An increase in mechanical load in the heart causes cardiac hypertrophy, either physiologically (heart development, exercise and pregnancy) or pathologically (high blood pressure and heart-valve regurgitation). Understanding cardiac hypertrophy is critical to comprehending the mechanisms of heart development and treatment of heart disease. However, the major molecular event that occurs during physiological or pathological hypertrophy is the dynamic process of sarcomeric addition, and it has not been observed. In this study, a custom-built second harmonic generation (SHG) confocal microscope was used to study dynamic sarcomeric addition in single neonatal CMs in a 3D culture system under acute, uniaxial, static, sustained stretch. Here we report, for the first time, live-cell observations of various modes of dynamic sarcomeric addition (and how these real-time images compare to static images from hypertrophic hearts reported in the literature): 1) Insertion in the mid-region or addition at the end of a myofibril; 2) Sequential addition with an existing myofibril as a template; and 3) Longitudinal splitting of an existing myofibril. The 3D cell culture system developed on a deformable substrate affixed to a stretcher and the SHG live-cell imaging technique are unique tools for real-time analysis of cultured models of hypertrophy.

The ability to place individual cells into an engineered microenvironment in a cell-culture model is critical for the study of in vivo-relevant cell-cell and cell-extracellular matrix interactions. Microfluidics provides a high-throughput modality to inject various cell types into a microenvironment. Laser guided systems provide the high spatial and temporal resolution necessary for single-cell micropatterning. Combining these two techniques, the authors designed, constructed, tested, and evaluated 1) a novel removable microfluidics-based cell-delivery biochip and 2) a combined system that uses the novel biochip coupled with a laser guided cell-micropatterning system to place individual cells into both 2D and 3D arrays. Cell-suspensions of chick forebrain neurons and glial cells were loaded into their respective inlet reservoirs and traversed the microfluidic channels until reaching the outlet ports. Individual cells were trapped and guided from the outlet of a microfluidic channel to a target site on the cell-culture substrate. At the target site, 2D and 3D pattern arrays were constructed with micron-level accuracy. Single-cell manipulation was accomplished at a rate of 150 μm/s in the radial plane and 50 μm/s in the axial direction of the laser beam. Results demonstrated that a single-cell can typically be patterned in 20-30 seconds, and that highly accurate and reproducible cellular arrays and systems can be achieved through coupling the microfluidics-based cell-delivery biochip with the laser guided system.

The basement membrane (BM), a network of laminin and collagen IV, mechanically supports individual cells and directly mediates cell-cell and cell-extracellular matrix (ECM) interactions. For example, the BM network that tightly encloses each cardiomyocyte (CM) mediates the alignment of CMs with collagen I in the ECM. Additionally, the BM-laminin is involved in the formation of gap junctions (GJs), which regulate electrical coupling between two CMs in the myocardium. The role of BM in GJ maturation remains unclear because of the complicated in vivo structures and lack of an ideal in vitro culturing mode. In this study, our laser cell-micropatterning system was used to place two neonatal CMs (NCMs) in contact on an aligned collagen gel (ACG) to study the relationship between GJ maturation and BM development. The results of double immunofluorescence staining and confocal imaging showed that BM-laminin was deposited earlier than the formation of GJs in the intercellular space and that newly expressed connexin 43 clusters were preferentially assembled near the deposited BM structures. Eventually the BM network surrounded the GJs.

Traditional cell-culture techniques lack the spatial control of single cells that is necessary to recreate the cell-cell contact arrangement found in tissue. Since Ashkins developed optical force-based cellmanipulation techniques [1], the laser microbeam has been used in a microscopic system to explore various biological interactions at molecular and cellular levels. These explorations of a single cell or subcellular organelle involve trapping (using a laser-tweezers microscope [2]) and guidance (using a laser-guided direct writing microscope [3,4]). When laser tweezers are used, a high numerical aperture (NA) microscope objective generates a strongly focused laser beam, which 3D traps a particle, such as a biological cell, in the beam's focal point. In laser-guided direct writing, a low NA microscope objective generates a weakly focused laser beam, which traps a particle in the beam axis and guides it to move along the direction of beam propagation.Based on these techniques, we have developed a laser cell-micropatterning system in which the laser beam is focused in a transition state between generating an optical trap and optical guidance [5]. Using this system, a single biological cell can be trapped in a typical (e.g., 30mm) cell culture dish and patterned onto a designated cell culture niche with very high spatial and temporal resolution [6][7][8].However, this and the other currently available laser-based single-cell-manipulation techniques can be used to pattern only spherical cells, not irregularly shaped cells such as rod-shape cardiomyocytes. The work stems from the use of a spatial light modulator (SLM) loaded with a computer generated phase map to shape a single laser beam into multiple microbeams analogous to techniques used in holographic optical tweezers (HOT) [9]. In contrast to the optical configuration in HOT, our system uses a low NA objective to produce multiple weakly focused laser microbeams in our multiple beam laser guidance system. Based on the cell image acquired during laser cell patterning, the multiple beams can be distributed around the outer contour of an irregularly shaped cell to achieve accurate cell patterning. In addition to describing the principle and practice of the system design, here we present what is to our knowledge the first achievement of patterning large, irregularly (rod) shaped adult rat cardiomyocytes (ACMs) in an end-to-end connected alignment to replicate the in vivo heart-muscle structure without use of substrate surface modifications that may interfere with in vivo-like cell-cell and cell-extracellular matrix interactions.The basic structure of the multiple-beam laser cell-patterning system is schematically shown in Figure 1. The cell suspension was loaded into the microfluidics-based cell feeding system built in the celldeposition chamber, with a microfluidic channel width of 200 µm. The guidance region (also the imaging region of the objective) was initially focused onto the outlet of the cell-feeding microfluidic channel by controlling the movement of the ce...

