Stereocomplex formation in AB di-block copolymers of poly(ε-caprolactone) (A) and poly(lactide) (B)

The thermal properties of two series of AB di-block copolymers of poly(ε-caprolactone) (A) and poly(lactide) (B) and their blends were studied. Each series contained poly(lactide) blocks of opposite chirality. The length of the poly(ε-caprolactone) blocks was not varied (DP = 70), whereas the poly(lactide) blocks were of varying length (DP = 5 - 80). Blends of polymers containing blocks of opposite chirality were prepared by mixing in solution. The melting temperature of the PLA phase was raised by approximately 55 °C in the blends due to stereocomplex formation. The melting temperatures of the crystalline PCL and PLA phases strongly depended on the composition of the block copolymers

Micro-computed tomographic assessment following extremely oversized partial postdilatation of drug-eluting stents

AIMS: To assess the spatial geometry of drug-eluting stents (DES) following extremely oversized proximal postdilatation. Interventions of distal left main (LM) disease generally require stenting across the LM bifurcation with inherent vessel tapering along this segment and a high likelihood of stent malapposition, which can be avoided by such postdilations. METHODS AND RESULTS: Sixteen DES (four 3.5 mm-samples of Cypher Select Plus, Taxus Liberté, Endeavor Resolute, Xience V) were deployed in water; 12 samples were then proximally postdilated with noncompliant 5.0 mm balloons at 18 atm. All samples were examined by micro-computed tomography. Taxus Liberté, Endeavor Resolute, and Xience V, showed increased cell areas in the transitional region (just distal to postdilated region), while Cypher Select showed its largest cells inside the postdilated region. Overall, the largest maximum cell area was observed in Endeavor Resolute, while Cypher Select showed the smallest (p<0.001, for both). In addition, the size of the very proximal postdilated cells was relatively small in most DES except Xience V. CONCLUSIONS: Extremely oversized partial stent postdilatation demonstrated significant between-DES differences in final spatial stent configuration and maximum cell size. These data could be of practical interest with regard to coronary interventions in LM stems with stenting across the LM bifurcation

Scanning electron microscopic assessment of the biodegradable coating on expanded biolimus-eluting stents

AIMS: Biodegradable coatings on drug-eluting stents (DES) may help to avoid adverse long-term effects of DES such as late/very late stent thrombosis which is partly attributed to durable polymers. As the post-expansion morphology of biodegradable coatings is greatly unknown, we investigated the polylactic acid coating on biolimus-eluting BioMatrix stents. METHODS AND RESULTS: Scanning electron microscopy (SEM) was used to carefully examine five 3.5mm stents following expansion at 6-14atm (maximum 7% overstretch). SEM examination demonstrated only mild cracks of the coating after stent expansion at 6 atm. An increase in expansion pressure, associated with mild stent overstretch, resulted in more severe cracks. Lifting of the coating together with few sites of partial detachment of fragments was noticed after stent expansion in water at 14atm; these irregularities further increased after aggressive oversized partial postdilatation with a 5.0mm non-compliant balloon with additional secondary cracks. CONCLUSIONS: SEM assessment suggests a relatively low elasticity of the biodegradable coating on BioMatrix stents. At nominal pressure, stents showed predominantly mild cracks of the coating, while cracks increased after slight overstretch. Aggressive overexpansion of the stent, such as sometimes required in left main bifurcation stenting, worsened cracks and led to some detachment of fragments of the coating in vitro

Coating irregularities of durable polymer-based drug-eluting stents as assessed by scanning electron microscopy

AIMS: To classify and quantify post-expansion irregularities in durable polymer-based coatings of drug-eluting stents (DES). METHODS AND RESULTS: Taxus Liberté, Endeavor Sprint, Endeavor Resolute and Xience V DES (three samples of each) were explored by light microscopy and scanning electron microscopy (SEM) following expansion at 14 atm in water. Incidence and size of irregularities were measured during thorough quantitative examinations of a 360 SEM images. DES types examined showed a significant difference in the incidence of irregularities (p<0.0001; 6.6+/-4.2/image at 60-fold magnification) with typical patterns specific for each DES. All types showed areas with bare metal-aspects, but incidence, shape, and size differed largely: Sprint showed the largest areas. Cracks were only found in Sprint and Resolute, while wrinkles were seen exclusively in Taxus Liberté and Xience V (p<0.0001). The coating of each DES type showed some inhomogeneity of distribution, but the incidence differed (p<0.0001) and was least in Taxus Liberté, which, on the other hand, was the only DES that showed webbing with large bare-metal exposure. CONCLUSIONS: The incidence and size of various coating irregularities on different types of DES varied widely. These data may be considered in ongoing discussions on the differences between DES and may serve as reference to compare novel DES