Publications by authors named "Bernard Senger"

46 Publications

A comparative in vivo study of new shade matching procedures.

Int J Comput Dent 2020 ;23(4):317-323

Aim: The aim of the present study was to compare six different methods of in vivo color matching: visual shade matching (3D-Master Linearguide shade guide) performed by 1) a novice practitioner, 2) an expert practitioner, 3) the new Rayplicker spectrometer, 4) the Trios III intraoral scanner, and 5) the Omnicam intraoral scanner compared with 6) the Easyshade V spectrophotometer, which was considered as the reference.

Materials And Methods: Color matching was performed using the 3D-Master references on the sound maxillary right central incisors of 40 subjects. The study first compared the number of colors found using each of the six methods. The references were then converted to the Commission Internationale de l'Eclairage (CIE) L*a*b* values, from which the difference ?E between either two methods ?was derived. Finally, the L* value was used to compare the luminosity measured by each of the six methods.

Results: The Rayplicker showed the smallest ?E compared with the Easyshade V. The expert found a closer color to the Easyshade V than did the novice, and both were closer to the Easyshade V than the two intraoral scanners. The intraoral scanners showed notable differences compared with the Easyshade V. The intraoral scanners also offered a reduced choice of colors and recorded the highest luminosities compared with the other methods.

Conclusion: Within the limitations of this study, the color matching by the Rayplicker was closest to that of the Easyshade V. The good performance of this new device means that it is a challenging competitor for the Easyshade V. Finally, the new methods based on intraoral scanners were less reliable than the spectrophotometers and the visual shade matching.
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January 2021

Effect of the Buffer on the Buildup and Stability of Tannic Acid/Collagen Multilayer Films Applied as Antibacterial Coatings.

ACS Appl Mater Interfaces 2020 May 6;12(20):22601-22612. Epub 2020 May 6.

Université de Strasbourg, CNRS, Institut Charles Sadron, UPR 22, 67034 Strasbourg Cedex 2, France.

The deposition of polyelectrolyte multilayers, obtained by the layer-by-layer (LbL) method, is a well-established technology to design biocompatible and antibacterial coatings aimed at preventing implant-associated infections. Several types of LbL films have been reported to exhibit antiadhesive and/or antibacterial (contact-killing or release-killing) properties governed not only by the incorporated compounds but also by their buildup conditions or their postbuildup treatments. Tannic acid (TA), a natural polyphenol, is known to inhibit the growth of several bacterial strains. In this work, we developed TA/collagen (TA/COL) LbL films built in acetate or citrate buffers at pH 4. Surprisingly, the used buffer impacts not only the physicochemical but also the antibacterial properties of the films. When incubated in physiological conditions, both types of TA/COL films released almost the same amount of TA depending on the last layer and showed an antibacterial effect against only for citrate-built films. Because of their granular topography, TA/COL citrate films exhibited an efficient release-killing effect with no cytotoxicity toward human gingival fibroblasts. Emphasis is put on a comprehensive evaluation of the physicochemical parameters driving the buildup and the antibacterial property of citrate films. Specifically, complexation strengths between TA and COL are different in the presence of the two buffers affecting the LbL deposition. This work constitutes an important step toward the use of polyphenols as an antibacterial agent when incorporated in LbL films.
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http://dx.doi.org/10.1021/acsami.0c04475DOI Listing
May 2020

Polyanionic Hydrogels as Reservoirs for Polycationic Antibiotic Substitutes Providing Prolonged Antibacterial Activity.

ACS Appl Mater Interfaces 2020 Apr 15;12(17):19258-19267. Epub 2020 Apr 15.

Institut National de la Santé et de la Recherche Médicale, INSERM Unité 1121 Biomaterials and Bioengineering, 11 rue Humann, 67085 Strasbourg Cedex, France.

Implantation of biomedical devices is often followed by bacterial infections that may seriously affect implant functionalities and lead to their failure. In the context of bacterial resistance to antibiotics, which is a growing problem worldwide, new strategies that are able to overcome these problems are needed. In this work, we introduce a new formulation of hyaluronic acid (HA)-based antimicrobial material: HA hydrogels loaded with polyarginine (PAR), a polycationic antibiotic substitute. The loading is possible through electrostatic interactions between negatively charged HA and positively charged PAR. Such hydrogels absorb high quantities of PAR, which are then gradually released from the hydrogel. This original system provides a long-lasting antibacterial effect on an in vitro model of repetitive infection, thus demonstrating a strong potential to fight multiple rounds of infections that are resistant to antibiotic treatment. In addition, HA-PAR hydrogels could be deposited onto/into medical devices such as wound dressings and mesh prostheses used in clinical applications. Finally, we performed first in vivo tests of hydrogel-coated mesh materials to verify their biocompatibility in a rat model, which show no difference between control HA hydrogel and PAR-loaded hydrogel in terms of inflammation.
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http://dx.doi.org/10.1021/acsami.9b23140DOI Listing
April 2020

A Pilot Study on Continuous Infusion of 4% Albumin in Critically Ill Patients: Impact on Nosocomial Infection via a Reduction Mechanism for Oxidized Substrates.

Crit Care Explor 2019 Sep 19;1(9):e0044. Epub 2019 Sep 19.

Inserm UMR 1121, Biomatériaux et Bioingénierie, département 11, Strasbourg, France.

Care-related infections affect up to 11% of ICU patients. Running therapeutic albumin is sometimes associated to less infection: whether a specific method of its infusion is of any interest to modulate innate defense is unknown. Our objectives were: 1) to test whether the method for albumin infusion is important to prevent care-related infections and 2) to analyze in vitro the antioxidative role of albumin on host defense proteins during shock (using vasostatin-I as an example).

