Bleeding-edge 3D printing research from Heidelberg University, USC, the University of Utah, and more.
With another summer drawing to a close, students will soon be returning to their classrooms to the relief of many parents and the chagrin of many teachers. Meanwhile, researchers at institutions of higher learning across the globe have been hard at work advancing 3D printing technology. Here are a few of the latest developments.
Closed-loop materials for DLP and SLA
Light-based 3D printing, including stereolithography (SLA) and digital light processing (DLP) has several advantages over other polymer processes, such as fused filament fabrication (FFF), including resolution and, at least in some circumstances, speed. However, one area where SLA and DLP are at a disadvantage compared to FFF is sustainability. The polymer resins used in the former processes are notoriously difficult to recycle but that could soon change thanks to efforts from engineers at the Institute for Molecular Systems Engineering and Advanced Materials (IMSEAM) at Heidelberg University.
A new metastable polymer developed there can be broken down into its molecular building blocks in seconds using a special chemical catalyst, enabling the material to be recovered and reused.
“The long molecular chain is held together by a single predetermined breaking point,” explained doctoral student Johannes Markhart in a press release. “As soon as a specific chemical trigger opens this site, the entire chain breaks down into its constituent parts within seconds at room temperature, like a row of dominoes.”
In experiments, Markhart and his colleagues used the metastable material to produce complex structures at micrometer scales before breaking them back down into polymer resin. According to the researchers, spectroscopic analyses confirmed that the chemical composition of the recycled polymer is identical to that of the starting material at the molecular level.
“Our approach shows that stability and recyclability do not have to be mutually exclusive,” said Professor Eva Blasco, who oversaw the research, in the same release. “We hope that it can pave the way for true chemical circularity and thus contribute to more sustainable manufacturing processes.”
The research is published in the journal Advanced Materials.
Recycling PET for filament
Another advancement in sustainable 3D printing comes from researchers at the Institute of Engineering and Rural Technology (IERT) and Motilal Nehru National Institute of Technology Allahabad (MNNIT) in India. They’ve developed a new filament extrusion system for converting waste PET from plastic bottles into FFF-compatible filament.
The researchers sorted, cleaned, dried, and shredded discarded bottles before processing the plastic into filament, which they then benchmarked against PLA pellets extruded on the same system. According to the team, the tensile strength of the PLA test specimens was ~11% higher than the PET (44 ± 3.6 MPa vs 39 ± 3.2 MPa). While that’s worse performance than what’s typical for virgin PET, the researchers contend that their findings nevertheless indicate that recycled PET can still be useful in certain applications, such as household goods or fashion products.
Their study also highlights the challenges of recycling PET for filament, particularly moisture management and dimensional consistency. While they grant that further optimization and material characterization are needed before recycled PET filaments could replace standard filaments in all applications, they also argue that they’ve demonstrated a practical basis for creating recycled polymer feedstocks in additive manufacturing (AM).
Their research is published in the journal Advanced Manufacturing.
MRI sensors for children and infants
While a one-size-fits-all approach has obvious benefits in medical device manufacturing, it also has one very obvious drawback: equipment that’s been designed to fit adults doesn’t always work well when used on children or infants. That’s why researchers at the University of Southern California have developed flexible MRI sensors that can be customized to individual patients.
What’s really exciting about this isn’t so much the customization but the time and cost: each sensor can be 3D printed in less than 10 minutes for roughly $30. They also performed better than off-the-shelf sensors, reportedly yielding a four-fold improvement in image contrast.
“By making customized MRI equipment faster and more affordable to produce, we have the potential to bring better imaging to patients who have traditionally had fewer options, especially infants and children,” said Yasser Khan in a press release. Khan, who oversaw the research, is assistant professor of electrical and computer engineering and biomedical engineering at USC. “We’re bringing a level of precision and customization to MRI that isn’t available today,” he said in the same release.
The process involves 3D printing conductive silver ink onto a thermoplastic elastomer that contours to the patient’s body and then connecting the resulting sensor, also known in this context as a coil, to an MRI system. The sensors were designed and built in Khan’s lab and tested in the Dynamic Imaging Science Center (DISC), which houses a unique MRI system.
The research is published in the journal Nature Communications.
Holographic nanoscale 3D printing
The phrase “layer-by-layer” has been used so often to describe 3D printing in contrast to conventional manufacturing processes that they’re practically synonymous, but the next generation of additive technologies are aiming to eschew that stratified method altogether. The latest example comes from the University of Utah, where engineers have demonstrated a new 3D printing method that uses a nanoscale photomask to diffract laser light into a holographic pattern, curing the feedstock in a single shot.
The researchers have already used the novel technique to print microtubule assemblies with individual diameters as small as 6 micrometers, with dimensional ratios of up to 120:1. But while these prints can include voids along their length and width, the researchers needed further refinements to create voids along the print’s height.
Their solution to this challenge was to take advantage of the different timescales between light exposure and the curing process, using computational engineering to design their photomasks such that printed regions intended to remain hollow voids are kept dark enough to avoid molecular crosslinking. The resulting shapes, including a hollow cylinder and cube, could be taken as a proof-of-concept for even larger prints, all done in a matter of seconds.
The research is published in the journal Science Advances.
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