Junjie Yao, Duke University; Shrike Yu Zhang, Harvard Medical School
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Researchers from Duke University and Harvard Medical School have introduced a new 3D printing method using soundwaves rather than light to build intricate structures deep within tissues.
This method, referred to as Deep-Penetrating Acoustic Volumetric Printing (DVAP), facilitates applications from bone healing to targeted drug delivery, symbolizing a major advancement in biocompatible ink technology.
Traditional 3D printing techniques often face limitations in reaching deep tissues due to the reliance on light-sensitive inks.
To overcome this hurdle, Y. Shrike Zhang, associate bioengineer at Brigham and Women’s Hospital and associate professor at Harvard Medical School, and Junjie Yao, associate professor of biomedical engineering at Duke, introduced DVAP.
Unlike light, ultrasound waves can penetrate more than 100 times deeper into tissues while maintaining spatial precision. “DVAP relies on the sono-thermal effect, which occurs when soundwaves are absorbed and increase the temperature to harden our ink,” explained Yao, in a statement.
“Ultrasound waves can penetrate more than 100 times deeper than light while still spatially confined, so we can reach tissues, bones and organs with high spatial precision that haven’t been reachable with light-based printing methods.”
The fundamental element of DVAP is an exclusive ink known as sono-ink. This is made up of hydrogels, microparticles, and specific molecules that interact with ultrasound waves.
Sono-ink, being a gel-like fluid, can be seamlessly injected into the areas of interest. Using a special ultrasound printing probe, scientists thereafter direct concentrated ultrasound waves into the ink, leading to solidification into intricate structures. These can vary from skeletal-like frameworks to hydrogel bubbles that are appropriate for organ placement.
“The ink is essentially a gel-like fluid, hence it can be conveniently injected into a specific area, and as the ultrasound printing probe is moved around, the materials in the ink join together and solidify,” clarified Zhang.
“Once it’s done, you can eliminate any excess ink that hasn’t hardened using a syringe,” he further noted. Sono-ink is designed to be adaptable, giving researchers the luxury to adjust its formulation for various applications including the durability, degradability, and even the color.
Junjie Yao, Duke University; Shrike Yu Zhang, Harvard Medical School
To demonstrate the potential of DVAP, the research team conducted three successful tests. In the first, they used the sono-ink to seal off a section in a goat’s heart, a procedure traditionally requiring open-chest surgery. The ultrasound waves penetrated 12 mm of tissue, securely bonding the ink to the heart tissue without causing damage. The flexible bond was observed to withstand movements mimicking a beating heart.
In the second test, the team demonstrated DVAP’s capacity for tissue reconstruction and regeneration by injecting sono-ink into a chicken leg bone defect model. The ink seamlessly bonded with the bone through 10 mm of skin and muscle tissue layers, causing no negative impact in any of the surrounding tissues.
The third test showcased DVAP’s role in therapeutic drug delivery. Adding a common chemotherapy drug to the sono-ink, the researchers delivered it to sample liver tissue. The hardened hydrogels slowly released the chemotherapy drug, diffusing into the liver tissue.
“We’re still far from bringing this tool into the clinic, but these tests reaffirmed the potential of this technology. We’re very excited to see where it can go from here,” said Zhang.
“Because we can print through tissue, it allows for a lot of potential applications in surgery and therapy that traditionally involve very invasive and disruptive methods,” Yao added. While still in the early stages, DVAP could be the start of a significant step toward revolutionizing biomedicine and personalized healthcare.
The team’s findings were published in the journal Science.
Study Abstract
Volumetric printing, a budding additive manufacturing method, creates objects by estimating printing speed and quality of the surface, eradicating the requirement of layer-by-layer ink renewal. Current volumetric printing methodologies heavily bank on light energy which instigates photopolymerization in clear inks, therefore, constricting material alternatives and construction dimensions. We introduce a self-amplifying sono-ink design along with a correlative focusing ultrasound composition method for deep-penetration acoustic volumetric printing (DAVP). We exploited experimentation and acoustic modelling to explore the dependency of acoustic printing behaviours on frequency and scanning rate. DAVP ensures fundamental characteristics of minor acoustic streaming, swift sonothermal polymerization, and extensive printing depth, sanctioning the printing of volumetric hydrogels and nanocomposites in various forms irrespective of their optical characteristics. DAVP also includes printing at centimetre depths through biological tissues, clearing the path for minimally invasive medicine.
“Why did the 3D printer go to therapy? Because it had too many layers of unresolved issues!”
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