Antibiotic-loaded biomaterials and the risks for the spread of antibiotic resistance following their prophylactic and therapeutic clinical use

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Membranes for Guided Bone Regeneration: A Road from Bench to Bedside

Bone resorption can negatively influence the osseointegration of dental implants. Barrier membranes for guided bone regeneration (GBR) are used to exclude nonosteogenic tissues from influencing the bone healing process. In addition to the existing barrier membranes available on the market, a growing variety of membranes for GBR with tailorable physicochemical properties are under preclinical evaluation. Hence, the aim of this review is to provide a comprehensive description of materials used for GBR and to report the main industrial and regulatory aspects allowing the commercialization of these medical devices (MDs). In particular, a summary of the main attributes defining a GBR membrane is reported along with a description of commercially available and under development membranes. Finally, strategies for the scaling-up of the manufacturing process and the regulatory framework of the main MD producers (USA, EU, Japan, China, and India) are presented. The description of the regulatory approval process of GBR membranes is representative of the typical path that medium- to high-risk MDs have to follow for an effective medical translation, which is of fundamental importance to increase the impact of biomedical research on public health.

Biomimetic biodegradable Ag@Au nanoparticle-embedded ureteral stent with a constantly renewable contact-killing antimicrobial surface and antibiofilm and extraction-free properties

Urinary tract infections (UTIs) caused by the contamination of the ureteral stent and the pain associated with secondary stent extractions are worldwide problems in the treatment of urinary tract disorders. Here, we reported a biodegradable, long-term antibacterial, and extraction-free ureteral stent with a constantly renewable contact-killing surface and an antibiofilm function achieved by constructing a hyperbranched poly(amide-amine)-capped Ag shell and Au core nanoparticle (Ag@Au NP)-embedded fiber membrane-structured poly(glycolic acid)/poly(lactic-co-glycolic acid) (PGA/PGLA) ureteral stent. The ureteral stent showed fast contact-killing properties, i.e., 5 min for Escherichia coli and 10 min for Staphylococcus aureus, with an inhibition rate higher than 99%. In addition, gradient degradation of PGA/PGLA endowed the stent with a self-cleaning property and long-term antibacterial function by continuous exfoliation of the stent surface, thereby exposing the inner Ag@Au NPs and eliminating adherent bacteria and proteins. Subsequently, in the 16-day in vitro degradation test, the stent showed durable bactericidal activity, less total release of Ag and Au elements (6.7%, ~8 μg), and low cytotoxicity (with a relative growth rate of >80% of L929 cells). In vivo experiments on a farm pig model showed that the stent exhibited a remarkable antibiofilm property and reduced the level of inflammatory and necrotic cells. After seven days of implantation, the stent showed a gradient degradation behavior and maintained structural integrity without the presence of any large fragments in the urinary system according to the B-ultrasonic examination. The as-developed biodegradable and renewable contact-killing antibacterial strategy was efficient in preparing the ureteral stent with antibiofilm and extraction-free properties to treat stent-induced UTI. Statement of significance This study presents a customized antibiofilm solution for biodegradable implants. Two particularly important aspects of this work are as follows.

A tailored positively-charged hydrophobic surface reduces the risk of implant associated infections

Implant-associated infections is one of the most challenging post-operative complications in bone-related implantations. To tackle this clinical issue, we developed a low-cost and durable surface coating for medical grade titanium implants that uses positively charged silane molecules. The in vitro antimicrobial tests revealed that the titanium surface coated with (3-aminopropyl) triethoxysilane, which has the appropriate length of hydrophobic alkyl chain and positive charged amino group, suppressed more than 90% of the initial bacterial adhesion of S. aureus, P. aeruginosa, and E. coli after 30 min of incubation. In terms of growth inhibitory rate, the treated surface was able to reduce 75.7% ± 11.9% of bacterial growth after a 24-hour culturing, thereby exhibiting superior anti-biofilm formation in the late stage. When implanted into the rat model infected by S. aureus, the treated surface eliminated the implant-associated infection through the mechanism of inhibition of bacterial adhesion on the implant surface. Additionally, the treated surface was highly compatible with mammalian cells. In general, our design demonstrated its potential for human clinical trials as a low-cost and effective antibacterial strategy to minimize post-operative implant-related bacterial infection.

Prevention of bone infection after open fracture using a chitosan with ciprofloxacin implant in animal model

PURPOSE

To evaluate different concentrations of ciprofloxacin to prevent infection after open fracture contaminated with S. aureus in rats using absorbable local delivery system.

METHODS

Fifty-two Wistar rats were assigned to six groups. After 4 weeks, all animals underwent 99mTc-ceftizoxima scintigraphy evaluation, callus formation measurement and histological analysis. ANOVA, t-Student and Kruskal Wallis were used for quantitative variables statistical analysis, whereas qui square and exact Fisher were used for qualitative variables.

RESULTS

Treatment using 25% and 50% of ciprofloxacin incorporated at the fracture fixation device were effective in preventing bone infection compared to control group (p<0.05). Chitosan were not effective in preventing bone infection when used alone compared to control group (p>0.05). Histological findings demonstrated bone-healing delay with 50% of ciprofloxacin. No difference in callus formation were observed (p>0.05).

CONCLUSION

Local delivery treatment for contaminated open fracture using chitosan with ciprofloxacin is effective above 25%.

Issues beyond resistance: inadequate antibiotic therapy and bacterial hypervirulence

The administration of antibiotics while critical for treatment, can be accompanied by potentially severe complications. These include toxicities associated with the drugs themselves, the selection of resistant organisms and depletion of endogenous host microbiota. In addition, antibiotics may be associated with less well-recognized complications arising through changes in the pathogens themselves. Growing evidence suggests that organisms exposed to antibiotics can respond by altering the expression of toxins, invasins and adhesins, as well as biofilm, resistance and persistence factors. The clinical significance of these changes continues to be explored; however, it is possible that treatment with antibiotics may inadvertently precipitate a worsening of the clinical course of disease. Efforts are needed to adjust or augment antibiotic therapy to prevent the transition of pathogens to hypervirulent states. Better understanding the role of antibiotic-microbe interactions and how these can influence disease course is critical given the implications on prescription guidelines and antimicrobial stewardship policies.

