Page 20 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

GENERAL INTRODUCTION
Bone defects
Large bone defects can occur as a result of trauma, tumor resection, or infection. These defects cannot be regenerated by natural self-repairing capacity of the bone and surgical intervention is required. Autografts are the golden standard for the treatment of large bone defects since they contain osteogenic cells, have osteoinductive properties, which is the ability to stimulate osteoprogenitor cells to differentiate into osteoblasts to form new bone, as well as osteoconductive properties, which is the ability to provide scaffold-like properties for new bone ingrowth, while avoiding immunogenic responses. However, use of autologous bone has drawbacks such as limited supply, donor site morbidity, and need for multiple surgeries. Currently, bone tissue engineering represents a promising alternative for the reconstruction of large bone defects [1].
Bone tissue engineering
Bone tissue engineering involves a combination of scaffolds, osteogenic cells, and physical/mechanical and/or chemical signals to replace, maintain, or enhance the function of damaged or diseased bone [2]. Scaffolds are a key component in bone tissue engineering to provide a microenvironment for cell activities. However, despite numerous efforts, successful applications of bone tissue engineering-based therapies in routine medical practice are limited, indicating the strong unmet need for improved strategies making use of “smart” scaffolds that provide adequate mechanical strength and stiffness, cell attachment properties, and effective stimulation of osteogenic behavior of either exogenously added or locally recruited regenerative cells.
Biomaterials in bone tissue engineering
The most commonly used materials for fabrication of bone tissue engineering scaffolds are ceramics, polymers, and demineralized bone. Since we aimed for 3D-bioprintable biomaterials (see below), we focused in this thesis on the polymer polycaprolactone (PCL) and a composite of the polymer poly (lactic-co-glycolic acid) (PLGA) with the ceramic β-tricalcium phosphate (β-TCP).
PCL is a biodegradable polymer in the family of poly(α-hydroxy esters). It is the most widely used polymer in 3D-printing due to its low melting (60°C) and glass transition (-60°C) temperatures which makes it easy to process. PCL has a slow degradation time in the order of two years, is a biocompatible polymer and is approved by the US Food and Drug Administration.
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