Monthly Archive for: ‘March, 2015’

Hybrid cell-soft nanoparticles aggregates

Hybrid cell-soft nanoparticles aggregates

Influence of the elasticity and volume fraction of added nanoparticles on the spreading of cellular aggregates

Françoise M. Winnik (1,2)
1. Department of Chemistry and Faculty of Pharmacy, University of Montreal, CP 6128 Succursale Centre Ville, Montreal QC H3C3J7, Canada.
2. WPI International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 Japan.
E-mail: francoise.winnik@umontreal.ca
Collaboration : Françoise Brochard-Wyart (Curie Institute, Physical Chemistry Curie, UMR 168, UPMC, Paris, France)
E-mail: francoise.brochard@curie.fr

We have been working for the last years on applying soft matter physics to study the biophysics of tissues (tissue rheology, aspiration, spreading, mechanosensitivity, wetting and dewetting, adhesion and fracture) using cellular aggregates are a model system.(1-4). They result from the aggregation of a few thousands of cells, and form spheroids because they act as a liquid and minimize their surface energy. While single cell migration has been studied extensively, much less is known about the migration of cell populations. We have studied and interpreted, by analogy with the physics of wetting, the dynamics of spreading of aggregates and the migration of cell clusters on solid and soft substrates (polymer gels). We have shown that the rigidity of the substrate controls the wetting transition, the spreading velocity and the migration of the whole aggregate.(7) Since aggregate spreading occurs during early embryonic development and is suspected to play a large roles in cancer metastasis, the results obtained from such analogies may have important implications in our understanding of both tissue development and cancer.
Recently we have focused on cellular aggregate – nanoparticles hybrid systems. It has been previously shown that nanoparticles can modify the mechanical properties of single cells in terms of adhesion area, proliferation and motility.(5-6) We have studied the spreading of hybrid cell-rigid nanoparticles aggregates and shown that they affect cell dispersion. In this project we will study how “jelly-like” particles can influence the collective cell behaviour.
We propose to study the cellular aggregate – nanoparticles system by varying the size, the shape and the elastic modulus of hydrophilic jelly particles (from kPa to MPa range) and the volume fraction Φ of the cells in this artificial matrix. The volume fraction Φ can be fixed during the aggregate fabrication, or Φ can increase with time by cell divisions. If Φ is small, we will follow the migrations of single cells in the matrix. When Φ increases, we will observe a fluidization of the aggregate at Φ=Φc. For Φ larger than Φc, we will study the dynamics of spreading versus the elastic modulus of the beads. We expect a modification of the cell-cell interactions if the nanoparticles act as glue between the cells, and an increase of the cohesion of the aggregates for stiffer particles. We will study both the statics and the dynamics of spreading of these hybrid aggregates.
The candidate will not be limited to this project and will have the opportunity to develop his/her own ideas in the field of cellular aggregates. The candidate should have a strong background in biophysics and be familiar with the chemistry of nanoparticles synthetized in the group of F.Winnik.

The position is for one year, renewable upon mutual agreement and is located in Tsukuba, Japan, at the MANA Center of NIMS (http://www.nims.go.jp/mana/).

Please send your CV, a letter of motivation and the name/address of three scientists who would be able to send a letter of evaluation to F. M. Winnik and F. Brochard-Wyart.

References
1. Guevorkian, K., Colbert, M.-J., Durth, M., Dufour, S. & Brochard-Wyart, F. Aspiration of Biological Viscoelastic Drops. Physical Review Letters 104, 1–4 (2010).
2. Guevorkian, K., Gonzalez-Rodriguez, D., Carlier, C., Dufour, S. & Brochard-Wyart, F. Mechanosensitive shivering of model tissues under controlled aspiration. Proceedings of the National Academy of Sciences of the United States of America 108, (2011).
3. Gonzalez-Rodriguez, D., Guevorkian, K., Douezan, S. & Brochard-Wyart, F. Soft matter models of developing tissues and tumors. Science (New York, N.Y.) 338, 910–7 (2012).
4. Beaune, G., Stirbat, T.-V., Khalifat, N., Cochet-Escartin, O., Garcia, S., Gurchenkov, V.-V., Murrell, M.-P., Sufour, S., Cuvelier, D. & Brochard-Wyart, F. How cells flow in the spreading of cellular aggregates. Proceedings of the National Academy of Sciences of the United States of America 111, (2014).
5. Yang, J.-A., Phan, H.-T., Vaidya, S. & Murphy, C.-J., Nanovacuums: Nanoparticle Uptake and Differential Cellular Migration on a Carpet of nanoparticles. Nano Letters 13, (2013).
6. Tay, C.-Y., Cai, P., Setyawati, M.-I., Fang, W., Tan, L.-P., Hong, C.H.L., Chen, X. & Leong, D.,-T., Nanoparticles strengthen intracellular tension and retard cellular migration. Nano Letters 14, (2014).
7. Douezan, S., Dumond, J. & Brochard-Wyart, F. Wetting transitions of cellular aggregates induced by substrate rigidity. Soft Matter 8, 4578 (2012).

