NIR-Reflective and Hydrophobic Bio-Inspired Nano-Holed Configurations on Titanium Alloy.

Near-infrared (NIR) radiation plays an important role in guided external stimulus therapies; its application in bone-related treatments is becoming more and more frequent. Therefore, metallic biomaterials that exhibit properties activated by NIR are promising for further orthopedic procedures. In this work, we present an adapted electroforming approach to attain a biomorphic nano-holed TiO2 coating on Ti6Al4V alloy. Through a precise control of the anodization conditions, structures revealed the formation of localized nano-pores arranged in a periodic assembly. This specific organization provoked higher stability against thermal oxidation and precise hydrophobic wettability behavior according to Cassie-Baxter's model; both characteristics are a prerequisite to ensure a favorable biological response in an implantable structure for guided bone regeneration. In addition, the periodically arranged sub-wavelength-sized unit cell on the metallic-dielectric structure exhibits a peculiar optical response, which results in higher NIR reflectivity. Accordingly, we have proved that this effect enhances the efficiency of the scattering processes and provokes a significant improvement of light confinement producing a spontaneous NIR fluorescence emission. The combination of the already favorable mechanical and biocompatibility properties of Ti6Al4V, along with suitable thermal stability, wetting, and electro-optical behavior, opens a promising path toward strategic bone therapeutic procedures.

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

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

Conducting Polyetheretherketone Nanocomposites with an Electrophoretically Deposited Bioactive Coating for Bone Tissue Regeneration and Multimodal Therapeutic Applications.

The use of polyetheretherketone (PEEK) has grown exponentially in the biomedical field in recent decades because of its outstanding biomechanical properties. However, its lack of bioactivity/osteointegration remains an unresolved issue toward its wide use in orthopedic applications. In this work, graphene nanosheets have been incorporated into PEEK to obtain multifunctional nanocomposites. Because of the formation of an electrical percolation network and the π-π* conjugation between graphene and PEEK, the resulting composites have achieved 12 orders of magnitude enhancement in their electrical conductivity and thereby enabled electrophoretic deposition of a bioactive/antibacterial coating consisting of stearyltrimethylammonium chloride-modified hydroxyapatite. The coated composite implant shows significant boosting of bone marrow mesenchymal stem cell proliferation in vitro. In addition, the strong photothermal conversion effect of the graphene nanofillers has enabled laser-induced heating of our nanocomposite implants, where the temperature of the implant can reach 45 °C in 150 s. The unique multifunctionality of the implant has also been demonstrated for photothermal applications such as enhancing bacterial eradication and tumor cell inhibition, as well as bone tissue regeneration in vivo. The results suggest the strong potential of our multifunctional implant in bone repair applications as well as multimodal therapy of challenging bone diseases such as osteosarcoma and osteomyelitis.

Spatiotemporal regulation of dynamic cell microenvironment signals based on an azobenzene photoswitch.

Dynamic biochemical and biophysical signals of cellular matrix define and regulate tissue-specific cell functions and fate. To recapitulate this complex environment in vitro, biomaterials based on structural- or degradation-tunable polymers have emerged as powerful platforms for regulating the "on-demand" cell-material dynamic interplay. As one of the most prevalent photoswitch molecules, the photoisomerization of azobenzene demonstrates a unique advantage in the construction of dynamic substrates. Moreover, the development of azobenzene-containing biomaterials is particularly helpful in elucidating cells that adapt to a dynamic microenvironment or integrate spatiotemporal variations of signals. Herein, this minireview, places emphasis on the research progress of azobenzene photoswitches in the dynamic regulation of matrix signals. Some techniques and material design methods have been discussed to provide some theoretical guidance for the rational and efficient design of azopolymer-based material platforms. In addition, considering that the UV-light response of traditional azobenzene photoswitches is not conducive to biological applications, we have summarized the recent approaches to red-shifting the light wavelength for azobenzene activation.

