The problem the researchers attacked is one of the most stubborn in cardiovascular engineering. Polymeric heart valves have been pursued since the mid-twentieth century because they promise the durability of mechanical prostheses combined with the gentle, physiological blood flow of biological ones. Polycarbonate urethane, or PCU, has long been a favorite matrix material thanks to its resilience, biocompatibility and ability to be formed into thin, flexible leaflets. Yet polymeric valves still suffer from thrombosis, calcification, viscoelastic creep and, above all, insufficient fatigue resistance under cyclic loading. Elevated mechanical stress has been linked for decades to structural deterioration and calcification in heart valves, and strain energy density is widely recognized as a fatigue-related parameter in elastomers. Reduce the mechanical demand inside each leaflet, the reasoning goes, and the valve should live longer.

The Technion team’s inspiration came from biology rather than materials chemistry. Native aortic valve leaflets owe their remarkable longevity to an organized collagen fiber network in which circumferentially dominant bundles carry most of the tensile load during diastole while preserving the radial compliance needed for the valve to swing open during systole. Earlier attempts at fiber reinforcement typically bolted simplified radial or cross-hatched meshes onto the leaflet surface, which risks mechanical damage and adverse blood–material interactions. The new approach instead buries the reinforcement entirely inside the leaflet volume, following curvilinear trajectories mapped from microscopy of porcine aortic leaflets, with fibers converging at the commissures just as collagen does in living tissue.

Realizing that architecture demanded an unusual manufacturing workflow. The researchers printed each valve not as a finished three-dimensional object but as a flat, unfolded sheet on a Prusa XL multi-material extrusion printer, depositing medical-grade Bionate 90A polycarbonate urethane as the matrix and stiffer PETG filaments as reinforcing fibers laid into preformed channels at roughly the leaflet’s mid-thickness. The flat construct was then wrapped around a stereolithography-printed mold, its edges thermally welded into a cylindrical root, and finally pressed in a heated two-part mold that generated the final leaflet geometry while consolidating the printed layers. Scanning electron microscopy confirmed that the PETG fibers remained fully encapsulated in a consolidated PCU matrix, with no visible interfacial gaps or debonding even after an hour of pulsatile flow testing corresponding to roughly 3,600 cardiac cycles.

To isolate the effect of fiber architecture, the team built four valve designs with identical geometry and an identical reinforcement volume fraction of about seven percent: an unreinforced baseline, a horizontal layout of thirteen circumferential fibers, a ply layout of crossing fibers in an X pattern, and the biomimetic network. Two leaflet thicknesses were compared computationally, 0.3 millimeters and a native-like 0.2 millimeters, with fiber diameters scaled accordingly from 0.15 to 0.10 millimeters. Finite element simulations in Abaqus, using a Marlow hyperelastic model calibrated against uniaxial tensile tests of the printed PCU, quantified stress, principal logarithmic strain and strain energy density at peak diastolic loading.

The results revealed a subtle and somewhat counterintuitive picture. No single metric crowned one design as the universal winner. The ply architecture produced the lowest localized peak stress, the horizontal layout most strongly restricted deformation, and the biomimetic design achieved the lowest strain energy density, 0.14 versus 0.18 megajoules per cubic meter in the unreinforced 0.3-millimeter valve, and 0.25 versus 0.34 megajoules per cubic meter in the thinner 0.2-millimeter version. Because strain energy density reflects the elastic energy stored in the material with every loading cycle, the biomimetic network’s advantage suggests reduced fatigue demand precisely where it matters most. Notably, the reinforcement’s influence grew dramatically as the leaflet thinned: in the thicker valve the matrix carried much of the load itself, while in the thinner design a greater share of stress flowed into the fibers, making the choice of architecture far more consequential.

Notched tensile experiments added a durability angle that pure simulation cannot provide. Coupons reinforced at 45 degrees to the loading direction absorbed the most energy before peak load and tolerated the greatest stretch, significantly outperforming unreinforced polymer in maximum nominal ligament stress. Inclined fibers, it turns out, help a damaged leaflet keep carrying load, a property that could prove decisive in resisting tear propagation over years of service.

The hydrodynamic payoff was verified in a pulsatile flow loop operating at a physiological cardiac output of five liters per minute, with measurements referenced to the ISO 5840 standard. High-speed imaging showed stable leaflet motion with no flutter in any configuration. The unreinforced valve opened widest, with a geometric orifice area of 2.34 square centimeters, while the three reinforced designs clustered between 1.89 and 1.95 square centimeters. Crucially, however, the effective orifice area, which captures actual flow performance, differed only modestly among all four designs, and regurgitation fractions were statistically indistinguishable. The biomimetic valve thus surrendered little functional performance while delivering the most favorable mechanical environment among the reinforced options.

The study is candid about its limits. The simulations used a structural-only formulation rather than full fluid–structure interaction, overpredicting valve opening, and the models assumed ideal circular fibers even though printed cross-sections became progressively elongated at smaller diameters. Long-term durability, accelerated wear, fatigue and creep testing remain to be done, and the authors emphasize that the workflow is a research prototyping platform rather than a clinically ready manufacturing route. A symmetric twisting mode observed during simulated closure of the thin biomimetic valve was traced to the free-edge fiber implementation, suggesting that tapered or staggered fiber terminations could resolve the instability without abandoning the biomimetic concept.

Even so, the demonstration marks a genuine milestone: proof that complex, load-aligned, fully embedded reinforcement architectures can be fabricated inside leaflets thinner than a human hair is thick, and that copying the heart’s own collagen blueprint is a viable engineering strategy rather than mere biomimetic poetry. If subsequent wear testing confirms the promise hinted at by the strain energy results, the humble 3D printer may one day produce valves that outlast the patients who receive them.

Subject of Research: Biomimetic fiber-reinforced 3D-printed polymeric aortic heart valves for improved leaflet stress distribution and durability

Article Title: Design and Fabrication of 3D-Printed Biomimetic Fiber-Reinforced Polymeric Aortic Valves for Improved Stress Distribution

Article References: Tal, O., Kreinin, Y., Korneyev, D., Levenberg, S., & Korin, N. (2026). Design and Fabrication of 3D-Printed Biomimetic Fiber-Reinforced Polymeric Aortic Valves for Improved Stress Distribution. Annals of Biomedical Engineering. https://doi.org/10.1007/s10439-026-04371-8

Image Credits: AI Generated

DOI: 10.1007/s10439-026-04371-8

Keywords: polymeric heart valves, biomimetic fiber reinforcement, multi-material 3D printing, polycarbonate urethane, aortic valve, finite element analysis, strain energy density, thermoforming, hemodynamics, collagen fiber architecture, additive manufacturing, cardiovascular engineering