Filament-free rotating-mandrel-assisted 3D printing of bioresorbable polylactic acid/iron composite stents: Effects of iron content

Poly (lactic acid) (PLA) and iron (Fe) are promising candidates for the development of bioresorbable vascular stents (BVSs). However, PLA stents generally require relatively thick struts to approach the mechanical strength of metallic stents. This study aimed to enhance PLA stents by incorporating Fe microparticles and to develop a direct pellet-based printing route for composite stent fabrication. To date, several studies have demonstrated 3D printing of polymer-based stents, but stent fabrication by screw-based material extrusion (SME) 3D printing remains limited. Therefore, a novel rotating-mandrel-assisted SME (RMA-SME) 3D printer was developed to directly fabricate stents from pellets. Subsequently, PLA/Fe composite stents with different Fe microparticle loadings were printed and systematically investigated. Specifically, their physical properties were characterised by measurements of mass, density, and water contact angle, together with optical microscopy, SEM imaging, XRD, DSC, TGA, and rheological analyses, and mechanical performance was evaluated by parallel radial compression testing, while their cytocompatibility was assessed using cytocompatibility assays. The results revealed that the average radial force increased by 15.7%, from 0.51 N/mm for pure PLA stents to 0.59 N/mm for stents containing 8 wt% Fe, but decreased to 0.46 and 0.43 N/mm when the Fe content increased to 15 wt% and 25 wt% Fe, respectively. SEM revealed that higher Fe contents (15-25 wt%) induced matrix cracking, interfacial voids, and particle agglomeration, which disrupted load transfer and explained the mechanical decline. Importantly, Fe incorporation up to 25 wt% significantly enhanced cell viability compared with pure PLA. To the best of our knowledge, this is the first report of 3D-printed PLA/Fe composite vascular stents, and the results demonstrate that the proposed RMA-SME approach is a feasible strategy for fabricating polymeric stents and potentially other biomedical scaffolds.