Mechanical properties of single living cells encapsulated in polyelectrolyte matrixes

Potential Role of the Anammoxosome in the Adaptation of Anammox Bacteria to Salinity Stress

The underlying adaptative mechanisms of anammox bacteria to salt stress are still unclear. The potential role of the anammoxosome in modulating material and energy metabolism in response to salinity stress was investigated in this study. The results showed that anammox bacteria increased membrane fluidity and decreased mechanical properties by shortening the ladderane fatty acid chain length of anammoxosome in response to salinity shock, which led to the breakdown of the proton motive force driving ATP synthesis and retarded energy metabolism activity. Afterward, the fatty acid chain length and membrane properties were recovered to enhance the energy metabolic activity. The relative transmission electron microscopy (TEM) area proportion of anammoxosome decreased from 55.9 to 38.9% under salinity stress. The 3D imaging of the anammox bacteria based on Synchrotron soft X-ray tomography showed that the reduction in the relative volume proportion of the anammoxosome and the concave surfaces was induced by salinity stress, which led to the lower energy expenditure of the material transportation and provided more binding sites for enzymes. Therefore, anammox bacteria can modulate nitrogen and energy metabolism by changing the membrane properties and morphology of the anammoxosome in response to salinity stress. This study broadens the response mechanism of anammox bacteria to salinity stress.

Analytical Models for Measuring the Mechanical Properties of Yeast

The mechanical properties of yeast play an important role in many biological processes, such as cell division and growth, maintenance of internal pressure, and biofilm formation. In addition, the mechanical properties of cells can indicate the degree of damage caused by antifungal drugs, as the mechanical parameters of healthy and damaged cells are different. Over the past decades, atomic force microscopy (AFM) and micromanipulation have become the most widely used methods for evaluating the mechanical characteristics of microorganisms. In this case, the reliability of such an estimate depends on the choice of mathematical model. This review presents various analytical models developed in recent years for studying the mechanical properties of both cells and their individual structures. The main provisions of the applied approaches are described along with their limitations and advantages. Attention is paid to the innovative method of low-invasive nanomechanical mapping with scanning ion-conductance microscopy (SICM), which is currently starting to be successfully used in the discovery of novel drugs acting on the yeast cell wall and plasma membrane.

Glioma stem cells invasive phenotype at optimal stiffness is driven by MGAT5 dependent mechanosensing

BACKGROUND

Glioblastomas stem-like cells (GSCs) by invading the brain parenchyma, remains after resection and radiotherapy and the tumoral microenvironment become stiffer. GSC invasion is reported as stiffness sensitive and associated with altered N-glycosylation pattern. Glycocalyx thickness modulates integrins mechanosensing, but details remain elusive and glycosylation enzymes involved are unknown. Here, we studied the association between matrix stiffness modulation, GSC migration and MGAT5 induced N-glycosylation in fibrillar 3D context.

METHOD

To mimic the extracellular matrix fibrillar microenvironments, we designed 3D-ex-polyacrylonitrile nanofibers scaffolds (NFS) with adjustable stiffnesses by loading multiwall carbon nanotubes (MWCNT). GSCs neurosphere were plated on NFSs, allowing GSCs migration and MGAT5 was deleted using CRISPR-Cas9.

RESULTS

We found that migration of GSCs was maximum at 166 kPa. Migration rate was correlated with cell shape, expression and maturation of focal adhesion (FA), Epithelial to Mesenchymal Transition (EMT) proteins and (β1,6) branched N-glycan binding, galectin-3. Mutation of MGAT5 in GSC inhibited N-glycans (β1-6) branching, suppressed the stiffness dependence of migration on 166 kPa NFS as well as the associated FA and EMT protein expression.

CONCLUSION

MGAT5 catalysing multibranched N-glycans is a critical regulators of stiffness induced invasion and GSCs mechanotransduction, underpinning MGAT5 as a serious target to treat cancer.

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field.

