Covalently-Attached, Surface-Eroding Polymer Coatings on Magnesium Alloys for Corrosion Control and Temporally Varying Support of Cell Adhesion

For degradable magnesium (Mg) alloy-based stents it would be desirable to delay early corrosion to maintain mechanical strength. Similarly, early after stent placement reduced thrombogenicity is an important feature, while chronically, endothelial cell adhesion and vessel integration are desirable. In this study, surface eroding polymers of amino-grafted poly(1,3-trimethylene carbonate) (PTMC-NH2) and PTMC-NH(2)combined with sulfobetaine bearing polymer PSB (PTMC-NHCO-PSB) are developed, and these polymers are covalently attached onto 6-phosphonohexanoic acid (PHA)-coated AZ31 Mg alloy surfaces in sequence. In vitro degradation testing in ovine plasma shows PTMC, PTMC-NH2, and PTMC-NHCO-PSB cast films experience a gradual thickness and mass loss with maintenance of smooth surfaces, confirming surface erosion behavior. The PTMC-NH(2)polymer is firmly bound to the PHA-modified AZ31 surface and demonstrates a resistance to peeling. PTMC, PTMC-NH2, and PTMC-NHCO-PSB coated AZ31 have a lower corrosion rate versus polylactide-co-glycolide coated and untreated AZ31. PTMC-NHCO-PSB coated AZ31 inhibits platelet deposition and smooth muscle cell adhesion and growth, but after 2-week immersion in plasma, this surface supports endothelial cell adhesion and growth. These results suggest PTMC-NHCO-PSB surface eroding coating offers a means of controlling corrosion while providing a temporally varying bio-functionality for biodegradable vascular stent applications.