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by Keyword: stability

Beedle, AEM, Garcia-Manyes, S, (2023). The role of single-protein elasticity in mechanobiology Nature Reviews Materials 8, 10-24

Mechanical force modulates the conformation and function of individual proteins, and this underpins many mechanically driven cellular processes. This Review addresses single-molecule force spectroscopy experiments conducted on proteins with a known role in mechanosensing and mechanotransduction in eukaryotic cells.; In addition to biochemical signals and genetic considerations, mechanical forces are rapidly emerging as a master regulator of human physiology. However, the molecular mechanisms that regulate force-induced functionalities across a wide range of scales, encompassing the cell, tissue or organ levels, are not well understood in comparison. With the advent, development and refining of single-molecule nanomechanical techniques that enable the conformational dynamics of individual proteins under the effect of a calibrated force to be probed, we have begun to acquire a comprehensive knowledge of the diverse physicochemical principles that regulate the elasticity of single proteins. Here, we review the major advances underpinning our current understanding of how the elasticity of single proteins regulates mechanosensing and mechanotransduction. We discuss the present limitations and future challenges of this prolific and burgeoning field.

JTD Keywords: Cadherin adhesion, Energy landscape, Extracellular-matrix protein, Focal adhesion kinase, Mechanical stability, Molecule force spectroscopy, Muscle protein, N2b element, Stranded-dna, Structural basis


Joseph A, Wagner AM, Garay-Sarmiento M, Aleksanyan M, Haraszti T, Söder D, Georgiev VN, Dimova R, Percec V, Rodriguez-Emmenegger C, (2022). Zwitterionic Dendrimersomes: A Closer Xenobiotic Mimic of Cell Membranes Advanced Materials 34, 2206288

Building functional mimics of cell membranes is an important task toward the development of synthetic cells. So far, lipid and amphiphilic block copolymers are the most widely used amphiphiles with the bilayers by the former lacking stability while membranes by the latter are typically characterized by very slow dynamics. Herein, we introduce a new type of Janus dendrimer containing a zwitterionic phosphocholine hydrophilic headgroup (JDPC ) and a 3,5-substituted dihydrobenzoate-based hydrophobic dendron. JDPC self-assembles in water into zwitterionic dendrimersomes (z-DSs) that faithfully recapitulate the cell membrane in thickness, flexibility, and fluidity, while being resilient to harsh conditions and displaying faster pore closing dynamics in the event of membrane rupture. This enables the fabrication of hybrid DSs with components of natural membranes, including pore-forming peptides, structure-directing lipids, and glycans to create raft-like domains or onion vesicles. Moreover, z-DSs can be used to create active synthetic cells with life-like features that mimic vesicle fusion and motility as well as environmental sensing. Despite their fully synthetic nature, z-DSs are minimal cell mimics that can integrate and interact with living matter with the programmability to imitate life-like features and beyond. This article is protected by copyright. All rights reserved.This article is protected by copyright. All rights reserved.

JTD Keywords: biological-membranes, bottom-up synthetic biology, chain, hybrid vesicles, hydroethidine, organization, polymersome, proteins, stability, synthetic cells, thickness, vesicle fusion, vesicle motility, vesicles, zwitterionic dendrimersomes, Biosensor, Biosensors, Bottom-up synthetic biology, Hybrid vesicles, Lipid-bilayers, Synthetic cells, Vesicle fusion, Vesicle motility, Zwitterionic dendrimersomes


Sole-Marti, X, Vilella, T, Labay, C, Tampieri, F, Ginebra, MP, Canal, C, (2022). Thermosensitive hydrogels to deliver reactive species generated by cold atmospheric plasma: a case study with methylcellulose Biomaterials Science 10, 3845-3855

