Publications by authors named "Andreas Best"

18 Publications

  • Page 1 of 1

Preparation of Monodisperse Giant Unilamellar Anchored Vesicles Using Micropatterned Hydrogel Substrates.

ACS Omega 2019 May 29;4(5):9393-9399. Epub 2019 May 29.

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.

Giant unilamellar vesicles (GUVs) are model membrane systems consisting of a single lipid bilayer separating an inner lumen from the outer solution, with dimensions comparable to that of eukaryotic cells. The importance of these biomimetic systems has recently grown with the development of easy and safe methods to assemble GUVs from complex biorelevant compositions. However, size and position control is still a key challenge for GUV formation and manipulation. Here, a gel-assisted formation method is introduced, able to produce arrays of giant unilamellar anchored vesicles (GUAVs) with a predetermined narrow size distribution. The approach based on micropatterned gel substrates of cross-linked poly(-isopropylacrylamide) allows performing parallel measurements on thousands of immobile unilamellar vesicles. Such power and flexibility will respond to the growing need for developing platforms of biomimetic constructs from cell-sized single bilayers.
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http://dx.doi.org/10.1021/acsomega.9b00912DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648857PMC
May 2019

Surfactants Mediate the Dewetting of Acrylic Polymer Films Commonly Applied to Works of Art.

ACS Appl Mater Interfaces 2019 Jul 20;11(30):27288-27296. Epub 2019 Jun 20.

Department of Chemistry , University of Florence and CSGI , Via della Lastruccia 3 , I-50019 Sesto Fiorentino , Firenze , Italy.

The removal of hydrophobic polymer coatings from artistic surfaces is a ubiquitous challenge in art restoration. Over the years, nanostructured fluids (NSFs), aqueous surfactant solutions containing a good solvent for the polymer, have been successfully applied in polymer removal interventions; however, the precise role of the surfactant in promoting polymer film dewetting is not fully understood. This contribution addresses the interaction of a NSF of water/propylene carbonate containing a nonionic surfactant with an acrylic polymer film commonly used in art conservation. Combining confocal microscopy and fluorescence correlation spectroscopy, we monitored the penetration of the fluid into the polymer film, defining its compositional changes and following the polymer swelling. The ensemble of results highlights that the surfactant role is twofold: (i) at the polymer-support interface, it promotes the detachment of the polymer film from the underlying support; (ii) inside the polymer film, it accelerates polymer swelling by increasing the chains' mobility.
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http://dx.doi.org/10.1021/acsami.9b04912DOI Listing
July 2019

Monitoring drug nanocarriers in human blood by near-infrared fluorescence correlation spectroscopy.

Nat Commun 2018 12 13;9(1):5306. Epub 2018 Dec 13.

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.

Nanocarrier-based drug delivery is a promising therapeutic approach that offers unique possibilities for the treatment of various diseases. However, inside the blood stream, nanocarriers' properties may change significantly due to interactions with proteins, aggregation, decomposition or premature loss of cargo. Thus, a method for precise, in situ characterization of drug nanocarriers in blood is needed. Here we show how the fluorescence correlation spectroscopy that is a well-established method for measuring the size, loading efficiency and stability of drug nanocarriers in aqueous solutions can be used to directly characterize drug nanocarriers in flowing blood. As the blood is not transparent for visible light and densely crowded with cells, we label the nanocarriers or their cargo with near-infrared fluorescent dyes and fit the experimental autocorrelation functions with an analytical model accounting for the presence of blood cells. The developed methodology contributes towards quantitative understanding of the in vivo behavior of nanocarrier-based therapeutics.
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http://dx.doi.org/10.1038/s41467-018-07755-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6294246PMC
December 2018

Impact of Branching on the Solution Behavior and Serum Stability of Starlike Block Copolymers.

Biomacromolecules 2019 01 11;20(1):375-388. Epub 2018 Dec 11.

Institute of Organic Chemistry , Johannes Gutenberg-Universität Mainz , Duesbergweg 10-14 , 55128 Mainz , Germany.

