  Microfluidics is an established multidisciplinary research domain with
widespread applications in the fields of medicine, biotechnology and
engineering. Conventional production methods of microfluidic chips have been
limited to planar structures, preventing the exploitation of truly
three-dimensional architectures for applications such as multi-phase droplet
preparation or wet-phase fibre spinning. Here the challenge of nanofabrication
inside a microfluidic chip is tackled for the showcase of a spider-inspired
spinneret. Multiphoton lithography, an additive manufacturing method, was used
to produce free-form microfluidic masters, subsequently replicated by soft
lithography. Into the resulting microfluidic device, a threedimensional
spider-inspired spinneret was directly fabricated in-chip via multiphoton
lithography. Applying this unprecedented fabrication strategy, the to date
smallest printed spinneret nozzle is produced. This spinneret resides tightly
sealed, connecting it to the macroscopic world. Its functionality is
demonstrated by wet-spinning of single-digit micron fibres through a
polyacrylonitrile coagulation process induced by a water sheath layer. The
methodology developed here demonstrates fabrication strategies to interface
complex architectures into classical microfluidic platforms. Using multiphoton
lithography for in-chip fabrication adopts a high spatial resolution technology
for improving geometry and thus flow control inside microfluidic chips. The
showcased fabrication methodology is generic and will be applicable to multiple
challenges in fluid control and beyond.
