Influence of Remodeled ECM and Co-culture with iPSC-Derived Cardiac Fibroblasts on the Mechanical Function of Micropatterned iPSC-Derived Cardiomyocytes

INTRODUCTION

In native heart tissue, functions of cardiac fibroblasts (CFs) include synthesis, remodeling, and degradation of the extracellular matrix (ECM) as well as secreting factors that regulate cardiomyocyte (CM) function. The influence of direct co-culture and CF-derived ECM on CM mechanical function are not fully understood.

METHODS

Here we use an engineered culture platform that provides control over ECM geometry and substrate stiffness to evaluate the influence of iPSC-CFs, and the ECM they produce, on the mechanical function of iPSC-CMs. Mechanical analysis was performed using digital image correlation to quantify maximum contractile strain, spontaneous contraction rate, and full-field organization of the contractions.

RESULTS

When cultured alone, iPSC-CFs produce and remodel the ECM into fibers following the underlying 15° chevron patterned ECM. The substrates were decellularized and confirmed to have highly aligned fibers that covered a large fraction of the pattern area before reseeding with iPSC-CMs, alone or in co-culture with iPSC-CFs. When seeded on decellularized ECM, larger maximum contractile strains were observed in the co-culture condition compared to the CM Only condition. No significant difference was found in contractile strain between the Matrigel and decellularized ECM conditions; however, the spontaneous contraction rate was lower in the decellularized ECM condition. A methodology for quantifying alignment of cell contraction across the entire field of view was developed based on trajectories approximating the cell displacements during contraction. Trajectory alignment was unaltered by changes in culture or ECM conditions.

CONCLUSIONS

These combined observations highlight the important role CFs play in vivo and the need for models that enable a quantitative approach to examine interactions between the CFs and CMs, as well as the interactions of these cells with the ECM.

Long-term organotypic brain slices cultured on collagen-based microcontact prints: A perspective for a brain-on-a-chip

Organotypic brain slices are three-dimensional 150 µm-thick sections of a postnatal day 10 mouse and can be cultured for several weeks in vitro. In such brain slices the complex cellular connections are preserved with a high viability. These brain slices can be connected to collagen-loaded microcontact prints to develop a simple brain-on-a-chip model. Using the microcontact printing technique, many peptides or proteins can be printed onto a semipermeable membrane and linked to brain slices. On these microcontact prints, brain-derived nerve fibers grow out, or microglia can get activated and migrate out, or also new brain vessels can be formed. Such a brain-on-a-chip model may allow to develop new drugs or a diagnostic method for neurodegenerative diseases.

Multicellular aligned bands disrupt global collective cell behavior

Mechanical stress patterns emerging from collective cell behavior have been shown to play critical roles in morphogenesis, tissue repair, and cancer metastasis. In our previous work, we constrained valvular interstitial cell (VIC) monolayers on circular protein islands to study emergent behavior in a controlled manner and demonstrated that the general patterns of cell alignment, size, and apoptosis correlate with predicted mechanical stress fields if radially increasing stiffness or contractility are used in the computational models. However, these radially symmetric models did not predict the existence of local regions of dense aligned cells observed in seemingly random locations of individual aggregates. The goal of this study is to determine how the heterogeneities in cell behavior emerge over time and diverge from the predicted collective cell behavior. Cell-cell interactions in circular multicellular aggregates of VICs were studied with time-lapse imaging ranging from hours to days, and migration, proliferation, and traction stresses were measured. Our results indicate that elongated cells create strong local alignment within preconfluent cell populations on the microcontact printed protein islands. These cells influence the alignment of additional cells to create dense, locally aligned bands of cells which disrupt the predicted global behavior. Cells are highly elongated at the endpoints of the bands yet have decreased spread area in the middle and reduced mobility. Although traction stresses at the endpoints of bands are enhanced, even to the point of detaching aggregates from the culture surface, the cells in dense bands exhibit reduced proliferation, less nuclear YAP, and increased apoptotic rates indicating a low stress environment. These findings suggest that strong local cell-cell interactions between primary fibroblastic cells can disrupt the global collective cellular behavior leading to substantial heterogeneity of cell behaviors in constrained monolayers. This local emergent behavior within aggregated fibroblasts may play an important role in development and disease of connective tissues. STATEMENT OF SIGNIFICANCE: Mechanical stress patterns emerging from collective cell behavior play critical roles in morphogenesis, tissue repair, and cancer metastasis. Much has been learned of these collective behaviors by utilizing microcontact printing to constrain cell monolayers (aggregates) into specific shapes. Here we utilize these tools along with long-term video microscopy tracking of individual aggregates to determine how heterogeneous collective behaviors unique to primary fibroblastic cells emerge over time and diverge from computed stress fields. We find that dense multicellular bands form from local collective behavior and disrupt the global collective behavior resulting in heterogeneous patterns of migration, traction stresses, proliferation, and apoptosis. This local emergent behavior within aggregated fibroblasts may play an important role in development and disease of connective tissues.

A versatile and tunable bio-patterning platform for the construction of various cell array biochips

In this work, we report a versatile and tunable platform for the construction of various cell array biochips using a simple soft lithographic approach to pattern polydopamine (PDA) arrays via microcontact printing (μCP). Instead of direct polymerization of PDA on the polydimethylsiloxane (PDMS) tips, dopamine monomers were first printed on the substrate followed by a self-oxidative polymerization step facilitated by ammonia vapor to grow PDA in situ, which greatly reduced the reaction time and prevented the PDMS tips from damaging. The improved robustness and utility of the PDMS tips allows the formation of tunable PDA array chips with controllable PDA feature size and shape. As a result, single cell, multi-cells and cell line arrays can be constructed. The obtained cell array chips showed high single cell capture efficiency, providing a standardized single cell array analysis platform. Meanwhile, the adhered cells can maintain excellent viability and proliferation ability on the PDA chips. Moreover, a cytotoxicity sensor with single cell resolution was enabled on the single cell array chip. This work provides a promising cell array biochip platform for high-throughput cellular analysis and cell screening.

Microcontact printing of gold nanoparticle at three-phase interface as flexible substrate for SERS detection of MicroRNA

The rigidity of traditional solid-state surface-enhanced Raman spectroscopy (SERS) substrate hampers their application in the curved structure for nonplanar surface test and in-situ detection. Traditionally, the flexible Raman substrates are often prepared by transferring printing of patterned nanoparticles on the flexible materials such as polymer, paper, etc. However，the replicate patterns are often produced by high-cost instruments. In this study, a low-cost and flexible SERS substrate is prepared by using a microcontact printing technology to transfer three-phase-assembled nanoparticles on a polydimethylsiloxane film, which can stabilize the assembled nanoparticles. Combining with the endonuclease Nt.BbvCI assisted amplification method, a SERS biosensor is constructed for microRNA 21 (miRNA 21) assay. This platform presents a wide dynamic range (100 fM ∼1 nM), achieving a fabulous sensitivity with limit of detection of 11.96 fM for miRNA 21. Furthermore, after being bent 90° for 50 times, the Raman intensity of the flexible substrate shows a negligible change. This versatile flexible substrate exhibits considerable potential for SERS analysis, which also opens a new avenue for preparing flexible devices.

