UC San Diego

Patients around the world who suffer from a host of debilitating conditions rely on medications for treatment. However, pharmaceutical researchers and drug developers face immense challenges to new drug discovery. Drug companies currently spend 10-15 years and upwards of $1 billion (USD) developing and testing a single new drug, and despite this, up to 90% of drug candidates ultimately fail to pass clinical trials and obtain FDA approval. A significant reason for this failure is the inability of traditional pre-clinical testing systems, such as cell monolayers in multi-well plates and animal models such as mice, to accurately predict drug toxicity and efficacy in humans. Recent studies have focused on engineering functional, three-dimensional tissue analogs that better mimic native human physiology in an in vitro system. As next-generation pre-clinical drug screening platforms, these human tissue analogs may provide a more accurate indication of the likelihood of a drug’s success or failure in humans, thus increasing the efficiency of drug development.

In this regard, organ-on-a-chip systems have shown great promise. In an organ-on-a-chip, engineered tissue constructs are housed in a microfluidic device in which nutrients are supplied and wastes are removed via the continuous perfusion of media, similar to the function of the blood vessel network in the human body. Due to their micro-scale size, these systems also minimize the amounts of reagents and drug compound required for testing, potentially reducing costs and circumventing supply limitations. Organs-on-chips for lung, gut, heart, and others have already been developed. Furthermore, in theory multiple individual organs-on-chips could be linked together to form a multi-organ “body-on-a-chip” system to recapitulate whole human physiology and study on- and off-target drug effects.

This dissertation is intended to contribute to the development of single- and multi-organ-on-a-chip systems in order to outline approaches to creating human tissue models in vitro and assess their feasibility in drug screening. Chapter 1 is a literature review of the current state of organ-on-a-chip research, past accomplishments, and future directions. In particular, I have highlighted how organs-on-chips may serve as valuable disease models by replicating human disease pathophysiology through the use of patient-specific cells, increasing the likelihood of researching and developing cures for rare diseases. In Chapter 2, I have detailed the development of a novel micro-physiological 3D model of skeletal muscle in a microfluidics device. Interestingly, despite its key role in supporting motion, strength, and activity in everyday life, few prior advancements had been made in skeletal-muscle-on-a-chip platforms. In addition to creating aligned 3D muscle microtissues, we have characterized their formation under various physical cues, developed a method to quantify force generated by the muscle strip, and performed a proof-of-concept small molecule screen to demonstrate the effect of muscle injury on structure, morphology, and function. In Chapter 3, I have extended the previous study by utilizing human induced-pluripotent stem cells (hiPSCs) to create 3D muscle microtissues which mimic human muscle physiology. Further, by using microfluidics to apply a cyclical mechanical load to the tissues through pulsatile flow, thus increasing and decreasing fluid pressure to simulate a “massage-like” phenomenon, I have shown an upregulation in myogenic maturation of the hiPSC-based muscle tissues. This demonstrates an additional feature of microfluidics that, to our knowledge, has not previously been explored. Further, we have shown that the muscle tissues contract in response to the neurotransmitter acetylcholine, indicating their functional maturation. This is the first development of a skeletal-muscle-on-a-chip with hiPSCs, and in the future, this system may be used for personalized medicine and disease modeling. In Chapter 4, I have detailed the development of a multi-organ “body-on-a-chip” system by integrating together individual 3D organs-on-chips of liver, heart, skeletal muscle, and cancer. Multi-organ platforms enable organ-organ cross-talk, which can be critical in applications ranging from fundamental biological research to drug development. We have demonstrated the viability, structural maturation, and function of each tissue under integrated co-culture conditions. Further, we have performed a cancer drug screen using 5-Fluorouracil and its pro-drug form, Tegafur, to illustrate liver metabolic activity and molecular cross-talk between organs that leads to cancer drug efficacy and off-target toxicity. This validates the value of a multi-organ system over individual organs-on-chips, where certain information may not manifest because there is no communication between tissues.