3D Printing of Heterogeneous Structures with Simultaneous Multi-Material Embedding

Publication in the journal International Journal of Extreme ManufacturingThe team led by researchers based at Key State Laboratory for Fluid Strength and Mechatronic Systems deposited different biomaterials simultaneously and precisely in the resulting area of ​​embedding medium with multiple individually controlled nozzles.

Compared with the traditional sequential printing method, the upgraded printing method can control the micro-deposition of bio-links to ensure the accuracy of position and structure morphology and improve the bonding strength between layers. This discovery could offer the potential for its widespread use in the fabrication of heterogeneity structures with soft biomaterials and soft composites.

One of the principal investigators, Associate Professor Hongzhao Zhou, commented: “The multi-material bioprinting technology offers different options of cells and biomaterials for the in vitro construction of heterogeneous structures that may be better representations of normal tissues/organs. Combined printing technology offers more possibilities for printing Various materials on complex three-dimensional structures.

However, the embedding medium has a greater viscosity than air, which may further affect the continuous position of the extruded bio-unit. The bioink is deposited in embedding medium and maintained approx. There is no guaranteed adhesion between adjacent threads. Because tissues can be built in vitro with multiple materials, it is really important to control the precise deposition of the ink in the embedding medium to build heterogeneous tissues.

In traditional combined printing, a simple and commonly used strategy is that adjacent filaments are designed spatially staggered to ensure that they can be connected to each other.

“The overlapping method has been shown to be effective when printing continuous structures with a single material. For complex structures with multiple materials, overlapping filaments may lead to uncontrolled stacking and compaction of adjacent filaments and compromise the spatial distribution of different materials in the printed structure,” said first author Dr. Zeke Gao.

In our work, we analyze the dynamics of the extruded bio-connector in the embedding medium. We evenly mix fluorescent microspheres in the ink to define the contours of the printed filaments, and simultaneously print the filaments in the embedding medium with different printing parameters. We can compare and verify experimental phenomena with the results of changes of key parameters in Theoretical analysis. This new printing method can achieve horizontal contact between microfilaments under a wide range of printing parameters.”

Co-first author Professor Jun Yin added, “Through the above experimental methods, the effects of printing parameters including printing speed and rheology of the embedding medium on the 3D shape of the printed filament are quantitatively evaluated. Under the conditions of high printing speed and low viscosity embedding medium, the filaments show Printed simultaneously with high resolution and an aspect ratio close to 1, which can adapt to the slide path and enable us to fabricate microstructures.”

“A thin-walled, double-layer structure was printed with each layer less than 200 μm thick. It was demonstrated that the intestine and liver models could be printed. The intestine showed a structure similar to the circular fold shape of a real organ. It ligates and is extracted from the embedding medium without significant weakening or distortion.”

Also, a peeling test was performed to check the bonding strength between the simultaneous printed sample, and the results were compared with the molded and the serial printed sample. We found that the bonding strength of the samples by simultaneous printing was much greater than that of the samples by serial printing under the same track. The proposed simultaneous printing method reduces the chance of contamination of the embedding medium for 3D printing of multilayer, multimaterial structures. It could be a direct solution to the existing structural integrity problems of such structures.”

The team studied a promising multi-material inline printing method for fabricating heterostructures with high precision and good structural integrity. With soft biomaterials and soft composites, this method can be used to build a tissue model in vitro.