A simple and reliable microfabrication process for a programmable microvalve array

We describe our reliable methodology for fabricating a complex programmable microvalve array (PMA) and its integration with a glass microcapillary electrophoresis chip. This methodology is applicable to any device that requires multilayered PDMS, multiple alignment processes, selective PDMS bonding, and multilayered integration with downstream sensing systems. Along with the detailed step-by-step process, we discuss essential quality assurance checks that can be performed throughout fabrication to assist in troubleshooting and maximizing chip yield.•Comprehensive instructions for designing and fabricating a programmable microvalve array.•Selective bonding of PDMS and glass by microcontact printing.•Numerous quality control procedures to boost chip yield.

Exploring the benefits of surface analysis techniques to develop double multilayer transfer printing of J-Aggregates cyanine dyes by integrating L-b-L and μCp processes

Layer-by-layer self-assembly (L-b-L assembly) makes possible to obtain polyelectrolyte multilayers (PEMs) and one of the polyelectrolytes could be replaced by a dye molecule to obtain multilayers which may exhibit optical properties of great interest. On the other hand, μCp has become a routine technique for the preparation of micro- and nanostructured surfaces. In our development in progress of a surface engineering strategy to transfer J-Agg cyanine dyes onto surfaces by integrating L-b-L process and μCp, this contribution highlights how surface analysis imaging techniques can bring valuable information for the development of the process involving a double Multilayers Transfer Printing (MTP) with a Moiré effect. Key parameters sustaining image interpretation are difference in deposit thickness (optical microscopy, atomic force microscopy, scanning electron microscopy), in roughness (atomic force microscopy and scanning electron microscopy), in charge effect (scanning electron microscopy) and the chemical contrast between unprinted and printed areas (time-of-flight secondary ion mass spectrometry).

Hydrophobic surface patterning with soft, wax-infused micro-stamps

HYPOTHESIS

Waxy hydrocarbons diffuse freely in polydimethylsiloxane (PDMS), and this capability can be leveraged to generate inexpensive surface micropatterns that modify adhesion and wetting.

EXPERIMENTS

Patterns are created by placing a waxy Parafilm sheet on the back of a PDMS stamp containing microscale surface features. When heated, the paraffin liquefies and diffuses through the stamp, creating a thin liquid layer on the micropatterned stamp surface; when placed in contact with a target surface, the layer solidifies and is retained on the target when the stamp is removed. Micropatterns were generated on different materials and surface topographies; pattern geometry was evaluated using optical profilometry and changes in wetting were evaluated using contact angle goniometry. Diffusion of paraffin through PDMS was evaluated using XPS.

FINDINGS

Wax micropatterns have submicron lateral resolution and thickness ranging from 85 to 380 nm depending on contact time. By using XPS analysis to track paraffin diffusion within the PDMS stamp during this process, we estimate the diffusion coefficient to be 5.3 × 10^-7 cm²/s at 65 °C. This means that the paraffin layer at the stamp surface replenishes in less than a second after stamping, so it can be used multiple times without re-inking to deposit complex, multi-layer paraffin patterns.

Methods for Processing Protein Aggregates into Surfaces

The processing of inclusion bodies (IBs) into surfaces is of great interest for cell culture applications due to the combined physical and biological cues these particles provide. The arrangement of these IBs into defined and tunable micropatterns can be useful for basic research purposes regarding the mechanical properties needed for cell adhesion and migration, among other responses. There are several approaches that can be used when functionalizing a substrate with IBs, regarding both the strategy used and also the kind of surface-particle interaction. The interaction between surface and IB can be mainly of three types: physisorption, electrostatic or covalent. This interaction can be controlled by depositing an appropriate self-assembled monolayer (SAM) on top of a substrate as an interface. Furthermore, several strategies can be used to immobilize IBs on surfaces in various configurations, like random deposition, micrometric printed geometries or gradient patterns.

Black Dots: High-Yield Traction Force Microscopy Reveals Structural Factors Contributing to Platelet Forces

Measuring the traction forces produced by cells provides insight into their behavior and physiological function. Here, we developed a technique (dubbed 'black dots') that microcontact prints a fluorescent micropattern onto a flexible substrate to measure cellular traction forces without constraining cell shape or needing to detach the cells. To demonstrate our technique, we assessed human platelets, which can generate a large range of forces within a population. We find platelets that exert more force have more spread area, are more circular, and have more uniformly distributed F-actin filaments. As a result of the high yield of data obtainable by this technique, we were able to evaluate multivariate mixed effects models with interaction terms and conduct a clustering analysis to identify clusters within our data. These statistical techniques demonstrated a complex relationship between spread area, circularity, F-actin dispersion, and platelet force, including cooperative effects that significantly associate with platelet traction forces. STATEMENT OF SIGNIFICANCE: Cells produce contractile forces during division, migration, or wound healing. Measuring cellular forces provides insight into their health, behavior, and function. We developed a technique that calculates cellular forces by seeding cells onto a pattern and quantifying how much each cell displaces the pattern. This technique is capable of measuring hundreds of cells without needing to detach them. Using this technique to evaluate human platelets, we find that platelets exerting more force tend to have more spread area, are more circular in shape, and have more uniformly distributed cytoskeletal filaments. Due to our high yield of data, we were able to apply statistical techniques that revealed combinatorial effects between these factors.

Effect of upstream priming on transient downstream platelet-substrate interactions

Upstream exposure of platelets to activating proteins 'primes' platelets for increased downstream adhesion, though the mechanics of platelet translocation before permanently arresting are not well understood. To investigate platelet translocation on platelet-binding proteins, primed platelets' transient contacts with immobilized proteins were recorded and analyzed. Using a microfluidic channel, representative of a vascular graft, platelet-activating proteins were covalently attached to the upstream priming, center, and downstream capture positions. Image sequences of platelet interactions with the center protein were captured as platelet-rich plasma (PRP) was perfused through the channel. There was an increase in both platelet pause events and net platelet adhesion on von Willebrand factor, collagen, or fibrinogen following upstream exposure to the same protein. Upstream priming also caused a decrease in average platelet velocity. The duration of transient platelet arrests on the protein-coated surface and the distance that platelets travel between pause events depended on the protein with which they were interacting. The most significant increase in platelet pause events frequency and decrease in average velocity occurred on immobilized von Willebrand factor, compared to the control with no upstream priming. These results demonstrate that platelet priming increases downstream platelet-protein interactions prior to permanent adhesion.