The size control of nanomedicines for tumor diagnosis and therapy is of high importance, since it enables or disables deep and sufficient tumor penetration. Amphiphilic star-shaped block copolypept(o)ides offer substantial promise to precisely adjust the hydrophobic core and the hydrophilic corona, independent of each other, and therefore simultaneously control the size dimension in the interesting size range from 10 to 30 nm. To gain access to core-shell structures of such sizes, 3-arm and 6-arm PeptoStars, based on poly(γ- tert-butyloxycarbonyl-l-glutamate)- b-polysarcosine (pGlu(O tBu)- b-pSar), were prepared via controlled living ring-opening polymerization (ROP) of the corresponding N-carboxyanhydrides. Moreover, size exclusion chromatography (SEC) proves the presence of well-defined star shaped polymers with molecular weights from 38 to 88 kg/mol with low polymer dispersities of 1.16 to 1.23. By varying the α-helical peptide core and maintain a constant polysarcosine corona, hydrodynamic size analyses revealed the importance of using a sufficiently large and dense hydrophilic shielding corona to prevent aggregation of the hydrophobic core and obtain uniform-sized spherical-shaped particles with hydrodynamic diameters below 24 nm. Fluorescence correlation spectroscopy (FCS) additionally demonstrates the absence of protein adsorption in human plasma for 6-arm polypept(o)ide stars and thus confirms polysarcosine as stealthlike material.
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http://dx.doi.org/10.1021/acs.biomac.8b01545DOI Listing
January 2019

Adsorption and Crystallization of Particles at the Air-Water Interface Induced by Minute Amounts of Surfactant.

Langmuir 2018 12 27;34(50):15526-15536. Epub 2018 Nov 27.

PASTEUR, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS , 75005 Paris , France.

Controlling the organization of particles at liquid-gas interfaces usually relies on multiphasic preparations and external applied forces. Here, we show that micromolar amounts of a conventional cationic surfactant induce, in a single step, both adsorption and crystallization of various types of nanometer- to micrometer-sized anionic particles at the air-water interface, without any additional phase involved or external forces other than gravity. Contrary to conventional surfactant-induced particle adsorption through neutralization and hydrophobization at a surfactant concentration close to the critical micellar concentration (CMC), we show that in our explored concentration regime (CMC/1000-CMC/100), particles adsorb with a low contact angle and maintain most of their charge, leading to the formation of two-dimensional assemblies with different structures, depending on surfactant ( C) and particle ( C) concentrations. At low C and C, particles are repulsive and form disordered assemblies. Increasing C in this regime increases the number of adsorbed particles, leading to the formation of mm-sized, highly ordered polycrystalline assemblies because of the long-range attraction mediated by the collective deformation of the interface. Increasing C decreases the particle repulsion and therefore the interparticle distance within the monocrystalline domains. A further increase in C (≈CMC/10) leads to a progressive neutralization of particles accompanied by the formation of disordered structures, ranging from densely packed amorphous ones to loosely packed gels. These results emphasize a new role of the surfactant to mediate both adsorption and crystallization of particles at liquid-gas interfaces and provide a practical manner to prepare two-dimensional ordered colloidal assemblies in a remarkably robust and convenient manner.
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http://dx.doi.org/10.1021/acs.langmuir.8b03233DOI Listing
December 2018

FRET Monitoring of Intracellular Ketal Hydrolysis in Synthetic Nanoparticles.

Angew Chem Int Ed Engl 2018 08 25;57(33):10760-10764. Epub 2018 Jul 25.

Department of Pharmaceutics, Ghent University, Belgium.

Degradable synthetic crosslinking is a versatile strategy to harness nanomaterials against disassembly in a complex physiological medium prompted by dilution effects or competitive interaction. In particular, chemical bonds such as ketals that are stable at physiological conditions but are cleaved in response to disease-mediated or intracellular conditions (e.g., a mildly acidic pH) are of great relevance for biomedical applications. Despite the range of spectroscopic or chromatographic analyses methods that allow chemical degradation in solution to be assessed, it is much less straightforward to interrogate synthetic nanomaterials for their degradation state when located inside a living organism. We demonstrate a method based on FRET analysis to monitor intracellular disassembly of block-copolymer-derived nanoparticles engineered with a FRET couple on separate polymer chains, which after self-assembly are covalently crosslinked with a pH-sensitive ketal-containing crosslinker.
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http://dx.doi.org/10.1002/anie.201803847DOI Listing
August 2018

Nanocarrier for Oral Peptide Delivery Produced by Polyelectrolyte Complexation in Nanoconfinement.