Tethered Poly(2-isopropyl-2-oxazoline) Chains: Temperature Effects on Layer Structure and Interactions Probed by AFM Experiments and Modeling

Tethered Poly(2-isopropyl-2-oxazoline) Chains: Temperature Effects on Layer Structure and Interactions Probed by AFM Experiments and Modeling

Junxue An, Xiaoyan Liu, Per Linse, Andra Dedinaite, Francoise M. Winnik and Per M. Claesson.

Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic−nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46°C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean- field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.

Quantum dot agglomerates in biological media and their characterization by asymmetrical flow field-flow fractionation

Quantum dot agglomerates in biological media and their characterization by asymmetrical flow field-flow fractionation

A. Moquin, K. D. Neibert, D. Maysinger and Françoise M. Winnik

The molecular composition of the biological environment of nanoparticles influences their physical properties and changes their pristine physicochemical identity. In order to understand, or predict, the interactions of cells with specific nanoparticles, it is critical to know their size, shape, and agglomeration state not only in their nascent state but also in biological media. Here, we use asymmetrical flow field-flow fractionation (AF4) with on-line multiangle light scattering (MALS), dynamic light scattering (DLS) and UV–Visible absorption detections to determine the relative concentration of isolated nanoparticles and agglomerates in the case of three types of semi-conductor quantum dots (QDs) dispersed in Dulbecco’s Modified Eagle Media (DMEM) containing 10% of fetal bovine serum (DMEM-FBS). AF4 analysis also yielded the size and size distribution of the agglomerates as a function of the time of QDs incubation in DMEM-FBS. The preferred modes of internalization of the QDs are assessed for three cell-types, N9 microglia, human hepatocellular carcinoma cells (HepG2) and human embryonic kidney cells (Hek293), by confocal fluorescence imaging of live cells, quantitative determination of the intracellular QD concentration, and flow cytometry. There is an excellent correlation between the agglomeration status of the three types of QDs in DMEM-FBS determined by AF4 analysis and their preferred mode of uptake by the three cell lines, which suggests that AF4 yields an accurate description of the nanoparticles as they encounter cells and advocates its use as a means to characterize particles under evaluation.

Phosphorylcholine-Modified Chitosan Films as Effective Promoters of Cell Aggregation: Correlation Between the Films Properties and Cellular Response

Phosphorylcholine-Modified Chitosan Films as Effective Promoters of Cell Aggregation: Correlation Between the Films Properties and Cellular Response

B. Qi, P. Kujawa, S. Toita, G. Beaume and F. M. Winnik.

This study describes chitosan-phosphorylcholine (CH-PC) films able to support the formation of cell aggregates (spheroids), which are important for tissue engineering and pharmacological studies. The surface topography, charge, thickness, and rheology of CH-PC thin films were characterized by AFM, zeta-potential measurements, SPR spectroscopy, and QCM-D measurements. The CH-PC films are highly hydrated gels, independently of the level of PC incorporation (15–40 mol-% PC/glucosamine units). QCM-D studies established that the amount of fibrinogen adsorbed on CH-PC films decreased with increasing PC content. CH-PC surfaces underwent a transition from moderately cell-adhesive (CH-PC15) to non-adhesive (CH-PC40). Optical micrographs of HUVEC and MCF-7 cell lines cultured on CH-PC surfaces showed that they form spheroids on CH-PC25 and CH-PC40 films.

Self-Association of the Thermosensitive Block Copolymer Poly(2-isopropyl-2-oxazoline)-b-poly(N-isopropylacrylamide) in Water-Methanol Mixtures

Self-Association of the Thermosensitive Block Copolymer Poly(2-isopropyl-2-oxazoline)-b-poly(N-isopropylacrylamide) in Water-Methanol Mixtures

R. Takahashi, X.P. Qiu, N. Xue, T. Sato, K. Terao and F. M. Winnik.

The dehydration and self-association of a novel thermosensitive diblock copolymer consisting of poly(2-isopropyl-2-oxazoline) and poly(N-isopropylacrylamide) (PIPOZ-b-PNIPAM) upon heating were studied in water and water–methanol (MeOH) mixtures by differential scanning calorimetry (DSC), turbidimetry, small-angle X-ray scattering (SAXS), and fluorescence depolarization. Although the difference of the phase-separation temperatures of the PIPOZ and PNIPAM homopolymers solutions was enhanced as the MeOH content in the mixed solvent increases, the DSC thermograms of PIPOZ-b-PNIPAM in water–MeOH mixtures were not bimodal, which indicates that the dehydration of each block does not occur independently. As a result, the amphiphilicity of this copolymer is weaker in the amphiphilic condition than that of the related thermosensitive block copolymer of PIPOZ and poly(2-ethyl-2-oxazoline) (PIPOZ-b-PEOZ) examined previously, which undergoes phase separation in hot water under the same conditions. Both PIPOZ-b-PNIPAM and PIPOZ-b-PEOZ solutions undergo a temperature-induced liquid–liquid phase separation, but the formation of the spherical micelle in the coexisting dilute phase is more difficult in the former solution. The colloidal stability of the coexisting concentrated phase depends on the mixed solvent composition. The colloids flocculate in conditions for which the copolymer is of intermediate amphiphilicity, as observed previously also in the PIPOZ-b-PEOZ solution, possibly due to the viscoelastic effect experienced by colloidal particles bearing on their interface chains of a more hydrophilic block.