3.3. Cell growth and desired differentiation in the scaffolds
First, we determined if the scaffolds support the cell growth and intercellular connections. As shown in Fig. 4 (F-actin staining), 1.5 days after seeding, the cells displayed a spherical morphology inside the scaffolds.
Seven days later, most of the cells stretched out and extended along the NF matrix walls.
The cells also produced significantly more connexin 43, a gap junction protein in differentiated
cardiomyocytes [37], at day 7 than day 1.5. As gap junctions are essential for many physiological processes, increased expression of connexin 43 with increasing 3D culture time indicated that these cells on the NF matrix were robust enough to communicate with one another for tissue construction [38,39].
Then, we investigated the differentiation of the CPCs in the scaffolds.
We detected a dramatic transition of the seeded cells in the scaffolds from cardiac progenitors to the three desired cell types (Fig. 5A).
At day 1.5, the cells showed strong expression of CPC marker ISL1 as indicated by intense green fluorescence, which was almost undetectable after 7 days of induction.
After 7 days of culture, the seeded cells were found growing evenly within the scaffolds (Fig. 5B), positively expressing cardiomyocyte marker (cTnT) and smooth muscle cell markers (SM-22a and a-SMA).
However, endothelial cell marker (CD31) expression was relatively weaker.
The differentiation profile in 3D scaffolds was consistent with that in 2D culture plates.
Moreover, RT-PCR assay showed that the differentiation trend in 3D scaffolds was similar to that in 2D culture plates (Fig. 5C).
When the induction proceeded further, the seeded cells lost their progenitor features and differentiated
into specific lineages.
The semi-quantification data as shown in Fig. 5D clearly indicated the robust differentiation under 3D culture.
Taken together, the above data indicated that the porous NF PLLA scaffolds favorably supported the cell extension, growth, and differentiation towards desired lineages in vitro.