Aaron Chen

Unconventional Low-Cost Fabrication and Patterning Techniques for Point of Care Diagnostics

The potential of rapid, quantitative, and sensitive diagnosis has led to many innovative ‘lab on chip’ technologies for point of care diagnostic applications. Because these chips must be designed within strict cost constraints to be widely deployable, recent research in this area has produced extremely novel non-conventional micro- and nano-fabrication innovations. These advances can be leveraged for other biological assays as well, including for custom assay development and academic prototyping. The technologies reviewed here leverage extremely low-cost substrates and easily adoptable ways to pattern both structural and biological materials at high resolution in unprecedented ways. These new approaches offer the promise of more rapid prototyping with less investment in capital equipment as well as greater flexibility in design. Though still in their infancy, these technologies hold potential to improve upon the resolution, sensitivity, flexibility, and cost-savings over more traditional approaches.

Integrated platform for functional monitoring of biomimetic heart sheets derived from human pluripotent stem cells

We present an integrated platform comprised of a biomimetic substrate and physiologically aligned human pluripotent stem cell-derived cardiomyocytes (CMs) with optical detection and algorithms to monitor subtle changes in cardiac properties under various conditions. In the native heart, anisotropic tissue structures facilitate important concerted mechanical contraction and electrical propagation. To recapitulate the architecture necessary for a physiologically accurate heart response, we have developed a simple way to create large areas of aligned CMs with improved functional properties using shrink-wrap film. Combined with simple bright field imaging, obviating the need for fluorescent labels or beads, we quantify and analyze key cardiac contractile parameters. To evaluate the performance capabilities of this platform, the effects of two drugs, E-4031 and isoprenaline, were examined. Cardiac cells supplemented with E-4031 exhibited an increase in contractile duration exclusively due to prolonged relaxation peak. Notably, cells aligned on the biomimetic platform responded detectably down to a dosage of 3 nM E-4031, which is lower than the IC50 in the hERG channel assay. Cells supplemented with isoprenaline exhibited increased contractile frequency and acceleration. Interestingly, cells grown on the biomimetic substrate were more responsive to isoprenaline than those grown on the two control surfaces, suggesting topography may help induce more mature ion channel development. This simple and low-cost platform could thus be a powerful tool for longitudinal assays as well as an effective tool for drug screening and basic cardiac research.

Shrink-induced sorting using integrated nanoscale magnetic traps

We present a plastic microfluidic device with integrated nanoscale magnetic traps (NSMTs) that separates magnetic from non-magnetic beads with high purity and throughput, and unprecedented enrichments. Numerical simulations indicate significantly higher localized magnetic field gradients than previously reported. We demonstrated >20 000-fold enrichment for 0.001% magnetic bead mixtures. Since we achieve high purity at all flow-rates tested, this is a robust, rapid, portable, and simple solution to sort target species from small volumes amenable for point-of-care applications. We used the NSMT in a 96 well format to extract DNA from small sample volumes for quantitative polymerase chain reaction (qPCR).

Tracking the mechanical dynamics of human embryonic stem cell chromatin

BackgroundA plastic chromatin structure has emerged as fundamental to the self-renewal and pluripotent capacity of embryonic stem (ES) cells. Direct measurement of chromatin dynamics in vivo is, however, challenging as high spatiotemporal resolution is required. Here, we present a new tracking-based method which can detect high frequency chromatin movement and quantify the mechanical dynamics of chromatin in live cells.ResultsWe use this method to study how the mechanical properties of chromatin movement in human embryonic stem cells (hESCs) are modulated spatiotemporally during differentiation into cardiomyocytes (CM). Notably, we find that pluripotency is associated with a highly discrete, energy-dependent frequency of chromatin movement that we refer to as a ‘breathing’ state. We find that this ‘breathing’ state is strictly dependent on the metabolic state of the cell and is progressively silenced during differentiation.ConclusionsWe thus propose that the measured chromatin high frequency movements in hESCs may represent a hallmark of pluripotency and serve as a mechanism to maintain the genome in a transcriptionally accessible state. This is a result that could not have been observed without the high spatial and temporal resolution provided by this novel tracking method.

Shrink-Induced Biomimetic Wrinkled Substrates for Functional Cardiac Cell Alignment and Culture

The anisotropic alignment of cardiomyocytes in native myocardium tissue is a functional feature that is absent in traditional in vitro cardiac cell culture. Microenvironmental factors cue structural organization of the myocardium, which promotes the mechanical contractile properties and electrophysiological patterns seen in mature cardiomyocytes. Current nano- and microfabrication techniques, such as photolithography, generate simplified cell culture topographies that are not truly representative of the multifaceted and multi-scale fibrils of the cardiac extracellular matrix. In addition, such technologies are costly and require a clean room for fabrication. This chapter offers an easy, fast, robust, and inexpensive fabrication of biomimetic multi-scale wrinkled surfaces through the process of plasma treating and shrinking prestressed thermoplastic. Additionally, this chapter includes techniques for culturing stem cells and their cardiac derivatives on these substrates. Importantly, this wrinkled cell culture platform is compatible with both fluorescence and bright-field imaging; real-time physiological monitoring of CM action potential propagation and contraction properties can elucidate cardiotoxicity drug effects.