Biomacromolecules 2015 Aug 24;16(8):2282-7. Epub 2015 Jul 24.

†Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.

The hydrophilic peptide YY (PYY) is a promising hormone-based antiobesity drug. We present a new concept for the delivery of PYY from pH-responsive chitosan-based nanocarriers. To overcome the drawbacks while retaining the merits of the polyelectrolyte complex (PEC) method, we propose a one-pot approach for the encapsulation of a hydrophilic peptide drug in cross-linked PEC nanocarriers. First, the hydrophilic peptide is encapsulated via polyelectrolyte complexation within water-in-oil miniemulsion droplets. In a second step, the PEC surface is reinforced by controlled interfacial cross-linking. PYY is efficiently encapsulated and released upon pH change. Such nanocarriers are promising candidates for the fight against obesity and, in general, for the oral delivery of protein drugs.
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http://dx.doi.org/10.1021/acs.biomac.5b00500DOI Listing
August 2015

Ultralow-intensity near-infrared light induces drug delivery by upconverting nanoparticles.

Chem Commun (Camb) 2015 Jan 19;51(2):431-4. Epub 2014 Nov 19.

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.

Mesoporous silica coated upconverting nanoparticles are loaded with the anticancer drug doxorubicin and grafted with ruthenium complexes as photoactive molecular valves. Drug release was triggered by 974 nm light with 0.35 W cm(-2). Such low light intensity minimized overheating problems and prevented photodamage to biological samples.
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http://dx.doi.org/10.1039/c4cc07489kDOI Listing
January 2015

Monitoring the dynamics of phase separation in a polymer blend by confocal imaging and fluorescence correlation spectroscopy.

Macromol Rapid Commun 2012 Sep 3;33(18):1568-73. Epub 2012 Jul 3.

Max-Planck-Institut für Polymerforschung, Mainz, Germany.

The phase separation of the polymer blend polystyrene/poly(methyl phenyl siloxane) (PS/PMPS) is studied in situ by laser scanning confocal microscopy (LSCM) and by fluorescence correlation spectroscopy (FCS) at macroscopic and microscopic length scales, respectively. It is shown for the first time that FCS when combined with LSCM can provide independent information on the local concentration within the phase-separated domains as well as the interfacial width.
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http://dx.doi.org/10.1002/marc.201200322DOI Listing
September 2012

DNA amplification via polymerase chain reaction inside miniemulsion droplets with subsequent poly(n-butylcyanoacrylate) shell formation and delivery of polymeric capsules into mammalian cells.

Macromol Biosci 2011 Aug 6;11(8):1099-109. Epub 2011 May 6.

Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, Germany.

There is a growing interest in the development of stable nanocapsules that could deliver the bioactive compounds within the living organism, and to release them without causing any toxic effects. Here the miniemulsion droplets were first used as "nanoreactors" for the amplification of single-molecule dsDNA template (476 and 790 base pairs) through PCR. Afterwards, each droplet was surrounded with a biodegradable PBCA shell by interfacial anionic polymerization, enabling therefore to deliver the PCR products into the cells. The size of the initial miniemulsion droplets and the final polymeric capsules was in the range of 250 and 320 nm, mainly depending on the type of the continuous phase and presence of dsDNA template molecules. The formation of PCR products was resolved with gel electrophoresis and detected with fluorescence spectroscopy in the presence of DNA specific dye (SYBRGreen). TEM studies were performed to prove the formation of the polymeric shell. The shell thickness was measured to be within 5-15 nm and the average molecular weight of the formed PBCA polymer was around 75000 g · mol(-1) . For the cell uptake experiments, the obtained nanocapsules were transferred from the organic phase into aqueous medium containing a water-soluble surfactant. The effect of the surfactant type (anionic, cationic or non-ionic) on the HeLa cell viability and nanocapsule uptake behavior was studied by CLSM and FACS. Confocal analysis demonstrated that nanocapsules stabilized with cationic (CTMA-Cl) and non-ionic (Lutensol AT50) surfactants show almost the same uptake, whereas capsules redispersed in anionic (SDS) surfactant possess a 30% higher uptake. The release of the encapsulated material within the cell was studied on the example of Cy5-labeled oligonucleotides showing the colocalization with mitochondria of MSCs cells.
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http://dx.doi.org/10.1002/mabi.201100003DOI Listing
August 2011

Note: An easy way to enable total internal reflection-fluorescence correlation spectroscopy (TIR-FCS) by combining commercial devices for FCS and TIR microscopy.

