Abstract
In the last two decades, a multidisciplinary approach on the delivery of cells to the body has advanced. On the one hand, the science of polymers focuses on the development of biocompatible materials for cell culturing and tissue engineering applications, while on the other hand (micro-)engineering has an important part in providing a specific topography that directs the cells and provides a more similar architecture to that of tissues. Soft and flexible elastomers have gained more and more interest, especially due to their biodegradability and tunable mechanical properties that can mimic the natural tissue. Herein, we report the design of novel poly(polyol sebacate) elastomers synthesized from monomers found within the human metabolism. The thermoset properties of these polymers as well as their optical transparency make them ideal materials for microsystems technology. Therefore, microfluidic devices were developed out of these polymers in order to facilitate the design of a tissue-engineered organ. A porous membrane was inserted in the microfluidic device to enable co- culture and distribution of nutrients to the cells. Furthermore, the reported polymers and microfluidic structure can serve a multitude of applications, from tissue engineering to point-of-care diagnostics or compound screening.The field of tissue engineering, pioneered by Robert Langer and his co- workers, combines the principles and methods of engineering and the life sciences towards the development of biological substitutes that restore, maintain, or improve tissue function. The new developments on the various strategies of tissue engineering (TE) are aiming to understand the complexity of tissue remodeling and the inter-dependency of many associated variables. This clearly makes it a highly multi-disciplinary field that combines the expertise of different areas. Material scientists, engineers and biologists, in this regard form an important triad. Materials science focuses on the synthesis and characterization of required materials for the engineers to design the material in a way that it resembles the internal structure of the respective tissue or organ. Herein, the role of biologists becomes important who provide knowledge on how to introduce cells in these systems in order to support their proliferation and differentiation into a specific tissue. Thus, a (bio)material is developed.
For further construction of bio(materials) as implantable tissue structures, the development of three-dimensional (3D) fluidic microsystems for cell culturing has become a necessity. Microfluidic technology offers a controlled environment, reduced reagent consumption and precision, promising an alternative for conventional biological laboratory methods. These microsystems involve the manipulation of small amounts of fluids using channels with dimensions at a micron level. Their specificity and flexibility is beyond the one of normal well plates or two-dimensional cell culturing films due to the ability to handle co-culture systems or to encompass from millions of cells to single cells, depending on a specific application.
In this context, the aim of the present work is to combine the knowledge of different fields of research in order to pave the way in the direction of 3D biodegradable fluidic microsystems for cell culturing and tissue engineering. The focus is laid on the development of biodegradable 3D microfluidic systems that can eventually sustain cell culturing and proliferation with subsequent tissue formation. Liver tissue is chosen as a model for the developed technology due to its complex structure that contains two main cell types, namely hepatocytes and endothelial cells, displaced in a three- layer architecture. The proposed research aims to overcome the shortcoming of the existing methods or technologies available worldwide, allowing the fabrication of such complex biodegradable microsystems.
The layout of the thesis is divided into different chapters that discuss specific topics towards the achievement of the final research objective. The multi- disciplinary aspect and collaboration between the different fields with varied competences is presented in Chapter 1.
The synthesis and characterization of novel poly(polyol sebacate)-derived elastomers is reported in Chapter 2. Poly(polyol sebacates) are thermoset materials and possess several characteristics such as biocompatibility, biodegradability, optical transparency etc. that makes them a good choice for developing microfluidic bioreactors. These polymers are approved by the U.S. Food and Drug Administration (FDA) for use in tissue engineering and implant applications. Details on the synthesis and characterization of the obtained pre-polymers are discussed in this chapter. Furthermore, as synthetic biomaterials that mimic the ECM have a wide range of biomedical applications, one of the polymer films was also functionalized with gelatin via a chemical immobilization technique that has never been applied up to now for poly (polyol sebacate)s. This comes as an improvement to the already existing physio-sorbtion methods that lead to protein removal from the material.
Chapter 3 presents the use of the scaffolding technique of electrospinning for the development of porous structures. These scaffolds provide the three- dimensionality cells need in order to differentiate and maintain the specific phenotypic expression, as they mimic the extracellular matrix and are included in a later step of the final microsystem technology. The scaffolds developed in this chapter can stand alone as cell delivering porous membranes and can serve various applications, from soft to hard tissue engineering. Other enabling applications of these types of scaffolds such as cardiovascular tissue engineering are also mentioned.
Microfabrication technology is an interesting tool used to impart a specific topography and is presented in Chapter 4. The technology developed herein comprises of a complex 3D architecture for microfluidic environments that can be potentially used in tissue engineering applications, such as in the design of a tissue-engineered organ. As vital organs contain multiple types of cells, a porous membrane prepared by a classical scaffolding technique (i.e. electrospinning) has been integrated in the microfluidic devices. This strategy would enable not only cell (co-)culture, but also distribution of nutrients and oxygen.
In Chapter 5 the biocompatibility of the developed materials and electrospun structures is evaluated with different cell lines, demonstrating their non- cytotoxicity and potential for liver tissue engineering.
In conclusion, a perspective on the synthesized polymers and their utility in microsystem technology is presented. The presented technology possesses the ability to relate to a variety of applications and can be easily transferred to all poly(polyol sebacates) present in literature. The unique feature of the developed microfluidic devices is the porous membrane that would impart the 3-dimensionality that cells need to grow, while the microchannels will guide the cells and align them in a specific way as to better mimic the native tissue.
| Date of Award | Nov 2016 |
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| Original language | English |