Schematic diagram showing the preparation of the cell-laden layer-shaped alginate hydrogels. STEP 1: A filter paper soaked in the cross-linking agent (CaCl2 or calcium gluconate) was placed on the bottom of each well of a 6-well culture plate. The alginate-hADSCs suspension was added above and covered with the second filter paper soaked in the same gelling agent. CaCl2 or calcium gluconate was added on the top of the construct and the plate was incubated for 45–60 min at 37°C in a humidified atmosphere of 5% CO2; STEP 2: The excess of the cross-linking agent was removed together with both of the filter papers used. The resulting thin layer hydrogel (5 mm thickness) was washed extensively with saline buffer and GCM.