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

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

Silver sulfadiazine-loaded electrospun ethyl cellulose/polylactic acid/collagen nanofibrous mats with antibacterial properties for wound healing

Recently, the electrospun nanofiber mats with appropriate properties for applications in the biomedical area has been more considered. In this regard, we successfully fabricated a novel antibacterial nanofiber mat (ethyl cellulose/poly lactic acid/collagen) (EC/PLA/collagen) incorporated with silver sulfadiazine (AgSD) and then analyzed with the required tests. AgSD was loaded in the developed mats with different contents (0.25%, 0.5% and 0.75%) and then electrospun to prepare nanofiber mats. To check the chemical structure of the developed mat, Fourier transform infrared spectroscopy (FTIR) was assessed. Surface morphological studies were performed by Scanning Electron Microscopy (SEM), which displayed uniform nanofiber mats without any bead formation. When the hydrophilicity was enhanced by decreasing the blending ratios of EC/PLA, the thermal stability of the nanofibers was reduced. The water contact angle (WCA) of NFs enhanced by decreasing the blending ratios of EC/PLA. The antibacterial properties showed the inhibition activity against Bacillus (9.71 ± 1.15 mm) and E. coli (12.46 ± 1.31 mm) bacteria. Besides, nanofibers have improved cell proliferation and adhesion with any cytotoxic effect on NIH 3T3 fibroblast cells. According these results, it seems that the developed mats would be effective scaffold for application in wound dressings.

Improved osteogenic activity and inhibited bacterial biofilm formation on andrographolide-loaded titania nanotubes

Background

Delivery of local drugs with a titania nanotube is an attractive approach to combat implant-related infection. Our earlier study has confirmed that nanotubes loaded with gentamicin could significantly improve the antibacterial ability. On this basis, the used andrographolide in this paper has a high antibacterial activity, which cannot only avoid the evolution of antibiotic-resistant bacteria but also has simultaneously excellent biocompatibility with osteogenic cells.

Methods

Two mg of andrographolide was loaded into titania nanotubes, which were fabricated into different diameters (50 and 100 nm) and 200 nm length by the method of lyophilization and vacuum drying. We chose a standard strain, Staphylococcus epidermidis (American Type Culture Collection 35984), and two clinical isolates, S. aureus 376 and S. epidermidis 389 to research the bacterial adhesion at 6, 12 and 24 hours and biofilm formation at 48, and 72 hours on the andrographolide-loaded nanotubes (NT-A) using the diffusion plate method. Smooth titanium (smooth Ti) and nanotubes with no drug loading (NT) were also inclusive and analyzed. Furthermore, the Sprague-Dawley (SD) rats mesenchymal stem cells were used to assess the influence of nanotubular topographies on the osteogenic differentiation of mesenchymal stem cells.

Results

Our results showed that NT-A could inhibit bacterial adhesion and biofilm formation on implant surfaces. NT-A and NT, especially those with 100 nm diameters, were found to significantly promoted cell attachment, proliferation, diffusion, and osteogenic differentiation when compared with smooth Ti, while the same diameter in NT-A and NT did not differ.

Conclusions

Titania nanotube modification and andrographolide loading can significantly improve the antibacterial ability and osteogenic activity of orthopedic implants. Nanotubes-based local delivery could be a promising strategy for combating implant-associated infection.

Self-Assembled Supramolecular Hybrid Hydrogel Beads Loaded with Silver Nanoparticles for Antimicrobial Applications

This Full Paper reports the formation of silver (Ag) NPs within spatially resolved two-component hydrogel beads, which combine a low-molecular-weight gelator (LMWG) DBS-CONHNH2 and a polymer gelator (PG) calcium alginate. The AgNPs are formed through in situ reduction of AgI , with the resulting nanoparticle-loaded gels being characterised in detail. The antibacterial activity of the nanocomposite gel beads was tested against two drug-resistant bacterial strains, often associated with hospital-acquired infections: vancomycin-resistant Enterococcus faecium (VRE) and Pseudomonas aeruginosa (PA14), and the AgNP-loaded gels showed good antimicrobial properties against both types of bacteria. It is suggested that the gel bead format of these AgNP-loaded hybrid hydrogels makes them promising versatile materials for potential applications in orthopaedics or wound healing.

One-Step Large-Scale Nanotexturing of Nonplanar PTFE Surfaces to Induce Bactericidal and Anti-inflammatory Properties

Here we demonstrate a simple and scalable nanotexturing method for both planar (films) and nonplanar (tubes) polytetrafluoroethylene (PTFE) surfaces using a commercial desktop oxygen plasma etcher. The simple process can generate semiordered nanopillar structures on both tubular and planar samples with high radial and axial uniformity. We found that the resulting surfaces exhibit good in vitro bactericidal and in vivo anti-inflammatory properties. When tested against Staphylococcus aureus, the nanotextured surfaces showed significantly decreased live bacteria coverage and increased dead bacteria coverage, demonstrating significant bactericidal functionality. Moreover, the etched planar PTFE films exhibited better healing and inflammatory responses in the subcutis of C57BL/6 mice over 7 and 21 days, evidenced by a thinner inflammatory band, lower collagen deposition, and decreased macrophage infiltration. Our results suggest the possibility of using this simple process to generate large scale biomimetic nanotextured surfaces with good antibiofouling properties to enhance the functionality of many implantable and other biomedical devices.

Urogynecological surgical mesh implants: New trends in materials, manufacturing and therapeutic approaches

Pelvic Organ Prolapse (POP) and Stress Urinary Incontinence (SUI) are two prevalent disorders affecting 30-40% of women worldwide. Current strategies to repair or improve these medical conditions are non-surgical options such as physiotherapy, or surgical options such as the use of vaginal meshes. The synthetic material polypropylene (PP), which has long been used for manufacturing these vaginal meshes, is associated with severe complications such as chronic pain, infection or mesh erosion. As a result of a widespread reporting and unacceptably high rates of complications, these issues have become a public health concern. Regulatory bodies have recently deemed the transvaginal placement of PP mesh in the pelvic floor (PF) no longer a suitable treatment method for PF repair, leading to the need for a novel approach to the manufacture and selection of materials for urogynecological meshes. Medical devices, such as vaginal meshes can be manufactured using a variety of techniques including injection moulding, electrospinning, hot-melt extrusion (HME) or more recently 3D printing. Over the past decade, the use of 3D printing within the medical device industry has expanded and offers a promising approach to manufacture patient-specific surgical mesh when combined with imaging tools. This review will summarise the current strategies to treat POP and SUI, the issues and use of current meshes for the treatment of these pelvic floor disorders (PFDs), and the future directions for the manufacture of more suitable urogynecological meshes, as well as their potential materials.