UV-photofunctionalization of a biomimetic coating for dental implants application.

Photofunctionalization mediated by ultraviolet (UV) rays changes the physico-chemical characteristics of titanium (Ti) and improves the biological activity of dental implants. However, the role of UV-mediated photofunctionalization of biofunctional Ti surfaces on the antimicrobial and photocatalytic activity remains unknown and was investigated in this study. Commercially pure titanium (cpTi) discs were divided into four groups: (1) machined samples without UV light application [cpTi UV-]; (2) plasma electrolytic oxidation (PEO) treated samples without UV light application [PEO UV-]; (3) machined samples with UV light application [cpTi UV+]; and (4) PEO-treated samples with UV light application [PEO UV+]. The surfaces were characterized according to their morphology, roughness, crystalline phase, chemical composition and wettability. The photocatalytic activity and proteins adsorption were measured. For the microbiological assay, Streptococcus sanguinis was grown on the disc surfaces for 1 h and 6 h, and the colony forming units and bacterial organization were evaluated. In addition, to confirm the non-cytotoxic effect of PEO UV +, human gingival fibroblast (HGF) cells were cultured in a monolayer onto each material surface and the cells viability and proliferation evaluated by a fluorescent cell staining method. PEO treatment increased the Ti surface roughness and wettability (p < 0.05). Photofunctionalization reduced the hydrocarbon concentration and enhanced human blood plasma proteins and albumin adsorption mainly for the PEO-treated surface (p < 0.05). PEO UV+ also maintained higher wettability values for a longer period and provided microbial reduction at 1 h of bacterial adhesion (p = 0.012 vs. PEO UV-). Photofunctionalization did not increase the photocatalytic activity of Ti (p > 0.05). Confocal microscopy analyses demonstrated that PEO UV+ had no cell damage effect on HGF cells growth even after 24 h of incubation. The photofunctionalization of a biofunctional PEO coating seems to be a promising alternative for dental implants as it increases blood plasma proteins adsorption, reduces initial bacterial adhesion and presents no cytotoxicity effect.

Soft-sheath, stiff-core microfiber hydrogel for coating vascular implants.

Vascular implants remain clinically challenged due to often-occurring thrombosis and stenosis. Critical to addressing these complications is the design of implant material surfaces to inhibit the activities of platelets, smooth muscle cells (SMCs) and inflammatory cells. Recent mechanobiology studies accentuate the significance of material elasticity to cells and tissues. We thus developed and characterized an implant coating composed of hybrid, viscoelastic microfibers with coaxial core-sheath nanostructure. The coating over metallic stent material was formed by first depositing coaxially-electrospun fibers of poly(L-lactic acid) core and polyethylene glycol dimethacrylate sheath, and then polymerizing fibers with various UV times. Material characterizations were performed to evaluate the coating structure, mechanical property and biocompatibility. Results showed that coaxial microfibers exhibited arterial-like mechanics. The soft surface, high water content and swelling ratio of the coaxial fibers resemble hydrogels, while they are mechanically strong with an elastic modulus of 172-729 kPa. The coating strength and surface elasticity were tunable with the photopolymerization time. Further, the elastic fibers, as conformal coating on stent metal, strongly reduced SMC overgrowth and discouraged platelet adhesion and activation, compared to bare metals. Importantly, after 7-day subcutaneous implantation, coaxial fiber-coated implants showed more favorable in vivo responses with reduced tissue encapsulation, compared to bare stent metals or those coated with a two-layered fiber mixture composed of fibers from individual polymers. The excellent biocompatibility aroused from nanostructural interfaces of hybrid fibers offering hydrated, soft, nonfouling microenvironments. Such integrated fiber system may allow creation of advanced vascular implants that possess physico-mechanical properties of native arteries.

Ultraviolet photofunctionalization of nanostructured titanium surfaces enhances thrombogenicity and platelet response.

