3D models of functional microstructures in Corethron criophilum created from reference images

3D models of functional microstructures in Corethron criophilum created from reference images

Created for the bachelor thesis "Lessons from 3D printing of the polar diatom Corethron criophilum" by Kevin Opelt

Context and methodology

Corethron criophilum is a species of Diatom of cosmopolitan distribution, but especially common in waters around Antarctica. 
Unique to the Corethron genus, its glass-like shell contains a complicated arrangement of hooks and spines on microscopic hinges.

Replicas of several microstructures were sculpted for 3D printing for the purposes of illustration and experimentation.
Models were created using a multitude of reference pictures from existing literature, modelled in the software Blender 3D, to be printed on an FDM (Fused Deposition Modelling) 3D printer.

Created as part of the Bachelor's Thesis of Kevin Opelt (Reg. Num. 01626491);
BAC thesis advisor: Associate Prof. Dipl.-Ing.in Dr.in techn. Ilse-Christine Gebeshuber

Technical details

The data consists of two stereolithography (.stl) files intended for 3D printing, "joint.stl" and "hook.stl", as well as "readme.txt".
Two images of the assembled prints are also provided, "joint_print.png" and "hook_print.png".

joint.stl

joint.stl recreates the joint connecting spines to the valve, specifically the one found in the "barbed spine" or "1-spine" valve. 
The joint consists of several separate meshes:

• Valve rim, a 1/14th segment of the circular valve rim including one socket. 
• Spine base, part of a barbed spine focused on the joint, its length cutting off at an abitrary point. It fits into the socket in a way that it cannot be removed once assembled.
• Spine barbs, a series of several small spikes attached to the spine. While sculpted as a separate mesh for simplicity, they overlap and should be printed as part of the spine base.
• Unknown structure, a mysterious structure slotting into the top of the joint that no literature known to the author references. The model consists of the T-shaped outside only, cutting off as it enters the joint due to lack of data.

Scale:
Note that the scale of digital models can vary depending on software used to interpret them.
The model was designed for the valve segment to be 5cm wide, resulting in an approx. 10,500:1 (10,475:1) scale if printed at this size. 
At this scale the joint has more than 0.3 mm of clearance, and as such could likely be scaled down while preserving functionality.

Suggested print orientation:
Rim and spine can be printed with minimal supports by splitting them along their symmetry plane and assembling them post-print; Spine placed on the cut, rim placed on the outer edges of the circle segment opposite to the cut, with supports under the socket hemisphere. 
Print-in-place is not recommended due to complexity (curved surfaces on the contact points). 
Unknown structure is designed to be printed upright with the cutoff as the base, with supports supporting the arms.

hook.stl

hook.stl recreates the hook at the end of the shorter spines in the "hooked spine" or "2-spine" valve. It is designed to be mounted on a wire in replacement of the spine, and thus has a socket added along its length that does not correspond to real structures. 
Both chiralities occur in real samples, usually grouped; The file only represents one chirality, as it can easily be mirrored before slicing.

Scale:
Note that the scale of digital models can vary depending on software used to interpret them.
The model was designed for 1 mm wall thickness / 4cm length, resulting in an approx. 2,500:1 (2550:1) scale if printed at that scale. This scale should fit a 0.8 mm wire, depending on printer accuracy. 
Printing at smaller scales is not recommended when using an FDM printer; larger scales may need some supports.

Suggested print orientation:
The long edge has a flattened section designed to be attached to the print bed. Slicing a 0.1 mm layer off can guarantee a perfect attachment plane if needed. A raft should be added to prevent tipping, but no further supports should be necessary. Ideally, some prints should be mirrored in the slicer.

readme.txt 

Replicates this scale, print and source information for quick reference.

Reference Image Sources

• "The Diatoms" by R. M. Crawford, F. E. Round and D. G. Mann
  (Cambridge University Press, 2007, ISBN 978-0-521-71469-3)

• "Investigating the click-stop mechanism in the diatom Corethron criophilum, optical and electron microscopy as well as micro-manipulation" by Matthias Schreitl and Matthias Willensdorfer, supervised by I. C. Gebeshuber
  (Project Works at TU Wien, 2008)

• "Micromechanics in biogenic hydrated silica: Hinges and interlocking devices in diatoms" by I. C. Gebeshuber and R. M. Crawford 
  (Proceedings of the IMechE, Part J: Journal of Engineering Tribology, Volume 220, Issue 8, 2006); DOI: 10.1243/13506501JET163

• "The spines of the centric diatom Corethron criophilum: Light microscopy of vegetative cell division" Richard M. Crawford and Friedel Hinz
  (European Journal of Phycology, Volume 30, Issue 2, 1994); DOI: 10.1080/09670269500650861

• "Mikroskopie als Hobby: Corethron pennatum (Grunow)" uploaded by Dipl. Ing. Peter Höbel (Uploaded July 2010); http://www.mikroskopie-ph.de/index-Corethron-3.html, accessed 25.02.2025