Design: In a prospective, randomized, open-label trial, shock patients were allocated to receive either continuously 4% albumin or intermittently 20% albumin, as long as they were infused with norepinephrine. A translational study including in vivo and in vitro analyses of albumin-vasostatin-I interactions is reported.

Setting: A tertiary ICU caring for 1,000 patients per year.

Patients: Fifty shock patients with serum albumin less than 20 g/L.

Interventions: In vivo colonization and nosocomial infections were recorded and time-dependent changes in serum albumin, chromogranin A, and vasostatin-I concentrations as well. In vitro, we studied biochemical albumin-vasostatin-I relationship using biochemical methods.

Measurements And Main Results: Over 18 days, we recorded a decrease in colonization (four vs 12 episodes; = 0.035) and nosocomial infection frequency (two vs 13 episodes; = 0.002) in patients infused continuously 4% albumin versus controls. In vitro, albumin interacts with the disulfide loop vasostatin-I (residues 17-40) and continuous 4% albumin infusion restores its oxidative status required for antimicrobial activity.

Conclusions: Continuous 4% albumin is effective in reducing care-related infections in shock patients by increasing the availability of antimicrobial vasostatin-I. This might guide future care of shock patients.
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http://dx.doi.org/10.1097/CCE.0000000000000044DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7063941PMC
September 2019

Photoresponsive Nanometer-Scale Iron Alginate Hydrogels: A Study of Gel-Sol Transition Using a Quartz Crystal Microbalance.

Langmuir 2019 09 20;35(35):11397-11405. Epub 2019 Aug 20.

Instituto de Ciencia y Tecnología de Polímeros (ICTP-CSIC) , c/Juan de la Cierva, 3 , 28006 Madrid , Spain.

Alginate/Fe hydrogels were fabricated on hyaluronic acid (HA) and poly(allylamine hydrochloride) (PAH) multilayers to yield photoresponsive nanometer-scale hydrogels. Light irradiation of the resulting hydrogels induced the photoreduction of "hard" Fe to "soft" Fe cations, leading to changes in the mechanical properties of the hydrogels related to their cross-linking behavior. The buildup and the phototriggered response of the supported alginate hydrogels were followed with a quartz crystal microbalance (QCM) using an open cell allowing light irradiation from an LED source on top of the hydrogel. The results were correlated to the release profiles of folic acid, employed herein as a drug model, obtained from light-irradiated supported iron alginate hydrogels.
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http://dx.doi.org/10.1021/acs.langmuir.9b01224DOI Listing
September 2019

Chromatin de-condensation by switching substrate elasticity.

Sci Rep 2018 08 23;8(1):12655. Epub 2018 Aug 23.

Inserm UMR-S1121, 11 rue Humann, 67085, Strasbourg, France.

Mechanical properties of the cellular environment are known to influence cell fate. Chromatin de-condensation appears as an early event in cell reprogramming. Whereas the ratio of euchromatin versus heterochromatin can be increased chemically, we report herein for the first time that the ratio can also be increased by purely changing the mechanical properties of the microenvironment by successive 24 h-contact of the cells on a soft substrate alternated with relocation and growth for 7 days on a hard substrate. An initial contact with soft substrate caused massive SW480 cancer cell death by necrosis, whereas approximately 7% of the cells did survived exhibiting a high level of condensed chromatin (21% heterochromatin). However, four consecutive hard/soft cycles elicited a strong chromatin de-condensation (6% heterochromatin) correlating with an increase of cellular survival (approximately 90%). Furthermore, cell survival appeared to be reversible, indicative of an adaptive process rather than an irreversible gene mutation(s). This adaptation process is associated with modifications in gene expression patterns. A completely new approach for chromatin de-condensation, based only on mechanical properties of the microenvironment, without any drug mediation is presented.
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http://dx.doi.org/10.1038/s41598-018-31023-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6107547PMC
August 2018

Control of Surface-Localized, Enzyme-Assisted Self-Assembly of Peptides through Catalyzed Oligomerization.

Langmuir 2017 08 7;33(33):8267-8276. Epub 2017 Aug 7.

Université de Strasbourg, CNRS, Institut Charles Sadron UPR 22, 23 rue du Loess, F-67034 Strasbourg Cedex, France.

Localized self-assembly allowing both spatial and temporal control over the assembly process is essential in many biological systems. This can be achieved through localized enzyme-assisted self-assembly (LEASA), also called enzyme-instructed self-assembly, where enzymes present on a substrate catalyze a reaction that transforms noninteracting species into self-assembling ones. Very few LEASA systems have been reported so far, and the control of the self-assembly process through the surface properties represents one essential step toward their use, for example, in artificial cell mimicry. Here, we describe a new type of LEASA system based on α-chymotrypsin adsorbed on a surface, which catalyzes the production of (KL)OEt oligopeptides from a KLOEt (K: lysine; L: leucine; OEt ethyl ester) solution. When a critical concentration of the formed oligopeptides is reached near the surface, they self-assemble into β-sheets resulting in a fibrillar network localized at the interface that can extend over several micrometers. One significant feature of this process is the existence of a lag time before the self-assembly process starts. We investigate, in particular, the effect of the α-chymotrypsin surface density and KLOEt concentration on the self-assembly kinetics. We find that the lag time can be finely tuned through the surface density in α-chymotrypsin and KLOEt concentration. For a given surface enzyme concentration, a critical KLOEt concentration exists below which no self-assembly takes place. This concentration increases when the surface density in enzyme decreases.
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http://dx.doi.org/10.1021/acs.langmuir.7b01532DOI Listing
August 2017

Computed Tomographic Study of the Pediatric Diaphragmatic Growth: Application to the Treatment of Congenital Diaphragmatic Hernia.

