Interesting question.
Depending what substances want to "print" with, and what substrate you
want to print on, the answer as to what mods are needed range from none
at all, to possibly rather major.
However, which inkjet printer type is critical to all of this.
There are basically two current technologies available. One is called
piezo and the other thermal. Then there are some variations on the thermal.
I will start with thermal because you need to under stand it's
functionality to be able to compare it to the piezo.
Thermal inkjet heads come in several designs. Some are designed for
single use (one cartridge full) and are in fact part of the replaceable
cartridge unit. HP, Lexmark (Dell) and older Canon models use(d) this
technology. The other versions, used in all newer Canon printers, and
some higher end HP models uses a separate print head which can be
replaced when it burns out, which typically takes 18-24 months with
moderate to high use.
The advantages of the single use type is that you get a new head with
each cartridge, so should the head burn out, or get damaged or clogged
beyond repair, the fix is as simple as a new cartridge. The advantages
of the long term is it saves money on the cost of the ink cartridges and
is environmentally better because there is less to toss away, and it
allows for a more sophisticated type of head design.
The single use cartridges can be refilled, and in some cases will last
numerous refills, however, all thermal inkjet printer heads do degrade
with use. The reason for this is due to how they operate.
Thermal printers deliver ink to the head via some channels. close to
the nozzle opening there is a very small resistor which when current is
applied heats up and causes the ink to begin to boil. The pressure
created from this steam bubble being produced pushes the ink in front of
it out of the nozzle. The ink cools again, moves forward via capillary
action and another bubble is created to do the same thing. Originally,
thermal inkjet heads could only produce one size droplet. As the
ability to make heads with more nozzles became feasible and cheap, some
modern thermal heads have two or three different nozzles sizes for each
dot location and they can fire the appropriate ones for the ink dot size
required. The heads degrade due to the limited number of times the
resistors can go through the heating and cooling cycles and from the
continual heating and cooling process which eventually fatigues and eats
away nozzles.
Thermal heads have become much more sophisticated over time in design
and precision, and for the standard inkjet use they are designed for,
they are equal in image quality to their competition, the piezo head design.
However, for non-conventional use, they have some problems related to
how they function.
1) they use heat and heat the liquids, in many cases this may damage or
destroy the liquid (such as live cells). In some cases some inks
special inks harden when heated which would clog the head completely.
2) the thermal system requires a volatile which can be boiled at a
specific temperature and is not flammable.
3) ink viscosity and size of components like solids becomes critical to
allow the material to move properly
Perhaps one advantage if these other issues above will not harm the
process, is that the heads are replaceable easily by the end user so if
you mess up, you don't need to bring the unit in for a head repair, or
simple lose the whole printer is head repair is too costly.
However, by far, the most versatile print head design for "alternative
use" is the piezo head design. All Epson printers, and several other
lessor known brands use this technology. A few HP models did, although
I don't know if any current models do. Piezo uses a mechanical pumping
action. Basically, there is an ink chamber and a channel that leads to
an opening or nozzle out of which comes the ink. The "pump" between the
chamber and the channel is a small circular piece of piezo electric
materials that is sealed and held in place all the way around the edges.
This material changes dimensions when current is applied to it,
causing it expand, and since it is somewhat flexible, and held in place
be the edges, it goes from a flat shape to a concave (or convex,
depending which side you are looking at) condition. This sudden
movement creates pressure on the ink in the column and forces a small
droplet to be pushes out of the nozzle. When the current is cut, the
disk goes flat again, which both pulls the ink in the column back
slightly to end the droplet, and also to pull more ink from the chamber
into the column. The beauty of this design is many fold:
1) It requires and generates almost no heat
2) The liquid doesn't need to contain a carrier which boils at a
specific temperature and is non-flammable
3) the viscosity of the liquid can fluctuate and in fact piezo heads
have detectors in them to alter the speed and voltage to the head to
compensate for viscosity of liquids and temperature changes at the head
(within limits).
4) Unlike thermal heads, the size of the droplet is not based upon the
nozzle size, but on the frequency of the vibration of the piezo
actuation. Faster and shorter pumping makes smaller droplets, so the
same nozzle can produce many drop sizes (some Epson models produce as
many as 7 drop sizes per nozzle).
5) The heads are designed to last the life of the printer and each piezo
unit is designed to run for hundreds of millions to billions of actions.
6) the voltage going to each nozzle in the head can be programmed into
the printer at the factory and with proprietary software.
So, although I have not read this article, my guess is that for most
modified applications, Epson piezo inkjet printers are used.
Some examples of how inkjet printers are used, besides the cell
"printing" are to print conductive traces onto circuit boards, to print
parts numbers on items and parts (like medicines (the print on pills or
capsules), to make transparent edible pictures for cakes (using food dye
inks onto an edible sugar/rice paper), to print logos and number codes
onto the outside of fruit (so you won't have to deal with those horrible
adhesive stickers on each orange) (they also use dot matrix and lasers
for marking fruits) for all sorts of permanent plastic printing (using
UV hardening inks) to distribute very very minute quantities of liquids
for medications onto a surface, and radioactive materials, to build very
detailed nano products, to place glues and adhesives onto very precise
areas, and building small plastic devices and models using UV setting
plastics.
One of the most interesting areas where inkjet printers are being used
is in the "printing" of OLED (Organic LED) displays. The LEDs and
electroluminescent plastics (red, green and blue) are loaded into inkjet
cartridges and printed onto the substrate.
Pretty much anything which requires precision positioning and
measurement of quantity can be handled with some type of inkjet technology.
Art
