Effect of pore size on tissue ingrowth and osteoconductivity in biodegradable Mg alloy scaffolds

Magnesium has mechanical properties similar to those of bone and is being considered as a potential bone substitute. In the present study, two different pore sized scaffolds of the Mg alloy LAE442, coated with magnesium fluoride, were compared. The scaffolds had interconnecting pores of either 400 (p400) or 500 mu m (p500). ss-TCP served as control. Ten scaffolds per time group (6, 12, 24, 36 weeks) were implanted in the trochanter major of rabbits. Histological analyses, mu CT scans, and SEM/EDX were performed. The scaffolds showed slow volume decreases (week 36 p400: 9.9%; p500: 7.5%), which were accompanied by uncritical gas releases. In contrast, ss-TCP showed accelerated resorption (78.5%) and significantly more new bone inside (18.19 +/- 1.47 mm(3)). Bone fragments grew into p400 (0.17 +/- 0.19 mm(3)) and p500 (0.36 +/- 0.26 mm(3)), reaching the centrally located pores within p500 more frequently. In particular, p400 displayed a more uneven and progressively larger surface area (week 36 p400: 253.22 +/- 19.44; p500: 219.19 +/- 4.76 mm(2)). A better osseointegration of p500 was indicated by significantly more trabecular contacts and a 200 mu m wide bone matrix being in the process of mineralization and in permanent contact with the scaffold. The number of macrophages and foreign body giant cells were at an acceptable level concerning resorbable biomaterials. In terms of ingrown bone and integrative properties, LAE442 scaffolds could not achieve the results of ss-TCP. In this long-term study, p500 appears to be a biocompatible and more osteoconductive pore size for the Mg alloy LAE442.