Case Study

Bioabsorbable BioMg® In‑Vivo Studies
Small Animal Study – Femoral Implants: BioMg® versus Lactosorb® Bioresorbable Polymer

Brief

Initial small animal in vivo tests on BioMg® have been conducted at the North Carolina State A & T University, under sponsorship of the National Science Foundation. Side-by-side femoral implants of BioMg® with Lactosorb (PLGA-based bioresorbable polymers) were placed in 12 rabbits for time points ranging from 2 weeks to 52 weeks. The goal of this study was to establish that the histological reaction surrounding the BioMg® implant is equivalent to that of the predicate material, in this case PLGA.

The observation of bone encapsulating the BioMg® implants was observed via the Micro CT images taken at the early time points in the study (Figure 3 below).

Implant Position

Figure 1 Orientation of femoral implants in study.

Suture Screw Design

Figure 2 Screws measured 3 mm dia. by 5 mm long for implants; both Magnesium alloy and PLGA were machined to the same geometry.

Images of Implants Over Time

Figure 3 Micro-CT images for BioMg® implants weeks 2, 4, 12 post surgery.

Implant Absorption After One Year

The histology data for the BioMg® samples after 52 week post surgery indicate the implant has experienced approximately 50 volume % absorption over the 52 weeks.

Figure 4 Histology slides for BioMg® implant 52 weeks post surgery.

Integration With New Bone

The implant appears to be encapsulated by new bone structure with a transition layer that has formed between the BioMg® implant and the surrounding new bone structure. By Scanning Electron Microscope (SEM) images and linear scans, the alloying elements were located in a) the residual implant, b) a transition corrosion layer and c) in new bone that encapsulated and replaced the implant. The SEM images for Mg, Ca and P are seen below.

Figure 5 SEM of residual implant after 52 weeks in vivo, with corrosion reaction layer and encapsulating new bone
Figure 6 Magnesium (Mg) Scan – Solid implant
Figure 7 Calcium (Ca) Scan - High in new bone
Figure 8 Phosphorous (P) Scan - High in new bone

Conclusion

These observations support the model of a slow stable surface absorption that occurs over time transforming the core implant to a new transition layer platform upon which new bone structure can connect to and replace over time. The transition layer becomes enriched in Calcium and Phosphorus during the bioabsorption process which is indicative of new bone formation.

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