13-Jun-17 New 3D-printed polymer stent overcomes many of the limitations of conventional nitinol stents for use with tissue-engineered heart valves, offering the potential of use in children, according to an article in 3D Printing and Additive Manufacturing.
Several development trends have paved the way toward this new kind of cardiac stent, for which technology is aligning with the need for minimally invasive implantation techniques for decellularized tissue-engineered heart valves (DTEHV), according to a Dutch study team.
The proof-of-concept study from Eindhoven University of Technology in the Netherlands describes the design and manufacture of a polymer stent with mechanical performance properties similar to that of conventional nitinol stents that have been used for heart-valve implantation in animal trials. The investigators created the computer-designed stents from a commercially available 3D polymer, conducted crush and crimping tests to validate the results predicted by the computational model, and used accelerated hydrolysis to assess degradability in the human body. Computational-based 3D-printed self-expandable and biodegradable polymer stents can be successfully designed, concluded María Sol Cabrera, Bart Sanders and colleagues at Eindhoven.
"By adopting 3D printing as a manufacturing method, we were able to evaluate the crimpability and self-expandability of our stent designs in the lab just a few minutes after completing our simulations," Cabrera wrote in an e-mail. "This allowed us to demonstrate that with a rational computational design, bioabsorbable polymers can be applied to produce strong stents that can ultimately replace the use of metals stents in paediatrics."
About 280,000 patients undergo heart-valve surgery every year, growing annually to an expected one million by 2050, the authors wrote. New DTEHV developments are promising in their capacity to remodel, based on sheep studies, which revealed rapid host-cell repopulation and extracellular matrix production, two indicators of stent-growth potential. Advances in valve development go hand in hand with the need for minimally invasive stent implantation, the team wrote. Limitations of current metal stent technology include a lack of growth capacity, which can lead to long-term complications such as hyperplasia. And bioabsorbable 3D-printed stents would enable clinicians to avoid another round of surgery to remove the implants after the new valve has integrated itself into the heart tissue.
The new polymer stent still lacks a key feature, however. If DTEHVs are to be used in children, they must be able to accommodate growth, which will require the development of new printing materials. Polymers have several other potential benefits, including a low rate of late thrombus formation, and less interference with MRI than metal stents, according to the authors, who are aiming for equivalent performance to nitinol stents used with valve implantation in sheep. A nitinol stent was used to design the polymer stent based on fused deposition modelling (FDM) technology combined with a commercially available thermoplastic copolyester elastomer (TPC). The polymer stent was composed of a repeating design with three rings of 40 struts, connected by tilted bridges. Tensile tests were used to mechanically characterize the TPC and used as input for the computational model. The authors tested FlexiFil (Formfutura), a flexible TPC filament used for FDM applications, and 3D-printed dog bone samples from the same material to assess the production procedure.
The optimization procedure is an iterative process that adjusts the polymer stent geometry to 1) allow crimpability of the stent to a diameter of 12 mm, and 2), obtain a [radial force] RF comparable to that of nitinol stents, Cabrera and colleagues explained. Parameters including width, thickness, and number of struts can be adjusted to modify the response of the polymer stent.
Previous News
Next News
{{comment.DateTimeStampDisplay}}
{{comment.Comments}}