The purpose of this study was to evaluate blood and platelet response to nanostructured TiO2 coatings and to investigate the effect of Ultraviolet (UV) light treatment on blood clotting ability, platelet activation and protein adhesion. Ti-6Al-4V titanium alloy plates (n = 138) were divided into three groups; a sol-gel derived MetAliveTM coating (MA); hydrothermal coating (HT); and a non-coated group (NC). Sixty nine titanium substrates were further treated with UV light for 1 h. The thrombogenicity of the titanium substrates was assessed using fresh human blood with a whole blood kinetic clotting time method. The platelet adhesion test was conducted to evaluate the morphology and adhesion behavior of the platelets on the titanium substrates. Human diluted plasma and bovine fibronectin were used to evaluate protein adsorption. Total clotting time for the UV treated HT, MA and NC titanium substrates was almost 40 min compared to 60 min for non-UV substrates, the total clotting time for the UV treated groups were significantly lower than that of the non UV NC group (p < 0.05). UV light treatment had significantly enhanced coagulation rates. The HT and MA substrates presented more platelet aggregation, spreading and pseudopod formation in comparison with the NC substrates. UV treatment did not affect the platelet activation and protein adsorption. This in vitro study concluded that nanostructured titanium dioxide implant surfaces obtained by sol-gel and hydrothermal coating methods increased coagulation rates and enhanced platelet response when compared with non-coated surfaces. UV light treatment clearly improved thrombogenicity of all examined Ti-6Al-4V surfaces.

Gold cleaning methods for preparation of cell culture surfaces for self-assembled monolayers of zwitterionic oligopeptides.

Self-assembled monolayers (SAMs) have been used to elucidate interactions between cells and material surface chemistry. Gold surfaces modified with oligopeptide SAMs exhibit several unique characteristics, such as cell-repulsive surfaces, micropatterns of cell adhesion and non-adhesion regions for control over cell microenvironments, and dynamic release of cells upon external stimuli under culture conditions. However, basic procedures for the preparation of oligopeptide SAMs, including appropriate cleaning methods of the gold surface before modification, have not been fully established. Because gold surfaces are readily contaminated with organic compounds in the air, cleaning methods may be critical for SAM formation. In this study, we examined the effects of four gold cleaning methods: dilute aqua regia, an ozone water, atmospheric plasma, and UV irradiation. Among the methods, UV irradiation most significantly improved the formation of oligopeptide SAMs in terms of repulsion of cells on the surfaces. We fabricated an apparatus with a UV light source, a rotation table, and HEPA filter, to treat a number of gold substrates simultaneously. Furthermore, UV-cleaned gold substrates were capable of detaching cell sheets without serious cell injury. This may potentially provide a stable and robust approach to oligopeptide SAM-based experiments for biomedical studies.

Surface-attached hydrogel coatings via C,H-insertion crosslinking for biomedical and bioanalytical applications (Review).

A novel method for the generation of surface-attached hydrogel coatings and their use in biomedical applications is discussed. This short review concentrates on surface architectures that are prepared from prepolymers carrying reactive groups suitable for crosslinking via C,H insertion reactions [C,H insertion crosslinking (CHic)]. Upon photochemical or thermal activation these groups do not only induce the crosslinking of the system, but also connect the forming gel to the surface as long as the surface itself consists of an organic material. C,H groups as the reaction partner are available in abundance at practically all types of organic surfaces such as biomaterials or polymers, rendering the technique almost universally applicable. Surface-attached gels prepared this way show unique swelling properties due to the confinement of the chains, as the obtained essentially two-dimensional gels can only swell in one dimension. This anisotropic swelling does not permit penetration of the layers by macromolecules so that the surfaces become bioinert, i.e., are strongly protein and cell repellent. It is discussed how this property can be used to control the interaction of surfaces with biological species ranging from the level of biomolecules to living cells. A combination of the CHic chemistry and microstructuring techniques opens further avenues for the study of the behavior of cells to the generation of novel bioanalytical devices.