Hydrogels have been recently proposed as suitable materials to generate reactive oxygen and nitrogen species (RONS) upon gas-plasma treatment, and postulated as promising alternatives to conventional cancer therapies. Acting as delivery vehicles that allow a controlled release of RONS to the diseased site, plasma-treated hydrogels can overcome some of the limitations presented by plasma-treated liquids in in vivo therapies. In this work, we optimized the composition of a methylcellulose (MC) hydrogel to confer it with the ability to form a gel at physiological temperatures while remaining in the liquid phase at room temperature to allow gas-plasma treatment with suitable formation of plasma-generated RONS. MC hydrogels demonstrated the capacity for generation, prolonged storage and release of RONS. This release induced cytotoxic effects on the osteosarcoma cancer cell line MG-63, reducing its cell viability in a dose-response manner. These promising results postulate plasma-treated thermosensitive hydrogels as good candidates to provide local anticancer therapies.

JTD Keywords: Cellulose, Phase-separation, Stability, Substituent, Thermoreversible gelation


Riera, Roger, Tauler, Jana, Feiner Gracia, Natàlia, Borrós, Salvador, Fornaguera, Cristina, Albertazzi, Lorenzo, (2022). Complex pBAE Nanoparticle Cell Trafficking: Tracking Both Position and Composition Using Super Resolution Microscopy Chemmedchem 17, e202100633

Nanomedicine emerged some decades ago with the hope to be the solution for most unmet medical needs. However, tracking materials at nanoscale is challenging to their reduced size, below the resolution limit of most conventional techniques. In this context, we propose the use of direct stochastic optical reconstruction microscopy (dSTORM) to study time stability and cell trafficking after transfection of oligopeptide end-modified poly(?-aminoester) (OM-pBAE) nanoparticles. We selected different combinations of cationic end oligopeptides (arginine - R; histidine - H; and lysine - K) among polymer libraries, since the oligopeptide combination demonstrated to be useful for different applications, such as vaccination and gene silencing. We demonstrate that their time evolution as well as their cell uptake and trafficking are dependent on the oligopeptide. This study opens the pave to broad mechanistic studies at nanoscale that could enable a rational selection of specific pBAE nanoparticles composition after determining their stability and cell trafficking.© 2022 The Authors. ChemMedChem published by Wiley-VCH GmbH.

JTD Keywords: cancer nanomedicine, cell trafficking, delivery, direct stochastic optical reconstruction microscopy (dstorm), nanoparticle stability, poly(beta-aminoester) nanoparticles, Direct stochastic optical reconstruction microscopy (dstorm), Poly(?-aminoester) nanoparticles, Poly(beta-amino ester)s


Castillo-Escario Y, Kumru H, Valls-Solé J, García-Alen L, Jané R, Vidal J, (2021). Quantitative evaluation of trunk function and the StartReact effect during reaching in patients with cervical and thoracic spinal cord injury Journal Of Neural Engineering 18,

Objective. Impaired trunk stability is frequent in spinal cord injury (SCI), but there is a lack of quantitative measures for assessing trunk function. Our objectives were to: (a) evaluate trunk muscle activity and movement patterns during a reaching task in SCI patients, (b) compare the impact of cervical (cSCI) and thoracic (tSCI) injuries in trunk function, and (c) investigate the effects of a startling acoustic stimulus (SAS) in these patients. Approach. Electromyographic (EMG) and smartphone accelerometer data were recorded from 15 cSCI patients, nine tSCI patients, and 24 healthy controls, during a reaching task requiring trunk tilting. We calculated the response time (RespT) until pressing a target button, EMG onset latencies and amplitudes, and trunk tilt, lateral deviation, and other movement features from accelerometry. Statistical analysis was applied to analyze the effects of group (cSCI, tSCI, control) and condition (SAS, non-SAS) in each outcome measure. Main results. SCI patients, especially those with cSCI, presented significantly longer RespT and EMG onset latencies than controls. Moreover, in SCI patients, forward trunk tilt was accompanied by significant lateral deviation. RespT and EMG latencies were remarkably shortened by the SAS (the so-called StartReact effect) in tSCI patients and controls, but not in cSCI patients, who also showed higher variability. Significance. The combination of EMG and smartphone accelerometer data can provide quantitative measures for the assessment of trunk function in SCI. Our results show deficits in postural control and compensatory strategies employed by SCI patients, including delayed responses and higher lateral deviations, possibly to improve sitting balance. This is the first study investigating the StartReact responses in trunk muscles in SCI patients and shows that the SAS significantly accelerates RespT in tSCI, but not in cSCI, suggesting an increased cortical control exerted by these patients.