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In this study, we developed a microfluidic biochip to perform laser guidance on two cell types, chick embryonic forebrain neurons and chick embryonic spinal cord neurons. The neurons we obtained from these two cell types have no difference in morphology as observed under a high-magnification microscope. However, when flowing in the microfluidic channel and simultaneously being laser-guided, the two cell types gained quite different guidance velocities under the same experimental conditions. The experimental results demonstrate that different cell types with the same morphology (e.g., size, shape, etc.) can be effectively distinguished from each other by measuring the difference of guidance velocities (the maximum flow velocities minus the initial flow velocities). This technique is expected to provide a new approach to high-throughput, label-free cell sorting with sensitivity.

Laser cell patterning is a distinctly effective technique for creating cell arrangements in culture that replicate in vivo tissue structure for studying contact-mediated cell-cell interactions. Conventional laser-based single-cell-manipulation techniques are limited by their inability to pattern irregularly shaped cells, such as rod-shaped cardiomyocytes. We report use of a spatial light modulator loaded with a computergenerated phase map to shape a single laser source into multiple laser-guidance beams distributed around the outer contour of an irregularly shaped cell to achieve accurate cell patterning. In addition to describing the principle and practice of the system design, we present what is to our knowledge the first achievement of patterning large, irregularly (rod) shaped adult rat cardiomyocytes in an end-to-end connected alignment to replicate the in vivo heart muscle cell connection without use of substrate surface modifications, which can interfere with in vivo-like cell-cell and cell-extracellular matrix interactions. Our research demonstrates that two-stage multiple beam laser guidance is effective: 1) A dual-beam configuration horizontally translates a cell from the outlet of the microfluidic cell delivery channel to a position above the cell deposition site and 2) A quad-beam configuration rapidly propels the cell axially through the suspension medium to the culture substrate with vertical movement of the cell patterning chamber. Our study reveals that 90% of the patterned cells maintained end-to-end connection 30 min after patterning, and mechanical junctions could be reinstalled between laser connected cells after overnight incubation. This demonstrates that multiple beam laser patterning is an outstanding tool for in vitro studying contact-mediated cell-cell interactions among irregularly shaped cells.

Chemical gradients and physical contact with the surrounding microenvironment play an important role in regulating axonal pathfinding. Traditional experiments for chemically-induced growth coneturning in vitro involve micropipettes filled with a guidance-cue solution. The localized chemical gradient generated through gravity-induced or pulsatile pressure application is used to evaluate the response of a single growth cone to the guidance-cue solution. Thus, the micropipette growth coneturning assay has intrinsic application deficits that limit the duration of signaling. Moreover, it does not account for spatial reproducibility. To improve spatial resolution and expose multiple individual growth cones to identical environmental conditions, we developed a biochip system that incorporates geometric and chemical signaling to regulate axonal pathfinding. With this system, we were able to passively generate chemical gradients for long periods of time (>1 d) at continual flowrates of ∼40 pL s −1 . Over the course of 4 DIV, angular distributions for axonal pathfinding of individual laser cellpatterned CFNs showed statistically different frequencies when a chemical guidance gradient was generated from a localized source. The biochip described here can be used to systematically test various chemical guidance molecules with high repeatability and longer durations. Abbreviations CFN chick forebrain neuron PBS phosphate buffer saline PDMS polydimethylsiloxane PLL poly-L-lysine FITC-BSA fluorescein isothiocyanate-labeled bovine serum albumin RECEIVED