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Gumí-Audenis, B., Giannotti, M. I., (2019). Structural and mechanical characterization of supported model membranes by AFM Biomimetic Lipid Membranes: Fundamentals, Applications, and Commercialization (ed. Kök, Fatma N., Arslan Yildiz, Ahu, Inci, Fatih), Springer International Publishing (Cham, Germany) , 1-27

Several cellular processes, including adhesion, signaling and transcription, endocytosis, and membrane resealing, among others, involve conformational changes such as bending, vesiculation, and tubulation. These mechanisms generally involve membrane separation from the cytoskeleton as well as strong bending, for which the membrane chemical composition and physicochemical properties, often highly localized and dynamic, are key players. The mechanical role of the lipid membrane in force triggered (or sensing) mechanisms in cells is important, and understanding the lipid bilayers’ physical and mechanical properties is essential to comprehend their contribution to the overall membrane. Atomic force microscopy (AFM)-based experimental approaches have been to date very valuable to deepen into these aspects. As a stand-alone, high-resolution imaging technique and force transducer with the possibility to operate in aqueous environment, it defies most other surface instrumentation in ease of use, sensitivity and versatility. In this chapter, we introduce the different AFM-based methods to assess topological and nanomechanical information on model membranes, specifically to supported lipid bilayers (SLBs), including several examples ranging from pure phospholipid homogeneous bilayers to multicomponent and phase-separated SLBs, increasing the bilayer complexity, in the direction of mimicking biological membranes.

Keywords: Atomic force microscopy, Force spectroscopy, Model membranes, Nanomechanics, Supported lipid bilayers


Sehgal, Poonam, Kong, Xinyu, Wu, Jun, Sunyer, Raimon, Trepat, Xavier, Leckband, Deborah, (2018). Epidermal growth factor receptor and integrins control force-dependent vinculin recruitment to E-cadherin junctions Journal of Cell Science 131, (6), jcs206656

This study reports novel findings that link E-cadherin (also known as CDH1)-mediated force-transduction signaling to vinculin targeting to intercellular junctions via epidermal growth factor receptor (EGFR) and integrins. These results build on previous findings that demonstrated that mechanically perturbed E-cadherin receptors activate phosphoinositide 3-kinase and downstream integrins in an EGFR-dependent manner. Results of this study show that this EGFR-mediated kinase cascade controls the force-dependent recruitment of vinculin to stressed E-cadherin complexes – a key early signature of cadherin-based mechanotransduction. Vinculin targeting requires its phosphorylation at tyrosine 822 by Abl family kinases (hereafter Abl), but the origin of force-dependent Abl activation had not been identified. We now present evidence that integrin activation, which is downstream of EGFR signaling, controls Abl activation, thus linking E-cadherin to Abl through a mechanosensitive signaling network. These findings place EGFR and integrins at the center of a positive-feedback loop, through which force-activated E-cadherin signals regulate vinculin recruitment to cadherin complexes in response to increased intercellular tension.This article has an associated First Person interview with the first author of the paper.

Keywords: Cadherin, Epidermal growth factor receptor, Force transduction, Magnetic twisting cytometry, Vinculin, Integrin


Martí Coma-Cros, Elisabet, Biosca, Arnau, Lantero, Elena, Manca, Maria, Caddeo, Carla, Gutiérrez, Lucía, Ramírez, Miriam, Borgheti-Cardoso, Livia, Manconi, Maria, Fernàndez-Busquets, Xavier, (2018). Antimalarial activity of orally administered curcumin incorporated in Eudragit®-containing liposomes International Journal of Molecular Sciences 19, (5), 1361

Curcumin is an antimalarial compound easy to obtain and inexpensive, having shown little toxicity across a diverse population. However, the clinical use of this interesting polyphenol has been hampered by its poor oral absorption, extremely low aqueous solubility and rapid metabolism. In this study, we have used the anionic copolymer Eudragit® S100 to assemble liposomes incorporating curcumin and containing either hyaluronan (Eudragit-hyaluronan liposomes) or the water-soluble dextrin Nutriose® FM06 (Eudragit-nutriosomes). Upon oral administration of the rehydrated freeze-dried nanosystems administered at 25/75 mg curcumin·kg−1·day−1, only Eudragit-nutriosomes improved the in vivo antimalarial activity of curcumin in a dose-dependent manner, by enhancing the survival of all Plasmodium yoelii-infected mice up to 11/11 days, as compared to 6/7 days upon administration of an equal dose of the free compound. On the other hand, animals treated with curcumin incorporated in Eudragit-hyaluronan liposomes did not live longer than the controls, a result consistent with the lower stability of this formulation after reconstitution. Polymer-lipid nanovesicles hold promise for their development into systems for the oral delivery of curcumin-based antimalarial therapies.

Keywords: Malaria, Curcumin, Nanomedicine, Oral administration, Lipid nanovesicles, Eudragit, Nutriose, Hyaluronan, Plasmodium yoelii


Dols-Perez, Aurora, Fumagalli, Laura, Gomila, Gabriel, (2018). Interdigitation in spin-coated lipid layers in air Colloids and Surfaces B: Biointerfaces 172, 400-406

In this study, we show that dry saturated phospholipid layers prepared by the spin-coating technique could present thinner regions associated to interdigitated phases under some conditions. The morphological characteristics of lipid layers of saturated phosphocholines, such as dilauroylphosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC), have been measured by Atomic Force Microscopy and revealed that the presence of interdigitated regions is not induced by the same parameters that induce them in hydrated samples. To achieve these results the effect of the lipid hidrocabonated chain length, the presence of alcohol in the coating solution, the spinning velocity and the presence of cholesterol were tested. We showed that DPPC and DSPC bilayers, on the one side, can show structures with similar height than interdigitated regions observed in hydrated samples, while, on the other side, DLPC and DMPC tend to show no evidence of interdigitation. Results indicate that the presence of interdigitated areas is due to the presence of lateral tensions and, hence, that they can be eliminated by releasing these tensions by, for instance, the addition of cholesterol. These results demonstrate that interdigitation in lipid layers is a rather general phenomena and can be observed in lipid bilayers in dry conditions.

