a | Temperature-responsive polymers with a defined sol-gel transition can be used to create patterned cell sheet layers, which can be temporally activated. 0, a, b and c represent different time points and t represents time, b | Light-responsive materials can be applied to produce spatially and temporally controlled peptide patterns based on the location of switchable crosslinkers and irradiation. Controlling the intensity, exposure time and location of irradiation enables the engineering of a material with defined zones, c | Magnetic beads can be conjugated to cell-specific antibodies to trigger cell migration and isolation upon application of a magnetic field. Magnetic beads can also be functionalized with a major histocompatibility complex (MHC) or anti-CD3 antibody to bind to the T cell receptor (TCR) or CD3 receptor on a single T cell. The distance of these beads can be quantitatively measured by Forster resonance energy transfer (FRET). Upon application of a magnetic field, the fluorescence intensity can be related to the strength of the TCR-MHC bond to identify autoreactive T cells.