Tailoring Common Hydrogels into 3D Cell Culture Templates

Nuclear deformation and cell division of single cell on elongated micropatterned substrates fabricated by DMD lithography

Cells sense mechanical signals from the surrounding environment and transmit them to the nucleus through mechanotransduction to regulate cellular behavior. Microcontact printing, which utilizes elastomer stamps, is an effective method for simulating the cellular microenvironment and manipulating cell morphology. However, the conventional fabrication process of silicon masters and elastomer stamps requires complex procedures and specialized equipment, which restricts the widespread application of micropatterning in cell biology and hinders the investigation of the role of cell geometry in regulating cell behavior. In this study, we present an innovative method for convenient resin stamp microfabrication based on digital micromirror device planar lithography. Using this method, we generated a series of patterns ranging from millimeter to micrometer scales and validated their effectiveness in controlling adhesion at both collective and individual cell levels. Additionally, we investigated mechanotransduction and cell behavior on elongated micropatterned substrates. We then examined the effects of cell elongation on cytoskeleton organization, nuclear deformation, focal adhesion formation, traction force generation, nuclear mechanics, and the growth of HeLa cells. Our findings reveal a positive correlation between cell length and mechanotransduction. Interestingly, HeLa cells with moderate length exhibit the highest cell division and proliferation rates. These results highlight the regulatory role of cell elongation in mechanotransduction and its significant impact on cancer cell growth. Furthermore, our methodology for controlling cell adhesion holds the potential for addressing fundamental questions in both cell biology and biomedical engineering.

Microfluidic harvesting of breast cancer tumor spheroid-derived extracellular vesicles from immobilized microgels for single-vesicle analysis

Investigating cellular and vesicular heterogeneity in breast cancer remains a challenge, which encourages the development of controllable in vitro systems that mimic the tumor microenvironment. Although three-dimensional cell culture better recapitulates the heterogeneity observed in tumor growth and extracellular vesicle (EV) biogenesis, the physiological relevance is often contrasted with the control offered by two-dimensional cell culture. Therefore, to challenge this misconception we developed a novel microfluidic system harboring highly tunable three-dimensional EV microbioreactors (^EVμBRs) to model micrometastatic EV release in breast cancer while capitalizing on the convenient, low-volume, and sterile interface provided by microfluidics. The diameter and cellular occupancy of the ^EVμBRs could be precisely tailored to various configurations, supporting the formation of breast cancer tumor spheroids. To immobilize the ^EVμBRs within a microchannel and facilitate EV extraction, oxygen inhibition in free-radical polymerization was repurposed to rapidly generate two-layer hydrodynamic traps in situ using a digital-micromirror device (DMD)-based ultraviolet (UV) projection system. Breast cancer tumor spheroid-derived EVs were harvested with as little as 20 μL from the microfluidic system and quantified by single-EV immunofluorescence for CD63 and CD81. Despite the low-volume extraction, differences in biomarker expression and coexpression of the tetraspanins on single EVs were observed. Furthermore, the ^EVμBRs were capable of recapitulating heterogeneity at a cellular and vesicular degree, indicating the utility and robustness of the microfluidic system to investigate physiologically relevant EVs in breast cancer and other disease models.

Rapid Prototyping of Organ-on-a-Chip Devices Using Maskless Photolithography

Organ-on-a-chip (OoC) and microfluidic devices are conventionally produced using microfabrication procedures that require cleanrooms, silicon wafers, and photomasks. The prototyping stage often requires multiple iterations of design steps. A simplified prototyping process could therefore offer major advantages. Here, we describe a rapid and cleanroom-free microfabrication method using maskless photolithography. The approach utilizes a commercial digital micromirror device (DMD)-based setup using 375 nm UV light for backside exposure of an epoxy-based negative photoresist (SU-8) on glass coverslips. We show that microstructures of various geometries and dimensions, microgrooves, and microchannels of different heights can be fabricated. New SU-8 molds and soft lithography-based polydimethylsiloxane (PDMS) chips can thus be produced within hours. We further show that backside UV exposure and grayscale photolithography allow structures of different heights or structures with height gradients to be developed using a single-step fabrication process. Using this approach: (1) digital photomasks can be designed, projected, and quickly adjusted if needed; and (2) SU-8 molds can be fabricated without cleanroom availability, which in turn (3) reduces microfabrication time and costs and (4) expedites prototyping of new OoC devices.

3D printing of sacrificial thioester elastomers using digital light processing for templating 3D organoid structures in soft biomatrices

