Ultraviolet Light Irradiation Research Articles

Visible-Light Cross-Linkable Multifunctional Hydrogels Loaded with Exosomes Facilitate Full-Thickness Skin Defect Wound Healing through Participating in the Entire Healing Process.

The management of severe full-thickness skin defect wounds remains a challenge due to their irregular shape, uncontrollable bleeding, high risk of infection, and prolonged healing period. Herein, an all-in-one OD/GM/QCS@Exo hydrogel was prepared with catechol-modified oxidized hyaluronic acid (OD), methylacrylylated gelatin (GM), and quaternized chitosan (QCS) and loaded with adipose mesenchymal stem cell-derived exosomes (Exos). Cross-linking of the hydrogel was achieved using visible light instead of ultraviolet light irradiation, providing injectability and good biocompatibility. Notably, the incorporation of catechol groups and multicross-linked networks in the hydrogels conferred strong adhesion properties and mechanical strength against external forces such as tensile and compressive stress. Furthermore, our hydrogel exhibited antibacterial, anti-inflammatory, and antioxidant properties along with wound-healing promotion effects. Our results demonstrated that the hydrogel-mediated release of Exos significantly promotes cellular proliferation, migration, and angiogenesis, thereby accelerating skin structure reconstruction and functional recovery during the wound-healing process. Overall, the all-in-one OD/GM/QCS@Exo hydrogel provided a promising therapeutic strategy for the treatment of full-thickness skin defect wounds through actively participating in the entire process of wound healing.

Hysteresis loops on voltage-current characteristics and optical responses of PEDOT:PSS/ZnO nanorods/ZnO:Ga heterostructure

Volage (V)-current (I) curves of the poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/ZnO nanorods (NRs)/ZnO:Ga (GZO) heterostructure exhibited a rectification behavior with hysteresis loops both in forward voltage (VF) and reverse voltage (VR) regions. The ultraviolet (UV) light irradiation of 360 nm led to the increase in the reverse current (IR), i.e. generation of photocurrent (PC), and the decrease in the hysteresis loop area in the VF region. In dark, the 1/V vs. ln (I/V2) plot revealed that the dominant carrier transport mechanisms in the low- and the high-VF regions are the direct tunneling and the Fowler-Nordheim (F-N) tunneling through the dipole layer formed at the interface between the PEDOT:PSS and ZnO NRs layers, respectively. On the contrary, the carrier transport in the middle-VF region in dark was dominated by the bulk-limited mechanisms, such as the space-charge-limited (SCL) conduction controlled by the single shallow traps, the trap-free SCL conduction, and the trap-filled-limit conduction controlled by the traps with Gaussian distribution. The UV light irradiation changed the carrier transport mechanism in the middle-VF region to the trap-free SCL conduction. The resistive switching related to the hysteresis loop was found to be caused by the trapping and detrapping of the injected carriers at the traps. In dark, the maximum forward current was increased by the repetition of the VF sweep of 0 V → 5 V → 0 V, but decreased by the repetition of the VR sweep of 0 V → -5V → 0 V, indicating the possibility of the resistive memory. At the low VRs, PC spectra showed a main peak at 350 nm, which is corresponding to slightly higher photon energy than the bandgap energy of ZnO. Moreover, the existence of the tail extending into the bandgap was also observed on the PC spectra. From the time response of PC, the depth of the trap state was estimated to be 0.64–0.77 eV.

Metal complexes with thiosemicarbazone derivative and isatine: A promising new class of materials for biomedical and environmental applications