UV-Curable Aliphatic Silicone Acrylate Organic-Inorganic Hybrid Coatings with Antibacterial Activity.

The most effective means to protect against bacterial invasion and to reduce the risk of healthcare-associated infections are antibacterial components synthesis. In this study, a novel process for the synthesis of organic-inorganic hybrid coatings containing silver nanoparticles is presented. Silver nanoparticles and polymer formation proceeds simultaneously through the in situ photoreduction of silver salt to silver nanoparticles and UV-crosslinking of bifunctional aliphatic silicone acrylate. The nanocomposite films with 0.5-1.43 wt % of silver nanoparticles concentration were obtained and investigated. The formation of silver nanoparticles in polymer matrix was confirmed via UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron spectroscopy, and energy dispersive spectroscopy. Our investigations clearly show the formation of silver nanoparticles in silicone acrylate network. Direct photoreduction of silver salt by UV-radiation in the organic media produced silver nanoparticles exhibiting cubic crystal structure. The size of nanoparticles was determined to be near 20 ± 5 nm. The antibacterial activities of coatings were determined using the disc diffusion and direct contact methods. UV-curable silicone acrylate hybrid coatings exhibited antibacterial activity against harmful bacteria strains.

Newly Developed Biocompatible Material: Dispersible Titanium-Doped Hydroxyapatite Nanoparticles Suitable for Antibacterial Coating on Intravascular Catheters.

BACKGROUND: Thirteen patients with chlorhexidine-silver sulfadiazine-impregnated catheters have experienced serious anaphylactic shock in Japan. These adverse reactions highlight the lack of commercially available catheters impregnated with strong antibacterial chemical agents. A system should be developed that can control both biocompatibility and antibacterial activity. SUMMARY: Hydroxyapatite (HAp) is biocompatible with bone and skin tissues. To provide antibacterial activity by using an external physical stimulus, titanium (Ti) ions were doped into the HAp structure. Highly dispersible, Ti-doped HAp (Ti-HAp) nanoparticles suitable as a coating material were developed. In 3 kinds of Ti-HAp [Ti/(Ca + Ti) = 0.05, 0.1, 0.2], the Ti content in the HAp was approximately 70% of that used in the Ti-HAp preparation, as determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). ICP-AES and X-ray diffraction showed Ti ions were well substituted into the HAp lattice. The nanoparticles were almost uniformly coated on a polyethylene (PE) sheet in a near-monolayer with a surface coverage ratio >95%. The antibacterial activity of the Ti-HAp nanoparticles containing 7.3% Ti ions and coating the sheet was evaluated by calculating the survival ratio of Pseudomonas aeruginosa on the coated sheet after ultraviolet (UV) irradiation. The Ti-HAp-coated sheet showed a 50% decrease in the number of P. aeruginosa compared with that on an uncoated control PE sheet after UV irradiation for 30 s. Key Messages: A system of biocompatibility and antibacterial activity with an on/off switch controlled by external UV stimulation was developed. The system is expected to be applicable in long-term implanted intravascular catheters.

Use of a DNA film on a self-assembled monolayer for investigating the physical process of DNA damage induced by core electron ionization.

PURPOSE: A novel two-layer sample composed of a deoxyribonucleic acid (DNA) film and self-assembled monolayer (SAM) was prepared on an inorganic surface to mimic the processes in which DNA is damaged by soft X-ray irradiation. MATERIALS AND METHODS: A mercaptopropyltrimethoxysilane (MPTS) SAM was formed on a sapphire surface, then oligonucleotide (OGN) molecules were adsorbed on the MPTS-SAM. The thicknesses and chemical states of the layers were determined by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray fine structure (NEXAFS) around the phosphorus (P) and sulfur (S) K-edges. To induce the damage to the OGN molecules, the sample was irradiated with synchrotron soft X-rays. The chemical state of the OGN molecules before and after irradiation was examined by NEXAFS around the nitrogen (N) K-edge region. RESULTS: The thickness of the MPTS-OGN layer was approximately 7.7 nm. The S atom of the OGN molecules was located at the bottom of the OGN layer. The peak shape of the N K-edge NEXAFS spectra of the MPTS-OGN layers clearly changed following irradiation. CONCLUSIONS: The MPTS-OGN layer formed on the sapphire surface. The chemical states and the structure of the interface were elucidated using synchrotron soft X-rays. The OGN molecules adsorbed on the MPTS films decomposed upon exposure to soft X-ray irradiation.

Characterization and Mechanism for the Protection of Photolytic Decomposition of N-Halamine Siloxane Coatings by Titanium Dioxide.

N-Halamine antibacterial materials have superior inactivation activities due to oxidative chlorine species. However, N-Cl bonds and bonds between N-halamine and substrates often decompose rapidly under UV irradiation, leading to unrecoverable loss of antimicrobial activity. In this study, titanium dioxide was covalently bonded onto N-halamine siloxane poly[5,5-dimethyl-3-(3'-triethoxysilylpropyl)hydantoin] (PSPH) via a sol-gel process. Experimental testing of the chlorinated cotton fabrics treated with TiO2/PSPH demonstrated that the residual oxidative chlorine in cotton-TiO2/PSPH-Cl was still effective for inactivating bacteria after 50 washing cycles and under UV light irradiation for 24 h. Quantum mechanical calculations found that TiO2 improves the UV stability of the PSPH-Cl system by increasing the activation barrier of the C-Si scission reaction responsible for the loss of the biocidal hydantoin moiety. SEM, XPS and FTIR spectra were used to characterize the coated cotton samples. Cotton-TiO2/PSPH-Cl samples exhibited good antibacterial activity against Staphylococcus aureus (ATCC 6538) and Escherichia coli O157:H7 (ATCC 43895). The storage stability and washing stability of treated cotton fabrics were also investigated.

Electrically driven intracellular and extracellular nanomanipulators evoke neurogenic/cardiomyogenic differentiation in human mesenchymal stem cells.

Nanomechanical intervention through electroactuation is an effective strategy to guide stem cell differentiation for tissue engineering and regenerative medicine. In the present study, we elucidate that physical forces exerted by electroactuated gold nanoparticles (GNPs) have a strong influence in regulating the lineage commitment of human mesenchymal stem cells (hMSCs). A novel platform that combines intracellular and extracellular GNPs as nano-manipulators was designed to trigger neurogenic/cardiomyogenic differentiation in hMSCs, in electric field stimulated culture condition. In order to mimic the native microenvironment of nerve and cardiac tissues, hMSCs were treated with physiologically relevant direct current electric field (DC EF) or pulsed electric field (PEF) stimuli, respectively. When exposed to regular intermittent cycles of DC EF stimuli, majority of the GNP actuated hMSCs acquired longer filopodial extensions with multiple branch-points possessing neural-like architecture. Such morphological changes were consistent with higher mRNA expression level for neural-specific markers. On the other hand, PEF elicited cardiomyogenic differentiation, which is commensurate with the tube-like morphological alterations along with the upregulation of cardiac specific markers. The observed effect was significantly promoted even by intracellular actuation and was found to be substrate independent. Further, we have substantiated the participation of oxidative signaling, G0/G1 cell cycle arrest and intracellular calcium [Ca(2+)]i elevation as the key upstream regulators dictating GNP assisted hMSC differentiation. Thus, by adopting dual stimulation protocols, we could successfully divert the DC EF exposed cells to differentiate predominantly into neural-like cells and PEF treated cells into cardiomyogenic-like cells, via nanoactuation of GNPs. Such a novel multifaceted approach can be exploited to combat tissue loss following brain injury or heart failure.

UV-activated 7-dehydrocholesterol-coated titanium implants promote differentiation of human umbilical cord mesenchymal stem cells into osteoblasts.