JTD Keywords: accelerometer, electromyography, impairment, individuals, movements, postural stability, reaction-time, reliability, sitting balance, smartphone, spinal cord injury, startle, startreact, strategies, stroke, trunk, Accelerometer, Electromyography, Sitting balance, Smartphone, Spinal cord injury, Startreact, Trunk


Abramov A, Maiti B, Keridou I, Puiggalí J, Reiser O, Díaz DD, (2021). A pH-Triggered Polymer Degradation or Drug Delivery System by Light-Mediated Cis/Trans Isomerization of o-Hydroxy Cinnamates Macromolecular Rapid Communications 42,

A new methodology for the pH-triggered degradation of polymers or for the release of drugs under visible light irradiation based on the cyclization of ortho-hydroxy-cinnamates (oHC) to coumarins is described. The key oHC structural motif can be readily incorporated into the rational design of novel photocleavable polymers via click chemistry. This main-chain moiety undergoes a fast photocleavage when irradiated with 455 nm light provided that a suitable base is added. A series of polyethylene glycol-alt-ortho-hydroxy cinnamate (polyethylene glycol (PEG)(n)-alt-oHC)-based polymers are synthesized and the time-dependent visible-light initiated cleavage of the photoactive monomer and polymer is investigated in solution by a variety of spectroscopic and chromatographic techniques. The photo-degradation behavior of the water-soluble poly(PEG(2000)-alt-oHC) is investigated within a broad pH range (pH = 2.1-11.8), demonstrating fast degradation at pH 11.8, while the stability of the polymer is greatly enhanced at pH 2.1. Moreover, the neat polymer shows long-term stability under daylight conditions, thus allowing its storage without special precautions. In addition, two water-soluble PEG-based drug-carrier molecules (mPEG(2000)-oHC-benzhydrol/phenol) are synthesized and used for drug delivery studies, monitoring the process by UV-vis spectroscopy in an ON/OFF intermittent manner.

JTD Keywords: coumarins, drug delivery, e/z-double bond isomerization, o-hydroxy cinnamates, polymer degradation, Aliphatic compounds, Antioxidant activity, Antitumor, Chromatographic techniques, Chromatography, Cis/trans isomerization, Controlled drug delivery, Coumarin derivatives, Coumarins, Drug delivery, Drug delivery system, E/z-double bond isomerization, Films, Hydrogels, Image enhancement, Light, Long term stability, O-hydroxy cinnamates, Particles, Photoactive monomers, Photodegradation, Polyethylene glycols, Polyethylenes, Polymer degradation, Responsive polymers, Salts, Structural motifs, Synthesis (chemical), Targeted drug delivery, Visible light photocatalysis, Visible-light irradiation


Feiner-Gracia N, Glinkowska Mares A, Buzhor M, Rodriguez-Trujillo R, Samitier Marti J, Amir RJ, Pujals S, Albertazzi L, (2021). Real-Time Ratiometric Imaging of Micelles Assembly State in a Microfluidic Cancer-on-a-Chip Acs Applied Bio Materials 4, 669-681

