Date of Award

December 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Pranav Soman

Keywords

Bone, Perfusion, Tissue Engineering

Subject Categories

Engineering

Abstract

Due to challenges associated with current clinical techniques used to treat bone defects, there has been an increased focus on finding a tissue engineered solution. However, while great progress in this field has been achieved, researchers have yet to suitably combine the proper biological and structural environments needed to serve as a complete bone tissue substitute that is comparable to modern clinical solutions.

To achieve the goal of creating a model bone tissue substitute which could eventually serve as a viable therapy for bone trauma, be it caused by congenital medical conditions, age related diseases or high impact forces, three areas of the engineered construct architecture and composition were identified and studied in a successive fashion. First, a soft, biocompatible matrix within which cells could be encapsulated was studied, followed by an investigation on how to combine the soft matrix with a 3D printed structural frame. Finally, user-defined perfusable vasculature was added to the soft matrix in order to create a model bone tissue engineering construct capable of possible in vivo implantation.

In Chapter 2 of this work, osteoblast-like human osteosarcoma cells (Saos-2) were encapsulated within gelatin methacrylate (GelMA) hydrogels and the effect of the hydrogel density on cellular morphology and mineralization was investigated. It was found that the less dense hydrogels allowed for increased cell viability and spreading, while the denser gels appeared to encourage more mineral deposition on the construct periphery.

Building upon Chapter 2, Chapter 3 focused on the 3D printing of polycaprolactone (PCL) and composite PCL cages which could be combined with the soft GelMA matrices used for cellular encapsulation. It was found that while PCL and PCL composite cages could be reproducibly printed via a Makerbot 3D printer, the structural strengths did not surpass those of standard poly lactic acid (PLA) thermoplastic cages. Furthermore, it was demonstrated that the cell-laden GelMA hydrogels containing encapsulated Soas-2 cells could be incorporated with the 3D printed structures for potential bone tissue engineering applications.

In Chapter 4, a simpler version of the cages produced in Chapter 3 were combined with sacrificial 3D printed polyvinyl alcohol (PVA) pipes and the dense cell-laden hydrogels investigated in Chapter 2 to create structurally supported, cell-laden hydrogel constructs. It was found that encapsulated cells could be stimulated to deposit mineral in the centers of the constructs via direct perfusion. However, in a larger version of the construct containing multiple pipes, mineralization was impeded due to diffusion issues caused by individual channel mineralization.

Finally, in Chapter 5 future strategies to improve upon the structurally supported cell-laden hydrogels are discussed which would solve the issues found in Chapter 4. Additionally, potential in vivo applications for this system are explored.

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