An in Situ Atomic Force Microscopy Study of Uric Acid Crystal Growth

Abstract

Kidney stones are heterogeneous polycrystalline aggregates that can consist of several different building blocks. A significant number of human stones contain uric acid crystals as a crystalline component, though the molecular-level growth of this important biomaterial has not been previously well-characterized. In the present study, in situ atomic force microscopy (AFM) is used to investigate the real-time growth on the (100) surface of uric acid (UA) single crystals as a function of fundamental solution parameters. Layer-by-layer growth on UA (100) was found to be initiated at screw dislocation sites and to proceed via highly anisotropic rates which depend on the crystallographic direction. The smallest b-steps exhibited minimum heights corresponding to two molecular layers, while fast-moving c-steps more commonly showed monolayer heights. Growth kinetics measured under a range of flow rates, supersaturation levels, and pH values reveal linear trends in the growth kinetics, with faster growth attained in solutions with higher supersaturation and/or pH. The calculated kinetic parameters for UA growth derived from these experiments are in good agreement with the values reported for other crystal systems.

Faceted crystal shape evolution during dissolution or growth

“…In recent years these spirals have been experimentally measured using AFM. [16][17][18][19] Alternatively, 2-D nuclei can be the source of steps on a crystal surface. These are generally not easily formed at low-super/under saturations; however, at highersuper/under saturations they are often the primary source of steps.…”

The Use of Scanning Probe Microscopy to Investigate Crystal-Fluid Interfaces

“…Quantitative measurements of velocity versus supersaturation are found in the literature for a variety of solution grown crystals including minerals such as calcite [33,34], barite [35,36], hydroxyapatite [37]; optical crystals such as ammonium dihydrogen phosphate (ADP) [38] and potassium dihydrogen phosphate (KDP) [39]; several proteins [40][41][42][43][44]; and organic crystals such as hydrogen bonded tapes [45] and uric acid [46]. Land and De Yoreo tabulate kinetic coefficients for several systems [41] demonstrating that they vary over several orders of magnitude.…”

“…Land and De Yoreo tabulate kinetic coefficients for several systems [41] demonstrating that they vary over several orders of magnitude. The study of velocity versus other solution variables such as ionic strength [47], pH [43,46], and temperature [36,38,48] have also been quantified.…”

Predicting crystal growth by spiral motion

“…It has been nearly 60 years since Burton et al (1951) first published their landmark work, predicting the growth of crystals via a spiral mechanism emanating from a screw dislocation. Since that time, many detailed experiments have observed this mechanism in action for a wide range of crystallizing materials (Yip & Ward 1996;Paloczi et al 1998;Vekilov & Alexander 2000;Sours et al 2005;Ranguelov et al 2006). As a result, the Burton, Cabrera and Frank (BCF) spiral growth mechanism is recognized as the most important modelling tool in the hands of crystal growers.…”