Biomaterial based strategies to reconstruct the nigrostriatal pathway in organotypic slice co-cultures

Protection or repair of the nigrostriatal pathway represents a principal disease-modifying therapeutic strategy for Parkinson's disease (PD). Glial cell line-derived neurotrophic factor (GDNF) holds great therapeutic potential for PD, but its efficacious delivery remains difficult. The aim of this study was to evaluate the potential of different biomaterials (hydrogels, microspheres, cryogels and microcontact printed surfaces) for reconstructing the nigrostriatal pathway in organotypic co-culture of ventral mesencephalon and dorsal striatum. The biomaterials (either alone or loaded with GDNF) were locally applied onto the brain co-slices and fiber growth between the co-slices was evaluated after three weeks in culture based on staining for tyrosine hydroxylase (TH). Collagen hydrogels loaded with GDNF slightly promoted the TH+ nerve fiber growth towards the dorsal striatum, while GDNF loaded microspheres embedded within the hydrogels did not provide an improvement. Cryogels alone or loaded with GDNF also enhanced TH+ fiber growth. Lines of GDNF immobilized onto the membrane inserts via microcontact printing also significantly improved TH+ fiber growth. In conclusion, this study shows that various biomaterials and tissue engineering techniques can be employed to regenerate the nigrostriatal pathway in organotypic brain slices. This comparison of techniques highlights the relative merits of different technologies that researchers can use/develop for neuronal regeneration strategies.

Engineering Shape-Controlled Microtissues on Compliant Hydrogels with Tunable Rigidity and Extracellular Matrix Ligands

In vitro models that recapitulate key aspects of native tissue architecture and the physical microenvironment are emerging systems for modeling development and disease. For example, the myocardium consists of layers of aligned and coupled cardiac myocytes that are interspersed with supporting cells and embedded in a compliant extracellular matrix (ECM). These cell-cell and cell-matrix interactions are known to be important regulators of tissue physiology and pathophysiology. In this protocol, we describe a method for mimicking the alignment, cell-cell interactions, and rigidity of the myocardium by engineering an array of square, aligned cardiac microtissues on polyacrylamide hydrogels. This entails three key methods: (1) fabricating elastomer stamps with a microtissue pattern; (2) preparing polyacrylamide hydrogel culture substrates with tunable elastic moduli; and (3) transferring ECM proteins onto the surface of the hydrogels using microcontact printing. These hydrogels can then be seeded with cardiac myocytes or mixtures of cardiac myocytes and fibroblasts to adjust cell-cell interactions. Overall, this approach is advantageous because shape-controlled microtissues encompass both cell-cell and cell-matrix adhesions in a form factor that is relatively reproducible and scalable. Furthermore, polyacrylamide hydrogels are compatible with the traction force microscopy assay for quantifying contractility, a critical function of the myocardium. Although cardiac microtissues are the example presented in this protocol, the techniques are relatively versatile and could have many applications in modeling other tissue systems.

Cell-ECM contact-guided intracellular polarization is mediated via lamin A/C dependent nucleus-cytoskeletal connection

Cell polarization plays a crucial role in dynamic cellular events, such as cell proliferation, differentiation, and directional migration in response to diverse extracellular and intracellular signals. Although it is well known that cell polarization entails highly orchestrated intracellular molecular reorganization, the underlying mechanism of repositioning by intracellular organelles in the presence of multiple stimuli is still unclear. Here, we show that front-rear cell polarization based on the relative positions of nucleus and microtubule organizing center is precisely controlled by mechanical interactions including cellular adhesion to extracellular matrix and nucleus-cytoskeletal connections. By modulating the size and distribution of fibronectin-coated adhesive spots located in the polarized cell shape mimicking micropatterns, we monitored the alterations in cell polarity. We found that the localization of individual adhesive spots is more dominant than the cell shape itself to induce intracellular polarization. Further, the degree of cell polarization was diminished significantly by disrupting nuclear lamin A/C. We further confirm that geometrical cue-guided intracellular polarization determines directional cell migration via local activation of Cdc42. These findings provide novel insights into the role of nucleus-cytoskeletal connections in single cell polarization under a combination of physical, molecular, and genetic cues, where lamin A/C acts as a critical molecular mediator in ECM sensing and signal transduction via nucleus-cytoskeletal connection.

Cell seeding simulation on micropatterned islands shows cell density depends on area to perimeter ratio, not on island size or shape

Protein micropatterned substrates have been used to control cell size, shape, and cell-cell contacts, characteristics that influence a range of cell behaviors from early cell differentiation to late stages of maturation. Knowing the initial island cell seeding density is important to interpreting results and understanding downstream cell behavior. While studies routinely report the intended or target cell seeding density, they do not report the actual cell seeding density on the islands. As cells proliferate, differences in initial cell seeding density could compound and may lead to misinterpretation of results. In this work, we present a cell seeding simulation and apply it to 100s of islands with a range of geometries (sizes and shapes) to explore how island cell seeding density relates to the target or unpatterned cell seeding density. We first experimentally validate the simulation and then show that normalized island cell seeding density depends on island size, shape, and spacing, but can be predicted solely from island area to perimeter ratio, A2P, via a power law relationship for a wide range of island geometries. Interestingly, normalized island cell seeding density is the same as the normalized unpatterned cell seeding density for A2P ≥ 17 µm. This simulation will help to design micropatterned substrates and to have more accurate representation of the island cell seeding density at the start of experiments. By knowing the island cell seeding density, we can more easily reproduce results across research groups to understand the roles of cell-cell contact and cell size and shape on cell behavior. STATEMENT OF SIGNIFICANCE: We present a cell seeding simulation on protein-micropatterned substrates and use it to simulate seeding across 100s of island geometries (size, shape, and spacing) covering two orders of magnitude in size. The simulation shows that island cell density varies significantly with island geometry compared to the target seeding density. However, island cell density can be predicted from one geometric parameter - the island's area to perimeter ratio. Results will help direct researchers on how to achieve uniform cell density across all island geometries. Since cell density and island shape both influence cell behaviors, such as differentiation, this simulation may help to isolate these factors, facilitate micropatterned substrate design, and provide a mechanism for more reproduceable results across studies.

