**Sirolimus-Eluting Electrospun-Produced Matrices as Coatings for Vascular Stents: Dependence of Drug Release on Matrix Structure and Composition of the External Environment**

**Zhanna K. Nazarkina 1,\*,**†**, Boris P. Chelobanov 1,**†**, Vera S. Chernonosova 1,2, Irina V. Romanova 1, Andrey A. Karpenko 2 and Pavel P. Laktionov 1,2**


Received: 19 May 2020; Accepted: 5 June 2020; Published: 12 June 2020

**Abstract:** Although a number of drug-eluting coatings for vascular stents (VSs) have been developed and are in commercial use, more e fficient stent coatings and drug delivery systems are needed. Sirolimus (SRL) is a clinically important drug with antiproliferative and immunosuppressive activities that is widely used for coating stents. Here, we characterized SRL-enriched matrices, intended for coating vascular stents, that were produced by electrospinning (ES) on a drum collector from a solution of polycaprolactone (PCL) and human serum albumin (HSA), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), dimethyl sulfoxide (DMSO), and SRL. The release of tritium-labeled SRL (3H-SRL) from matrices in phosphate-bu ffered saline (PBS) or human blood plasma (BP) was studied. The introduction of DMSO in the ES blend decreased SRL release. The use of BP significantly accelerated SRL release through binding with serum biomolecules. The exchange of PBS or BP after every time point also increased SRL release. The maximum SRL release in BP was observed at 3 days. The matrices produced from the ES solution with DMSO and HSA released no more than 80% SRL after 27 days in BP, even under medium exchange conditions. Therefore, PCL-based matrices containing HSA, SRL, and DMSO can be used for coating VSs with prolonged SRL delivery.

**Keywords:** sirolimus; electrospinning; drug release; polycaprolactone; 3D matrix; drug-eluting stents
