Stanford researchers have taken a major step toward addressing one of the biggest hurdles in organ bioprinting: building realistic vascular networks capable of sustaining lab-grown tissue. Their new platform, published June 12 in , accelerates the design of these blood vessel systems and translates them into 3D printable models—bringing the promise of personalized, functional organs closer to reality.
A model of a vascular tree printed using a 3D bioprinter. Image via Andrew Brodhead.
Overcoming the Vascular Barrier in Organ Bioprinting
More than 100,000 people in the U.S. are currently on organ transplant waiting lists, many for years—and some won’t survive the wait. Even when a donor organ becomes available, the risk of immune rejection remains high. To overcome these limitations, regenerative medicine researchers are working to fabricate organs like hearts, kidneys, and livers using a patient’s own cells.
A critical challenge in this process is replicating the body’s intricate vasculature Blood flows from large arteries into smaller vessels that deliver oxygen and nutrients to cells, which must be very close to these vessels to survive—especially in demanding organs like the heart. Vascular networks differ widely between organs and individuals, making it difficult and time-consuming to create accurate models. Many researchers rely on standardized structures that work for small tissues but don’t scale well for larger, complex organs.
“The ability to scale up bioprinted tissues is currently limited by the ability to generate vasculature for them – you can’t scale up these tissues without providing a blood supply,” said Alison Marsden, Professor of pediatrics and of bioengineering at Stanford in the Schools of Engineering and Medicine and co-senior author on the paper.
3D bioprinted soft tissue scaffold with vascularization channels designed and produced by 3D Systems and CollPlant. Photo via 3D Systems.
Accelerating Realistic Vascular Network Generation
The Stanford team developed an algorithm that rapidly generates vascular trees that resemble real human blood vessel networks, and converts them into instructions for 3D printing. Their algorithm runs roughly 200 times faster than prior methods and can model complex organ geometries.
To ensure even blood distribution and structural feasibility, the algorithm integrates fluid dynamics simulations. The designs avoid vessel collisions and maintain a closed-loop system with one entry and exit. The team has made the tool publicly available through the open-source SimVascular project.
“It took about five hours to generate a computer model of a tree to vascularize a human heart. We were able to get to a density where any cell in the model would have been about 100 to 150 microns away from the nearest blood vessel, which is pretty good,” said Zachary Sexton, a postdoctoral scholar in Marsden’s lab. “That task hadn’t been done before, and probably would have taken months with previous algorithms.”
Toward Fully Functional Organs: Overcoming the Remaining Hurdles
While current 3D printers aren’t yet capable of printing every feature in these dense networks, the team demonstrated proof of concept by printing a simplified version with 500 branches. They also tested a bioprinted tissue ring embedded with human embryonic kidney cells and 25 vessels. When pumped with a nutrient-rich fluid, the cells near the printed network remained alive.
“We show these vessels can be designed, printed, and can keep cells alive,” said Mark Skylar-Scott, assistant professor of bioengineering and co-senior author. “We know that there’s work to do to speed up the printing, but we now have this pipeline to generate different vascular trees very efficiently and create a set of instructions to print them.”
Manufacturing on Demand
The researchers noted that these printed networks are not yet functional blood vessels—they are structural channels lacking muscle, endothelial, and other cell types needed for biological function. “This is the first step toward generating really complex vascular networks,” said Dominic Rütsche, a postdoctoral scholar in Skylar-Scott’s lab and co-first author. “We can print them at never-before-seen complexities, but they are not yet fully physiological vessels. We’re working on that.”
Researchers are also investigating ways to stimulate the growth of the smallest blood vessels—those too tiny or densely packed to be printed directly—while also working to enhance 3D bioprinter speed and precision. Additionally, they focus on cultivating the vast number of cells required to print a complete heart.
Microvascular structure. Image via Flam3D.
Vascular 3D Printing
In 2024, researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Science (SEAS) developed a novel method for 3D printing vascular networks. Developed from a previous method called sacrificial writing in functional tissue, this new method named coaxial SWIFT (co-SWIFT) enables the creation of interconnected networks of blood vessels embedded within human cardiac tissue, enhancing the viability of producing implantable human organs.
Back in 2021, Scientists from the Israel Institute of Technology (Technion) used 3D printing to create a functional network of large and small blood vessels capable of supplying blood to implanted tissues.
Led by Professor Shulamit Levenberg, this research aimed to bypass the need for pre-transplant steps and reduce the risk of implant rejection by using patient-specific tissues. After testing the vascular network in rats, the team planned to adapt the technology for larger animals, advancing toward lab-grown tissues suitable for transplantation.
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Author: Paloma Duran
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