© 2020 American Chemical Society. The performance of supramolecular nanocarriers as drug delivery systems depends on their stability in the complex and dynamic biological media. After administration, nanocarriers are challenged by physiological barriers such as shear stress and proteins present in blood, endothelial wall, extracellular matrix, and eventually cancer cell membrane. While early disassembly will result in a premature drug release, extreme stability of the nanocarriers can lead to poor drug release and low efficiency. Therefore, comprehensive understanding of the stability and assembly state of supramolecular carriers in each stage of delivery is the key factor for the rational design of these systems. One of the main challenges is that current 2D in vitro models do not provide exhaustive information, as they fail to recapitulate the 3D tumor microenvironment. This deficiency in the 2D model complexity is the main reason for the differences observed in vivo when testing the performance of supramolecular nanocarriers. Herein, we present a real-time monitoring study of self-assembled micelles stability and extravasation, combining spectral confocal microscopy and a microfluidic cancer-on-a-chip. The combination of advanced imaging and a reliable 3D model allows tracking of micelle disassembly by following the spectral properties of the amphiphiles in space and time during the crucial steps of drug delivery. The spectrally active micelles were introduced under flow and their position and conformation continuously followed by spectral imaging during the crossing of barriers, revealing the interplay between carrier structure, micellar stability, and extravasation. Integrating the ability of the micelles to change their fluorescent properties when disassembled, spectral confocal imaging and 3D microfluidic tumor blood vessel-on-a-chip resulted in the establishment of a robust testing platform suitable for real-time imaging and evaluation of supramolecular drug delivery carrier's stability.

JTD Keywords: cancer-on-a-chip, complex, delivery, endothelial-cells, in-vitro, microfluidic, model, nanoparticle, penetration, shear-stress, stability, supramolecular, Cancer-on-a-chip, Cell-culture, Micelle, Microfluidic, Nanoparticle, Stability, Supramolecular


Feiner-Gracia, N., Olea, R. A., Fitzner, R., El Boujnouni, N., Van Asbeck, A. H., Brock, R., Albertazzi, L., (2019). Super-resolution imaging of structure, molecular composition, and stability of single oligonucleotide polyplexes Nano Letters 19, (5), 2784-2792

The successful application of gene therapy relies on the development of safe and efficient delivery vectors. Cationic polymers such as cell-penetrating peptides (CPPs) can condense genetic material into nanoscale particles, called polyplexes, and induce cellular uptake. With respect to this point, several aspects of the nanoscale structure of polyplexes have remained elusive because of the difficulty in visualizing the molecular arrangement of the two components with nanometer resolution. This limitation has hampered the rational design of polyplexes based on direct structural information. Here, we used super-resolution imaging to study the structure and molecular composition of individual CPP-mRNA polyplexes with nanometer accuracy. We use two-color direct stochastic optical reconstruction microscopy (dSTORM) to unveil the impact of peptide stoichiometry on polyplex structure and composition and to assess their destabilization in blood serum. Our method provides information about the size and composition of individual polyplexes, allowing the study of such properties on a single polyplex basis. Furthermore, the differences in stoichiometry readily explain the differences in cellular uptake behavior. Thus, quantitative dSTORM of polyplexes is complementary to the currently used characterization techniques for understanding the determinants of polyplex activity in vitro and inside cells.

JTD Keywords: dSTORM, Gene delivery, Polyplexes, Stability, Super-resolution microscopy


Elosegui-Artola, A., Andreu, I., Beedle, A. E. M., Lezamiz, A., Uroz, M., Kosmalska, A. J., Oria, R., Kechagia, J. Z., Rico-Lastres, P., Le Roux, A. L., Shanahan, C. M., Trepat, X., Navajas, D., Garcia-Manyes, S., Roca-Cusachs, P., (2017). Force triggers YAP nuclear entry by regulating transport across nuclear pores Cell 171, (6), 1397-1410

YAP is a mechanosensitive transcriptional activator with a critical role in cancer, regeneration, and organ size control. Here, we show that force applied to the nucleus directly drives YAP nuclear translocation by decreasing the mechanical restriction of nuclear pores to molecular transport. Exposure to a stiff environment leads cells to establish a mechanical connection between the nucleus and the cytoskeleton, allowing forces exerted through focal adhesions to reach the nucleus. Force transmission then leads to nuclear flattening, which stretches nuclear pores, reduces their mechanical resistance to molecular transport, and increases YAP nuclear import. The restriction to transport is further regulated by the mechanical stability of the transported protein, which determines both active nuclear transport of YAP and passive transport of small proteins. Our results unveil a mechanosensing mechanism mediated directly by nuclear pores, demonstrated for YAP but with potential general applicability in transcriptional regulation. Force-dependent changes in nuclear pores control protein access to the nucleus.

