Growth factor priming of synovium-derived stem cells for cartilage tissue engineering

Abstract

This study investigated the potential use of synovium-derived stem cells (SDSCs) as a cell source for cartilage tissue engineering. Harvested SDSCs from juvenile bovine synovium were expanded in culture in the presence (primed) or absence (unprimed) of growth factors (1 ng/mL transforming growth factor-β(1), 10 ng/mL platelet-derived growth factor-ββ, and 5 ng/mL basic fibroblast growth factor-2) and subsequently seeded into clinically relevant agarose hydrogel scaffolds. Constructs seeded with growth factor-primed SDSCs that received an additional transient application of transforming growth factor-β(3) for the first 21 days (release) exhibited significantly better mechanical and biochemical properties compared to constructs that received sustained growth factor stimulation over the entire culture period (continuous). In particular, the release group exhibited a Young's modulus (267±96 kPa) approaching native immature bovine cartilage levels, with corresponding glycosaminoglycan content (5.19±1.45%ww) similar to native values, within 7 weeks of culture. These findings suggest that SDSCs may serve as a cell source for cartilage tissue engineering applications.

FIG. 1.

Schematic of the study design. Synovium-derived stem cells (SDSCs) were expanded in two-dimensional (2D) culture with (primed) or without (unprimed) growth factors. Once in 3D culture, the culture medium was supplemented with transforming growth factor (TGF)-β₃ for the first 21 days (release) or throughout the study (continuous).

FIG. 2.

(A) Representative image of aggregated SDSCs emanating from the construct on the right half of the image (20× magnification). (B) Viability of the floating cell mass in the culture media as indicated by pervasive green fluorescence of the cells (40× magnification). Color images available online at www.liebertonline.com/tea

FIG. 3.

Representative gross morphology of constructs seeded with growth factor primed synovium cells at day 49 (Study B). The continuous group (left panel) had final average dimensions of φ=4.67±0.23 mm, thickness=2.91±0.11 mm, and the release group (right panel) had final dimensions of φ=4.81±0.19 mm, thickness=2.98±0.11 mm (n=5). Color images available online at www.liebertonline.com/tea

FIG. 4.

(A) Schematic of the experimental groups, (B) equilibrium Young's modulus, and (C) glycosaminoglycan (GAG) (%ww) for constructs cultured over 8-week study period. Solid line indicates release at day 21 time point (*p<0.05). Color images available online at www.liebertonline.com/tea

FIG. 5.

Representative GAG and collagen staining at days 0 and 49 (A) alcian blue staining (GAG) and (B) picrosirius red staining (collagen) for constructs seeded with growth factor primed SDSCs. Color images available online at www.liebertonline.com/tea

FIG. 6.

Representative immunohistochemical staining for (A) type II collagen (green), (B) type VI collagen (green), and (C) negative control image (red for cell nuclei) at day 49 (40× magnification). Color images available online at www.liebertonline.com/tea

FIG. 7.

Comparison of the Young's modulus (E_Y) normalized to day 0 values for the initial study (triangles) and the repeat study (circles). TGF-β₃ was added to the culture media either for a transient period of time (release: filled symbols) or continuously throughout the 3D culture (continuous: open symbols). All groups were primed in 2D culture with a growth factor cocktail.