hMSC response to stretch is unclear due to spreading on static soft gels.

<p>Micrographs of hMSCs cultured statically (left column) and following ∼10% cyclic equibiaxial strain (right column) for 6 hours on soft gels (0.3 kPa, top row) and stiff gels (50 kPa, bottom row). Staining for f-actin (green) and nuclei (blue) shows that hMSCs on soft gels (static and stretched) have unorganized actin fibers whereas cells on stiff gels have more organized actin fibers. Unlike VICs, hMSCs spread well on soft gels and stretch appears to increase the spread area of the cells slightly on stiff gels. Scale bar = 100 µm.</p

Average strain (± SD) within central region used for analysis of cell morphology for equibiaxial stretch (round loading post) and uniaxial stretch (Arctangle™ loading post).

<p>Average strain (± SD) within central region used for analysis of cell morphology for equibiaxial stretch (round loading post) and uniaxial stretch (Arctangle™ loading post).</p

Strain field in region of interest is roughly uniform for equibiaxial stretch.

<p>Strain maps for a soft gel (0.3 kPa) undergoing equibiaxial strain in the X (A), Y (B), and XY (shear, C) directions demonstrating relatively homogenous strain and minimal shear within the area of analysis of cell morphology (dashed box). (D) CAD representation of the circular loading platen over which the silicone membrane is stretched by vacuum pressure. Scale bars = 5 mm.</p

Schematic of polyacrylamide gel on flexible silicone membrane under static (A) and stretched (B) conditions.

<p>Top view of a 22 mm diameter collagen-coated gel (∼70 µm thickness) is cast into a 35 mm diameter flexible-bottomed Flexcell™ well (C) and STREX well (C, insert). Image of Flexcell™ well (D) stretched above an Arctangle™ loading post and labeled with retroreflective beads for strain field analysis. Rectangle shows region analyzed in HDM software, arrows point to edge of gel. Scale bars = 10 mm in all panels.</p

Strain field in region of interest is roughly uniform for pure uniaxial stretch.

<p>Strain maps for a soft gel (0.3 kPa) undergoing pure uniaxial strain in the X (A), Y (B), and XY (shear, C) directions demonstrating relatively homogenous strain and minimal shear within the area of analysis of cell morphology (dashed box). (D) CAD representation of the Arctangle™ loading platen over which the silicone membrane is stretched by vacuum pressure. Scale bars = 5 mm.</p

VICs on soft (0.3 kPa) and stiff (50 kPa) gels cultured under static and pure uniaxial stretch conditions (1 Hz, 10% stretch, 6 hrs).

<p>Cells cultured on soft substrates appear to have less realignment with stretch compared to the classic realignment perpendicular to the direction of stretch on the stiff substrates. Scale bar = 100 µm.</p

When cyclically stretched, cells on stiff substrates reduce spread area whereas cells on soft substrates increase spread area: Area (A) and perimeter (B) of VICs cultured on low (0.3 kPa) and high (50 kPa) stiffness gels subjected to 10% cyclic stretch at 1 Hz for 6 hours (grey bars) or static (black bars) culture.

<p>Shape factor (C) quantifies how rounded a cell is (a shape factor of 1 is perfectly circular, whereas a shape factor of 0 is extremely spread with many extensions). Cells of low and high shape factor are shown in C. Brackets above bars show significance between individual groups (two-way ANOVA, p<0.05).</p