Effect of pH change on size and nanomechanical behavior of whey protein microgels

Microgels specific structural and functional features are attracting high research interest in several applications such as bioactives and drug delivery or functional food ingredients. Whey protein microgels (WPM) are obtained by heat treatment of whey protein isolate (WPI) in order to promote intramolecular cross-linking. In the present work, atomic force microscopy (AFM) was used in contact mode and in liquid to investigate WPM particles topography and mechanical properties at the nanoscale at native pH (6.5) and acid pH (5.5 and 3.0). Prior to AFM, WPM particles were captured on a gold substrate via low energy interactions by means of specific monoclonal antibodies. AFM images clearly showed an increase in the size of WPM particles induced by pH decrease. AFM in force spectroscopy mode was employed to monitor the elasticity of WPMs. The obtained effective Young's modulus data showed a significant increase in stiffness at pH 5.5 and pH 3.0, over 15-fold compared to native pH. These findings indicate that the mechanical profile of the WPM network varied with the pH decrease. The WPM topographic and nanomechanical changes induced by acidification were most likely due to substantial changes in the shape and inner structure of WPM particles. Our results suggest that internally cross-linked structures, modified by acidification could display interesting functional properties when used as a food ingredient.

Dynamics of rebounding Bacillus subtilis spores determined using image-charge detection

A novel image-charge detection technique was used to investigate the mechanical elasticity of bare bacterial spores during high-velocity impact. Spores of Bacillus subtilis introduced to vacuum using electrospray and aerodynamic acceleration impacted and rebounded off of a glass plate. A dual-stage, asymmetric image-charge detector measured the velocity and direction of each spore both before and after impact with the glass surface. Two ranges of impact velocity were investigated, with average initial velocities of 197 ± 17 and 145 ± 12 m/s. Impacts were strongly inelastic, with most of the translational kinetic energy lost upon impact, similar to polystyrene particles of similar size under similar impact velocities. Specifically, 69% (± 16%) and 74% (± 11%) of initial kinetic energy was lost in impacts at the two velocity ranges, respectively. The average coefficients of restitution for the two velocity regimes were 0.53 ± 0.15 and 0.49 ± 0.12. There was no statistically significant difference in the fractional kinetic energy loss between these two populations. The variance of these results is much larger than experiments using polystyrene spheres of comparable size. These results imply significant plastic deformation of the spore-a striking result given that spores of this strain of B. subtilis are known to survive impacts on glass at these velocities. Triboelectric charge transfer during impact was also observed. Although much is known about spore elasticity from static measurements, this is the first study to investigate the elastic properties of bacterial spores in a dynamic scenario, as well as the first demonstration of an image charge detector for measurements of rebounding particles.

Atomic Force Microscopy Study of the Topography and Nanomechanics of Casein Micelles Captured by an Antibody

Casein micelles (CMs) are colloidal phospho-protein-mineral complexes naturally present in milk. This study used atomic force microscopy (AFM) in a liquid environment to evaluate the topography and nanomechanics of single native CMs immobilized by a novel capture method. The proposed immobilization method involves weak interactions with the antiphospho-Ser/Thr/Tyr monoclonal antibody covalently bound to a carboxylic acid self-assembled monolayer (SAM) on a gold surface. This capture strategy was compared to the commonly used covalent immobilization method of CMs via carbodiimide chemistry. With this conventional method, CMs remained mainly mobile during AFM measurements in liquid, disturbing the evaluation of their average size and elastic properties. Conversely, when captured by the specific antibody, they were successfully immobilized and their integrity was preserved during the AFM measurement. The characterization of both CM topography and elastic properties was carried out in a liquid ionic environment at native pH 6.6. The CMs' capture efficiency via antibody was concurrently proved by surface plasmon resonance. The calculation of casein micelles' width, height, and contact angle was carried out from the recorded 2D AFM images. CMs were characterized by a mean width of 148 ± 8 nm and a mean height of 42 ± 1 nm. Weak forces were applied to single captured CMs. The obtained force versus indentation curves were fitted using the Hertz model in order to evaluate their elastic properties. The elasticity distribution of native CMs exhibited a unimodal trend with a peak centered at 269 ± 14 kPa.

AFM resolves effects of ethambutol on nanomechanics and nanostructures of single dividing mycobacteria in real-time

Dynamic nanomechanics and nanostructures of dividing and anti-mycobacterial drug treated mycobacterium remain to be fully elucidated. Atomic force microscopy (AFM) is a promising nanotechnology tool for characterization of these dynamic alterations, especially at the single cell level. In this work, single dividing mycobacterium JLS (M.JLS) before and after anti-mycobacterial drug (ethambutol, EMB) treatment was in situ quantitatively analyzed, suggesting that nanomechanics would be referred as a sensitive indicator for evaluating efficacy of anti-mycobacterial drugs. Dynamic evidence on the contractile ring and septal furrow of dividing M.JLS implied that inhibition of contractile ring formation would be a crucial process for EMB to disturb M.JLS division. These results could facilitate further explaining the regulation mechanism of the contractile ring as well as nanomechanical roles of the cell wall in the course of mycobacterial division. This work describe a new way for further elucidating the mechanisms of mycobacterial division and anti-mycobacterial drug action, as well as the drug-resistance developing mechanism of pathogenic mycobacteria.