Keywords: Spin-coating, Lipid layers, Atomic Force Microscopy, Interdigitation


Crespo-Villanueva, Adrián, Gumí-Audenis, Berta, Sanz, Fausto, Artzner, Franck, Mériadec, Cristelle, Rousseau, Florence, Lopez, Christelle, Giannotti, M. I., Guyomarc'h, Fanny, (2018). Casein interaction with lipid membranes: Are the phase state or charge density of the phospholipids affecting protein adsorption? Biochimica et Biophysica Acta (BBA) - Biomembranes 1860, (12), 2588-2598

Casein micelles are ~200 nm electronegative particles that constitute 80 wt% of the milk proteins. During synthesis in the lactating mammary cells, caseins are thought to interact in the form of ~20 nm assemblies, directly with the biological membranes of the endoplasmic reticulum and/or the Golgi apparatus. However, conditions that drive this interaction are not yet known. Atomic force microscopy imaging and force spectroscopy were used to directly observe the adsorption of casein particles on supported phospholipid bilayers with controlled compositions to vary their phase state and surface charge density, as verified by X-ray diffraction and zetametry. At pH 6.7, the casein particles adsorbed onto bilayer phases with zwitterionic and liquid-disordered phospholipid molecules, but not on phases with anionic or ordered phospholipids. Furthermore, the presence of adsorbed caseins altered the stability of the yet exposed bilayer. Considering their respective compositions and symmetry/asymmetry, these results cast light on the possible interactions of casein assemblies with the organelles’ membranes of the lactating mammary cells.

Keywords: Casein proteins, Phospholipid membrane, Supported lipid bilayer, Atomic force microscopy


Caddeo, C., Manca, M. L., Matos, M., Gutierrez, G., Díez-Sales, O., Peris, J. E., Usach, I., Fernàndez-Busquets, X., Fadda, A. M., Manconi, M., (2017). Functional response of novel bioprotective poloxamer-structured vesicles on inflamed skin Nanomedicine: Nanotechnology, Biology, and Medicine 13, (3), 1127-1136

Resveratrol and gallic acid, a lipophilic and a hydrophilic phenol, were co-loaded in innovative, biocompatible nanovesicles conceived for ensuring the protection of the skin from oxidative- and inflammatory-related affections. The basic vesicles, liposomes and glycerosomes, were produced by a simple, one-step method involving the dispersion of phospholipid and phenols in water or water/glycerol blend, respectively. Liposomes and glycerosomes were modified by the addition of poloxamer, a stabilizer and viscosity enhancer, thus obtaining viscous or semisolid dispersions of structured vesicles. The vesicles were spherical, unilamellar and small in size (~70 nm in diameter). The superior ability of the poloxamer-structured vesicles to promote the accumulation of both phenols in the skin was demonstrated, as well as their low toxicity and great ability to protect fibroblasts from chemically-induced oxidative damage. The in vivo administration of the vesicular phenols on TPA (phorbol ester)-exposed skin led to a significant reduction of oedema and leukocyte infiltration.

Keywords: Fibroblasts, Mice, Phenol, Phospholipid vesicle, Poloxamer, Skin inflammation


Vitonyte, J., Manca, M. L., Caddeo, C., Valenti, D., Peris, J. E., Usach, I., Nacher, A., Matos, M., Gutiérrez, G., Orrù, G., Fernàndez-Busquets, X., Fadda, A. M., Manconi, M., (2017). Bifunctional viscous nanovesicles co-loaded with resveratrol and gallic acid for skin protection against microbial and oxidative injuries European Journal of Pharmaceutics and Biopharmaceutics , 114, 278-287

Resveratrol and gallic acid were co-loaded in phospholipid vesicles aiming at protecting the skin from external injuries, such as oxidative stress and microbial infections. Liposomes were prepared using biocompatible phospholipids dispersed in water. To improve vesicle stability and applicability, the phospholipids and the phenols were dispersed in water/propylene glycol or water/glycerol, thus obtaining PEVs and glycerosomes, respectively. The vesicles were characterized by size, morphology, physical stability, and their therapeutic efficacy was investigated in vitro. The vesicles were spherical, unilamellar and small in size: liposomes and glycerosomes were around 70 nm in diameter, while PEVs were larger (∼170 nm). The presence of propylene glycol or glycerol increased the viscosity of the vesicle systems, positively affecting their stability. The ability of the vesicles to promote the accumulation of the phenols (especially gallic acid) in the skin was demonstrated, as well as their low toxicity and great ability to protect keratinocytes and fibroblasts from oxidative damage. Additionally, an improvement of the antimicrobial activity of the phenols was shown against different skin pathogens. The co-loading of resveratrol and gallic acid in modified phospholipid vesicles represents an innovative, bifunctional tool for preventing and treating skin affections.

Keywords: Fibroblasts, Keratinocytes, Phenol, Phospholipid vesicle, Skin pathogens


Gumí-Audenis, Berta, Costa, Luca, Carlá, Francesco, Comin, Fabio, Sanz, Fausto, Giannotti, M. I., (2016). Structure and nanomechanics of model membranes by atomic force microscopy and spectroscopy: Insights into the role of cholesterol and sphingolipids Membranes , 6, (4), 58

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

Keywords: Atomic force microscopy, Force spectroscopy, Lipid membranes, Supported lipid bilayers, Nanomechanics, Cholesterol, Sphingolipids, Membrane structure, XR-AFM combination


Vila, M., García, A., Girotti, A., Alonso, M., Rodríguez-Cabello, J. C., González-Vázquez, A., Planell, J. A., Engel, E., Buján, J., Garcíaa-Honduvilla, N., Vallet-Regí, M., (2016). 3D silicon doped hydroxyapatite scaffolds decorated with Elastin-like Recombinamers for bone regenerative medicine Acta Biomaterialia 45, 349-356

The current study reports on the manufacturing by rapid prototyping technique of three-dimensional (3D) scaffolds based on silicon substituted hydroxyapatite with Elastin-like Recombinamers (ELRs) functionalized surfaces. Silicon doped hydroxyapatite (Si-HA), with Ca10(PO4)5.7(SiO4)0.3(OH)1.7h0.3 nominal formula, was surface functionalized with two different types of polymers designed by genetic engineering: ELR-RGD that contain cell attachment specific sequences and ELR-SNA15/RGD with both hydroxyapatite and cells domains that interact with the inorganic phase and with the cells, respectively. These hybrid materials were subjected to in vitro assays in order to clarify if the ELRs coating improved the well-known biocompatible and bone regeneration properties of calcium phosphates materials. The in vitro tests showed that there was a total and homogeneous colonization of the 3D scaffolds by Bone marrow Mesenchymal Stromal Cells (BMSCs). In addition, the BMSCs were viable and able to proliferate and differentiate into osteoblasts. Statement of Significance Bone tissue engineering is an area of increasing interest because its main applications are directly related to the rising life expectancy of the population, which promotes higher rates of several bone pathologies, so innovative strategies are needed for bone tissue regeneration therapies. Here we use the rapid prototyping technology to allow moulding ceramic 3D scaffolds and we use different bio-polymers for the functionalization of their surfaces in order to enhance the biological response. Combining the ceramic material (silicon doped hydroxyapatite, Si-HA) and the Elastin like Recombinamers (ELRs) polymers with the presence of the integrin-mediate adhesion domain alone or in combination with SNA15 peptide that possess high affinity for hydroxyapatite, provided an improved Bone marrow Mesenchymal Stromal Cells (BMSCs) differentiation into osteoblastic linkage.

