Design and manufacturing of a new generation of bioresorbable stents by 3D printing.
In the interdisciplinary project Stentprint “Conception and fabrication of a new generation of bioresorbable stents by 3D printing”, led by the iPrint Institute “Bioprinting” research group, additive manufacturing was used for the fabrication of bioresorbable implants in the cardiac field. This project has been funded by the University of Applied Sciences and Arts Western Switzerland and was initiated thanks to a collaboration with the department of Cardiology of the University of Fribourg. Acute coronary syndromes are associated with high morbidity and mortality rates of utmost clinical importance. The resulting high social and economic impact calls for novel therapeutic strategies. The current standard of care is the balloon-expandable, drug-eluting metallic stent.
More than 5 million implantations of coronary stents are performed worldwide each year. However, late stent thrombosis represents an aggravating bane of coronary stenting. The medical and industrial communities have started developing new temporary stents with increased biocompatibility. Consequently, the first fully-bioresorbable drugeluting stent (BRS) was introduced into clinical practice in 2012. The most currently developed BRS are based on polylactide (PLA).
Although PLA permits sufficient artery support, hydrolysis of PLA is associated in vivo with vascular inflammation. Recent data shows increased vascular fragility and questions on PLA security in light of an increased risk of late thrombosis. The search for the next generation of stents focuses on (i) new materials and designs presenting optimal mechanical, biocompatibility and bioresorbability properties and (ii) innovative methods to foster rapid healing or re-endothelialization of injured vessels.
We aimed to provide a proof of concept that manufacturing stents by 3D printing with melt-extrusion (also called fused deposition modelling or FDM) using bioresorbable polymers is possible for the required small dimensions of a stent (coronary scaffold). This funding allowed us to develop and construct a lab-built 3D printing platform for scaffold printing.
We gained experience with this technology, performed first printing tests and manufactured first stent prototypes with poly -caprolactone (PCL) as biomaterial. In addition, different innovative instruments for the fabrication and characterization of the printed scaffolds have been developed and successfully used: a screw melt-microextruder that can work under protective gas / vacuum, a rotational axis for tubular coronary scaffold printing, a strainstress measurement unit for thin polymers fibers and an Iris radial force measurement unit. Our 3D printing platform is located in a biosafety cabinet class II for printing under sterile conditions (clean-room environment).