Scientists from Israel, China and Singapore have developed a novel method of 3D printing hydrogels into other polymers to create complex hybrid microstructures.
Utilizing a custom DLP 3D printer and a water-soluble photoinitiator, the team were able to induce covalent bonding between a super-stretchy PEGDA and other UV-curable resins. Ultimately, the researchers’ approach allowed them to create several unique micro-devices, such as a malleable drug-releasing stent and a soft actuator with potential multifunctional robotics applications.
Creating hybrid polymer networks
Hydrogels are essentially water-based polymer networks that can either be combined with other plastics to create structures with enhanced strength, or to add new functionalities altogether. While many of these hybrid devices have proved particularly useful within biomedical applications, they’ve also been restricted to hydrogel-rubber combinations, somewhat limiting their versatility.
Using DLP 3D printing, on the other hand, it’s now possible to produce complex hydrogel structures, and the scientists recently adopted the technology to create laticed objects that could be stretched by up to 1300%. However, despite these developments, the team found they were unable to effectively bond their hydrogels with many other curable resins, due to the limitations of existing systems.
As a result, the scientists opted to develop a custom ‘bottom-up’ DLP 3D printer, in which UV light is projected from below the build area through a precursor-coated glass plate. During printing, the plate moves from side-to-side, applying the precursor while alternating between two polymers layer-by-layer, effectively combining them into hybrid structures.
3D printing multifunctional devices
In order to test the efficacy of their custom machine, the researchers opted to 3D print a part that was split evenly between the flexible PEGDA hydrogel and a transparent elastomer. The resulting object featured strong covalent bonds between the materials, and the team were able to compress it by up to 50% without causing them to break.
The researchers then upped the ante by combining three materials: a rigid polymer, PEGDA and commercial elastomer, into a novel foam-like structure. In this case, the team were not only able to stretch the part without debonding it, but to tune its mechanical behavior by adjusting the hydrogel’s mixing ratio and water content.
Putting their learnings into practise, the scientists deployed their custom 3D printer to create a hydrogel-loaded methacrylate cardiovascular stent. Using a shape memory polymer enabled the team to program the device’s rigidity at certain temperatures, making it malleable at 37°C but stiffer 20°C, while allowing it to adapt to the size of different blood vessels if applied within end-use scenarios.
Similarly, to demonstrate the electronics applications of their approach, the researchers 3D printed a pneumatic actuator within an integrated hydrogel–based strain sensor. The soft robotic device proved to be highly-stretchable, and its novel functionality potentially paves the way for more complex conductive hybrid devices to be built in future.
Growing multi-material competition
The potential of multi-material 3D printed parts in opening new additive applications has led to the creation of several novel machines in recent years.
Automation company Infotech, for instance, has partnered with adhesives manufacturer DELO to develop a new multi-material desktop 3D printer. Based on the firm’s IP-500 Desktop Dispenser, the machine uses a multi-head system to dispense multiple liquid resins at once.
In a similar vain, scientists from the Japan-based Yokohama National University (YNU) have devised a new multi-material SLA 3D printing method. The team’s system suspends resins in a droplet state, allowing it to produce multicolored parts more efficiently which contain fewer voids.
Elsewhere, researchers from Martin Luther University Halle-Wittenberg (MLU) have combined extrusion and inkjet-based technologies to develop a novel hybrid 3D printing process. The new approach has also yielded drug delivery devices, capable of being loaded with active medical ingredients at the production stage.
The researchers’ findings are detailed in their paper titled “3D printing of highly stretchable hydrogel with diverse UV curable polymers,” which was co-authored by Qi Ge, Zhe Chen, Jianxiang Cheng, Biao Zhang, Yuan-Fang Zhang, Honggeng Li, Xiangnan He, Chao Yuan, Ji Liu, Shlomo Magdassi and Shaoxing Qu.
The collaborative research was conducted by the Southern University of Science and Technology, Zhejiang University, Northwestern Polytechnical University, Singapore University of Technology and Design, Hunan University and the Hebrew University of Jerusalem.
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Featured image shows an isotropic picture of one of the researchers’ 3D printed hybrid structures. Image via the Science Advances journal.