Standardized playbook for multi-material projection-based bioprinting

Precisely reconstructing the intricate architectures of natural biological tissues remains a long-standing objective in 3D bioprinting. Projection-based 3D printing demonstrates the highest Resolution/Time for Manufacturing ratio among all 3D printing technologies and is considered a highly promising bioprinting method.

The Zhejiang University team developed a multi-material projection-based 3D bioprinting (PBBP) system employing a synergistic cleaning strategy called "fluid-controlled rinsing with negative pressure-assisted capillary adsorption." Through systematic investigation of multi-material printability, they achieved standardized, high-fidelity, high-resolution printing of composite bioink structures.

"Due to the absence of systematic investigations and mature printing systems," explained Yong He, who led the research. "Critical scientific and engineering challenges persist, including significant variations in photopolymerization characteristics of multi-component bioinks, undefined material compatibility combinations, unavoidable cross-contamination issues, and the lack of standardized evaluation criteria for multi-material printing resolution."

The study was published in Research on January 31, 2025, which is the first Science Partner Journal launched by the American Association for the Advancement of Science (AAAS) in collaboration with the China Association for Science and Technology (CAST). He is a professor of mechanical engineering in Zhejiang University.

"As bioprinting technologies advance, multi-material printing represents an inevitable trajectory for field development," emphasized Prof. He. "Establishing standardized, universally applicable evaluation frameworks, process standards, and manufacturing platforms remains crucial for accelerating widespread adoption."

This study establishes a foundational PBBP framework featuring a vat-switching device capable of six-material synchronous printing. The system integrates dedicated operational software, mechanical monitoring, visualization modules, laser calibration, and flexible peeling mechanisms to ensure stability and operability.

"Our bodies are full of composite structures combining soft and hard tissues—think bone-to-cartilage junctions or skin-muscle interfaces," Prof. He explained. "That’s why we use biocompatible inks with varying stiffness to mimic these distinct tissues. But when materials differ too drastically in strength, you risk mechanical mismatches or weak bonding at their interfaces."

A hydrogel bonding "rulebook" rooted in fracture energy analysis. By measuring how much energy it takes to tear apart combined soft-hard hydrogels, they established printable window for material combinations. Experiments demonstrated how microscopic interface patterns expand printable combinations.

"Cross-contamination remains a major challenge in multi-material printing, which can be categorized as infiltration or residual contamination," Prof. He stated. The study developed standardized testing protocols for viscous bioink penetration while investigating factors influencing infiltration rates. Systematic optimization of fluid flushing and negative pressure-assisted capillary adsorption parameters effectively eliminated contamination risks.

"Resolution is a key metric for evaluating 3D printing capabilities," Prof. He emphasized. "We developed a resolution testing model to systematically analyze printing accuracy, identifying and decoupling error sources through comprehensive testing."