Rev Sci Instrum 2011 Mar;82(3):036105

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.

Total internal reflection-fluorescence correlation spectroscopy (TIR-FCS) is a powerful method for studying dynamic processes at liquid-solid interfaces that may have numerous applications in biology, physics, and material science. Despite of its power and versatility, however, the use of TIR-FCS is still rather limited. The main reason for this is the need of a complex, in-house constructed optical setup whose assembly and adjustment is a quite difficult task. Clearly, the availability of ready to use, commercial TIR-FCS setups will strongly boost the application of this important method in many research areas. In this note we show that although such setups are still not available in the market, a proper combination of commercial devices for confocal fluorescence correlation spectroscopy and for total internal reflection microscopy may enable TIR-FCS in a way that do not require any special optical alignments. Furthermore, we demonstrate the capabilities of the setup by measuring the diffusion coefficient of single dye molecule and quantum dots in the very proximity of a water-glass interface.
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http://dx.doi.org/10.1063/1.3557412DOI Listing
March 2011

Three-dimensional ferroelectric domain visualization by Cerenkov-type second harmonic generation.

Opt Express 2010 Aug;18(16):16539-45

Max-Planck Institute for Polymer Research, Mainz 55128, Germany.

We show that focusing a laser light onto the boundary between antiparallel ferroelectric domains leads to the non-collinear generation of two second harmonic (SH) beams. The beams are emitted in a plane normal to the domain boundaries at the angles that satisfy the Cerenkov-type phase matching condition. Moreover, these beam disappear when the laser light is focused on a homogenous part of a single domain. We utilize this effect for 3-dimensional visualization of fine details of the ferroelectric domain pattern with a submicron accuracy.
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http://dx.doi.org/10.1364/OE.18.016539DOI Listing
August 2010

Direct studies of liquid flows near solid surfaces by total internal reflection fluorescence cross-correlation spectroscopy.

Opt Express 2009 Nov;17(23):21149-58

Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128, Mainz, Germany.

We present a new method to study flow of liquids near solid surface: Total internal reflection fluorescence cross-correlation spectroscopy (TIR-FCCS). Fluorescent tracers flowing with the liquid are excited by evanescent light, produced by epi-illumination through the periphery of a high numerical aperture oil-immersion objective. The time-resolved fluorescence intensity signals from two laterally shifted observation volumes, created by two confocal pinholes are independently measured. The cross-correlation of these signals provides information of the tracers' velocities. By changing the evanescent wave penetration depth, flow profiling at distances less than 200 nm from the interface can be performed. Due to the high sensitivity of the method fluorescent species with different size, down to single dye molecules can be used as tracers. We applied this method to study the flow of aqueous electrolyte solutions near a smooth hydrophilic surface and explored the effect of several important parameters, e.g. tracer size, ionic strength, and distance between the observation volumes.
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http://dx.doi.org/10.1364/OE.17.021149DOI Listing
November 2009

Direct measurements of hydrophobic slippage using double-focus fluorescence cross-correlation.

Phys Rev Lett 2009 Mar 20;102(11):118302. Epub 2009 Mar 20.

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119991 Moscow, Russia.

We report the results of direct measurements of velocity profiles in a microchannel with hydrophobic and hydrophilic walls, using a new high-precision method of double-focus spatial fluorescence cross correlation under a confocal microscope. In the vicinity of both walls the measured velocity profiles do not go to zero by supplying a plateau of constant velocity. This apparent slip is proven to be due to a Taylor dispersion, an augmentation by shear diffusion of nanotracers in the direction of flow. Comparing the velocity profiles near the hydrophobic and hydrophilic walls for various conditions shows that there is a true slip length due to hydrophobicity. This length, of the order of several tens of nanometers, is independent of the electrolyte concentration and shear rate.
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http://dx.doi.org/10.1103/PhysRevLett.102.118302DOI Listing
March 2009

Diffusion in polymer solutions studied by fluorescence correlation spectroscopy.

