Tolba Emad, Müller Werner E G, Abd El-Hady Bothaina M, Neufurth Meik, Wurm Frederik, Wang Shunfeng, Schröder Heinz C, Wang Xiaohong
ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany.
J Mater Chem B. 2016 Jan 21;4(3):376-386. doi: 10.1039/c5tb02228b. Epub 2015 Dec 8.
In human bone, amorphous calcium carbonate (ACC) is formed as a precursor of the crystalline carbonated apatite/hydroxyapatite (HA). Here we describe that the metastable ACC phase can be stabilized by inorganic polyphosphate (polyP) that is also used as a phosphate source for the non-enzymatic carbonate/phosphate exchange during HA formation. This polymer was found to suppress the transformation of ACC into crystalline CaCO at a percentage of 5% [w/w] ("CCP5") with respect to CaCO and almost completely at 10% [w/w] ("CCP10"). Both preparations (CaCO/polyP) are amorphous, but also contain small amounts of vaterite, as revealed by XRD, FTIR and SEM analyses. They did not affect the growth/viability of SaOS-2 cells. Cell culture and Ca release experiments revealed that the CaCO particles formed in the presence of polyP (CaCO/polyP) are degradable and, unlike calcite, become disintegrated with time during the cell culture incubation. Again in contrast to calcite, "CCP5" and "CCP10" were found to exhibit osteogenic activity and induce the expression of alkaline phosphatase gene in SaOS-2 cells as well as in human mesenchymal stem cells (MSC). In vivo studies in rats, using PLGA microspheres inserted in the muscles of the back of the animals, revealed that the encapsulated "CCP10" is not only biocompatible but also supports the regeneration at the implant region. We conclude that ACC containing small amounts of vaterite has osteogenic potential and offers superior properties compared to the biologically inert calcite with respect to a potential application as a scaffold material for bone implants.
在人体骨骼中，无定形碳酸钙（ACC）作为结晶碳酸磷灰石/羟基磷灰石（HA）的前体形成。在此我们描述，亚稳态的ACC相可被无机多聚磷酸盐（polyP）稳定，polyP在HA形成过程中还用作非酶促碳酸根/磷酸根交换的磷源。发现这种聚合物在相对于碳酸钙5%[w/w]（“CCP5”）的比例下抑制ACC向结晶碳酸钙的转变，在10%[w/w]（“CCP10”）时几乎完全抑制。XRD、FTIR和SEM分析表明，两种制剂（碳酸钙/多聚磷酸盐）均为无定形，但也含有少量球霰石。它们不影响SaOS-2细胞的生长/活力。细胞培养和钙释放实验表明，在多聚磷酸盐存在下形成的碳酸钙颗粒（碳酸钙/多聚磷酸盐）是可降解的，与方解石不同，在细胞培养孵育过程中会随时间分解。同样与方解石不同，“CCP5”和“CCP10”被发现具有成骨活性，并能诱导SaOS-2细胞以及人间充质干细胞（MSC）中碱性磷酸酶基因的表达。在大鼠体内的研究中，将PLGA微球植入动物背部肌肉，结果表明，包封的“CCP10”不仅具有生物相容性，还能支持植入区域的再生。我们得出结论，含有少量球霰石的ACC具有成骨潜力，与生物惰性的方解石相比，在作为骨植入支架材料的潜在应用方面具有更优越的性能。