JTD Keywords: Atomic force microscopy, Hippo pathway, Mechanosensing, Mechanotransduction, Molecular mechanical stability, Nuclear mechanics, Nuclear pores, Nuclear transport, Rigidity sensing, Transcription regulation


Obiols-Rabasa, M., Oncins, G., Sanz, F., Tadros, T. F., Solans, C., Levecke, B., Booten, K., Esquena, J., (2017). Investigation of the elastic and adhesion properties of adsorbed hydrophobically modified inulin films on latex particles using Atomic Force Microscopy (AFM) Colloids and Surfaces A: Physicochemical and Engineering Aspects , 524, 185-192

Graft polymer surfactants provide very good colloidal stability because of strong steric repulsions between adsorbed surfactant films. The elastic and adhesion properties of adsorbed hydrophobically modified inulin polymer surfactant (INUTEC NRA) have been directly measured using Atomic Force Microscopy (AFM) measurements. For this purpose, poly(methyl methacrylate/butyl acrylate), P(MMA/BuA), latexes prepared in the presence of the hydrophobically modified inulin (INUTEC NRA) were used. These latexes (diameter 118 nm and polydispersity index of 1.05) showed a very high colloidal stability in water and in the presence of electrolyte (up to 0.2 mol dm−3 KBr). The latexes were deposited on mica, which was silanated to enhance the adhesion of the latex particles to the surface. A silicon nitride tip with approximately 10 nm diameter that also contained an adsorbed layer of surfactant was used in the AFM apparatus. The tip was allowed to approach, contact thereafter the particles with an applied force of 12.5 nN, and finally detach from the film. Both elastic (Young’s) modulus of the film and adhesion force were studied. The results showed that the adsorbed surfactant films are highly elastic and their elastic modulus and adhesion force did not change significantly with the presence of Na2SO4 up to 0.05 mol dm−3. The high elastic contribution to the steric interaction ensures strong repulsion between the latex particles both in water and at high electrolyte concentrations. In addition, the lack of dependence of adhesion force on electrolyte concentration ensures uniform deposition of the latex particles on a flat substrate as for example in coating applications. These results show the advantages of using a graft polymer surfactant for enhancing the stability of particle suspensions, as illustrated in previous investigations.

JTD Keywords: AFM, Colloidal stability, Interaction forces, Steric repulsion


Tassinari, E., Aznar, S., Urcola, I., Prieto, A., Hüttener, M., Juárez, A., (2016). The incC sequence is required for R27 plasmid stability Frontiers in Microbiology 7, (6), Article 629

IncHI plasmids account for multiple antimicrobial resistance in Salmonella and other enterobacterial genera. These plasmids are generally very stable in their bacterial hosts. R27 is the archetype of IncHI1 plasmids. A high percentage of the R27-encoded open reading frames (ORFs) (66.7%) do not show similarity to any known ORFs. We performed a deletion analysis of all non-essential R27 DNA sequences to search for hitherto non-identified plasmid functions that might be required for plasmid stability. We report the identification of a short DNA sequence (incC) that is essential for R27 stability. That region contains several repeats (incC repeats), belongs to one of the three-plasmid replicons (R27 FIA-like) and is targeted by the R27 E protein. Deletion of the incC sequence drastically reduces R27 stability both in Escherichia coli and in Salmonella, the effect being more pronounced in this latter species. Interfering with incC-E protein interaction must lead to a reduced IncHI1 plasmid stability, and may represent a new approach to combat antimicrobial resistance.

