Microfabrication of {pH}-responsive 3D hydrogel structures via two-photon polymerization of high-molecular-weight poly(ethylene glycol) diacrylates

3D pH-responsive microstructures by two-photon lithography (2 PL) in poly(ethylene glycol) diacrylates (PEG-DAs) hydrogels are particularly suitable for biosensing as structural and functional components. So far, 2 PL patterning of hydrogels have been successfully achieved only for low molecular-weight (<= 700 Da MMw) PEG-DAs, which is unfortunately not mechanically compliant with single cell and tissues stiffness. We report an optimised protocol to setup a 2 PL fabrication of high MMw (10 kDa) PEG-DA-based formulations, suitable for pH sensing in soft biological tissues. Two different shapes (pyramids and domes) were obtained and tested for mechanical characterization and pH responsiveness at the microscale. Fast pH-induced swelling (< 15 min) in microstructures allows for envisioning high MMw PEG-DA-based micro and nanostructures via 2 PL as a tunable pH responsive tool for biosensing applications in cell and tissue.