Parallelized DNA tethered bead measurements to scrutinize DNA mechanical structure

Tethering beads to DNA offers a panel of single molecule techniques for the refined analysis of the conformational dynamics of DNA and the elucidation of the mechanisms of enzyme activity. Recent developments include the massive parallelization of these techniques achieved by the fabrication of dedicated nanoarrays by soft nanolithography. We focus here on two of these techniques: the Tethered Particle motion and Magnetic Tweezers allowing analysis of the behavior of individual DNA molecules in the absence of force and under the application of a force and/or a torque, respectively. We introduce the experimental protocols for the parallelization and discuss the benefits already gained, and to come, for these single molecule investigations.

A novel method for quantifying traction forces on hexagonal micropatterned protein features on deformable poly-dimethyl siloxane sheets

Many methods exist for quantifying cellular traction forces, including traction force microscopy and microfabricated post arrays. However, these methodologies have limitations, including a requirement to remove cells to determine undeflected particle locations and the inability to quantify forces of cells with low cytoskeletal stiffness, respectively. Here we present a novel method of traction force quantification that eliminates both of these limitations. Through the use of a hexagonal pattern of microcontact-printed protein spots, a novel computational algorithm, and thin surfaces of polydimethyl siloxane (PDMS) blends, we demonstrate a system that:

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quantifies cellular forces on a homogeneous surface that is stable and easily manufactured.

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utilizes hexagonal patterns of protein spots and computational geometry to quantify cellular forces without need for cell removal.

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quantifies cellular forces in cells with low cytoskeletal rigidity.

The Heterogeneity of Renal Stem Cells and Their Interaction with Bio- and Nano-materials

For a long time, the kidney has been considered incapable of regeneration. Instead, in recent years, studies have supported the existence of heterogeneity of renal stem/progenitor cells with the ability to regenerate both glomerular and tubular epithelial cells. Indeed, several studies evidence that renal progenitor cells, releasing chemokines, growth factors, microvesicles, and transcription factors through paracrine mechanisms, can induce tissue regeneration and block pathological processes of the kidney. In this chapter the potentiality of the kidney regenerative processes is considered and reviewed, and the main classes of stem/progenitor cells that might contribute to the renal tissue renewal is analyzed. Moreover, we evaluate the role of biomaterials in the regulation of cellular functions, specifically addressing renal stem/progenitor cells. Materials can be synthesized and tailored in order to recreate a finely structured microenvironment (by nanostructures, nanofibers, bioactive compounds, etc.) with which the cells can interact actively. For instance, by patterning substrates in regions that alternately promote or prevent protein adsorption, cell adhesion and spreading processes can be controlled in space. We illustrate the potentiality of nanotechnologies and engineered biomaterials in affecting and enhancing the behavior of renal stem/progenitor cells. Although there are still many challenges for the translation of novel therapeutics, advances in biomaterials and nanomedicine have the potential to drastically change the clinical and therapeutic landscape, even in combination with stem cell biology.

A label-free diffraction-based sensing displacement immunosensor to quantify low molecular weight organic compounds

Herein we present a diffractometric immunosensor to quantify low molecular weight organic compounds in a label-free, simple, and sensitive fashion. The approach is based on patterning analyte analogues (haptens) on solid surfaces according to a diffractive structure, and then loading specific antibodies on them to be subsequently displaced by free analytes in solution. This displacement generates a measurable change in the diffractive response that enables to quantify the analyte concentration. In this study we address the fabrication, optimization, and assessment of these diffractive structures of biological probes and their application to the analysis of atrazine, an organic compound extensively used as pesticide. This immunosensor displays well-correlated dose-response curves that reach a detection limit of 1.1 ng mL^-1 of atrazine in label-free conditions. From a general viewpoint, this study also aims to provide insights into exploiting this approach towards prospective in-field analysis and screening strategies to sense multiple low molecular weight compounds in label-free conditions.

Effects of upstream shear forces on priming of platelets for downstream adhesion and activation

Platelets in flowing blood are sometimes exposed to elevated shear forces caused by anastomotic stenosis at the blood vessel-vascular implant interface. The objective of this study was to determine how effective upstream shear forces are in priming platelets for downstream adhesion and activation. Flow chambers with upstream stenotic regions (shear rates of 400-1000 s^-1) were manufactured by relief molding of polydimethylsiloxane. Downstream from the stenotic regions, microcontact printing was used to covalently immobilize three different proteins (fibrinogen, collagen, or von Willebrand factor) to serve as platelet capture agents. Anticoagulated whole blood was perfused through the flow chambers and platelet adhesion to the downstream capture region was quantified. It was found that transient exposure of platelets to increased shear forces resulted in higher platelet adhesion on all three proteins. The duration of the platelet exposure to elevated shear forces was varied by changing the length of the stenotic regions. The results indicated that, in addition to the magnitude of shear forces, the duration of exposure to these forces was also an important factor in priming platelets. The effect of upstream shear forces on platelet activation was assessed by quantifying P-selectin, integrin α_IIbβ₃, lysosomal glycoprotein, and phosphatidylserine exposure using flow cytometry. The results suggested that increased shear forces were capable of increasing the priming of platelets for downstream activation. This study implicates the anastomotic region(s) of vascular implants as a locus of platelet pre-activation that may lead to thrombus formation downstream.

STATEMENT OF SIGNIFICANCE

A synthetic small-diameter vascular graft can often become stenotic due to intimal fibrous hyperplasia, either generally along the inside of the graft or at the anastomotic regions, leading to an increased shear force on flowing platelets. Our lab is studying how the upstream platelet preactivation (aka "priming") in flowing blood affects their downstream adhesion and activation. This manuscript describes a study in which priming of platelets is achieved by upstream stenotic narrowing in a microfluidic flow chamber. Such experimental design was intended to mimic a vascular implant with stenotic upstream anastomosis and downstream exposed platelet protein agonists. Understanding how the pre-activated platelets respond to imperfect vascular implant surfaces downstream is an important factor in designing better vascular implants.

Microenvironmental Modulation of Calcium Wave Propagation Velocity in Engineered Cardiac Tissues

Introduction

In the myocardium, rapid propagation of action potentials and subsequent calcium waves is critical for synchronizing the contraction of cardiac myocytes and maximizing cardiac output. In many pathological settings, diverse remodeling of the tissue microenvironment is correlated with arrhythmias and decreased cardiac output, but the precise impact of tissue remodeling on propagation is not completely understood. Our objective was to delineate how multiple features within the cardiac tissue microenvironment modulate propagation velocity.

Methods

To recapitulate diverse myocardial tissue microenvironments, we engineered substrates with tunable elasticity, patterning, composition, and topography using two formulations of polydimethylsiloxane (PDMS) micropatterned with fibronectin and gelatin hydrogels with flat or micromolded features. We cultured neonatal rat ventricular myocytes on these substrates and quantified cell density, tissue alignment, and cell shape. We used a fluorescent calcium indicator, high-speed microscopy, and newly-developed analysis software to record and quantify calcium wave propagation velocity (CPV).