Eur J Pediatr Surg 2017 Apr 11;27(2):177-180. Epub 2016 Apr 11.

Department of Pediatric Surgery, Hôpitaux Universitaires de Strasbourg, Strasbourg, Alsace, France.

 The prosthesis commonly used for the treatment of congenital diaphragmatic hernia (CDH) lacks elasticity to replace the diaphragm's mechanical properties and does not follow the natural growth of the child treated.  To determine the appropriate properties required for the prostheses, a CT study on healthy patients was conducted.  Two methods of diaphragmatic surface analysis are assessed: the diaphragmatic surface is either estimated using surface 2D estimations (method 1), or calculated using length measures on thoracoabdominal CT scans from children (method 2). Patients are divided into two groups depending on their age: group 1:  = 9; median age: 2.0 months (0.1-9.5); group 2:  = 9; median age: 182.6 months (158.5-235.5). Growth factor between the two groups is calculated and the two methods are statistically compared.  The ratio group 2/group 1 of the diaphragmatic surfaces was 4.3 ± 0.2 on the left side and 4.0 ± 0.2 on the right side for method 1, and 5.1 ± 0.2 on the left side and 5.1 ± 0.3 on the right side for method 2. The difference in the median values between both methods is statistically significant for both the left and right sides ( = 0.022 and  = 0.002, respectively). Hence, the two methods cannot be used exchangeably.  The treatment of CDH with large defect remains a challenge because of the high incidence of hernia recurrence probably due to prosthesis defect; thus it is important to estimate the diaphragmatic surface precisely. We aim to develop a prosthesis material that can be commonly used and found a mean diaphragmatic growth factor of approximately 4 to 5 from early childhood to adolescence.
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http://dx.doi.org/10.1055/s-0036-1582242DOI Listing
April 2017

Stretch-Induced Helical Conformations in Poly(l-lysine)/Hyaluronic Acid Multilayers.

ACS Appl Mater Interfaces 2016 06 8;8(24):14958-65. Epub 2015 Dec 8.

Institut National de la Santé et de la Recherche Médicale, INSERM Unité 1121 , 11 rue Humann, 67085 Strasbourg Cedex, France.

We investigate the effect of stretching on the secondary structure of cross-linked poly(l-lysine)/hyaluronic acid (PLL/HA) multilayers. We show that stretching these films induces changes in the secondary structure of PLL chains. Our results suggest that not only α- but also 310-helices might form in the film under stretching. Such 310-helices have never been observed for PLL so far. These changes of the secondary structure of PLL are reversible, i.e., when returning to the nonstretched state one recovers the initial film structure. Using molecular dynamics simulations of chains composed of 20 l-lysine residues (PLL20), we find that these chains never adopt a helical conformation in water. In contrast, when the end-to-end distance of the chains is restrained to values smaller than the mean end-to-end distance of free chains, a distance domain rarely explored by the free chains, helical conformations become accessible. Moreover, the formation of not only α- but also 310-helices is predicted by the simulations. These results suggest that the change of the end-to-end distance of PLL chains in the stretched film is at the origin of the helix formation.
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http://dx.doi.org/10.1021/acsami.5b08302DOI Listing
June 2016

Film Self-Assembly of Oppositely Charged Macromolecules Triggered by Electrochemistry through a Morphogenic Approach.

Langmuir 2015 Sep 8;31(37):10208-14. Epub 2015 Sep 8.

Institut Charles Sadron , UPR 22, Centre National de la Recherche Scientifique, Strasbourg, France.

The development of new surface functionalization methods that are easy to use, versatile, and allow local deposition represents a real scientific challenge. Overcoming this challenge, we present here a one-pot process that consists in self-assembling, by electrochemistry on an electrode, films made of oppositely charged macromolecules. This method relies on a charge-shifting polyanion, dimethylmaleic-modified poly(allylamine) (PAHd), that undergoes hydrolysis at acidic pH, leading to an overall switching of its charge. When a mixture of the two polyanions, PAHd and poly(styrenesulfonate) (PSS), is placed in contact with an electrode, where the pH is decreased locally by electrochemistry, the transformation of PAHd into a polycation (PAH) leads to the continuous self-assembly of a nanometric PAH/PSS film by electrostatic interactions. The pH decrease is obtained by the electrochemical oxidation of hydroquinone, which produces protons locally over nanometric distances. Using a negatively charged enzyme, alkaline phosphatase (AP), instead of PSS, this one-pot process allows the creation of enzymatically active films. Under mild conditions, self-assembled PAH/AP films have an enzymatic activity which is adjustable simply by controlling the self-assembly time. The selective functionalization of microelectrode arrays by PAH/AP was achieved, opening the route toward miniaturized biosensors.
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http://dx.doi.org/10.1021/acs.langmuir.5b02749DOI Listing
September 2015

Bioactive Seed Layer for Surface-Confined Self-Assembly of Peptides.

Angew Chem Int Ed Engl 2015 Aug 15;54(35):10198-201. Epub 2015 Jul 15.

Institut Charles Sadron, CNRS-UPR 22, 23 rue du Loess, 67034 Strasbourg Cedex (France).

