title: Impact of surface porosity and topography on the mechanical behavior of high strength biomedical polymers.
abstract: The ability to control the surface topography of orthopedic implant materials is desired to improve osseointegration but is often at the expense of mechanical performance in load bearing environments. Here we investigate the effects of surface modifications, roughness and porosity, on the mechanical properties of a set of polymers with diverse chemistry and structure. Both roughness and surface porosity resulted in samples with lower strength, failure strain and fatigue life due to stress concentrations at the surface; however, the decrease in ductility and fatigue strength were greater than the decrease in monotonic strength. The fatigue properties of the injection molded polymers did not correlate with yield strength as would be traditionally observed in metals. Rather, the fatigue properties and the capacity to maintain properties with the introduction of surface porosity correlated with the fracture toughness of the polymers. Polymer structure impacted the materials relative capacity to maintain monotonic and cyclic properties in the face of surface texture and porosity. Generally, amorphous polymers with large ratios of upper to lower yield points demonstrated a more significant drop in ductility and fatigue strength with the introduction of porosity compared to crystalline polymers with smaller ratios in their upper to lower yield strength. The latter materials have more effective dissipation mechanisms to minimize the impact of surface porosity on both monotonic and cyclic damage.
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, J. Erskine Love Building, Atlanta, GA 30332, United States. Electronic address: nevans3@gatech.edu.
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Evans
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, J. Erskine Love Building, Atlanta, GA 30332, United States. Electronic address: cirvin3@gatech.edu.
authors.forename: Cameron W
authors.initials: CW
authors.lastname: Irvin
authors.affiliation: MedShape, Inc., 1575 Northside Drive, NW, Suite 440, Atlanta, GA 30318, United States; Vertera, Inc., 739 Trabert Ave NW, Suite F, Atlanta, GA 30318, United States. Electronic address: david.safranski@medshape.com.
authors.forename: David L
authors.initials: DL
authors.lastname: Safranski
authors.affiliation: Department of Mechanical Engineering and Materials Science, Duke University, Box 90300 Hudson Hall, Durham, NC 27708-0287, United States. Electronic address: ken.gall@duke.edu.
authors.forename: Ken
authors.initials: K
authors.lastname: Gall
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D008422:Materials Testing; D016348:Osseointegration; D011108:Polymers / Q000737:chemistry*; D016062:Porosity; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: D001672:Biocompatible Materials; D011108:Polymers
keywords: Notch; Osseointegration; Polyetheretherketone; Surface porous; Topography