Abstract
In this work, we show that vertical, high aspect-ratio (HAR) photonic crystals (PhCs), consisting of periodic arrays of 5 µm wide gaps with depth of 50 µm separated by 3 µm thick silicon walls, fabricated by electrochemical micromachining, can be used as three-dimensional microincubators, allowing cell lines to be selectively grown into the gaps. Silicon micromachined dice incorporating regions with different surface profiles, namely flat silicon and deeply etched PhC, were used as microincubators for culturing adherent cell lines with different morphology and adhesion properties. We extensively investigated and compared the proliferative behavior on HAR PhCs of eight human cell models, with different origins, such as the epithelial (SW613-B3; HeLa; SW480; HCT116; HT29) and the mesenchymal (MRC-5V1; CF; HT1080). We also verified the contribution of cell sedimentation into the silicon gaps. Fluorescence microscopy analysis highlights that only cell lines that exhibit, in the tested culture condition, the behavior typical of the mesenchymal phenotype are able to penetrate into the gaps of the PhC, extending their body deeply in the narrow gaps between adjacent silicon walls, and to grow adherent to the vertical surfaces of silicon. Results reported in this work, confirmed in various experiments, strongly support our statement that such three-dimensional microstructures have selection capabilities with regard to the cell lines that can actively populate the narrow gaps. Cells with a mesenchymal phenotype could be exploited in the next future as bioreceptors, in combination with HAR PhC optical transducers, e.g., for label-free optical detection of cellular activities involving changes in cell adhesion and/or morphology (e.g., apoptosis) in a three-dimensional microenvironment.
Highlights
The rapid progress in the development of new micro- and nanotechnologies together with the improvements in cell culture has led to the development of cell biosensors for clinical diagnostics, drug discovery, and detection of toxic agents or food research [1,2,3,4], with consequent direct benefits for human health and undoubted advantages in terms of industrial efficiency and animal welfare
As a result of the various experiments of cell seeding on silicon, we verified that seeding on silicon dice fitting in a 12-well plates allowed the best density to be reached by minimizing the number of cells that remain attached to the surrounding plastic surface of the well, instead of silicon
To establish a more general finding relative to the capability of cells to actively colonize the deep gaps of silicon high aspect-ratio (HAR) photonic crystals (PhCs), we investigated the behavior of eight cell lines with different morphology and adhesion properties
Summary
The rapid progress in the development of new micro- and nanotechnologies together with the improvements in cell culture has led to the development of cell biosensors for clinical diagnostics, drug discovery, and detection of toxic agents or food research [1,2,3,4], with consequent direct benefits for human health and undoubted advantages in terms of industrial efficiency and animal welfare These sensors use living cells as bioreceptors and allow cell morpho-functional changes and/or detachment, induced by exposure to environmental perturbations, to be monitored by a suitable transduction method (i.e., optical, electrical). 3-D cell cultures represent a potential bridge to cover the gap between animal models and human studies
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