Pore characterization of PM Mg–0.6Ca alloy and its degradation behavior under physiological conditions

Abstract

Several material parameters affect degradation characteristics of Mg and its alloys under physiological conditions. Porous Mg materials are interesting for their simultaneous degradation and drug delivery capabilities. However, an increase in pore surface area is detrimental to both degradation resistance and subsequent mechanical properties. The present work aims at determining the threshold porosity value in Mg–0.6Ca specimens produced by powder metallurgy (PM) below which low degradation rates persist with acceptable mechanical properties. Seven different porous Mg–0.6Ca specimens containing both closed and open pore structures were fabricated with porosities ranging from 3% to 21%. Degradation profiles were obtained via a semi static immersion test over 16 days under physiological conditions using Dulbecco's modified Eagle's medium with Glutamax and 10% fetal bovine serum as supplements. The results are related to morphological pore parameters like pore size distribution, pore interconnectivity and pore curvatures that were quantified using an ex situ µCT analysis. In general, with decreasing porosity a decrease in pore interconnectivity is seen followed by rounding of the pores. Low degradation rates (MDR < 0.3 mm/year) are observed in specimens until 10% porosity, however, the upper bound for reproducible degradation is observed to be in specimens until 12% porosity. This porosity level also marks the transition from closed to open pore nature with a simultaneous change in pore interconnectivity from less than 10% to greater than 95%, below and above this porosity level, respectively. The tensile strength and elongation to failure recorded for specimens with 10% porosity were 70 MPa and 2%, respectively displaying positive traits of both homogenous degradation and mechanical properties. The results suggest that high pore interconnectivity is the dominant factor controlling degradation and mechanical properties in porous Mg-0.6Ca specimens. The results also indicate a good sintering response of Mg-0.6Ca specimens providing further material development towards biomaterial applications.