Keywords: Bone marrow Mesenchymal Stromal Cells (BMSCs), Bone repair, Elastin-like Recombinamers (ELRs), Rapid prototyped 3D scaffolds, Silicon doped hydroxyapatite (Si-HA), Tissue engineering


Valle-Delgado, J. J., Fernàndez-Busquets, X., (2016). Rapid diagnostic tests for malaria: Past, present and future Future Microbiology , 11, (11), 1379-1382

Manca, M. L., Castangia, I., Zaru, M., Nácher, A., Valenti, D., Fernàndez-Busquets, X., Fadda, A. M., Manconi, M., (2015). Development of curcumin loaded sodium hyaluronate immobilized vesicles (hyalurosomes) and their potential on skin inflammation and wound restoring Biomaterials 71, 100-109

In the present work new highly biocompatible nanovesicles were developed using polyanion sodium hyaluronate to form polymer immobilized vesicles, so called hyalurosomes. Curcumin, at high concentration was loaded into hyalurosomes and physico-chemical properties and in vitro/in vivo performances of the formulations were compared to those of liposomes having the same lipid and drug content. Vesicles were prepared by direct addition of dispersion containing the polysaccharide sodium hyaluronate and the polyphenol curcumin to a commercial mixture of soy phospholipids, thus avoiding the use of organic solvents. An extensive study was carried out on the physico-chemical features and properties of curcumin-loaded hyalurosomes and liposomes. Cryogenic transmission electron microscopy and small-angle X-ray scattering showed that vesicles were spherical, uni- or oligolamellar and small in size (112-220 nm). The in vitro percutaneous curcumin delivery studies on intact skin showed an improved ability of hyalurosomes to favour a fast drug deposition in the whole skin. Hyalurosomes as well as liposomes were biocompatible, protected in vitro human keratinocytes from oxidative stress damages and promoted tissue remodelling through cellular proliferation and migration. Moreover, in vivo tests underlined a good effectiveness of curcumin-loaded hyalurosomes to counteract 12-O-tetradecanoilphorbol (TPA)-produced inflammation and injuries, diminishing oedema formation, myeloperoxydase activity and providing an extensive skin reepithelization. Thanks to the one-step and environmentally-friendly preparation method, component biocompatibility and safety, good in vitro and in vivo performances, the hyalurosomes appear as promising nanocarriers for cosmetic and pharmaceutical applications.

Keywords: Cell oxidative stress, Hyaluronic acid/Hyaluronan, Phospholipid vesicles, Polyphenols, Skin inflammation, Wound healing


Castangia, I., Nácher, A., Caddeo, C., Merino, V., Díez-Sales, O., Catalán-Latorre, A., Fernàndez-Busquets, X., Fadda, A. M., Manconi, M., (2015). Therapeutic efficacy of quercetin enzyme-responsive nanovesicles for the treatment of experimental colitis in rats Acta Biomaterialia 13, 216-227

Biocompatible quercetin nanovesicles were developed by coating polyethylene glycol-containing vesicles with chitosan and nutriose, aimed at targeting the colon. Uncoated and coated vesicles were prepared using hydrogenated soy phosphatidylcholine and quercetin, a potent natural anti-inflammatory and antioxidant drug. Physicochemical characterization was carried out by light scattering, cryogenic microscopy and X-ray scattering, the results showing that vesicles were predominantly multilamellar and around 130 nm in size. The in vitro release of quercetin was investigated under different pH conditions simulating the environment of the gastrointestinal tract, and confirmed that the chitosan/nutriose coating improved the gastric resistance of vesicles, making them a potential carrier system for colon delivery. The preferential localization of fluorescent vesicles in the intestine was demonstrated using the In Vivo FX PRO Imaging System. Above all, a marked amelioration of symptoms of 2,4,6-trinitrobenzenesulfonic acid-induced colitis was observed in animals treated with quercetin-loaded coated vesicles, favoring the restoration of physiological conditions. Therefore, quercetin-loaded chitosan/nutriose-coated vesicles can represent a valuable therapeutic tool for the treatment of chronic intestinal inflammatory diseases, and presumably a preventive system, due to the synergic action of antioxidant quercetin and beneficial prebiotic effects of the chitosan/nutriose complex.

Keywords: Chitosan/nutriose complex, Colon targeting, Phospholipid vesicles, Quercetin, Rat colitis


Gumí-Audenis, B., Carlà, F., Vitorino, M. V., Panzarella, A., Porcar, L., Boilot, M., Guerber, S., Bernard, P., Rodrigues, M. S., Sanz, F., Giannotti, M. I., Costa, L., (2015). Custom AFM for X-ray beamlines: in situ biological investigations under physiological conditions Journal of Synchrotron Radiation , 22, 1364-1371

A fast atomic force microscope (AFM) has been developed that can be installed as a sample holder for grazing-incidence X-ray experiments at solid/gas or solid/liquid interfaces. It allows a wide range of possible investigations, including soft and biological samples under physiological conditions (hydrated specimens). The structural information obtained using the X-rays is combined with the data gathered with the AFM (morphology and mechanical properties), providing a unique characterization of the specimen and its dynamics in situ during an experiment. In this work, lipid monolayers and bilayers in air or liquid environment have been investigated by means of AFM, both with imaging and force spectroscopy, and X-ray reflectivity. In addition, this combination allows the radiation damage induced by the beam on the sample to be studied, as has been observed on DOPC and DPPC supported lipid bilayers under physiological conditions.

Keywords: In situ atomic force microscopy, Grazing-incidence scattering and reflectivity, Radiation damage, Model lipid membranes


Palleja, T., Balsa, R., Tresanchez, M., Moreno, J., Teixido, M., Font, D., Marco, S., Pomareda, V., Palacin, J., (2014). Corridor gas-leak localization using a mobile Robot with a photo ionization detector sensor Sensor Letters , 12, (6-7), 974-977

The use of an autonomous mobile robot to locate gas-leaks and air quality monitoring in indoor environments are promising tasks that will avoid risky human operations. However, these are challenging tasks due to the chaotic gas profile propagation originated by uncontrolled air flows. This paper proposes the localization of an acetone gas-leak in a 44 m-length indoor corridor with a mobile robot equipped with a PID sensor. This paper assesses the influence of the mobile robot velocity and the relative height of the PID sensor in the profile of the measurements. The results show weak influence of the robot velocity and strong influence of the relative height of the PID sensor. An estimate of the gas-leak location is also performed by computing the center of mass of the highest gas concentrations.

