochemistry Alters the Pore-Forming Activity of Nylon-3 Polymers

Amphiphilic nylon-3 polymers have been reported to mimic the biological activities of natural antimicrobial peptides, with high potency against bacteria and minimal toxicity toward eukaryotic cells. Amphiphilic balance, determined by the proportions of hydrophilic and lipophilic subunits, is considered one of the most important features for achieving this activity profile for nylon-3 polymers and many other antimicrobial polymers. Insufficient hydrophobicity often correlates with weak activities against bacteria, whereas excessive hydrophobicity correlates with high toxicity toward eukaryotic cells. To ask whether factors beyond amphiphilic balance influence polymer activities, we synthesized and evaluated new nylon-3 polymers with two stereoisomeric subunits, each bearing an ethyl side chain and an aminomethyl side chain. Subunits that differ only in stereochemistry are predicted to contribute equally to amphiphilic balance, but we observed that the stereochemical difference correlates with significant changes in biological activity profile. Antibacterial activities were not strongly affected by subunit stereochemistry, but the ability to disrupt eukaryotic cell membranes varied considerably. Experiments with planar lipid bilayers and synthetic liposomes suggested that eukaryotic membrane disruption results from polymer-mediated formation of large pores. Collectively, our results suggest that factors other than amphiphilic balance influence the membrane activity profile of synthetic polymers. Subunits that differ in stereochemistry are likely to have distinct conformational propensities, which could potentially lead to differences in the average shapes of polymer chains, even when the subunits are heterochiral. These findings highlight a dimension of polymer design that should be considered more broadly in efforts to improve specificity and efficacy of antimicrobial polymers.

Antifouling and Antibacterial Polymer-Coated Surfaces Based on the Combined Effect of Zwitterions and the Natural Borneol

The development and application of natural antibacterial materials have always been the focus of biomedical research. Borneol as a natural antibacterial compound has received extensive attention. However, the hydrophobicity caused by its unique structure limits its application range to a certain extent. In this study, we combine zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) with a complex bicyclic monoterpene structure borneol compound and prepare an excellent antifouling and antibacterial surface via the Schiff-base bond. The prepared coating has excellent hydrophilicity verified by the contact angle (CA), and its polymer layer is confirmed by X-ray photoelectron spectroscopy (XPS). The zwitterion MPC and borneol moieties in the copolymer play a coordinating role, relying on super hydration and the special stereochemical structure to prevent protein adsorption and inhibit bacterial adhesion, respectively, which are demonstrated by bovine serum albumin (BSA) adsorption and antibacterial activity test. Moreover, the water-soluble borneol derivative as the antibacterial surfaces we designed here was biocompatible toward MRC-5 (lung fibroblasts), as showed by in vitro cytotoxicity assays. Such results indicate the potential application of the as-prepared hydrophilic surfaces in the biomedical materials.

Nanohole-boosted electron transport between nanomaterials and bacteria as a concept for nano-bio interactions

Biofilms contribute to bacterial infection and drug resistance and are a serious threat to global human health. Antibacterial nanomaterials have attracted considerable attention, but the inhibition of biofilms remains a major challenge. Herein, we propose a nanohole-boosted electron transport (NBET) antibiofilm concept. Unlike known antibacterial mechanisms (e.g., reactive oxygen species production and cell membrane damage), nanoholes with atomic vacancies and biofilms serve as electronic donors and receptors, respectively, and thus boost the high electron transport capacity between nanomaterials and biofilms. Electron transport effectively destroys the critical components (proteins, intercellularly adhered polysaccharides and extracellular DNA) of biofilms, and the nanoholes also significantly downregulate the expression of genes related to biofilm formation. The anti-infection capacity is thoroughly verified both in vitro (human cells) and in vivo (rat ocular and mouse intestinal infection models), and the nanohole-enabled nanomaterials are found to be highly biocompatible. Importantly, compared with typical antibiotics, nanomaterials are nonresistant and thereby exhibit high potential for use in various applications. As a proof-of-principle demonstration, these findings hold promise for the use of NBET in treatments for pathogenic bacterial infection and antibiotic drug resistance.

The membrane-targeting mechanism of host defense peptides inspiring the design of polypeptide-conjugated gold nanoparticles exhibiting effective antibacterial activity against methicillin-resistant Staphylococcus aureus

Multidrug-resistant bacterial infections are a grand challenge to global medical and health systems. Therefore, it is urgent to develop versatile antibacterial strategies that can combat bacterial resistance without displaying toxicity. Here, we synthesize antibacterial polypeptide-conjugated gold nanoparticles that exhibit potent antibacterial activities against clinically isolated multiple drug resistance Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus, and excellent in vitro and in vivo biocompatibility. The antibacterial mechanism study indicates that over-production of reactive oxygen species results in the killing of bacteria. The overall antibacterial performance of these polypeptide-conjugated gold nanoparticles and the convenient synthesis of these polypeptides via lithium hexamethyldisilazide-initiated fast ring-opening polymerization on α-amino acid N-carboxyanhydride imply the potential application of this strategy in treating bacterial infections.

Extracellular matrix scaffold crosslinked with vancomycin for multifunctional antibacterial bone infection therapy

The treatment of acute and chronic bone infections remains a major clinical challenge. The various factors released by the bacteria, acidic environment, and bacterial colonies in the bone grooves and implanted synthetic materials collectively promote the formation of biofilms. Dormant bacteria and biofilms cause infections that are difficult to cure and that can develop chronically. Therefore, a new antibacterial material was synthesized in the present study for multifunctional bone infection therapy and consists of specific demineralized extracellular cancellous bone (SDECM) crosslinked with vancomycin (Van) by means of electrostatic interactions and chemical bonds. It was verified in vitro that the new material (Van-SDECM) not only has pH-sensitive release and biofilm inhibition properties, but also maintains sustained bactericidal ability accompanied by the degradation of the scaffold, which does not affect its favorable osteogenic performance. The infectious bone defect in vivo model further confirms the comprehensive anti-infective and osteogenic ability of the Van-SDECM. Further, these favorable properties are due to the pH-sensitive sustained release sterilization and scaffold contact antibacterial properties, accompanied by osteoclast activity inhibition, osteogenesis promotion and immunoregulation effects. This study provides a new drug-scaffold composite preparation method based on a native-derived extracellular matrix scaffold.

