  Additive fabrication of biocompatible 3D structures out of liquid hydrogel
solutions has become pivotal technology for tissue engineering, soft robotics,
biosensing, drug delivery, etc. Electron and X-ray lithography are well suited
to pattern nanoscopic features out of dry polymers, however, the direct
additive manufacturing in hydrogel solutions with these powerful tools is hard
to implement due to vacuum incompatibility of hydrated samples. In this work,
we resolve this principal impediment and demonstrate a technique for in-liquid
hydrogel 3D-sculpturing separating high vacuum instrumentation and volatile
sample with ultrathin molecularly impermeable membranes transparent to
low-energy electrons and soft X-rays. Using either scanning focused electron or
synchrotron soft X-ray beams, the principle of the technique, particularities
of the in-liquid crosslinking mechanism and factors affecting the ultimate gel
feature size are described and validated through the comparison of experiments
and simulations. The potential of this technique is demonstrated on a few
practical examples such as encapsulation of nanoparticles and live-cell as well
as fabrication of mesoscopic 3D-hydrogel structures via modulation of the beam
energy