Silver nanoparticle-coated “cyborg” microorganisms: rapid assembly of polymer-stabilised nanoparticles on microbial cells

Silver nanoparticles-coated “cyborg” cells.

Nanocoating of single cells: from maintenance of cell viability to manipulation of cellular activities

The chronological progresses in single-cell nanocoating are described. The historical developments in the field are divided into biotemplating, cytocompatible nanocoating, and cells in nano-nutshells, depending on the main research focuses. Each subfield is discussed in conjunction with the others, regarding how and why to manipulate living cells by nanocoating at the single-cell level.

Nanomechanical analysis of yeast cells in CdSe quantum dot biosynthesis

QD biosynthesis affects the mechanical strength of yeast cells. The intracellular synthesis of CdSe QD in yeast cells incubated with Na2 SeO3 and subsequently with CdCl2 increases the glucan content of their cell walls, resulting in their enhanced mechanical strength.

Mechanical properties of human amniotic fluid stem cells using nanoindentation

The aim of this study was to obtain nanomechanical properties of living cells focusing on human amniotic fluid stem (hAFS) cell using nanoindentation techniques. We modified the conventional method of atomic force microscopy (AFM) in aqueous environment for cell imaging and indentation to avoid inherent difficulties. Moreover, we determined the elastic modulus of murine osteoblast (OB6) cells and hAFS cells at the nucleus and cytoskeleton using force-displacement curves and Hertz theory. Since OB6 cell line has been widely used, it was selected to validate and compare the obtained results with the previous research studies. As a result, we were able to capture high resolution images through utilization of the tapping mode without adding protein or using fixation methods. The maximum depth of indentation was kept below 15% of the cell thickness to minimize the effect of substrate hardness. Nanostructural details on the surface of cells were visualized by AFM and fluorescence microscopy. The cytoskeletal fibers presented remarkable increase in elastic modulus as compared with the nucleus. Furthermore, our results showed that the elastic modulus of hAFS cell edge (31.6 kPa) was lower than that of OB6 cell edge (42.2 kPa). In addition, the elastic modulus of nucleus was 13.9 kPa for hAFS cell and 26.9 kPa for OB6 cells. Differences in cell elastic modulus possibly resulted from the type and number of actin cytoskeleton organization in these two cell types.

Single cell stiffness measurement at various humidity conditions by nanomanipulation of a nano-needle

This paper presents a method for single cell stiffness measurement based on a nano-needle and nanomanipulation. The nano-needle with a buffering beam was fabricated from an atomic force microscope cantilever by the focused ion beam etching technique. Wild type yeast cells (W303) were prepared and placed on the sample stage inside an environmental scanning electron microscope (ESEM) chamber. The nanomanipulator actuated the nano-needle to press against a single yeast cell. As a result, the deformation of the cell and nano-needle was observed by the ESEM system in real-time. Finally, the stiffness of the single cell was determined based on this deformation information. To reveal the relationship between the cell stiffness and the environmental humidity conditions, the cell stiffness was measured at three different humidity conditions, i.e. 40, 70 and 100%, respectively. The results show that the stiffness of a single cell is reduced with increasing humidity.

Morphology and nanomechanics of sensory neurons growth cones following peripheral nerve injury

A prior peripheral nerve injury in vivo, promotes a rapid elongated mode of sensory neurons neurite regrowth in vitro. This in vitro model of conditioned axotomy allows analysis of the cellular and molecular mechanisms leading to an improved neurite re-growth. Our differential interference contrast microscopy and immunocytochemistry results show that conditioned axotomy, induced by sciatic nerve injury, did not increase somatic size of adult lumbar sensory neurons from mice dorsal root ganglia sensory neurons but promoted the appearance of larger neurites and growth cones. Using atomic force microscopy on live neurons, we investigated whether membrane mechanical properties of growth cones of axotomized neurons were modified following sciatic nerve injury. Our data revealed that neurons having a regenerative growth were characterized by softer growth cones, compared to control neurons. The increase of the growth cone membrane elasticity suggests a modification in the ratio and the inner framework of the main structural proteins.

