From the archive, originally posted by: [ spectre ]

“We know that people are going to use the printer to try to make
weapons [and] sex toys and drug paraphernalia,” he says. “This is
obviously not what we’re hoping they are going to build. We are hoping
they are going to build more and better RepRaps.”

Open source 3D printer copies itself
Self-replicating printer frees-up 3D printing under GNU
BY Ulrika Hedquist  /  8 April, 2008

Based in the Waitakeres, in West Auckland, software developer and
artist Vik Olliver is part of a team developing an open-source, self-
copying 3D printer. The RepRap (Replicating Rapid-prototyper) printer
can replicate and update itself. It can print its own parts, including
updates, says Olliver, who is one of the core members of the RepRap
team. The 3D printer works by building components up in layers of
plastic, mainly polylactic acid (PLA), which is a bio-degradable
polymer made from lactic acid. The technology already exists, but
commercial machines are very expensive. They also can’t copy
themselves, and they can’t be manipulated by users, says Olliver.

RepRap has a different idea. The team, which is spread over New
Zealand, the UK and the US, develops and gives away the designs for
its much cheaper machine, which also has self-copying capabilities. It
wants to make the machine available to anybody — including small
communities in the developing world, as well as people in the
developed world, says Olliver. Accordingly, the RepRap machine is
distributed, at no cost, under the GNU (General Public Licence).

RepRap’s open-source project aims to keep on improving the machine.
“So it can do what people want it to do”, says Olliver. Improvements
will go back to users and, in this way, the machine as a whole
evolves, he says. The idea of evolution is important, he adds. The
device Olliver is creating now will probably bear very little
resemblance to the device that will appear on everybody’s desks in the
future, he says. “We want to make sure that everything is open, not
just the design and the software you control it with, but the entire
tool-chain, from the ground up,” he says. Olliver works for Catalyst
IT, a Wellington-based open-source business system provider. He is
fortunate enough to get “Google-time” from the company, which means he
is allowed to work on his own research projects one day a week — just
like employees at Google. This has led to considerable developments in
the RepRap project in the last six months, his says.

New features include, for example, heads that can be changed for
different kinds of plastic. A head that deposits low melting-point
metal is in development, he says. The metal melts at a lower
temperature than that at which plastic melts, which means the metal
can be put inside plastic, says Olliver. “That means, in theory, we
could build structures like motors.” RepRap also allows people to
build circuits in 3D, as well as various shapes, with the result that
objects, such as a cell phone, don’t have to be flat, he says. There
are at least seven copies of the RepRap machine in the world that
Olliver knows about. The 3D printer also allows for a new and
fascinating way of communicating: Olliver can design something at home
in New Zealand, which then appears on another researcher’s desk, in
Bath, in the UK, or the other way around.

At the moment, the RepRap uses two different kinds of plastic — PLA, a
relatively rigid plastic, which is ideal for making objects such as
corner brackets; and a more flexible plastic for making, for example,
iPod cases, he says. But having the machine copy itself is the most
useful thing the team can make it do, and that is the primary goal of
the project, says Olliver. However, it can also be used to make other
things, such as wine glasses — definitely water-tight, he adds — and
plastic parts for machines. When Computerworld talked to him, Olliver
had just printed out a small part to fix his blender. “We know that
people are going to use the printer to try to make weapons [and] sex
toys and drug paraphernalia,” he says. “This is obviously not what
we’re hoping they are going to build. We are hoping they are going to
build more and better RepRaps.”

Hydrogels make programmed chemical origami  /  22 February 2007

Israeli scientists have created elastic sheets which buckle into pre-
programmed 3D shapes on command. Just as crisps crinkle up when fried,
the millimetre-thick gels constructed by Yael Klein and co-workers
from the Hebrew University of Jerusalem automatically crumple into
flower-like structures when heated. They flatten out again when cooled
in water. A sheet can be programmed to fold into any particular shape,
thanks to the researchers’ understanding of the gels’ chemistry;
though the options available – domes, tubes and sombrero-like
structures – won’t cause origami experts sleepless nights.

Different structures of sheets with radially symmetric target metrics.
(A) A thick sheet (t = 0.75 mm) with relatively flat hyperbolic metric
adopts a configuration with only three waves. Thinner (t = 0.3 mm)
sheets with larger gradients in monomer concentration form two
generations of waves (B). Symmetric surfaces of positive curvature,
such as in (C), can be combined with negative curvature margins to
obtain a wavy sombrero-like structure. The controllable folding occurs
because the sheets are made from a cross-linked elastic hydrogel,
consisting mainly of the polymer N-isopropylacrylamide (NIPA), which
shrinks by driving out water above 33°C. Dilute NIPA gels shrink a lot
because they contain more water. Gels with high NIPA concentrations
shrink only a moderate amount. Klein’s team took advantage of this by
changing the spatial concentration of NIPA across the material,
creating a thin sheet that constricts a lot in some places and a
little in others when heated. Because of these varying constrictive
stresses, the gel deforms or buckles.