Vitamin D metabolites are essential for bone regeneration and mineral homeostasis. The vitamin D precursor 7-dehydrocholesterol can be used after UV irradiation to locally produce active vitamin D by osteoblastic cells. Furthermore, UV-irradiated 7-dehydrocholesterol is a biocompatible coating for titanium implants with positive effects on osteoblast differentiation. In this study, we examined the impact of titanium implants surfaces coated with UV-irradiated 7-dehydrocholesterol on the osteogenic differentiation of human umbilical cord mesenchymal stem cells. First, the synthesis of cholecalciferol (D3) was achieved through the incubation of the UV-activated 7-dehydrocholesterol coating for 48 h at 23℃. Further, we investigated in vitro the biocompatibility of this coating in human umbilical cord mesenchymal stem cells and its potential to enhance their differentiation towards the osteogenic lineage. Human umbilical cord mesenchymal stem cells cultured onto UV-irradiated 7-dehydrocholesterol-coated titanium implants surfaces, combined with osteogenic supplements, upregulated the gene expression of several osteogenic markers and showed higher alkaline phosphatase activity and calcein blue staining, suggesting increased mineralization. Thus, our results show that the use of UV irradiation on 7-dehydrocholesterol -treated titanium implants surfaces generates a bioactive coating that promotes the osteogenic differentiation of human umbilical cord mesenchymal stem cells, with regenerative potential for improving osseointegration in titanium-based bone anchored implants.

Preparation and characterization of laser cladding wollastonite derived bioceramic coating on titanium alloy.

The bioceramic coating is fabricated on titanium alloy (Ti6Al4V) by laser cladding the preplaced wollastonite (CaSiO3) powders. The coating on Ti6Al4V is characterized by x-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy, and attenuated total reflection Fourier-transform infrared. The interface bonding strength is measured using the stretching method using an RGD-5-type electronic tensile machine. The microhardness distribution of the cross-section is determined using an indentation test. The in vitro bioactivity of the coating on Ti6Al4V is evaluated using the in vitro simulated body fluid (SBF) immersion test. The microstructure of the laser cladding sample is affected by the process parameters. The coating surface is coarse, accidented, and microporous. The cross-section microstructure of the ceramic layer from the bottom to the top gradually changes from cellular crystal, fine cellular-dendrite structure to underdeveloped dendrite crystal. The coating on Ti6Al4V is composed of CaTiO3, CaO, α-Ca2SiO4, SiO2, and TiO2. After soaking in the SBF solution, the calcium phosphate layer is formed on the coating surface.

Design of Albumin-Coated Microbubbles Loaded With Polylactide Nanoparticles.

OBJECTIVES: A protocol was designed to produce albumin-coated microbubbles (MBs) loaded with functionalized polylactide (PLA) nanoparticles (NPs) for future drug delivery studies. METHODS: Microbubbles resulted from the sonication of 5% bovine serum albumin and 15% dextrose solution. Functionalized NPs were produced by mixing fluorescent PLA and PLA-polyethylene glycol-carboxylate conjugates. Nanoparticle-loaded MBs resulted from the covalent conjugation of functionalized NPs and MBs. Three NP/MB volume ratios (1/1, 1/10, and 1/100) and unloaded MBs were produced and compared. Statistical evaluations were based on quantitative analysis of 3 parameters at 4 time points (1, 4, 5, and 6 days post MB fabrication): MB diameter using a circle detection routine based on the Hough transform, MB number density using a hemocytometer, and NP-loading yield based on MB counts from fluorescence and light microscopic images. Loading capacity of the albumin-coated MBs was evaluated by fluorescence. RESULTS: Loaded MB sizes were stable over 6 days after production and were not significantly different from that of time-matched unloaded MBs. Number density evaluation showed that only 1/1 NP/MB volume ratio and unloaded MB number densities were stable over time, and that the 1/1 MB number density evaluated at each time point was not significantly different from that of unloaded MBs. The 1/10 and 1/100 NP/MB volume ratios had unstable number densities that were significantly different from that of unloaded MBs (P < .05). Fluorescence evaluation suggested that 1/1 MBs had a higher NP-loading yield than 1/10 and 1/100 MBs. Quantitative loading evaluation suggested that the 1/1 MBs had a loading capacity of 3700 NPs/MB. CONCLUSIONS: A protocol was developed to load albumin MBs with functionalized PLA NPs for further drug delivery studies. The 1/1 NP/MB volume ratio appeared to be the most efficient to produce stable loaded MBs with a loading capacity of 3700 NPs/MB.

