MLU researchers combine extrusion and inkjetting to develop novel hybrid 3D printing process

A team of researchers from Martin Luther University Halle-Wittenberg (MLU) have developed a new hybrid additive manufacturing process combining both extrusion and inkjet-based 3D printing.

The approach can be used to integrate liquid inks directly into solid material matrices, allowing, say, active medical ingredients to be incorporated into drug delivery devices at the initial manufacturing stage. The team has also identified applications in structural engineering, whereby fluorescent liquids can be housed in solid structural components, enabling users to monitor cracks in a visual manner.

Professor Wolfgang Binder, co-author of the project, states, “The future lies in more complex methods that combine several production steps. That is why we were looking for a way to integrate liquids directly into the material during the printing process.”

Solid 3D printed oral drug delivery device housing an active liquid ingredient inside. Photo via MLU.
Solid 3D printed oral drug delivery device housing an active liquid ingredient inside. Photo via MLU.

Combining solids and liquids

3D printing, in general, yields solid parts as an end product. In cases where liquids are used as a raw material, they are either cured or cooled into a solid form before leaving the build chamber. Therefore, if the final component is to contain a section of liquid, this must be added after the printing is complete, which can be costly, difficult, or just downright tedious.

With the goal of automating this otherwise highly manual process, the MLU team combined an FDM extruder with an inkjet dispenser in a custom-built hybrid laboratory setup. The system is capable of dispensing individual droplets of liquid between the layers of extruded filament, enabling precise multi-phase material integration in a targeted manner.

Applications of dual-phase 3D printing

Throughout the study, the MLU team tested the system with two different use cases. First, the machine was used to integrate an active liquid agent into a biodegradable capsule, creating an ingestible drug delivery device with a core-shell structure. Binder adds, “We were able to prove that the active ingredient was not affected by the printing process and remained active.”

Next, the researchers incorporated a luminous liquid into a polymer capsule (FDM printed in PCL), whereby the liquid would leak if the outer shell sustained damage and formed a crack. While micro-damage to metals is easily detectable with today’s X-ray technology, the same cannot be said for plastics, but the novel MLU approach could indeed provide a new method of doing so. Binder explains, “You could imprint something like this into a small part of a plastic product that is exposed to particularly high levels of stress.”

Beyond the two tested in the study, the researchers also identified a number of other potential applications of the novel technology, such as 3D printed batteries. In this case, the solid electrodes and casing would be extruded, while the liquid electrolyte would be deposited into closed-off internal chambers. As such, one comprehensive system could perform all of the functionality of an entire battery assembly line.

The 3D printing of a PCL part with a luminous oil inside. Image via MLU.
The 3D printing of a PCL part with a luminous oil inside. Image via MLU.

Further details of the study can be found in the paper titled ‘3D Printing of Core–Shell Capsule Composites for Post‐Reactive and Damage Sensing Applications‘. It is co-authored by Wolfgang Binder and Harald Rupp.

The ability to print with multiple materials opens up a whole host of new use cases for additive manufacturing. Researchers from Yokohama National University recently devised a new 3D printing method capable of fabricating multicolor microstructures using different materials. The SLA-based technique works by suspending multiple resins in a droplet state, where they can be exchanged during printing without causing voids or cross-contamination.

Elsewhere, at Columbia University’s School of Engineering, scientists have previously unveiled their own take on SLS 3D printing, which enables multiple powders to be sintered in the same print job. The system inverts the laser so that it points upwards, and replaces the powder bed with modular glass plates. The result is the ability to incorporate multiple polymer powders into a single part.

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Featured image shows a solid 3D printed oral drug delivery device housing an active liquid ingredient inside. Photo via MLU.

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