Low temperature additive manufacturing of three dimensional scaffolds for bone-tissue engineering applications: Processing related challenges and property assessment

In the last two decades, additive manufacturing (AM) has made significant progress towards the fabrication of biomaterials and tissue engineering constructs. One direction of research is focused on the development of mechanically stable implants with patient-specific size/shape and another direction has been to fabricate tissue-engineered scaffolds with designed porous architecture to facilitate vascularization. Among AM techniques, three dimensional powder printing (3DPP) is suitable for fabrication of bone related prosthetic devices, while three dimensional plotting (3DPL) is based on extrusion of biopolymers to create artificial tissues. In the present review, we aim to develop a better understanding of the science and engineering aspects of these low temperature AM techniques (3DPP and 3DPL) in the context of the bone-tissue engineering applications. While recognizing multiple property requirements of a 3D scaffold, the central theme is to discuss the critical roles played by the binder and powder properties together with the interplay among processing parameters in the context of the physics of binder-material interaction for the fabrication of implants with predefined architecture having structural complexity. An effort also has been exerted to discuss the existing challenges to translate the design concepts and material/binder formulations to develop implantable scaffolds with a more emphasis on bioceramics and biopolymers. Summarizing, this review highlights the need to adopt intelligent processing approaches and targeted application-specific biocompatibility characterization, while fabricating mechanically stable and biologically functionalized 3D tissue equivalents.