Nanoscale imaging and characterization of Caenorhabditis elegans epicuticle using atomic force microscopy

Uncovering the relationship between macrophages and polypropylene surgical mesh

Currently, in vitro testing examines the cytotoxicity of biomaterials but fails to consider how materials respond to mechanical forces and the immune response to them; both are crucial for successful long-term implantation. A notable example of this failure is polypropylene mid-urethral mesh used in the treatment of stress urinary incontinence (SUI). The mesh was largely successful in abdominal hernia repair but produced significant complications when repurposed to treat SUI. Developing more physiologically relevant in vitro test models would allow more physiologically relevant data to be collected about how biomaterials will interact with the body. This study investigates the effects of mechanochemical distress (a combination of oxidation and mechanical distention) on polypropylene mesh surfaces and the effect this has on macrophage gene expression. Surface topology of the mesh was characterised using SEM and AFM; ATR-FTIR, EDX and Raman spectroscopy was applied to detect surface oxidation and structural molecular alterations. Uniaxial mechanical testing was performed to reveal any bulk mechanical changes. RT-qPCR of selected pro-fibrotic and pro-inflammatory genes was carried out on macrophages cultured on control and mechanochemically distressed PP mesh. Following exposure to mechanochemical distress the mesh surface was observed to crack and craze and helical defects were detected in the polymer backbone. Surface oxidation of the mesh was seen after macrophage attachment for 7 days. These changes in mesh surface triggered modified gene expression in macrophages. Pro-fibrotic and pro-inflammatory genes were upregulated after macrophages were cultured on mechanochemically distressed mesh, whereas the same genes were down-regulated in macrophages exposed to control mesh. This study highlights the relationship between macrophages and polypropylene surgical mesh, thus offering more insight into the fate of an implanted material than existing in vitro testing.

Worms eat oil: Alcanivorax borkumensis hydrocarbonoclastic bacteria colonise Caenorhabditis elegans nematodes intestines as a first step towards oil spills zooremediation

The environmental hazards of oil spills cannot be underestimated. Bioremediation holds promise among various approaches to tackle oil spills in soils and sediments. In particular, using oil-degrading bacteria is an efficient and self-regulating way to remove oil spills. Using animals for oil spills remediation is in its infancy, mostly due to the lack of efficient oil-degrading capabilities in eukaryotes. Here we show that Caenorhabditis elegans nematodes survive for extended periods (up to 22 days) on pure crude oil diet. Moreover, we report for the first time the use of Alcanivorax borkumensis hydrocarbonoclastic bacteria for colonisation of C. elegans intestines, which allows for effective digestion of crude oil by the nematodes. The worms fed and colonised by A. borkumensis demonstrated the similar or even better longevity, resistance against oxidative and thermal stress and reproductivity as those animals fed with Escherichia coli bacteria (normal food). Importantly, A. borkumensis-carrying nematodes were able to accumulate oil droplet from oil-contaminated soils. Artificial colonisation of soil invertebrates with oil-degrading bacteria will be an efficient way to distribute microorganisms in polluted soil, thus opening new avenues for oil spills zooremediation.

Dark-field hyperspectral microscopy for label-free microplastics and nanoplastics detection and identification in vivo: A Caenorhabditis elegans study

Microplastics pollution is a serious ecological threat, severely affecting environments and human health. Tackling microplastics pollution requires an effective methodology to detect minute polymer particles in environmental samples and organisms. Here were report a novel methodology to visualise and identify nanoscale (down to 100 nm) and microscale synthetic commercially-available uniform spherical polymer particles using dark-field hyperspectral microscopy in visible-near infrared (400-1000 nm) wavelength range. Polystyrene particles with diameters between 100 nm-1 μm, polymethacrylate 1 μm and melamine formaldehyde 2 μm microspheres suspended in pure water samples were effectively imaged and chemically identified based on spectral signatures and image-assisted analysis. We succeeded in visualisation and spectral identification of pure and mixed nano- and microplastics in vivo employing optically-transparent Caenorhabditis elegans nematodes as a model to demonstrate the ingestion and tissue distribution of microplastics. As we demonstrate here, dark-field hyperspectral microscopy is capable for differentiating between chemically-different microplastics confined within live invertebrate intestines. Moreover, this optical technology allows for quantitative identification of microplastics ingested by nematodes. We believe that this label-free non-destructive methodology will find numerous applications in environmental nano- and microplastics detection and quantification, investigation of their biodistribution in tissues and organs and nanotoxicology.

