3D printed droplet generation devices for serial femtosecond crystallography enabled by surface coating

Austin Echelmeier, Daihyun Kim, Jorvani Cruz Villarreal, Jesse Coe, Sebastian Quintana, Gerrit Brehm, Egatz-Gomez Ana Egatz-Gomez, Reza Nazari, Raymond G. Sierra, Jason E. Koglin, Alexander Batyuk, Mark S. Hunter, Se BastienBoutet, Nadia Zatsepin, Richard A. Kirian, Thomas D. Grant, Petra Fromme, Alexandra Ros

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


The role of surface wetting properties and their impact on the performance of 3D printed microfluidic droplet generation devices for serial femtosecond crystallography (SFX) are reported. SFX is a novel crystallography method enabling structure determination of proteins at room temperature with atomic resolution using X-ray free-electron lasers (XFELs). In SFX, protein crystals in their mother liquor are delivered and intersected with a pulsed X-ray beam using a liquid jet injector. Owing to the pulsed nature of the X-ray beam, liquid jets tend to waste the vast majority of injected crystals, which this work aims to overcome with the delivery of aqueous protein crystal suspension droplets segmented by an oil phase. For this purpose, 3D printed droplet generators that can be easily customized for a variety of XFEL measurements have been developed. The surface properties, in particular the wetting properties of the resist materials compatible with the employed two-photon printing technology, have so far not been characterized extensively, but are crucial for stable droplet generation. This work investigates experimentally the effectiveness and the long-term stability of three different surface treatments on photoresist films and glass as models for our 3D printed droplet generator and the fused silica capillaries employed in the other fluidic components of an SFX experiment. Finally, the droplet generation performance of an assembly consisting of the 3D printed device and fused silica capillaries is examined. Stable and reproducible droplet generation was achieved with a fluorinated surface coating which also allowed for robust downstream droplet delivery. Experimental XFEL diffraction data of crystals formed from the large membrane protein complex photosystem I demonstrate the full compatibility of the new injection method with very fragile membrane protein crystals and show that successful droplet generation of crystal-laden aqueous droplets intersected by an oil phase correlates with increased crystal hit rates.

Original languageEnglish (US)
Pages (from-to)997-1008
Number of pages12
JournalJournal of Applied Crystallography
StatePublished - 2019


  • Droplet generation
  • Injection
  • Microfluidic devices
  • Serial crystallography

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology


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