Advances continue to be made in the progressive field of bioprinting, pushing toward increased ability to 3D print human tissue.

A study completed by a collaboration of researchers from UCLA, Brigham and Women’s Hospital and Harvard Medical School, the University of Santiago de CompostelaUC San Diego, and Sharif University of Technology is introducing something new to 3D bioprinting – the ability to print with multiple materials.

Bioengineer Ali Khademhosseini, the Levi James Knight, Jr. Professor of Engineering at the university’s Samueli School of Engineering, and his collaborators created a method that automatically builds therapeutic biomaterials from several materials. The technique uses a specially adapted 3D printer that could help advance the field of regenerative medicine by making it possible to 3D print complex artificial tissues on demand.

Ali Khademhossein

“Tissues are wonderfully complex structures, so to engineer artificial versions of them that function properly, we have to recreate their complexity. Our new approach offers a way to build complex biocompatible structures made from different materials,” said Khademhosseini, who also has faculty appointments in bioengineering, chemical and biomolecular engineering, and in the university’s David Geffen School of Medicine.

The study, titled “Microfluidics-Enabled Multimaterial Maskless Stereolithographic Bioprinting,” was funded by the Office of Naval Research and the National Institutes of Health and recently published in Advanced Materials.

The abstract reads, “A stereolithography‐based bioprinting platform for multimaterial fabrication of heterogeneous hydrogel constructs is presented. Dynamic patterning by a digital micromirror device, synchronized by a moving stage and a microfluidic device containing four on/off pneumatic valves, is used to create 3D constructs. The novel microfluidic device is capable of fast switching between different (cell‐loaded) hydrogel bioinks, to achieve layer-by-layer multimaterial bioprinting. Compared to conventional stereolithography‐based bioprinters, the system provides the unique advantage of multimaterial fabrication capability at high spatial resolution. To demonstrate the multimaterial capacity of this system, a variety of hydrogel constructs are generated, including those based on poly(ethylene glycol) diacrylate (PEGDA) and gelatin methacryloyl (GelMA). The biocompatibility of this system is validated by introducing cell‐laden GelMA into the microfluidic device and fabricating cellularized constructs. A pattern of a PEGDA frame and three different concentrations of GelMA, loaded with vascular endothelial growth factor, are further assessed for its neovascularization potential in a rat model. The proposed system provides a robust platform for bioprinting of high‐fidelity multimaterial microstructures on demand for applications in tissue engineering, regenerative medicine, and biosensing, which are otherwise not readily achievable at high speed with conventional stereolithographic biofabrication platforms.”

The 3D bioprinter designed by Khademhosseini has two key components: a custom-built microfluidic chip (pictured) and a digital micromirror.

Khademhosseini, also the director of the Center for Minimally Invasive Therapeutics and an associate director of the California NanoSystems Institute, designed a customized 3D printer, which the team’s new stereolithographic technique uses to 3D print tissue scaffolds out of various hydrogels. The bioprinter has two important components: a custom-built microfluidic chip that has multiple inlets, each of which prints out a different material, and a digital micromirror, which is an array of over a million, independently-moving tiny mirrors.

Examples of PEGDA-50% constructs printed by the open-chamber setup.

The micromirrors are used to direct light onto the print surface, which illuminates the outline of the 3D printed object and triggers the molecular bonds that cause the materials to firm up into a solid. During 3D printing, the unique mirror array indicates the shape of subsequent new layers by switching the light pattern.

First, the researchers just focused on making simple shapes, like pyramids, but soon moved on to complex 3D structures that imitated muscle-skeleton connective tissues and parts of muscle tissue. They also 3D printed shapes that could eventually be used as biological models for studying cancer, as they mimicked tumors with blood vessel networks. These 3D printed structures were successfully implanted in rats, and were not rejected.

The team’s innovative bioprinting technique is a major advancement over conventional stereolithographic bioprinting, which uses just one type of material, as it is the first one to use multiple materials for automated stereolithographic bioprinting. The demonstration bioprinter used a total of four types of bioinks, but according to the researchers, the process is able to “accommodate as many inks as needed.”

Examples of cell patterning. a) A muscle stripe-like shape: C2C12-loaded GelMA-7% immediately after bioprinting. b) A star shape: MSCs printed in a PEGDA-50%
pattern after 24 h. c) A reticular network made by osteoblast-loaded GelMA-7% immediately after bioprinting. The designed mask is shown for each case.

Authors of the paper include first author Amir K. Miri, Daniel Nieto, Luis Iglesias, Hossein Goodarzi Hosseinabadi, Sushila Maharjan, Guillermo U. Ruiz‐Esparza, Parastoo Khoshakhlagh, Amir Manbachi, Mehmet Remzi Dokmeci, Shaochen Chen, Su Ryon Shin, co-senior author Yu Shrike Zhang, and Khademhosseini.

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[Source/Images: UCLA]

 

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