Researchers at the University of Minnesota and the University of Washington have developed a 3D printing method that replicates the directional mechanics of human tissue, bringing greater realism to medical simulation and surgical training.
Human tissues are anisotropic, meaning their stiffness and elasticity vary by direction due to aligned collagen and elastin fibers. Conventional cast silicone models cannot mimic this behavior, so Mechanical Engineering Professor Michael McAlpine’s team from University of Minnesota developed a 3D printing method that introduces anisotropy by controlling filament geometry at the voxel scale.
By adjusting print-line height, spacing, and material composition, they created structures with stiffness ratios matching real tissue. Published in Science Advances, a mathematical model accurately predicted these effects, and tests confirmed tunable anisotropy comparable to human skin, exceeding 1.5:1 along the printed fiber direction.
Anisotropic skin model for surgical training
To demonstrate the method, the researchers produced a 3D printed model of human neck tissue used for cricothyrotomy training, a high-stakes emergency airway procedure. Known as a “cric-skin puck,” the model consists of layered silicone tissues representing the skin and subcutaneous regions, with mechanical behavior tailored to replicate the anisotropic properties of human neck tissue.
The print path for each layer was generated through a custom algorithm that oriented print lines according to measured collagen fiber directions in the neck, derived from polarization-sensitive optical coherence tomography scans. This ensured that the local mechanical response of the printed simulant corresponded to real tissue structure.
The system used a standard gantry-based extrusion printer equipped with a volumetric dosing pump to ensure consistent filament deposition. Adjustments to nozzle position compensated for the curvature of the nonplanar surface, maintaining precise deposition on the model’s hyperbolic geometry.
These refinements allowed the production of patient-specific, mechanically accurate simulants without requiring multi-axis robotic systems.
To further enhance realism, the researchers integrated fluid-filled microcapsules into the printed tissue to reproduce bleeding when cut. The capsules were fabricated using a microfluidic double-emulsion process, enclosing water-based red dye within a thin polystyrene shell.
Mixed into a shear-thinning hydrogel, the capsules were deposited between the printed skin and subcutaneous layers and later sealed. When compressed or incised, the capsules ruptured and released the colored liquid, simulating the flow of blood. The capsules remained stable for weeks without leakage and could be tailored in size and rupture strength through flow-rate adjustments during fabrication.
A comparative acceptability study was conducted with paramedics from the King County Medic One organization in Seattle. Participants performed cricothyrotomies on both conventional cast silicone pucks and the 3D printed anisotropic versions.
Survey responses indicated that the 3D printed models provided a more realistic tactile response when palpating and cutting, as well as more convincing bleeding behavior. The differences were statistically significant, particularly in categories related to skin feel and incision realism.
The process is compatible with standard 3D printing hardware and materials, offering scalability for medical training applications.
Because anisotropy is achieved through print geometry rather than embedded fibers or complex composites, the method avoids increases in stiffness that have limited previous designs. The same framework could be adapted to other organ models, allowing directional tuning of mechanical properties to match those of cardiac, vascular, or musculoskeletal tissues.
Expanding 3D printing in medical simulation
As a classic use case, 3D printing helps create anatomically and mechanically accurate training models for various surgeries and to develop realistic test platforms for medical devices requiring precise mechanical response.
In 2021, medical anatomical models manufacturer Biomodex launched a 3D printed training system for transseptal puncture (TP), designed to replicate the geometry, feel, and haptic feedback of real cardiac tissue while remaining ultrasound-compatible. The model consisted of a reusable heart frame and a single-use septum cartridge that could be pierced during practice.
Using its proprietary INVIVOTECH and ECHOTECH processes, Biomodex printed multi-material anatomical twins that mimicked both the mechanical and acoustic properties of human tissue. The system enabled electrophysiologists to train with realistic biomechanics and imaging guidance, shortening learning curves for this complex cardiac procedure.
Researchers at the University of the West of England’s Center for Fine Print Research developed 3D printed organ simulators that replicated the appearance, elasticity, and consistency of human tissue for surgical training.
Funded by Norwegian University of Science and Technology (NTNU)’s ApPEARS program and led by David Huson, the project combined 3D printing and casting to produce low-cost, high-fidelity models of the duodenum, gallbladder, liver, pancreas, and bile duct for laparoscopic bile duct exploration training. Made from multiple materials rather than silicone, the prototypes also replicated the acoustic properties of soft tissue, allowing realistic ultrasound-guided practice and reducing reliance on cadavers or animal models.
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Featured image shows design and characterization of cellular voxel models. Image via Science Advances.