JTD Keywords: Antimicrobial resistance, E protein, IncC, IncHI1 plasmids, Plasmid R27, Plasmid stability


Andrade, F., Fonte, P., Oliva, M., Videira, M., Ferreira, D., Sarmento, B., (2015). Solid state formulations composed by amphiphilic polymers for delivery of proteins: Characterization and stability International Journal of Pharmaceutics 486, (1-2), 195-206

Abstract Nanocomposite powders composed by polymeric micelles as vehicles for delivery proteins were developed in this work, using insulin as model protein. Results showed that size and polydispersity of micelles were dependent on the amphiphilic polymer used, being all lower than 300 nm, while all the formulations displayed spherical shape and surface charge close to neutrality. Percentages of association efficiency and loading capacity up to 94.15 ± 3.92 and 8.56 ± 0.36, respectively, were obtained. X-ray photoelectron spectroscopy (XPS) measurements confirmed that insulin was partially present at the hydrophilic shell of the micelles. Lyophilization did not significantly change the physical characteristics of micelles, further providing easily dispersion when in contact to aqueous medium. The native-like conformation of insulin was maintained at high percentages (around 80%) after lyophilization as indicated by Fourier transform infrared spectroscopy (FTIR) and far-UV circular dichroism (CD). Moreover, Raman spectroscopy did not evidenced significant interactions among the formulation components. The formulations shown to be physically stable upon storage up to 6 months both at room-temperature (20 C) and fridge (4 C), with only a slight loss (maximum of 15%) of the secondary structure of the protein. Among the polymers tested, Pluronic® F127 produced the carrier formulations more promising for delivery of proteins.

JTD Keywords: Amphiphilic polymers, Insulin, Lyophilization, Polymeric micelles, Stability


Rajasekaran, Vijaykumar, Aranda, Joan, Casals, Alicia, Pons, Jose L., (2015). An adaptive control strategy for postural stability using a wearable robot Robotics and Autonomous Systems , 73, 16-23

Abstract Wearable robots are expected to expand the use of robotics in rehabilitation since they can widen the assistance application context. An important aspect of a rehabilitation therapy, in terms of lower extremity assistance, is balance control. In this article, we propose and evaluate an adaptive control strategy for robotic rehabilitation therapies to guarantee static stability using a wearable robot. Postural balance control can be implemented either acting on the hip, on the ankle joint or on both, depending on the kind of perturbation acting on the subject: internal or external. Internal perturbations can be produced by any voluntary movement of the body, such as bending the trunk. External perturbations, in the form of an impact force, are applied by the exoskeleton without any prior notice to observe the proactive response of the subject. We have used a 6 degree of freedom planar lower limb exoskeleton, H1, to perform this analysis. The developed control strategy has been designed to provide the necessary assistance, related to balance recovery and postural stability, under the “Assist-as-needed” paradigm. The interaction forces between orthosis and subject are monitored, as they play a relevant role in the definition of assistive and resistive movements to be applied to the joints. The proposed method has been tested with 5 healthy subjects in presence of internal and external disturbances. The results demonstrate that knowing the stability limit of each subject, in combination with a therapeutically selected scaling factor, the proposed adaptive control helps in providing an effective assistance in therapy. This method is efficient in handling the individual and combined effect of external perturbations acting on any joint movements.

JTD Keywords: Exoskeleton controls, Postural stability, Balance controls, Adaptive control


Mir, M., Lugo, R., Tahirbegi, I. B., Samitier, J., (2014). Miniaturizable ion-selective arrays based on highly stable polymer membranes for biomedical applications Sensors 14, (7), 11844-11854

Poly(vinylchloride) (PVC) is the most common polymer matrix used in the fabrication of ion-selective electrodes (ISEs). However, the surfaces of PVC-based sensors have been reported to show membrane instability. In an attempt to overcome this limitation, here we developed two alternative methods for the preparation of highly stable and robust ion-selective sensors. These platforms are based on the selective electropolymerization of poly(3,4-ethylenedioxythiophene) (PEDOT), where the sulfur atoms contained in the polymer covalently interact with the gold electrode, also permitting controlled selective attachment on a miniaturized electrode in an array format. This platform sensor was improved with the crosslinking of the membrane compounds with poly(ethyleneglycol) diglycidyl ether (PEG), thus also increasing the biocompatibility of the sensor. The resulting ISE membranes showed faster signal stabilization of the sensor response compared with that of the PVC matrix and also better reproducibility and stability, thus making these platforms highly suitable candidates for the manufacture of robust implantable sensors.