Antibiotics Application Strategies to Control Biofilm Formation in Pathogenic Bacteria

BACKGROUND

The establishment of a biofilm by most pathogenic bacteria has been known as one of the resistance mechanisms against antibiotics. A biofilm is a structural component where the bacterial community adheres to the biotic or abiotic surfaces by the help of Extracellular Polymeric Substances (EPS) produced by bacterial cells. The biofilm matrix possesses the ability to resist several adverse environmental factors, including the effect of antibiotics. Therefore, the resistance of bacterial biofilm-forming cells could be increased up to 1000 times than the planktonic cells, hence requiring a significantly high concentration of antibiotics for treatment.

METHODS

Up to the present, several methodologies employing antibiotics as an anti-biofilm, antivirulence or quorum quenching agent have been developed for biofilm inhibition and eradication of a pre-formed mature biofilm.

RESULTS

Among the anti-biofilm strategies being tested, the sub-minimal inhibitory concentration of several antibiotics either alone or in combination has been shown to inhibit biofilm formation and down-regulate the production of virulence factors. The combinatorial strategies include (1) combination of multiple antibiotics, (2) combination of antibiotics with non-antibiotic agents and (3) loading of antibiotics onto a carrier.

CONCLUSION

The present review paper describes the role of several antibiotics as biofilm inhibitors and also the alternative strategies adopted for applications in eradicating and inhibiting the formation of biofilm by pathogenic bacteria.

Recombinant expression of sericin-cecropin fusion protein and its functional activity

OBJECTIVE

Silk sericin is a natural polymer with potential utility in biomedical and biotechnological applications. Recombinantly expressed sericin ensures a source of pure protein with no contamination and with multiple properties when expressed as a fusion protein. Hence, the present paper aims to recombinantly express a functional silk sericin fusion protein.

RESULTS

In order to develop a more effective sericin protein, we have attempted to recombinantly express a part of sericin sequence, which represents a highly conserved and internally repetitive unit of the sericin1 protein, and its fusion with cecropin B, a potent antimicrobial peptide. Both difficult-to-express proteins were expressed in Escherichia coli and purified by nickel-charged affinity resin. Further, functional assay demonstrated that both proteins were individually active against Gram-positive and negative bacteria, with enhanced bactericidal activity observed in sericin-cecropin B fusion protein.

CONCLUSIONS

To our knowledge, this is the first report not only on the recombinant expression of sericin as a fusion protein but also the bactericidal possibility of the 38-amino acid serine-rich motif of sericin protein. We also discuss the potential biomedical and biotechnological applications of this sericin hybrid protein.

The state of the art of osseointegration for limb prosthesis

Osseointegration (OI) is the direct attachment of bone onto a titanium implant. Recently, the term is used to describe "transdermal" implants that allow an external prosthesis to be connected directly to the skeleton. This technology eliminates the challenges of conventional socket-based prostheses, such as skin breakdown and poor fit, which are common in patients with major extremity amputations. Osseointegration patients demonstrate encouraging improvements in quality of life and function. Patients report improvement in prosthetic use, prosthetic mobility, global health, and pain reduction on a variety of clinical assessment tools. Various implants have been developed for osseointegration for amputees. These implants use a variety of fixation strategies and surface augments to allow for successful integration into the host bone. Regardless of design, all OI implants face similar challenges, particularly infections. Other challenges include the inability to determine when integration has occurred and the inability to detect loss of integration. These challenges may be met by incorporating sensing systems into the implants. The percutaneous nature of the metal devices can be leveraged so that internal sensors need not be wireless, and can be interrogated by external monitoring systems, thus providing crucial, real-time information about the state of the implant. The purpose of this review is to (1) review the basic science behind osseointegration, (2) provide an overview of current implants, practice patterns, and clinical outcomes, and (3) preview sensor technologies which may prove useful in future generations of transdermal orthopaedic implants.

Mechanism of Action of Surface Immobilized Antimicrobial Peptides Against Pseudomonas aeruginosa

Bacterial colonization and biofilm development on medical devices can lead to infection. Antimicrobial peptide-coated surfaces may prevent such infections. Melimine and Mel4 are chimeric cationic peptides showing broad-spectrum antimicrobial activity once attached to biomaterials and are highly biocompatible in animal models and have been tested in Phase I and II/III human clinical trials. These peptides were covalently attached to glass using an azidobenzoic acid linker. Peptide attachment was confirmed using X-ray photoelectron spectroscopy and amino acid analysis. Mel4 when bound to glass was able to adopt a more ordered structure in the presence of bacterial membrane mimetic lipids. The ability of surface bound peptides to neutralize endotoxin was measured along with their interactions with the bacterial cytoplasmic membrane which were analyzed using DiSC(3)-5 and Sytox green, Syto-9, and PI dyes with fluorescence microscopy. Leakage of ATP and nucleic acids from cells were determined by analyzing the surrounding fluid. Attachment of the peptides resulted in increases in the percentage of nitrogen by 3.0% and 2.4%, and amino acid concentrations to 0.237 nmole and 0.298 nmole per coverslip on melimine and Mel4 coated surfaces, respectively. The immobilized peptides bound lipopolysaccharide and disrupted the cytoplasmic membrane potential of Pseudomonas aeruginosa within 15 min. Membrane depolarization was associated with a reduction in bacterial viability by 82% and 63% for coatings melimine and Mel4, respectively (p < 0.001). Disruption of membrane potential was followed by leakage of ATP from melimine (1.5 ± 0.4 nM) or Mel4 (1.3 ± 0.2 nM) coated surfaces compared to uncoated glass after 2 h (p < 0.001). Sytox green influx started after 3 h incubation with either peptide. Melimine coatings yielded 59% and Mel4 gave 36% PI stained cells after 4 h. Release of the larger molecules (DNA/RNA) commenced after 4 h for melimine (1.8 ± 0.9 times more than control; p = 0.008) and after 6 h with Mel4 (2.1 ± 0.2 times more than control; p < 0.001). The mechanism of action of surface bound melimine and Mel4 was similar to that of the peptides in solution, however, their immobilization resulted in much slower (approximately 30 times) kinetics.

