A model of Kyiv’s Saint Sophia Cathedral in the blue and yellow of the Ukrainian flag, made using the iCLIP method for 3D printing, which allows for the use of multiple types — or colors — of resin in a single object. (Image credit: William Pan)

Stanford engineers recently designed a 3D-printing method that’s not only upwards of 5 to 10 times faster than the current quickest high-resolution printer available but is also capable of using multiple types of resin in a single object — potentially allowing researchers to use thicker resins with better mechanical and electrical properties.

“This new technology will help to fully realize the potential of 3D printing,” said Joseph DeSimone, Sanjiv Sam Gambhir Professor in Translational Medicine and Professor of Radiology and Chemical Engineering at Stanford. “It will allow us to print much faster, helping to usher in a new era of digital manufacturing, as well as to enable the fabrication of complex, multi-material objects in a single step.”

The new design improves upon continuous liquid interface production (CLIP) — a 3D-printing method created by DeSimone and his colleagues in 2015. The new method — injection CLIP (iCLIP) — sees researchers use mounted syringe pumps to add additional resin at key points.

“The resin flow in CLIP is a very passive process; you’re just pulling the object up and hoping that suction can bring material to the area where it’s needed,” said Gabriel Lipkowitz, a Stanford PhD student in Mechanical Engineering. “With this new technology, we actively inject resin onto the areas of the printer where it’s needed.”

The resin is delivered through conduits that are printed simultaneously with the design. The conduits can be removed after completion or can be incorporated into the design, akin to how veins and arteries are built into the human body.

With the additional resin injection, iCLIP aims to print with multiple resin types throughout the printing process. The researchers tested the printer with as many as three different syringes, each with a different-colored resin. They successfully printed models of famous structures from different countries in the color of each respective country’s flag.

“The ability to make objects with variegated material or mechanical properties is a holy grail of 3D printing,” Lipkowitz says. “The applications range from very efficient energy-absorbing structures to objects with different optical properties, and advanced sensors.”

Now, the team is working on software to optimize the design of the fluid distribution network for each printed piece. It wants designers to have fine control over the boundaries between resin types and potentially further speed up the printing process.

Here is a Tech Briefs interview (edited for clarity) with Lipkowitz.

Tech Briefs: What inspired the desire to improve upon CLIP?

Lipkowitz: We were excited by how significantly CLIP was able to accelerate additive manufacturing over previous methods such as stereolithography and digital light projection, to achieve widespread commercial adoption, but were frustrated that it could not go even faster. We knew that the free radical photopolymerization reaction that solidifies the object from the liquid resin was essentially instantaneous, but nobody was addressing the “elephant in the room” problem in vat photopolymerization, the mass transport (resin reflow) issues. This inspired our injection approach.

Tech Briefs: What were the biggest technical challenges?

Lipkowitz: After having identified the problem — insufficient flow through the dead zone gap during printing — probably the biggest technical challenge was controlling the fluid dynamics at play during the highly complex printing process to alleviate this issue. While at the macroscopic scale printing may look seamless, as the object grows from a pool of resin, this belies the truly chaotic fluid mechanics occurring at the build region, which we sought to re-engineer. That drove our careful integration of the various mechatronic parts of the printer — UV light engine, linear motion stage, and syringe pump — and the calibration experiments we performed.

Tech Briefs: Can you explain in simple terms how the new iCLIP technology works?

Lipkowitz: In the traditional process, CLIP, resin flow is a passive process; pulling the object up brings material to the area where it’s needed — or fails to if you’re printing with high-performance viscous materials or very quickly. With this new technology, iCLIP, we actively inject resin onto the areas of the printer where it’s needed.

Specifically, resin is delivered through microfluidic channels that are printed simultaneously with the part, in a similar way to how capillaries grow in our body. By administering pressure-driven flow through these channels, we fundamentally change the fluid pressure profiles within the build region to overcome the otherwise substantial suction forces that cause print failures.

Tech Briefs: What types of objects has the team 3D-printed?

Lipkowitz: In addition to the primitive geometries used to calibrate our injection process — cylindrical parts of precisely controlled geometries coordinated to print speeds, which were useful for theoretical calculations — along with the multi-color prints of historically important buildings to demonstrate our system’s multi-material capabilities, we printed lattice structures with multi-walled carbon nanotubes (MWCNTS), which are too viscous to flow through the dead zone without injection.

Tech Briefs: How far has the technology advanced from CLIP to iCLIP?

Lipkowitz: We were able to demonstrate 5- to 10-fold improvements in printing speed with our iCLIP approach, compared with the existing method; specifically, we quantified this metric by measuring the linear draw rate at which print failures occur in both processes. Moreover, we were able to print with resins roughly 3- to 5-fold more viscous with injection than without.

Tech Briefs: What’s the next step with regards to your research/testing?

Lipkowitz: Now that we have shown that iCLIP can print with multiple resins, we’re working on developing software to carefully tune the geometry of the microfluidic network to achieve such multi-material design goals. This generative design software encodes the fluid dynamics of the printing process, taking a part that a designer wants to print and automatically generates not only the microfluidic distribution system, but also the flow rates to administer different resins to achieve a multi-material goal.

Tech Briefs: How far away are we from iCLIP becoming available to the average person? From being completely ubiquitous?

Lipkowitz: Because the hardware changes to the physical printer are quite minimal — we only add a pressure-driven syringe pump system to the build platform — we anticipate iCLIP being very feasible to implement at a technical level, when paired with the fluid dynamics control software we are actively working on.

Tech Briefs: Do you have any advice for design engineers aiming to bring their ideas to market?

Lipkowitz: An overarching goal of the iCLIP process is to “co-design” a part for the manufacturing process used to fabricate it, carefully taking into account both the physical constraints and opportunities. To that end, I’d advise designers to, whether using iCLIP or other digital fabrication methods, proactively take into account the constraints of the manufacturing process they’re using as they design, instead of waiting for a fabrication failure to redesign. It might take more time at the beginning, but in the long term it will save time and work.