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Drug Eluting Coronary Stent Coatings

Part 10: Drug Eluting Heart Stent Coatings

Copyright ©1996 American Heart Association

Edelman, E. R. et al. Circulation 1996;94:1199-1202

Angioplasty and Stenting are Competitive ProceduresDivergent processes of vascular repair after balloon angioplasty

and stenting of an atherosclerotic vessel

Divergent processes of vascular repair after balloon angioplasty and stenting of an atherosclerotic vessel. Balloon angioplasty (top) compresses and fractures the atherosclerotic plaque (light gray) and tunica media (black), slightly enlarging the artery. After a few days, a thin layer of platelet-rich thrombus (dark gray) lines the lumen and fills the dissection plane. The lumen shrinks from combined effects of early elastic recoil and later formation of a fibrocellular neointima (speckled area). Stent deployment after angioplasty (bottom) compresses the dissection plane and enlarges the lumen while stretching the artery with minimal elastic recoil. Within hours to days after stenting, caps of thrombus infiltrated with inflammatory cells (dark gray) form over stent struts (black rectangles), particularly abundant at sites of deep injury. Over ensuing weeks, a neointima forms (speckled area), thicker where injury is more severe. Although intimal growth after stenting is greater than after balloon angioplasty, the residual lumen is also larger, as the scaffolding of the stent maintains luminal dimensions. Late changes in arterial size are not depicted because the contribution of remodeling to restenosis after angioplasty or stenting remains incompletely characterized. (Figure prepared by James Squire.)

Edelman, E. R. et al. Circulation 1996;94:1199-1202

Stents scrape blood vessel walls. This injury causes reblockage.

Edelman and Squire

Stents scrape blood vessel walls

Edelman and Squire

Drug Eluting Coated Stent

3.0mm X 2.3mm

420μ X 550μ 300μ X 390μ


A Different Manufacturer’sDrug Eluting Coated Stent

3.0mm X 2.3mm

420μ X 550μ 300μ X 390μ

A Different Manufacturer’sDrug Eluting Coated Stent

IR Spectrum of PC 1036 from Biomaterials 21 (2000) 1847-1859

Phosphatidyl Choline (PC)coating, invented byBiocompatibles, Ltd., usedon some Medtronic andAbbott Drug ElutingCoronary Stents.

Spectra of coatings obtainedoff the actual stent surfacesshow the PC coating and theanti-restenosis drug it elutes.

All drug was extracted fromthe Abbott stent but PCcoating remains.

IR Spectra of pure PC, PC 1036, Medtronic Stent Coating, and Abbott Stent Coating

The Pure PC’s IR shows most of the vibrations present in the PC 1036 coating.

The PC 1036 IR was published back when Biocompatibles, Ltd. was trying to “drum up” big company interest in their materials. [This particular spectrum is slightly distorted (an “enlarged” 1090 vibration) because it is a surface spectrum (obtained via ATR) of a PC polymer in which the hydrophilic PC moieties have been rotated preferentially to the surface by contact with water. The 1090 is the C-O-P stretching vibration.]

The Medtronic (Endeavor™) and Abbott (BiodivYsio™) stent coating spectra were obtained by reflection off the stents’ surfaces.

The stent coatings are excellent matches to the spectrum of PC 1036. Since this is the coating Biocompatibles, Ltd. developed for the BiodivYsio stent, I believe it is the PC coating on the Medtronic and Abbott stents. EDAX can be run using the SEM to see if silicon is detected from the PC 1036 TSMA component. The literature published by Biocompatibles, Ltd. suggests a TSMA content of 3 to 5%. At this loading EDAX should detect the silicon.

Biocompatibles, Ltd. developed the PC-coatedBiodivYsio™ stent and marketed a number of PCpolymers. One of these polymers, PC1036, appearsto be the PC coating on the BiodivYsio stent,now a product of Abbott. It also appears to bethe coating Abbott has licensed to Medtronic forthe Endeavor stent.

PC 1036 is made using the four acrylic monomersshown here.>2-methacryloyloxyethyl phosphorylcholine (MPC)>lauryl methacrylate (LMA)>hydroxypropyl methacrylate (HPMA)>3-trimethoxysilylpropyl methacrylate (TSMA)

MPC supplies the PC functionality to the polymer.LMA helps the polymer adhere to metal surfaces.TSMA makes the polymer crosslinkable, whichimproves its adhesion and cohesion and helps control its rate of drug elution.HPMA is a co-crosslinker that, used with TSMA at 25% loading, gave good mechanical properties.AIBN (azoisobutyronitrile) initiates polymerization.

PC 1036 Biocompatibles, Ltd.

Biocompatibles, Ltd. paper

TSMA Hydrolysis initiates the Crosslinking of the Coating

The Drug Elution Rate is determined mainly by the extent of crosslinking.The hydroxy groups of the HPMA moiety will crosslink with TSMA also.

Biocompatibles, Ltd. paper