Atomic force microscopy of biological samples

Fourier transform-based post-processing drift compensation and calibration method for scanning probe microscopy

Scanning probe microscopy (SPM) is ubiquitous in nanoscale science allowing the observation of features in real space down to the angstrom resolution. The scanning nature of SPM, wherein a sharp tip rasters the surface during which a physical setpoint is maintained via a control feedback loop, often implies that the image is subject to drift effects, leading to distortion of the resulting image. While there are in-operando methods to compensate for the drift, correcting the residual linear drift in obtained images is often neglected. In this paper, we present a reciprocal space-based technique to compensate the linear drift in atomically-resolved scanning probe microscopy images without distinction of the fast and slow scanning directions; furthermore this method does not require the set of SPM images obtained for the different scanning directions. Instead, the compensation is made possible by the a priori knowledge of the lattice parameters. The method can also be used to characterize and calibrate the SPM instrument.

Probe chip nanofabrication enabled reverse tip sample scanning probe microscopy concept and measurements

We introduce a new scanning probe microscopy (SPM) concept called reverse tip sample scanning probe microscopy (RTS SPM), where the tip and sample positions are reversed as compared to traditional SPM. The main benefit of RTS SPM over the standard SPM configuration is that it allows for simple and fast tip changes. This overcomes two major limitations of SPM which are slow data acquisition and a strong dependency of the data on the tip condition. A probe chip with thousands of sharp integrated tips is the basis of our concept. We have developed a nanofabrication protocol for Si based probe chips and their functionalization with metal and diamond coatings, evaluated our probe chips for various RTS SPM applications (multi-tip imaging, SPM tomography, and correlative SPM), and showed the high potential of the RTS SPM concept.

Mechanical properties of human tumour tissues and their implications for cancer development

The mechanical properties of cells and tissues help determine their architecture, composition and function. Alterations to these properties are associated with many diseases, including cancer. Tensional, compressive, adhesive, elastic and viscous properties of individual cells and multicellular tissues are mostly regulated by reorganization of the actomyosin and microtubule cytoskeletons and extracellular glycocalyx, which in turn drive many pathophysiological processes, including cancer progression. This Review provides an in-depth collection of quantitative data on diverse mechanical properties of living human cancer cells and tissues. Additionally, the implications of mechanical property changes for cancer development are discussed. An increased knowledge of the mechanical properties of the tumour microenvironment, as collected using biomechanical approaches capable of multi-timescale and multiparametric analyses, will provide a better understanding of the complex mechanical determinants of cancer organization and progression. This information can lead to a further understanding of resistance mechanisms to chemotherapies and immunotherapies and the metastatic cascade.

Evaluation of Surface Structure and Morphological Phenomena of Caucasian Virgin Hair with Atomic Force Microscopy

Background and Objectives: Atomic force microscopy (AFM) as a type of scanning microscopy (SPM), which has a resolution of fractions of a nanometer on the atomic scale, is widely used in materials science. To date, research using AFM in medicine has focused on neurodegenerative diseases, osteoporosis, cancer tumors, cell receptors, proteins and the DNA mismatch repair (MMR) system. Only a few small studies of hair imaging have been conducted, mostly in biotechnology or cosmetology. Thanks to the possibilities offered by AFM imaging, dermatologists can non-invasively assess the condition of hair and its possible disorders. Our goal was to capture images and microscopically analyze morphological changes in the surface of healthy hair. Materials and Methods: In this study, three to five hairs were collected from each person. Each hair was examined at nine locations (0.5; 1.0; 1.5; 2.0; 3.5; 4.5; 5.5; 6.5 and 7.0 cm from the root). At least 4 images (4-10 images) were taken at each of the 9 locations. A total of 496 photos were taken and analyzed. Metric measurements of hair scales, such as apparent length, width and scale step height, were taken. Results: This publication presents the changes occurring in hair during the natural delamination process. In addition, morphoological changes visualized on the surface of healthy hair (pitting, oval indentations, rod-shaped macro-fibrillar elements, globules, scratches, wavy edge) are presented. A quantitative analysis of the structures found was carried out. Conclusions: The findings of this study can be used in further research and work related to the subject of human hair. They can serve as a reference for research on scalp and hair diseases, as well as hair care.

Cell wall dynamics: novel tools and research questions

Years ago, a classic textbook would define plant cell walls based on passive features. For instance, a sort of plant exoskeleton of invariable polysaccharide composition, and probably painted in green. However, currently, this view has been expanded to consider plant cell walls as active, heterogeneous, and dynamic structures with a high degree of complexity. However, what do we mean when we refer to a cell wall as a dynamic structure? How can we investigate the different implications of this dynamism? While the first question has been the subject of several recent publications, defining the ideal strategies and tools needed to address the second question has proven to be challenging due to the myriad of techniques available. In this review, we will describe the capacities of several methodologies to study cell wall composition, structure, and other aspects developed or optimized in recent years. Keeping in mind cell wall dynamism and plasticity, the advantages of performing long-term non-invasive live-imaging methods will be emphasized. We specifically focus on techniques developed for Arabidopsis thaliana primary cell walls, but the techniques could be applied to both secondary cell walls and other plant species. We believe this toolset will help researchers in expanding knowledge of these dynamic/evolving structures.

Visualizing the membrane disruption action of antimicrobial peptides by cryo-electron tomography

The abuse of antibiotics has led to the emergence of multidrug-resistant microbial pathogens, presenting a pressing challenge in global healthcare. Membrane-disrupting antimicrobial peptides (AMPs) combat so-called superbugs via mechanisms different than conventional antibiotics and have good application prospects in medicine, agriculture, and the food industry. However, the mechanism-of-action of AMPs has not been fully characterized at the cellular level due to a lack of high-resolution imaging technologies that can capture cellular-membrane disruption events in the hydrated state. Previously, we reported PepD2M, a de novo-designed AMP with potent and wide-spectrum bactericidal and fungicidal activity. In this study, we use cryo-electron tomography (cryo-ET) and high-speed atomic force microscopy (HS-AFM) to directly visualize the pepD2M-induced disruption of the outer and inner membranes of the Gram-negative bacterium Escherichia coli, and compared with a well-known pore-forming peptide, melittin. Our high-resolution cryo-ET images reveal how pepD2M disrupts the E. coli membrane using a carpet/detergent-like mechanism. Our studies reveal the direct membrane-disrupting consequence of AMPs on the bacterial membrane by cryo-ET, and this information provides critical insights into the mechanisms of this class of antimicrobial agents.

