Confinement and mechanical stiffening behavior of tyrosine-derived polycarbonate thin films

PMSE 78

Khaled A. Aamer, khaled.aamer@nist.gov1, Christopher M. Stafford1, Lee J. Richter, lee.richter@nist.gov2, Joachim Kohn, kohn@biology.rutgers.edu3, and Matthew L. Becker, matthew.becker@nist.gov1. (1) Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899, (2) Surface and Microanalysis Science Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899, (3) New Jersey Center for Biomaterials, Rutgers University, Piscataway, NJ 08854
Amino acid derived desaminotyrosyl tyrosine polycarbonates p(DT)c constitute an important class of biomaterials being used progressively as thin film coatings on next generation biomedical devices including drug-eluting stents.1 Although the interactions in vitro of the implanted p(DT)c coated devices and the bio-environment are mediated by the adsorbed protein layer, the mechanical properties of these polymer thin films play a large role in determining the overall performance of the coatings and/or the device. Recent reports have highlighted mechanical failures in the form of cracking of cardiovascular stents. Our results suggest that assumptions correlating the modulus properties of thin films to the corresponding modulus of the bulk material may be flawed. In this work, the elastic modulus of p(DT)c derived polymer thin films is measured as a function of both composition and thickness. The elastic modulus of polymer thin films composed of ethyl ester p(DT)c polycarbonates, p(DTE)c, the iodinated analog p(I2-DTE)c, Figure 1, and their discrete blends of (25:75, 50:50, 75:25, 90:10) by mass ratio, respectively, were measured by SIEBIMM (strain-induced elastic buckling instability for mechanical measurements) method. The measured elastic moduli were found to increase in both the homopolymer materials and the blends as the thickness of the respective films decreased.