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International Journal of Bioprinting 3D bioprinting of nerve guidance conduits

channel cryopolymerized GelMA gel conduits. The has not yet undergone severe degeneration. SCs still retain
results suggested that such conduits could support the good proliferation and guidance ability, exhibit strong
attachment, proliferation, and survival of adipose-derived axonal growth, and show no significant local scarring.
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stem cells and upregulate their neurotrophic factor mRNA At this time, excessive support is unnecessary, as a simple
expression. After implantation in rats, the bioconduits structural hollow conduit may be preferred to provide
successfully supported reinnervation across a 10 mm sciatic basic mechanical support with axonal guidance. In
nerve gap. The results, in both functional and histological advanced injury, the distal nerve tissue exhibits significant
assessments, were comparable to those of autografts, degeneration and scar deposition, a decline in the number
highlighting its potential clinical utility in peripheral nerve and function of SCs, a deteriorated local regenerative
regeneration. AM can also be exploited in combination microenvironment, and reduced axonal regenerative
with nerve image data to successfully produce complex potential. In such cases, hollow conduits often struggle to
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bifurcation nerve injuries. Johnson et al. 3D-printed a rat function well, and a conduit that is more supportive, such
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sciatic nerve bifurcation model by scanning its anatomical as multi-channel conduits, porous structure conduits, or
structures, and the acquired data were further used to micropattern conduits, should be chosen. In addition, in
guide the preparation of bifurcated NGCs. advanced nerve injury, scar tissue formation is one of the

2.6. Selection strategies key factors hindering regeneration. Massive deposition of
Different structural types of nerve conduits offer distinct collagen with other extracellular matrices leads to tissue
advantages in terms of functional performance and tissue sclerosis, which forms a physical barrier, interferes with the
compatibility. Therefore, selecting the most appropriate direction of axonal growth, and may induce the formation
conduit type based on the specific characteristics of a of neuromas. Therefore, the selection of nerve conduits
nerve injury remains a critical challenge in both current with anti-scarring or pro-regenerative functions is crucial
research and clinical practice. A thorough understanding in advanced nerve repair. Micropatterned conduits can
of the structural and functional attributes of each conduit effectively guide the directional growth of axons and
type is essential for evaluating their suitability and reduce the obstruction of regeneration by scarring. The
developing optimal application strategies across diverse characteristics of different conduit structures and their
clinical scenarios, thereby enhancing the efficacy of suitability are summarized in Table 2. In summary, the
nerve regeneration. selection of appropriate NGC structures not only facilitates
the reconstruction of axonal guidance pathways but also
Hollow conduits have significant limitations in guiding optimizes cellular behavior and promotes the localized
directional axonal growth due to the lack of morphological accumulation of neurotrophic factors, thereby accelerating
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cues and biochemical signals, and are usually applied to nerve regeneration and enhancing functional recovery.
short-distance nerve defects (<5 mm). In contrast, multi-
channel conduits could help to minimize axonal vagrancy 3. Biomaterials for nerve conduit
by providing a larger surface area for cell attachment and
a more defined growth pathway, making them suitable The structure of the conduit significantly influences
for the repair of medium-distance (5–8 mm) defects. The the overall outcome of the nerve regeneration process.
porous conduit provides excellent permeability, allowing Nevertheless, structural design alone is insufficient to
the free exchange of nutrients and molecular signals inside achieve optimal nerve repair; the choice of materials also
and outside the conduit and promoting the elimination plays a critical role. Properties of the conduit material,
of metabolic wastes while contributing to the adhesion, such as biocompatibility, mechanical performance,
migration, and proliferation of SCs. Surface micropatterned degradation rate, and bioactivity, directly impact its
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conduits provide a significant enhancement of axonal functionality during nerve regeneration. Therefore, a
orientation through specific microstructures, such as synergistic interplay between material and structure is
grooves or gradient arrangements, and are particularly essential. A proper design of the structure provides the
suitable for the repair of larger gap defects. necessary space and orientation for nerve repair, while
suitable materials ensure that the structure remains stable
In addition to the structural characteristics of the in the physiological environment to support the growth,
conduit, different tissue states, biological responses, and proliferation, and differentiation of neural cells. The
regenerative potentials at various process stages place organic integration of both elements is key to achieving
unique requirements on the nerve conduit’s selection effective nerve regeneration.
strategy. The timing of post-injury treatment can be
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divided into early stage (<4 weeks) and advanced stage The selection of biomaterials for NGCs is based on
(>4–6 weeks). In the early stage of injury, the distal nerve the following requirements: (i) good processability, (ii)

Volume 11 Issue 4 (2025) 40 doi: 10.36922/IJB025140120