Halloysite/Keratin Nanocomposite for Human Hair Photoprotection Coating

We propose a novel keratin treatment of human hair by its aqueous mixtures with natural halloysite clay nanotubes. The loaded clay nanotubes together with free keratin produce micrometer-thick protective coating on hair. First, colloidal and structural properties of halloysite/keratin dispersions and the nanotube loaded with this protein were investigated. Above the keratin isoelectric point (pH = 4), the protein adsorption into the positive halloysite lumen is favored because of the electrostatic attractions. The ζ-potential magnitude of these core-shell particles increased from -35 (in pristine form) to -43 mV allowing for an enhanced colloidal stability (15 h at pH = 6). This keratin-clay tubule nanocomposite was used for the immersion treatment of hair. Three-dimensional-measuring laser scanning microscopy demonstrated that 50-60% of the hair surface coverage can be achieved with 1 wt % suspension application. Hair samples have been exposed to UV irradiation for times up to 72 h to explore the protection capacity of this coating by monitoring the cysteine oxidation products. The nanocomposites of halloysite and keratin prevent the deterioration of human hair as evident by significant inhibition of cysteic acid. The successful hair structure protection was also visually confirmed by atomic force microscopy and dark-field hyperspectral microscopy. The proposed formulation represents a promising strategy for a sustainable medical coating on the hair, which remediates UV irradiation stress.

Caenorhabditis elegans revisited by atomic force microscopy - Ultra-structural changes of the cuticle, but not in the intestine after treatment with Combretum mucronatum extract

Assessing the internal morphology of Caenorhabditis elegans by a topographical technique like atomic force microscopy (AFM) is a challenging process. As a prerequisite for a successful image acquisition, direct contact between the structure of interest and the AFM probe needs to be established. To gain this insight into the morphology of cuticle and intestine in C. elegans before and after treatment with a tannin-enriched hydro-ethanolic extract from Combretum mucronatum, we developed an approach based on polyethylene glycol embedding, ultra-sectioning, de-embedding and hexamethyldisilazane-dehydration prior to measuring in ambient conditions by intermittent contact mode AFM. The used experimental protocol allowed a facile and fast insight into the ultrastructure of treated versus untreated C. elegans individuals, directly leading to the identification of treatment-associated morphological alterations in the cuticle but not the intestine of C. elegans. Additionally, the presented ultra-microtomy based protocol could allow future insight into virtually any tissue or organism by AFM.

Selective Antimicrobial Effects of Curcumin@Halloysite Nanoformulation: A Caenorhabditis elegans Study

Alterations in the normal gastrointestinal microbial community caused by unhealthy diet, environmental factors, and antibiotic overuse may severely affect human health and well-being. Novel antimicrobial drug formulations targeting pathogenic microflora while not affecting or even supporting symbiotic microflora are urgently needed. Here we report fabrication of a novel antimicrobial nanocontainer based on halloysite nanotubes loaded with curcumin and protected with a dextrin outer layer (HNTs+Curc/DX) and its effective use to suppress the overgrowth of pathogenic bacteria in Caenorhabditis elegans nematodes. Nanocontainers have been obtained using vacuum-facilitated loading of hydrophobic curcumin into halloysite lumens. We have applied UV-vis and infrared spectroscopy, thermogravimetry and microscopy to characterize the HNTs+Curc/DX nanocontainers. In experiments in vitro we found that HNTs+Curc/DX effectively suppressed the growth of Serratia marcescens cells, whereas Escherichia coli bacteria were not affected. We applied HNTs+Curc/DX nanocontainers to alleviate the S. marcescens infection in C. elegans nematodes in vivo. The nematodes ingest HNTs+Curc/DX at 4-6 ng per worm, which results in improvement of the nematodes' fertility and life expectancy. Remarkably, treatment of S. marcescens-infected nematodes with HNTs+Curc/DX nanocontainers completely restored the longevity, demonstrating the enhanced bioavailability of hydrophobic curcumin. We believe that our results reported here open new avenues for fabrication of effective antimicrobial nanoformulations based on hydrophobic drugs and clay nanotubes.

Atomic force microscopy for imaging and nanomechanical characterisation of live nematode epicuticle: A comparative Caenorhabditis elegans and Turbatrix aceti study

Atomic force microscopy (AFM), a powerful tool in interdisciplinary biomedical research, has been applied here to investigate the surface of live nematodes epicuticle. We have used AFM in PeakForce Tapping non-resonant imaging and nanomechanical characterisation mode to investigate and compare the surface features of epicuticle of two free-living microscopic nematodes, Caenorhabditis elegans and Turbatrix aceti. We have successfully immobilised live anesthetized adult nematodes on glass supports using either layer-by-layer-deposited polyelectrolyte films or bioadhesive coatings, which allowed for imaging the living nematodes in native environment. We have obtained AFM images and corresponding nanomechanical maps of annular rings and furrows, demonstrating the differences in topography and structure between the species. Our results demonstrate that AFM in PeakForce Tapping mode can be used to image and characterise surfaces of relatively-large live immobilised multicellular organisms, which can be further applied to a number of invertebrates.

Molecular dynamics of the halloysite nanotubes

We report large-scale and long-time molecular dynamics simulations demonstrating the transformation of a single kaolin alumosilicate sheet to a halloysite nanotube. The models we consider contain up to 5 × 10⁵ atoms, which is two orders of magnitude larger than that used in previous theoretical works. It was found that the temperature plays a crucial role in the formation of the rolled geometry of the halloysite. For the models with periodic boundary conditions, we observe the tendency to form twin-tube structures, which is confirmed experimentally by atomic force microscopy imaging. The molecular dynamics calculations show that the rate of the rolling process is very sensitive to the choice of the winding axis and varies from 5 ns to 25 ns. The effects of the open boundary conditions and the initial form of the kaolin alumosilicate sheet are discussed. Our simulation results are consistent with experimental TEM and AFM halloysite tube imaging.

