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Open-source 3D printer developed for biomaterials fabrication

23 February 2016

Researchers modify a commercial-grade CO2 laser cutter to create OpenSLS, an open-source selective laser sintering platform that can print intricate 3D objects.

Tissue-engineering scaffolds built using Rice University's OpenSLS (photo: Jeff Fitlow/Rice University)

OpenSLS, which was built by Rice University bioengineering researchers using low-cost, open-source microcontrollers, cost less than $10,000 to build; commercial SLS platforms typically start around $400,000 and can cost up to $1 million.

"SLS technology has been around for more than 20 years, and it's one of the only technologies for 3D printing that has the ability to form objects with dramatic overhangs and bifurcations," says Jordan Miller, an assistant professor of bioengineering at Rice who specializes in using 3D printing for tissue engineering and regenerative medicine. "SLS technology is perfect for creating some of the complex shapes we use in our work, like the vascular networks of the liver and other organs."

Commercial SLS machines generally don't allow users to fabricate objects with their own powdered materials, which is something that's particularly important for researchers who want to experiment with biomaterials for regenerative medicine and other biomedical applications.

"Designing our own laser-sintering machine means there's no company-mandated limit to the types of biomaterials we can experiment with for regenerative medicine research," says Ian Kinstlinger, a graduate student in Miller's group who designed several of the hardware and software modifications for OpenSLS. The team showed that the machine could print a series of intricate objects from both nylon powder, commonly used for high-resolution 3D sintering, and from polycaprolactone (PCL) a non-toxic polymer that's commonly used to make templates for studies on engineered bone.

"In terms of price, OpenSLS brings this technology within the reach of most labs, and our goal from the outset has been to do this in a way that makes it easy for other people to reproduce our work and help the field standardise on equipment and best practices," Kinstlinger says. "We've open-sourced all the hardware designs and software modifications and shared them via Github."

OpenSLS works differently than most traditional extrusion-based 3D printers, which create objects by squeezing melted plastic through a needle as they trace out two-dimensional patterns. Three-dimensional objects are then built up from successive 2D layers. In contrast, the SLS laser shines down onto a flat bed of plastic powder. Wherever the laser touches powder, it melts or sinters the powder at the laser's focal point to form a small volume of solid material. By tracing the laser in two dimensions, the printer can fabricate a single layer of the final part.

In SLS, after each layer is finished, a new layer of powder is laid down and the laser reactivates to trace the next layer.

"Because the sintered object is fully supported in 3D by powder, the technique gives us access to incredibly complex architectures that other 3D printing techniques simply cannot produce," says Miller, who first identified commercial CO2 laser cutters as prime candidates for a low-cost, versatile selective sintering machine in early 2013. "The cutter's laser is already in the correct wavelength range - around 10 micrometres - and the machines come with hardware to control laser power and the X-axis and Y-axis with high precision." 

Tests with PCL, a bio-compatible plastic that can be used in medical implants for humans, is of particular interest.

"Biology in the body can take advantage of architectural complexity in 3D parts, but different shapes and surfaces are useful under different circumstances," says Miller.

For example, the increased surface area found on rough surfaces and in interconnected pore structures are preferred in some situations, while other biological applications call for smooth surfaces.

Kinstlinger addressed each possibility with PCL by developing an efficient way to smooth the rough surfaces of PCL objects that came out of the printer. He found that exposing the parts to solvent vapour for short time periods (around five minutes) provided a very smooth surface due to surface-tension effects.

In tests using human bone marrow stromal cells, Kinstlinger found that the vapour-smoothed PCL structures worked well as templates for engineered tissues that have some of the same properties as natural bone. he says the stem cells stuck to the surface of the templates, survived, differentiated down a bone lineage and deposited calcium across the entire scaffold.

"Our work demonstrates that OpenSLS provides the scientific community with an accessible platform for the study of laser sintering and the fabrication of complex geometries in diverse plastics and biomaterials," says Miller. "And it's another win for the open-source community."

Details about how to build the OpenSLS system are available here.

The design specs and performance of Rice's OpenSLS platform are described in an open-access paper published in PLOS ONE.

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