The combination of multi-functional ingredients-loaded hydrogels and three-dimensional printed porous titanium alloys for infective bone defect treatment

Biomaterial with the dual-functions of bone regeneration and antibacterial is a novel therapy for infective bone defects. Three-dimensional (3D)-printed porous titanium (pTi) benefits bone ingrowth, but its microporous structure conducive to bacteria reproduction. Herein, a multifunctional hydrogel was prepared from dynamic supramolecular assembly of sodium tetraborate (Na2B4O7), polyvinyl alcohol (PVA), silver nanoparticles (AgNPs) and tetraethyl orthosilicate (TEOS), and composited with pTi as an implant system. The pTi scaffolds have ideal pore size and porosity matching with bone, while the supramolecular hydrogel endows pTi scaffolds with antibacterial and biological activity. In vitro assessments indicated the 3D composite implant was biocompatible, promoted bone marrow mesenchymal stem cells (BMSCs) proliferation and osteogenic differentiation, and inhibited bacteria, simultaneously. In vivo experiments further demonstrated that the implant showed effective antibacterial ability while promoting bone regeneration. Besides distal femur defect, the innovative scaffolds may also serve as an ideal biomaterial (e.g. dental implants) for other contaminated defects.

Silicon-calcium phosphate ceramics and silicon-calcium phosphate cements: Substrates to customize the release of antibiotics according to the idiosyncrasies of the patient

Bone substitutes based on calcium phosphates can be classified in two major groups: ceramics and cements. Both are biomaterials with excellent biocompatibility that have been studied as local delivery systems for drugs. This study aims to evaluate drug-release kinetics in silicon beta-tricalcium phosphate ceramics (Si-β-TCP) and in silicon calcium phosphate cements (Si-CPCs). We want to investigate if the differences in composition and in structure of the Si-β-TCP and the Si-CPC may influence for drug loading and in its release kinetics from the biomaterial. The results obtained indicate that all drug-loaded materials were efficient to tailor drug release kinetics and inhibited the growth of Staphylococcus aureus. The cements prepared with high concentrations of silicon (80% Si-CPC) present zero-order release kinetics, independent of the drug concentration loaded. Si-β-TCP and Si-CPC offer a simple technology that could serve to personalize the delivery of bioactive molecules according to each patient's needs in the treatment of bone conditions, not only limited to prophylaxis, but also for the treatment of bone infection.

Multi Dynamic Extraction: An Innovative Method to Obtain a Standardized Chemically and Biologically Reproducible Polyphenol Extract from Poplar-Type Propolis to Be Used for Its Anti-Infective Properties

Antimicrobial activity is a well-known property of propolis, making it a candidate for antimicrobial surfaces in biomedical devices. Nevertheless, large-scale use of propolis as an anti-infective agent is limited by the heterogeneity of its chemical composition and consequent variation in antimicrobial activity. The aim of this study was to demonstrate that the multi dynamic extraction (M.E.D.) method produces standardized polyphenolic mixtures from poplar-type propolis, with reproducible chemical composition and anti-microbial activity, independently from the chemical composition of the starting raw propolis. Three raw propolis samples, from Europe, America, and Asia, were analyzed for their polyphenol chemical composition by means of HPLC-UV and then combined to obtain three mixtures of propolis, which werme submitted to the M.E.D. extraction method. The chemical composition and the antimicrobial activity of M.E.D. propolis against bacteria and fungi were determined. The three M.E.D. propolis showed similar chemical compositions and antimicrobial activities, exhibiting no relevant differences against antibiotic-susceptible and antibiotic-resistant strains. The batch-to-batch reproducibility of propolis extracts obtained with the M.E.D. method encourages the design of drugs alternative to traditional antibiotics and the development of anti-infective surface-modified biomaterials.

Hydroxyapatite/silver electrospun fibers for anti-infection and osteoinduction

Bone implant materials cause the most common complication of bone infections in orthopedic surgery, resulting in implant failure. Antibiotic treatment of bone infections leads to problems such as bacterial resistance and reduced osteogenic capacity. In this study, dopamine (DA) was self-polymerized on the surface of Polylactic acid (PLLA)/Hydroxyapatite (HA) nanowire composite fibers to form an adhesive polydopamine (PDA) membrane, and a stable silver-nanoparticles (Ag-NPs) coating layer was constructed on it by electrochemically driven Ag⁺ coordination and chelation through Polypyrrole (PPy) mediation, achieving steady and slow release of Ag-NPs. With optimized DA soaking time of 24 h and soaking concentration of 0.5 g·L^-1, nanoparticles were uniformly distributed on PLLA/HA/PDA/PPy/Ag composite fibers and the hydrophilicity of the composite fibers was well-behaved. Besides, the composite fibers possessed good physiological stability and 100% antibacterial rate against Escherichia coli (E. coli) as well as Staphylococcus aureus (S. aureus). In addition, the composite fibers had promoted apatite nucleation and growth on surface and good cytocompatibility with osteoblasts, indicating ability of inducing osteogenic differentiation. In summary, a multi-functional PLLA/HA/PDA/PPy/Ag composite fiber with long-term antibacterial property, bioactivity and osteoinductivity was successfully constructed by electrospinning and electrochemical deposition.

Eluted 25-hydroxyvitamin D3 from radially aligned nanofiber scaffolds enhances cathelicidin production while reducing inflammatory response in human immune system-engrafted mice