The design and control of molecular systems that self-assemble spontaneously and exclusively at or near an interface represents a real scientific challenge. We present here a new concept, an active seed layer that allows to overcome this challenge. It is based on enzyme-assisted self-assembly. An enzyme, alkaline phosphatase, which transforms an original peptide, Fmoc-FFY(PO4 (2-) ), into an efficient gelation agent by dephosphorylation, is embedded in a polyelectrolyte multilayer and constitutes the "reaction motor". A seed layer composed of a polyelectrolyte covalently modified by anchoring hydrogelator peptides constitutes the top of the multilayer. This layer is the nucleation site for the Fmoc-FFY peptide self-assembly. When such a film is brought in contact with a Fmoc-FFY(PO4 (2-) ) solution, a nanofiber network starts to form almost instantaneously which extents up to several micrometers into the solution after several hours. We demonstrate that the active seed layer allows convenient control over the self-assembly kinetics and the geometric features of the fiber network simply by changing its peptide density.
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http://dx.doi.org/10.1002/anie.201504761DOI Listing
August 2015

Correction: Multivalency: influence of the residence time and the retraction rate on rupture forces measured by AFM.

J Mater Chem B 2015 Apr 9;3(15):3098. Epub 2015 Mar 9.

Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Villers-lès-Nancy, F-54600, France.

Correction for 'Multivalency: influence of the residence time and the retraction rate on rupture forces measured by AFM' by Jalal Bacharouche et al., J. Mater. Chem. B, 2015, 3, 1801-1812.
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http://dx.doi.org/10.1039/c5tb90039eDOI Listing
April 2015

Multivalency: influence of the residence time and the retraction rate on rupture forces measured by AFM.

J Mater Chem B 2015 Mar 26;3(9):1801-1812. Epub 2015 Jan 26.

Université de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Villers-lès-Nancy, F-54600, France.

The Bell-Evans theory relative to rupture forces between non-covalently interacting molecules predicts that the rupture force increases linearly with the logarithm of the force loading rate. Here we investigate by force spectroscopy performed with an atomic force microscope (AFM) the rupture forces between surfaces covered by β-cyclodextrin (β-CD) molecules and AFM tips coated with adamantane (AD) groups. The β-CD molecules are either deposited through a self-assembled monolayer (SAM) or grafted on poly(allylamine hydrochloride) chains (PAH-CD) that are adsorbed on the substrate. The AD groups are fixed covalently on the AFM tip through either a one-AD or a four-AD platform linked to the tip though a PEO chain. It is found that while the rupture forces between AFM tips covered with tetravalent AD molecules and SAM-CD surfaces do not exceed twice those found with tips covered by monovalent AD molecules, the rupture forces increase by a factor of 20 on PAH-CD substrates for a tetravalent AD covered tip compared to a monovalent one. Thus, there seems to exist a synergistic effect between the molecule multivalence and the polymeric nature of the CD-covered substrate. As found in the literature, we observe an increase of the intensity of the rupture forces between the AD-covered AFM tip and the β-CD covered substrate with the contact time over timescales up to several seconds. Finally, we find that when the host-guest system involves the multivalency of the AD guest and/or the polymeric nature of the host the mean rupture force decreases with the loading rate in contrast to what is predicted by the Bell-Evans theory. We tentatively explain this "anti-Bell-Evans" behavior by the possibility of rebinding during the rupture process. This effect should have important implications in the understanding of forces at the cellular level.
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http://dx.doi.org/10.1039/c4tb01261eDOI Listing
March 2015

A new biomimetic route to engineer enzymatically active mechano-responsive materials.

Chem Commun (Camb) 2015 Apr;51(26):5622-5

ICS (UPR22-CNRS), 23 rue du Loess, 67034, Strasbourg, France.

Using modified β-galactosidase covalently linked to cross-linked polyelectrolyte multilayers (PEM), catalytically active materials have been designed. Their enzymatic activity can be modulated, partially in a reversible way, simply by stretching. This strategy, based on enzyme conformational changes, constitutes a new tool for the development of biocatalytic mechano-responsive materials.
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http://dx.doi.org/10.1039/c5cc00329fDOI Listing
April 2015

Cell Alignment Driven by Mechanically Induced Collagen Fiber Alignment in Collagen/Alginate Coatings.

Tissue Eng Part C Methods 2015 Sep 17;21(9):881-8. Epub 2015 Mar 17.

1 Institut National de la Santé et de la Recherche Médicale , UMR-S 1121, "Biomaterials and Bioengineering", Strasbourg, France .

For many years it has been a major challenge to regenerate damaged tissues using synthetic or natural materials. To favor the healing processes after tendon, cornea, muscle, or brain injuries, aligned collagen-based architectures are of utmost interest. In this study, we define a novel aligned coating based on a collagen/alginate (COL/ALG) multilayer film. The coating exhibiting a nanofibrillar structure is cross-linked with genipin for stability in physiological conditions. By stretching COL/ALG-coated polydimethylsiloxane substrates, we developed a versatile method to align the collagen fibrils of the polymeric coating. Assays on cell morphology and alignment were performed to investigate the properties of these films. Microscopic assessments revealed that cells align with the stretched collagen fibrils of the coating. The degree of alignment is tuned by the stretching rate (i.e., the strain) of the COL/ALG-coated elastic substrate. Such coatings are of great interest for strategies that require aligned nanofibrillar biological material as a substrate for tissue engineering.
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http://dx.doi.org/10.1089/ten.TEC.2014.0479DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4553373PMC
September 2015

Cell guidance into quiescent state through chromatin remodeling induced by elastic modulus of substrate.

Biomaterials 2015 Jan 29;37:144-55. Epub 2014 Oct 29.