J Phys Chem B 2009 Mar;113(11):3355-9

Max-Planck-Institute for Polymer Research, Mainz, Germany.

We employed fluorescence correlation spectroscopy (FCS) to study the diffusion of molecular and macromolecular tracers in polystyrene solutions over a broad range of concentrations (c) and molecular weights (M(w,m)) of the matrix polymer. Molecular tracer diffusion scales only with the matrix concentration and superimposes on a single, nonpolymer specific, curve. On the contrary, the diffusion of macromolecular tracers in solutions of matrix polymers with M(w,m) sufficiently larger than the tracer molecular weight scales with c/c(p)*, where c(p)* is the tracer overlap concentration. We further demonstrate that FCS can address local and global dynamics simultaneously.
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http://dx.doi.org/10.1021/jp809707yDOI Listing
March 2009

Effect of capillary pressure and surface tension on the deformation of elastic surfaces by sessile liquid microdrops: an experimental investigation.

Langmuir 2008 Oct 23;24(19):10565-8. Epub 2008 Aug 23.

Max Planck Institute for Polymer Research, Mainz, Germany.

Sessile liquid drops are predicted to deform an elastic surface onto which they are placed because of the combined action of the liquid surface tension at the periphery of the drop and the capillary pressure inside the drop. Here, we show for the first time the in situ experimental confirmation of the effect of capillary pressure on this deformation. We demonstrate micrometer-scale deformations made possible by using a low Young's modulus material as an elastic surface. The experimental profiles of the deformed surfaces fit well the theoretical predictions for surfaces with a Young's modulus between 25 and 340 kPa.
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http://dx.doi.org/10.1021/la801862mDOI Listing
October 2008

Arrays of microlenses with variable focal lengths fabricated by restructuring polymer surfaces with an ink-jet device.

Opt Express 2007 Jul;15(15):9877-82

We report of a method for fabricating two-dimensional, regular arrays of polymer microlenses with focal lengths variable between 0.2 and 4.5 mm. We first make concave microlenses by ink-jetting solvent on a polymer substrate with a commercial drop-on-demand device. Solvent evaporation restructures the surface by a series of combined effects, which are discussed. In the second step we obtain convex elastomeric microlenses by casting the template made in the first step. We demonstrate the good optical quality of the microlenses by characterising their surfaces with atomic force microscopy and white light interferometry, and by directly measuring their focal lengths with ad-hoc confocal laser scanning microscopy.
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http://dx.doi.org/10.1364/oe.15.009877DOI Listing
July 2007

Impact of micropatterned surfaces on neuronal polarity.

J Neurosci Methods 2004 Apr;134(2):191-8

Max-Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.

Experimental control over cellular polarity in a neuronal network is a promising tool to study synapse formation and network behavior. We aimed to exploit a mechanism described by Stenger et al. [J. Neurosci. Methods 82 (1998) 167] to manipulate the direction of axonal versus dendritic outgrowth on a micropattern. The group had used laser ablation to create patterns of aminated silanes for cell attachment on a background of repellent fluorinated silanes. The pattern offered continuous adhesive pathways for axonal and interrupted pathways for dendritic outgrowth. By microcontact printing, we created similar patterns containing continuous and interrupted pathways consisting of extracellular matrix proteins on a background of polystyrene. Neuronal polarity was determined on the functional level through double patch clamp measurements, detecting synapses and their orientation. Although our pattern reproduced the properties that were assumed to be critical for the described effect, namely contrasting pathways of different adhesiveness, we failed to reproduce the above results. It is indicated that other qualities of alternative pathways than mere differences in adhesiveness are required to orient neuronal polarity in vitro. We suggest that the effect observed by Stenger et al. has to be attributed to less universal characteristics of the micropattern, e.g. to the specific chemical groups that were utilized.
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http://dx.doi.org/10.1016/j.jneumeth.2003.11.004DOI Listing
April 2004