Native Pig Neutrophil Products: Insights into Their Antimicrobial Activity

Cationic antimicrobial peptides are molecules with potential applications for treating infections due to their antimicrobial and immunomodulatory properties. The aim of this work was to explore the antimicrobial activity and mechanisms of action of a porcine neutrophil cathelicidin mixture (MPPN). Gram-positive and Gram-negative bacteria were used to determine the minimum inhibitory concentration (MIC) and experiments of both time-kill kinetics and effects on growth curves were performed. Planar black lipid bilayer conductance was measured to analyze the interaction of MPPN with lipid bilayers. Visualization of bacterial surfaces and membrane alterations was achieved using atomic force microscopy and transmission electron microscopy. The effects on the activity of efflux pumps (EPs) were studied with an intracellular accumulation of acridine orange (AO) assay. In E. coli, MPPN behaves as a bactericide at high concentrations and as a bacteriostatic at lower concentrations. The bacteriostatic effect was also observed for slightly shorter periods in S. enterica. The mixture was not active on S. aureus. The increase in AO accumulation in the presence of MPPN indicates that, at least in E. coli, the mixture causes inhibition of the EP function. Observed and detected variable conductance events demonstrate a strong MPPN effect on lipid bilayers. Damage to the structure of treated E. coli indicates that MPPN induces alterations in the bacterial surface. The use of AMPs capable of inhibiting EP can be seen as a good tool to combat antimicrobial resistance since they could be used alone or in combination with other conventional antibiotics to which bacteria have become resistant.

Insights in Cell Biomechanics through Atomic Force Microscopy

We review the advances obtained by using Atomic Force Microscopy (AFM)-based approaches in the field of cell/tissue mechanics and adhesion, comparing the solutions proposed and critically discussing them. AFM offers a wide range of detectable forces with a high force sensitivity, thus allowing a broad class of biological issues to be addressed. Furthermore, it allows for the accurate control of the probe position during the experiments, providing spatially resolved mechanical maps of the biological samples with subcellular resolution. Nowadays, mechanobiology is recognized as a subject of great relevance in biotechnological and biomedical fields. Focusing on the past decade, we discuss the intriguing issues of cellular mechanosensing, i.e., how cells sense and adapt to their mechanical environment. Next, we examine the relationship between cell mechanical properties and pathological states, focusing on cancer and neurodegenerative diseases. We show how AFM has contributed to the characterization of pathological mechanisms and discuss its role in the development of a new class of diagnostic tools that consider cell mechanics as new tumor biomarkers. Finally, we describe the unique ability of AFM to study cell adhesion, working quantitatively and at the single-cell level. Again, we relate cell adhesion experiments to the study of mechanisms directly or secondarily involved in pathologies.

A novel biocompatible polymer derived from D-mannitol used as a vector in the field of genetic engineering of eukaryotic cells

The design and preparation of new vectors to transport genetic material and increase the transfection efficiency continue being an important research line. Here, a novel biocompatible sugar-based polymer derived from D-mannitol has been synthesized to be used as a gene material nanocarrier in human (gene transfection) and microalga cells (transformation process). Its low toxicity allows its use in processes with both medical and industrial applications. A multidisciplinary study about the formation of polymer/p-DNA polyplexes has been carried out using techniques such as gel electrophoresis, zeta potential, dynamic light scattering, atomic force microscopy, and circular dichroism spectroscopy. The nucleic acids used were the eukaryotic expression plasmid pEGFP-C1 and the microalgal expression plasmid Phyco69, which showed different behaviors. The importance of DNA supercoiling in both transfection and transformation processes was demonstrated. Better results were obtained in microalga cells nuclear transformation than in human cells gene transfection. This was related to the plasmid's conformational changes, in particular to their superhelical structure. It is noteworthy that the same nanocarrier has been used with eukaryotic cells from both human and microalga.

Cytoskeletal anchorage of different Dsg3 pools revealed by combination of hybrid STED/SMFS-AFM

Desmoglein 3 (Dsg3) is a desmosomal cadherin mediating cell adhesion within desmosomes and is the antigen of the autoimmune blistering skin disease pemphigus vulgaris. Therefore, understanding of the complex desmosome turnover process is of high biomedical relevance. Recently, super resolution microscopy was used to characterize desmosome composition and turnover. However, studies were limited because adhesion measurements on living cells were not possible in parallel. Before desmosomal cadherins are incorporated into nascent desmosomes, they are not bound to intermediate filaments but were suggested to be associated with the actin cytoskeleton. However, direct proof that adhesion of a pool of desmosomal cadherins is dependent on actin is missing. Here, we applied single-molecule force spectroscopy measurements with the novel single molecule hybrid-technique STED/SMFS-AFM to investigate the cytoskeletal anchorage of Dsg3 on living keratinocytes for the first time. By application of pharmacological agents we discriminated two different Dsg3 pools, only one of which is anchored to actin filaments. We applied the actin polymerization inhibitor Latrunculin B to modify the actin cytoskeleton and the PKCα activator PMA to modulate intermediate filament anchorage. On the cellular surface Dsg3 adhesion was actin-dependent. In contrast, at cell-cell contacts, Dsg3 adhesion was independent from actin but rather is regulated by PKC which is well established to control desmosome turn-over via intermediate filament anchorage. Taken together, using the novel STED/SMFS-AFM technique, we demonstrated the existence of two Dsg3 pools with different cytoskeletal anchorage mechanisms.

AFM advanced modes for dental and biomedical applications

Several analytical methods have been employed to elucidate bonding mechanisms between dental hard tissues, luting agents and restorative materials. Atomic Force Microscopy (AFM) imaging that has been extensively used in materials science, but its full capabilities are poorly explored by dental research community. In fact, commonly used to obtain topographic images of different surfaces, it turns out that AFM is an underestimated technique considering that there are dozens of basic and advanced modes that are scarcely used to explain properties of biomaterials. Thus, this paper addresses the use of phase-contrast imaging, force-distance curves, nanomechanical and Kelvin probe force techniques during AFM analysis to explore topological, nanomechanical and electrical properties of Y-TZP samples modified by different surface treatments, which has been widely used to promote adhesive enhancements to such substrate. The AFM methods are capable of access erstwhile inaccessible properties of Y-TZP which allowed us to describe its adhesive properties correctly. Thus, AFM technique emerges as a key tool to investigate the complex nature of biomaterials and highlighting its inherent interdisciplinarity that can be successfully used for bridging fragmented disciplines such as solid-state physics, microbiology and dental sciences.

