Dynamic Micropatterning of Cells on Nanostructured Surfaces Using a Cell-friendly Photoresist

Surface nanotopography and cell shape modulate tumor cell susceptibility to NK cell cytotoxicity

Natural killer (NK) cells are innate cytotoxic lymphocytes exerting cytotoxicity against virally infected cells and tumor cells. NK cell cytotoxicity is primarily determined by biochemical signals received from ligands expressed on target cell surfaces, but it is also possible that biophysical environments of tumor cells, such as nanoscale surface topography typically existing on extracellular matrixes (ECMs) or cell morphology determined by ECM spaces or cell density, regulate NK cell cytotoxicity. In this study, micro/nanofabrication technology was applied to examine this possibility. Tumor cells were plated on flat or nanogrooved surfaces, or micropatterned into circular or elliptical geometries, and the effects of surface topography and tumor cell morphology on NK cell cytotoxicity were investigated. NK cells exhibited significantly higher cytotoxicity against tumor cells on nanogrooved surfaces or tumor cells in elliptical patterns than tumor cells on flat surfaces or tumor cells in circular patterns, respectively. The amounts of stress fiber formation in tumor cells positively correlated with NK cell cytotoxicity, indicating that increased cellular tension of tumor cells, either mediated by nanogrooved surfaces or elongated morphologies, was a key factor regulating NK cell cytotoxicity. These results may provide insight into the design of NK cell-based cancer immunotherapy.

Fabrication of 2D and 3D Cell Cluster Arrays Using a Cell-Friendly Photoresist

Cells in 3D behave differently than cells in 2D. We develop a new method for the fabrication of 2D and 3D cell cluster arrays on an identical substrate using a cell-friendly photoresist, which enables comparative study between cells in 2D and 3D cell clusters. The fabricated cell cluster arrays maintain their structure up to 3 days with good viability. Using this method, 2D and 3D cancer cell clusters with comparable sizes are fabricated, and natural killer (NK) cell cytotoxicity assays are performed to assess how dimensionality of cancer cell clusters influence their susceptibility to immune cell-mediated killing.

In Situ Subcellular Detachment of Cells Using a Cell-Friendly Photoresist and Spatially Modulated Light

Dynamic adhesion and detachment of subcellular regions occur during cell migration, thus a technique allowing precise control of subcellular detachment of cells will be useful for cell migration study. Previous methods for cell detachment were developed either for harvesting cells or cell sheets attached on surfaces with low resolution patterning capability, or for detaching subcellular regions located on predefined electrodes. In this paper, a method that allows in situ subcellular detachment of cells with ≈1.5 µm critical feature size while observing cells under a fluorescence microscope is introduced using a cell-friendly photoresist and spatially modulated light. Using this method, a single cell, regions in cell sheets, and a single focal adhesion complex within a cell are successfully detached. Furthermore, different subcellular regions of migrating cells are detached and changes in cell polarity and migration direction are quantitatively analyzed. This method will be useful for many applications in cell detachment, in particular when subcellular resolution is required.

Designing Nanostructured Ti6Al4V Bioactive Interfaces with Directed Irradiation Synthesis toward Cell Stimulation to Promote Host-Tissue-Implant Integration

A new generation of biomaterials are evolving from being biologically inert toward bioactive surfaces, which can further interact with biological components at the nanoscale. Here, we present directed irradiation synthesis (DIS) as a novel technology to selectively apply plasma ions to bombard any type of biomaterial and tailor the nanofeatures needed for in vitro growth stimulation. In this work, we demonstrate for the first time, the influence of physiochemical cues (e.g., self-organized topography at nanoscale) of medical grade Ti₆Al₄V results in control of cell shape, adhesion, and proliferation of human aortic smooth muscle stem cells. The control of surface nanostructures was found to be correlated to ion-beam incidence angle linked to a surface diffusive regime during irradiation synthesis with argon ions at energies below 1 keV and a fluence of 2.5 × 10¹⁷ cm^-2. Cell viability and cytoskeleton morphology were evaluated at 24 h, observing an advance cell attachment state on post-DIS surfaces. These modified surfaces showed 84% of cell biocompatibility and an increase in cytoplasmatic protusions ensuring a higher cell adhesion state. Filopodia density was promoted by a 3-fold change for oblique incidence angle DIS treatment compared to controls (e.g., no patterning) and lamellipodia structures were increased more than a factor of 2, which are indicators of cell attachment stimulation due to DIS modification. In addition, the morphology of the nanofeatures were tailored, with high fidelity control of the main DIS parameters that control diffusive and erosive regimes of self-organization. We have correlated the morphology and the influence in cell behavior, where nanoripple formation is the most active morphology for cell stimulation.