Drug-loaded polyelectrolyte microcapsules for sustained targeting of cancer cells

In this review we will overview novel nanotechnological nanocarrier systems for cancer therapy focusing on recent development in polyelectrolyte capsules for targeted delivery of antineoplastic drugs against cancer cells. Biodegradable polyelectrolyte microcapsules (PMCs) are supramolecular assemblies of particular interest for therapeutic purposes, as they can be enzymatically degraded into viable cells, under physiological conditions. Incorporation of small bioactive molecules into nano-to-microscale delivery systems may increase drug's bioavailability and therapeutic efficacy at single cell level giving desirable targeted therapy. Layer-by-layer (LbL) self-assembled PMCs are efficient microcarriers that maximize drug's exposure enhancing antitumor activity of neoplastic drug in cancer cells. They can be envisaged as novel multifunctional carriers for resistant or relapsed patients or for reducing dose escalation in clinical settings.

Robotic palpation-based mechanical property mapping for diagnosis of prostate cancer

PURPOSE

The aim of this study was to estimate the mechanical properties (elasticity) of normal and cancer prostate tissues and to develop a tissue elasticity map for the diagnosis and localization of prostate cancer.

MATERIALS AND METHODS

A total of 735 sites from 35 radical prostatectomy specimens were used in the experiments using a robotic palpation system, and the elasticities of the specimens were estimated by a tissue characterization algorithm. The estimated elasticities from 21 regions were separated into normal and cancer tissues using the pathological information, and a tissue elasticity map was developed using numerical functions and a nonlinear surface-fitting method.

RESULTS

The mean elastic moduli of the normal and cancer tissues were 15.25 ± 5.88 and 28.80 ± 11.20 kPa, respectively. The base region had the highest elasticity, followed by the medial and apex regions. These results demonstrated the ability to separate the cancer tissue from the normal tissue based on its elastic modulus. The tissue elasticity mapping was carried out using the estimated elasticity and nonlinear surface fitting. The proposed map showed the elasticity and was used to estimate the elastic modulus of the prostate at any given region.

CONCLUSION

Tissue elasticity may be an important indicator of prostate cancer because the pathologic changes alter the tissue properties, including cell integrity and intercellular matrix. This work provides quantitative and objective information for the diagnosis of prostate cancer. In addition, these results may have implications for the localization of prostate cancers.

Detection of populations of amyloid-like protofibrils with different physical properties

We used tapping mode atomic force microscopy to study the morphology of the amyloid protofibrils formed at fixed conditions (low pH with high ionic strength) by self-assembly of the N-terminal domain of the hydrogenase maturation factor HypF. Although all protofibrils in the sample share a beaded structure and similar values of height and width, an accurate analysis of contour length and end-to-end distance and the comparison of experimental data with theoretical predictions based on the worm-like chain model show that two different populations of protofibrils are present. These populations are characterized by different physical properties, such as persistence length, bending rigidity and Young's modulus. Fluorescence quenching measurements on earlier globular intermediates provide an independent evidence of the existence of different populations. The finding that differences in mechanical properties exist even within the same sample of protofibrils indicates the presence of different subpopulations of prefibrillar aggregates with potentially diverse tendencies to react with undesired molecular targets. This study describes a strategy to discriminate between such different subpopulations that are otherwise difficult to identify with conventional analyses.

Effects of Morphology vs. Cell-Cell Interactions on Endothelial Cell Stiffness

Biological processes such as atherogenesis, wound healing, cancer cell metastasis, and immune cell transmigration rely on a delicate balance between Cell-Cell and cell-substrate adhesion. Cell mechanics have been shown to depend on substrate factors such as stiffness and ligand presentation, while the effects of Cell-Cell interactions on the mechanical properties of cells has received little attention. Here, we use atomic force microscopy to measure the Young's modulus of live human umbilical vein endothelial cells (HUVECs). In varying the degree of Cell-Cell contact in HUVECs (single cells, groups, and monolayers), we observe that increased cell stiffness correlates with an increase in cell area. Further, we observe that HUVECs stiffen as they spread onto a glass substrate. When we weaken Cell-Cell junctions (i.e., through a low dose of cytochalasin B or treatment with a VE-cadherin antibody), we observe that cell-substrate adhesion increases, as measured by focal adhesion size and density, and the stiffness of cells within the monolayer approaches that of single cells. Our results suggest that while morphology can roughly be used to predict cell stiffness, Cell-Cell interactions may play a significant role in determining the mechanical properties of individual cells in tissues by careful maintenance of cell tension homeostasis.