Results

For all substrates, tissue alignment and cell aspect ratio were higher in aligned compared to isotropic tissues. Isotropic CPV and longitudinal CPV were similar across conditions, but transverse CPV was lower on micromolded gelatin hydrogels compared to micropatterned soft and stiff PDMS. In aligned tissues, the anisotropy ratio of CPV (longitudinal CPV/transverse CPV) was lower on micropatterned soft PDMS compared to micropatterned stiff PDMS and micromolded gelatin hydrogels.

Conclusion

Propagation velocity in engineered cardiac tissues is sensitive to features in the tissue microenvironment, such as alignment, matrix elasticity, and matrix topography, which may underlie arrhythmias in conditions with pathological tissue remodeling.

Fabrication of Biomolecule Microarrays for Cell Immobilization Using Automated Microcontact Printing

Biomolecule microarrays are generally produced by conventional microarrayer, i.e., by contact or inkjet printing. Microcontact printing represents an alternative way of deposition of biomolecules on solid supports but even if various biomolecules have been successfully microcontact printed, the production of biomolecule microarrays in routine by microcontact printing remains a challenging task and needs an effective, fast, robust, and low-cost automation process. Here, we describe the production of biomolecule microarrays composed of extracellular matrix protein for the fabrication of cell microarrays by using an automated microcontact printing device. Large scale cell microarrays can be reproducibly obtained by this method.

Microcontact printing of polydopamine on thermally expandable hydrogels for controlled cell adhesion and delivery of geometrically defined microtissues

Scaffold-free harvest of microtissue with a defined structure has received a great deal of interest in cell-based assay and regenerative medicine. In this study, we developed thermally expandable hydrogels with spatially controlled cell adhesive patterns for rapid harvest of geometrically controlled microtissue. We patterned polydopamine (PD) on to the hydrogel via microcontact printing (μCP), in linear shapes with widths of 50, 100 and 200μm. The hydrogels facilitated formation of spatially controlled strip-like microtissue of human dermal fibroblasts (HDFBs). It was possible to harvest and translocate microtissues with controlled widths of 61.4±14.7, 104.3±15.6, and 186.6±22.3μm from the hydrogel to glass substrates by conformal contact upon expansion of the hydrogel in response to a temperature change from 37 to 4°C, preserving high viability, extracellular matrix, and junction proteins. Microtissues were readily translocated in vivo to the subcutaneous tissue of mouse. The microtissues were further utilized as a simple assay model for monitoring of contraction in response to ROCK1 inhibitor. Collectively, micro-sized patterning of PD on the thermally expandable hydrogels via μCP holds promise for the development of microtissue harvesting systems that can be employed to ex vivo tissue assay and cell-based therapy.

STATEMENT OF SIGNIFICANCE

Harvest of artificial tissue with controlled cellular arrangement independently from external materials has been widely studied in cell-based assay and regenerative medicine. In this study, we developed scaffold-free harvest system of microtissues with anisotropic arrangement and controlled width by exploiting thermally expandable hydrogels with cell-adhesive patterns of polydopamine formed by simple microcontact printing. Cultured strips of human dermal fibroblasts on the hydrogels were rapidly delivered to various targets ranging from flat coverglass to mice subcutaneous tissue by thermal expansion of the hydrogel at 4°C for 10min. These were further utilized as a drug screening model responding to ROCK1 inhibitor, which imply its versatile applicability.

Protein micropatterns printed on glass: Novel tools for protein-ligand binding assays in live cells

Micrometer-sized patterns of proteins on glass or silica surfaces are in widespread use as protein arrays for probing with ligands or recombinant proteins. More recently, they have been used to capture the surface proteins of mammalian cells seeded onto them, and to arrange these surface proteins into pattern structures. Binding of small molecule ligands or of other proteins, transmembrane or intracellular, to these captured surface proteins can then be quantified. However, reproducible production of protein micropatterns on surfaces can be technically difficult. In this review, we outline the wide potential and the current practical uses of printed protein micropatterns in a historical overview, and we detail some potential pitfalls and difficulties from our own experience, as well as ways to circumvent them.

Enzyme Deposition by Polydimethylsiloxane Stamping for Biosensor Fabrication

High-performance biosensors were fabricated by efficiently transferring enzyme onto Pt electrode surfaces using a polydimethylsiloxane (PDMS) stamp. Polypyrrole and Nafion were coated first on the electrode surface to act as permselective films for exclusion of both anionic and cationic electrooxidizable interfering compounds. A chitosan film then was electrochemically deposited to serve as an adhesive layer for enzyme immobilization. Glucose oxidase (GOx) was selected as a model enzyme for construction of a glucose biosensor, and a mixture of GOx and bovine serum albumin was stamped onto the chitosan-coated surface and subsequently crosslinked using glutaraldehyde vapor. For the optimized fabrication process, the biosensor exhibited excellent performance characteristics including a linear range up to 2 mM with sensitivity of 29.4 ± 1.3 μA mM^-1 cm^-2 and detection limit of 4.3 ± 1.7 μM (S/N = 3) as well as a rapid response time of ~2 s. In comparison to those previously described, this glucose biosensor exhibits an excellent combination of high sensitivity, low detection limit, rapid response time, and good selectivity. Thus, these results support the use of PDMS stamping as an effective enzyme deposition method for electroenzymatic biosensor fabrication, which may prove especially useful for the deposition of enzyme at selected sites on microelectrode array microprobes of the kind used for neuroscience research in vivo.

Revealing the Role of Microscale Architecture in Immune Synapse Function Through Surface Micropatterning

The immune synapse has emerged as a compelling example of structural complexity within cell-cell interfaces. This chapter focuses on the use of microcontact printing to isolate and investigate how spatial organization of signaling molecules drives the function of immune cells. In the process detailed here, multiple rounds of microcontact printing are combined to create patterned surfaces that control the relative spatial localization of CD3 and CD28 signaling in T cells, effectively replacing an antigen presenting cell with an engineered surface. A set of approaches used to address key issues of T cell activation are described and discussed.

Capillary-Driven Microfluidic Chips for Miniaturized Immunoassays: Patterning Capture Antibodies Using Microcontact Printing and Dry-Film Resists

The miniaturization of immunoassays using microfluidic devices is attractive for many applications, but an important challenge remains the patterning of capture antibodies (cAbs) on the surface of microfluidic structures. Here, we describe how to pattern cAbs on planar poly(dimethylsiloxane) (PDMS) stamps and how to microcontact print the cAbs on a dry-film resist (DFR). DFRs are new types of photoresists having excellent chemical resistance and good mechanical, adhesive, and optical properties. Instead of being liquid photoresists, DFRs are thin layers that are easy to handle, cut, photo-pattern, and laminate over surfaces. We show how to perform a simple fluorescence immunoassay using anti-biotin cAbs patterned on a 50-μm-thick DF-1050 DFR, Atto 647N-biotin analytes, and capillary-driven chips fabricated in silicon.

