Mechanical Measurement and Stimulation of Human Pluripotent Stem Cell-Derived Cardiomyocytes

The emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for studying cardiac physiologies, disease modeling, cardiotoxicity testing, and therapeutic discoveries. Challenges still exist in realizing the capability of sensing and evaluating the functional properties of cardiac cell/tissue models in situ (i.e., on the platforms). In particular, generating sufficient forces of contraction during the rhythmic beating of cardiomyocytes plays a central role in pumping oxygen-rich blood through the circulatory system. Developing new platforms and technologies to assess the beating behaviors and contractile functions of in vitro cardiac models is essential to provide information on cell/tissue physiologies, drug-induced inotropic responses, and mechanisms of cardiac diseases. This thesis focuses on developing biosensing technologies/platforms for the measurement of contractile functions of in vitro cardiac models. In vitro cardiac cell/tissue models were established by using Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (iPSC-CMs) generated with the human proteome to avoid the potential species-dependent differences. Firstly, a label-free imaging technique was developed to offer a cytotoxic-free method for long-term measurement of dynamic beating trajectories, beating amplitude, beating propagation, and conduction velocities of cardiomyocyte monolayers, avoiding the perturbation and cytotoxicity induced by fluorescent dyes. Next, a carbon-based biosensing platform integrated with flexible biosensing components was developed for continuous measurement of multiple parameters of cardiac functional properties in vitro, including contractility, beating rate, beating rhythm, and field potential. In addition, a microdevice array integrated both contraction sensing and mechanical stimulation functions was also developed to recapitulate the mechanical microenvironment of myocardium in vitro and characterize the effect of mechanical strain magnitude on the maturation of iPSC-CMs. Highlighted applications and discoveries enabled by these developed platforms were summarized and discussed in aspects of investigating fundamental cardiac physiologies (e.g., iPSC-CM maturation under mechanical stimulation), drug testing (e.g., isoproterenol, verapamil, blebbistatin, and E-4031), and disease modeling (e.g., drug-induced cardiac arrhythmia and arrhythmogenic right ventricular cardiomyopathy (ARVC)).Ph.D

Analysis and optimization of electrochemiluminescence periodic signal processing based on singular value decomposition

Electrochemiluminescence (ECL) detection is one of the most prevailing electrochromism approaches to test biotin and chemicals. As thorny ECL signals by impurities are devastative in judging the right substance and its concentration precisely, it is crucial to dispose the noise and process it into smooth curves without filtering essential biochemical information conveyed in the signal. This contribution investigates Singular Value Ratio (SVR) spectrum to extract periodic signals from every noise ECL signal. A novel improved method of rearranging periodic compositions from complex signals is proposed. Finally, actual ECL signal generated by Ru(bpy)32+ is analyzed and optimized to demonstrate that the improved technique is efficacious and feasible. Keywords: Electrochemiluminescence (ECL), Periodic signal extraction, Singular value decomposition (SVD), Singular value ratio (SVR

Integrated assembly and photopreservation of topographical micropatterns

Micromanipulation techniques that are capable of assembling nano/micromaterials into usable structures such as topographical micropatterns (TMPs) have proliferated rapidly in recent years, holding great promise in building artificial electronic and photonic microstructures. Here, a method is reported for forming TMPs based on optoelectronic tweezers in either “bottom-up” or “top-down” modes, combined with in situ photopolymerization to form permanent structures. This work demonstrates that the assembled/cured TMPs can be harvested and transferred to alternate substrates, and illustrates that how permanent conductive traces and capacitive circuits can be formed, paving the way toward applications in microelectronics. The integrated, optical assembly/preservation method described here is accessible, versatile, and applicable for a wide range of materials and structures, suggesting utility for myriad microassembly and microfabrication applications in the future

Microdevice Platform for Continuous Measurement of Contractility, Beating Rate, and Beating Rhythm of Human-Induced Pluripotent Stem Cell-Cardiomyocytes inside a Controlled Incubator Environment

The heart completes a complex set of tasks, including the initiation or propagation of an electrical signal with regularity (proper heart rate and rhythm) and generating sufficient force of contraction (contractility). Probing mechanisms of heart diseases and quantifying drug efficacies demand a platform that is capable of continuous operation inside a cell incubator for long-term measurement of cardiomyocyte (CM) monolayers. Here, we report a microdevice array that is capable of performing continuous, long-term (14 days) measurement of contractility, beating rate, and beating rhythm in a monolayer of human-induced pluripotent stem cell-CMs (hiPSC-CMs). The device consists of a deformable membrane with embedded carbon nanotube (CNT)-based strain sensors. Contraction of the hiPSC-CMs seeded on the membrane induces electrical resistance change of the CNT strain sensor. Continuously reading the sensor signals revealed that hiPSC-CMs started to beat from day 2 and plateaued on day 5. Average contractile stress generated by a monolayer of hiPSC-CMs was determined to be 2.34 ± 0.041 kPa with a beating rate of 1.17 ± 0.068 Hz. The device arrays were also used to perform comprehensive measurement of the beating rate, rhythm, and contractility of the hiPSC-CMs and quantify the cell responses to different concentrations of agonists and antagonists, which altered the average contractile stress to the range of 1.15 ± 0.13 to 3.96 ± 0.53 kPa. The continuous measurement capability of the device arrays also enabled the generation of Poincaré plots for revealing subtle changes in the beating rhythm of hiPSC-CMs under different drug treatments