Strain sensors are provided that include a flexible substrate, a sheet affixed to the flexible substrate, and two or more microelectrodes printed at spaced locations onto either the sheet or the flexible substrate, wherein the sheet includes a carbon nanotube network, the sheet having a top side and an opposing second side. The two or more microelectrodes are printed at spaced locations onto the top side of the sheet or onto a side of the flexible substrate facing the second side of the sheet. Methods are provided for fabricating a strain sensor wherein the sheet is arranged between the printed microelectrodes and the flexible substrate or wherein the second side of the sheet is arranged atop or across the printed microelectrodes. Methods are also provided for measuring strain in a structure via the strain sensors affixed or integrated therein.