JTD Keywords: Biomedicine, Electrochemistry, Endoscope, Implantable device, Ion-selective electrode (ISE) sensor, Ischemia, pH detection, Biocompatibility, Chemical sensors, Electrochemistry, Electrodes, Electropolymerization, Endoscopy, Functional polymers, Implants (surgical), Ion selective electrodes, Medical applications, Polyvinyl chlorides, Stabilization, Biomedical applications, Biomedicine, Implantable devices, Ion selective sensors, Ischemia, Membrane instability, pH detection, Poly(3 ,4 ethylenedioxythiophene) (PEDOT), Ion selective membranes


Redondo-Morata, L., Giannotti, M. I., Sanz, F., (2014). Structural impact of cations on lipid bilayer models: Nanomechanical properties by AFM-force spectroscopy Molecular Membrane Biology , 31, (1), 17-28

Atomic Force Microscopy (AFM) has become an invaluable tool for studying the micro-and nanoworlds. As a stand-alone, high-resolution imaging technique and force transducer, it defies most other surface instrumentation in ease of use, sensitivity and versatility. The main strength of AFM relies on the possibility to operate in an aqueous environment on a wide variety of biological samples, from single molecules-DNA or proteins-to macromolecular assemblies like biological membranes. Understanding the effect of mechanical stress on membranes is of primary importance in biophysics, since cells are known to perform their function under a complex combination of forces. In the later years, AFM-based Force-Spectroscopy (AFM-FS) has provided a new vista on membrane mechanics in a confined area within the nanometer realm, where most of the specific molecular interactions take place. Lipid membranes are electrostatically charged entities that physiologically coexist with electrolyte solutions. Thus, specific interactions with ions are a matter of considerable interest. The distribution of ions in the solution and their interaction with the membranes are factors that substantially modify the structure and dynamics of the cell membranes. Furthermore, signaling processes are modified by the membrane capability of retaining ions. Supported Lipid Bilayers (SLBs) are a versatile tool to investigate phospholipid membranes mimicking biological surfaces. In the present contribution, we review selected experiments on the mechanical stability of SLBs as models of lipid membranes by means of AFM-FS, with special focus on the effect of cations and ionic strength in the overall nanomechanical stability.

JTD Keywords: Atomic force microscopy, Cations, Force spectroscopy, Lipid bilayer, Mechanical stability


Redondo-Morata, L., Giannotti, M. I., Sanz, F., (2012). AFM-based force-clamp monitors lipid bilayer failure kinetics Langmuir 28, (15), 6403-6410

The lipid bilayer rupture phenomenon is here explored by means of atomic force microscopy (AFM)-based force clamp, for the first time to our knowledge, to evaluate how lipid membranes respond when compressed under an external constant force, in the range of nanonewtons. Using this method, we were able to directly quantify the kinetics of the membrane rupture event and the associated energy barriers, for both single supported bilayers and multibilayers, in contradistinction to the classic studies performed at constant velocity. Moreover, the affected area of the membrane during the rupture process was calculated using an elastic deformation model. The elucidated information not only contributes to a better understanding of such relevant process, but also proves the suitability of AFM-based force clamp to study model structures as lipid bilayers. These findings on the kinetics of lipid bilayers rupture could be extended and applied to the study of other molecular thin films. Furthermore, systems of higher complexity such as models mimicking cell membranes could be studied by means of AFM-based force-clamp technique.

