Significance: Bioresorbable vascular scaffolds (BVSs) are poised to replace permanent metal stents for the treatment of coronary heart disease (CHD), which claims over 7 million lives each year. BVSs support the artery for 6 mo but completely dissolve in 2 y, eliminating serious long-term complications. The first clinically approved BVS is made from a brittle material, poly ( l -lactide) (PLLA), yet it does not fracture during crimping or deployment. We used X-ray microdiffraction to discover multiple, micron-scale morphologies in the crimped BVS, which confer ductility to PLLA and resist fracture upon deployment. Contrary to intuition, the crimping process enhances scaffold strength, a result that researchers should keep in mind when designing thinner scaffolds to make BVSs broadly applicable to CHD.

Significance: The molecular basis of the mysterious ability of the clinically approved bioresorbable vascular scaffold to maintain radial strength after 9 mo of hydrolysis—despite a ∼40% reduction in the poly l -lactide molecular weight Mn —is an unexpected gradient in degradation revealed by X-ray microdiffraction. Hydrolysis is slowest in the 100- × 30-µm region where stress is concentrated during arterial contractions. This favorable gradient in hydrolysis arises from gradients in morphology created during crimping onto the angioplasty balloon: Small regions that undergo elongational deformation (<3% of scaffold) resist hydrolysis after deployment. This remarkably small amount of material (too low to detect in Mn measurements) has a disproportionate impact on strength because it forms precisely where the scaffold is most vulnerable to failure.

Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable vascular scaffolds (BVSs) made from poly l-lactide (PLLA) overcome these complications by supporting the occluded artery for 3–6 months and then being completely resorbed in 2–3 years, leaving behind a healthy artery. The BVS that recently received clinical approval is, however, relatively thick (~150 µm, approximately twice as thick as metal stents ~80 µm). Thinner scaffolds would facilitate implantation and enable treatment of smaller arteries. The key to a thinner scaffold is careful control of the PLLA microstructure during processing to confer greater strength in a thinner profile. However, the rapid time scales of processing (~1 s) defy prediction due to a lack of structural information. Here, we present a custom-designed instrument that connects the strain-field imposed on PLLA during processing to in situ development of microstructure observed using synchrotron X-ray scattering. The connection between deformation, structure and strength enables processing–structure–property relationships to guide the design of thinner yet stronger BVSs.

In photopolymerization systems, “shadow cure” may be defined as polymerization which extends into regions which are not illuminated by the incident initiating light source. The objective of this study is to evaluate the use of fluorescent additives for polymerization in masked regions that are unilluminated by the incident initiating light. Two different fluorescent dyes are investigated: fluorescein (FL) and eosin Y spirit soluble (EYss). A systematic series of studies was performed to characterize the effects of fluorescence intensity, the incident light intensity, and the presence of a diphenyl iodonium salt on the observed degree of shadow cure. It was concluded that shadow cure may be enhanced if one or more fluorescent compounds emit fluorescent light at wavelengths absorbed by the dye in a two- or three-component photoinitiator system. The addition of DPI to the two-component systems containing MDEA and FL or EYss led to a significant enhancement in the observed shadow cure. This result was attributed to the fact that DPI will increase both the number of active centers and the mobility of the active centers as a result of the electron transfer reactions in which it participates.

Poly(L-lactide) (PLLA) is a semicrystalline, biocompatible and biodegradable polymer widely employed in many applications (food packaging, biomedical devices, drug delivery systems). This work deals with nanocomposites of PLLA and tungsten disulfide (WS₂) nanotubes (NTs) as a novel material to obtain thinner and stronger bioresorbable vascular scaffolds. We studied the influence of WS₂ NTs on the mechanical properties of PLLA-WS₂ films. Polarized optical microscopy reveals a high degree of orientation of the polymer molecules in stretched films that further increases with a post-stretching annealing treatment. At the same time, X-ray diffraction (XRD) and Raman spectroscopy confirm enhancement of the crystallinity induced by the WS₂ NTs.