Several alternatives to nerve grafting have been developed to treat peripheral nerve injuries, including nerve conduits that use supportive cells. A team of researchers from Kyoto University focused on a novel completely biological, tissue-engineered, scaffold-free 3D bioprinted conduit for nerve regeneration. The study was published in the PLOS one scientific journal.
The scientists developed six scaffold-free conduits from human normal dermal fibroblasts using a Cyfuse 3D bioprinter. Twelve adult male rats with immune deficiency underwent mid-thigh-level transection of the right sciatic nerve. The resulting 5-mm nerve gap was bridged using 8-mm Bio 3D conduits (Bio 3D group, n = 6) and silicone tube (silicone group, n = 6). Several assessments were conducted to examine nerve regeneration eight weeks post-surgery. The study confirmed that scaffold-free 3D bioprinted conduits, composed entirely of fibroblast cells, promote nerve regeneration in a rat sciatic nerve model.
This study was supported by JSPS KAKENHI Grant Number 15K10441. Cyfuse provided access to its Regenova 3D bioprinter, which was used in this study, and contributed financially to this study via a Collaborative Research Agreement with Kyoto University. Cyfuse also provided support in the form of salaries for authors and provided research grants. The company did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Treatment of peripheral nerve injury remains challenging, especially in motor nerves with long gaps. Autologous nerve grafting is considered to be the gold standard treatment of nerve injuries that involve an interstump gap [2,3]. However, autologous nerve grafting has several disadvantages, including: limited supply; mismatch of the caliber diameter; and donor site morbidity, such as the loss of native function and neuroma formation.
Several alternative treatments for peripheral nerve injury have been developed. For example, some nerve defects have been repaired both experimentally and in clinical practice by bridging the gap with tube-like materials (tubulization). Several nerve conduits using an extracellular matrix, vascularity and supportive cells have been developed to improve the quality of regenerated nerves. However, the seeding efficacy and viability of supportive cells injected in nerve grafts remain unclear. In addition, the regenerative capacity of nerve conduits remains inferior to that of autografts. Furthermore, synthetic nerve conduits are associated with a risk of infection and low biocompatibility.
To address these potential problems, the researchers used 3D bioprinting to create a completely biological, tissue-engineered, and scaffold-free conduit (Bio 3D conduit) using the Cyfuse-Regenova Kenzan method to create scaffold-free tubular tissue from homogeneous multicellular spheroids via a 3D bioprinter-based system. In this system, which utilizes the cellular characteristic of self-assembly, cells cultured in a bioreactor over 24 hours aggregate to form a homogeneous multicellular spheroid structure. Following this aggregation, medical grade stainless needles were used as temporal fixators, called a “needle-array” system, to skewer assembled spheroids until the spheroids are fused. After one week, spheroids were removed and cultured in the bioreactor to obtain a structurally sound scaffold-free construct. This system produces completely biological tubular structures without the need for foreign materials.
The researchers used fibroblasts to generate the Bio 3D conduits, because fibroblasts are easy to culture and proliferate in vitro, and it has also been reported that the process of nerve regeneration requires fibroblasts. They confirmed that Bio 3D conduits promote peripheral nerve regeneration based on assessments conducted eight weeks post-surgery in rats receiving Bio 3D conduits compared to the control group using a silicone tube.
Additional studies are needed to determine the efficacy of Bio 3D conduits in clinical applications. For example, the mechanisms of degradation of Bio 3D conduits have not been identified. Therefore, a future study should pre-label cells of the spheroids to trace the degraded Bio 3D conduits. A future study also should evaluate the viability of the cells of the spheroids. Furthermore, in the peripheral nerve fields, the mechanical strength and flexibility of the nerve conduit depends on the joint movement. Future studies should evaluate the mechanical strength of the Bio 3D conduits, for example by measuring the bending strength of Bio 3D conduits made from fibroblasts, uBMSCs, and other cells types. At this time the researchers concluded that the Bio 3D conduit promotes peripheral nerve regeneration and may be useful in peripheral nerve injuries with longer gaps and in clinical applications.