The MiStent coronary drug-eluting stent, an important overseas transformation project of Kossel Medtech, has officially entered the Chinese market with two major advantages of "rapid healing and long-lasting efficacy", providing a new clinical option for PCI surgeries.

This issue will introduce the design story behind the realization of the "long-lasting efficacy" function of the MiStent coronary drug-eluting stent.

1. Encapsulated Sirolimus Crystals

The coating of the MiStent coronary drug-eluting stent is composed of a rapidly bioabsorbable PLGA polymer and sirolimus crystals embedded therein. Sirolimus crystals refer to the close arrangement of individual drug molecules to form a lattice structure, as shown in the figure:

Sirolimus molecules are compressed into a lattice structure

2. Polymer Degradation and Drug Crystal Release

When the PLGA polymer degrades, it softens and detaches from the metal stent platform. Over time, the polymer coating increasingly integrates into the surrounding tissues. The crystalline sirolimus embedded in the polymer also enters the surrounding tissues with it. The PLGA polymer of the MiStent coronary drug-eluting stent completely detaches from the stent within 45 - 60 days and is completely absorbed within 90 days.

3. Dissolution of Drug Crystals and Release of Individual Drug Molecules

For individual sirolimus molecules to interact with receptors in arterial tissues, they must first dissociate from the lattice, then diffuse into the intercellular spaces of tissues, and finally pass through the cell membrane to reach the target cells. This process achieves a slow and continuous drug elution effect, and the efficacy can be maintained for up to 9 months, fully covering the coating degradation time, continuously inhibiting the excessive proliferation of vascular smooth muscle, and minimizing the incidence of in-stent restenosis.

Morphological changes of sirolimus drugs

Sirolimus drug release curve