Biomedical subjects

Didier Falconnet

Publications and source records attributed to Didier Falconnet.

5 recordsLinked to original sources

PubMed2006

Surface engineering approaches to micropattern surfaces for cell-based assays.

The ability to produce patterns of single or multiple cells through precise surface engineering of cell culture substrates has promoted the development of cellular bioassays that provide entirely new insights into the factors that control cell adhesion to material surfaces, cell proliferation, differentiation and molecular signaling pathways. The ability to control shape and spreading of attached cells and cell-cell contacts through the form and dimension of the cell-adhesive patches with high precision is important. Commitment of stem cells to different specific lineages depends strongly on cell shape, implying that controlled microenvironments through engineered surfaces may not only be a valuable approach towards fundamental cell-biological studies, but also of great importance for the design of cell culture substrates for tissue engineering. Furthermore, cell patterning is an important tool for organizing cells on transducers for cell-based sensing and cell-based drug discovery concepts. From a material engineering standpoint, patterning approaches have greatly profited by combining microfabrication technologies, such as photolithography, with biochemical functionalization to present to the cells biological cues in spatially controlled regions where the background is rendered non-adhesive ("non-fouling") by suitable chemical modification. The focus of this review is on the surface engineering aspects of biologically motivated micropatterning of two-dimensional (flat) surfaces with the aim to provide an introductory overview and critical assessment of the many techniques described in the literature. In particular, the importance of non-fouling surface chemistries, the combination of hard and soft lithography with molecular assembly techniques as well as a number of less well known, but useful patterning approaches, including direct cell writing, are discussed.

Adsorption↗

PubMed2005

Pattern stability under cell culture conditions--a comparative study of patterning methods based on PLL-g-PEG background passivation.

Despite the rapidly increasing number of publications on the fabrication and use of micro-patterns for cell studies, comparatively little is know about the long-term stability of such patterns under cell culture conditions. Here, we report on the long-term stability of cellular patterns created by three different patterning techniques: selective molecular assembly patterning, micro-contact printing and molecular assembly patterning by lift-off. We demonstrate that although all three techniques were combined with the same background passivation chemistry based on assembly of a PEG-graft copolymer, there are considerable differences in the long-term stability between the three different pattern types under cell culture conditions. Our results suggest that these differences are not cell-dependent but are due to different (substrate-dependent) interactions between the patterned substrate, the passivating molecule and the serum containing cellular medium.

3T3 Cells↗

PubMed2005

A novel crossed microfluidic device for the precise positioning of proteins and vesicles.

Herein we present a novel way to create arrays of different proteins or lipid vesicles using a crossed microfluidic device. The concept relies on the combination of I) a designated two-step surface chemistry, which allows activation for subsequent binding events, and II) crossing microfluidic channels for the local functionalization by separated laminar streams. Besides its simplicity and cost efficiency, this concept has the advantage that it keeps the proteins in a hydrated environment throughout the experiment. We have demonstrated the feasibility of such a device to create a chessboard pattern of different fluorescently labeled lipid vesicles, which offers the possibility to contain biomolecules, drugs or membrane proteins.

Equipment Design↗

PubMed2005

Tuned graft copolymers as controlled coatings for DNA microarrays.

DNA microarrays have become a powerful tool for expression profiling and other genomics applications. A critical factor for their sensitivity is the interfacial coating between the chip substrate and the bound DNA. Such a coating has to embrace the divergent requirements of tightly binding the capture probe DNA during the spotting process and of minimizing the nonspecific binding of target DNA during the hybridization assay. To fulfill these conditions, most coatings require a passivation step. Here we demonstrate how the chain density of a graft copolymer with a polycationic backbone, poly(l-lysine)-graft-poly(ethylene glycol), can be tuned such that the binding capacity during capture probe deposition is maximized while the nonspecific binding during hybridization assays is kept to a minimum, thus alleviating the requirement for a separate passivation procedure. Evidence for the superior performance of such coatings in terms of signal-to-noise ratio and spot quality is presented using an evanescent field-based fluorescent sensing technique (the ZeptoREADER). The surface architecture is further characterized using optical waveguide lightmode spectroscopy and time-of-flight secondary ion mass spectrometry. Finally, in a model assay, we demonstrate that expression changes can be detected from 1 microg of total mRNA sample material with a limit of detectable differential expression of +/-1.5.

DNA↗

PubMed2004

Micropatterning of DNA-tagged vesicles.

We present a novel concept for the creation of lipid vesicle microarrays based on a patterning approach termed Molecular Assembly Patterning by Lift-off (MAPL). A homogeneous MAPL-based single-stranded DNA microarray was converted into a vesicle array by the use of vesicles tagged with complementary DNAs, permitting sequence-specific coupling of vesicles to predefined surface regions through complementary DNA hybridization. In the multistep process utilized to fulfill this achievement, active spots consisting of PLL-g-PEGbiotin with a resistant PLL-g-PEG background, as provided by the MAPL process, was converted into a DNA array by addition of complexes of biotin-terminated DNA and NeutrAvidin. This was then followed by addition of POPC vesicles tagged with complementary cholesterol-terminated DNA, thus providing specific coupling of vesicles to the surface through complementary DNA hybridization. Quartz crystal microbalance with dissipation (QCM-D) and optical waveguide lightmode spectroscopy monitoring were used to optimize the multistep surface modification process. It was found that the amount of adsorbed biotinDNA-NeutrAvidin complexes decreases with increasing molar ratio of biotinDNA to NeutrAvidin and decreasing ionic strength of the buffer solution. Modeling of the QCM-D data showed that the shape of the immobilized vesicles depends on the amount of available anchoring groups between the vesicles and the surface. Fluorescent microscopy images confirmed the possibility to create well-defined patterns of DNA-tagged, fluorescently labeled vesicles in the micrometer range.

Biotin↗