Researchers from the University of Wisconsin-Madison University (UW-Madison) have 3D printed blood vessels that enable cardiac patients to monitor their blood pressure remotely.
The research team’s implantable tubular structures emit piezoelectric pulses which act to alert patients when their blood pressure is either getting too high or too low. Leveraging the Wisconsin team’s new pressure-powered devices, medical staff could now be able to diagnose potentially fatal heart diseases, and intervene at an earlier stage.
“This artificial vessel can produce electric pulses based on pressure fluctuation which will be able to tell precisely the blood pressure in the vessel without using any additional power source,” said Xudong Wang, Professor at UW-Madison. “Because of its 3D geometry, the electric pulse profile will be able to tell if there is an irregular motion due to blockage inside in the very early stages.”
The necessity of 3D printed blood vessels
Vascular replacement surgery is becoming an increasingly common method of treating non-functional blood vessels. Recent studies have revealed that around 450,000 prosthetic vascular grafts are implanted each year in the U.S. alone. In order to keep up with rising demand, a new rapid production process is needed, and 3D printing offers a faster, customized alternative to conventional casting or molding techniques.
While additive manufactured blood vessels can be manufactured more quickly than existing grafts, they could still malfunction without the patient displaying any premonitory symptoms. Given that 40 to 60 percent of vascular implants fail within their first year, monitoring grafts in real-time is both essential to patient survival, and the future application of 3D printing in production.
Currently, implanted blood vessels are monitored via a series of ultrasound or CT scanning appointments, but these are not very cost or time effective. Check-ups are not only invasive, but they aren’t timely enough to detect complications and prevent failure before it’s too late. Additionally, when graft failure does occur, treating them is a complex and potentially lethal procedure. With studies at the Albert Einstein College of Medicine indicating a mortality rate of up to five percent, graft repairs should be avoided where possible.
Ferroelectric additive manufacturing materials
Aiming to develop a safer and less invasive alternative to conventional vascular monitoring techniques, the Madison team turned to ferroelectric materials. The polarized composites are ideal for pressure and motion sensing tasks due to their piezoelectric responses, which allow them to be powered by the movements of the human body.
Previous attempts to 3D print blood vessels using motion-powered techniques have struggled to generate a strong enough electric field to enable long-term postpoling. To combat this, the Madison team utilized a composite consisting of 35 percent sodium potassium niobate (KNN) and 65 percent PVDF polymer to fabricate their vessels. KNN-based materials also possess curing temperatures of up to 400oC, and this allows them to maintain a ferroelectric field during high temperature 3D printing.
To align the di-poles of the 3D printed material, the team applied an electric field of 0.5–4 kV mm−1 between the print core and the printer’s bottom plate. The combination of the electric charge and the high processing temperatures, allowed the composite’s ferroelectric poles to align instantaneously in the extruded material. As the printing process progressed, the researchers found that rapid poling was achieved in-situ, avoiding the need for postpoling altogether.
In order to demonstrate the printability of their ferroelectric composite, the team used a Fused Deposition Modelling (FDM) 3D printer to produce parts in a range of geometries. The researchers’ helix and spiral-shaped parts exhibited desirable piezoelectric outputs, much higher than those fabricated using barium titanate (BTO) alternative composites. Printing parameters could also be customized to tailor the piezoelectricity of printed objects to their future end-use applications.
The Wisconsin-Madison 3D printed vessels
To create their additive arteries, the Wisconsin team 3D printed a polarized tube consisting of sinusoidal lattices with a thickness of 0.2 mm. Biocompatible silver paste was then applied to its inner and exterior sides, and the structure was enclosed in a 2mm thick polydimethylsiloxane (PDMS) shell.
In tensile and bending tests, the artificial artery exhibited a tissue-like stretchability and flexibility. With a lowered tensile modulus of 5.68 MPa, and flexural modulus of 10.35 MPa, the 3D printed vessel shared the strength features of human arteries. As the fabricated structure consisted only of biocompatible components (PVDF, KNN, and PDMS), it also demonstrated cell viability, making it suitable for future implantation.
Using an artificial circulation system, the team evaluated the blood pressure sensing capability of their 3D printed vein. An actuator connected to a pneumatic syringe pumped fluid in and out of the artificial artery, inducing a periodic pressure change inside. The researchers then simulated the symptoms of hypertension, increasing the rate of blood flow by 40 to 80 percent. Two adjacent voltage peaks were recorded, indicating the pressure sensing abilities of the team’s additive arteries.
According to the researchers, their electrically-charged FDM 3D printing technique could be used to fabricate a wide variety of smart biological systems, with real-time sensing functions.
“This is an easy, scalable technology,” concluded Wang. “Our new printable composite material allows us to make a 3D structure in one step that can show multi-functionality right out of manufacture.”
Artificial blood vessels and 3D printing
Scientists at a number of universities have leveraged 3D printing to create vascular networks in recent years, with the aim of improving implants and cardio care for patients.
Rice University scientists developed a 3D printing method which allowed them to create artificial vascular networks from powdered sugar. The team produced sacrificial templates from laser-sintered carbohydrate powders, without the need for support structures.
Researchers from the University of Nottingham and Queen Mary University of London, 3D printed a protein capable of organising graphene oxide into vascular tissues. By precisely controlling the mixture of the two components, the scientists produced robust biocompatible structures.
A research team from Boston University’s College of Engineering developed a 3D printed vascular patch which encourages blood vessel growth. The novel fabrication method could be used to treat ischemia, a condition relating to the inadequate blood supply of an organ.
The researchers’ findings are detailed in their paper titled “Multifunctional Artificial Artery from Direct 3D Printing with Built‐In Ferroelectricity and Tissue‐Matching Modulus for Real‐Time Sensing and Occlusion Monitoring,” which was published in the Advanced Functional Materials journal. The report was co-authored by Jun Li, Yin Long, Fan Yang, Hao Wei, Ziyi Zhan, Yizhan Wang, Jingyu Wang, Cheng Li, Corey Carlos, Yutao Dong, Yongjun Wu, Weibo Cai and Xudong Wang.
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Featured image shows a diagram of blood flowing through the UW-Madison team’s 3D printed artery. Image via the Advanced Functional Materials journal.