Adjusting a polymer formulation for an optimal bioresorbable stent: a 6-month follow-up study

AIMS: To assess the impact of the composition in L- and D- of lactic acid stereo copolymers without drug elution on the in situ behaviour of prototype stents in terms of biomechanics and biocompatibility. METHODS AND RESULTS: PLA50, 75, and 92 stereo-copolymer stents (L/D lactic acid ratio from 1 to 11.5) were processed using the injection moulding facilities of Arterial Remodeling Technologies (Noisy le Roi, France). The resulting 3 mm outer diameter tubes having a diameter at the desired nominal size were laser-cut and crimped on regular angioplasty balloons and chemically sterilised prior to implantation in iliac rabbit arteries. Acute recoil was higher in PLA50 and PLA75 stent-treated arteries than in those with PLA92 stents (17.4 ± 11.4 vs. 13.5 ± 7.6 vs. 4.1 ± 3.8 %, respectively, p=0.001). At one month, in-stent area was higher in PLA92 than in PLA50 and PLA75 stented arteries (5.9 ± 0.6 vs. 1.6 ± 1.6 vs. 2.6 ± 3.2 mm², respectively, p<0.001). Re-endothelialisation was complete, and inflammation was mild around the struts, similar among the three stents. Late lumen loss and neointimal area were low and similar in PLA92 stent-treated arteries one and six months after angioplasty (0.2 ± 0.2 vs. 0.3 ± 0.2 mm, p=0.60; 0.5 ± 0.5 vs. 0.5 ± 0.8 mm², p=0.72, respectively). At six months, inflammation decreased compared to one-month follow-up (1.4 ± 0.5 vs. 0.6 ± 0.5, p=0.006). CONCLUSIONS: A stereo-copolymer composition strongly influences biomechanical properties of PLA bioresorbable stents in agreement with what has been known for a long time from other applications, but not biocompatibility. PLA92 stents appeared as presenting acceptable acute deployment and 6-month favourable outcome in the rabbit model despite the absence of drugs.