Metal complexes with thiosemicarbazones and isatine have been shown to exhibit a wide range of biological activities, including antibacterial, antifungal, and anticancer activity. These complexes have also been shown to be effective photocatalysts for degrading dyes, making them a subject of significant interest. This article presents the synthesis and characterization of mixed ligand complexes of isatine-thiosemicarbazones to explore their biological activity and potential for photocatalytic applications. In this study, we synthesized mixed ligand complexes of isatine-thiosemicarbazones with various metal ions, including Cu(II), Cd(II), and Fe(III). Characterization techniques such as elemental analysis, infrared (IR), mass spectrometry (MS), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) were utilized to understand their structural composition and morphological properties. The complexes exhibited remarkable antibacterial activity against Escherichia coli, Staphylococcus aureus, Streptococcus mutants, and antifungal effects on Candida albicans. Notably, the Fe-complex demonstrated the highest activity, followed by the Cu-complex and Cd-complex. Strong anticancer effects were observed against human liver HepG2 and breast MDA cancer cells, with the Fe-complex displaying the highest activity. Additionally, the complexes displayed significant photocatalytic activity in the decomposition of rose bengal dye using ultraviolet light irradiation, with the Cu-complex showing the highest degradation efficiency. The results indicate that these mixed ligand metal complexes have potential therapeutic applications as antibacterial, antifungal, and anticancer agents. Moreover, they suggest their prospective utility as photocatalysts for the remediation of dye-contaminated wastewater.

A Three-Dimensional Open-Framework Tin(II) Sulfate with Near-Unity Photoluminescence Quantum Yield.

A new open-framework tin(II) sulfate, formulated as C4H12N2·Sn(SO4)2·H2O, was prepared under the structure-directing effect of piperazine. This compound features a 3D structure with 16-ring channels. Under ultraviolet light irradiation, it emits bright yellow luminescence with a near-unity photoluminescence quantum yield. Theoretical calculations were carried out to understand the luminescence mechanism.

Development and Application of a Nano-Gas Sensor for Monitoring and Preservation of Ancient Books in the Library

Monitoring the gas composition in library environments is crucial for the preservation of ancient books. In this study, TiO2 NTs/CNTs composites were synthesized via a hydrothermal method and utilized as nano-gas sensors for NO2 detection. The surface morphology and element composition of the samples were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Additionally, the gas sensitivity of the prepared TiO2 nanocomposites was evaluated at different temperatures, both with and without ultraviolet light irradiation. The results demonstrate that the synthesized TiO2 NTs/CNTs samples exhibit a large specific surface area due to their titanium dioxide nanotubes (TiO2 NTs) and carbon nanotubes (CNTs) composition. Moreover, these samples display excellent gas sensitivity under ultraviolet light irradiation at temperatures of 120 °C. Compared to uncomposited and non-ultraviolet light irradiated samples, the sensor response rate is significantly improved, enabling effective monitoring of NO2 gas in library environments conducive to preserving ancient books. Overall, our findings highlight that the developed TiO2 NTs/CNTs nano gas sensor holds great potential for monitoring and safeguarding ancient books.

Photorewriting, Time-Resolved Encryption, and Unclonable Anticounterfeiting with Artificial Intelligence Authentication via a Reversible Photoswitchable System.

In the fields of photolithographic patterning, optical anticounterfeiting, and information encryption, reversible photochromic materials with solid-state fluorescence are emerging as a potential class of systems. A design strategy for reversible photochromic materials has been proposed and synthesized through the introduction of photoactive thiophene groups into the molecular backbone of aryl vinyls, compounds with unique aggregation-induced emission properties, and solid-state reversible photocontrollable fluorescence and color-changing properties. This work develops novel photochromic inks, films, and cellulose hydrogels for enhancing the security of information encryption and anticounterfeiting technologies. They achieve rapid and reversible color change under ultraviolet light irradiation. Dependent upon the rate of color change, higher levels of time-resolved security can be achieved. This feature is important for enhancing the confidentiality of encrypted information and the reliability of security labels. Color-changing cellulose hydrogels, inks, and films consisting of three photochromic fluorescent molecules have quick photoactivity, great photoreversibility and photostability, and good processability, making them ideal for time-delayed anticounterfeiting and smart encryption. Furthermore, specialized algorithms are used to construct convolutional neural networks, and image analysis is performed on these systems, thus solving the current problem of the time-consuming information decryption process. This artificial intelligence method offers new opportunities for enhanced data encryption.