INSERM UMR 1121, 11 rue Humann, 67085 Strasbourg, France; Faculté de Chirurgie Dentaire, Université de Strasbourg, 8 rue Sainte-Elisabeth, 67000 Strasbourg, France; Fédération de Médecine Translationnelle, Strasbourg, France. Electronic address:

Substrate stiffness is known to strongly influence the fate of adhering cells. Yet, little is known about the influence of the substrate stiffness on chromatin. Chromatin integrates a multitude of biochemical signals interpreted by activation or gene silencing. Here we investigate for the first time the organization of chromatin of epithelial cells on substrate with various mechanical properties. On stiff substrates (100-200 kPa), where cells preferentially adhere, chromatin is mainly found in its euchromatin form. Decreasing the Young modulus to 50 kPa is correlated with a partial shift from euchromatin to heterochromatin. On very soft substrates (≪10 kPa) this is accompanied by cell lysis. On these very soft substrates, histone deacetylase inhibition by adding a drug preserves acetylated histone and thus maintains the euchromatin form, thereby keeping intact the nuclear envelope as well as a residual intermediate filament network around the nucleus. This allows cells to survive in a non-adherent state without undergoing proliferation. When transfer on a stiff substrate these cells retain their capacity to adhere, to spread and to enter a novel mitotic cycle. A similar effect is observed on soft substrates (50 kPa) without need of histone deacetylase inhibition. These new results suggest that on soft substrates cells might enter in a quiescence state. Cell quiescence may thus be triggered by the Young modulus of a substrate, a major result for strategies focusing on the design of scaffold in tissue engineering.
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http://dx.doi.org/10.1016/j.biomaterials.2014.10.023DOI Listing
January 2015

Influence of the interaction strength between supramolecular complexes on the topography of neutral polymer multilayer films.

Langmuir 2014 Jun 27;30(22):6479-88. Epub 2014 May 27.

Institut Charles Sadron, Centre National de la Recherche Scientifique, Université de Strasbourg , UPR 22, 23 rue du Loess, BP 84047, 67034, Strasbourg Cedex 2, France.

Step-by-step polymer film buildup processes lead to polymer coatings, e.g., polyelectrolyte multilayers, of various structures ranging from continuous smooth films to droplet like discontinuous coatings. Yet, the origin of these different behaviors depending upon the system is not yet known. This study is a first attempt to rationalize the evolution of the coating structure as a function of the strength of the interactions between the polymers constituting the film. We investigated the influence of the strength of noncovalent host-guest interactions between cyclodextrin (CD) and pyrene (Py), ferrocene (Fc) or adamantane (Ad) on the structure of neutral poly(N-hydroxypropylmethacrylamide) (PHPMA) multilayers films formed in a step-by-step manner. In solution, the strength of the inclusion complex (measured by log K where K is the complex association constant) is increasing in the order Py/β-CD < Fc/β-CD < Ad/β-CD and can be further varied in the presence of different sodium salts at different ionic strengths. Depending upon this strength, the buildup process is limited to the formation of isolated aggregates for PHPMA-CD/PHPMA-Py, leading to smooth continuous films for PHPMA-CD/PHPMA-Fc and to droplet-like films, not entirely covering the substrate, for PHPMA-CD/PHPMA-Ad. To study the influence of the strength of the host-guest interactions on the film topography, PHPMA-CD/PHPMA-Fc films were built in the presence of different sodium salts at different ionic strengths. For low host-guest interactions, only isolated aggregates are formed on the substrate. As the strength of the host-guest interactions increases (increase of log K), the formed films go through a droplet-like structure, before becoming continuous but rough for stronger interactions. When the interaction strength is further increased, the roughness of the films decreases, leading to a smooth continuous film before becoming rough again at still higher interaction strength. Smooth continuous multilayers seem thus to be obtained for an optimal range of the interaction strength.
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http://dx.doi.org/10.1021/la501403mDOI Listing
June 2014

Nanosized films based on multicharged small molecules and oppositely charged polyelectrolytes obtained by simultaneous spray coating of interacting species.

Langmuir 2013 Nov 13;29(47):14536-44. Epub 2013 Nov 13.

Centre National de la Recherche Scientifique (CNRS), Institut Charles Sadron (UPR 22) , 23 rue du Loess, 67034 Strasbourg Cedex, France.

Simultaneous spraying of polyelectrolytes and small multicharged molecules of opposite charges onto a vertical substrate leads to continuous buildups of organic films. Here, we investigate the rules governing the buildup of two such systems: poly(allylamine hydrochloride)/sodium citrate (PAH/citrate) and PAH/sulfated α-cyclodextrin (PAH/CD-S). Special attention is paid to the film growth rate as a function of the spraying rate ratio of the two constituents. This parameter was varied by increasing the spraying rate of one of the constituents while maintaining constant that of the other. For PAH/CD-S systems, whatever the constituent (PAH or CD-S) whose spraying rate was kept fixed, the film growth rate first increases and passes through a maximum before decreasing when the spraying rate of the other constituent is increased. For PAH/citrate, the film growth rate reaches a plateau value when the spraying rate of citrate is increased while that of PAH is maintained constant, whereas when the spraying rate of citrate is maintained constant and that of PAH is increased, a behavior similar to that of PAH/CD-S is observed. The composition of PAH/CD-S sprayed films determined by X-ray photoelectron spectroscopy is independent of the spraying rate ratio of the two constituents and corresponds to one allylamine for one sulfate group. For PAH/citrate, by increasing the PAH/citrate spraying rate ratio, the carboxylic/nitrogen ratio in the film increases and tends to 1. There is thus always a deficit of carboxylic groups (COO(-) + COOH) with respect to amines (NH2 + NH3(+)). Yet, the ratio (COO(-)/NH3(+)) is always close to 1, ensuring exact charge compensation. The film morphology determined by atomic force microscopy is granular for PAH/CD-S and is smooth and liquid-like for PAH/citrate. A model based on strong (respectively weak) interactions between PAH and CD-S (respectively citrate) is proposed to explain these features.
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http://dx.doi.org/10.1021/la403580dDOI Listing
November 2013

Contribution of soft substrates to malignancy and tumor suppression during colon cancer cell division.