Recent progress in using zein nanoparticles-loaded nanocomposites for food packaging applications

Biopolymers are important due to their exceptional functional and barrier properties and also their non-toxicity and eco-friendly nature for various food, biomedical, and pharmaceutical applications. However, biopolymers usually need reinforcement strategies to address their poor mechanical, thermal, and physical properties as well as processability aspects. Several natural nanoparticles have been proposed as reinforcing agents for biopolymeric food packaging materials. Among them, zein nanoparticles (ZNPs) have attracted a lot of interest, being an environmentally friendly material. The purpose of the present review paper is to provide a comprehensive overview of the ZNPs-loaded nanocomposites for food packaging applications, starting from the synthesis, characteristics and properties of ZNPs, to the physicochemical properties of the ZNPs-loaded nanocomposites, in terms of morphology, permeability, solubility, optical features, hydrophobic/hydrophilic behavior, structural characteristics, thermal features, and mechanical attributes. Finally, at the end of this review, some considerations about the safety issues and gastrointestinal fate of ZNPs, as well as the use of ZNPs-based nanocomposites as food packaging, are reported, taking into account that, despite the enormous benefits, nanotechnology also presents some risks associated to the use of nanometric materials.

Interaction of miR-155 with Human Serum Albumin: An Atomic Force Spectroscopy, Fluorescence, FRET, and Computational Modelling Evidence

This study investigated the interaction between Human Serum Albumin (HSA) and microRNA 155 (miR-155) through spectroscopic, nanoscopic and computational methods. Atomic force spectroscopy together with static and time-resolved fluorescence demonstrated the formation of an HSA/miR-155 complex characterized by a moderate affinity constant (KA in the order of 104 M−1). Förster Resonance Energy Transfer (FRET) experiments allowed us to measure a distance of (3.9 ± 0.2) nm between the lone HSA Trp214 and an acceptor dye bound to miR-155 within such a complex. This structural parameter, combined with computational docking and binding free energy calculations, led us to identify two possible models for the structure of the complex, both characterized by a topography in which miR-155 is located within two positively charged pockets of HSA. These results align with the interaction found for HSA and miR-4749, reinforcing the thesis that native HSA is a suitable miRNA carrier under physiological conditions for delivering to appropriate targets.

Rapid immunomagnetic co-capture assay for quantification of lung Cancer associated exosomes

Exosomes derived from biological fluids have the potential to serve as a biomarker for the early detection of various cancers. However, the lack of reliable enrichment and detection methods posed a challenge for its clinical utility. In this work, we designed a rapid co-capture-based approach for targeted enrichment and detection of lung cancer-derived exosomes from human plasma. This method relies on the formation of a sandwich complex around the exosomes that involves magnetic nanoparticles coupled to CD151 to assist in the immunomagnetic selection of lung-derived exosomes and a secondary detection antibody (CD81) coupled to horseradish peroxidase for signal amplification. The performance of the co-capture method to detect exosomes has been optimized with known exosome concentrations in human plasma and exhibited good linearity (10⁸-10⁵ exosomes mL^-1) with a detection limit of 60.4 exosomes μL^-1. This study further investigated the potential of the developed assay to differentiate healthy and lung cancer patients using 18 clinical samples by quantifying the CD151+/ CD81+ lung-derived exosomes. In conclusion, this study demonstrated a rapid co-capture-based approach that offers simultaneous isolation and detection of exosomes compatible with low sample volume for detecting lung cancer patients.

Chemical fixation creates nanoscale clusters on the cell surface by aggregating membrane proteins

Chemical fixations have been thought to preserve the structures of the cells or tissues. However, given that the fixatives create crosslinks or aggregate proteins, there is a possibility that these fixatives create nanoscale artefacts by aggregation of membrane proteins which move around freely to some extent on the cell surface. Despite this, little research has been conducted about this problem, probably because there has been no method for observing cell surface structures at the nanoscale. In this study, we have developed a method to observe cell surfaces stably and with high resolution using atomic force microscopy and a microporous silicon nitride membrane. We demonstrate that the size of the protrusions on the cell surface is increased after treatment with three commonly used fixatives and show that these protrusions were created by the aggregation of membrane proteins by fixatives. These results call attention when observing fixed cell surfaces at the nanoscale.

Atomic force microscopy imaging shows that cell fixation can lead to unwanted aggregation of membrane proteins.

Assessing Collagen D-Band Periodicity with Atomic Force Microscopy

The collagen superfamily includes more than fifty collagen and/or collagen-like proteins with fibril-forming collagen type I being the most abundant protein within the extracellular matrix. Collagen type I plays a crucial role in a variety of functions, it has been associated with many pathological conditions and it is widely used due to its unique properties. One unique nano-scale characteristic of natural occurring collagen type I fibers is the so-called D-band periodicity, which has been associated with collagen natural structure and properties, while it seems to play a crucial role in the interactions between cells and collagen and in various pathological conditions. An accurate characterization of the surface and structure of collagen fibers, including D-band periodicity, on collagen-based tissues and/or (nano-)biomaterials can be achieved by Atomic Force Microscopy (AFM). AFM is a scanning probe microscope and is among the few techniques that can assess D-band periodicity. This review covers issues related to collagen and collagen D-band periodicity and the use of AFM for studying them. Through a systematic search in databases (PubMed and Scopus) relevant articles were identified. The study of these articles demonstrated that AFM can offer novel information concerning D-band periodicity. This study highlights the importance of studying collagen D-band periodicity and proves that AFM is a powerful tool for investigating a number of different properties related to collagen D-band periodicity.

Exosomes and Exosomal Non-coding RNAs Are Novel Promises for the Mechanism-Based Diagnosis and Treatments of Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide and has a significant impact on human health and substantial costs. Currently, there is a lack of accurate biomarkers for the diagnosis and prognosis of AF. Moreover, the long-term efficacy of the catheter ablation in the AF is unsatisfactory. Therefore, it is necessary to explore new biomarkers and treatment strategies for the mechanism-based AF. Exosomes are nano-sized biovesicles released by nearly all types of cells. Since the AF would be linked to the changes of the atrial cells and their microenvironment, and the AF would strictly influence the exosomal non-coding RNAs (exo-ncRNAs) expression, which makes them as attractive diagnostic and prognostic biomarkers for the AF. Simultaneously, the exo-ncRNAs have been found to play an important role in the mechanisms of the AF and have potential therapeutic prospects. Although the role of the exo-ncRNAs in the AF is being actively investigated, the evidence is still limited. Furthermore, there is a lack of consensus regarding the most appropriate approach for exosome isolation and characterization. In this article, we reviewed the new methodologies available for exosomes biogenesis, isolation, and characterization, and then discussed the mechanism of the AF and various levels and types of exosomes relevant to the AF, with the special emphasis on the exo-ncRNAs in the diagnosis, prognosis, and treatment of the mechanism-based AF.