Vitamin D₃ modulates immune response, induces endogenous antimicrobial peptide production, and enhances innate immunity to defend against infections. These findings suggest that incorporating vitamin D₃ into medical devices or scaffolds could positively modulate host immune response and prevent infections. In the current study, we evaluated host responses and endogenous antimicrobial peptide production using 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds in human immune system-engrafted mice. We transformed traditional 2D electrospun nanofiber membranes into radially aligned PCL nanofiber scaffolds using the concept of solid of revolution and an innovative gas-foaming technique. Such scaffolds can promote rapid cellular infiltration and neovascularization. The infiltrating immune cells within subcutaneously implanted 25(OH)D₃-containing scaffolds mainly consisted of human macrophages in the M1 phase (CCR7⁺), mice macrophages in the M2 phase (CD206⁺), and human cytotoxic T cells (CD8⁺) other than few human T-helper cells (CD4⁺). The 25(OH)D₃-eluting nanofiber scaffolds significantly inhibited the production of pro-inflammatory cytokines (TNF-α, IL-6), while accelerating the production of anti-inflammatory cytokines (IL-4, IL-10) within the scaffolds. Additionally, we observed increased expression of human cathelicidin LL-37 within the 25(OH)D₃-eluting scaffolds, while no LL-37 expression was observed in the control. Together, these findings support further work in the design of vitamin D₃-eluting medical devices or scaffolds for modulating immune response and promoting antimicrobial peptide production. This could potentially reduce the inflammatory response, prevent infections, and eventually improve success rates of implants. STATEMENT OF SIGNIFICANCE: Transplant failure of medical devices, grafts, scaffolds, and tissue-engineered constructs due to inflammation and infection causes not only economic losses but also sufferings of second operation to the patient. Positive modulation of the host response to implants, scaffolds, and tissue-engineered constructs is likely to reduce the failure rate. Vitamin D₃ plays an important role in modulating the immune response. It is able to not only reduce inflammation and induce endogenous antimicrobial peptide production but also prevent multidrug resistance and other side effects of traditional antibiotics. In this study, host responses to 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds were evaluated in human immune system-engrafted mice. The 25(OH)D₃-eluting medical devices or scaffolds were able to modulate positive immune response and promote antimicrobial peptide production. This work presented an innate immunity-enhancing approach for reducing the inflammatory response and preventing infections, likely resulting in improvement of success rates of implants.

Antibacterial Properties of a Novel Zirconium Phosphate-Glycinediphosphonate Loaded with Either Zinc or Silver

A novel compound consisting of a zirconium phosphate-glycinediphosphonate (ZPGly) has recently been introduced. This 2D-structured material forming nanosheets was exfoliated under appropriate conditions, producing colloidal aqueous dispersions (ZPGly-e) which were then loaded with zinc (Zn/ZPGly) or silver ions. Silver ions were subsequently reduced to produce metallic silver nanoparticles on exfoliated ZPGly nanosheets (Ag@ZPGly). In the search for new anti-infective materials, the present study investigated the properties of colloidal dispersions of ZPGly-e, Zn/ZPGly, and Ag@ZPGly. Ag@ZPGly was found to be a bactericidal material and was assayed to define its minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) on the five most prevalent pathogens of orthopaedic implant infections, namely: Staphylococcus aureus ATCC25923, Staphylococcus epidermidis RP62A, Enterococcus faecalis ATCC29212, Escherichia coli ATCC51739, and Pseudomonas aeruginosa ATCC27853. MIC and MBC were in the range of 125–250 μg/mL and 125–1000 μg/mL, respectively, with E. coli being the most sensitive species. Even colloidal suspensions of exfoliated ZPGly nanosheets and Zn/ZPGly exhibited some intrinsic antibacterial properties, but only at greater concentrations. Unexpectedly, Zn/ZPGly was less active than ZPGly-e.

Suppressing Antibacterial Resistance: Chemical Binding of Monolayer Quaternary Ammonium Salts to Polymethyl Methacrylate in an Aqueous Solution and its Clinical Efficacy

Antibacterial resistance (ABR) poses an enormous threat to human health. ABR mainly develops due to bacteria being constantly exposed to diluted levels of disinfectants. Here, we propose a method for suppressing ABR through the chemical binding of disinfectants to polymethyl methacrylate (PMMA) device surfaces in solutions of 5%, 10%, and 20% disinfectant concentrations. PMMA discs were fabricated from a commercial orthodontic acrylic resin system (Ortho-Jet) and quaternary ammonium salts (QAS), 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (42% in methanol), were used as the disinfectant. The PMMA surfaces were activated in 3 M sulfuric acid at 80 °C for 5 h for the esterification of hydrolyzed QAS to PMMA. Fourier transform infrared difference spectra confirmed that the carboxy-terminated PMMA was chemically bound to the QAS. In vitro cell viability tests using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assays revealed that 5%QAS-c-PMMA was more biocompatible than 10%QAS-c-PMMA and 20%QAS-c-PMMA. The results of antibacterial tests and clinical trials demonstrated the excellent antibacterial power of 5%QAS-c-PMMA. This method is the first solution-based approach to successfully avoid disinfectant leakage and subsequent ABR, as revealed by mass spectrometry studies of the solution obtained by agitating the disinfectant-bound PMMA for 28 days.

Bioactivity and Bactericidal Mechanism of Histidine-Rich β-Hairpin Peptide Against Gram-Negative Bacteria

Antibacterial peptides (APMs) are a new type of antibacterial substance. The relationship between their structure and function remains indistinct; in particular, there is a lack of a definitive and fixed template for designing new antimicrobial peptides. Previous studies have shown that porcine Protegrin-1 (PG-1) exhibits considerable antimicrobial activity and cytotoxicity. In this study, to reduce cytotoxicity and increase cell selectivity, we designed histidine-rich peptides based on the sequence template RR(XY)₂X^DPGX(YX)₂RR-NH₂, where X represents I, W, V, and F. The results showed that the peptides form more β-hairpin structures in a lipid-rich environment that mimics cell membranes. Among them, the antimicrobial peptide HV2 showed strong antibacterial activity against Gram-negative strains and almost no toxicity to normal cells. The results of our analysis of its antibacterial mechanism showed that peptide HV2 acts on the bacterial cell membrane to increase its permeability, resulting in cell membrane disruption and death. Furthermore, peptide HV2 inhibited bacterial movement in a concentration-dependent manner and had a more robust anti-inflammatory effect by inhibiting the production of TNF-α. In summary, peptide HV2 exhibits high bactericidal activity and cell selectivity, making it a promising candidate for future use as an antibiotic.