Keywords: Gas source detection, LIDAR sensor, Mobile robot, PID sensor, SLAM, Acetone, Air quality, Gases, Indoor air pollution, Mobile robots, Robots, Air quality monitoring, Autonomous Mobile Robot, Gas sources, Indoor environment, Leak localization, LIDAR sensors, Profile propagation, SLAM, Ionization of gases


Fernàndez-Busquets, X., (2014). Toy kit against malaria: Magic bullets, LEGO, Trojan horses and Russian dolls Therapeutic Delivery , 5, (10), 1049-1052

Dalmases, M., Torres, M., Márquez-Kisinousky, L., Almendros, I., Planas, A. M., Embid, C., Martínez-Garcia, M. A., Navajas, D., Farré, R., Montserrat, J. M., (2014). Brain tissue hypoxia and oxidative stress induced by obstructive apneas is different in young and aged rats Sleep , 37, (7), 1249-1256

Study Objectives: To test the hypotheses that brain oxygen partial pressure (PtO2) in response to obstructive apneas changes with age and that it might lead to different levels of cerebral tissue oxidative stress. Design: Prospective controlled animal study. Setting: University laboratory. Participants: Sixty-four male Wistar rats: 32 young (3 mo old) and 32 aged (18 mo). Interventions: Protocol 1: Twenty-four animals were subjected to obstructive apneas (50 apneas/h, lasting 15 sec each) or to sham procedure for 50 min. Protocol 2: Forty rats were subjected to obstructive apneas or sham procedure for 4 h. Measurements and Results: Protocol 1: Real-time PtO2 measurements were performed using a fast-response oxygen microelectrode. During successive apneas cerebral cortex PtO2 presented a different pattern in the two age groups; there was a fast increase in young rats, whereas it remained without significant changes between the beginning and the end of the protocol in the aged group. Protocol 2: Brain oxidative stress assessed by lipid peroxidation increased after apneas in young rats (1.34 ± 0.17 nmol/mg of protein) compared to old ones (0.63 ± 0.03 nmol/mg), where a higher expression of antioxidant enzymes was observed. Conclusions: The results suggest that brain oxidative stress in aged rats is lower than in young rats in response to recurrent apneas, mimicking obstructive sleep apnea. This could be due to the different PtO2 response observed between age groups and the increased antioxidant expression in aged rats.

Keywords: Aging, Animal model, Obstructive apnea, Oxidative stress, Tissue oxygenation, antioxidant, glutathione disulfide, aged, animal experiment, animal model, animal tissue, apnea, arterial oxygen saturation, article, brain cortex, brain oxygen tension, brain tissue, controlled study, groups by age, hypoxia, lipid peroxidation, male, nonhuman, oxidative stress, pressure, priority journal, rat


Dols-Perez, A., Fumagalli, L., Gomila, G., (2014). Structural and nanomechanical effects of cholesterol in binary and ternary spin-coated single lipid bilayers in dry conditions Colloids and Surfaces B: Biointerfaces 116, 295-302

We investigate the effects of Cholesterol (Chol) in the structural and nanomechanical properties of binary and ternary spin-coated single lipid bilayers made of Dioleoylphosphatidylcholine (DOPC) and Sphingomyelin (SM) in dry conditions. We show that for the DOPC/Chol bilayers, Chol induces an initial increase of the bilayer thickness, followed by decrease for concentrations above 30% Chol. The mechanical properties, instead, appear practically insensitive to the Chol content. For the SM/Chol bilayers we have observed both the thinning of the bilayer and the decrease of the force necessary to break it for Chol content above 40. mol%. In both binary mixtures phase separation is not observed. For ternary single bilayers of DOPC/SM/Chol, Chol induces phase segregation and the formation of domains resembling lipid rafts. The domains show a thickness and mechanical response clearly distinct from the surrounding phase and dependent on the relative Chol content. Based on the results obtained for the binary mixtures, DOPC- and SM-enriched domains can be identified. We highlight that many of the effects of Chol reported here for the dry multicomponent single lipid bilayers resemble closely those observed in hydrated bilayers, thus offering an additional insight into their properties.

Keywords: AFM, Air-stable lipid layer, Force spectroscopy, Lipid raft, Spin-coating


Serra, T., Ortiz-Hernandez, M., Engel, E., Planell, J. A., Navarro, M., (2014). Relevance of PEG in PLA-based blends for tissue engineering 3D-printed scaffolds Materials Science and Engineering: C 38, (1), 55-62

Achieving high quality 3D-printed structures requires establishing the right printing conditions. Finding processing conditions that satisfy both the fabrication process and the final required scaffold properties is crucial. This work stresses the importance of studying the outcome of the plasticizing effect of PEG on PLA-based blends used for the fabrication of 3D-direct-printed scaffolds for tissue engineering applications. For this, PLA/PEG blends with 5, 10 and 20% (w/w) of PEG and PLA/PEG/bioactive CaP glass composites were processed in the form of 3D rapid prototyping scaffolds. Surface analysis and differential scanning calorimetry revealed a rearrangement of polymer chains and a topography, wettability and elastic modulus increase of the studied surfaces as PEG was incorporated. Moreover, addition of 10 and 20% PEG led to non-uniform 3D structures with lower mechanical properties. In vitro degradation studies showed that the inclusion of PEG significantly accelerated the degradation rate of the material. Results indicated that the presence of PEG not only improves PLA processing but also leads to relevant surface, geometrical and structural changes including modulation of the degradation rate of PLA-based 3D printed scaffolds.

Keywords: 3D-printing, Polylactic acid, Rapid prototyping, Scaffold, Surface characterization


Bennetts, Victor, Schaffernicht, Erik, Pomareda, Victor, Lilienthal, Achim, Marco, Santiago, Trincavelli, Marco, (2014). Combining non selective gas sensors on a mobile robot for identification and mapping of multiple chemical compounds Sensors 14, (9), 17331-17352

In this paper, we address the task of gas distribution modeling in scenarios where multiple heterogeneous compounds are present. Gas distribution modeling is particularly useful in emission monitoring applications where spatial representations of the gaseous patches can be used to identify emission hot spots. In realistic environments, the presence of multiple chemicals is expected and therefore, gas discrimination has to be incorporated in the modeling process. The approach presented in this work addresses the task of gas distribution modeling by combining different non selective gas sensors. Gas discrimination is addressed with an open sampling system, composed by an array of metal oxide sensors and a probabilistic algorithm tailored to uncontrolled environments. For each of the identified compounds, the mapping algorithm generates a calibrated gas distribution model using the classification uncertainty and the concentration readings acquired with a photo ionization detector. The meta parameters of the proposed modeling algorithm are automatically learned from the data. The approach was validated with a gas sensitive robot patrolling outdoor and indoor scenarios, where two different chemicals were released simultaneously. The experimental results show that the generated multi compound maps can be used to accurately predict the location of emitting gas sources.