Density Functional Theory and Atomic Force Microscopy Study of Oleate Functioned on Siderite Surface

Efficiently discovering the interaction of the collector oleate and siderite is of great significance for understanding the inherent function of siderite weakening hematite reverse flotation. For this purpose, investigation of the adsorption behavior of oleate on siderite surface was performed by density functional theory (DFT) calculations associating with atomic force microscopy (AFM) imaging. The siderite crystal geometry was computationally optimized via convergence tests. Calculated results of the interaction energy and the Mulliken population verified that the collector oleate adsorbed on siderite surface and the covalent bond was established as a result of electrons transferring from O1 atoms (in oleate molecule) to Fe1 atoms (in siderite lattice). Therefore, valence-electrons’ configurations of Fe1 and O1 changed into 3d6.514s0.37 and 2s1.832p4.73 from 3d6.214s0.31 and 2s1.83p4.88 correspondingly. Siderite surfaces with or without oleate functioned were examined with the aid of AFM imaging in PeakForce Tapping mode, and the functioned siderite surface was found to be covered by vesicular membrane matters with the average roughness of 16.4 nm assuring the oleate adsorption. These results contributed to comprehending the interaction of oleate and siderite.

The physicochemical fingerprint of Necator americanus

Necator americanus, a haematophagous hookworm parasite, infects ~10% of the world's population and is considered to be a significant public health risk. Its lifecycle has distinct stages, permitting its successful transit from the skin via the lungs (L3) to the intestinal tract (L4 maturing to adult). It has been hypothesised that the L3 larval sheath, which is shed during percutaneous infection (exsheathment), diverts the immune system to allow successful infection and reinfection in endemic areas. However, the physicochemical properties of the L3 larval cuticle and sheath, which are in direct contact with the skin and its immune defences, are unknown. In the present study, we controlled exsheathment, to characterise the sheath and underlying cuticle surfaces in situ, using atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). AFM revealed previously unseen surface area enhancing nano-annuli exclusive to the sheath surface and confirmed greater adhesion forces exist between cationic surfaces and the sheath, when compared to the emergent L3 cuticle. Furthermore, ToF-SIMS elucidated different chemistries between the surfaces of the cuticle and sheath which could be of biological significance. For example, the phosphatidylglycerol rich cuticle surface may support the onward migration of a lubricated infective stage, while the anionic and potentially immunologically active heparan sulphate rich deposited sheath could result in the diversion of immune defences to an inanimate antigenic nidus. We propose that our initial studies into the surface analysis of this hookworm provides a timely insight into the physicochemical properties of a globally important human pathogen at its infective stage and anticipate that the development and application of this analytical methodology will support translation of these findings into a biological context.

Nematode Epicuticle Visualisation by PeakForce Tapping Atomic Force Microscopy

The free-living soil nematode Caenorhabditis elegans has become an iconic experimental model animal in biology. This transparent animal can be easily imaged using optical microscopy to visualise its organs, tissues, single cells and subcellular events. The epicuticle of C. elegans nematodes has been studied at nanoscale using transmission and scanning (SEM) electron microscopies. As a result, imaging artefacts can appear due to embedding the worms into resins or coating the worms with a conductive gold layer. In addition, fixation and contrasting may also damage the cuticle. Conventional tapping mode atomic force microscopy (AFM) can be applied to image the cuticle of the dried nematodes in air, however this approach also suffers from imaging defects. Ideally, the nematodes should be imaged under conditions resembling their natural environment. Recently, we reported the use of PeakForce Tapping AFM mode for the successful visualisation and numerical characterisation of C. elegans nematode cuticle both in air and in liquid ( Fakhrullina et al., 2017 ). We imaged the principal nematode surface structures and characterised mechanical properties of the cuticle. This protocol provides the detailed description of AFM imaging of liquid-immersed C. elegans nematodes using PeakForce Tapping atomic force microscopy.

Temperature-Controlled Three-Stage Switching of Wetting, Morphology, and Protein Adsorption

The novel polymeric coatings of oligoperoxide-graft-poly(4-vinylpyridine-co-oligo(ethylene glycol)ethyl ether methacrylate246) [oligoperoxide-graft-P(4VP-co-OEGMA246)] attached to glass were successfully fabricated. The composition, thickness, morphology, and wettability of resulting coatings were analyzed using X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, and contact angle measurements, respectively. In addition, adsorption of the bovine serum albumin was examined with fluorescence microscopy. The thermal response of wettability and morphology of the coatings followed by that of protein adsorption revealed two distinct transitions at 10 and 23 °C. For the first time, three stage switching was observed not only for surface wetting but also for morphology and protein adsorption. Moreover, the influence of the pH on thermo-sensitivity of modified surfaces was shown.