New materials for additive manufacturing are used for a diverse range of applications, including 3D paints for making human tissue-like cells; a hardenable stainless steel powder for surgical instruments; and a sustainable composite reinforced with bamboo fibers that resembles wood when printed.
In the medical industry, 3D paints that were developed at Northwestern University’s Shah Tissue Engineering and Additive Manufacturing Lab (Chicago) became commercially available in 2017, and include hyperelastic bone and highly conductive 3D graphene. Both can be seeded with or without stem cells to grow bone-like cells, in the case of hyperelastic bone (available from a Shah lab spinoff, Dimension Inx LLC, Chicago); and nerve and muscle-like cells, with 3D graphene (available from Millipore-Sigma, Milwaukee).
The 3D paints can be used together to make a structure with two or more materials.
“That’s huge because if you look at any tissue or organ in our body, it’s not a monolithic, one-kind-of-material,” said Adam Jakus, chief technology officer for Dimension Inx. “It’s a mixture of so many different things, of gradients, and distinct materials. A good example would be to look at a cartilage replacement in the knee. In most cases for knee replacement surgery, they have to replace part of the bone and the cartilage, and it’s all connected. And it changes across that gradient from pure bone to pure cartilage.”
Not only can the paints be used together, they can be printed consecutively on the same machine, opening the door to making a human-machine interface. Other paints can be used for metals and alloys . “If you want to paint stainless steel, in the same way if you’re painting white on a wall and you want to change to blue you don’t change the way you’re painting the wall just because you change your color,” Jakus said. “So, printing hyperelastic bone, or 3D graphene, or metals or even ceramics, you paint it the same way.”
Products made with Dimension’s paints may be implanted during surgery with instruments made of EOS’ new hardenable stainless steel.
Material experts at EOS GmbH (Munich, Germany), the company that makes direct metal laser sintering printers as well as metal and polymeric powders to use with them, developed EOS StainlessSteel 17-4PH IndustryLine, an H900 heat-hardenable stainless steel powder with good corrosion resistance that was designed for medical applications. It can be used to make surgical instruments that withstand the rigors of the operating room and repeated sterilizations.
Laura Gilmour, global medical business development manager at EOS’ North American technology innovation center in Austin, TX, said EOS develops materials that help people use 3D printers for medical applications “with things that they’re used to, to start. So, the idea is that we would arm you with the same material properties that you’re used to from 17-4PH that meets a certain ASTM standard [A564]. And it’s a hardenable material.”
EOS StainlessSteel GPI is another 17-4PH stainless steel that EOS offers that’s not H900 hardenable.
Applications for 3D-printed surgical instruments might be more in the realm of mass specialization than of mass production, Gilmour said.
“If you’re going to be making a million [parts], it might not be the right application,” Gilmour said. “But, for example, at spinal device makers, they might have surgeons that have a particular surgical technique that they’re comfortable with, or a different way of accessing the spine, or a different patient population, and they would need a specific instrument that doesn’t go with your standard set that you send to hospitals with your implant. So, the benefit in the medical field is to be able to quickly turn over those types of instruments that are helpful to a surgeon’s special surgical technique.”
Parts built from EOS StainlessSteel 17-4PH can be machined, shot-peened and polished in as-built or heat-treated states, according to the EOS StainlessSteel 17-4PH IndustryLine data sheet. “Solution annealing together with aging treatment are necessary in order to achieve proper hardness and mechanical properties,” Gilmour said. “Due to the layer-wise building method, the parts have a certain anisotropy which can be eased by solution annealing.”
The material’s tensile strength is 1310 MPa and increases to 1358.1 MPa after heat treatment, according to company supplied data. Elongation in the as-built state is 21%, but decreases to 12.5% after annealing.
While the medical industry uses new materials for biologics and instruments, other industries are interested in 3D printing too.
Techmer PM (Clinton, TN), a global designer and supplier of polymer modifiers and engineered compounds, entered the 3D printing market in a big way—as in large part additive manufacturing.
“A few years ago, we were still trying to identify our role within the 3D world,” said Tom Drye, vice president of emerging markets for Techmer. “Fortunately, we worked on several projects that have helped us develop our expertise as a materials design company.”
Techmer found its niche in pellet-fed, large-part printing, in which parts are printed at 50–500 lb (23–227 kg) per hour. The company also does some work with filaments and with powder systems. Among its many custom solutions is recent materials design work Techmer did with Branch Technology (Chattanooga, TN) on an engineered material used to print a structure that placed first in NASA’s 3D-Printed Habitat Challenge earlier this year.
Also new is a 100% renewable compound that uses PLA as its base resin and that’s reinforced with bamboo fibers. A counter and chairs made from the sustainable materials were on display at Design Miami in 2016. Drye said its most likely use will be for single-use packaging, displays, and components where a natural look is desired.
“In addition to introducing an element of sustainability, what I really love about it is it looks like wood,” said Don Edens, Techmer’s emerging market manager.
In the short time that it’s made off-the-shelf pellets for additive manufacturing, Techmer has developed compounds that include carbon fiber-reinforced formulations of ABS, PETG and PC; CFRPs with PA6 and PA612 as base resins; and composites able to withstand high temperatures (more than 350°F, or about 177°C) with carbon fibers in PPS, PPSU, PEI, PEK and PEEK base resins.
Because it’s a supplier to large printers, the marine, automotive and aerospace industries are big end-users of Techmer’s materials in parts and tools.
“Aerospace is on it like a duck on a Junebug,” Edens said. “In the near future, everything from jetliners to satellites will be assembled differently because of 3D-printed parts. That’s why the aerospace industry is scrambling to find innovative ways to apply the technology. It’s a game changer for them in terms of speed and design flexibility.”
Using conventional methods, aerospace manufacturers will produce a tool or mold to make a specific part by first buying a big block of steel, then shaping it to the desired geometry. Then they’ll do a carbon fiber layup. With lead time on the block, letting it cure, then the subtractive work, the process can take six months to a year or more.
With additive manufacturing, aerospace manufacturers can design a part, print a tool and make the part in one week, Edens said. “And you’re not locked in that design for 14 months,” Edens said during a panel discussion earlier this year at HOUSTEX 2017. “If you say you need a little more angle in one direction, you just reprint the tool.”
The newer technology not only decreases lead time for aerospace OEMs and Tier manufacturers, it also decreases labor and tool maintenance. There’s less waste compared to traditional manufacturing techniques, which require longer setup times and higher material costs, Edens said.
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