Page 281 - IJB-10-3

International Journal of Bioprinting 3D bioscaffolds with SR1 for vasculogenesis

light on the controlled and sustained release of SR1 multinucleated giant cells, and lymphocytes, occurred in
from the nanoparticles. This dynamic release profile, the scaffold-implanted groups (NP@Sc and SNP@Sc) with
in conjunction with the observed bone regeneration fibroblastic connective tissue surrounding the implanted
outcomes, presents promising avenues for advancing material. In contrast, the infiltration of inflammatory
our understanding of the therapeutic potential of SR1 in cells was decreased in every experimental group 4 weeks
promoting effective bone healing. after implantation. Inflammation is a typical response at
the injury site and a necessary process in wound healing.
In vitro studies revealed significant insights into the
mechanisms underlying the observed outcomes. Flow Regardless of the location and type of injury, the series
of inflammation, regeneration, and remodeling occurs in
cytometry analysis demonstrated that SR1 treatment the process of bone tissue regeneration. In the current
45
led to a higher percentage of CD34 cells, particularly study, the acute inflammatory response after surgery
+
in the SNP groups, accompanied by notable increases was completed in 7 days and peaked within 24 h.
46
in expression of c-kit, CXCR4, VEGFR2, and VE- However, the infiltration of inflammatory cells, which
cadherin—the representative markers of EPCs. CD34 was observed in the NP@Sc and SNP@Sc groups 2 weeks
is a transmembrane phosphoglycoprotein that is after implantation, appeared to have been triggered by
widely known as a marker of hematopoietic stem the implanted materials. Prolonged inflammation after
cells and progenitor cells. Additionally, CD34 is a an acute inflammatory response delayed bone healing
known marker of many other cell types, including 2 weeks after implantation in the scaffold-implanted
mesenchymal stromal cells, epithelial progenitors, groups. Finally, the timely termination of inflammation
47
and vascular endothelial progenitors. According to accelerated bone regeneration, and the percentage of the
39
a previous study showing that SR1 enhances CD34 area of newly formed bone in the SNP@Sc group was
+
+
40
cell expansion. CD34 cell populations in the three significantly higher than that of the other groups 4 weeks
groups of EPCs were evaluated using flow cytometry. after the operation.
Furthermore, angiogenic biomarkers were double-
labeled with CD34 and analyzed by means of flow In general, proliferation of ECs and fibroblasts induces
cytometry analysis, which used CD117 (also known as angiogenesis. Furthermore, CD31 and α-SMA are widely
c-kit; stem cell growth factor receptor) for stemness, known markers of ECs and pericytes or smooth muscle
VEGFR2 (KDR) for evaluating endothelial maturity, 41,42 cells, respectively, which are the constituent cells in the
CD184 (also known as homing receptor chemokine mature blood vessels. Thus, vessels can be distinguished
C-X-C receptor-4, CXCR4) for migration ability, with immunofluorescence staining of anti-CD31 and anti-
43
+
+
and CD144 (also known as VE-cadherin) for vascular α-SMA antibodies, through which CD31 and α-SMA
-
+
epithelia (i.e., nascent blood vessels) forming ability. indicate mature blood vessels, while CD31 and α-SMA
44
48
Additionally, two cell proliferation assays (CCK-8 and indicate immature ones.
EdU assays) and wound healing assays were conducted The current in vivo studies showed that SR1 is
to evaluate the effect of SR1 on EPCs (Figure 1A, C, effective in bone regeneration and angiogenesis 4 weeks
and D). To summarize the in vitro results, we concluded after surgery. Therefore, MCT scanning after Microfil
that SR1 may upregulate the functional abilities of EPCs compound perfusion was conducted to visualize the
and maybe effective in expanding the CD34 population vascular network with a special focus on that time
+
in EPCs. period. Immunofluorescence staining revealed that
In the current study, the sustained release of SR1 in rat SR1 contributed to the formation of both immature
calvarial defects was successful. However, there was no and mature blood vessels, suggesting its potential to
statistically significant difference between the groups at enhance angiogenesis. The Microfil compound perfusion
2 weeks after the operation in MCT data (Figure 4B–D). experiment reinforced this notion, highlighting the
The reason for this result can be found in the histological capacity of SR1 to enhance angiogenesis in both defect
analysis data; semi-quantitative scoring evaluation of cell sites and surrounding areas.
type and tissue response in the cranial defective area 2 and While this study presents promising outcomes
4 weeks after implantation was conducted according to the regarding the beneficial impact of SR1 on bone regeneration
International Organization for Standardization 10993-6 and angiogenesis, further research encompassing a wider
for local biological effects (Table S1 in Supplementary range of released SR1 concentrations is necessary. This is
File). Regarding the features of the cranial defective area instrumental for optimizing the release method and for
2 weeks after implantation (Figure 5A), heavy infiltration ensuring the long-term treatment implications from the
of inflammatory cells, mainly composed of macrophages, eventual clinical application of sustained SR1 release.

Volume 10 Issue 3 (2024) 273 doi: 10.36922/ijb.1931