Rice Researchers Build Open-Source Laser Sintering Printer to Create Biomaterials

Bioengineers at Rice University have developed OpenSLS, an open-source, selective laser sintering platform, by altering a commercial-grade CO₂ laser cutter.

The OpenSLS is capable of printing complex 3D objects, ranging from biomaterials to powdered plastics. It is nearly 40 times cheaper than those currently available in the market, and offers researchers a chance to work with their own customized powdered materials.

Rice’s OpenSLS platform has the same design specifications and performance as other commercially available selective laser sintering (SLS) platforms. The system is described in an open-access paper published in PLOS ONE.

Low-cost, open-source microcontrollers were used to construct the OpenSLS. The platform costs less than $10,000 to construct, whereas the starting price for commercial SLS platforms is generally about $400,000, and can go 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. 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.

Jordan Miller, Assistant Professor of Bioengineering, Rice University

He added that commercial SLS machines don't normally give users the opportunity to fabricate objects using their own powdered materials, which is actually vital for researchers who aim to work 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.

Ian Kinstlinger, Graduate Student, Rice University

The Rice team demonstrated that the machine was capable of printing a series of complex objects using nylon powder, a frequently used material for high-resolution 3D sintering, as well as polycaprolactone (PCL), a non-toxic polymer which is frequently used to build templates for research 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 standardize on equipment and best practices. We’ve open-sourced all the hardware designs and software modifications and shared them via Github.

Ian Kinstlinger, Graduate Student, Rice University

OpenSLS functions differently to most conventional extrusion-based 3D printers, which construct objects by pressing melted plastic via a needle as they trace out 2D patterns, 3D objects are then constructed using the successive 2D layers.

The SLS laser operates by shining down onto a flat bed of plastic powder. When the laser touches powder, the powder begins to sinter or melt at the focal point of the laser to form a solid material with small volume. The printer is able to fabricate a single layer of the final component by tracing the laser in two dimensions.

The process is a bit like finishing a creme brulee, when a chef sprinkles out a layer of powdered sugar and then heats the surface with a torch to melt powder grains together and form a solid layer. Here, we have powdered biomaterials, and our heat source is a focused laser beam.

Jordan Miller, Assistant Professor of Bioengineering, Rice University

In the SLS process a new layer of powder has to be laid down once each layer is finished, and then the laser reactivates to trace the subsequent 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.

Jordan Miller, Assistant Professor of Bioengineering, Rice University

In early 2013 Miller, an active participant in the open-source maker movement, was the first to identify commercial CO2 laser cutters as key contenders for an economical, versatile selective sintering machine.

Generally laser cutters are used to make jewelry, acrylic figurines, toys, trophies, and other commercial products.

The cutter’s laser is already in the correct wavelength range — around 10 micrometers — and the machines come with hardware to control laser power and the x-axis and y-axis with high precision.

Jordan Miller, Assistant Professor of Bioengineering, Rice University

In 2013 Miller hosted a four-week crash course in hardware prototyping called the Advanced Manufacturing Research Institute (AMRI). An AMRI participant Andreas Bastian, who is an artist and engineer, took up the challenge to develop an open-source SLS printer. He created an integrated, high-accuracy z-axis and powder-handling system, and incorporated it with open-source, 3D printer electronics from Ultimachine.com. Miller explained that Bastian used the laser-cutting features of the machine to manufacture several of the acrylic components for the powder-handling system.

You can actually cut most of the required parts with the same laser cutter you are in the process of upgrading. It’s around $2,000 in parts to build OpenSLS, and adding the parts to an existing laser cutter and calibrating the machine typically takes a couple of days.

Jordan Miller, Assistant Professor of Bioengineering, Rice University

By the time Bastian graduated from Rice in the fall of 2013, “we had demonstrated proof of concept,” Miller said, “but a great deal of additional work still needed to be done to show that OpenSLS could be useful for bioengineering, and that is what Ian and the rest of the team accomplished.”

Miller acknowledged that Kinstlinger’s experiments with PCL, a biocompatible plastic that can be used in medical implants for humans, were vital.

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

Jordan Miller, Assistant Professor of Bioengineering, Rice University

Kinstlinger illustrated that in some cases increased surface area found on rough surfaces and in interconnected pore structures are preferred, while in other biological applications smooth surfaces are preferred.

Kinstlinger took into consideration all of the possibilities with PCL by creating an efficient method to make the rough surfaces of PCL objects smooth as they came out of the printer. He discovered that by exposing the components to solvent vapor for brief periods, about 5 minutes, provided a highly smooth surface due to the surface-tension effects.

While conducting tests using human bone marrow stromal cells (a type of adult stem cells capable of differentiating to form skin, bone, blood vessels and other tissues), Kinstlinger found that the vapor-smoothed PCL structures functioned well as templates for engineered tissues with a few of the same properties as natural bone.

The stem cells stuck to the surface of the templates, survived, differentiated down a bone lineage and deposited calcium across the entire scaffold.

Ian Kinstlinger, Graduate Student, Rice University

Miller said, “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. And it’s another win for the open-source community.”

Rice University provided the funding for this research. The other authors include Samantha Paulsen, Daniel Hwang, Anderson Ta and David Yalacki, all from Rice; and Tim Schmidt of the Lansing Makers Network in Lansing, Mich.