Implantable antimicrobial biomaterials for local drug delivery in bone infection models

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

Electrophoretic deposition of GHK-Cu loaded MSN-chitosan coatings with pH-responsive release of copper and its bioactivity

Despite the fact that titanium has been widely applied in the replacement of bone defects, prosthesis failure still occurred because of the lack of adequate bone-bonding ability and the incidence of post-surgery infections. Concentration-dependent effects of therapeutic copper ions (Cu²⁺) for antibacterial and osteogenic activity have been well-established in the field of biomedical application. In this study, we prepared mesoporous silica nanoparticles (MSN) and MSN-COOH with uniform sphere size (~100 nm) and developed multifunctional chitosan coatings loaded with MSN@GHK-Cu (glycyl-L-histidyl-l-lysine-Cu²⁺) as a suitable strategy by electrophoretic deposition (EPD). The microstructure and composition of the coating were comprehensively characterized by using SEM, XRD, FTIR, and TEM, respectively. The functional activity of Cu²⁺ releasing from the surface was dependent on the pH value of the titanium surface. Through the controllable release of Cu²⁺, the coating achieved not only inhibited adhesion of bacteria but also had good cytocompatibility. The coating based on EPD technique could be considered as a promising surface modification approach for the controlled delivery in situ of drug or other biomolecules.

Antimicrobial peptides prevent bacterial biofilm formation on the surface of polymethylmethacrylate bone cement

PURPOSE

Antibiotic-loaded polymethylmethacrylate-based bone cement has been implemented in orthopaedics to cope with implant-related infections associated with the formation of bacterial biofilms. In the context of emerging bacterial resistance to current antibiotics, we examined the efficacy of short antimicrobial peptide-loaded bone cement in inhibiting bacterial adhesion and consequent biofilm formation on its surface.

METHODOLOGY

The ability of α-helical antimicrobial peptides composed of 12 amino acid residues to prevent bacterial biofilm [methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa and Escherichia coli] formation on the surface of model implants made from polymethylmethacrylate-based bone cement was evaluated by colony-forming unit (c.f.u.) counting of bacteria released by sonication from the biofilms formed on their surfaces. The biofilms on model implant surfaces were also visualized by light microscopy after staining with tetrazolium dye (MTT) and by scanning electron microscopy.

RESULTS

When incorporated in the implants, these peptides caused a mean reduction in the number of bacterial cells attached to implants' surfaces (by five orders of magnitude), and 88 % of these implants showed no bacterial adhesion after being exposed to growth media containing various bacteria.

CONCLUSION

The results showed that the antibiofilm activity of these peptides was comparable to that of the antibiotics, but the peptides exhibited broader specificity than the antibiotics. Given the rapid development of antibiotic resistance, antimicrobial peptides show promise as a substitute for antibiotics for loading into bone cements.

UV-Responsive Multilayers with Multiple Functions for Biofilm Destruction and Tissue Regeneration

The increasing demands of surgical implantation highlight the significance of anti-infection of medical devices, especially antibiofilm contamination on the surface of implants. The biofilms developed by colonized microbes will largely hinder the adhesion of host cells, leading to failure in long-term applications. In this work, UV-responsive multilayers were fabricated by stepwise assembly of poly(pyrenemethyl acrylate- co-acrylic acid) (P(PA- co-AA)) micelles and chitosan on different types of substrates. Under UV irradiation, the cleavage of pyrene ester bonds in the P(PA- co-AA) molecules resulted in the increase of roughness and hydrophilicity of the multilayers. During this process, reactive oxygen species were generated in situ within 10 s, which destroyed the biofilms of Staphylococcus aureus, leading to the degradation of the bacterial matrix. The antibacterial rate was above 99.999%. The UV-irradiated multilayers allowed the attachment and proliferation of fibroblasts, endothelial cells, and smooth muscle cells, benefiting tissue integration of the implants. When poly(dimethylsiloxane) slices with the multilayers were implanted in vivo and irradiated by UV, the density of bacteria and the inflammatory level (judging from the number of neutrophils) decreased significantly. Moreover, formation of neo blood vessels surrounding the implants was observed after implantation for 7 days. These results reveal that the photoresponsive multilayers endow the implants with multifunctions of simultaneous antibiofilm and tissue integration, shedding light for applications in surface modification of implants in particular for long-term use.

Electrospun polycaprolactone/hydroxyapatite/ZnO nanofibers as potential biomaterials for bone tissue regeneration

Fabricating a bioartificial bone graft possessing structural, mechanical and biological properties mimicking the real bone matrix is a major challenge in bone tissue engineering. Moreover, the developed materials are prone to microbial invasion leading to biomaterial centered infections which might limit their clinical translation. In the present study, biomimetic nanofibrous scaffolds of Poly ɛ-caprolactone (PCL)/nano-hydroxyapatite (nHA) were electrospun with 1wt%, 5wt%, 10wt%, 15wt% and 30wt% of zinc oxide (ZnO) nanoparticles in order to understand the optimal concentration range of (ZnO) nanoparticles balancing both biocompatibility and osteoregeneration. The developed nanofibrous scaffolds were successfully characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), contact angle, fourier transform infrared spectroscopy (FTIR), wide-angle X-Ray diffraction (WAXD), brunaueremmett Teller (BET) surface area and tensile testing. Biocompatibility of the developed scaffolds at in vitro level was evaluated by culturing MG-63 cells and investigating the impact on cell viability, proliferation, protein adsorption, alkaline phosphatase (ALP) activity and biomineralization. The PCL/nHA scaffolds exhibited a 1.2-fold increase in cell viability and proliferation, while incorporation of ZnO nanoparticles to PCL/nHA imparted antimicrobial activity to the scaffolds with a progressive increase in the antimicrobial efficacy with increasing ZnO concentration. The results of cell viability were supported by ALP activity and mineralization assay, wherein, PCL/nHA/ZnO scaffolds showed higher ALP activity and better mineralization capacity as compared to pristine PCL. Although, the PCL/nHA/ZnO scaffolds with 10, 15 and 30wt% of ZnO particles exhibited superior antimicrobial efficacy against both gram-negative (E. coli) and gram-positive (S. aureus) bacteria, a significant decrease in the cell viability and mechanical properties was observed at higher concentrations of ZnO namely 15 and 30%. Amongst the various ZnO concentrations studied optimal cell viability, antimicrobial effect and mechanical strength were observed at 10wt.% ZnO concentration. Thus, the present study revealed that the biomimetic tri-component PCL/nHA/ZnO scaffolds with ZnO concentration range of ≤ 10% could be ideal for achieving optimal biocompatibility (cell proliferation, biomineralization, and antimicrobial capacity) and mechanical stability thus making it a promising biomaterial substrate for bone tissue regeneration.