JTD Keywords: Chain-Length, Spectroscopy, Nanomechanics, Microscopy, Elasticity, Stability, Membranes, Reveals, Fusion, Ions


Valle-Delgado, J. J., Molina-Bolívar, J. A., Galisteo-González, F., Gálvez-Ruiz, M. J., (2011). Evidence of hydration forces between proteins Current Opinion in Colloid and Interface Science , 16, (6), 572-578

Proteins are fundamental molecules in biology that are also involved in a wide range of industrial and biotechnological processes. Consequently, many works in the literature have been devoted to the study of protein-protein and protein-surface interactions in aqueous solutions. The results have been usually interpreted within the frame of the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for colloidal systems. However, against the DLVO predictions, striking evidence of repulsive forces between proteins at high salt concentrations has been observed in different works based on the analysis of the second virial coefficient or on the direct measurement of protein interaction with an atomic force microscope. Hydration forces due to the adsorption of hydrated cations onto the negatively charged protein surfaces have been invoked to rationalize this anomalous repulsion. The hydration forces between proteins provide protein-covered particles with a non-DLVO colloidal stability at high salt concentrations, as different studies in the literature has proven. This review summarizes the most relevant results published so far on the presence of hydration forces between proteins and protein-coated colloidal particles.

JTD Keywords: Colloidal particles, Colloidal stability, Hydrated ions, Hydration forces, Proteins


Falasconi, M., Gutierrez, A., Pardo, M., Sberveglieri, G., Marco, S., (2010). A stability based validity method for fuzzy clustering Pattern Recognition , 43, (4), 1292-1305

An important goal in cluster analysis is the internal validation of results using an objective criterion. Of particular relevance in this respect is the estimation of the optimum number of clusters capturing the intrinsic structure of your data. This paper proposes a method to determine this optimum number based on the evaluation of fuzzy partition stability under bootstrap resampling. The method is first characterized on synthetic data with respect to hyper-parameters, like the fuzzifier, and spatial clustering parameters, such as feature space dimensionality, clusters degree of overlap, and number of clusters. The method is then validated on experimental datasets. Furthermore, the performance of the proposed method is compared to that obtained using a number of traditional fuzzy validity rules based on the cluster compactness-to-separation criteria. The proposed method provides accurate and reliable results, and offers better generalization capabilities than the classical approaches.

JTD Keywords: Fuzzy c-means, Cluster validity, Number of clusters, Cluster stability


Pla, M., Fernandez, Javier G., Mills, C. A., Martinez, E., Samitier, J., (2007). Micro/nanopatterning of proteins via contact printing using high aspect ratio PMMA stamps and NanoImprint apparatus Langmuir 23, (16), 8614-8618

Micro- and nanoscale protein patterns have been produced via a new contact printing method using a nanoimprint lithography apparatus. The main novelty of the technique is the use of poly(methyl methacrylate) (PMMA) instead of the commonly used poly(dimethylsiloxane) (PDMS) stamps. This avoids printing problems due to roof collapse, which limits the usable aspect ratio in microcontact printing to 10:1. The rigidity of the PMMA allows protein patterning using stamps with very high aspect ratios, up to 300 in this case. Conformal contact between the stamp and the substrate is achieved because of the homogeneous pressure applied via the nanoimprint lithography instrument, and it has allowed us to print lines of protein similar to 150 nm wide, at a 400 nm period. This technique, therefore, provides an excellent method for the direct printing of high-density sub-micrometer scale patterns, or, alternatively, micro-/nanopatterns spaced at large distances. The controlled production of these protein patterns is a key factor in biomedical applications such as cell-surface interaction experiments and tissue engineering.

JTD Keywords: Soft lithography, Cell-adhesion, Microstructures, Fabrication, Stability, Patterns


Mills, C. A., Pla, M., Martin, C., Lee, M., Kuphal, M., Sisquella, X., Martinez, E., Errachid, A., Samitier, J., (2007). Structured thin organic active layers and their use in electrochemical biosensors Measurement & Control , 40, (3), 88-91