2011 IR&D Annual Report

Post-Implantation Analysis of 3D Mg Alloy Scaffolds, 01-R8211

Principal Investigators
XingGuo Cheng
Todd Bredbenner

Inclusive Dates:  03/01/09 – 07/01/11

Background — In response to the clinical need for synthetic scaffolds for bone repair and regeneration, SwRI has recently completed an internal research project to develop multifunctional Mg alloy scaffolds for bone repair and regeneration.  Two types of coated, three-dimensional, wrapped cylindrical AZ31 Mg alloy scaffolds were evaluated in a critical size rabbit ulna defect model.  X-ray radiograph, gross examination and biomechanical testing indicated that significant radio-dense material formed at the bone defect site, resulting in partial to full biomechanical restoration.  The objective of this project is to further investigate the bone repair and regeneration capabilities of the SwRI-designed Mg alloy scaffold.

Approach — To investigate the bone regeneration capabilities, four major tasks have been proposed: 1) ESEM-EDX analysis and mapping of Mg alloy implanted ulna defect, 2) Histology analysis, 3) Image analysis of micro-CT data, and 4) Blood c reactive protein analysis of rabbit serum after implantation by using an enzyme-linked immunosorbent assay (ELISA).

Accomplishments — SEM-EDX analysis of the Mg alloy implant surface indicated that a highly mineralized bone-like organic-inorganic matrix was formed on the surface.  EDX mapping indicates close integration of the Mg alloy degradation product with the bone-like tissue.  Methods were successfully developed and implemented to analyze the spatial distribution of tissue surrounding Mg AZ31 scaffolds in a rabbit ulna defect model.  Two-dimensional analyses of tissue adjacent to scaffolds were quantified, and variation in the three-dimensional structure of the tissue density distributions was qualitatively demonstrated between the scaffold groups.  The CRP protein level after implantation was less than 100 fold, indicating there is no acute-phase inflammatory response of biocompatible Mg alloy implants.  This study confirms the formation of new bone-like matrix due to Mg alloy, suggesting the SwRI-designed Mg alloy bioactive scaffold is promising for bone repair.

Figure 1. (a) SEM image; (b) Optical image of implant; (c) EDX spectrum indicates formation 
			of bone-like matrix; (d) Histology indicates collagen deposition; e) 
			2D tissue distrubtion; f) 3D tissue distribution of 
			radio-dense bone-like tissue in and surrounding Mg alloy scaffold.
Figure 1. (a) SEM image; (b) Optical image of implant; (c) EDX spectrum indicates formation of bone-like matrix; (d) Histology indicates collagen deposition; e) 2D tissue distribution; f) 3D tissue distribution of radio-dense bone-like tissue in and surrounding Mg alloy scaffold.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.
04/15/14