Near-unity quantum yield and long-term emission stability in halide perovskite nanocrystal glass composite

Metal halide perovskites are promising optoelectronic materials due to their outstanding luminescent properties. However, the instability of perovskites has long been the bottleneck to their practical applications. Here Cs4PbBr6 nanocrystals based glass composite (Cs4PbBr6 NCs@glass) are successfully prepared, which displays green emission color (520 nm), narrow bandwidth (23 nm) and a near-unity photoluminescence quantum yield (PLQY). The H2O molecules permeating in the lattice of Cs4PbBr6 were found to be a crucial role in the subband energy emission. The Cs4PbBr6 NCs@glass has excellent emission stability; maintains 93 % of initial PL intensity after ultraviolet light irradiation for over 5000 h. In addition, by adjusting the halogen content, we have achieved tunable emission color from blue (450 nm) to green (520 nm) and red (670 nm) on Cs4PbX6 NCs@glass (X = Cl, Br, I), which covers up to 127 % of the National Television Systems Board (NTSC) standard system. Our finding indicates the commercial applications of perovskite materials in lighting and display.

HfTiO4 transparent thick film phosphors activated with Eu3+, Dy3+, and Tb3+ ions

Hafnium (Hf)-based double oxides show promise as high-efficiency scintillators due to large effective atomic numbers and high relative density. However, the preparation of these scintillation crystals is challenging due to their high melting points and incongruent melting behavior. In the present study, we demonstrated that the chemical vapor deposition (CVD) of single-phase HfTiO4 films on quartz glass substrate was successfully deposited at temperatures ranging from 973 to 988 K, with a TiO2 molar ratio in the precursor vapor of 25–45 mol% TiO2. The deposition rate of HfTiO4 reached 36 µm h−1. The films exhibited an in-line transmittance of 78 % relative to the raw glass substrate at a wavelength of 600 nm. When activated with Eu3+, Dy3+, and Tb3+ ions, the HfTiO4 films displayed red, yellow, and green photoluminescence emissions originated from the 4f–4f transitions of each trivalent rare-earth ion under ultraviolet light irradiation. HfTiO4 exhibited no intrinsic background emission, suggesting that the addition of a selected activator could yield a phosphor with the desired emission color range.

BaTi0.85Zr0.15O3/MOF-5 nanocomposite: Synthesis, characterization and photocatalytic activity toward tetracycline

It has been proposed that oriented anchoring strategies can be used to organize BaTi0.85Zr0.15O3 (BTZ) quantum dots (QD) with MOF-5 to provide highly efficient catalytic degradation of tetracycline (TC). This study presents the preparation of [Zn4O (BDC)3] (BDC = benzene-1,4dicarboxylate) metal–organic framework-5 (MOF-5)/BTZ nanocomposites by a facile one-pot solvent-thermal precipitation method. The as-synthesized samples were identified by XRD, TG-DTG, UV–VIS DRS, FESEM, FTIR, BET, TEM, PL, and EDX characterization techniques. The photocatalytic ability of nanocomposite BTZ (30 %wt)/MOF-5 was particularly impressive among the binary photocatalysts. In a 10 ppm solution of TC, BTZ (30 wt%)/MOF-5 demonstrated superior photodegradation activity, with 95 % degradation efficiency of TC determined by HPLC. The best response was achieved at pH 11 with catalyst dosages of 0.2 g/L, irradiation time of 150 min, and CTC of 10 ppm. An internal electric field was suggested to mediate the direct Z-scheme charge transfer mechanism between BTZ and MOF-5. The improvement was achieved by fabricating BTZ and MOF-5 in an indirect Z-scheme heterojunction system. Photogenerated electron-hole separation can be accelerated by BTZ/MOF-5 with improved redox capabilities. Overall, taking advantage of an enhanced redox capacity under ultraviolet (UV) light irradiation, this study demonstrates how to promote efficient antibiotic degradation using MOF-based nanocomposites. Moreover, photodegradation kinetics were studied using the Hinshelwood formula, giving 0.0113 min−1 (slope) and 61.32 min as t1/2. In the COD experiment, mineralized TC molecules had y = -0.0144 + 0.0444x, r2 = 0.9942, and k = 0.0144 min−1 (t1/2 = 48.12 min).

