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

Abstract

Due to the positive effects of magnesium substitution on the mechanical properties and the degradation rate of the clinically well-established calcium phosphate cements (CPCs), calcium magnesium phosphate cements (CMPCs) are increasingly being researched as bone substitutes. A post-treatment alters the materials’ physical properties and chemical composition, reinforcing the structure and modifying the degradation rate. By alkaline post-treatment with diammonium hydrogen phosphate (DAHP, (NH4)2HPO4), the precipitation product struvite is formed, while post-treatment with an acidic phosphate solution [e.g., phosphoric acid (PA, H3PO4)] results in precipitation of newberyite and brushite. However, little research has yet been conducted on newberyite as a bone substitute and PA post-treatment of CMPCs has not been described in the accessible literature so far. Therefore, in the present study, the influence of an alkaline (DAHP) or acid (PA) post-treatment on the biocompatibility, degradation behavior, and osseointegration of cylindrical scaffolds (h = 5.1 mm, Ø = 4.2 mm) produced from the ceramic cement powder Ca0.75Mg2.25(PO4)2 by the advantageous manufacturing technique of three-dimensional (3D) powder printing was investigated in vivo. Scaffolds of the material groups Mg225d (DAHP post-treatment) and Mg225p (PA post-treatment) were implanted into the cancellous part of the lateral femoral condyles in rabbits. They were evaluated up to 24 weeks by regular clinical, X-ray, micro-computed tomographic (µCT), and histological examinations as well as scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis and compared with tricalcium phosphate (TCP). All materials showed excellent biocompatibility and rapid osseointegration. While TCP degraded only slightly, the CMPCs showed almost complete degradation. Mg225d demonstrated significantly faster loss of form and demarcability from surrounding bone, scaffold volume reduction, and significantly greater degradation on the side towards the bone marrow than to the cortex than Mg225p. Simultaneously, numerous bone trabeculae have grown into the implantation site. While these were mostly located on the side towards the cortex in Mg225d, they were more evenly distributed in Mg225p and showed almost the same structural characteristics as physiological bone after 24 weeks in Mg225p. Based on these results, the acid post-treated 3D powder-printed Mg225p is a promising degradable bone substitute that should be further investigated.

Physicochemical degradation of calcium magnesium phosphate (stanfieldite) based bone replacement materials and the effect on their cytocompatibility

“…1.6.5, Thermo Fisher Scientific Inc., Waltham, USA). The porosity of Ca3, Mg225A, and Mg225B has been published elsewhere [26] and was (42.1 ± 0.8) % for Ca3, (26.9 ± 3.0) % for Mg225A, and (27.9 ± 1.7) % for Mg225B.…”

“…The lowest porosity was measured for Mg275A, which was (13.1 ± 3.4) %. The porosity of Ca3 was (42.1 ± 0.8) % [26] and thus significantly higher compared to CMPs.…”

“…The highest compressive strength ((16.8 ± 4.8) MPa) was determined for Mg225A, followed by Mg275A ((12.6 ± 1.7) MPa), Mg275B ((11.7 ± 2.5) MPa), and Mg225B ((10.5 ± 2.3) MPa). CMPs showed porosities of (26.9 ± 3.0) % for Mg225A [26], (27.9 ± 1.7) % for Mg225B [26], and (21.1 ± 5.2) % for Mg275B (figure 4(b)). The lowest porosity was measured for Mg275A, which was (13.1 ± 3.4) %.…”

In Vivo Investigation of 3D-Printed Calcium Magnesium Phosphate Wedges in Partial Load Defects

“…So far, however, there is little research on the in vivo investigation of CMPCs. They have already been investigated in smaller, unloaded defect models, in which excellent biocompatibility, rapid degradation behavior and good osseointegration were observed [21,23,24].…”

“…In addition, 3D powder-printed scaffolds offer a high microporosity that promotes the ingrowth of vessels, cells and nutrients by facilitating diffusion into the scaffold, which has a positive effect on osteogenesis [27,30]. The production method is suitable for processing bone substitutes based on CPCs, MPCs or CMPCs, which have shown excellent biocompatibility, favorable degradation behavior and osteoconductivity both in vitro [27,29,31] and in vivo [23,24].…”