Degradation of magnetic nanoparticles mimicking lysosomal conditions followed by AC susceptibility.

BACKGROUND: A deeper knowledge on the effects of the degradation of magnetic nanoparticles on their magnetic properties is required to develop tools for the identification and quantification of magnetic nanoparticles in biological media by magnetic means. METHODS: Citric acid and phosphonoacetic acid-coated magnetic nanoparticles have been degraded in a medium that mimics lysosomal conditions. Magnetic measurements and transmission electron microscopy have been used to follow up the degradation process. RESULTS: Particle size is reduced significantly in 24 h at pH 4.5 and body temperature. These transformations affect the magnetic properties of the compounds. A reduction of the interparticle interactions is observed just 4 h after the beginning of the degradation process. A strong paramagnetic contribution coming from the degradation products appears with time. CONCLUSIONS: A model for the in vivo degradation of magnetic nanoparticles has been followed to gain insight on the changes of the magnetic properties of iron oxides during their degradation. The degradation kinetics is affected by the particle coating, in our case being the phosphonoacetic acid-coated particles degraded faster than the citric acid-coated ones.

Effective protection of biological membranes against photo-oxidative damage: Polymeric antioxidant forming a protecting shield over the membrane.

We have prepared a chitosan polymer modified with gallic acid in order to develop an efficient protection strategy biological membranes against photodamage. Lipid bilayers were challenged with photoinduced damage by photosensitization with methylene blue, which usually causes formation of hydroperoxides, increasing area per lipid, and afterwards allowing leakage of internal materials. The damage was delayed by a solution of gallic acid in a concentration dependent manner, but further suppressed by the polymer at very low concentrations. The membrane of giant unilamellar vesicles was covered with this modified macromolecule leading to a powerful shield against singlet oxygen and thus effectively protecting the lipid membrane from oxidative stress. The results have proven the discovery of a promising strategy for photo protection of biological membranes.

Surface Disinfection Enabled by a Layer-by-Layer Thin Film of Polyelectrolyte-Stabilized Reduced Graphene Oxide upon Solar Near-Infrared Irradiation.

We report an antibacterial surface that kills airborne bacteria on contact upon minutes of solar near-infrared (NIR) irradiation. This antibacterial surface employs reduced graphene oxide (rGO), a well-known near-infrared photothermal conversion agent, as the photosensitizer and is prepared by assembling oppositely charged polyelectrolyte-stabilized rGO sheets (PEL-rGO) on a quartz substrate with the layer-by-layer (LBL) technique. Upon solar irradiation, the resulting PEL-rGO LBL multilayer efficiently generates rapid localized heating and, within minutes, kills >90% airborne bacteria, including antibiotic-tolerant persisters, on contact, likely by permeabilizing their cellular membranes. The observed activity is retained even when the PEL-rGO LBL multilayer is placed underneath a piece of 3 mm thick pork tissue, indicating that solar light in the near-infrared region plays dominant roles in the observed activity. This work may pave the way toward NIR-light-activated antibacterial surfaces, and our PEL-rGO LBL multilayer may be a novel surface coating material for conveniently disinfecting biomedical implants and common objects touched by people in daily life in the looming postantibiotic era with only minutes of solar exposure.