Centre for Musculoskeletal Research, Institute for Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.
Department for Functional Materials in Medicine and Dentistry, University of Würzburg, Pleicherwall 2, D-97070 Würzburg, Germany.
Acta Biomater. 2014 Jul;10(7):3279-87. doi: 10.1016/j.actbio.2014.04.020. Epub 2014 Apr 24.
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.
本研究旨在通过最大限度地提高水泥的凝固程度来避免未反应的富含钙的水泥原料，因为这些原料在溶解后可以直接将 Ca(2+) 输送到水泥基质，同时通过降低孔隙率来减少 Ca(2+) 向凝固水泥基质的扩散，从而防止在 brushite 形成型生物水泥中形成羟磷灰石再沉淀。此外，还测试了一种基于形成镁磷酸盐矿物鸟粪石（MgNH4PO4·6H2O）的生物水泥，由于镁含量高，它应该可以防止低溶解度羟磷灰石再沉淀的形成。通过改变混合水泥的粉末与液体的比例以及材料的植入位置来制造不同孔隙率的水泥，将这些材料植入绵羊的机械性非负重股骨缺损中长达 10 个月。虽然较高孔隙率的 brushite 水泥在 10 个月后定量转化为结晶八钙磷酸盐，从而减缓了水泥的再吸收，但较低孔隙率的 brushite 水泥改性被发现具有化学稳定性，没有再沉淀形成，也没有从植入物表面发生少量水泥再吸收。相比之下，由于缺乏矿物再沉淀，形成鸟粪石的水泥降解得更快，在植入 10 个月后几乎完全降解。