Keywords: Environmental monitoring, Gas discrimination, Gas distribution mapping, Service robots, Open sampling systems, PID, Metal oxide sensors


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.

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


Serra, T., Planell, J. A., Navarro, M., (2013). High-resolution PLA-based composite scaffolds via 3-D printing technology Acta Biomaterialia 9, (3), 5521-5530

Fabrication of new biodegradable scaffolds that guide and stimulate tissue regeneration is still a major issue in tissue engineering approaches. Scaffolds that possess adequate biodegradability, pore size, interconnectivity, bioactivity and mechanical properties in accordance with the injured tissue are required. This work aimed to develop and characterize three-dimensional (3-D) scaffolds that fulfill the aforementioned requirements. For this, a nozzle-based rapid prototyping system was used to combine polylactic acid and a bioactive CaP glass to fabricate 3-D biodegradable scaffolds with two patterns (orthogonal and displaced double layer). Scanning electron microscopy and micro-computer tomography showed that 3-D scaffolds had completely interconnected porosity, uniform distribution of the glass particles, and a controlled and repetitive architecture. Surface properties were also assessed, showing that the incorporation of glass particles increased both the roughness and the hydrophilicity of the scaffolds. Mechanical tests indicated that compression strength is dependent on the scaffold geometry and the presence of glass. Preliminary cell response was studied with primary mesenchymal stem cells (MSC) and revealed that CaP glass improved cell adhesion. Overall, the results showed the suitability of the technique/materials combination to develop 3-D porous scaffolds and their initial biocompatibility, both being valuable characteristics for tissue engineering applications.

Keywords: Rapid prototyping, Scaffold, Polylactic acid, Biodegradable, Composite


Hoyo, J., Guaus, E., Oncins, G., Torrent-Burgués, J., Sanz, F., (2013). Incorporation of Ubiquinone in supported lipid bilayers on ITO Journal of Physical Chemistry B , 117, (25), 7498-7506

Ubiquinone (UQ) is one of the main electron and proton shuttle molecules in biological systems, and dipalmitoylphosphatidylcholine (DPPC) is one of the most used model lipids. Supported planar bilayers (SPBs) are extensively accepted as biological model membranes. In this study, SPBs have been deposited on ITO, which is a semiconductor with good electrical and optical features. Specifically, topographic atomic force microscopy (AFM) images and force curves have been performed on SPBs with several DPPC:UQ ratios to study the location and the interaction of UQ in the SPB. Additionally, cyclic voltammetry has been used to understand the electrochemical behavior of DPPC:UQ SPBs. Obtained results show that, in our case, UQ is placed in two main different positions in SPBs. First, between the DPPC hydrophobic chains, fact that originates a decrease in the breakthrough force of the bilayer, and the second between the two leaflets that form the SPBs. This second position occurs when increasing the UQ content, fact that eventually forms UQ aggregates at high concentrations. The formation of aggregates produces an expansion of the SPB average height and a bimodal distribution of the breakthrough force. The voltammetric response of UQ depends on its position on the bilayer.

Keywords: Bimodal distribution, Biological models, Dipalmitoyl phosphatidylcholine, Electrochemical behaviors, Hydrophobic chains, Supported lipid bilayers, Supported planar bilayers, Voltammetric response


Giraldo, B. F., Chaparro, J. A., Caminal, P., Benito, S., (2013). Characterization of the respiratory pattern variability of patients with different pressure support levels Engineering in Medicine and Biology Society (EMBC) 35th Annual International Conference of the IEEE , IEEE (Osaka, Japan) , 3849-3852

One of the most challenging problems in intensive care is still the process of discontinuing mechanical ventilation, called weaning process. Both an unnecessary delay in the discontinuation process and a weaning trial that is undertaken too early are undesirable. In this study, we analyzed respiratory pattern variability using the respiratory volume signal of patients submitted to two different levels of pressure support ventilation (PSV), prior to withdrawal of the mechanical ventilation. In order to characterize the respiratory pattern, we analyzed the following time series: inspiratory time, expiratory time, breath duration, tidal volume, fractional inspiratory time, mean inspiratory flow and rapid shallow breathing. Several autoregressive modeling techniques were considered: autoregressive models (AR), autoregressive moving average models (ARMA), and autoregressive models with exogenous input (ARX). The following classification methods were used: logistic regression (LR), linear discriminant analysis (LDA) and support vector machines (SVM). 20 patients on weaning trials from mechanical ventilation were analyzed. The patients, submitted to two different levels of PSV, were classified as low PSV and high PSV. The variability of the respiratory patterns of these patients were analyzed. The most relevant parameters were extracted using the classifiers methods. The best results were obtained with the interquartile range and the final prediction errors of AR, ARMA and ARX models. An accuracy of 95% (93% sensitivity and 90% specificity) was obtained when the interquartile range of the expiratory time and the breath duration time series were used a LDA model. All classifiers showed a good compromise between sensitivity and specificity.

Keywords: autoregressive moving average processes, feature extraction, medical signal processing, patient care, pneumodynamics, signal classification, support vector machines, time series, ARX, autoregressive modeling techniques, autoregressive models with exogenous input, autoregressive moving average model, breath duration time series, classification method, classifier method, discontinuing mechanical ventilation, expiratory time, feature extraction, final prediction errors, fractional inspiratory time, intensive care, interquartile range, linear discriminant analysis, logistic regression analysis, mean inspiratory flow, patient respiratory volume signal, pressure support level, pressure support ventilation, rapid shallow breathing, respiratory pattern variability characterization, support vector machines, tidal volume, weaning trial, Analytical models, Autoregressive processes, Biological system modeling, Estimation, Support vector machines, Time series analysis, Ventilation


Redondo-Morata, Lorena, Oncins, Gerard, Sanz, Fausto, (2012). Force spectroscopy reveals the effect of different ions in the nanomechanical behavior of phospholipid model membranes: The case of potassium cation Biophysical Journal , 102, (1), 66-74