Microcontact-Printed Hydrogel Microwell Arrays for Clonal Muscle Stem Cell Cultures

Adult muscle stem cells (also called satellite cells) are an anatomically defined population of cells that are essential for muscle regeneration. In aging and dystrophic diseases, muscle stem cells (MuSCs) exhibit functional and molecular heterogeneity; therefore, single-cell assay technologies are critical to illuminate the mechanisms of pathological stem cell dysfunction. Here, we describe the process of generating mechanically tunable hydrogels with micro-scale well features ("microwells") using micro-contact printing for clonal muscle stem cell culture assays. Microcontact printing (μCP) is a simple and versatile method for generating cell culture substrates for micro-scale features for spatially restricting the cultures of single cells and their progeny. We explain how to use photolithography and polydimethylsiloxane casting to generate stamps capable of printing purified extracellular matrix proteins onto soft, hydrated poly(ethylene glycol) hydrogels to generate arrayed microwells in a defined pattern. We summarize methods to analyze the viability, migration, and differentiation of individual MuSC clones within hydrogel microwell cultures.

Protein patterning by microcontact printing using pyramidal PDMS stamps

Micro-contact printing, μCP, is a well-established soft-lithography technique for printing biomolecules. μCP uses stamps made of Poly(dimethylsiloxane), PDMS, made by replicating a microstructured silicon master fabricated by semiconductor manufacturing processes. One of the problems of the μCP is the difficult control of the printing process, which, because of the high compressibility of PDMS, is very sensitive to minute changes in the applied pressure. This over-sensitive response leads to frequent and/or uncontrollable collapse of the stamps with high aspect ratios, thus decreasing the printing accuracy and reproducibility. Here we present a straightforward methodology of designing and fabricating PDMS structures with an architecture which uses the collapse of the stamp to reduce, rather than enlarge the variability of the printing. The PDMS stamp, organized as an array of pyramidal micro-posts, whose ceiling collapses when pressed on a flat surface, replicates the structure of the silicon master fabricated by anisotropic wet etching. Upon application of pressure, depending on the size of, and the pitch between, the PDMS pyramids, an air gap is formed surrounding either the entire array, or individual posts. The printing technology, which also exhibits a remarkably low background noise for fluorescence detection, may find applications when the clear demarcation of the shapes of protein patterns and the distance between them are critical, such as microarrays and studies of cell patterning.

Heparin micropatterning onto fouling-release perfluoropolyether-based polymers via photobiotin activation

A simple method for constructing versatile ordered biotin/avidin arrays on UV-curable perfluoropolyethers (PFPEs) is presented. The goal is the realization of a versatile platform where any biotinylated biological ligands can be further linked to the underlying biotin/avidin array. To this end, microcontact arrayer and microcontact printing technologies were developed for photobiotin direct printing on PFPEs. As attested by fluorescence images, we demonstrate that this photoactive form of biotin is capable of grafting onto PFPEs surfaces during irradiation. Bioaffinity conjugation of the biotin/avidin system was subsequently exploited for further self-assembly avidin family proteins onto photobiotin arrays. The excellent fouling release PFPEs surface properties enable performing avidin assembly step simply by arrays incubation without PFPEs surface passivation or chemical modification to avoid unspecific biomolecule adsorption. Finally, as a proof of principle biotinylated heparin was successfully grafted onto photobiotin/avidin arrays.

Understanding the Role of ECM Protein Composition and Geometric Micropatterning for Engineering Human Skeletal Muscle

Skeletal muscle lost through trauma or disease has proven difficult to regenerate due to the challenge of differentiating human myoblasts into aligned, contractile tissue. To address this, we investigated microenvironmental cues that drive myoblast differentiation into aligned myotubes for potential applications in skeletal muscle repair, organ-on-chip disease models and actuators for soft robotics. We used a 2D in vitro system to systematically evaluate the role of extracellular matrix (ECM) protein composition and geometric patterning for controlling the formation of highly aligned myotubes. Specifically, we analyzed myotubes differentiated from murine C2C12 cells and human skeletal muscle derived cells (SkMDCs) on micropatterned lines of laminin compared to fibronectin, collagen type I, and collagen type IV. Results showed that laminin supported significantly greater myotube formation from both cells types, resulting in greater than twofold increase in myotube area on these surfaces compared to the other ECM proteins. Species specific differences revealed that human SkMDCs uniaxially aligned over a wide range of micropatterned line dimensions, while C2C12s required specific line widths and spacings to do the same. Future work will incorporate these results to engineer aligned human skeletal muscle tissue in 2D for in vitro applications in disease modeling, drug discovery and toxicity screening.

Synaptic compartmentalization by micropatterned masking of a surface adhesive cue in cultured neurons

Functions of neuronal circuit are fundamentally modulated by its quality and quantity of connections. Assessment of synapse, the basic unit for a neuronal connection, is labor-intensive and time-consuming in conventional culture systems, due to the small size and the spatially random distribution. In the present study, we propose a novel 'synapse compartmentalization' culture system, in which synapses are concentrated at controlled locations. We fabricated a negative dot array pattern by coating the entire surface with poly-l-lysine (PLL) and subsequent microcontact printing of 1) substrates which mask positive charge of PLL (Fc, BSA and laminin), or 2) a chemorepulsive protein (Semaphorin 3F-Fc). By combination of physical and biological features of these repulsive substrates, functional synapses were robustly concentrated in the PLL-coated dots. This synapse compartmentalization chip can be combined with the various high-throughput assay formats based on the synaptic morphology and function. Therefore, this quantifiable and controllable dot array pattern by microcontact printing will be potential useful for bio-chip platforms for the high-density assays used in synapse-related neurobiological studies.