Imaging Techniques for Detecting Prokaryotic Viruses in Environmental Samples

Viruses are the most abundant biological entities on Earth with an estimate of 1031 viral particles across all ecosystems. Prokaryotic viruses-bacteriophages and archaeal viruses-influence global biogeochemical cycles by shaping microbial communities through predation, through the effect of horizontal gene transfer on the host genome evolution, and through manipulating the host cellular metabolism. Imaging techniques have played an important role in understanding the biology and lifestyle of prokaryotic viruses. Specifically, structure-resolving microscopy methods, for example, transmission electron microscopy, are commonly used for understanding viral morphology, ultrastructure, and host interaction. These methods have been applied mostly to cultivated phage-host pairs. However, recent advances in environmental genomics have demonstrated that the majority of viruses remain uncultivated, and thus microscopically uncharacterized. Although light- and structure-resolving microscopy of viruses from environmental samples is possible, quite often the link between the visualization and the genomic information of uncultivated prokaryotic viruses is missing. In this minireview, we summarize the current state of the art of imaging techniques available for characterizing viruses in environmental samples and discuss potential links between viral imaging and environmental genomics for shedding light on the morphology of uncultivated viruses and their lifestyles in Earth's ecosystems.

Mechanism of megaloblastic anemia combined with hemolysis

Megaloblastic anemia (MA) patients often exhibit hemolysis, but it is not clear whether there are other hemolytic mechanisms in addition to intramedullary hemolysis. We retrospectively analyzed the clinical characteristics of 124 MA patients, measured erythrocyte physical parameters in two patients with hemolysis and one healthy volunteer by atomic force microscopy, and measured 18F-FDG uptake in one MA patient with hemolysis. In multivariate analysis, hemolysis was associated with mean corpuscular volume (MCV) and indirect bilirubin. A receiver operating characteristic curve analysis, with sensitivity of 83.1% and specificity of 68.7%, suggested that the MCV cutoff value that predicts hemolysis is 116.4 fL. Hb was negatively correlated with MCV in the hemolysis group (r = −0.317, P = 0.007) but not in the nonhemolysis group. The erythrocyte peak-valley value, average cell surface roughness and surface area in the MA patients with hemolysis were significantly lower than those in controls (P < 0.05). 18F-FDG uptake by the liver and spleen was diffuse and increased in MA patients undergoing hemolysis. MA combined with extramedullary hemolysis could be caused by macrophages removing mechanically damaged erythrocytes and the retention of erythrocytes with decreased deformability when blood circulates through narrow spaces in the liver and spleen.

Benefits of cryopreservation as long-term storage method of encapsulated cardiosphere-derived cells for cardiac therapy: A biomechanical analysis

Cardiosphere-derived cells (CDCs) encapsulated within alginate-poly-L-lysine-alginate (APA) microcapsules present a promising treatment alternative for myocardial infarction. However, clinical translatability of encapsulated CDCs requires robust long-term preservation of microcapsule and cell stability, since cell culture at 37 °C for long periods prior to patient implantation involve high resource, space and manpower costs, sometimes unaffordable for clinical facilities. Cryopreservation in liquid nitrogen is a well-established procedure to easily store cells with good recovery rate, but its effects on encapsulated cells are understudied. In this work, we assess both the biological response of CDCs and the mechanical stability of microcapsules after long-term (i.e., 60 days) cryopreservation and compare them to encapsulated CDCs cultured at 37 °C. We investigate for the first time the effects of cryopreservation on stiffness and topographical features of microcapsules for cell therapy. Our results show that functionality of encapsulated CDCs is optimum during 7 days at 37 °C, while cryopreservation seems to better guarantee the stability of both CDCs and APA microcapsules properties during longer storage than 15 days. These results point out cryopreservation as a suitable technique for long-term storage of encapsulated cells to be translated from the bench to the clinic.

pH-dependent disintegration of insulin amyloid fibrils monitored with atomic force microscopy and surface-enhanced Raman spectroscopy

Aggregation of insulin into amyloid fibrils is characterized by the conversion of the native secondary structure of the peptide into an enriched ß-sheet conformation. In vitro, the growth or disintegration of amyloid fibrils can be influenced by various external factors such as pH, temperature etc. While current studies mainly focus on the influence of environmental conditions on the growth process of insulin fibrils, the present study investigates the effect of pH changes on the morphology and secondary structure of mature fibrils. In the experiments, insulin is fibrillated at pH 2.5 and the grown mature fibrils are suspended in pH 4-7 solutions. The obtained structures are analyzed by atomic force microscopy (AFM) and surface-enhanced Raman spectroscopy (SERS). Initially grown mature fibrils from pH 2.5 solutions show a long and intertwined morphology. Increasing the solution pH initiates the gradual disintegration of the filamentous morphology into unordered aggregates. These observations are supported by SERS experiments, where the spectra of the mature fibrils show mainly a β-pleated sheet conformation, while the amide I band region of the amorphous aggregates indicate exclusively α-helix/unordered structures. The results demonstrate that no complex reagent is required for the disintegration of insulin fibrils. Simply regulating the pH of the environment induces local changes in the protonation state within the peptide chains. This effectively disrupts the well-ordered β-sheet structure network based on hydrogen bonds.

Epididymosomes: A potential male fertility influencer

During transit and storage in epididymis, spermatozoa undergo final maturation, acquire motility, functional competence and the ability to fertilise an oocyte. Epididymal secretions contain a complex biochemical milieu of diverse inorganic ions, proteins, metabolites and other molecules. Since it is believed that spermatozoa are translationally silent, proteins appearing in them are thought to be synthesised elsewhere, including epididymis, and then incorporated to the cells. One of the important mechanisms suggested to be involved in transfer of epididymal secretions to spermatozoa is through exosomes called epididymosomes. Epididymosomes released from the epididymal epithelium contain proteins, noncoding RNAs and distinct set of lipids that are transferred to spermatozoa while they pass through the different epididymal regions. Owing to the importance of these molecules for sperm maturation and fertilising ability, research on epididymosomes has gained increasing attention during the last decade. This review is focused on epididymosomes, with emphasis on recent advances in the understanding of mechanisms of epididymosomal cargo transfer to spermatozoa and potential roles of epididymosomes in sperm function and beyond. Possibilities of utilising the molecular signatures of epididymosomes as a tool for male fertility assessment are also discussed.