A dual-functional implant with an enzyme-responsive effect for bacterial infection therapy and tissue regeneration

Biomaterial-associated bacterial infection is one of the major causes of implant failure. The treatment of such an implant infection typically requires the elimination of bacteria and acceleration of tissue regeneration around implants simultaneously. To address this issue, an ideal implanted material should have the dual functions of bacterial infection therapy and tissue regeneration at the same time. Herein, an enzyme-responsive nanoplatform was fabricated in order to treat implant-associated bacterial infection and accelerate tissue regeneration in vivo. Firstly, Ag nanoparticles were pre-encapsulated in mesoporous silica nanoparticles (MSNs) by a one-pot method. Then, poly-l-glutamic acid (PG) and polyallylamine hydrochloride (PAH) were assembled by the layer-by-layer (LBL) assembly technique on MSN-Ag to form LBL@MSN-Ag nanoparticles. Furthermore, the LBL@MSN-Ag nanoparticles were deposited on the surface of polydopamine-modified Ti substrates. PG is a homogeneous polyamide composed of an amide linkage, which can be degraded by glutamyl endonuclease secreted by Staphylococcus aureus. Inductively coupled plasma spectroscopy (ICP) results proved that the LBL@MSN-Ag particles show a significant enzyme responsive release of Ag ions. Furthermore, results of antibacterial experiments in vitro showed that the Ti substrates modified with an LBL@MSN-Ag nanocoating presented an excellent antibacterial effect. As for an animal experiment in vivo, in a bacterium infected femur-defect rat model, the modified Ti implants effectively treated bacterial infection. More importantly, the results of micro-CT, haematoxylin-eosin staining and Masson's trichrome staining demonstrated that the modified Ti implants significantly promoted the formation of new bone tissue after implantation for 4 weeks. The present system paves the way for developing the next generation of implants with the functions of treating bacterial infection and promoting tissue regeneration.

Sustainable, Site-Specific Linkage of Antimicrobial Peptides to Cotton Textiles

A new general method to covalently link a peptide to cotton via thiazolidine ring formation is developed. Three different analogues of an ultrashort antibacterial peptide are synthesized to create an antibacterial fabric. The chemical ligation approach to the heterogeneous phase made up of insoluble cellulose fibers and a peptide solution in water is adapted. The selective click reaction occurs between an N-terminal cysteine on the peptide and an aldehyde on the cotton matrix. The aldehyde is generated on the primary alcohol of glucose by means of the enzyme laccase and the cocatalyst 2,2,6,6-tetramethylpiperidine-1-oxyl. This keeps the pyranose rings intact and may bring a benefit to the mechanical properties of the fabric. The presence of the peptide on cotton is demonstrated through instant colorimetric tests, UV spectroscopy, IR spectroscopy, and X-ray photoelectron spectroscopy analysis. The antibacterial activity of the peptides is maintained even after their covalent attachment to cotton fibers.

One-Step Curable, Covalently Immobilized Coating for Clinically Relevant Surfaces That Can Kill Bacteria, Fungi, and Influenza Virus

Microbial attachment and subsequent colonization onto surfaces lead to the spread of deadly community-acquired and hospital-acquired (nosocomial) infections. Cationic polymeric coatings have gained enormous attention to tackle this scenario. However, non-biodegradable cationic polymer coated surfaces suffer from accumulation of microbial debris leading to toxicity and consequent complexities. Synthetic reproducibility and sophisticated coating techniques further limit their application. In this present study, we have developed one-step curable, covalent coatings based on two organo- and water-soluble small molecules, quaternary benzophenone-based ester and quaternary benzophenone-based amide, which can cross-link on surfaces upon UV irradiation. Upon contact, the coating completely killed bacteria and fungi in vitro including drug-resistant pathogens methicillin-resistant Staphylococcus aureus (MRSA) and fluconazole-resistant Candida albicans spp. The coating also showed antiviral activity against notorious influenza virus with 100% killing. The coated surfaces also killed stationary-phase cells of MRSA, which cannot be eradicated by traditional antibiotics. Upon hydrolysis, the surfaces switched to an antifouling state displaying significant reduction in bacterial adherence. To the best of our knowledge, this is the first report of an antimicrobial coating which could kill all of bacteria, fungi, and influenza virus. Taken together, the antimicrobial coating reported herein holds great promise to be developed for further application in healthcare settings.

Small Molecules with Membrane-Active Antibacterial Activity

This spotlight on application provides a brief overview of our research exploration, focusing on the research of small molecules with membrane-active antibacterial activity that mimic host-defense peptides (HDPs). The development of antimicrobial HDP agents is an emerging research area as they circumvent the potential disadvantages of HDPs. The small molecules are preferable for development due to their low production cost and potential of more practical applications. In recent years, we conducted research on the design of antibacterial agents based on small molecules including hydantoins, acylated reduced amides, biscyclic guanidines, and dimeric alkylamides of lysines. We herein sketch our journey on the exploration of the antimicrobial activity of these few classes of molecules and hopefully share our insight in the future design of small-molecular-weight antibiotic agents with membrane-active activity that mimic HDPs.