That buckling, the researchers have found, is mathematically
predictable, so long as the sheet is sufficiently thin that it will
prefer to curl into a third dimension than stretch out in the same
dimension. Given a three-dimensional structure, the team can prescribe
the hydrogel concentration gradient required for a cross-linked gel to
crumple into that shape when heated. Valves and nozzles are programmed
to mix the hydrogel in the required concentrations. Adding a catalyst
polymerises the lot into an elastic sheet, ready for folding  (see
movie, below).

Randall Kamien, of the University of Pennsylvania, US, noted that
possible applications could include ‘smart’ materials which fold to
particular shapes in response to changing temperature. In turn, these
the shapes could release certain chemicals. The researchers suggest
that other materials which shrink in response to a signal – not just
heat, for example, but also light, pH, or glucose level – could be
used to make self-folding 3D shapes.

Similar smart responses are seen in nature: the Venus fly trap closes
on its prey by pumping ions from one cell to another, which forces a
leaf’s curvature to change in much the same way as the gels are forced
to buckle. And, said co-author Eran Sharon, the same principles could
play a role in the development of wrinkled natural structures, like
flower petals. The physics of stress and curvature, not genetics,
might be responsible for these 3D shapes.


Eran Sharon
email : erans [at] vms [dot] huji [dot] ac [dot] il
“Eran Sharon is a member of the nonlinear dynamics group at the Racah
Institute of Physics at The Hebrew University of Jerusalem, where he
received his Ph.D. in physics. His research interests include the
spontaneous formation of structured fluid flows as well as the origins
of mechanical instabilities and their role in the growth of plants.”


“The edge of a torn plastic sheet forms a complex three-dimensional
fractal shape. We have found that the shape results from a simple
elongation of the sheet in the direction along its edge. Natural
growth processes in some leaves, flowers and vesicles could lead to a
similar elongation and hence to the generation of characteristic wavy

Nature 419, 579 (10 October 2002) | doi:10.1038/419579a
Mechanics: Buckling cascades in free sheets
Eran Sharon1, Benoît Roman1, Michael Marder1, Gyu-Seung Shin1,2 and
Harry L. Swinney1


“Chemical origami” shrinks 2D discs into 3D objects  /  Feb 23, 2007

Physicists in Israel have invented a neat method of making elaborate
3D structures from flat 2D discs. The trick is to pre-treat a gel disc
half the size of a beer coaster with a monomer solution “blueprint”
that selectively shrinks when heated. The technique, which cleverly
demonstrates the link between 2D and 3D geometry, could be used by
engineers to create self-assembling prototypes (Science 315 1116).

It’s quite easy to see how simple 3D objects could be created using
the principle. For example, if the solution were only applied to the
edges, only they would shrink when heated, and the disc would form a
bowl-shaped object. But more complex “chemical origami” would need an
intricate application pattern, and it is difficult to predict 2D
patterns that will accurately translate into the 3D objects desired.

The problem is that surfaces in 3D do not follow the same “Euclidean”
geometry as those in 2D. In non-Euclidean geometry, the angles of a
triangle do not add to 180°, and parallel lines are not straight but
curved. This is why, for example, it is impossible to draw a map of
the Earth on a flat sheet of paper without compressing the polar
regions – in other words, the grid formed by the lines of latitude and
longitude has squares that become distorted in size. What engineers
would be keen to do, however, is the opposite: design a structure as a
grid on a flat 2D object and then “activate” the third dimension by
giving each grid square the right amount of a certain stimulus.

Eran Sharon and colleagues from the Hebrew University of Jerusalem
have now done just that by calculating a “metric” – a tensor that
characterizes how local distances ought to vary over a surface when
activated. Using this metric as a blueprint, the physicists applied
the monomer solution N-isopropylacrylamide (i.e. the stimulus) in
varying spatial concentration over the surface of the disc. When the
disc was then heated over 33 °C, the regions of higher concentration
shrunk more (in other words, local distance was reduced) and hence
created deeper bends under the resultant stress.

Sharon’s team created a range of structures varying in complexity,
from slightly wavy crisp-like objects to those that look like a
sombrero. Randall Kamien, a physicist from the University of
Pennsylvania, told Physics Web that the technique could be used in the
engineering of prototypes. “You could imagine a printer that prints a
metric into a flat sheet, which you heat, and it forms the desired 3D
object,” he said.