Rational Design of Short Peptide Variants by Using Kunitzin-RE, an Amphibian-Derived Bioactivity Peptide, for Acquired Potent Broad-Spectrum Antimicrobial and Improved Therapeutic Potential of Commensalism Coinfection of Pathogens

Commensalism coinfection of pathogens has seriously jeopardized human health. Currently, Kunitzin-RE, as an amphibian-derived bioactivity peptide, is regarded as a potential antimicrobial candidate. However, its antimicrobial properties were unsatisfactory. In this study, a set of shortened variants of Kunitzin-RE was developed by the interception of a peptide fragment and single-site mutation to investigate the effect of chain length, positive charge, hydrophobicity, amphipathicity, and secondary structure on antimicrobial properties. Among them, W8 (AARIILRWRFR) significantly broadened the antimicrobial spectrum and showed the highest antimicrobial activity (GM_all = 2.48 μM) against all the fungi and bacteria tested. Additionally, W8 showed high cell selectivity and salt tolerance in vitro, whereas it showed high effectiveness against mice keratitis cause by infection by C. albicans 2.2086. Additionally, it also had obviously lipopolysaccharide-binding ability and a potent membrane-disruptive mechanism. Overall, these findings contributed to the design of short antimicrobial peptides and to combat the serious threat of commensalism coinfection of pathogens.

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

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

Intrawound Antibiotic Powder Decreases Frequency of Deep Infection and Severity of Heterotopic Ossification in Combat Lower Extremity Amputations

BACKGROUND

Amputations sustained owing to combat-related blast injuries are at high risk for deep infection and development of heterotopic ossification, which can necessitate reoperation and place immense strain on the patient. Surgeons at our institution began use of intrawound antibiotic powder at the time of closure in an effort to decrease the rate of these surgical complications after initial and revision amputations, supported by compelling clinical evidence and animal models of blast injuries. Antibiotic powder may be useful in reducing the risk of these infections, but human studies on this topic thus far have been inconclusive.

PURPOSE

We sought to determine whether administration of intrawound antibiotic powder at the time of closure would (1) decrease the risk of subsequent deep infections of major lower-extremity combat-related amputations, and (2) limit formation and decrease severity of heterotopic ossification common in the combat-related traumatic residual limb.

METHODS

Between 2009 and 2015, 252 major lower extremity initial and revision amputations were performed by a single surgeon. Revision cases were excluded if performed specifically to address deep infection, leaving 223 amputations (88.5%) for this retrospective analysis. We reviewed medical records to collect patient information, returns to the operating room for subsequent infection, and microbiologic culture results. We also reviewed radiographs taken at least 3 months after surgery to determine the presence and severity of heterotopic ossification using the Walter Reed classification system. We grouped cases according to whether limbs underwent initial or revision amputations, and whether the limbs had a history of a prior infection. Apart from the use of antibiotic powder and duration of followup, the groups did not differ in terms of age, mechanism of injury, or sex. We then calculated the absolute risk reduction for infection and heterotopic ossification and the number needed to treat to prevent an infection.

RESULTS

Overall, administration of antibiotic powder resulted in a 13% absolute risk reduction of deep infection (14 of 82 [17%] versus 42 of 141 [30%]; p = 0.03; 95% CI, 0.20%-24.72%). In revision amputation surgery, the absolute risk reduction of infection with antibiotic powder use was 16% overall (eight of 58 versus 17 of 57; 95% CI, 1.21%-30.86%), and 25% for previously infected limbs (eight of 46 versus 14 of 33; 95% CI, 4.93%-45.14%). The number needed to treat to prevent one additional deep infection in amputation surgery is eight in initial amputations, seven in revision amputations, and four for revision amputation surgery on previously infected limbs. With the numbers available, we observed no reduction in the risk of heterotopic ossification with antibiotic powder use, but severity was decreased in the treatment group in terms of the number of residual limbs with moderate or severe heterotopic ossification (three of 12 versus 19 of 34; p = 0.03).

CONCLUSIONS

Our findings show that administration of intrawound antibiotic powder reduces deep infection in residual limbs of combat amputees, particularly in the setting of revision amputation surgery in apparently aseptic residual limbs at the time of the surgery. Furthermore, administration of antibiotic powder for amputations at time of initial closure decreases the severity of heterotopic ossification formation, providing a low-cost adjunct to decrease the risk of two complications common to amputation surgery.Level of Evidence Level III, therapeutic study.

Synthesis and characterization of Ciprofloxacin-containing divinyl oligomers and assessment of their biodegradation in simulated salivary esterase

OBJECTIVE

Two leading causes contributing to dental restoration replacement are the marginal breakdown at the composite/dentin interface and secondary caries mediated by bacteria. The objective of the present study was to synthesize oligomers which incorporated enhanced bio-stability but would also be able to generate antimicrobial function if they underwent degradation.

METHODS

Stability was incorporated into the oligomers by generating structural features that would physically hinder the availability of hydrolytically sensitive groups in the oligomers. As a proof-of concept for the antibacterial feature, antimicrobial function was achieved by covalently incorporating Ciprofloxacin (CF) into the backbone of cross-linking divinyl oligomers (referred to as EDV and HLH-CFPEG). The hydrolytic stability of the oligomers was studied in simulated human salivary esterase and compared to the commercial monomer 2,2-bis[4(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (BisGMA).

RESULTS

Both drug oligomers were found to be significantly more stable than BisGMA. Upon degradation, both drug oligomers released CF differentially in free form. Polymer synthesis from resin formulations containing 15wt% HLH-CFPEG showed a high degree of vinyl group conversion and gel content, and under hydrolytic conditions showed the release of CF during a 28-day monitoring study period.

SIGNIFICANCE

HLH-CFPEG can be used in dental resin adhesive systems for local delivery of CF to the marginal interface. Minimizing the growth of Streptococcus mutans at the marginal site can improve longevity by reducing esterase activity derived specifically from S. mutans.

Improved antibacterial properties of collagen I/hyaluronic acid/quaternized chitosan multilayer modified titanium coatings with both contact-killing and release-killing functions

The HACC-based multilayer could inhibit the colonization of bacteria via contact-killing and release-killing.