How do metal cations affect the stability and structure of phospholipid bilayers? What role does ion binding play in the insertion of proteins and the overall mechanical stability of biological membranes? Investigators have used different theoretical and microscopic approaches to study the mechanical properties of lipid bilayers. Although they are crucial for such studies, molecular-dynamics simulations cannot yet span the complexity of biological membranes. In addition, there are still some experimental difficulties when it comes to testing the ion binding to lipid bilayers in an accurate way. Hence, there is a need to establish a new approach from the perspective of the nanometric scale, where most of the specific molecular phenomena take place. Atomic force microscopy has become an essential tool for examining the structure and behavior of lipid bilayers. In this work, we used force spectroscopy to quantitatively characterize nanomechanical resistance as a function of the electrolyte composition by means of a reliable molecular fingerprint that reveals itself as a repetitive jump in the approaching force curve. By systematically probing a set of bilayers of different composition immersed in electrolytes composed of a variety of monovalent and divalent metal cations, we were able to obtain a wealth of information showing that each ion makes an independent and important contribution to the gross mechanical resistance and its plastic properties. This work addresses the need to assess the effects of different ions on the structure of phospholipid membranes, and opens new avenues for characterizing the (nano)mechanical stability of membranes.

Keywords: Molecular-dynamics simulation, Liquid expanded monolayers, Lipid-bilayers, Hofmeister series, Monovalent salt, Phosphatidylcholine, Microscopy, Binding, Surfaces, NaCl


Hoyo, J., Guaus, E., Torrent-Burgués, J., Sanz, F., (2012). Electrochemical behaviour of mixed LB films of ubiquinone - DPPC Journal of Electroanalytical Chemistry , 669, 6-13

The structure and the electrochemical behaviour of Langmuir and Langmuir-Blodgett (LB) films of the biological ubiquinone-10 (UQ) and a mixture of dipalmytoilphosphatidylcholine (DPPC) and UQ at the molar ratios DPPC:UQ 5:1 and 10:1 have been investigated. The surface pressure-area isotherms of the Langmuir films and the AFM images of the LB films show the formation of a monolayer in the DPPC:UQ mixture till a certain surface pressure is attained, and then at higher surface pressures the UQ is progressively expelled. The cyclic voltammograms of DPPC:UQ LB films formed on indium tin oxide, ITO, at different surface pressures show one reduction and one oxidation peak at low surface pressures, but two or even more reduction and oxidations peaks at medium and high surface pressures. The electrochemical behaviour is correlated with the film structure.

Keywords: Cyclic voltammetry, Electron transfer, Langmuir-Blodgett, Lipid monolayer, Modified ITO electrode, Ubiquinone


Serra, T., Navarro, M., Planell, J. A., (2012). Fabrication and characterization of biodegradable composite scaffolds for tissue engineering Innovative Developments in Virtual and Physical Prototyping 5th International Conference on Advanced Research and Rapid Prototyping (ed. Margarida, T., Ferreira, D.), Taylor & Francis (Leiria, Portugal) VR@P, 67-72

In this study, polylactic acid (PLA) and polyethylene glycol (PEG) were combined with soluble CaP glass particles and processed by rapid prototyping to obtain fully biodegradable structures for Tissue Engineering applications. The obtained 3D biodegradable structures were characterized in terms of their architecture and mechanical properties. The scaffold morphology, internal micro-architecture and mechanical properties were evaluated using Scanning Electron Microscopy (SEM), micro-computed tomography (micro-CT) and mechanical testing, respectively. Well defined structures with pore size of 350-400μm (in the axial view), struts width of approximately 70-80μm, and a porosity ranging between 60-65% were obtained. The combination RP and PLA/PEG/CaP glass turned into promising fully degradable, mechanically stable, bioactive and biocompatible composite scaffolds for TE.

Keywords: Axial view, Biodegradable composites, Composite scaffolds, Glass particles, Mechanically stable, Micro architectures, Micro computed tomography (micro-CT), Poly lactic acid, Scaffold morphology, Tissue engineering applications, Well-defined structures, Bioactive glass, Mechanical properties, Mechanical testing, Polyethylene glycols, Polymer blends, Rapid prototyping, Scaffolds (biology), Scanning electron microscopy, Computerized tomography


Chaparro, J.A., Giraldo, B.F., Caminal, P., Benito, S., (2012). Performance of respiratory pattern parameters in classifiers for predict weaning process Engineering in Medicine and Biology Society (EMBC) 34th Annual International Conference of the IEEE , IEEE (San Diego, USA) , 4349-4352

Weaning trials process of patients in intensive care units is a complex clinical procedure. 153 patients under extubation process (T-tube test) were studied: 94 patients with successful trials (group S), 38 patients who failed to maintain spontaneous breathing and were reconnected (group F), and 21 patients with successful test but that had to be reintubated before 48 hours (group R). The respiratory pattern of each patient was characterized through the following time series: inspiratory time (TI), expiratory time (TE), breathing cycle duration (TTot), tidal volume (VT), inspiratory fraction (TI/TTot), half inspired flow (VT/TI), and rapid shallow index (f/VT), where f is respiratory rate. Using techniques as autoregressive models (AR), autoregressive moving average models (ARMA) and autoregressive models with exogenous input (ARX), the most relevant parameters of the respiratory pattern were obtained. We proposed the evaluation of these parameters using classifiers as logistic regression (LR), linear discriminant analysis (LDA), support vector machines (SVM) and classification and regression tree (CART) to discriminate between patients from groups S, F and R. An accuracy of 93% (98% sensitivity and 82% specificity) has been obtained using CART classification.

Keywords: Accuracy, Indexes, Logistics, Regression tree analysis, Support vector machines, Time series analysis, Autoregressive moving average processes, Medical signal processing, Pattern classification, Pneumodynamics, Regression analysis, Sensitivity, Signal classification, Support vector machines, Time series, SVM, T-tube testing, Autoregressive models-with-exogenous input, Autoregressive moving average models, Breathing cycle duration, Classification-and-regression tree, Expiratory time, Extubation process, Half inspired flow, Inspiratory fraction, Inspiratory time, Intensive care units, Linear discriminant analysis, Logistic regression, Rapid shallow index, Respiratory pattern parameter performance, Sensitivity, Spontaneous breathing, Support vector machines, Tidal volume, Time 48 hr, Time series, Weaning process classifiers


Redondo, L., Giannotti, M. I., Sanz, F., (2012). Stability of lipid bilayers as model membranes: Atomic force microscopy and spectroscopy approach Atomic force microscopy in liquid (ed. Baró, A. M., Reifenberger, R. G.), Wiley-VCH Verlag GmbH & Co.KGaA (Weinheim, Germany) Part I: General Atomic Force Microscopy, 259-284

van Zanten, T. S., Garcia-Parajo, M. F., (2012). Super-resolution near-field optical microscopy Comprehensive Biophysics (ed. Egelman, E. H.), Elsevier (Desdren, Germany) Volume 2: Biophysical Techniques for Characterization of Cells, 144-164

Near-field optical microscopy is a technique not limited by the laws of diffraction that enables simultaneous high-resolution fluorescence and topographic measurements at the nanometer scale. This chapter highlights the intrinsic advantages of near-field optics in the study of cellular structures. The first part of the chapter lays the foundations of the near-field concept and technical implementation of near-field scanning optical microscopy (NSOM), whereas the second part of the chapter focuses on applications of NSOM to the study of model membranes and cellular structures on the plasma membrane. The last part of the chapter discusses further directions of near-field optics, including optical antennas and fluorescence correlation spectroscopy approaches in the near-field regime.