An upstream signaling gene calmodulin regulates the synthesis of insect wax via activating fatty acid biosynthesis pathway

Insect wax accumulates on the surface of insect cuticle, which acts as an important protective barrier against rain, ultraviolet light radiation, pathogens, etc. The waxing behavior, wax composition and molecular mechanism underling wax biosynthesis are unclear in dustywings. Herein, the current study determined the vital developmental stage for waxing behavior in dustywings, examined the components of waxy secretions, and identified key regulatory genes for wax biosynthesis. The wax glands were mainly located on the thorax and abdomen of dustywing adults. The adults spread the waxy secretions over their entire body surface. The metabolomics analysis identified 32 lipids and lipid-like molecules, 15 organic acids and derivatives, 7 benzenoids, etc. as the main components of waxy secretions. The fatty acids represented the largest proportion of the category of lipid and lipid-like molecules. The conjoint analysis of metabolomics and transcriptomics identified two crucial genes fatty acyl-CoA reductase (CsFAR) and calmodulin (CsCaM) for wax biosynthesis. The down-regulation of these genes via nanocarrier-mediated RNA interference technology significantly reduced the amount of wax particles. Notably, the RNAi of CsCaM apparently suppressed the expression of most genes in fatty acid biosynthesis pathway, indicating the CsCaM might act as a main upstream regulator of fatty acid biosynthesis pathway.

Material and Antibacterial Properties of Spinel-Structure Ca-Doped ZnCo2O4 Thin Films

In the preparation of Zn(Co1−xCax)2O4 thin films with doping content ratio Cax = 0.00–0.20, analysis shows that no impurity phase is formed in spinel-structure thin films, while doping calcium reduces the grain size of the thin films and the planarization of the surface microstructure. Increasing the doping content ratio of calcium will reduce the ability of the film to absorb blue and ultraviolet light, and reduce the characteristic absorption of ZnCo2O4. The energy gap of Zn(Co1−xCax)2O4 film increases from 2.46 eV at Cax = 0.00 to 2.51 eV at Cax = 0.15. Moreover, doping Ca+2 to replace Co+3 increases the conductivity and carrier concentration, for which the optimal doping ratio is Cax = 0.07. The film resistivity decreases from 270.5 Ω-cm (undoped) to 15.4 Ω-cm (Cax = 0.07) and the carrier concentration increases from 2.54 × 1015 (undoped) to 6.25 × 1017 cm−3 (Cax = 0.07). Under ultraviolet light irradiation and in an environment without any light source, the film exhibits anti–E. coli resistance as high as 99.94% and 99.99%. Thus, P-type Zn(Co1−xCax)2O4 films can be used for antibacterial and electronic components.

Lanthanide-based Single-Chain Nanoparticles as "Visual" Pass/Fail Sensors of Maximum Permissible Concentration of Cu2+ Ions in Drinking Water.

The maximum permissible concentration (m.p.c.) of Cu2+ ions in drinking water, as set by the World Health Organization (WHO) is m.p.c. (Cu2+)WHO = 30 μM, whereas the US Environmental Protection Agency (EPA) establishes a more restrictive value of m.p.c. (Cu2+)EPA = 20 μM. Herein, we develop-for the first time ever-a family of m.p.c. (Cu2+) "visual" pass/fail sensors based on water-soluble lanthanide-containing single-chain nanoparticles (SCNPs) exhibiting an average hydrodynamic diameter less than 10 nm. Both europium (Eu)- and terbium (Tb)-based SCNPs allow excessive Cu2+ to be readily detected in water, as indicated by the red-to-transparent and green-to-transparent changes, respectively, under ultra-violet (UV) light irradiation, occurring at 30 μM Cu2+ in both cases. Complementary, dysprosium (Dy)-based SCNPs show a yellow color-to-transparent transition under UV light irradiation at approximately 15 μM Cu2+. Eu-, Tb- and Dy-containing SCNPs prove to be selective for Cu2+ ions as they do not respond against other metal ions, such as Fe2+, Ag+, Co2+, Ba2+, Ni2+, Hg2+, Pb2+, Zn2+, Fe3+, Ca2+, Mn2+, Mg2+ or Cr3+. These new m.p.c. (Cu2+) "visual" pass/fail sensors are thoroughly characterized by a combination of techniques, including size exclusion chromatography, dynamic light scattering, inductively coupled plasma-mass spectrometry, as well as infrared, UV and fluorescence spectroscopy. This article is protected by copyright. All rights reserved.

Highly luminescent and stable CsPbBr3 perovskite nanocrystals coated with polyethersulfone for white light-emitting diode applications.