PLoS One 2013 22;8(10):e78468. Epub 2013 Oct 22.

Inserm UMR 1121, Strasbourg, France ; Université de Strasbourg, Faculté de Chirurgie Dentaire, Strasbourg, France ; Fédération de Médecine Translationnelle, Strasbourg, France.

In colon cancer, a highly aggressive disease, progression through the malignant sequence is accompanied by increasingly numerous chromosomal rearrangements. To colonize target organs, invasive cells cross several tissues of various elastic moduli. Whether soft tissue increases malignancy or in contrast limits invasive colon cell spreading remains an open question. Using polyelectrolyte multilayer films mimicking microenvironments of various elastic moduli, we revealed that human SW480 colon cancer cells displayed increasing frequency in chromosomal segregation abnormalities when cultured on substrates with decreasing stiffness. Our results show that, although decreasing stiffness correlates with increased cell lethality, a significant proportion of SW480 cancer cells did escape from the very soft substrates, even when bearing abnormal chromosome segregation, achieve mitosis and undergo a new cycle of replication in contrast to human colonic HCoEpiC cells which died on soft substrates. This observation opens the possibility that the ability of cancer cells to overcome defects in chromosome segregation on very soft substrates could contribute to increasing chromosomal rearrangements and tumor cell aggressiveness.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0078468PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3805547PMC
May 2014

Self-construction of supramolecular polyrotaxane films by an electrotriggered morphogen-driven process.

Langmuir 2013 Aug 13;29(34):10776-84. Epub 2013 Aug 13.

INSERM, UMR-S 1121, Biomatériaux et Bioingénierie, 11 rue Humann, F-67085 Strasbourg Cedex, France.

The design of films using a one-pot process has recently attracted increasing interest in the field of polymer thin film formation. Herein we describe the preparation of one-pot supramolecular polyrotaxane (PRX) films using the morphogen-driven self-construction process. This one-pot buildup strategy where the film growth is triggered by the electrochemical formation and diffusion of a catalyst in close vicinity of the substrate has recently been introduced by our group. A one-pot mixture was used that contained (i) poly(acrylic acid) (PAA) functionalized by azide groups grafted on the polymer chain through oligo(ethylene glycol) (EG) arms, leading to PAA-EG13-N3, (ii) cyclodextrins (α and β CD), as macrocycles that can be threaded along EG arms, (iii) alkyne-functionalized stoppers (ferrocene or adamantane), to cap the PRX assembly by click chemistry, and (iv) copper sulfate. The one-pot mixture solution was brought into contact with a gold electrode. Cu(I), the morphogen, was generated electrochemically from Cu(II) at the electrode/one-pot solution interface. This electrotriggered click reaction leads to the capping of polypseudorotaxane yielding to PRXs. The PRXs can self-assemble through lateral supramolecular interactions to form aggregates and ensure the cohesion of the film. The film buildup was investigated using different types of CD and alkyne functionalized stoppers. Supramolecular PRX aggregates were characterized by X-ray diffraction measurements. The film topographies were imaged by atomic force microscopy. The influence of the concentration in CD and the presence of a competitor were studied as well. The stability of the resulting film was tested in contact with 8 M urea and during the electrochemical oxidation of ferrocene.
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http://dx.doi.org/10.1021/la402454eDOI Listing
August 2013

Bioaffinity sensor based on nanoarchitectonic films: control of the specific adsorption of proteins through the dual role of an ethylene oxide spacer.

Langmuir 2013 Jun 11;29(24):7488-98. Epub 2013 Feb 11.

Centre National de la Recherche Scientifique, Unité Propre de Recherche 22, Institut Charles Sadron, Strasbourg, France.

The identification and quantification of biomarkers or proteins is a real challenge in allowing the early detection of diseases. The functionalization of the biosensor surface has to be properly designed to prevent nonspecific interactions and to detect the biomolecule of interest specifically. A multilayered nanoarchitecture, based on polyelectrolyte multilayers (PEM) and the sequential immobilization of streptavidin and a biotinylated antibody, was elaborated as a promising platform for the label-free sensing of targeted proteins. We choose ovalbumin as an example. Thanks to the versatility of PEM films, the platform was built on two types of sensor surface and was evaluated using both optical- and viscoelastic-based techniques, namely, optical waveguide lightmode spectroscopy and the quartz crystal microbalance, respectively. A library of biotinylated poly(acrylic acids) (PAAs) was synthesized by grafting biotin moieties at different grafting ratios (GR). The biotin moieties were linked to the PAA chains through ethylene oxide (EO) spacers of different lengths. The adsorption of the PAA-EOn-biotin (GR) layer on a PEM precursor film allows tuning the surface density in biotin and thus the streptavidin adsorption mainly through the grafting ratio. The nonspecific adsorption of serum was reduced and even suppressed depending on the length of the EO arms. We showed that to obtain an antifouling polyelectrolyte the grafting of EO9 or EO19 chains at 25% in GR is sufficient. Thus, the spacer has a dual role: ensuring the antifouling property and allowing the accessibility of biotin moieties. Finally, an optimized platform based on the PAA-EO9-biotin (25%)/streptavidin/biotinylated-antibody architecture was built and demonstrated promising performance as interface architecture for bioaffinity sensing of a targeted protein, in our case, ovalbumin.
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http://dx.doi.org/10.1021/la3045779DOI Listing
June 2013

Stretch-induced biodegradation of polyelectrolyte multilayer films for drug release.