Keywords: Biological membranes, Cell membrane nanoscale compartmentalization, Cellular nanodomains, Fluorescence correlation spectroscopy in reduced volumes, Immunoreceptor imaging, Lipid rafts, Near-field scanning optical microscopy, Optical nano-antennas, Shear force imaging, Single molecule detection, Super-resolution microscopy


Manzo, C., van Zanten, T. S., Garcia-Parajo, M. F., (2011). Nanoscale fluorescence correlation spectroscopy on intact living cell membranes with NSOM probes Biophysical Journal , 100, (2), L8-L10

Characterization of molecular dynamics on living cell membranes at the nanoscale is fundamental to unravel the mechanisms of membrane organization and compartmentalization. Here we demonstrate the feasibility of fluorescence correlation spectroscopy (FCS) based on the nanometric illumination of near-field scanning optical microscopy (NSOM) probes on intact living cells. NSOM-FCS applied to fluorescent lipid analogs allowed us to reveal details of the diffusion hidden by larger illumination areas. Moreover, the technique offers the unique, advantages of evanescent axial illumination and straightforward implementation of multiple color excitation. As such, NSOM-FCS represents a powerful tool to study a variety of dynamic processes occurring at the nanometer scale on cell membranes.

Keywords: Mode wave-guides, Lipid rafts, Difussion, Organization, Aperture


Garcia-Manyes, S., Redondo-Morata, L., Oncins, G., Sanz, F., (2010). Nanomechanics of lipid bilayers: Heads or tails? Journal of the American Chemical Society American Chemical Society 132, (37), 12874-12886

Understanding the effect of mechanical stress on membranes is of primary importance in biophysics. Here we use force spectroscopy AFM to quantitatively characterize the nanomechanical stability of supported lipid bilayers as a function of their chemical composition. The onset of plastic deformation reveals itself as a repetitive jump in the approaching force curve, which represents a molecular fingerprint for the bilayer mechanical stability. By systematically probing a set of chemically distinct supported lipid bilayers (SLBs), we first show that both the headgroup and tail have a decisive effect on their mechanical properties. While the mechanical stability of the probed SLBs linearly increases by 3.3 nN upon the introduction of each additional -CH2- in the chain, it exhibits a significant dependence on the phospholipid headgroup, ranging from 3 nN for DPPA to 66 nN for DPPG. Furthermore, we also quantify the reduction of the membrane mechanical stability as a function of the number of unsaturations and molecular branching in the chemical structure of the apolar tails. Finally, we demonstrate that, upon introduction of cholesterol and ergosterol, contrary to previous belief the mechanical stability of membranes not only increases linearly in the liquid phase (DLPC) but also for phospholipids present in the gel phase (DPPC). Our results are discussed in the framework of the continuum nucleation model. This work highlights the compelling effect of subtle variations in the chemical structure of phospholipid molecules on the membrane response when exposed to mechanical forces, a mechanism of common occurrence in nature.

Keywords: Atomic-force microscopy, Molecular-dynamics simulation, Aqueous-electrolyte solutions, Supported planar membranes, Phospholipid-bilayers, Biological-membranes, Physical-properties, Fluid membranes, Model membranes, Chain-length


Garcia-Manyes, S., Sanz, F., (2010). Nanomechanics of lipid bilayers by force spectroscopy with AFM: A perspective Biochimica et Biophysica Acta - Biomembranes , 1798, (4), 741-749

Lipid bilayers determine the architecture of cell membranes and regulate a myriad of distinct processes that are highly dependent on the lateral organization of the phospholipid molecules that compose the membrane. Indeed, the mechanochemical properties of the membrane are strongly correlated with the function of several membrane proteins, which demand a very specific, highly localized physicochemical environment to perform their function. Several mesoscopic techniques have been used in the past to investigate the mechanical properties of lipid membranes. However, they were restricted to the study of the ensemble properties of giant bilayers. Force spectroscopy with AFM has emerged as a powerful technique able to provide valuable insights into the nanomechanical properties of supported lipid membranes at the nanometer/nanonewton scale in a wide variety of systems. In particular, these measurements have allowed direct measurement of the molecular interactions arising between neighboring phospholipid molecules and between the lipid molecules and the surrounding solvent environment. The goal of this review is to illustrate how these novel experiments have provided a new vista on membrane mechanics in a confined area within the nanometer realm, where most of the specific molecular interactions take place. Here we report in detail the main discoveries achieved by force spectroscopy with AFM on supported lipid bilayers, and we also discuss on the exciting future perspectives offered by this growing research field.

Keywords: Force spectroscopy, Atomic force microscopy, Lipid bilayer, Nanomechanics


van Zanten, T. S., Cambi, A., Garcia-Parajo, M. F., (2010). A nanometer scale optical view on the compartmentalization of cell membranes Biochimica et Biophysica Acta - Biomembranes , 1798, (4), 777-787

For many years, it was believed that the laws of diffraction set a fundamental limit to the spatial resolution of conventional light microscopy. Major developments, especially in the past few years, have demonstrated that the diffraction barrier can be overcome both in the near- and far-field regime. Together with dynamic measurements, a wealth of new information is now emerging regarding the compartmentalization of cell membranes. In this review we focus on optical methods designed to explore the nanoscale architecture of the cell membrane, with a focal point on near-field optical microscopy (NSOM) as the first developed technique to provide truly optical super-resolution beyond the diffraction limit of light. Several examples illustrate the unique capabilities offered by NSOM and highlight its usefulness on cell membrane studies, complementing the palette of biophysical techniques available nowadays.

