  The great flexibility of direct laser writing arises from the possibility to
fabricate precise three-dimensional structures on very small scales as well as
the broad range of applicable materials. However, there is still a vast number
of promising materials which are currently inaccessible requiring the
continuous development of novel photoresists. Here, a new bio-sourced resist is
reported which relies on the monomeric unit of chitin, N-acetyl-D-glucosamine,
expanding the existing plant-based biopolymer resists by a bio-based monomer
from the animal kingdom. In addition it is shown that combined use of two
photoinitiators is advantageous over the use of a single one. In our approach,
the first photoinitator is a good two-photon absorber at the applied
wavelength, while the second photoinitiator exhibits poor two-photon absorbtion
abilities, but is better suited for crosslinking of the monomer. The first
photoinitiator absorbs the light acting as a sensitizer and transfers the
energy to the second initiator, which subsequently forms a radical and
initializes the polymerization. This sensitization effect enables a new route
to utilize reactive photointiators with a small two-photon absorption
cross-section for direct laser writing without changing their chemical
structure.
