Microfluidic platforms for establishment of biological barriers

Abstract

In the process of drug development, preclinical testing evaluates a potential drug candidate's efficiency and toxicity prior to clinical trials. As frequently used models in the study of drug efficacy, barriers play an important role in the regulation of molecular transport. However, conventional in vitro tests carried out on Petri dishes or Transwells have defects in mimicking real in vivo environments. They fail to simulate morphologies and micromechanical conditions, which may lead to incorrect predictions. In vivo tests carried out on animal models are less reproducible as non-human cells or tissues are involved. Therefore, platforms providing a proper environment for culturing human cells are in high demand. Enlightened by advancements in microfabrication and three-dimensional tissue engineering, the emerging field of organ-on-a-chip presents promising flatforms to overcome challenges in biomimetic barrier construction. This thesis introduces several innovative platforms for creating biomimetic barriers. In Chapter 3, we utilize the transparency and conductivity of Indium Tin Oxide (ITO) to introduce a novel in vitro microfluidics chip platform for flat-shaped barriers. The results demonstrated faster fluctuations in the pH and TEER of the BRB compared to monolayer cells, confirming the interaction between these two cell types that facilitates BRB integrity and validates the platform's construction. This platform allows for real-time monitoring of barrier integration and pH values in the extracellular microenvironment. Utilizing this system, we achieved real-time pH measurement and trans-epithelial electrical resistance (TEER) measurement of an in vitro BRB (blood-retinal barrier) over a continuous 17-hour period. The results demonstrated faster fluctuations in the pH and TEER of the BRB compared to monolayer cells, confirming the interactions between these two cell types that facilitate BRB integrity and validates the platform's construction. In Chapter 4, acknowledging that many in vivo barriers develop in tubular environments, we incorporated controllable curvature wrinkles into the insert-based model, creating tubular bases for the associated cells. This maintains the insert-based model's benefits over the hydrogel model, such as smaller scale and easier permeability studies. Barriers cultured in this model demonstrated a mechanical microenvironment closer to in vivo and, conditions, resulting in increased secretion of barrier-associated proteins with enhanced barrier properties. In summary, we proposed two novel in vitro barrier microfluidic chips. Improved extracorporeal barrier systems using ITO electrodes permit more precise barrier, monitoring and control. The introduction of creases or self-assembled materials to form pipeline structures offers new perspectives for extracorporeal barrier chip. development. We anticipate that the broad applicability of these platforms to similar barriers will bridge the gap between in vitro tests and clinical trials, offering significant contributions to drug development and pathological studies.