Simultaneously improving the stability and photoluminescence quantum yield (PLQY) of all inorganic perovskite nanocrystals (NCs) is crucial for their practical utilization in various optoelectronic devices. Here, CsPbBr3 NCs coated with polyethersulfone (PES) were prepared via an in-situ co-precipitation method. The sulfone groups in PES bind to undercoordinated lead ion (Pb2+) on the CsPbBr3 NCs, resulting in significant reduction of surface defects, thus enhancing the PLQY from 74.2% to 88.3%. Meanwhile, the PES-coated NCs exhibit high water resistance and excellent heat and light stability, maintaining over 85% of the initial PL intensity under thermal aging (70°C, 4h) and continuous 365 nm ultraviolet (UV) light irradiation (24 W, 8h) conditions. By contrast, the PL intensity of the control NCs dramatically dropped to less than 40%. Finally, a diode emitting bright white light was fabricated utilizing the PES-coated CsPbBr3 NCs, which exhibits a color gamut of ~110% NTSC standard.

Plasma electrolytic formation and characterization of MnWO4/WO3 film heterostructures

MnWO4/WO3 p-n heterojunction films were fabricated using a one-step method consisting of the plasma electrolytic oxidation (PEO) of titanium in homogeneous electrolytes containing paratungstate ions and stable water-soluble EDTA-chelated manganese. The influences of the formation current density and W: Mn molar ratio of the electrolyte, which was varied from 1:2 to 2:1, on the composition, morphology, and optical and photocatalytic properties of the resulting coatings were studied. X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, and ultraviolet diffuse reflectance spectroscopy were used to characterize the formed composites. Regardless of the W:Mn ratio of the electrolyte, the coatings contained crystalline t-WO3 and m-MnWO4. Depending on the formation conditions, the optical band gap energies of the composites varied from 2.63 to 3.01 eV. The largest absorption red shift and lowest band gap energy were observed in the film composite formed in an electrolyte with W:Mn = 2:1, at a current density of 0.2 A cm−2. Composites obtained in electrolytes with W:Mn ratios of 2:1 and 1:1 exhibited photocatalytic activity in the degradation of rhodamine C and methyl orange dyes in the presence of 10 mmol L−1 H2O2 under ultraviolet and visible light irradiation. The role of hydrogen peroxide in this dye degradation on PEO-coated composites under light irradiation is discussed.

The Electronic Impact of Light-Induced Degradation in CsPbBr3 Perovskite Nanocrystals at Gold Interfaces.

The understanding of the interfacial properties in perovskite devices under irradiation is crucial for their engineering. In this study we show how the electronic structure of the interface between CsPbBr3 perovskite nanocrystals (PNCs) and Au is affected by irradiation of X-rays, near-infrared (NIR), and ultraviolet (UV) light. The effects of X-ray and light exposure could be differentiated by employing low-dose X-ray photoelectron spectroscopy (XPS). Apart from the common degradation product of metallic lead (Pb0), a new intermediate component (Pbint) was identified in the Pb 4f XPS spectra after exposure to high intensity X-rays or UV light. The Pbint component is determined to be monolayer metallic Pb on-top of the Au substrate from underpotential deposition (UPD) of Pb induced from the breaking of the perovskite structure allowing for migration of Pb2+.

Fabrication of Liquid-Metal Printed 2D Tin Oxide Nanosheets for Optoelectronic Applications

Liquid-metal printed processes have been recently developed as a novel strategy to grow ultrathin 2D oxide materials, which are transferred from liquid-metal surfaces to substrates. In this study, we fabricated liquid-metal printing 2D tin oxide (SnO) nanosheets on SiO2/Si and glass substrates. A large lateral-sized 2D SnO nanosheets of >100 µm and a thickness of approximately 6.3 nm was fabricated. The 2D SnO nanosheets exhibited a strong optical absorption in the ultraviolet and violet region and its bandgap was estimated to be approximately 2.9 eV. The 2D SnO nanosheets on glass substrates with patterned gold electrodes generated a photocurrent under ultraviolet (UV) light irradiation, demonstrating a potential for optoelectronic applications such as UV detectors.

