Synthesis and structural elucidation of tricalcium silicate biomaterials

三鈣矽酸鹽（Tricalcium silicate, C3S）屬於生醫陶瓷材料的一種，是目前常見牙髓填補材料MTA之主要成分，由於其操作性質優異，生物活性及生物相容性佳，被視為極具潛力的新興生醫材料。在製備三鈣矽酸鹽的過程中，需在1400 degreeC，晶相為三斜晶系（triclinic），雖含少量二鈣矽酸鹽（C2S）和氧化鈣（CaO），但純度已比傳統固相合成法高出許多；藉由加入1–2 wt%的氟離子，不但在1400 degreeC可以得到幾乎純相的triclinic F-C3S，在1100–1250 degreeC也得到菱形晶系（rhombohedral）F-C3S。氟離子不但降低合成溫度，也有提高產物純度的效果。此外，藉由固態核磁共振的技術，我們發現以沉澱法製備的triclinic F-C3S結晶性極高，相較於rhombohedral F-C3S在29Si譜Q0位置出現一個寬波，triclinic F-C3S的光譜解析度極佳，相同化學位移範圍得到七根半高寬僅0.5 ppm的訊號，此七根訊號可視為九種不等價（nonequivalent）的Si，透過29Si– 29Si DQ/SQ 同核關聯性實驗進一步得到Si與Si之間的距離關係，並搭配晶體結構，最後解出兩種可能的對應關係。 材料的硬化時間（setting time）及微硬度（microhardness）測試方面，triclinic C3S皆比rhombohedral C3S表現出色，且triclinic C3S在加入氟離子後，更使硬化時間縮短一半，微硬度增加一倍以上，材料性質更趨優異。整體來說，加入氟離子對於三鈣矽酸鹽有許多正面效應，使三鈣矽酸鹽在未來能有更好的應用性。Tricalcium silicate (Ca3SiO5, C3S), the main component of mineral trioxide aggregate (MTA), is a potential dental material because of its favorable sealing ability, bioactivity, and biocompatibility. Pure phase of C3S, however, could only be obtained at 1400 degreeC or above. The requirement of high temperature and the poor compressive strength of C3S are undesirable for its clinical applications. Fluoride ions, as a fluxing reagent, can significantly lower the calcination temperature for C3S formation. In this study, C3S are prepared in the presence of NaF by co-precipitation method. By adding 0 to 2 wt% of NaF, different polymorphs of C3S are obtained from 1100 to 1400 degreeC. At 1400 degreeC, the triclinic phase of C3S is the major product, with or without the addition of fluoride. At a temperature of 1100 to 1250 degreeC, the rhombohedral phase of C3S could be obtained by doping 1 to 2 wt% of NaF. In the absence of fluoride ions, however, only dicalcium silicate (C2S) would be formed. In addition to lowering the formation temperature, the setting time and microhardness of C3S can also be improved by the addition of fluorides. The 29Si magic-angle spinning NMR spectra of the rhombohedral C3S show a broad Q0 peak spanning the range from -69 to -75 ppm, whereas there are seven distinct sharp peaks (FWHM ~0.5 ppm) in the same chemical shift range of the Q0 site for the triclinic C3S samples. In other words, the triclinic phase of C3S has significantly higher crystallinity than the rhombohedral phase. Based on a series of 29Si–29Si double-quantum/single-quantum spectra, we have narrowed down the spectral assignments of the resolved seven resonances to two possible scenarios