Long-Term Tri-Modal In Vivo Tracking of Engrafted Cartilage-Derived Stem/Progenitor Cells Based on Upconversion Nanoparticles.

Cartilage-derived stem/progenitor cells (CSPCs) are a potential choice for seed cells in osteal and chondral regeneration, and the outcomes of their survival and position distribution in vivo form the basis for the investigation of their mechanism. However, the current use of in vivo stem cell tracing techniques in laboratories is relatively limited, owing to their high operating costs and cytotoxicity. Herein, we performed tri-modal in vivo imaging of CSPCs during subcutaneous chondrogenesis using upconversion nanoparticles (UCNPs) for 28 days. Distinctive signals at accurate positions were acquired without signal noise from X-ray computed tomography, magnetic resonance imaging, and upconversion luminescence. The measured intensities were all significantly proportional to the cell numbers, thereby enabling real-time in vivo quantification of the implanted cells. However, limitations of the detectable range of cell numbers were also observed, owing to the imaging shortcomings of UCNPs, which requires further improvement of the nanoparticles. Our study explores the application value of upconversion nanomaterials in the tri-modal monitoring of implanted stem cells and provides new perspectives for future clinical translation.

A randomized, controlled clinical trial of autologous stromal vascular fraction cells transplantation to promote mechanical stretch-induced skin regeneration.

BACKGROUND: The regeneration response of the skin to mechanical stretching in vivo has been explored in reconstructive surgery to repair large-scale deformities. The ability of the skin to regenerate limits the reconstructive outcome. Here, we propose an approach in which autologous stromal vascular fraction (SVF) cells and mechanical stretching are combined to overcome this limitation and promote skin regeneration. METHODS: This randomized, blinded, placebo-controlled clinical trial screened 22 participants undergoing tissue expansion with exhausted regeneration. Twenty eligible participants received intradermal injections of the SVF or placebo treatments. Follow-ups were conducted at 4, 8, and 12 weeks to assess efficacy and at 2 years to assess safety. The primary endpoint was the expanded skin thickness at 12 weeks. The secondary endpoints included skin thickness at 4 and 8 weeks, the expansion index (EI), and the skin texture score at 12 weeks. RESULTS: The skin thickness of the SVF group was significantly higher than that of the control group at both 8 weeks (mean difference 0.78 [95% CI - 1.43 to - 0.11]; p = 0.018) and 12 weeks (0.65 [95% CI - 1.30 to - 0.01]; p = 0.046). In the SVF group, the increase in skin thickness was significant at 4 weeks (0.49 [95% CI - 0.80 to - 0.06]; p = 0.010) to 8 weeks (0.45 [95% CI - 0.92 to 0.02]; p = 0.026) and maintained after 12 weeks, whereas that in the control group was reduced after 8 weeks (0.42 [95% CI - 0.07 to 0.91]; p = 0.037). The SVF group showed greater EI increases than the control group (0.50 [95% CI - 0.00 to 0.99]; p = 0.047). The skin texture scores in the SVF group were greater than those in the control group at 12 weeks. Histologically, SVF-treated expanded skin showed more proliferating cells and blood vessels, and the extracellular matrix volume increased. No severe adverse events occurred. CONCLUSIONS: Transplantation of SVF cells can expedite the potency of mechanical stretch-induced skin regeneration and provide clinical reconstruction with plentiful tissue. TRIAL REGISTRATION: This trial was registered with the Chinese Clinical Trial Registry, ChiCTR2000039317 (registered 23 October 2020-retrospectively registered).

Effect of tissue expansion on chondrocyte sheets in cartilage composite reconstruction.

Flap prelamination has been successfully established in tissue engineering; however, cartilage generation through combination of an expanded flap and chondrocyte sheets has not been reported. Herein, we investigate the effect of tissue expansion on chondrocyte sheets in prelaminating an expanded chondrocutaneous flap. Chondrocyte sheets were implanted into a tissue expander capsule following which capsule inflation was performed weekly. At 4 and 12 weeks post implantation, the specimens were examined with histology and immunohistochemistry analyses. Extracellular matrix (ECM) formation and type II collagen deposition in the regenerated cartilage tissue in vivo were also examined. After 4 weeks of implantation, the generated cartilage was phenotypically stable with minimal hypertrophy, while that formed after the 12-week expansion showed visible hypertrophic differentiation. To evaluate the effect of static pressure and/or hypoxic conditions generated by the expanding tissue, static pressure and/or hypoxic conditions were reproduced in vitro. The chondrocyte sheets stimulated by mechanical static pressure and hypoxia maintained their chondrogenic phenotype. The expression of aggrecan, collagen II, Sox-9, and HIF-1α was increased in chondrocyte sheets cultured in 2% oxygen (hypoxia); however, aggrecan, collagen II, and Sox-9 were downregulated in the static pressure/normoxia group. These results suggest that the expanded environment promoted cartilage formation by the chondrocyte cell sheets, while mechanical forces and hypoxic conditions in vitro allowed chondrocyte cell sheets to retain their chondrogenic phenotype.