3D Printing Awakens Renewed Interest in Polymeric Heart Valves for Patient-Specific Treatment

Authors Charles D. Resor and Deepak L Batte review the recent work of André R. Studart and his co-researchers in creating artificial heart valves via 3D printing. Their findings are outlined in their recently published article, ‘Polymeric Heart Valves: Back to the Future?’ Along with this is the work previously performed by Studart, et al. predominantly referred to in ‘Bioinspired Heart Valve Prosthesis Made by Silicone Additive Manufacturing.’

While the authors discuss the continued progression of heart valves and replacements, they highlight the work of Studart and his co-researchers, in their creation of a silicone-based polymeric heart valve—harkening back to medical trends beginning in the 1960s. Employing some of the classic benefits of 3D printing, the medical scientists fabricated a prototype with a patient-specific crimpable polymer stent using decidedly more modern methods.

Today, most heart valves as prosthetics are either mechanical or ‘biprosthetic,’ which is the more preferred type (making up 80 to 90 percent of the aortic valve replacements in the US), usually consisting of xenograft tissue valves.

(A) Biological design of native leaflets showing the fiber alignment across the leaflet. Redrawn fromSauren.35(B and C) The relaxation of elastin fibers and bunching of collagen during systole (B) and the stretching of elastin fibers and collagen fiber bundles during diastole (C). Redrawn from Schoenand Levy.36(D–F) Synthetic heart valve (D) featuring (E) bioinspired leaflet architecture and (F) patient-specific geometry of the aorta root.Labels: (1) collagen fiber; (2) elastin fiber; (3) aortic root; (4) hard silicone fiber; (5) soft silicone leaflet. (Image from ‘Bioinspired Heart Valve Prosthesis Made by Silicone Additive Manufacturing‘)

“Now with the advancement of transcatheter aortic valve replacement (TAVR), in which the aortic valve is replaced via a catheter-based crimped valve through, typically, the femoral arterial approach rather than via open cardiac surgery, bioprosthetic valves now account for greater than 90% of all prostheses in the aortic position in certain countries, a percentage that is likely to increase with newer TAVR data and increased availability of the procedure,” state the researchers.

Historically, earlier valves have been created with a variety of materials to include silicone, polyurethane, and other polymers—only to meet with failure structurally, or in causing calcification or thrombosis. Even with the tremendous amount of progress made recently in creating prosthetic heart valves, there have been continued challenges in manufacturing a ‘durable, thrombus-resistant valve,’ which the scientists state would be best from a catheter-based approach. As polymer synthesis has been refined over time, to include a realistic promise for crimpable valves—polymers have become more interesting overall in the manufacturing of valves—whether stand-alone or as scaffolds.

The prototype is an ‘impressive’ valve prototype which has the added advantage of allowing for patient-specific treatment—a wave of the future in medicine, and one which is certainly more than a trend as it eliminates so many problems which emanate from the previous necessity of the one-size-fits-all culture. With the ability to create models directly from 3D scans, or in other cases create implants laden with stem cells from a patient, complications are substantially reduced—meaning much better outcomes overall.

While the ‘in vitro’ assessments are promising, they require more testing, and especially due to so much previous research of limitations regarding polymer valves.

“Other groups have reported polymeric valves achieving ISO minimum standards for in vitro valve testing, and whether silicone or a newer polymer results in the optimal valve material remains to be seen. In potentially complementary work, tissue-engineered valves have reached the stage of successful animal implantation, though serious questions regarding durability persist,” concluded the researchers. “Whether polymeric valve stent struts or valve leaflets such as these can supplement tissue-engineered valves remains to be seen.

“The field of polymeric and tissue-engineered heart valves has long been a promising one. The known limitations of current bioprosthetic and mechanical valves have inspired extensive research with these alternatives, but the impressive science behind them remains at the level of the benchtop and animal testing.”

Manufacturing Workflow of Bioinspired Synthetic Valves(A) Aortic root is imaged by CT and converted to a digital mesh.(B) Two mandrels are created: one representing the inner surface of the valve, the other matching the measured aortic root.(C) The valve is virtually positioned into the patient’s aortic root anatomy and the leaflets are built up to match the root geometry.(D) The valve mandrel is sprayed with a soft silicone ink to create the actual leaflets.(E) Reinforcement fibers and inter-leaflet triangles are printed using direct ink writing.(F) A temporary cap that matches the aorta geometry is over-molded on the printed valve and a stent-like structure is printed before the cap is removed (Image from ‘Bioinspired Heart Valve Prosthesis Made by Silicone Additive Manufacturing‘)

3D printed implants and medical models and prototypes have lent enormous value to the medical field—and on so many levels—from advantages to patients with more options for specific treatment and better diagnoses, for medical students to practice, and for surgeons to speak with patients and their families and to describe procedures in pre-operative education, along with being able to use the models as surgical planning tools. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Multi-material Additive Manufacturing Process Used for the Fabrication of Customized Silicone Heart Valves(A) After reconstructing the anatomy of the recipient’s aortic root from CT/MRI data, two mandrel supports are designed and 3D printed bystereolithography.(B) The valve-shaped Mandrel I is mounted in the hybrid additive manufacturing setup, whereby thin layers of a soft silicone are sprayed on, generatingthe leaflets.(C) Stiff reinforcement patterns are designed in CAD (computer-aided design) and printed on the sprayed leaflets using a custom-built non-planar 3Dprinter.(D and E) Customized inter-leaflet triangles are printed to enable patient-specific geometries (D). The polymerized printed part (Ei) is combined with thenegative mold of the root-shape Mandrel II (Eii) to allow over-molding of the sacrificial cap (light pink).(F) The combined valve and cast is sprayed with a soft silicone membrane.(G and H) The outer surface shape is measured by laser (G) and finally a hexachiral auxetic pattern is printed over the surface (H).(I) Valve section of the fabricated parts displaying various printed reinforcement patterns.(J) Complete heart valve replacement systems including customized leaflets and synthetic aortic root (Image from ‘Bioinspired Heart Valve Prosthesis Made by Silicone Additive Manufacturing‘)