Motile Human Neutrophils Sense Ligand Density Over Their Entire Contact Area

Neutrophils are key components of the immune system and motility is central their function during the inflammatory response. We have previously demonstrated that neutrophils are capable of switching their motile phenotype between amoeboid-like and keratocyte-like in response to the ligand density of adhesion molecules (Henry et al. in Int Biol 6:348-356, 2014). In this study, we engineered planar micropatterned surfaces that presented adhesion molecules in local islands of high density, separated by regions largely devoid of ligands. By controlling the geometry of islands we made arrays in which the local (on island) adhesion density was high but the global (multi-island) adhesion density over the entire cell-substrate interface was low. Neutrophils in contact with these island arrays assumed a well-spread and directionally-persistent motile phenotype (keratocyte-like) in contrast to the classical amoeboid morphology they display on uniform fields of high adhesion density. By virtue of our rationally designed substrates, we were able to conclude that neutrophils were integrating the stimulation received across their entire contact interface; furthermore, they were able to mount this whole cell response on the timescale of seconds. This work demonstrates the capacity of adhesive microenvironments to direct the phenotype of cell motility, which has broader implications in physiologic processes such as inflammation and cancer metastasis.

High-content imaging with micropatterned multiwell plates reveals influence of cell geometry and cytoskeleton on chromatin dynamics

Understanding the mechanisms underpinning cellular responses to microenvironmental cues requires tight control not only of the complex milieu of soluble signaling factors, extracellular matrix (ECM) connections and cell-cell contacts within cell culture, but also of the biophysics of human cells. Advances in biomaterial fabrication technologies have recently facilitated detailed examination of cellular biophysics and revealed that constraints on cell geometry arising from the cellular microenvironment influence a wide variety of human cell behaviors. Here, we create an in vitro platform capable of precise and independent control of biochemical and biophysical microenvironmental cues by adapting microcontact printing technology into the format of standard six- to 96-well plates to create MicroContact Printed Well Plates (μCP Well Plates). Automated high-content imaging of human cells seeded on μCP Well Plates revealed tight, highly consistent control of single-cell geometry, cytoskeletal organization, and nuclear elongation. Detailed subcellular imaging of the actin cytoskeleton and chromatin within live human fibroblasts on μCP Well Plates was then used to describe a new relationship between cellular geometry and chromatin dynamics. In summary, the μCP Well Plate platform is an enabling high-content screening technology for human cell biology and cellular engineering efforts that seek to identify key biochemical and biophysical cues in the cellular microenvironment.

Facile functionalization and assembly of live cells with microcontact-printed polymeric biomaterials

The functionalization and assembly of live cells with microfabricated polymeric biomaterials have attracted considerable interest in recent years, but the conventional methods suffer from high cost, high complexity, long processing time or inadequate capability. The present study reports on the development of a novel method for functionalizing and assembling live cells by integrating microcontact printing of polymeric biomaterials with a temperature-sensitive sacrificial layer prepared by spin-coating. This method has been used not only to functionalize live cells with microscopic polyelectrolyte and thermoplastic structures of various sizes and shapes, but also to assemble the cells into macroscopic stripes and sheets. The method is applicable to multiple types of cells, including human leukemic cells, mouse embryonic stem cells and human mesenchymal stem cells in the forms of single cells and cell aggregates. In addition, the microcontact-printed structures can be prepared using biodegradable and biocompatible polyelectrolytes and thermoplastic. The unique combination of low cost, ease of use and high versatility renders this method potentially useful for diverse biomedical applications, including drug delivery, cell tracking and tissue engineering.

Astrocytes alignment and reactivity on collagen hydrogels patterned with ECM proteins

To modulate the surface properties of collagen and subsequent cell-surface interactions, a method was developed to transfer protein patterns from glass coverslips to collagen type I hydrogel surfaces. Two proteins and one proteoglycan found in central nervous system extracellular matrix as well as fibrinogen were patterned in stripes onto collagen hydrogel and astrocytes were cultured on these surfaces. The addition of the stripe protein patterns to hydrogels created astrocyte layers in which cells were aligned with underlying patterns and had reduced chondroitin sulfate expression compared to the cells grown on collagen alone. Protein patterns were covalently cross-linked to the collagen and stable over four days in culture with no visible cellular modifications. The present method can be adapted to transfer other types of protein patterns from glass coverslips to collagen hydrogels.

Simultaneous patterning of two different types of nanoparticles into alternating domains of a striped array of a polymer blend in a single spin-casting step

A fast and convenient method is developed for simultaneously patterning inorganic nanoparticles with different optical, electronic or magnetic functionality to specific surface regions, by spin-casting onto microcontact printed substrates blend solutions in which the two nanoparticle types are functionalized with surface polymer brush layers of different surface energies. The process is based on phase separation of different nanoparticles based on their immiscible brush layers during spin-casting, with the underlying surface energy heterogeneity of the patterned substrate directing the different NP types to domains of different surface energies. Here, we specifically demonstrate the simultaneous localization of cadmium sulfide quantum dots (CdS QDs), addressed with a surface layer of polystyrene (PS), and silver nanoparticles (Ag NPs), addressed with a surface layer of poly(methyl methacrylate) (PMMA), onto the non-polar and polar surface domains, respectively, of hydrophilic glass patterned with hydrophobic octadecyltrichlorosilane (OTS) stripe arrays with micron-scale periodicities. In order to prevent gelation of solvent-swollen polymer-brush coated NPs during spin casting, which effects strong kinetic constraints on phase separation and localization, PS, PMMA or PS/PMMA homopolymer blends of sufficiently high Mw were added to the NP blends to increase the free volume between approaching NPs. The process parameters were fine-tuned to obtain control over defects in the obtained patterns.

Micropatterned porous membranes for combinatorial cell-based assays

Here, we describe a protocol for producing micropatterned porous membranes which can be used for combinatorial cell-based assays. We use contact printing to pattern the surface of a porous filter membrane with a thin layer of polydimethylsiloxane (PDMS). This allows the porosity of the filter membrane to be altered at selected locations. Cells can be grown on one side of the filter membrane, while drugs and reagents can be deposited on the porous areas of the other side of the membrane. The reagents can diffuse through the pores of the membrane to the cells. The first part of the protocol describes how to design a stamp and use it to contact print PDMS. The second part describes how to create microprinted membranes for cell-based assays. The method is simple, highly customizable, can be performed at the bench, and can be used to perform combinatorial or time-dependent cell-based assays.

Controlling cell geometry on substrates of variable stiffness can tune the degree of osteogenesis in human mesenchymal stem cells

The physical properties of the extracellular matrix (ECM) play an important role in regulating tissue-specific human mesenchymal stem cell (MSC) differentiation. Protein-coated hydrogels with tunable stiffness have been shown to influence lineage specific gene expression in MSCs. In addition, the control of cell shape - either through changing substrate stiffness or restricting spreading with micropatterning - has proved to be important in guiding the differentiation of MSCs. However, few studies have explored the interplay between these physical cues during MSC lineage specification. Here, we demonstrate geometric control of osteogenesis in MSCs cultured on micropatterned polyacrylamide gels. Cells cultured on fibronectin-coated gels express markers associated with osteogenesis in a stiffness dependent fashion with a maximum at ~30kPa. Controlling the geometry of single cells across the substrate demonstrates elevated osteogenesis when cells are confined to shapes that promote increased cytoskeletal tension. Patterning MSCs across hydrogels of variable stiffness will enable the exploration of the interplay between these physical cues and their relationship with the mechanochemical signals that guide stem cell fate decisions.

