In this work, calcium oxalate (CaOx) precursors were stabilized by poly(acrylic acid) (PAA) as an additive under in vitro crystallization assays involving the formation of pre-nucleation clusters of CaOx via a non-classical crystallization (NCC) pathway. The in vitro crystallization of CaOx was carried out in the presence of 10, 50 and 100 mg/L PAA by using automatic calcium potentiometric titration experiments at a constant pH of 6.7 at 20 °C. The results confirmed the successful stabilization of amorphous calcium oxalate II and III (ACOII and ACO III) nanoparticles formed after PNC in the presence of PAA and suggest the participation and stabilization of polymer-induced liquid-precursor (PILP) in the presence of PAA. We demonstrated that PAA stabilizes CaOx precursors with size in the range of 20–400 nm. PAA additive plays a key role in the in vitro crystallization of CaOx stabilizing multi-ion complexes in the pre-nucleation stage, thereby delaying the nucleation of ACO nanoparticles. Indeed, PAA additive favors the formation of more hydrated and soluble phase of ACO nanoparticles that are bound by electrostatic interactions to carboxylic acid groups of PAA during the post-nucleation stage. These findings may help to a better understanding of the pathological mineralization resulting in urolithiasis in mammals.

Biominerals fulfill various physiological functions in living organisms, however, pathological mineralization can also occur generating mineral pathologies such as the formation of calcium oxalate (CaOx) calculi in the urinary tract. Inspired by the ability of living organisms to generate biogenic minerals using biological organic matrices, and the need to understand the mechanisms of crystallization, three-dimensional fibrillary meshes based on chitosan fibers with random and controlled topology by electrospinning were manufactured. Chitosan was selected due to its active role on in vitro crystallization and its physicochemical properties, which allows the exposure of their functional chemical groups that could selectively stabilize hydrated crystalline forms of CaOx. CaOx crystals were generated on conductive tin indium oxide (ITO) glass substrates modified with electrospun chitosan fibers by using electrocrystallization (EC) technique. The chitosan fibers and the resulting CaOx crystals were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques, which demonstrated that the chemical nature and topology of the three-dimensional fibers used as organic template are key factors in the control of type, morphology, and crystallographic orientation of CaOx.

Abstract:In our crystallization experiments, the influence of alginate from Chilean Lessonia nigrescens and functionalized multi-walled carbon nanotubes (MWCNTs) was tested through electrocrystallization (EC) and gas diffusion (GD) methods on the crystal growth of calcium carbonate (CaCO 3 ) and their possible stabilization of proto-structures in amorphous CaCO 3 (ACC) state through pre-nucleation clusters (PNC) essays with automatic potentiometric titrations were performed. CaCO 3 crystals obtained in the in vitro above-mentioned crystallization systems were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDS) and powder X-ray diffractometer (XRD). Our experimental findings showed that ALG and functionalized MWCNTs stabilized truncated and agglomerated vaterite-like particles through GD and EC methods. While, on the other hand, we obtained qualitative information about induction or inhibition of CaCO 3 nucleation that was provided by potentiometric titrations.

The electrocrystallization (EC) of calcium oxalate (CaOx) crystals in the presence of multiwalled carbon nanotubes (MWCNTs) functionalized with itaconic acid (IA) and the monoester derivatives monomethylitaconate or mono-octadecylitaconate, which were used as new IA-ester templates supported on indium tin oxide glass substrate as working electrode, was performed by applying a 9 mA current at 37 and 60 °C for 5 min. Under the above EC reaction conditions, a broad variety of CaOx morphologies and crystal forms was found. The morphology control and coexistence of CaOx monohydrate (COM) and CaOx dihydrate was achieved through in vitro EC according to X-ray diffraction spectra. We found that all the functionalized MWCNTs were more efficient inhibitors of CaOx crystallization than the typical citrate model, where MWCNT-IA was the most effective stabilizing template of COM crystals, because carboxylic acid groups of IA moieties in MWCNT-IA would be better Ca 2+ ions binding sites than IA ester groups.