Guided cell adhesion, orientation, morphology and differentiation on silicon substrates photolithographically micropatterned with a cell-repellent cross-linked poly(vinyl alcohol) film

In this work, silicon substrates with poly(vinyl alcohol) (PVA) patterns created by a simple, low-cost and high-fidelity photolithographic procedure were evaluated with respect to cell adhesion and alignment, viability, metabolic activity, proliferation and cell cycle progression using the human glioblastoma cell-line U87MG and human skin fibroblasts. In addition, rat adrenal pheochromocytoma cells (PC-12) were employed to evaluate a modified photolithographic protocol appropriate for adhesion of cells requiring extracellular matrix components to adhere on the surface and to demonstrate that the proposed patterned substrates could provide unhindered cell differentiation. Regarding U87MG cells and skin fibroblasts, it was found that as the stripes width increased from 10 to 50 μm, the percentage of cells attached to Si versus the total area (Si + PVA) increased from 78% and 72% to 98.5% and 94.5% (p < 0.05), for U87MG cells and skin fibroblasts, respectively, with optimum cell alignment (≥95% of adherent cells with fidelity between 0.90 and 1.0; p < 0.05) for stripes width ranging between 20 and 22.5 μm. Concerning the viability, metabolic activity and proliferation of adherent cells, no statistically significant differences were observed compared to cells cultured onto non-patterned surfaces. Regarding PC-12 cells, a modification of the patterning procedure was followed involving coating of the substrate with type IV collagen prior to the photolithographic procedure, since they could not adhere on plain Si substrates. It was found that PC-12 cells adhere selectively (>95%) to collagen-coated Si stripes when the pattern width was equal to or wider than 10 μm. Following treatment with nerve growth factor, approximately 80% (p < 0.05) of the adherent cells differentiated to neuron-like cells extending neurites exclusively within the pattern. Given that the proposed patterning procedure allows highly selective cell adhesion without affecting cell proliferation, metabolic activity, and differentiation it could serve as a useful tool in various fields including tissue engineering, cell-based sensors and analytical microsystems.

Microtechnologies for Cell Microenvironment Control and Monitoring

A great breadth of questions remains in cellular biology. Some questions cannot be answered using traditional analytical techniques and so demand the development of new tools for research. In the near future, the development of highly integrated microfluidic analytical platforms will enable the acquisition of unknown biological data. These microfluidic systems must allow cell culture under controlled microenvironment and high throughput analysis. For this purpose, the integration of a variable number of newly developed micro- and nano-technologies, which enable control of topography and surface chemistry, soluble factors, mechanical forces and cell–cell contacts, as well as technology for monitoring cell phenotype and genotype with high spatial and temporal resolution will be necessary. These multifunctional devices must be accompanied by appropriate data analysis and management of the expected large datasets generated. The knowledge gained with these platforms has the potential to improve predictive models of the behavior of cells, impacting directly in better therapies for disease treatment. In this review, we give an overview of the microtechnology toolbox available for the design of high throughput microfluidic platforms for cell analysis. We discuss current microtechnologies for cell microenvironment control, different methodologies to create large arrays of cellular systems and finally techniques for monitoring cells in microfluidic devices.

Retracted Article: Cell orientation, proliferation, and differentiation on poly(l-lactide) spherulites

We show cytoskeleton and nuclear alignment on PLLA crystallized at 140 °C. Cell proliferation and differentiation were also promoted significantly and we study the effect of polymer spherulites on cell orientation, proliferation and differentiation.