Cardiac Exosomes in Ischemic Heart Disease- A Narrative Review

Ischemic heart disease (IHD) is the primary cause of death globally. IHD is associated with the disruption of blood supply to the heart muscles, which often results in myocardial infarction (MI) that further may progress to heart failure (HF). Exosomes are a subgroup of extracellular vesicles that can be secreted by virtually all types of cells, including cardiomyocytes, cardiac fibroblasts, endothelial cells, and stem and progenitor cells. Exosomes represent an important means of cell–cell communication through the transport of proteins, coding and non-coding RNA, and other bioactive molecules. Several studies show that exosomes play an important role in the progression of IHD, including endothelial dysfunction, the development of arterial atherosclerosis, ischemic reperfusion injury, and HF development. Recently, promising data have been shown that designates exosomes as carriers of cardioprotective molecules that enhance the survival of recipient cells undergoing ischemia. In this review, we summarize the functional involvement of exosomes regarding IHD. We also highlight the cardioprotective effects of native and bioengineered exosomes to IHD, as well as the possibility of using exosomes as natural biomarkers of cardiovascular diseases. Lastly, we discuss the opportunities and challenges that need to be addressed before exosomes can be used in clinical applications.

Methods for Studying Endometrial Pathology and the Potential of Atomic Force Microscopy in the Research of Endometrium

The endometrium lines the uterine cavity, enables implantation of the embryo, and provides an environment for its development and growth. Numerous methods, including microscopic and immunoenzymatic techniques, have been used to study the properties of the cells and tissue of the endometrium to understand changes during, e.g., the menstrual cycle or implantation. Taking into account the existing state of knowledge on the endometrium and the research carried out using other tissues, it can be concluded that the mechanical properties of the tissue and its cells are crucial for their proper functioning. This review intends to emphasize the potential of atomic force microscopy (AFM) in the research of endometrium properties. AFM enables imaging of tissues or single cells, roughness analysis, and determination of the mechanical properties (Young’s modulus) of single cells or tissues, or their adhesion. AFM has been previously shown to be useful to derive force maps. Combining the information regarding cell mechanics with the alternations of cell morphology or gene/protein expression provides deeper insight into the uterine pathology. The determination of the elastic modulus of cells in pathological states, such as cancer, has been proved to be useful in diagnostics.

Atomic Force Microscopy Reveals that the Drosophila Telomere-Capping Protein Verrocchio Is a Single-Stranded DNA-Binding Protein

Atomic force microscopy (AFM) is a scanning probe technique that allows visualization of biological samples with a nanometric resolution. Determination of the physical properties of biological molecules at a single-molecule level is achieved through topographic analysis of the sample adsorbed on a flat and smooth surface. AFM has been widely used for the structural analysis of nucleic acid-protein interactions, providing insights on binding specificity and stoichiometry of proteins forming complexes with DNA substrates. Analysis of single-stranded DNA-binding proteins by AFM requires specific single-stranded/double-stranded hybrid DNA molecules as substrates for protein binding. In this chapter we describe the protocol for AFM characterization of binding properties of Drosophila telomeric protein Ver using DNA constructs that mimic the structure of chromosome ends. We provide details on the methodology used, including the procedures for the generation of DNA substrates, the preparation of samples for AFM visualization, and the data analysis of AFM images. The presented procedure can be adapted for the structural studies of any single-stranded DNA-binding protein.

Elastic moduli of lipid membranes: Reproducibility of AFM measures

Membrane elastic properties play a major role in membrane remodeling events, such as vesicle fusion and fission. They are also crucial in drug delivery by liposomes. Different experimental techniques are available to measure elastic properties. Among them, atomic force microscopy (AFM) presents the unique advantage of being directly applicable to nano-sized liposomes. Unfortunately, different AFM measures reported in the literature show little agreement among each other and are difficult to compare with measures of bending modulus obtained by other experimental techniques or by molecular simulations. In this work we determine the bending rigidity of Egg PC liposomes in terms of Young modulus via AFM measurements, using two different tip shapes and different cantilever force constants. We interpret the measures using the Hertz and Shell models, and observe a clear dependency of the Young modulus values on the tip properties and on the interpretative theory. The effect of the AFM tip shape is less important than the effect of the cantilever force constant, and the mathematical model has a major effect on the interpretation of the data. The Shell theory provides the closest agreement between AFM data and other experimental data for the membrane bending modulus. Finally, we compare the results to calculations of bending modulus from molecular dynamics simulations of membrane buckles. Simulations provide values of bending modulus consistent with literature data, but the agreement with AFM experiments is reasonable only for some specific experimental conditions.

Collagen-Supplemented Incubation Rapidly Augments Mechanical Property of Fibroblast Cell Sheets

Cell sheet technology using UpCell™ (Thermo Fisher Scientific, Roskilde, Denmark) plates is a modern tool that enables the rapid creation of single-layered cells without using extracellular matrix (ECM) enzymatic digestion. Although this technique has the advantage of maintaining a sheet of cells without needing artificial scaffolds, these cell sheets remain extremely fragile. Collagen, the most abundant ECM component, is an attractive candidate for modulating tissue mechanical properties given its tunable property. In this study, we demonstrated rapid mechanical property augmentation of human dermal fibroblast cell sheets after incubation with bovine type I collagen for 24 h on UpCell plates. We showed that treatment with collagen resulted in increased collagen I incorporation within the cell sheet without affecting cell morphology, cell type, or cell sheet quality. Atomic force microscopy measurements for controls, and cell sheets that received 50 and 100 μg/mL collagen I treatments revealed an average Young's modulus of their respective intercellular regions: 6.6 ± 1.0, 14.4 ± 6.6, and 19.8 ± 3.8 kPa during the loading condition, and 10.3 ± 4.7, 11.7 ± 2.2, and 18.1 ± 3.4 kPa during the unloading condition. This methodology of rapid mechanical property augmentation of a cell sheet has a potential impact on cell sheet technology by improving the ease of construct manipulation, enabling new translational tissue engineering applications.

Single-particle virology

The development of advanced experimental methodologies, such as optical tweezers, scanning-probe and super-resolved optical microscopies, has led to the evolution of single-molecule biophysics, a field of science that allows direct access to the mechanistic detail of biomolecular structure and function. The extension of single-molecule methods to the investigation of particles such as viruses permits unprecedented insights into the behavior of supramolecular assemblies. Here we address the scope of viral exploration at the level of individual particles. In an era of increased awareness towards virology, single-particle approaches are expected to facilitate the in-depth understanding, and hence combating, of viral diseases.

Nanoscale Characteristics of Ocular Lipid Thin Films Using Kelvin Probe Force Microscopy

Purpose

To describe the use of Kelvin probe force microscopy (KPFM) to investigate the electrical surface potential of human meibum and to demonstrate successful use of this instrument on both human meibum and a meibum model system (six-lipid stock [6LS]) to elucidate nanoscale surface chemistry and self-assembly characteristics.

