Page 21 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

However, PCL is hydrophobic in nature and lacks biological recognition sites, and therefore needs surface modification for enhanced cellular attachment, proliferation, and differentiation [3].
PLGA is another polyester which is a copolymer of poly lactic acid (PLA) and poly glycolic acid (PGA). One of the main advantages of PLGA is that its degradation rate can be controlled by the relative percentages of PLA and PGA in the copolymer. PLA is more hydrophobic than PGA and therefore, lactide-rich PLGA copolymers are less hydrophilic and degrade more slowly. Degradation of PLGA can range from several weeks to several months depending on the molecular weight and copolymer ratio [4]. PLGA has a higher intrinsic mechanical stiffness than PCL which is more ductile than PLGA [5]. However, PLGA itself lacks osteoconductivity [6], and therefore bone biomimetic materials such as hydroxyapatite (HA) and β-TCP are extensively used as a composite with PLGA [7-9]. β-TCP has tailorable bioresorbability in contrast to HA, which has a significantly lower dissolution rate, around 10 wt% per year in vivo [10]. However, since calcium phosphates display intrinsic brittleness, composites with them and various polymers are an obvious method of choice by combining the benefits and overcoming the limitations of the individual components.
3D-printing of tissue engineering scaffolds
3D scaffold fabrication techniques can be categorized into conventional or additive manufacturing (AM) methods. Conventional methods such as freeze drying, solvent casting-porogen leaching, gas foaming etc. can produce porous spongy scaffolds that resemble the micro-structure of cancellous bone. However, these fabrication methods have limitations such as toxic solvent residues, inaccurate control of the internal structure, and poor ability to customize for specific defect sites [11]. To tackle these limitations, there has been a trend in recent years to fabricate tissue engineering scaffolds using AM technology. AM is a relatively new technology in which the final structure is built by stacked layers of material. In short, the shape of the defect site is first identified using medical imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI). Geometrical modelling is then conducted to generate a 3D CAD model with controlled internal structure and geometry fitting the defect site. The 3D scaffold is then printed layer by layer according to the designed model.
Extrusion-based 3D-printing, which dispenses material strands via either pneumatic, piston-driven, or screw-driven force [12] through a nozzle and positions them via computer- controlled motion of the printing head or the collecting stage, is the most widely used AM system for the fabrication of tissue engineering scaffolds. It allows processing of different biomaterials with high reproducibility and flexibility, and offers possibilities for printing various biological
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