Design and Validation of Vascularized Organ on Chip for Skin and Bone Toxicity Testing

Abstract

A major challenge in toxicity is to define relevant in-vitro systems that accurately predict the effects in human. Recently, organ on chip with relevant physiological cellular microenvironment is predicted to be perfect platform to replace animal testing. In addition, vascularized system is suggested as efficient in-vitro model for studying complex biological phenomena in tissues. Therefore, this thesis is focus on application of multiscale microfluidic devices in developing new vascularized organ on chip for toxicity testing, which focus separately on skin and bone.

For skin tissue engineering, creating in-vitro models of the skin is challenging, but advances have been made by numerous researchers in constructing skin on chip models. However, current models lack of perfusable and functional blood vessels which are crucial for drugs discovery and therapeutics strategies. Here, we present a perfusable vascularized skin model in open-top microfluidic device by integrating the skin keratinocytes at the top layer and perfusable vessel networks at the bottom layer that mimicking the skin anatomy structure. Besides, this platform also convenient for various drugs and chemicals testing and thus can be an alternative platform to existing avascular skin models.

As proof of concept, microfluidic device was developed as in-vitro skin irritation model. In the absence of the vascularization in current in-vitro models, cells viability has been used as typical parameters for measuring toxicity level in skin irritation testing. In response to the chemical stimuli, keratinocytes secrete various cytokines and growth factors which promote angiogenesis and vascular permeability. The proposed skin irritation model assesses the toxicity of sodium lauryl sulfate based on quantification of angiogenesis within a microfluidic platform. The angiogenesis response was further observed by using steartrimonium chloride to show the potential of this platform in studying the irritation mechanism of uncommon agents. The proposed platform can be adapted as a potential platform for further skin toxicity assays in cosmetic and pharmaceutical testing applications.

On the other hand, the ideal platform for engineering bone tissues should have suitable three-dimensional structures with interconnected pores due to the uniqueness of in-vivo bone microenvironment with inorganic mineral hydroxyapatite. Current in-vitro systems fail to fully integrate three-dimensional microvasculature with bone tissue microenvironment which decreases similarity of the in-vivo systems. Here, mineralized microfluidic platform was developed for designing and manipulating a vascularized bone tissue model in a microfluidic device. In response to various concentration of hydroxyapatite, the angiogenesis sprouts were sensitively controlled. This new mineralized microvascular platform offers a new approach for investigation of complex biological phenomena as well as for analysis of drug responses and toxicities in bone tissues.

Besides, hydroxyapatite have been reported to have inhibitory function on the proliferation of many kinds of tumor cells. For further observation, a new mineralized tumor microenvironment was developed by incorporating tumor cells, stromal cells with hydroxyapatite in a microfluidic. Cancer cells characteristics including angiogenesis responses and tumor spheroids growth were observed with the effect of mineralized tumor microenvironment. Therefore, this study provides a novel in-vitro platform on mineralized tumor microenvironment that will be a valuable tool for understanding bone cancer metastasis phenomena.

With the important of blood vessels in tissue engineering, vascularized skin and bone on chip was successfully developed to overcome the limitation in current in-vitro models. Although more studies are still required, the proposed skin and bone platform offers new approaches for analysis toxicities in bone and skin tissues. Thus, these platforms can be alternatives solution to meet the toxicity testing requirements in pharmaceutical and cosmetic industry.