The synthesized scaffold exhibited an elastic modulus of 3.21 KPa and was confirmed to display β-sheet aggregation. Atomic force microscopy revealed the interconnected nanostructure network of the Nano-SDF, with a fiber diameter of approximately 30 nm. The study also demonstrated the safety of Nano-SDF for stem cells, revealing no induction of a toxic response during prolonged in vitro expansion. Compared to the R-GSIK scaffold, initial cell attachment and neurite outgrowth were significantly higher when NSCs were cultivated on the Nano-SDF. Moreover, the behavioral parameters significantly improved in groups treated with NSCs and the Nano-SDF compared to the control groups. Our findings also revealed a significant difference in IFN-γ between the combination group (Nano-SDF with NSCs) and the sham group. The most remarkable result from our data was that synaptogenesis markers were significantly improved when rats were treated with stem cells and the Nano-SDF. Our findings support using the Nano-SDF in neural tissue engineering, as it promotes regeneration after TBI and provide a supportive environment for cell growth and function.
Recent studies have shown that self-assembling peptide-based hydrogels hold promise for treating TBI [37–41]. Nano-scaffolds used in neural tissue engineering possess several essential characteristics. Firstly, they should be biocompatible and biodegradable, meaning they do not cause adverse reactions and can be safely absorbed by the body over time [42, 43]. To ensure that the novel Nano-SDF was safe for NSCs, we evaluated its cytotoxicity, comparing survival rates and apoptosis with those induced by the R-GSIK. Our findings showed that the Nano-SDF was safe for stem cells and did not produce a toxic reaction during long-term in vitro expansion. This result is consistent with several studies demonstrating that nano-scaffold biomaterials, inspired by SAPs, possess outstanding biocompatibility, biodegradability, and a microenvironment that mimics the ECM [44–48]. For instance, different designs of self-assembly peptides, such as β-sheet, α-helix, collagen-like peptides, elastin-like polypeptides, and peptide amphiphiles, have additional functionalities and potential biomedical applications in bio-printing, tissue engineering, and drug delivery [47].
Furthermore, Nano-scaffolds should promote cell adhesion, proliferation, and differentiation, facilitate controlled release of bioactive molecules for enhanced cell behavior and tissue regeneration, and have a high surface area-to-volume ratio allowing extensive cell-scaffold interaction [49–54].These characteristics are achieved by mimicking the natural ECM of neural tissue, which provides a supportive environment for cell growth and function [41, 51, 55]. Our data demonstrated that initial cell adhesion, migration, and differentiation of NSCs were significantly improved when encapsulated in the Nano-SDF compared to the R-GSIK. This study supports earlier evidence that SDF-1 enhances the survival, migration, and differentiation of NSCs, which are essential for brain development and repair [56–58]. Our novel nano-scaffold incorporated a functional motif of SDF-1 in an innovative three-dimensional milieu, which provided a supportive environment for cell growth and function.
Moreover, nano-scaffolds should possess suitable mechanical properties, such as stiffness and elasticity, aligned with the target neural tissue, to provide optimal support [49, 59–62]. For example, Young’s elastic modulus of SAP hydrogels used in neural tissue engineering is an important parameter that can affect cell behavior and tissue regeneration [63]. The Young's elastic modulus of SAPs can vary depending on the specific type of SAP and its concentration [63, 64]. Recently, to improve the mechanical stability of the RADA16 peptide hydrogel, two different forms of RADA16 were conjugated with an Arg-Gly-Asp sequence and a photocrosslinkable diacrylated poly(-caprolactone)-b-poly(ethylene glycol)-b-poly(-caprolactone) triblock copolymer [71]. In consistency with previous studies, the Young's modulus of the Nano-SDF was 3.21 kPa, which falls within the range of neural tissue elasticity and could be suitable for various applications. These findings suggest that the Nano-SDF possesses good mechanical stability and cytocompatibility, which holds great potential for applications in neural tissue engineering and regenerative medicine. Inducing synaptogenesis by SAPs holds excellent potential for improving outcomes for patients with TBI [72, 73]. For instance, a recent study found that a new type of SAP scaffold could be a substrate for neurite outgrowth and synapse formation [74]. Our study demonstrated that the Nano-SDF could support neurite outgrowth in vitro and the formation of functional synapses in vivo. This aligns with earlier observations, which showed that SAPs could mimic the natural ECM, enhancing various cells' attachments, growth, and differentiation [74–76]. As we previously demonstrated in a TBI model, the Nano-SDF exhibits modulatory effects on neuroinflammatory pathways and apoptosis. The findings suggest that the Nano-SDF has potential as a tool for promoting synaptogenesis and neuronal regeneration through mitigating neuroinflammation and apoptosis [77, 78].