Materials and Methods

6LS and meibum were analyzed in this study. Mica-supported thin films were created using the Langmuir-Blodgett trough. Topography and electrical surface potential were quantified using simultaneous atomic force microscopy/KPFM imaging.

Results

Both lipid mixtures formed thin film patches on the surface of the mica substrate, with large aggregates resting atop. The 6LS had aggregate heights ranging from 41 to 153 nm. The range in surface potential was 33.0 to 125.9 mV. The meibum thin films at P = 5 mN/m had aggregates of 170 to 459 nm in height and surface potential ranging from 15.9 to 76.1 mV, while thin films at P = 10 mN/m showed an aggregate size range of 147 to 407 nm and a surface potential range of 11.5 to 255.1 mV.

Conclusions

This study showed imaging of the differences in electrical surface potential of meibum via KPFM and showed similarities in nanoscale topography. 6LS was also successfully analyzed, showing the capabilities of this method for use in both in vitro and ex vivo ocular research.

Translational Relevance

This study describes the use of KPFM for the study of ocular surface lipids for the first time and outlines possibilities for future studies to be carried out using this concept.

The Physical Microenvironment of Tumors: Characterization and Clinical Impact

The tumor microenvironment plays a critical role in tumorigenesis and metastasis. As tightly controlled extracellular matrix homeostasis is lost during tumor progression, a dysregulated extracellular matrix can significantly alter cellular phenotype and drive malignancy. Altered physical properties of the tumor microenvironment alter cancer cell behavior, limit delivery and efficacy of therapies, and correlate with tumorigenesis and patient prognosis. The physical features of the extracellular matrix during tumor progression have been characterized; however, a wide range of methods have been used between studies and cancer types resulting in a large range of reported values. Here, we discuss the significant mechanical and structural properties of the tumor microenvironment, summarizing their reported values and clinical impact across cancer type and grade. We attempt to integrate the values in the literature to identify sources of reported differences and commonalities to better understand how aberrant extracellular matrix dynamics contribute to cancer progression. An intimate understanding of altered matrix properties during malignant transformation will be crucial in effectively detecting, monitoring, and treating cancer.

Atomic Force Microscopy in Mechanoimmunology Analysis: A New Perspective for Cancer Immunotherapy

Immunotherapy has remarkable success outcomes against hematological malignancies with high rates of complete remission. To date, many studies have been conducted to increase its effectiveness in other types of cancer. However, it still yields unsatisfying results in solid tumor therapy. This limitation is partly attributed to the lack of understanding of how immunotherapy works in cancer from other perspectives. The traditional studies focus on the biological and chemical perspectives to determine which molecular substrates are involved in the immune system that can eradicate cancer cells. In the last decades, accumulating evidence has shown that physical properties also play important roles in the immune system to combat cancer, which is studied in mechanoimmunology. Mechanoimmunology analysis requires special tools; and herein, atomic force microscopy (AFM) appears as a versatile tool to determine and quantify the mechanical properties of a sample in nanometer precisions. Owing to its multifunctional capabilities, AFM can be used to explore immune system function from the physical perspective. This review paper explains the mechanoimmunology of how immune systems work through AFM, which includes mechanosignaling, mechanosensing, and mechanotransduction, with the aim to deepen the understanding of the mechanistic role of immunotherapy for further development in cancer treatment.

Probing the surface ultrastructure of Brevibacillus laterosporus using atomic force microscopy

One of the main obstacles to studying the surface ultrastructure of microbial cells by atomic force microscopy (AFM) is determining how to immobilize live cells on the AFM substrates. Each method has its own advantages and disadvantages. The aim of this study was to characterize a new simple and inexpensive method using two types of polyethersulfone (PES) membrane filters that differ in pore size (micropore and nanopore) to immobilize live and dead Brevibacillus laterosporus for AFM imaging. B. laterosporus was easily trapped by the microporous PES membrane, facilitating the successful AFM scanning of the bacterial surface ultrastructure. In addition, B. laterosporus strongly attached to the nanoporous membranes and withstood the pulling forces exerted by the AFM tip during scanning. These methods of immobilization did not affect the cell viability. The nanostructure and roughness of the bacterial surface were also observed for live, fixed, and air-dried cells. Live and dead bacteria displayed similar morphologies at low resolution, while at high resolution, live bacteria displayed a more convoluted surface ("brain-like structure").

Characterization of the elastic properties of extracellular matrix models by atomic force microscopy

Tissue elasticity is a critical regulator of cell behavior in normal and diseased conditions like fibrosis and cancer. Since the extracellular matrix (ECM) is a major regulator of tissue elasticity and function, several ECM-based models have emerged in the last decades, including in vitro endogenous ECM, decellularized tissue ECM and ECM hydrogels. The development of such models has urged the need to quantify their elastic properties particularly at the nanometer scale, which is the relevant length scale for cell-ECM interactions. For this purpose, the versatility of atomic force microscopy (AFM) to quantify the nanomechanical properties of soft biomaterials like ECM models has emerged as a very suitable technique. In this chapter we provide a detailed protocol on how to assess the Young's elastic modulus of ECM models by AFM, discuss some of the critical issues, and provide troubleshooting guidelines as well as illustrative examples of AFM measurements, particularly in the context of cancer.

Advances in Imaging Plant Cell Walls

Understanding of cell wall architecture, including the crosslinking of cell wall polymers, provides crucial information for elucidating the relationship between cell wall structure and cell function. Moreover, examination of the cell wall informs efforts to improve biomass breakdown in bioreactor conditions. Over the past decades, imaging techniques have been used extensively to reveal the structural organization and chemical composition of cell walls, but detailed imaging of the native composition and architecture of the cell wall remains challenging. Here, we review progress in the development of cell wall imaging techniques. In particular, we focus on several advanced, label-free techniques for imaging cell walls and their potential applications in investigation of the biological functions of plant cell walls.

