The Effects of Static and Dynamic Loading on Biodegradable Magnesium Pins In Vitro and In Vivo

Youngmi Koo,Jagannathan Sankar,Nan Huang,Zhongyun Dong,Ruben Kotoka,Hae-Beom Lee,Yeoheung Yun

doi:10.1038/s41598-017-14836-5

Abstract

Here we systematically assess the degradation of biodegradable magnesium pins (as-drawn pure Mg, as-cast Mg-Zn-Mn, and extruded Mg-Zn-Mn) in a bioreactor applying cyclical loading and simulated body fluid (SBF) perfusion. Cyclical mechanical loading and interstitial flow accelerated the overall corrosion rate, leading to loss of mechanical strength. When compared to the in vivo degradation (degradation rate, product formation, uniform or localized pitting, and stress distribution) of the same materials in mouse subcutaneous and dog tibia implant models, we demonstrate that the in vitro model facilitates the analysis of the complex degradation behavior of Mg-based alloys in vivo. This study progresses the development of a suitable in vitro model to examine the effects of mechanical stress and interstitial flow on biodegradable implant materials.

Highlights

Developing a simplified in vitro model that replicates in vivo behavior is critical for the rapid development and clinical application of biodegradable metals
Bioreactor, static immersion, and mouse subcutaneous implantation tests were performed on the three types of Mg-based pins to explore degradation behavior. 2D cross-section and 3D surface morphology micro-CT images were compared in terms of: (1) fluidic flow and (2) mechanical stress (Fig. 2)
The degradation of all Mg pins was accelerated under these conditions, with significant pitting corrosion seen under cyclical loading with interstitial flow

Summary

Introduction

Developing a simplified in vitro model that replicates in vivo behavior is critical for the rapid development and clinical application of biodegradable metals. A feedback-loop testing approach with in vivo and in vitro correlation will enhance our understanding of biodegradable metal degradation. Simulating biodegradable metal-based alloy mechanics and developing a relevant in vitro test bed is necessary to expedite clinical translation of new materials. We report the systematic study of magnesium alloy degradation behavior with a focus on the role of mechanical stress in an interstitial flow perfusion environment. We exploit a bioreactor test bed (cyclical load/ interstitial flow) that mimics the in vivo orthopedic device environment to understand degradation behavior. We systematically compared complete degradation time, effects of stress, and their correlations in vitro and in vivo (mouse subcutaneous and dog tibia implant models)

Methods

Results

Conclusion