Mechanical property characterization of prostate cancer using a minimally motorized indenter in an ex vivo indentation experiment

OBJECTIVES

To measure the mechanical property of prostatic tissues using a minimally motorized indenter and to determine whether measurable differences in mechanical property exist between cancerous and noncancerous tissues in an ex vivo experiment.

METHODS

A total of 552 sites from 46 prostate specimens taken during radical prostatectomy underwent an indentation experiment with a minimally motorized indenter, and the elastic modulus (Young's modulus) of the tissue was estimated.

RESULTS

The mean elastic modulus of the regions containing cancer and noncancer was 24.1 ± 14.5 and 17.0 ± 9.0 kPa, respectively. In the noncancerous regions, the prostate was separated into 5 parts according to the post hoc test for comparing the elastic modulus between the 2 groups: part 1, lateral apex; part 2, medial apex; part 3, lateral-mid; part 4, lateral base; and part 5, medial-mid and medial base. In the regions containing cancer tissue, the prostate was also separated into 5 parts: part 1, lateral apex and medial apex; part 2, lateral-mid; part 3, lateral base; part 4, medial base; and part 5, medial-mid. The elastic modulus was greater in the tissue with a Gleason score of 8 than in the other tissue. The elastic modulus was significantly greater in the tissue with a tumor volume >5 cm(3) than in the other tissue.

CONCLUSIONS

We determined the elastic moduli of prostatic tissue as a quantitative and objective parameter according to the regions of the prostate, the presence of cancerous tissue, the tumor volume, and the Gleason score.

Neuronal elasticity as measured by atomic force microscopy

A cell's form and function is determined to a great extent by its cellular membrane and the underlying cytoskeleton. Understanding changes in the cellular membrane and cytoskeleton can provide insight into aging and disease of the cell. The atomic force microscope (AFM) allows unparalled resolution for the imaging of these cellular components and the ability to probe their mechanical properties. This report describes our progress toward the use of AFM as a tool in neuroscience applications. Elasticity measurements are reported on living chick embryo dorsal root ganglion and sympathetic neurons in vitro. The neuronal cellular body and growth cones regions are examined for variations in cellular maturity. In addition, cellular changes due to exposure to various environmental conditions and neurotoxins are investigated. This report includes data obtained on different AFM systems, using various AFM techniques and thus also provides knowledge of AFM instruments and methodology.

Cleaning AFM colloidal probes by mechanically scrubbing with supersharp "brushes"

Contamination control of atomic force microscope (AFM) tips (including standard but supersharp imaging tips and particle/colloidal probes) is very important for reliable AFM imaging and surface/interface force measurements. Traditional cleaning methods such as plasma, UV-ozone and solvent treatments have their shortcomings. Here, we demonstrate that calibration gratings with supersharp spikes can be employed to scrub away contaminants accumulated on a colloidal sphere probe by scanning the probe against the spikes at high load at constant-force mode. The present method is superior to traditional cleaning methods in several aspects. First, accumulated lump-like organic/inorganic material can be removed; second, removal is non-destructive and highly efficient based on a "targeted removal" strategy; third, removal and probe shape/morphology study can be completed in a single step (we report, to our best knowledge, the first evidence of the wear of the colloidal sphere during force measurements); and fourth, both colloidal/particle probes and standard but supersharp AFM imaging tips can be treated.

Quantitative mechanical evaluation and analysis of Drosophila embryos through the stages of embryogenesis

The fruit fly Drosophila embryo is one of the most important model organisms in genetics and developmental biology research. To better understand the biomechanical properties involved in Drosophila embryo research, this work presents a mechanical characterization of living Drosophila embryos through the stages of embryogenesis. Measurements of the mechanical forces of Drosophila embryos are implemented using a novel, in situ, and minimally invasive force sensing tool with a resolution in the range of microN. The measurements offer an essential understanding of penetration force profiles during the microinjection of Drosophila embryos. Sequentially quantitative evaluation and analysis of the mechanical properties, such as Young's modulus, stiffness, and mechanical impedance of living Drosophila embryos are performed by extracting the force measurements throughout the stages of embryogenesis. Experimental results illustrate the changing mechanical properties of Drosophila embryos during development, and thus mathematical models are proposed. The evaluation provides a critical step toward better understanding of the biomechanical properties of Drosophila embryos during embryogenesis, and could contribute to more efficient and significant genetic and embryonic development research on Drosophila.

