Effects of the reinforcement morphology on the fatigue properties of hydroxyapatite reinforced polymers.
The objective of this study was to examine the effects of the hydroxyapatite (HA) reinforcement morphology and content on the fatigue behavior of HA reinforced high density polyethylene (HDPE). To this end, HDPE was reinforced with 20 and 40 vol% of either HA whiskers or an equiaxed HA powder, and tested in four-point bending fatigue under simulated physiological conditions. The fatigue life, mechanical property degradation and failure surfaces were compared between experimental groups. HDPE reinforced with HA whiskers exhibited a four- to five-fold increase (p < 0.001, T-test) in fatigue life compared to an equiaxed powder for either the 20 and 40 vol% reinforcement level. Composites containing 40 vol% HA exhibited decreased fatigue life compared to those with 20 vol% HA for either reinforcement morphology (p < 0.0001, ANOVA). HA whisker reinforced HDPE exhibited less stiffness loss, permanent deformation (creep) and energy dissipation at a given number of cycles compared to HA powder. Thus, HA whisker reinforced HDPE was more tolerant of fatigue damage due to either microcracking or polymer plasticity. Scanning electron microscopy of failure surfaces and surface microcracks showed evidence of toughening by uncracked ligaments, crack tip plasticity, polymer fibril bridging and HA whisker pullout. The results of this study suggest that the use of HA whiskers, in place of HA powder, is a straightforward means to improve the fatigue life and damage tolerance of HA reinforced polymers for synthetic bone substitutes.
Kane
Robert J
RJ
Department of Aerospace and Mechanical Engineering, The University of Notre Dame, Notre Dame, Indiana 46556, USA. rroeder@nd.edu
Converse
Gabriel L
GL
Roeder
Ryan K
RK
D001672:Biocompatible Materials / Q000737:chemistry*; D019245:Compressive Strength; D017886:Durapatite / Q000737:chemistry*; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D020959:Polyethylene / Q000737:chemistry*; D013718:Tensile Strength
D001672:Biocompatible Materials; D020959:Polyethylene; D017886:Durapatite