VIRUS (part 1)
by Erik Es - Amsterdam, August 7, 2018
Whilst recovering from a bout of flu I decided to
make a nice 3D model of a virus. 

Viruses come in many different shapes. One
type looks like a sort of lunar lander. These are
called "bacteriophages" (Greek: bacteria-
eaters). Like all viruses they are very very
small. You need a very strong electron
microscope to see them, and even those can
just about make them visible. They look like
Check the scale in the left image: 100 nm is
one tenth of a thousandth of a millimeter...
Keep in mind that these creatures are not
organisms - they have no heart, no nerves, no
brain, no eyes, no ears, no bones, nothing.
Still, their behaviour is quite complex, which I
find completely baffling.

As you can see in the drawing, bacteriophages
have a 6-sided lantern-shaped body. A thin
hollow tube at the bottom ends in a "mouth"
with small "teeth". Around this mouth there are
6 very simple "legs" (but remember: no bones,
no muscles, no nerves...).

Inside the hollow body it carries small strands
of DNA. As viruses have no means of sexual
reproduction, they have developed a completely
different and amazing system of procreation.

When the virus detects (?!) a living cell of the
right type, it lands itself on the cell's outer wall
and attaches itself to it. It looks very much like
a lunar lander after touching down on the moon.
After landing it bends its "knees" until the
"mouth" part touches the cell. The little teeth
now drill a small round hole in the wall of the
cell, like a cookie-cutter shark. 

The virus then injects the strands of DNA into
the cell. With its purpose fulfilled, the virus now
disintegrates. It doesn't actually "die", because
it was never really "alive" in the first place...

Inside the cell, the virus' DNA now inserts itself
into the DNA of the cell. By doing this it
completely changes the behaviour of the cell.
Instead of performing its normal duties, the cell
now turns into a virus factory - it starts to
produce new viruses, and lots of them...
These viruses then take off, looking for other
cells to invade. A very effective system.

There are over 1000000000000000000000
times more viruses than there are humans on
our planet. When you have a flu, there are
trillions of them in you alone...
We are not aware of this because they are far
too small to be seen - or rather, WE are far too
large to see one.

So I decided to make a printable 3D model of a
bacteriophage, so large that we CAN see one,
but still small enough to fit on your hand.
However, the shape of the virus posed several
major challenges...

I wanted the legs to be really thin, as close as
possible to the original. But with such thin legs
it would be very hard to print the model in one
piece. The legs would be too thin to print nicely
(unless I would make the model VERY large...).
Also, the "grain" of the print (caused by the
print layers) would cause the legs to be very
weak. Too weak. 

So I decided to print the legs separately, laying
down flat. That way they can be printed much
nicer, and because the layers do not "cross" the
legs they are MUCH stronger - strong enough to
hold the body, even though they are very thin.

With the teeth of the virus now left as the
bottom part of the body, the model would be
resting on these pointed teeth during printing -
not a good idea. It also seemed like I would
have to make six holes around the mouth to
hold the legs, which would also cause problems
with structural integrity.

The solution I came up with was to make 3
pairs of legs instead of 6 single ones. Now all I
needed was some slots at the bottom of the
base to connect the legs.

Perhaps you have seen (or even made) model
animals like this :
These come as kits, with all the parts cut
out of a wooden plate. The parts have small
slots that allow them to be connected by just
sliding them onto each other.

As you can see, these parts are all connected
under 90 degree angles. I thought it would
probably be possible to use this system, but
instead of 2 parts at 90 degrees, I needed to
slot 3 parts together at 60 degree angles.

Here you can see how I managed to do this:
As you can see I also added the teeth to the
legs. This way the teeth can also be printed
nice and sharp, and it leaves a much better
base for the rest of the model, with enough
material touching the print bed to hold the rest
of the model firmly in place during printing (see
the red parts in the right image):
With the body printed hollow, the model is
suitable for "insertion printing", so I can drop
the strands of DNA inside the body just before it
starts to close up.

Now all I needed to do was figure out how to
make the DNA... quite a challenge. 

Read my next blog to see how I did this, and to
see the end result: