Page 15 - MSAM-2-2

Materials Science in Additive Manufacturing Union of 2D nanomaterials and 3D printing

applying electrical stimuli through conductive graphene GelMA, which may have insufficient mechanical strength
within the gelatin matrix significantly influenced MSC for certain applications . Gasparotto et al. created
[92]
differentiation into Schwann cell-like phenotypes and their 3D-printed scaffolds using either PLA or graphene@
paracrine activity. Schwann cell markers were detected in PLA with a specific pattern . They tested the scaffolds
[93]
80% of the cells, and they secreted increased amounts of with various types of cells, including iPSCs, neuronal-like
nerve growth factor (NGF). These findings suggest that cells, immortalized fibroblasts, and myoblasts. They found
applying electrical stimuli within 3D gelatin matrices may that both types of filaments had cell viability rates above
be a promising strategy for nerve regeneration, surpassing 90%, indicating no significant impact on cell vitality. The
other transdifferentiation procedures involving electrical scaffolds also did not affect cell proliferation, as shown
stimuli on 2D substrates and chemical stimuli on 3D by a 3- to 5-fold increase in cell number between 24 and
gelatin scaffolds. 72 h after seeding, consistent with the SH-SY5Y cell line’s
It is necessary to verify the performance of biomaterials doubling time of 27 h. When iPSCs were seeded onto
in a complex physiological environment through in vivo the scaffolds, graphene increased the expression of Pax6
experiments due to several limitations of in vitro evaluation and Nestin, indicating a tendency toward the neuronal
(e.g., lack of complexity and difficulty in mimicking lineage, regardless of the scaffold microtopography. Jakus
ECM). In vivo studies of graphene have revealed several et al. developed a 3D printable graphene (3DG) composite
characteristics that are not observable in experiments ink, comprising mostly graphene and a minority of
in vitro , including the graphene’s biodistribution in the biocompatible elastomer polylactide-co-glycolide, which
[87]
[94]
body, immunological responses to graphene exposure, the can be printed under ambient conditions (Figure 5) .
ability of graphene to penetrate the blood-brain barrier, The resulting 3DG material exhibited high mechanical
and potential long-term toxicity. Huang et al. developed a strength and flexibility, with electrical conductivities
nerve scaffold by combining a graphene mesh tube (GMT) exceeding 800 S/m. In vitro studies demonstrated that
and double-network (DN) hydrogels composed of alginate the 3DG scaffold was capable of supporting adhesion,
and GelMA and incorporating netrin-1 (Figure 4) . viability, proliferation, and neurogenic differentiation
[88]
The GMT/DN hydrogel possessed suitable mechanical of human mesenchymal SCs (hMSCs), leading to a
strength and exceptional electrical conductivity, making it significant upregulation of glial and neuronal genes. The
an ideal candidate for peripheral nerve (PN) regeneration. in vivo experiments demonstrated that 3DG had promising
The scaffold aided the proliferation and alignment of SCs, biocompatibility for at least 30 days. Moreover, the surgical
outperforming pure DN hydrogel. In vivo experiments tests on a human cadaver nerve model showed that the
demonstrated that the addition of netrin-1 into the 3DG scaffold had excellent properties for handling and
GMT/DN scaffold proved effective in promoting PN could be applied to surgical procedures with ease.
regeneration and restoring denervated muscle, surpassing Multi-layered graphene is a favorable substrate for cell
the regenerative capability of autografts. growth and tissue engineering applications due to its large
Recent tissue engineering studies have shown an surface area and high oxygen content [95,96] . It possesses
increasing trend of using SCs as a promising cell source for more edges and defects than single-layered graphene,
nerve regeneration [89,90] . Unlike Schwann cells, which are creating a larger surface area for cell attachment and
primarily used in PN regeneration, SCs can differentiate growth. In addition, multi-layered graphene contains more
into various cell types and regenerate both the central and oxygen-containing functional groups on its surface, which
peripheral nervous systems . In addition, SCs can be enhances its biocompatibility and promotes cell adhesion
[91]
obtained in large quantities and possess immunomodulatory and proliferation [97,98] . These properties of multi-layered
properties, positioning them as a promising candidate for graphene facilitate cell growth and tissue engineering
promoting tissue repair . Thus, NSCs offer a versatile applications. Furthermore, the presence of multiple layers
[92]
and scalable cell source that is increasingly used in tissue in graphene provides a degree of mechanical flexibility that
engineering research for repairing a wide range of nerve can be beneficial in certain tissue engineering applications
injuries. Furthermore, researchers have investigated the where the substrate needs to deform in response to the
use of synthetic polymers such as polylactic acid (PLA), surrounding tissue [99,100] . Researchers utilized a combination
poly(lactic-co-glycolic acid) (PLGA), and polycaprolactone of 3D printing and layer-by-layer casting techniques to
(PCL) as bioinks in 3D printing for tissue engineering produce porous scaffolds with multiple layers coated
applications, aiming to develop more robust and durable with PDA and arginylglycylaspartic acid (RGD) [101] . In
3D-printed structures by incorporating synthetic the study, scaffolds were constructed using either single-
polymers into bioinks. These materials offer improved layered graphene (SG) or multilayered graphene (MG)
mechanical properties compared to bioinks composed of and PCL and incorporated macropores with microneedles

Volume 2 Issue 2 (2023) 9 https://doi.org/10.36922/msam.0620