MIVT found a way to place HAp (green layers) on stents made of chromium cobalt, stainless steel, and titanium, and make the coating flexible enough to remain intact during stent placement.

The problem surrounding conventional drug-eluting stents (DES) is that restenosis still recurs in about 8% of patients, putting them back at square one. A recent stent coating may solve the problem. To address the limitations, MIV Therapeutics Inc. Atlanta, (mivtherapeutics.com) has developed a DES, VESTAsync, a polymer-free material delivering 60% less drug than currently available DES today. MIVT says results from the first human trial of its drug-eluting stent suggests that it has efficacy of a DES with the safety profile of a bare metal stent, with superior deliverability.

“Results from the recent trials tests were obtained with 60% less drug delivered from a 0.6-micron coating that is entirely polymer-free,” says test-team leader Jose Costa of the Institute Dante Pazzanese of Cardiology in Sao Paulo, Brazil. Conventional coatings are 14 to 15-microns thick.

A close up shows the porosity of HAp. MIVT technology, some licensed from the University of British Columbia, includes a way to coat stents with HAp. The ceramic is brittle, but it can be flexible if it’s thin enough.

The problem with polymer coating is that it effects delicate tissue of blood vessels and causes negative reactions, such as restenosis. “Polymers do two things,” says MIVT President and CTO Mark Landy. “They create excessive inflammation and have to carry more drug than is needed. Even resorbable polymers, which break down into monomers, create issues. The logical step is to remove the polymer and substitute a more biocompatible or naturally occurring material.

MIVT says its thin, ceramic coating protects surrounding tissue from potentially harmful interactions with bare metallic stents. “This coating is derived from hydroxyapatite (Hap), an organic material that has demonstrated excellent in vivo safety and biocompatibility,” says Landy. Hap is porous and makes up bone and the matrix of teeth. Landy say it is widely used as a bone substitute and for coatings on implantable orthopedic, and dental devices.

Conventional Hap however, is brittle and bonds weakly to metal. MIVT says its Hap coating meets the stringent technical requirements for use on cardiovascular stents. “Our drug-eluting stent's ultra thin 600-nm drug coating is only 1/10th the thickness one competitive DES and 1/30th of another,” says Landy.