An apparatus for loading material into a stent strut can comprise a cover sleeve. The cover sleeve is elastic so that it can reduce in diameter so as to press against the stent strut, and expand in diameter so as to be spaced apart from the stent strut. The stent strut can include a lumen into which material is injected. When pressed against the stent strut, the cover sleeve seals side openings to the lumen and prevents injected material from leaking out of the side openings during the injection process.