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

Abstract

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 µm (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, µCT 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 mm3). Bone fragments grew into p400 (0.17 ± 0.19 mm3) and p500 (0.36 ± 0.26 mm3), 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 mm2). A better osseointegration of p500 was indicated by significantly more trabecular contacts and a 200 µm 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.

In vivo investigation of open-pored magnesium scaffolds LAE442 with different coatings in an open wedge defect

“…86,87 The alloy LAE442 showed improved osteoconductive properties in a previous study where 500 µm interconnecting pores were used, therefore this pore size was also chosen for the scaffolds in the present study. 21,61 The delayed ingrowth of bone tissue in the present study was also reported by Lalk et al, 20 who found non mineralized bone tissue in the center of porous AX30 cylinders after 24 weeks. However, it must also be noted that the wedge used in the present study was much larger compared to the cylindrical implants, and thus the distance for ingrowing tissue into the scaffold center was much greater.…”

“…The slow degradation of the magnesium alloy LAE442 was also observed on small-sized porous LAE442 cylinders which were investigated in the greater trochanter of the femur in the rabbit model. [21][22][23]60,61 When comparing the coatings in the present study, it was noticed that the wedges coated only with MgF 2 (group 1) showed an overall greater volume loss than the wedges additionally coated with CaP (group 2). This indicates that additional coatings slow down degradation and at the same time gas formation.…”

“…Crack formation was also seen in other in vivo studies of implants or bone substitutes made of LAE442 or Mg all oys. 27,60,61,66,67 According to Mueller et al, 67 cracks occur in magnesium alloys due to gas evolution during degradation.…”

“…The presence of some macrophages and only a few foreign body giant cells in the present study was related to scaffold degradation and removal of corrosion products, as also reported in the literature. 17,19,61 These cells occur physiologically as part of a foreign body reaction in implanted biodegradable materials. 60,89 Blood vessels were detected in the histological examination at all times and their quantity increased over time.…”

Comparison of degradation behavior and osseointegration of 3D powder-printed calcium magnesium phosphate cement scaffolds with alkaline or acid post-treatment

“…Following von Doernberg et al (2006) , the implantation area was divided into three ROIs at ×25 magnification using three rings (IR = inner ring, MR = medial ring, OR = outer ring), with the diameter of the OR ( Ø = 4.24 mm) corresponding to the scaffold diameter ( Figure 1F ). In each ROI, a scoring system modified according to von Doernberg et al (2006) , Kleer-Reiter et al (2021) and Augustin et al (2022) was used to assess in the initial scaffold cross section the percentage area of scaffold material, bone, granulation tissue/bone marrow and resorption zone (cell- and connective tissue-rich annular zone within the scaffold cross section) as well as the percentage of scaffold material enclosed by bone ( Table 4 ). In each ROI, a second scoring system ( Table 4 ) was used to evaluate the ingrowing tissue at cellular level (fibrous cells/tissue, adipocytes, precursor cells, vascularization/blood vessels, macrophages, foreign body cells (FBC), osteoblasts, osteoclasts, osteoid) in a field of view with fixed position at ×100 magnification.…”