Collagen-silica bio-composite enriched with Cynodon dactylon extract for tissue repair and regeneration

Development of biomaterials for tissue engineering applications is of great interest to meet the demand of different clinical requirements. The wound heal dressing biomaterials should necessarily contain well-defined therapeutic components and desirable physical, chemical and biological properties to support optimal delivery of therapeutics at the site of the wound. In this study, we developed collagen-silica wound heal scaffold incorporated with the extract of Cynodon dactylon, characterized and evaluated for its wound heal potential in vitro and in vivo against collagen (Col) and Collagen-silica (CS) scaffolds that served as controls. The prepared Collagen-Silica-Cynodon extract (CSCE) scaffold exhibits porous morphology with preferable biophysical, chemical, mechanical and mass transfer properties besides its controlled biodegradation at the wound site. Stability of CSCE was found to be better than that of native collagen due to intermolecular interactions between collagen and constituents of C. dactylon as confirmed by FTIR analysis. Notably, in vitro biocompatibility assay using DAPI and Rhodamine 123 staining demonstrated that the proliferation of NIH3T3 fibroblast cells was better for CSCE when compared to the Col and CS scaffolds. In vivo wound healing experiments with full-thickness excision wounds in wistar rat model demonstrated that the wounds treated with CSCE showed accelerated healing with enhanced collagen deposition when compared to wounds treated with Col and CS scaffolds, and these studies substantiated the efficacy of CSCE scaffold for treating wounds.

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

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

Self-assembling antimicrobial peptides on nanotubular titanium surfaces coated with calcium phosphate for local therapy

Bacterial infection is a serious medical problem leading to implant failure. The current antibiotic based therapies rise concerns due to bacterial resistance. The family of antimicrobial peptides (AMP) is one of the promising candidates as local therapy agents due to their broad-spectrum activity. Despite AMPs receive increasing attention to treat infection, their effective delivery to the implantation site has been limited. Here, we developed an engineered dual functional peptide which delivers AMP as a biomolecular therapeutic agent onto calcium phosphate (Ca-P) deposited nanotubular titanium surfaces. Dual functionality of the peptide was achieved by combining a hydroxyapatite binding peptide-1 (HABP1) with an AMP using a flexible linker. HABP functionality of the peptide provided a self-coating property onto the nano-topographies that are designed to improve osteointegration capability, while AMP offered an antimicrobial protection onto the implant surface. We successfully deposited calcium phosphate minerals on nanotubular titanium oxide surface using pulse electrochemical deposition (PECD) and characterized the minerals by XRD, FT-IR, FE-SEM. Antimicrobial activity of the engineered peptide was tested against S. mutans (gram- positive) and E. coli (gram-negative) both in solution and on the Ca-P coated nanotubular titanium surface. In solution activity of AMP and dual functional peptide have the same Minimum Inhibitory Concentration (MIC) (32 mg/mL). The peptide also resulted in the reduction of the number of bacteria both for E.coli and S. mutans compare to control groups on the surface. Antimicrobial features of dual functional peptides are strongly correlated with their structures suggesting tunability in design through linkers regions. The dual-function peptide offers single-step solution for implant surface functionalization that could be applicable to any implant surface having different topographies.

Antimicrobial quaternary ammonium organosilane cross-linked nanofibrous collagen scaffolds for tissue engineering

Introduction

In search for cross-linkers with multifunctional characteristics, the present work investigated the utility of quaternary ammonium organosilane (QOS) as a potential cross-linker for electrospun collagen nanofibers. We hypothesized that the quaternary ammonium ions improve the electrospinnability by reducing the surface tension and confer antimicrobial properties, while the formation of siloxane after alkaline hydrolysis could cross-link collagen and stimulate cell proliferation.

Materials and methods

QOS collagen nanofibers were electrospun by incorporating various concentrations of QOS (0.1%–10% w/w) and were cross-linked in situ after exposure to ammonium carbonate. The QOS cross-linked scaffolds were characterized and their biological properties were evaluated in terms of their biocompatibility, cellular adhesion and metabolic activity for primary human dermal fibroblasts and human fetal osteoblasts.

Results and discussion

The study revealed that 1) QOS cross-linking increased the flexibility of otherwise rigid collagen nanofibers and improved the thermal stability; 2) QOS cross-linked mats displayed potent antibacterial activity and 3) the biocompatibility of the composite mats depended on the amount of QOS present in dope solution – at low QOS concentrations (0.1% w/w), the mats promoted mammalian cell proliferation and growth, whereas at higher QOS concentrations, cytotoxic effect was observed.

Conclusion

This study demonstrates that QOS cross-linked mats possess anti-infective properties and confer niches for cellular growth and proliferation, thus offering a useful approach, which is important for hard and soft tissue engineering and regenerative medicine.

Antibacterial surface modification of titanium implants in orthopaedics

The use of biomaterials in orthopaedics for joint replacement, fracture healing and bone regeneration is a rapidly expanding field. Infection of these biomaterials is a major healthcare burden, leading to significant morbidity and mortality. Furthermore, the cost to healthcare systems is increasing dramatically. With advances in implant design and production, research has predominately focussed on osseointegration; however, modification of implant material, surface topography and chemistry can also provide antibacterial activity. With the increasing burden of infection, it is vitally important that we consider the bacterial interaction with the biomaterial and the host when designing and manufacturing future implants. During this review, we will elucidate the interaction between patient, biomaterial surface and bacteria. We aim to review current and developing surface modifications with a view towards antibacterial orthopaedic implants for clinical applications.

Reducing Bacterial Infections and Biofilm Formation Using Nanoparticles and Nanostructured Antibacterial Surfaces

With the rapid spreading of resistance among common bacterial pathogens, bacterial infections, especially antibiotic-resistant bacterial infections, have drawn much attention worldwide. In light of this, nanoparticles, including metal and metal oxide nanoparticles, liposomes, polymersomes, and solid lipid nanoparticles, have been increasingly exploited as both efficient antimicrobials themselves or as delivery platforms to enhance the effectiveness of existing antibiotics. In addition to the emergence of widespread antibiotic resistance, of equal concern are implantable device-associated infections, which result from bacterial adhesion and subsequent biofilm formation at the site of implantation. The ineffectiveness of conventional antibiotics against these biofilms often leads to revision surgery, which is both debilitating to the patient and expensive. Toward this end, micro- and nanotopographies, especially those that resemble natural surfaces, and nonfouling chemistries represent a promising combination for long-term antibacterial activity. Collectively, the use of nanoparticles and nanostructured surfaces to combat bacterial growth and infections is a promising solution to the growing problem of antibiotic resistance and biofilm-related device infections.