Fully light-modulated memristor based on ZnO/MoOx heterojunction for neuromorphic computing

Emerging optoelectronic memristors are promising candidates to develop neuromorphic computing, owing to the combined advantages of photonics and electronics. However, the reversible modulation on device conductance usually requires complicated operations involving hybrid optical/electrical signals. Herein, we design a fully light-modulated memristor based on ZnO/MoOx heterojunction, which exhibits potentiation and depression behaviors under the irradiation of ultraviolet and visible light, respectively. Several basic synaptic functions have been emulated by utilizing optical signals, including short-term/long-term plasticity and spike-number-dependent plasticity. Based on the all-optical modulation characteristics, low-level image pre-processing (including contrast enhancement and noise reduction) is demonstrated. Furthermore, logic operations (“AND,” “NOTq,” and “NIMP”) can be performed by combining various optical signals in the same device. The memristive switching mechanism under optical stimulus can be attributed to barrier change at the heterojunction interface. This work proposes a fully light-modulated memristor based on ZnO/MoOx heterojunction that may promote the development of neuromorphic computing with high efficiency.

Large-Scale, Stretchable, Self-Protective, and Multifunctional Perovskite Luminescent Filament with Ultra-High Stability.

Lead halide perovskites possess great application potential in flexible displays and wearable optoelectronics owing to their prominent optoelectronic properties. However, the intrinsic instability upon moisture, heat, and ultraviolet (UV) light irradiation hinders their development and application. In this work, an ultra-stable CsPbX3 (X = Cl, Br, I) perovskite luminescent filament (PLF) with high stretchability (≈2400%) and luminescence performance (photoluminescence quantum yield (PLQY) of 24.5%, tunable emission spectrum, and high color purity) is introduced by a facile environmental-friendly wet-spinning technology via solvent extraction. Benefiting from the in situ encapsulation of the hydrophobic thermoplastic polyurethane (TPU) and the chelation of Lewis base CO in TPU with Lewis acid Pb2+, the CsPbBr3 PLF demonstrates ultra-high photoluminescence (PL) stability when stored in ambient air and high humidity circumstance, annealed at 50 °C, and dipped in water for 30 days, illuminated under ultraviolet light for 300 min, and immersed in organic solvents and solutions with pH of 1-13 for 5 min, respectively. Impressively, it retains 80% of its initial PL after being recycled five times. Overall, the CsPbX3 PLF demonstrates promising prospects in multifunctional applications, including organic dyes and tensile strain sensing, flexible pattern displays, secondary anti-counterfeiting, and hazard warning systems.

Accessing 3,4-Dihydroquinolinone from N-Arylacrylamides via Tetralone-Mediated Energy Transfer and 1,3-Hydrogen Shift.

Herein, we introduce a tetralone-mediated photocyclization method of N-arylacrylamides. The protocol proceeds smoothly to deliver a diverse set of 3,4-dihydroquinolinones in moderate to good yields with excellent functional group compatibility and readily allows for late-stage modifications of a number of complex drug molecules. Mechanistic studies reveal that the present systems with ultraviolet light irradiation enable the cyclization via energy transfer and exclusive 1,3-hydrogen shift.

Facile green synthesis of Ag doped TiO2 nanoparticles using maple leaf for bisphenol-A degradation and its antibacterial properties

Significant advancements are being made in environmentally friendly chemistry through the use of biosynthetic techniques for material synthesis. This study presents a novel and eco-conscious method for producing silver-doped TiO2 (Ag–TiO2) nanoparticles using maple leaves extract.. The synthesis process ingeniously involves combining maple leaf extract with silver and titanium dioxide precursors. Using advanced characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), reveals the characteristic crystal structure, surface complexity and fascinating morphology of the nanoparticles. These results explain the remarkable catalytic ability of Ag–TiO2 nanoparticles (NPs) in effectively degrading BPA under visible and ultraviolet (UV) light irradiation. Ag–TiO2 NPs show the BPA degradation of 94.42% (visible) and 96.83% (UV). In addition, these nanoparticles demonstrate good ability to combat a wide range of threatening pathogenic bacteria. The doping of Ag into TiO2 reveals the enhancement of inhibition growth against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli). This work opens up broad potential for applications in the treatment of BPA-containing wastewater and the development of environmentally friendly antimicrobial materials.