Novosphingobium sp. PP1Y as a novel source of outer membrane vesicles

Outer membrane vesicles (OMVs) are nanostructures of 20-200 nm diameter deriving from the surface of several Gram-negative bacteria. OMVs are emerging as shuttles involved in several mechanisms of communication and environmental adaptation. In this work, OMVs were isolated and characterized from Novosphingobium sp. PP1Y, a Gram-negative non-pathogenic microorganism lacking LPS on the outer membrane surface and whose genome was sequenced and annotated. Scanning electron microscopy performed on samples obtained from a culture in minimal medium highlighted the presence of PP1Y cells embedded in an extracellular matrix rich in vesicular structures. OMVs were collected from the exhausted growth medium during the mid-exponential phase, and purified by ultracentrifugation on a sucrose gradient. Atomic force microscopy, dynamic light scattering and nanoparticle tracking analysis showed that purified PP1Y OMVs had a spherical morphology with a diameter of ca. 150 nm and were homogenous in size and shape. Moreover, proteomic and fatty acid analysis of purified OMVs revealed a specific biochemical "fingerprint", suggesting interesting details concerning their biogenesis and physiological role. Moreover, these extracellular nanostructures do not appear to be cytotoxic on HaCaT cell line, thus paving the way to their future use as novel drug delivery systems.

Atomic force microscopy for single molecule characterisation of protein aggregation

The development of atomic force microscopy (AFM) has opened up a wide range of novel opportunities in nanoscience and new modalities of observation in complex biological systems. AFM imaging has been widely employed to resolve the complex and heterogeneous conformational states involved in protein aggregation at the single molecule scale and shed light onto the molecular basis of a variety of human pathologies, including neurodegenerative disorders. The study of individual macromolecules at nanoscale, however, remains challenging, especially when fully quantitative information is required. In this review, we first discuss the principles of AFM with a special emphasis on the fundamental factors defining its sensitivity and accuracy. We then review the fundamental parameters and approaches to work at the limit of AFM resolution in order to perform single molecule statistical analysis of biomolecules and nanoscale protein aggregates. This single molecule statistical approach has proved to be powerful to unravel the molecular and hierarchical assembly of the misfolded species present transiently during protein aggregation, to visualise their dynamics at the nanoscale, as well to study the structural properties of amyloid-inspired functional nanomaterials.

Extracellular Vesicle Quantification and Characterization: Common Methods and Emerging Approaches

Extracellular vesicles (EVs) are a family of small membrane vesicles that carry information about cells by which they are secreted. Growing interest in the role of EVs in intercellular communication, but also in using their diagnostic, prognostic and therapeutic potential in (bio) medical applications, demands for accurate assessment of their biochemical and physical properties. In this review, we provide an overview of available technologies for EV analysis by describing their working principles, assessing their utility in EV research and summarising their potential and limitations. To emphasise the innovations in EV analysis, we also highlight the unique possibilities of emerging technologies with high potential for further development.

Atomic Force Microscopy on Biological Materials Related to Pathological Conditions

Atomic force microscopy (AFM) is an easy-to-use, powerful, high-resolution microscope that allows the user to image any surface and under any aqueous condition. AFM has been used in the investigation of the structural and mechanical properties of a wide range of biological matters including biomolecules, biomaterials, cells, and tissues. It provides the capacity to acquire high-resolution images of biosamples at the nanoscale and allows at readily carrying out mechanical characterization. The capacity of AFM to image and interact with surfaces, under physiologically relevant conditions, is of great importance for realistic and accurate medical and pharmaceutical applications. The aim of this paper is to review recent trends of the use of AFM on biological materials related to health and sickness. First, we present AFM components and its different imaging modes and we continue with combined imaging and coupled AFM systems. Then, we discuss the use of AFM to nanocharacterize collagen, the major fibrous protein of the human body, which has been correlated with many pathological conditions. In the next section, AFM nanolevel surface characterization as a tool to detect possible pathological conditions such as osteoarthritis and cancer is presented. Finally, we demonstrate the use of AFM for studying other pathological conditions, such as Alzheimer's disease and human immunodeficiency virus (HIV), through the investigation of amyloid fibrils and viruses, respectively. Consequently, AFM stands out as the ideal research instrument for exploring the detection of pathological conditions even at very early stages, making it very attractive in the area of bio- and nanomedicine.

Analysis of DNA-Protein Complexes by Atomic Force Microscopy Imaging: The Case of TRF2-Telomeric DNA Wrapping

Atomic force microscopy (AFM) is a non-optical microscopy that enables the acquisition at the nanoscale level of a 3D topographical image of the sample. For 30 years, AFM has been a valuable tool in life sciences to study biological samples in the field of tissue, cellular and molecular imaging, of mechanical properties and of force spectroscopy. Since the early beginnings of the technique, AFM has been extensively exploited as an imaging tool for structural studies of nucleic acids and nucleoprotein complexes. The morphometric analysis performed on the images can unveil specific structural and functional aspects of the sample, such as the multimerization state of proteins bound to DNA, or DNA conformational changes led by the DNA-binding proteins. Herein, a method for analyzing a complex formed by a telomeric DNA sequence wrapped around the TRF2 binding protein is presented. The described procedure could be applied to the study of any type of DNA-protein complex.

Cerium oxide nanoparticles at the nano-bio interface: size-dependent cellular uptake

The authors investigated the role of different size and morphology of cerium oxide nanoparticles (CNPs) in cellular uptake and internalization at the nano-bio interface. Atomic force microscopy (AFM) has been utilized to record changes in the membrane elasticity as a function of ceria particle morphology and concentration. Young's Modulus was estimated in presence and absence of CNPs of different sizes by gauging the membrane elasticity of CCL30 (squamous cell carcinoma) cells. Significant change in Young's Modulus was observed for CNP treatments at higher concentrations, while minimum membrane disruption was observed at lower concentrations. Studies using blocking agents specific to energy-dependent cellular internalization pathways indicated passive cellular uptake for smaller CNPs (3-5 nm). Other observations showed that larger CNPs were unable to permeate the cell membrane, which indicates an active uptake mechanism by the cell membrane. The ability of smaller CNPs (3-5 nm) to permeate the cell membrane without energy consumption by uptake pathways suggests potential for use as nanovectors for the delivery of bioactive molecules. Specifically, the passive uptake mechanism allows for the delivery of surface-bound molecules directly to the cytoplasm, avoiding the extreme chemical conditions of endosomal pathways.