Micropatterning hydroxy-PAAm hydrogels and Sylgard 184 silicone elastomers with tunable elastic moduli

This protocol describes a simple method to deposit protein micropatterns over a wide range of culture substrate stiffness (three orders of magnitude) by using two complementary polymeric substrates. In the first part, we introduce a novel polyacrylamide hydrogel, called hydroxy-polyacrylamide (PAAm), that permits to surmount the intrinsically nonadhesive properties of polyacrylamide with minimal requirements in cost or expertize. We present a protocol for tuning easily the rigidity of "soft" hydroxy-PAAm hydrogels between ~0.5 and 50 kPa and a micropatterning method to locally deposit protein micropatterns on these hydrogels. In a second part, we describe a protocol for tuning the rigidity of "stiff" silicone elastomers between ~100 and 1000 kPa and printing efficiently proteins from the extracellular matrix. Finally, we investigate the effect of the matrix rigidity on the nucleus of primary endothelial cells by tuning the rigidity of both polymeric substrates. We envision that the complementarity of these two polymeric substrates, combined with an efficient microprinting technique, can be further developed in the future as a powerful mechanobiology platform to investigate in vitro the effect of mechanotransduction cues on cellular functions, gene expression, and stem cell differentiation.

Microfabricated environments to study collective cell behaviors

Coordinated cell movements in epithelial layers are essential for proper tissue morphogenesis and homeostasis. Microfabrication techniques have proven to be very useful for studies of collective cell migration in vitro. In this chapter, we briefly review the use of microfabricated substrates in providing new insights into collective cell behaviors. We first describe the development of micropatterned substrates to study the influence of geometrical constraints on cell migration and coordinated movements. Then, we present an alternative method based on microfabricated pillar substrates to create well-defined gaps within cell sheets and study gap closure. We also provide a discussion that presents possible pitfalls and sheds light onto the important parameters that allow the study of long-term cell culture on substrates of well-defined geometries.

Micropatterning on micropost arrays

Micropatterning of cells can be used in combination with microposts to control cell shape or cell-to-cell interaction while measuring cellular forces. The protocols in this chapter describe how to make SU8 masters for stamps and microposts, how to use soft lithography to replicate these structures in polydimethylsiloxane, and how to functionalize the surface of the microposts for cell attachment.

Micropatterned, multicomponent supported lipid bilayers for cellular systems

Lipid bilayer membranes are a central structural feature of living cells, providing a wide range of functions including partitioning of organelles, mediating cell interaction with the environment, and modulating intracellular signaling processes. By capturing the fluidity of the natural membranes in a reductionist in vitro model, substrate supported lipid bilayers have emerged as a compelling model system for these structures. Furthermore, the ability to control the composition and mobility of this system at micro- and nanoscales inspired several new routes of biological and biotechnological investigation. Here, we describe key methods used to create multicomponent lipid bilayers, discuss design considerations important to making these systems, and demonstrate this process in the specific context of understanding juxtacrine cell signaling. Different fabrication techniques were combined to first pattern a surface with barriers to lipid diffusion and then spatially control the exposure of this surface to lipid vesicles, leading to local formation of bilayers of different composition. This multicomponent system was used as a platform for to mimic the natural organization of T cells and antigen presenting cells by presenting ligands to the T cell receptor and lymphocyte function-associated antigen-1 that are tethered to separate, closely juxtaposed regions of bilayer. Other technologies like using photochemical polymerization of lipids to pattern bilayers have also been discussed. The information gathered from evaluating membrane interactions in patterned lipid bilayers may lead to the development of membrane-based biomedical devices for conducting novel cell-based assays and potentially high-throughput drug screens targeting membranes or membrane-associated components.

Patterned hydrogels for simplified measurement of cell traction forces

To understand mechanobiology, a quantitative understanding of how cells interact mechanically with their environment is needed. Cell mechanics is important to study as they play a role in cell behaviors ranging from cell signaling to epithelial to mesenchymal transition in physiological processes such as development and cancer. To study changes in cell contractile behavior, numerous quantitative measurement techniques have been developed based on the measurement of deformations of a substrate from an initial state. Herein, we present details on a technique we have developed for the measurements of 2D cellular traction forces with the goal of facilitating adaptation of this technique by other investigators. This technique is flexible in that it utilizes well-studied methods for microcontact printing and fabrication of polyacrylamide hydrogels to generate regular arrays of patterns that can be transferred onto the hydrogels. From the deformation of the arrays, an automated algorithm can be used to quantitatively determine the traction forces exerted by the cells onto the adhesion points. The simplicity and flexibility of this technique make it a useful contribution to our toolbox for measurement of cell traction forces.

Microfluidic immunodetection of cancer cells via site-specific microcontact printing of antibodies on nanoporous surface

We demonstrate an efficient method for cancer cell capture via cell line-specific protein deposition on nanoporous surface in microfluidic channels. Specifically, anti-epithelial cell adhesion molecules (EpCAM) were microcontact printed onto nanoporous silica substrate with optimal pore size of 4 nm, porosity of 52.4 ± 0.2%, and thin film thickness of 130 ± 0.5 nm. SkBr3, Colo205, and MDA-MB-435 cancer cells suspended in buffer solution were captured on the stamped nanoporous silica substrate. The method demonstrated significantly higher numbers of captured EpCAM-positive cancer cells within anti-EpCAM stamped areas. For site-selective cell capture, grooved microfluidic channels were designed to investigate effects of local confinement due to the laminar flows. Both theoretical modeling and experiments show that the integration of the microfluidic channels greatly enhances cell capture. Patterning of anti-EpCAM in areas of downward flow (optimal regions for cell capture), generated by grooves of the microchannel, enables higher capture numbers than that of stamped areas of upward flow (non-optimal). Fluorescence microscopy images were acquired for captured SkBr3 and Colo205 cells using anti-EpCAM on the nanoporous silica substrate. It was shown that higher numbers of cells were captured across all EpCAM-positive cell lines in optimal areas versus non-optimal areas. Spatial control and large scale patterning of proteins enable novel designs and productions of cost effective, high throughput, and integrated detection and analysis systems. Site-selective detection provides the capability of defining optimal locations for cell capture based on various channel geometries and flow profile. The demonstrated method shows great potential for point-of-care cancer diagnostic tools to quantify the progression and status of the disease.