Additive Manufacturing of Material Scaffolds for Bone Regeneration: Toward Application in the Clinics

Abstract

Additive manufacturing (AM) allows the fabrication of customized bone scaffolds in terms of shape, pore size, material type and mechanical properties. Combined with the possibility to obtain a precise 3D image of the bone defects using computed tomography or magnetic resonance imaging, it is now possible to manufacture implants for patient-specific bone regeneration. This paper reviews the state-of-the-art of the different materials and AM techniques used for the fabrication of 3D-printed scaffolds in the field of bone tissue engineering. Their advantages and drawbacks are highlighted. For materials, specific criteria, were extracted from a literature study: biomimetism to native bone, mechanical properties, biodegradability, ability to be imaged (implantation and follow-up period), histological performances and sterilization process. AM techniques can be classified in three major categories: extrusion-based, powder-based and liquid-base. Their price, ease of use and space requirement are analyzed. Different combinations of materials/AM techniques appear to be the most relevant depending on the targeted clinical applications (implantation site, presence of mechanical constraints, temporary or permanent implant). Finally, some barriers impeding the translation to human clinics are identified, notably the sterilization process.

Keywords: 3D printing; additive manufacturing; bone regeneration; scaffolds; tissue engineering.

Figure 1

Major implantation sites in the body where synthetic bone graft substitutes are used for bone repair For each implantation site, the different types of implantable materials already used in clinics (biodegradable polymers, non-biodegradable polymers, ceramics, metals) are presented.

Figure 2

The three major types of AM techniques: extrusion-based techniques, powder-based techniques and vat photopolymerization techniques For each one, the types of materials that can be used and their form (filament, paste, powder…) are indicated.

Figure 3

(a) Price of the AM machines indicated on a scale in k$ From left to right: extrusion-based machines, vat photopolymerization machines (VPP) and powder-based machines, these later ones being the most expensive ones. (b) Ease of use of the different machines, assessed based on the training required and the complexity of the machine The scale corresponds to the difficulty level, from easy to difficult. From left to right: extrusion-based machines, VPP machines and powder-based machines. (c) Space requirement of each technique estimated in m³. From left to right: extrusion-based machines, VPP machines and powder-based machines.