Behavior of a Metal Organic Framework Thin-Film at Elevated Temperature and Pressure as Studied with an Autoclave-Inserted Atomic Force Microscope

Bridging the gap in studying surface reactions, processes, and morphology and measuring at (catalytic) relevant conditions is crucial for our understanding of the working principles of porous crystalline materials. Scanning tunneling microscopy is limited because of the required conductivity of the sample, whereas atomic force microscopy (AFM) is often challenging in use owing to the physical mechanism underlying the technique. Herein, we report a tailor‐made autoclave‐inserted AFM, able to measure at ∼20 bar and ∼110 °C. First, we show the ability to obtain nanometer resolution on well‐defined test samples at before‐mentioned conditions. Second, to demonstrate the possibilities of analyzing morphological evolutions at elevated temperatures and pressures, we use this setup to measure the stability of a surface‐anchored metal‐organic framework (SURMOF) in‐situ at pressures of 1–20 bar in the temperature range between 20 and 60 °C. It was found that the showcase HKUST‐1 material has a good physical stability, as it is hardly damaged from exposure to pressures up to 20 bar. However, its thermal stability is weaker, as exposure to elevated T damaged the material by influencing the interaction between organic linker and metal cluster. In‐situ measurements at elevated T also showed an increased mobility of the material when working at such conditions. Combining the strength of AFM at elevated T and p with ex‐situ AFM and spectroscopic measurements on this MOF showcases an example of how porous materials can be studied at (industrially) relevant conditions using the autoclave‐inserted AFM.

Sensing the Ultrastructure of Bacterial Surfaces and Their Molecular Binding Forces Using AFM

In this protocol, we provide a detailed step-by-step bacterial surface imaging and molecular analysis procedure. With SPM (scanning probe microscopy)-based dynamic force microscopy (DFM) imaging, we achieved a so far unprecedented resolution of ~1 nm on the outer surface layer of Tannerella forsythia and monitored the production of curli fibers on Escherichia coli in physiological conditions. Moreover, using these immobilization methods, single-molecule force spectroscopy experiments were conducted on living bacterial cells.

Nano-Enabled Approaches to Chemical Imaging in Biosystems

Understanding and predicting how biosystems function require knowledge about the dynamic physicochemical environments with which they interact and alter by their presence. Yet, identifying specific components, tracking the dynamics of the system, and monitoring local environmental conditions without disrupting biosystem function present significant challenges for analytical measurements. Nanomaterials, by their very size and nature, can act as probes and interfaces to biosystems and offer solutions to some of these challenges. At the nanoscale, material properties emerge that can be exploited for localizing biomolecules and making chemical measurements at cellular and subcellular scales. Here, we review advances in chemical imaging enabled by nanoscale structures, in the use of nanoparticles as chemical and environmental probes, and in the development of micro- and nanoscale fluidic devices to define and manipulate local environments and facilitate chemical measurements of complex biosystems. Integration of these nano-enabled methods will lead to an unprecedented understanding of biosystem function.

Raman, AFM and SNOM high resolution imaging of carotene crystals in a model carrot cell system

Three non-destructive and complementary techniques, Raman imaging, Atomic Force Microscopy and Scanning Near-field Optical Microscopy were used simultaneously to show for the first time chemical and structural differences of carotenoid crystals. Spectroscopic and microscopic scanning probe measurements were applied to the released crystals or to crystals accumulated in a unique, carotenoids rich callus tissue growing in vitro that is considered as a new model system for plant carotenoid research. Three distinct morphological crystal types of various carotenoid composition were identified, a needle-like, rhomboidal and helical. Raman imaging using 532 and 488 nm excitation lines provided evidence that the needle-like and rhomboidal crystals had similar carotenoid composition and that they were composed mainly of β-carotene accompanied by α-carotene. However, the presence of α-carotene was not identified in the helical crystals, which had the characteristic spatial structure. AFM measurements of crystals identified by Raman imaging revealed the crystal topography and showed the needle-like and rhomboidal crystals were planar but they differed in all three dimensions. Combining SNOM and Raman imaging enabled indication of carotenoid rich structures and visualised their distribution in the cell. The morphology of identified subcellular structures was characteristic for crystalline, membraneous and tubular chromoplasts that are plant organelles responsible for carotenoid accumulation in cells.

Imaging Bacterial Cell Wall Biosynthesis

Peptidoglycan is an essential component of the cell wall that protects bacteria from environmental stress. A carefully coordinated biosynthesis of peptidoglycan during cell elongation and division is required for cell viability. This biosynthesis involves sophisticated enzyme machineries that dynamically synthesize, remodel, and degrade peptidoglycan. However, when and where bacteria build peptidoglycan, and how this is coordinated with cell growth, have been long-standing questions in the field. The improvement of microscopy techniques has provided powerful approaches to study peptidoglycan biosynthesis with high spatiotemporal resolution. Recent development of molecular probes further accelerated the growth of the field, which has advanced our knowledge of peptidoglycan biosynthesis dynamics and mechanisms. Here, we review the technologies for imaging the bacterial cell wall and its biosynthesis activity. We focus on the applications of fluorescent d-amino acids, a newly developed type of probe, to visualize and study peptidoglycan synthesis and dynamics, and we provide direction for prospective research.

Atomic Force Microscopy Provides New Mechanistic Insights into the Pathogenesis of Pemphigus

Autoantibodies binding to the extracellular domains of desmoglein (Dsg) 3 and 1 are critical in the pathogenesis of pemphigus by mechanisms leading to impaired function of desmosomes and blister formation in the epidermis and mucous membranes. Desmosomes are highly organized protein complexes which provide strong intercellular adhesion. Desmosomal cadherins such as Dsgs, proteins of the cadherin superfamily which interact via their extracellular domains in Ca2+-dependent manner, are the transmembrane adhesion molecules clustered within desmosomes. Investigations on pemphigus cover a wide range of experimental approaches including biophysical methods. Especially atomic force microscopy (AFM) has recently been applied increasingly because it allows the analysis of native materials such as cultured cells and tissues under near-physiological conditions. AFM provides information about the mechanical properties of the sample together with detailed interaction analyses of adhesion molecules. With AFM, it was recently demonstrated that autoantibodies directly inhibit Dsg interactions on the surface of living keratinocytes, a phenomenon which has long been considered the main mechanism causing loss of cell cohesion in pemphigus. In addition, AFM allows to study how signaling pathways altered in pemphigus control binding properties of Dsgs. More general, AFM and other biophysical studies recently revealed the importance of keratin filaments for regulation of Dsg binding and keratinocyte mechanical properties. In this mini-review, we reevaluate AFM studies in pemphigus and keratinocyte research, recapitulate what is known about the interaction mechanisms of desmosomal cadherins and discuss the advantages and limitations of AFM in these regards.

Polymers and biopolymers at interfaces

This review updates recent progress in the understanding of the behaviour of polymers at surfaces and interfaces, highlighting examples in the areas of wetting, dewetting, crystallization, and 'smart' materials. Recent developments in analysis tools have yielded a large increase in the study of biological systems, and some of these will also be discussed, focussing on areas where surfaces are important. These areas include molecular binding events and protein adsorption as well as the mapping of the surfaces of cells. Important techniques commonly used for the analysis of surfaces and interfaces are discussed separately to aid the understanding of their application.