Crystallization of Calcium Carbonate in Alginate and Xanthan Hydrogels

Abstract

Calcium carbonate polymorphs were crystallized in alginate and xanthan hydrogels in which a degree of entanglement was altered by the polysaccharide concentration. Both hydrogels contain functional groups (COOH and OH) attached at diverse proportions on saccharide units. In all systems, the precipitation process was initiated simultaneously with gelation, by the fast mixing of the calcium and carbonate solutions, which contain the polysaccharide molecules at respective concentrations. The initial supersaturation was adjusted to be relatively high in order to ensure the conditions suitable for nucleation of all CaCO 3 polymorphs and amorphous phase(s). In the model systems (no polysaccharide), a mixture of calcite, vaterite and amorphous calcium carbonate initially precipitated, but after short time only calcite remained. In the presence of xanthan hydrogels, precipitation of either, calcite single crystals, porous polyhedral aggregates, or calcite/vaterite mixtures were observed after five days of ageing, because of different degrees of gel entanglement. At the highest xanthan concentrations applied, the vaterite content was significantly higher. In the alginate hydrogels, calcite microcrystalline aggregates, rosette-like and/or stuck-like monocrystals and vaterite/calcite mixtures precipitated as well. Time resolved crystallization experiments performed in alginate hydrogels indicated the initial formation of a mixture of calcite, vaterite and amorphous calcium carbonate, which transformed to calcite after 24 h of ageing.

Porous Alginate Scaffolds Assembled Using Vaterite CaCO3 Crystals

“…Therefore, there was no need to eliminate CaCO 3 crystals in order to form the pores, and even vice versa, the crystals have been kept in the final scaffold architecture. A straightforward approach for the fabrication of composite CaCO 3 -alginate gel materials was first employed nearly one decade ago and has been based on the simultaneous growth of CaCO 3 crystals and gelation of alginate hydrogel [138,139,140,141,142]. In this design, calcium carbonate crystals grow in the presence of the gel and get entrapped inside this polymer matrix.…”

“…), the final distribution of crystals and the macrostructure of the scaffold cannot be controlled since the crystallization of CaCO 3 is a spontaneous and highly sensitive process. In addition, the presence of calcite and sometimes amorphous calcium carbonate has been detected [139]. For some cases, a significant decrease in the size of CaCO 3 crystals resulted in the formation of nano-CaCO 3 that found its application in drug delivery but was not suitable for the fabrication of macro-porous scaffolds [141].…”

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

“…Previous studies suggested that the prismatic shapes of travertine calcite crystals are related to crystalline lattice and growth morphologies being affected by impurities, concentrations of Mg, phosphate or sulphate, high fluid supersaturation with respect to carbonates, and presence of microbial biofilms (Folk et al, 1985; Folk, 1993, 1994; Tracy et al, 1998; Bosak and Newman, 2005; Di Benedetto et al, 2011; Jones and Peng, 2014a; Jones, 2017a). Numerous experimental studies on the precipitation of carbonate crystals confirm that crystal morphology is influenced by the presence of impurities, hydrogels, polymers and various organic molecules (Gower and Tirrell, 1998; Falini et al, 2000; Meldrum and Hyde, 2001; Kato et al, 2002; Cölfen, 2003; Oaki and Imai, 2003; Chekroun et al, 2004; Tong et al, 2004; Bosak and Newman, 2005; Sand et al, 2011; Keller and Plank, 2013; Tobler et al, 2014; Kosanović et al, 2017). Konopacka-Lyskawa et al (2017) showed that calcite crystal morphology changes from scalenohedral to rhombo-scalenohedral elongated crystals and crystal size decreases at increasing organic compound concentrations.…”

Application of Polymers as a Tool in Crystallization—A Review

“…The study gave a better explanation of the influence of silk fibroin concentration and its structure on CaCO 3 crystals’ growth. Nindiyasari et al investigated the influence of the porosity of the growth medium on the crystallization of CaCO 3 in hydrogels with different gelatin solid contents [ 14 ], whereas Kosanović et al crystallized CaCO 3 polymorphs in alginate and xanthan hydrogels in which the degree of entanglement was altered by the polysaccharide concentration [ 15 ]. Crystallization experiments performed in alginate hydrogels indicated the initial formation of a mixture of calcite, vaterite and amorphous CaCO 3 .…”