Control of in vivo mineral bone cement degradation.
The current study aimed to prevent the formation of hydroxyapatite reprecipitates in brushite-forming biocements by minimizing the availability of free Ca(2+) ions in the cement matrix. This was achieved by both maximizing the degree of cement setting to avoid unreacted, calcium-rich cement raw materials which can deliver Ca(2+) directly to the cement matrix after dissolution, and by a reduction in porosity to reduce Ca(2+) diffusion into the set cement matrix. In addition, a biocement based on the formation of the magnesium phosphate mineral struvite (MgNH4PO4·6H2O) was tested, which should prevent the formation of low-solubility hydroxyapatite reprecipitates due to the high magnesium content. Different porosity levels were fabricated by altering the powder-to-liquid ratio at which the cements were mixed and the materials were implanted into mechanically unloaded femoral defects in sheep for up to 10 months. While the higher-porosity brushite cement quantitatively transformed into crystalline octacalcium phosphate after 10 months, slowing down cement resorption, a lower-porosity brushite cement modification was found to be chemically stable with the absence of reprecipitate formation and minor cement resorption from the implant surface. In contrast, struvite-forming cements were much more degradable due to the absence of mineral reprecipitates and a nearly quantitative cement degradation was found after 10 months of implantation.
Centre for Musculoskeletal Research, Institute for Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.
Britta
B
Kanter
Department for Functional Materials in Medicine and Dentistry, University of Würzburg, Pleicherwall 2, D-97070 Würzburg, Germany.
Martha
M
Geffers
Centre for Musculoskeletal Research, Institute for Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.
Anita
A
Ignatius
Department for Functional Materials in Medicine and Dentistry, University of Würzburg, Pleicherwall 2, D-97070 Würzburg, Germany. Electronic address: uwe.gbureck@fmz.uni-wuerzburg.de.
Uwe
U
Gbureck
D000818:Animals; D001843:Bone Cements / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D005260:Female; D008855:Microscopy, Electron, Scanning; D012756:Sheep
D001843:Bone Cements; D002118:Calcium
Bone replacement material; Brushite; Calcium magnesium phosphate cement; Hydroxyapatite; Struvite