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Cell-Imprint Surface Modification by Contact Photolithography-Based Approaches: Direct-Cell Photolithography and Optical Soft Lithography Using PDMS Cell Imprints

Shahin Bonakdar, Hanie Kavand, Philippe Renaud, Harald Van Lintel

New cell-imprint surface modification techniques based on direct-cell photolithography and optical soft lithography using poly(dimethylsiloxane) (PDMS) cell imprints are presented for enhanced cell-based studies. The core concept of engineering materials for cell-based studies is the material's ability to redesign the physicochemical characteristics of the cellular niche. There is a growing interest in direct molding from cells (cell imprinting). These negative copies of cell surface topographies have been shown to affect cell shape and direct mesenchymal stem cells' differentiation. Analyzing the results is however challenging as cells seeded on these substrates do not always end up in a cell pattern, which leads to decreased effectiveness and biased quantification. To gain control over cell seeding into the patterns and avoid unwanted cell population outside the cell-imprinted surface needs to be modified. From this perspective, the standard optical contact lithography process was modified and cells were introduced to the cleanroom. Direct-cell photolithography was used for a single-step PDMS cell-imprint (chondrocytes as the molding template) surface modification down to single-cell (approximately 5 mu m in diameter) resolution. As cells come in a variety of shapes, sizes, and optical profiles, a complementary optical soft lithography-based photomask fabrication technique is also reported. The simplicity of the fabrication process makes this cell-imprint surface modification technique compatible with any adherent cell type and leads to efficient cell-based studies.

AMER CHEMICAL SOC2019

Dielectrophoresis‐assisted creation of cell aggregates under flow conditions using planar electrodes

Jonathan Bastien Cottet, Soufian Lasli, Philippe Renaud, Harald Van Lintel

We present a microfluidic platform allowing dielectrophoresis-assisted formation of cell aggregates of controlled size and composition under flow conditions. When specific ex- perimental conditions are met, negative dielectrophoresis allows efficient concentration of cells towards electric field minima and subsequent aggregation. This bottom-up assembly strategy offers several advantages with respect to the targeted application: first, dielec- trophoresis offers precise control of spatial cell organization, which can be adjusted by optimizing electrode design. Then, it could contribute to accelerate the establishment of cell-cell interactions by favoring close contact between neighboring cells. The trapping ge- ometry of our chip is composed of eight electrodes arranged in a circle. Several parameters have been tested in simulations to find the best configurations for trapping in flow. Those configurations have been tested experimentally with both polystyrene beads and human embryonic kidney cells. The final design and experimental setup have been optimized to trap cells and release the created aggregates on demand.

2019

Efficacy of pulsed electromagnetic fields and electromagnetic fields tuned to the ion cyclotron resonance frequency of Ca2+ on chondrogenic differentiation

Hanie Kavand, Philippe Renaud, Harald Van Lintel

Previous studies provide strong evidence for the therapeutic effect of electromagnetic fields (EMFs) on different tissues including cartilage. Diverse exposure parameters applied in scientific reports and the unknown interacting mechanism of EMF with biological systems make EMF studies challenging. In 1985, Liboff proposed that when magnetic fields are tuned to the cyclotron resonance frequencies of critical ions, the motion of ions through cell membranes is enhanced, and thus biological effects appear. Such exposure system consists of a weak alternating magnetic field (B-1) in the presence of a static magnetic field (B-0) and depends on the relationship between the magnitudes of B-0 and B-1 and the angular frequency omega. The purpose of the present study is to determine the chondrogenic potential of EMF with regards to pulsed EMF (PEMF) and the ion cyclotron resonance (ICR) theory. We used different stimulating systems to generate EMFs in which cells are either stimulated with ubiquitous PEMF parameters, frequently reported, or parameters tuned to satisfy the ICR for Ca2+ (including negative and positive control groups). Chondrogenesis was analysed after 3 weeks of treatment. Cell stimulation under the ICR condition showed positive results in the context of glycosaminoglycans and type II collagen synthesis. In contrast, the other electromagnetically stimulated groups showed no changes compared with the control groups. Furthermore, gene expression assays revealed an increase in the expression of chondrogenic markers (COL2A1, SOX9, and ACAN) in the ICR group. These results suggest that the Ca2+ ICR condition can be an effective factor in inducing chondrogenesis.

WILEY2019