Biofabrication allows for the templating of structural features in materials on cellularly-relevant size scales, enabling the generation of tissue-like structures with controlled form and function. This is particularly relevant for growing organoids, where the application of biochemical and biomechanical stimuli can be used to guide the assembly and differentiation of stem cells and form architectures similar to the parent tissue or organ. Recently, ablative laser-scanning techniques was used to create 3D overhang features in collagen hydrogels at size scales of 10-100µm and supported the crypt-villus architecture in intestinal organoids. As a complementary method, providing advantages for high-throughput patterning, we printed thioester functionalized poly(ethylene glycol) (PEG) elastomers using digital light processing (DLP) and created sacrificial, 3D shapes that could be molded into soft (G' < 1000 Pa) hydrogel substrates. Specifically, three-arm 1.3 kDa PEG thiol and three-arm 1.6 kDa PEG norbornene, containing internal thioester groups, were photopolymerized to yield degradable elastomers. When incubated in a solution of 300 mM 2-mercaptoethanol (pH 9.0), 1 mm thick 10 mm diameter elastomer discs degraded in <2 h. Using DLP, arrays of features with critical dimensions of 37 ± 4µm, resolutions of 22 ± 5µm, and overhang structures as small as 50µm, were printed on the order of minutes. These sacrificial thioester molds with physiologically relevant features were cast-molded into Matrigel and subsequently degraded to create patterned void spaces with high fidelity. Intestinal stem cells (ISCs) cultured on the patterned Matrigel matrices formed confluent monolayers that conformed to the underlying pattern. DLP printed sacrificial thioester elastomer constructs provide a robust and rapid method to fabricate arrays of 3D organoid-sized features in soft tissue culture substrates and should enable investigations into the effect of epithelial geometry and spacing on the growth and differentiation of ISCs.

The effects of surface topography modification on hydrogel properties

Hydrogel has been an attractive biomaterial for tissue engineering, drug delivery, wound healing, and contact lens materials, due to its outstanding properties, including high water content, transparency, biocompatibility, tissue mechanical matching, and low toxicity. As hydrogel commonly possesses high surface hydrophilicity, chemical modifications have been applied to achieve the optimal surface properties to improve the performance of hydrogels for specific applications. Ideally, the effects of surface modifications would be stable, and the modification would not affect the inherent hydrogel properties. In recent years, a new type of surface modification has been discovered to be able to alter hydrogel properties by physically patterning the hydrogel surfaces with topographies. Such physical patterning methods can also affect hydrogel surface chemical properties, such as protein adsorption, microbial adhesion, and cell response. This review will first summarize the works on developing hydrogel surface patterning methods. The influence of surface topography on interfacial energy and the subsequent effects on protein adsorption, microbial, and cell interactions with patterned hydrogel, with specific examples in biomedical applications, will be discussed. Finally, current problems and future challenges on topographical modification of hydrogels will also be discussed.

Quantitative developmental biology in vitro using micropatterning

Micropatterning encompasses a set of methods aimed at precisely controlling the spatial distribution of molecules onto the surface of materials. Biologists have borrowed the idea and adapted these methods, originally developed for electronics, to impose physical constraints on biological systems with the aim of addressing fundamental questions across biological scales from molecules to multicellular systems. Here, I approach this topic from a developmental biologist's perspective focusing specifically on how and why micropatterning has gained in popularity within the developmental biology community in recent years. Overall, this Primer provides a concise overview of how micropatterns are used to study developmental processes and emphasises how micropatterns are a useful addition to the developmental biologist's toolbox.

Roadmap for the multiscale coupling of biochemical and mechanical signals during development

The way in which interactions between mechanics and biochemistry lead to the emergence of complex cell and tissue organization is an old question that has recently attracted renewed interest from biologists, physicists, mathematicians and computer scientists. Rapid advances in optical physics, microscopy and computational image analysis have greatly enhanced our ability to observe and quantify spatiotemporal patterns of signalling, force generation, deformation, and flow in living cells and tissues. Powerful new tools for genetic, biophysical and optogenetic manipulation are allowing us to perturb the underlying machinery that generates these patterns in increasingly sophisticated ways. Rapid advances in theory and computing have made it possible to construct predictive models that describe how cell and tissue organization and dynamics emerge from the local coupling of biochemistry and mechanics. Together, these advances have opened up a wealth of new opportunities to explore how mechanochemical patterning shapes organismal development. In this roadmap, we present a series of forward-looking case studies on mechanochemical patterning in development, written by scientists working at the interface between the physical and biological sciences, and covering a wide range of spatial and temporal scales, organisms, and modes of development. Together, these contributions highlight the many ways in which the dynamic coupling of mechanics and biochemistry shapes biological dynamics: from mechanoenzymes that sense force to tune their activity and motor output, to collectives of cells in tissues that flow and redistribute biochemical signals during development.

Lymphocyte perform reverse adhesive haptotaxis mediated by integrins LFA-1

Cell Guidance by anchored molecules, or haptotaxis, is crucial in development, immunology and cancer. Adhesive haptotaxis, or guidance by adhesion molecules, is well established for mesenchymal cells like fibroblasts, whereas its existence remains unreported for amoeboid cells that require less or no adhesion to migrate. We show here in vitro that amoeboid human T lymphocytes develop adhesive haptotaxis versus densities of integrin ligands expressed by high endothelial venules. Moreover, lymphocytes orient towards increasing adhesion with VLA-4 integrins, like all mesenchymal cells, but towards decreasing adhesion with LFA-1 integrins, which has never been observed. This counterintuitive ‘reverse haptotaxis’ cannot be explained with the existing mesenchymal mechanisms of competition between cells’ pulling edges or of lamellipodia growth activated by integrins, which favor orientation towards increasing adhesion. Mechanisms and functions of amoeboid adhesive haptotaxis remain unclear, however multidirectional integrin-mediated haptotaxis may operate around transmigration ports on endothelium, stromal cells in lymph nodes, and inflamed tissue where integrin ligands are spatially modulated.