Date of Award

December 2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

James H. Henderson

Subject Categories

Engineering

Abstract

Cell behaviors, such as motility and differentiation, which are highly regulated by the complex 3D in vivo microenvironment, have been extensively studied in the past decades to better understand the mechanisms of development, disease, and healing. Due to the highly complex nature of the in vivo environment and limited resources and access to study cell behaviors in vivo, great efforts have been made to develop in vitro systems to mimic the in vivo microenvironment for a better understanding of cell-microenvironment interactions. However, most of the commonly used in vitro systems are static, which cannot mimic the dynamics of the microenvironment in vivo. In this dissertation, our goal was to create a 3D complex in vitro microenvironment that can dynamically change its internal architecture and to employ such in vitro dynamic complex microenvironment to study cell motility and differentiation behaviors for the application of tissue engineering, regenerative medicine, and cancer metastasis.

In this work, 3D dynamic shape memory scaffolds were developed and employed to investigate cell motility and differentiation behaviors when the cellular microenvironment dynamically changes in vitro. The scaffolds have fibrous structure, which can potentially mimic the collagen matrix fibrous structure in vivo. And, more importantly, the scaffolds can dynamically change internal architecture on command, which can potentially mimic the dynamic ECM architectural change in vivo during tissue development and cancer metastasis.

To achieve this goal, the first part of this dissertation (Chapter 2 – 3) developed a programmable 3D shape memory electrospun scaffold that can dynamically change fiber alignment upon triggering under cytocompatible conditions. In these chapters, the programmable dynamic 3D scaffold was employed to study stem cell motility, cancer cell polarization, and cancer cell motility, for ultimate application in stem cell homing and cancer metastasis studies. Stem cell motility, cancer cell motility, and cancer cell morphology were found to be directed by shape-memory-actuated changes in scaffold internal architecture.

In Chapter 4, the objective was to investigate stem cell differentiation when cells undergo dynamic scaffold internal architectural change for the application of bone tissue engineering and critical-sized bone defect treatment. The shape memory electrospun scaffold investigated in Chapter 2 and Chapter 3, as well as a shape memory foam scaffold, were employed to examine the human adipose-derived mesenchymal stem cells osteogenic differentiation capacity. We found that the dynamic change of the scaffold internal architecture would not hinder the stem cell osteogenic differentiation.

In Chapter 5, we utilized a scaffold-free 3D culture system and investigated the effect of a non-scaffold-related factor—low oxygen tension—on mature chondrocytes dedifferentiation behavior for the application of cartilage tissue engineering. Low oxygen has been frequently implicated as a limitation associated with synthetic 3D scaffolds when the scaffolds have small pore size or poor interconnectivity, or both, due to the fact that low oxygen and limited nutrient diffusion can cause cell death. However, low oxygen tension during culture could be beneficial for cartilage tissue engineering, as cartilage is an avascular tissue and low oxygen is present in vivo during chondrogenesis and in adult articular cartilage.

Finally, in Chapter 6, conclusions and future directions are discussed and summarized.

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