ABSTRACT
In the present review, we have briefly summarized the injuries in the nerve system, including the central nervous system (CNS) and peripheral nervous system (PNS), and the bio-engineering methods for treating these injuries. Among these, the development and application of three-dimensional (3D) printing were mainly introduced for nerve regeneration. Initially, in the field of nerve regeneration, the application of 3D printing was limited to the PNS for constructing nerve conduits, while with the development of biomaterials science in recent years, such as generation of a type of bio-ink, 3D printing has been gradually applied in the treatment of spinal cord injury and traumatic brain injury. From the growing literature in this field, it is clear that researchers in academic and industrial fields are interested in the advantages and challenges of 3D printing for the treatment of nerve system diseases. As a newly developed technique, 3D printing is still in its infancy, though significant progress has been achieved in recent years. Due to the complexity, functionality, and variety in the nerve system, 3D printed constructs for the treatment of nerve system diseases is still a major challenge. For example, different tissues (PNS, brain, spinal cord) are composed of multiple types of cells with complex biochemistries and geometries of the extracellular matrix. Thus, the accurate reconstruction of the tissue structure with suitable cell location using 3D printing technology is very important for tissue regeneration and functional recovery. 3D printing has been reported to be able to construct some sophisticated structures that better mimic in vivo microenvironment. Overall, for better scaffold printing using 3D printing technique in nerve regeneration, the scaffold design, preparation of bio-ink, and precise printing should be considered thoroughly and comprehensively. For better functional recovery of the nerve system, printing with growth factors, cells, chemical functionalization, and conductivity along with suitable mechanical properties leading to printable and cell-friendly systems will pave the way for much better treatment of nerve system diseases.
