A Micro-Comb Test System for In Situ Investigation of Infiltration and Crystallization Processes

Abstract

Abstract:The investigation of mineralization and demineralization processes is important for the understanding of many phenomena in daily life. Many crystalline materials are exposed to decay processes, resulting in lesions, cracks, and cavities. Historical artifacts, for example, often composed of calcium carbonate (CaCO 3 ), are damaged by exposure to acid rain or temperature cycles. Another example for lesions in a crystalline material is dental caries, which lead to the loss of dental hard tissue, mainly composed of hydroxyapatite (HAp). The filling of such cavities and lesions, to avoid further mineral loss and enable or support the remineralization, is a major effort in both areas. Nevertheless, the investigation of the filling process of these materials into the cavities is difficult due to the non-transparency and crystallinity of the concerned materials. In order to address this problem, we present a transparent, inexpensive, and reusable test system for the investigation of infiltration and crystallization processes in situ, being able to deliver datasets that could potentially be used for quantitative evaluation of the infiltration process. This was achieved using a UV-lithography-based micro-comb test system (MCTS), combined with self-assembled monolayers (SAMs) to mimic the surface tension/wettability of different materials, like marble, sandstone, or human enamel. Moreover, the potential of this test system is illustrated by infiltration of a CaCO 3 crystallization solution and a hydroxyapatite precursor (HApP) into the MCTS.

Penetration Coefficients of Commercial Nanolimes and a Liquid Mineral Precursor for Pore-Imitating Test Systems—Predictability of Infiltration Behavior

“…A possible solution to the described methodical gap was presented by us in 2017, in the form of an artificial pore-imitating microcomb test system (MCTS) [ 29 ]. It constituted a new example of so-called micromodels which have been utilized extensively in the literature [ 24 , 30 ] and enable the direct visualization of pore-scale processes relevant to different porous media [ 31 , 32 ].…”

“…It constituted a new example of so-called micromodels which have been utilized extensively in the literature [ 24 , 30 ] and enable the direct visualization of pore-scale processes relevant to different porous media [ 31 , 32 ]. Their ability to directly monitor infiltration, drying, and (re)crystallization processes in confined geometries and real time using light microscopy was demonstrated by Gruber and Wolf et al (2017), using an aqueous calcium phosphate crystallization solution [ 29 ]. The imitation of the target material was achieved by tuning the wettability of the device to match hydroxyapatite for dental applications and two calcite-containing rock species for stone conservation.…”

“…The imitation of the target material was achieved by tuning the wettability of the device to match hydroxyapatite for dental applications and two calcite-containing rock species for stone conservation. This was achieved by coating the MCTS with thin layers of chromium and gold combined with a subsequent application of mixed thiol–gold self-assembled monolayers (SAMs) to create more hydrophilic or hydrophobic surfaces [ 29 , 33 , 34 , 35 ]. This system was later used to study the infiltration, drying, and crystallization process of commercial NLs as well as calcium-based complex coacervates (CCs) as a potential novel remineralization solution in pores that were also modified to imitate rock [ 35 ].…”

“…While the MCTS constituted a significant step forward in the efforts to visualize and understand the behavior of liquids in porous materials for stone conservation, it exhibited several issues [ 29 , 35 ]. The most significant of these was the connectivity of the single device parts: not all channels were successfully sealed off tightly.…”

Editorial for Special Issue “Nucleation of Minerals: Precursors, Intermediates and Their Use in Materials Chemistry”

“…Liquid [12] and amorphous mineral precursors can, in principle, be used to fill cavities, which may occur in historical artefacts or dental lesions. Gruber et al [13] present a transparent, inexpensive, and reusable test system for the investigation of infiltration and crystallization processes by using a micro-comb test system. Ossorio et al [14] perform synchrotron-based small-and wide-angle X-ray scattering to examine the precipitation of gypsum from solution, which occur via primary particles that aggregate and transform/re-organize towards the final precipitate, with and without the addition of Mg 2+ and citrate.…”