Microbioreactors for 3-dimensional tissue

Abstract

Three-dimensional (3D) cell culture and tissue engineering offer a unique avenue for therapeutic interventions. A 3D tissue model potentially revolutionizes the challenges to mimic the in vivo physiological conditions. Recent advances in microfluidic technology have accelerated the development of 3D tissue models. For instance, droplet-based microfluidics allows tiny droplets to serve as bioreactors. This thesis introduces for the first time a new approach using liquid marble, which is generated by encapsulating an aqueous liquid droplet with a hydrophobic powder. This platform is reliable for 3D scaffold-free tissue engineering. This technology is more versatile and more adaptable than existing hanging-drop systems and other scaffold-based microfluidic systems. The use of liquid marble as a bioreactor has led to a number of interesting applications. The first application is culturing multiple cell spheroids. For this purpose, a novel cell culture protocol with floating the liquid marble was developed. As a proof of concept, spheroids of olfactory ensheathing cells (OECs) were grown in a liquid marble. The liquid marble was generated simply by encapsulating a droplet of medium containing cells with hydrophobic powder. The powder coating creates a robust, porous and apparently elastic shell, which allows gas exchange. The liquid marble was then floated by placing it on a liquid bath. The interfaces between the hydrophobic coating and the supporting liquid bath are separated by an air layer. This air layer contributes to the low friction and facilitates liquid marble to move. The mobility enhances internal flow and allows cell-cell interaction. Further, the liquid bath also helps to increase relative humidity and minimize evaporation. This protocol provides an opportunity to explore the interaction of different cell types to form co-culture spheroids. The second application is the use of liquid marble as a 3D in-vitro model for cell-cell interactions. Liquid marbles create a distinct microenvironment for cell growth and interaction. The insertion of a second cell type was modeled by coalescence of the two liquid marbles. The merged liquid marble serves as an environment for the interaction between two distinct cell types. As a model of the hostile environment, nerve debris and meningeal fibroblast were grown to generate co-cultured spheroid that mimics the features of spinal cord injury (SCI). We then assessed the potential of Olfactory Ensheathing Cells (OECs) to interact with the nerve debris within an fibroblastic tissue. Altogether, the results indicate the feasibility of a liquid marble for studying the survival and adherence of transplanted cells. This liquid marble is achievable for developing the test model for cell-based therapy. The third application is the use a liquid marble as the bioreactor for slow-release of drugs and factors as well as minimizing evaporation. A spherical agarose gel was loaded with growth factor and embedded within a liquid marble. The release of growth factor showed a significant increase in cell aggregation and subsequent production of larger spheroids. This model promises a wide range of studies that requires sustained release. Generally, liquid marbles are subjected to evaporation. Thus, the evaporation rate in the presence of the agarose gel was evaluated. The experiments showed that there was no obvious trend in the volumetric changes due to both water absorption and water loss due to evaporation. The results indicate that liquid marbles can be used to study the efficacy of drug delivery. The final application is the use of slow release growth factor to form a toroid tissue. The embedded agarose gel inside a liquid marble releases a growth factor to attract and assemble cells into a tissue with the shape of a toroid. The harvested toroid tissue was placed on non-adherence well plate and treated with the growth factor to investigate its closure. The geometric growth during the closure process was then measured and modelled. The application is promising for high-throughput screening of drugs on 3D wound healing. All four applications provides a proof of concept for the use of liquid marbles as bioreactors and further expansion towards 3D tissue models for drug discovery.