Iryna Polishchuk

Bioinspired passive anti-biofouling surfaces preventing biofilm formation

Biofilm formation enables bacteria to grow under unfavorable conditions, provides them with protection, and increases their resistance to antimicrobial agents. Once a biofilm has formed, it is difficult, and in some systems, impossible to treat. Strategies based on the release of biocidal agents have shown only transient efficiency. Herein, we present a novel bioinspired passive approach to the prevention of surface biofilm attachment by exploiting superhydrophobic surfaces formed via the self-assembly of paraffin or fluorinated wax crystals. Our surfaces show exceptional ability to inhibit biofilm formation of both Gram-positive Bacillus cereus and Gram-negative Pseudomonas aeruginosa over a 7 day period (up to 99.9% inhibition).

Coherently aligned nanoparticles within a biogenic single crystal: A biological prestressing strategy

Many roads to being tough A number of routes exist to increase toughness in both natural and human-made materials—for example, using secondary phases and precipitates or exploiting tailored architectures and shaped crystals. Polishchuk et al. detail the nanoscale internal structure of calcitic microlenses formed by a brittlestar (see the Perspective by Duffy). The segregation of magnesium-rich particles forms a secondary phase that places compressive stresses on the host matrix. This toughening mechanism resembles Guinier-Preston zones known in classical metallurgy. Science, this issue p. 1294 see also p. 1254 Coherent precipitation, known in metal alloys to provide substantial hardening and strengthening, is observed in a biomineral. In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii. This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.

Calcite Single Crystals as Hosts for Atomic‐Scale Entrapment and Slow Release of Drugs

Doxorubicin (DOX)/CaCO3 single crystals act as pH responsive drug carrier. A biomimetic approach demonstrates that calcite single crystals are able, during their growth in the presence of doxorubicin, to entrap drug molecules inside their lattice along specific crystallographic directions. Alterations in lattice dimensions and microstructural parameters are determined by means of high-resolution synchrotron powder diffraction measurements. Confocal microscopy confirms that doxorubicin is uniformly embedded in the crystal and is not simply adsorbed on the crystal surface. A slow release of DOX was obtained preferentially in the proximity of the crystals, targeting cancer cells.

Sponge-associated bacteria mineralize arsenic and barium on intracellular vesicles

Arsenic and barium are ubiquitous environmental toxins that accumulate in higher trophic-level organisms. Whereas metazoans have detoxifying organs to cope with toxic metals, sponges lack organs but harbour a symbiotic microbiome performing various functions. Here we examine the potential roles of microorganisms in arsenic and barium cycles in the sponge Theonella swinhoei, known to accumulate high levels of these metals. We show that a single sponge symbiotic bacterium, Entotheonella sp., constitutes the arsenic- and barium-accumulating entity within the host. These bacteria mineralize both arsenic and barium on intracellular vesicles. Our results indicate that Entotheonella sp. may act as a detoxifying organ for its host.

Synthesis of calcium carbonate in trace water environments

Calcium carbonate (CaCO3) was synthesized from diverse water-free alcohol solutions, resulting in the formation of vaterite and calcite precipitates, or stable particle suspensions, with the dimensions and morphologies depending upon the conditions used. The obtained results shed light on the importance of solvation during crystallization of CaCO3 and open a novel synthetic route for its precipitation in organic solvents.

Additives influence the phase behavior of calcium carbonate solution by a cooperative ion-association process

Amorphous calcium carbonate (ACC) has been widely found in biomineralization, both as a transient precursor and a stable phase, but how organisms accurately control its formation and crystallization pathway remains unclear. Here, we aim to illuminate the role of biologically relevant additives on the phase behaviour of calcium carbonate solution by investigating their effects on the formation of ACC. Results show that divalent cations like magnesium (Mg2+) ions and negatively charged small organic molecules like aspartic acid (Asp) have little/no effect on ACC formation. However, the particle size of ACC is significantly reduced by poly(aspartic acid) (pAsp) with long chain-length, but no effect on the position of the phase boundary for ACC formation was observed. Phosphate (PO4 3-) ions are even more effective in reducing ACC particle size, and shift the phase boundary for ACC formation to lower concentrations. These phenomena can be explained by a cooperative ion-association process where the formation of ACC is only influenced by additives that are able to attract either Ca2+ ions or CO3 2- ions and, more importantly, introduce an additional long range interaction between the CaCO complexes and promote the phase separation process. The findings corroborate with our proposed model of ACC formation via spinodal decomposition and provide a more realistic representation of how biology can direct mineralization processes.

Insights on the interaction of calcein with calcium carbonate and its implications in biomineralization studies

The effects of calcein, a fluorescent marker commonly used to assess mineral growth in calcifying organisms, on calcite and aragonite structure have been investigated. Calcein is entrapped within calcite and aragonite and modifies the shape and morphology of both polymorphs. Moreover, in the presence of Mg2+, it inhibits aragonite formation in favor of magnesium calcite.