The effects of cell sizes, environmental conditions, and growth phases on the strength of individual W303 yeast cells inside ESEM

We performed in situ measurements of mechanical properties of individual W303 wild-type yeast cells by using an integrated environmental scanning electron microscope (ESEM)-nanomanipulator system. Compression experiments to penetrate the cell walls of single cells of different cell sizes (about 3-6 micro m diameter), environmental conditions (600 Pa and 3 mPa), and growth phases (early log, mid log, late log and saturation) were conducted. The compression experiments were performed inside ESEM, embedded with a 7 DOF nanomanipulator with a sharp pyramidal end effector and a cooling stage, i.e., a temperature controller. ESEM itself can control the chamber pressure. Data clearly show an increment in penetration force, i.e., 96 +/- 2, 124 +/- 10, 163 +/- 1, and 234 +/- 14 nN at 3, 4, 5, and 6 micro m cell diameters, respectively. Whereas, 20-fold increase in penetration forces was recorded at different environmental conditions for 5 micro m cell diameter, i.e., 163 +/- 1 nN and 2.95 +/- 0.23 mu N at 600 Pa (ESEM mode) and 3 mPa (HV mode), respectively. This was further confirmed from quantitative estimation of average cell rigidity through the Hertz model, i.e., ESEM mode (3.31 +/- 0.11 MPa) and HV mode (26.02 +/- 3.66 MPa) for 5 micro m cell diameter. Finally, the penetration forces at different cell growth phases also show the increment pattern from log (early, mid, and late) to saturation phases, i.e., 161 +/- 25, 216 +/- 15, 255 +/- 21, and 408 +/- 41 nN, respectively.

Directed positioning of single cells in microwells fabricated by scanning probe lithography and wet etching methods

Scanning probe microscopy has emerged as a powerful technique for mapping the surface morphology of biological specimens, including proteins and cells. In addition to providing measurements of topographic images, it enables the fabrication of micro-/nanostructures with a high spatial resolution. Herein, we demonstrate a simple and reliable method for the preparation of single Escherichia coli bacterial cell arrays using pre-fabricated microwell structures. Using a <100>-oriented silicon substrate, microwell arrays with inclined sidewalls were fabricated by scanning probe lithography and sequential chemical wet etching. The trapping efficiency of single cells was optimized by controlling the geometries of the microwells. These data suggest that single-cell arrays may be applicable in a variety of areas, including drug testing and toxicology, as well as basic cell biology.

Morphology, mechanical properties and viability of encapsulated cells

The morphological and mechanical properties of encapsulated yeast cells (Saccharomyces cerevisiae) have been investigated by atomic force microscopy (AFM). Single living cells have been coated through the alternate deposition of oppositely charged polyelectrolyte (PE) layers. The properties of cells coated by different numbers of PE layers and from PE solutions of different ionic strength have been investigated. AFM imaging indicates an increase in PE coating stability when decreasing the solution ionic strength. The Young's moduli of the different examined systems have been evaluated through a quantitative analysis of force-distance curves by using the Hertz-Sneddon model. The analysis indicates an increase in hybrid system stiffness when lowering the ionic strength of the PE solution. An evaluation of the viability of encapsulated cells was obtained by confocal laser scanning microscopy (CLSM) measurements. CLSM analysis indicates that cells preserve their subcellular structure and duplication capability after encapsulation. By coupling AFM and CLSM data, a correlation between local stiffness and duplication rate was obtained.

Multilayer nanoencapsulation. New approach for immune protection of human pancreatic islets

Immune protection of artificial tissue by means of pancreatic islet microencapsulation is a very ambitious new approach to avoid life-long immune suppression. But the success in the utilization of the alginate-beads with incorporated islets is unfortunately limited. Some of the problems cannot be solved by a two-component system, so polymer encapsulation of the microbeads was tested to improve the properties. In the present paper a pure nanoencapsulation multilayer approach was tested in order to reduce the size of the capsule and possibly apply in the future a multilayer capsule with individual properties in each layer or region of the capsule. Different polycations were attached in a self-assembly process. The advantage in using the surface charge of islets as binding site for the polyions is the guarantee of complete coverage after the second layer. Release of insulin was determined to characterize the function of the islets after encapsulation as well as the permeability of the capsule. Fluorescence microscopy was used to visualize the polyelectrolyte layers. Finally by means of an immune assay, the protection capability of the capsule was proved. In these first measurements the encapsulation with a multilayer nanocapsule was shown to be a possible alternative to the more space-consuming and random islet-trapping microencapsulation.