Nov.20, 2011

3D printing is in the news all the time. The FabLabs where you can make products from 3D printer are established everywhere. You can print a car part, a toy or a lamp with this new digital fabrication. Or you prefer to work at home? That is also possible. You can order the DIY 3D printer kits for less than $1500.

Even though the technique may still have limitations, but comparing to only text and images on paper this 3D objects is still impressing.

There are roughly two types of techniques for 3D printing, each with numerous variations. The first is based on stitching materials together from a large reservoir, for instance a container with powder on what a printer head squirt a substance to bind stuff. The powder make desired area hard. Then a new layer of powder is sprayed. Instead of powder you can use liquid polymer that (UV) light is used to make layer by layer hard, or metal powder which sintered with a laser. The resolution of these printers is around 50 microns (one twentieth of a millimeter).

The second type of printer is based on the layer by layer spraying material, usually molten polymer. Almost all self-built 3D printers are made according to this principle. The disadvantage is that you always need a support material, you can not print overhangs or individual links of a chain. You can print in details, but the layer thickness depends on the opening of the nozzle for the polymer, typically about half a millimeter in diameter to less than one tenth millimeter.

The popular materials for DIY 3D printer kits are Polylactic Acid (PLA) and ABS (acrylonitrile-butadiene-styrene), the material made of Lego bricks. The disadvantage of ABS is that it tends to warp during printing. This can be solved by cooling down the nozzle during printing.

The plastic is melted in the head of printer and are pushed through the nozzle by a stepper motor. The printer then spray the polymer layer by layer in the right form, powered by a standard PC USB port. Since this year the designers can choose different colors poly lactate. Previously, only black and white can use. Many other types of plastic are not yet available for this type of printers.

Nevertheless, 3D printing has already been used in medical industry. You can custom prosthesis by firstly print composite models, then use desired prosthetic material. Several researchers claim that they can print organs. The American Anthony Atala gives presentations of printing a kidney. The kidney consists of a plastic and is therefore far from being viable. The American company Novo Orga prints blood vessels with living cells, but has not yet implanted into patients.

UMC Utrecht in Netherland is trying using a 3D printer to print living material. Jos Malda, assistant professor of Orthopaedics group wants to repair knees instead of artificial knee. He explains: "As the cartilage of a joint wears out there are often active cells in the joint. Often the tissue develops osteoarthritis, but it is a temporary solution. "

Malda will implant something similar to existing cartilage which is made of several layers organized collagen to give strength. Cells in these layers have different functions. They make new collagen for strength and proteoglycans and sugar-containing proteins that act as a sponge to guarantee the flexibility and strength of cartilage. 

The implant consists of hydrogel which is mixed with different living cells. For making this hydrogel with cells in the right shape, a 3D printer is applied. The device looks much like the printers that use molten polymer. The print heads spray hydrogel layers mixed with the appropriate cells in the right place, in the shape of the defect knee of the patient.

Researchers are still searching for the right hydrogel. This should obviously not be poisonous, the cells may not interfere with growth of tissue. Yet it must be sturdy enough to print. The first tests were done by cross-linking of alginate with calcium ions gels. But alginate required in low concentrations are not strong enough.

Together with Wim Hennink, professor of pharmacy in Utrecht, a polymer is designed to meet all those requirements. A block copolymer consisting of a functionalized poly-lactate and polyethylene glycol can with a little heat make it sturdy enough to print while still stay in shape. After printing, the light can make the material hard. Cells (chondrocytes) that the researchers mixed survived. It is now important to find out whether the cells also produce enough tissue to make new cartilage. Within four years the researchers will know if implant is growing well and safe. It can be then tested in patients.


Posted in 3D Print Technology

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