Langmuir 2012 Sep 11;28(38):13550-4. Epub 2012 Sep 11.

Institut National de la Santé et de la Recherche Médicale, INSERM Unité 977, 11 rue Humann, 67085 Strasbourg Cedex, France.

The design of stimuli-responsive polymer assemblies for the controlled release of bioactive molecules has raised considerable interest these two last decades. Herein, we report the design of mechanically responsive drug-releasing films made of polyelectrolyte multilayers. A layer-by-layer (LbL) reservoir containing biodegradable polyelectrolytes is capped with a mechanosensitive LbL barrier and responds to stretching by a total enzymatic degradation of the film. This strategy is successfully applied for the release in solution of an anticancer drug initially loaded within the architecture.
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http://dx.doi.org/10.1021/la302550qDOI Listing
September 2012

Collagen-based fibrillar multilayer films cross-linked by a natural agent.

Biomacromolecules 2012 Jul 13;13(7):2128-35. Epub 2012 Jun 13.

Institut National de la Santé et de la Recherche Médicale , INSERM UMR 977, Biomaterials and Tissue Engineering, Strasbourg, France.

Surface functionalization plays an important role in the design of biomedical implants, especially when layer forming cells, such as endothelial or epithelial cells, are needed. In this study, we define a novel nanoscale surface coating composed of collagen/alginate polyelectrolyte multilayers and cross-linked for stability with genipin. This buildup follows an exponential growth regime versus the number of deposition cycles with a distinct nanofibrillar structure that is not damaged by the cross-linking step. Stability and cell compatibility of the cross-linked coatings were studied with human umbilical vein endothelial cells. The surface coating can be covered by a monolayer of vascular endothelial cells within 5 days. Genipin cross-linking renders the surface more suitable for cell attachment and proliferation compared to glutaraldehyde (more conventional cross-linker) cross-linked surfaces, where cell clumps in dispersed areas were observed. In summary, it is possible with the defined system to build fibrillar structures with a nanoscale control of film thickness, which would be useful for in vivo applications such as inner lining of lumens for vascular and tracheal implants.
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http://dx.doi.org/10.1021/bm300529aDOI Listing
July 2012

Mobility of proteins in highly hydrated polyelectrolyte multilayer films.

J Phys Chem B 2012 May 24;116(17):5269-78. Epub 2012 Apr 24.

Institut National de la Santé et de la Recherche Médicale, Unité 977, Strasbourg, France.

The lateral diffusion of a protein (human serum albumin labeled with fluorescein isothiocyanate) within a highly hydrated polyelectrolyte film is studied. The film is built up with poly(L-lysine) as polycation and hyaluronate as polyanion. Fluorescence recovery after photobleaching is used to evaluate the mobility of the labeled protein. Spatial Fourier transformation is applied to the fluorescence intensity recorded at various times after bleaching of a narrow rectangular area within an image representative of the film. This approach necessitates no hypothesis on the intensity distribution at the end of the bleaching provided that the bleach has not appreciably changed the concentration ratios of the different diffusing species. Furthermore, under the hypothesis that molecules move according to Fick's law, we represent the Fourier transform by a weighted sum of exponentials each containing another diffusion coefficient and evaluate the proportion attached to each term of this sequence using the simulated annealing method. A criterion, combining goodness-of-fit and the entropy characterizing the diffusion coefficient spectrum, is proposed to avoid overinterpretation of the experimental data. The optimum spectrum of the diffusion coefficient is then extracted from the time evolution of the light intensity at various albumin concentrations within the films. It appears that the mobility, quantified by the amount of tracer molecules having a diffusion coefficient smaller than, e.g., 0.1 μm(2)/s, undergoes a transition between 20 and 2000 μg/mL of internal concentration. This suggests that the mutual interactions of the albumin molecules and the interactions between fluorescently labeled albumin and the film network become increasingly important in the reduction of the albumin mobility as the albumin concentration increases.
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http://dx.doi.org/10.1021/jp300028vDOI Listing
May 2012

Cyto-mechanoresponsive polyelectrolyte multilayer films.

J Am Chem Soc 2012 Jan 20;134(1):83-6. Epub 2011 Dec 20.

Centre National de la Recherche Scientifique, Institut Charles Sadron, UPR 22, 67034 Strasbourg Cedex, France.

Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion.
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http://dx.doi.org/10.1021/ja208970bDOI Listing
January 2012

Electrochemically triggered assembly of films: a one-pot morphogen-driven buildup.

Angew Chem Int Ed Engl 2011 May 14;50(19):4374-7. Epub 2011 Apr 14.

Institut Charles Sadron (UPR 22), Centre National de la Recherche Scientifique, 23 rue du Loess, 67034 Strasbourg, France.

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http://dx.doi.org/10.1002/anie.201007436DOI Listing
May 2011

Dynamic aspects of films prepared by a sequential deposition of species: perspectives for smart and responsive materials.

Adv Mater 2011 Mar 25;23(10):1191-221. Epub 2011 Jan 25.

Institut National de la Santé et de la Recherche Médicale, Unité 977, 11 rue Humann, Strasbourg Cedex, France.