Keywords: Membrane nanodomain, Lipid raft, Single molecule detection, Near-field scanning optical microscopy, Super-resolution optical microscopy


Olivares, A. L., Marshal, E., Planell, J. A., Lacroix, D., (2009). Finite element study of scaffold architecture design and culture conditions for tissue engineering Biomaterials 30, (30), 6142-6149

Tissue engineering scaffolds provide temporary mechanical support for tissue regeneration and transfer global mechanical load to mechanical stimuli to cells through its architecture. In this study the interactions between scaffold pore morphology, mechanical stimuli developed at the cell microscopic level, and culture conditions applied at the macroscopic scale are studied on two regular scaffold structures. Gyroid and hexagonal scaffolds of 55% and 70% porosity were modeled in a finite element analysis and were submitted to an inlet fluid flow or compressive strain. A mechanoregulation theory based on scaffold shear strain and fluid shear stress was applied for determining the influence of each structures on the mechanical stimuli on initial conditions. Results indicate that the distribution of shear stress induced by fluid perfusion is very dependent on pore distribution within the scaffold. Gyroid architectures provide a better accessibility of the fluid than hexagonal structures. Based on the mechanoregulation theory, the differentiation process in these structures was more sensitive to inlet fluid flow than axial strain of the scaffold. This study provides a computational approach to determine the mechanical stimuli at the cellular level when cells are cultured in a bioreactor and to relate mechanical stimuli with cell differentiation.

Keywords: Tissue engineering, Scaffold, Rapid prototyping, Computational fluid dynamics, Finite element


Nussio, M. R., Oncins, G., Ridelis, I., Szili, E., Shapter, J. G., Sanz, F., Voelcker, N. H., (2009). Nanomechanical characterization of phospholipid bilayer islands on flat and porous substrates: A force spectroscopy study Journal of Physical Chemistry B , 113, (30), 10339-10347

In this study, we compare for the first time the nanomechanical properties of lipid bilayer islands on flat and porous surfaces. 1,2-Dimyzistoyl-sn-glycero-3-phosphatidylcholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayers were deposited on flat (silicon and mica) and porous silicon (pSi) substrate surfaces and examined using atomic force spectroscopy and force volume imaging. Force spectroscopy measurements revealed the effects of the underlying substrate and of the lipid phase on the nanomechanical properties of bilayers islands. For mica and silicon, significant differences in breakthrough force between the center and the edges of bilayer islands were observed for both phospolipids. These differences were more pronounced for DMPC than for DPPC, presumably due to melting effects at the edges of DMPC bilayers. In contrast, bilayer islands deposited on pSi yielded similar breakthrough forces in the central region and along the perimeter of the islands, and those values in turn were similar to those measured along the perimeter of bilayer islands deposited on the flat substrates. The study also demonstrates that pSi is suitable solid support for the formation of pore-spanning phospholipid bilayers with potential applications in transmembrane protein studies, drug delivery, and biosensing.

Keywords: Black lipid-membranes, Gold surfaces, Supported bilayers, Channel activity, Micro-BLMS, Silicon, Proteins, Vesicles, AFM, Temperature measurement


Bravo, R., Arimon, M., Valle-Delgado, J. J., Garcia, R., Durany, N., Castel, S., Cruz, M., Ventura, S., Fernàndez-Busquets, X., (2008). Sulfated polysaccharides promote the assembly of amyloid beta(1-42) peptide into stable fibrils of reduced cytotoxicity Journal of Biological Chemistry , 283, (47), 32471-32483

The histopathological hallmarks of Alzheimer disease are the self-aggregation of the amyloid beta peptide (A beta) in extracellular amyloid fibrils and the formation of intraneuronal Tau filaments, but a convincing mechanism connecting both processes has yet to be provided. Here we show that the endogenous polysaccharide chondroitin sulfate B (CSB) promotes the formation of fibrillar structures of the 42-residue fragment, A beta(1-42). Atomic force microscopy visualization, thioflavin T fluorescence, CD measurements, and cell viability assays indicate that CSB-induced fibrils are highly stable entities with abundant beta-sheet structure that have little toxicity for neuroblastoma cells. We propose a wedged cylinder model for A beta(1-42) fibrils that is consistent with the majority of available data, it is an energetically favorable assembly that minimizes the exposure of hydrophobic areas, and it explains why fibrils do not grow in thickness. Fluorescence measurements of the effect of different A beta(1-42) species on Ca2+ homeostasis show that weakly structured nodular fibrils, but not CSB-induced smooth fibrils, trigger a rise in cytosolic Ca2+ that depends on the presence of both extracellular and intracellular stocks. In vitro assays indicate that such transient, local Ca2+ increases can have a direct effect in promoting the formation of Tau filaments similar to those isolated from Alzheimer disease brains.

Keywords: AFM, Alzheimers-disease, Chondroitin sulfate, Heparan-sulfate, Lipid-bilayers, Beta-peptide, In-vitro, Neurodegenerative diseases, Extracellular-matrix, Prion protein


Oncins, G., Torrent-Burgues, J., Sanz, F., (2008). Nanomechanical properties of arachidic acid Langmuir-Blodgett films Journal of Physical Chemistry C , 112, (6), 1967-1974

The nanomechanical properties of Langmuir-Blodgett monolayers of arachidic acid extracted at surface pressures of 1, 15, and 35 mN/m and deposited on mica were investigated by atomic force microscopy, force spectroscopy, and lateral force microscopy. It was experimentally demonstrated that the arachidic acid molecular orientation depends on the extraction pressure. According to this, tilting angles of 50, 34, and 22 degrees with respect to the surface perpendicular were detected and identified as conformations that maximize van der Waals interactions between the arachidic acid alkyl chains. The vertical force needed to puncture the monolayers with the AFM tip strongly depends on the molecular tilting angles attained at different monolayer extraction surface pressures, obtaining values that range from 13.07 +/- 3.24 nN for 50 degrees to 22.94 +/- 5.49 nN for 22 degrees tilting angles. The different molecular interactions involved in the monolayer cohesion are discussed and quantitatively related to the experimental monolayer breakthrough forces. The friction measurements performed from low vertical forces up to monolayer disruption reveal the existence of three well-defined regimes: first, a low friction response due to the elastic deformation of the monolayer, which is followed by a sharp increase in the friction force due to the onset of a sudden plastic deformation. The last regime corresponds to the monolayer rupture and the contact between tip and substrate. The friction coefficient of the substrate is seen to depend on the monolayer extraction pressure, a fact that is discussed in terms of the relationship between the sample compactness and its rupture mechanism.

Keywords: AFM, SAM, Reflection-absortion spectroscopy, Lipid-bilayers, Frictional-properies, Molecular-structure, Thermal behavior, Nanometer-scale, Chain-length, LB films