VIRUS (part 2)
by Erik Es - Amsterdam, August 7, 2018
I needed some strands of DNA for my model of
a virus.
(see: INSERTION PRINTS #3: VIRUS - part 1)

This posed quite a challenge. DNA is shaped
like a rope ladder (as used to board a ship or
exit a hovering helicopter) which is first twisted
into a "spiral ladder" and then coiled up like an
old-fashioned telephone cable.

To achieve this shape (or something like it) I
made a model that consists of many small flat
discs, each slightly higher than the next,
arranged in a "spiral staircase" shape. After
many tests, trying out different configurations
and print settings like speed and temperature,
I managed to print a springy coil like this:
The trick here is that each turn of the coil is
laid down onto the one below it. Finding the
right speed/temperature settings was tricky:
too hot and the whole thing becomes a solid
piece (as the plastic fuses with the layer it is
resting on), too cold and the spiral will not form
in a nice regular pattern.
But after some persistent experimenting I
managed to get it right.

These coils are very springy. If you bend one
and then let go, it springs back and wobbles
(like the spring you find in a ballpoint pen) until
it comes to rest in its original position.
Cool. VERY cool... but still too closely wound to
look like DNA...

So next I dip them into hot water and then pull
gently on both ends. This causes the springy
coil to stretch without breaking. Again it took
some experimenting to find the right
temperature for the water (and the right amount
of time to dunk the print), but after some
failures I ended up with the shape I was looking
I then cut this spiral into smaller pieces which
can fit into the body of the virus. 

All that remains is to insert these pieces into
the body while it is being printed. As always
with insertion printing, timing is essential.
There is only a small window of time to insert
the DNA pieces - too early and they will stick
out too far at the top, so the print head will hit
them and fuse them into the wall of the print
(start again...), too late and the top of the virus
is closing in too much, so there is not enough
space to drop the pieces in without them
getting hit by the print head.

When I get it right it looks like this:
To finish the model I remove the support
structure that helped to support the roof of the
"mouth" part, and clean up the "fur" at the top
(caused by "cool head lift", meaning the printer
pauses a few seconds between layers and
moves to the side, so the fan can cool the top,
before putting on the next layer).

Here's a picture of the finished parts:
I then insert the 3 pairs of legs. The virus then
looks like this:
Another amazing 3D print for sale
at Printed In Space.

Next time you are suffering from flu, remember
what amazing processes are happening inside
your body...