The combined application of stem cells and three-dimensional bioprinting scaffolds for the repair of spinal cord injury

Abstract

Spinal cord injury is considered one of the most difficult injuries to repair and has one of the worst prognoses for injuries to the nervous system. Following surgery, the poor regenerative capacity of nerve cells and the generation of new scars can make it very difficult for the impaired nervous system to restore its neural functionality. Traditional treatments can only alleviate secondary injuries but cannot fundamentally repair the spinal cord. Consequently, there is a critical need to develop new treatments to promote functional repair after spinal cord injury. Over recent years, there have been several developments in the use of stem cell therapy for the treatment of spinal cord injury. Alongside significant developments in the field of tissue engineering, three-dimensional bioprinting technology has become a hot research topic due to its ability to accurately print complex structures. This led to the loading of three-dimensional bioprinting scaffolds which provided precise cell localization. These three-dimensional bioprinting scaffolds could repair damaged neural circuits and had the potential to repair the damaged spinal cord. In this review, we discuss the mechanisms underlying simple stem cell therapy, the application of different types of stem cells for the treatment of spinal cord injury, and the different manufacturing methods for three-dimensional bioprinting scaffolds. In particular, we focus on the development of three-dimensional bioprinting scaffolds for the treatment of spinal cord injury.

Figure 1

Different stem cells play different primary roles when transplanted to a lesion site in the spinal cord. NSCs and iPSCs can differentiate into neuron-like cells and oligodendrocytes while HSCs mainly inhibit the proliferation of astrocytes. ESCs have the strongest ability to promote remyelination while MSCs can secrete growth factors and exhibit anti-inflammation, pro-angiogenic and anti-apoptosis properties. Created using Adobe illustrator (version 2017 cc). ESCs: Embryonic stem cells; HSCs: hematopoietic stem cells; iPSCs: induced pluripotent stem cells; MSCs: mesenchymal stem cells; NSCs: neural stem cells.

Figure 2

The most prevalent 3D bioprinting methods used for tissue engineering applications. (A) Inkjet bioprinting; (B) micro-extrusion bioprinting; (C) SLA bioprinting; and (D) FDM bioprinting. Created using Adobe illustrator (version 2017 cc). FDM: Fused deposition modelling; SLA: stereolithography.

Figure 3

The combined application of stem cells and three-dimensional bioprinting scaffolds in the repair of spinal cord injury. Created with Adobe illustrator (version 2017 cc).