The deposition of surface coatings using a step-by-step approach from mutually interacting species allows the fabrication of so called "multilayered films". These coatings are very versatile and easy to produce in environmentally friendly conditions, mostly from aqueous solution. They find more and more applications in many hot topic areas, such as in biomaterials and nanoelectronics but also in stimuli-responsive films. We aim to review the most recent developments in such stimuli-responsive coatings based on layer-by-layer (LBL) depositions in relationship to the properties of these coatings. The most investigated stimuli are based on changes in ionic strength, temperature, exposure to light, and mechanical forces. The possibility to induce a transition from linear to exponential growth in thickness and to change the charge compensation from "intrinsic" to "extrinsic" by controlling parameters such as temperature, pH, and ionic strength are the ways to confer their responsiveness to the films. Chemical post-modifications also allow to significantly modify the film properties.
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http://dx.doi.org/10.1002/adma.201003309DOI Listing
March 2011

Covalent layer-by-layer assemblies of polyelectrolytes and homobifunctional spacers.

Langmuir 2010 Jul;26(14):12351-7

Institut National de la Santé et de la Recherche Médicale, UMR 977, 11 rue Humann, 67085 Strasbourg Cedex, France.

The step-by-step buildup of organic films through physical or covalent bonds is usually performed by the alternating adsorption of two types of polymeric chains. Overcompensation of the interacting groups after each deposition step (e.g., charge overcompensation in the case of polyelectrolyte multilayers) allows the buildup process to proceed. This overcompensation is intimately linked to the polymeric nature of the interacting species. We report here another type of film architecture also based on step-by-step construction but involving the covalent bonding, through the Sharpless click reaction, between polyelectrolytes (i.e., polyanions) and neutral bifunctional molecules. The films are built by the Cu(I)-catalyzed click reaction of poly(acrylic acid) (PAA) functionalized with ethylene glycol (EG) arms, each ending with either an alkyne or an azide group, and bifunctionalized EG spacers ended with either alkyne or azide functions. We prove that these systems lead to the regular buildup of films that cover the whole substrate surface and whose roughness varies as the thickness of the film core. The effects of various parameters on film buildup are investigated. The grafting density of reactive moieties along the PAA chains has no influence on the thickness increment per bilayer. EG spacers bifunctionalized with alkyne groups reacting with PAA chains functionalized with azide arms give films that grow more rapidly than those obtained with azide-functionalized EG spacers and alkyne-functionalized PAA chains. The influence of the length of the EG arm (grafted on PAA) and of the EG spacer on the film buildup is also investigated: longer arms or longer spacers lead to larger thickness increments per bilayer, except for very large spacers of 50 EG units for which the thickness is the smallest probably because of size exclusion effects during the deposition.
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http://dx.doi.org/10.1021/la101670gDOI Listing
July 2010

Turbidity diagrams of polyanion/polycation complexes in solution as a potential tool to predict the occurrence of polyelectrolyte multilayer deposition.

J Colloid Interface Sci 2010 Jun 21;346(1):163-71. Epub 2010 Feb 21.

Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche 977, 11 rue Humann, 67085 Strasbourg Cedex, France.

Surface functionalization with polyelectrolyte multilayer films (PEM films) has become very popular owing to its simplicity and versatility. However, even if some research is already available, this field of surface chemistry lacks a systematic knowledge of how the polyelectrolyte structure and solution conditions influence the growth of PEM films. In this investigation, we focus on the possible relationship between turbidity of polycation and polyanion mixtures in solution, and the buildup of PEM films made from the same polyelectrolytes in the same physicochemical conditions, namely pH, temperature and ionic strength. It comes out that for six different polycation/polyanion combinations there is a clear correlation between the turbidity evolution of polycation/polyanion complexes with the salt concentration and the evolution of the film deposition with the same parameter. In this investigation, the complexes in solution were prepared in conditions where the ratio between the number of cationic to anionic groups was close to unity. Even if there is a correlation between turbidity in solution and PEM film deposition, we found some exceptions in the low salt concentration regime. This work is an extension of the preliminary works of Cohen Stuart (D. Kovačević et al. Langmuir 18 (2002) 5607-5612) and Sukishvili et al. (S.A. Sukhishvili, E. Kharlampieva and V. Izumrudov, Macromolecules 39 (2006) 8873-8881).
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http://dx.doi.org/10.1016/j.jcis.2010.02.042DOI Listing
June 2010

Selective and uncoupled role of substrate elasticity in the regulation of replication and transcription in epithelial cells.

J Cell Sci 2010 Jan;123(Pt 1):29-39

Institut National de la Santé et de la Recherche Médicale, INSERM Unité 977, 67085 Strasbourg Cedex, France.

Actin cytoskeleton forms a physical connection between the extracellular matrix, adhesion complexes and nuclear architecture. Because tissue stiffness plays key roles in adhesion and cytoskeletal organization, an important open question concerns the influence of substrate elasticity on replication and transcription. To answer this major question, polyelectrolyte multilayer films were used as substrate models with apparent elastic moduli ranging from 0 to 500 kPa. The sequential relationship between Rac1, vinculin adhesion assembly, and replication becomes efficient at above 200 kPa because activation of Rac1 leads to vinculin assembly, actin fiber formation and, subsequently, to initiation of replication. An optimal window of elasticity (200 kPa) is required for activation of focal adhesion kinase through auto-phosphorylation of tyrosine 397. Transcription, including nuclear recruitment of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), occurred above 50 kPa. Actin fiber and focal adhesion signaling are not required for transcription. Above 50 kPa, transcription was correlated with alphav-integrin engagement together with histone H3 hyperacetylation and chromatin decondensation, allowing little cell spreading. By contrast, soft substrate (below 50 kPa) promoted morphological changes characteristic of apoptosis, including cell rounding, nucleus condensation, loss of focal adhesions and exposure of phosphatidylserine at the outer cell surface. On the basis of our data, we propose a selective and uncoupled contribution from the substrate elasticity to the regulation of replication and transcription activities for an epithelial cell model.
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http://dx.doi.org/10.1242/jcs.053520DOI Listing
January 2010
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