Formation and structure of calcium carbonate thin films and nanofibers precipitated in the presence of poly(allylamine hydrochloride) and magnesium ions

That the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) exerts a significant influence on CaCO₃ precipitation challenges the idea that only anionic additives have this effect. Here, we show that in common with anionic polyelectrolytes such as poly(aspartic acid), PAH supports the growth of calcite thin films and abundant nanofibers. While investigating the formation of these structures, we also perform the first detailed structural analysis of the nanofibers by transmission electron microscopy (TEM) and selected area electron diffraction. The nanofibers are shown to be principally single crystal, with isolated domains of polycrystallinity, and the single crystal structure is even preserved in regions where the nanofibers dramatically change direction. The formation mechanism of the fibers, which are often hundreds of micrometers long, has been the subject of intense speculation. Our results suggest that they form by aggregation of amorphous particles, which are incorporated into the fibers uniquely at their tips, before crystallizing. Extrusion of polymer during crystallization may inhibit particle addition at the fiber walls and result in local variations in the fiber nanostructure. Finally, we investigate the influence of Mg²+ on CaCO₃ precipitation in the presence of PAH, which gives thinner and smoother films, together with fibers with more polycrystalline, granular structures

Our bones : strength, flexibility and…fractals!

The combined hardness and toughness of bone cannot be explained by the mere mixture of proteins and calcium phosphate mineral. To solve this conundrum, a deeper insight into the structure of this remarkable material is required. Using advanced threedimensional nanoscale imaging of the mineral in human bone, we highlighted the importance of its structural organization

Time-Resolved in situ Raman Spectroscopic Observations of a Biomineralization Model System

The mechanisms underlying the formation of nanocrystalline apatite in vertebrate hard tissues (i.e. bones and teeth) remain nebulous. The long-held view of biomineralization via “classical crystallization theory”, or ion-by-ion addition from solution, is challenged by “non-classical” theories in which the pathway proceeds through transient precursor phases [1]. The presence of an amorphous calcium phosphate (ACP) mineral precursor has been observed during the formation of zebrafish fin bones and dental enamel [2, 3]. However, the sample preparation necessary for electron microscopy and ethical considerations inherent to vertebrate samples preclude in situ observations of apatite mineralization

Combining rules and dialogue:exploring stakeholder perspectives on preventing sexual boundary violations in mental health and disability care organizations

BACKGROUND: Sexual boundary violations (SBV) in healthcare are harmful and exploitative sexual transgressions in the professional–client relationship. Persons with mental health issues or intellectual disabilities, especially those living in residential settings, are especially vulnerable to SBV because they often receive long-term intimate care. Promoting good sexual health and preventing SBV in these care contexts is a moral and practical challenge for healthcare organizations. METHODS: We carried out a qualitative interview study with 16 Dutch policy advisors, regulators, healthcare professionals and other relevant experts to explore their perspectives on preventing SBV in mental health and disability care organizations. We used inductive thematic analysis to interpret our data. RESULTS: We found three main themes on how healthcare organizations can prevent SBV in mental health and disability care: (1) setting rules and regulations, (2) engaging in dialogue about sexuality, and (3) addressing systemic and organizational dimensions. CONCLUSION: Our findings suggest that preventing SBV in mental health and disability care organizations necessitates setting suitable rules and regulations and facilitating dialogue about positive aspects of sexuality and intimacy, as well as about boundaries, and inappropriate behaviors or feelings. Combining both further requires organizational policies and practices that promote transparency and reflection, and focus on creating a safe environment. Our findings will help prevent SBV and promote sexual health in mental health and disability care organizations

In situ mechanical and molecular investigations of collagen/apatite biomimetic composites combining Raman spectroscopy and stress-strain analysis

We report the design, fabrication and application of a novel micro-electromechanical device coupled to a confocal Raman microscope that enables in situ molecular investigations of micro-fibers under uniaxial tensile load. This device allows for the mechanical study of micro-fibers with diameters in the range between 10 and 100 lm and lengths of several hundred micrometers. By exerting forces in the mN range, the device enables an important force range to be accessed between that of atomic force microscopy and macroscopic stress-strain measurement devices. The load is varied using a stiffness-calibrated glass micro-needle driven by a piezo-translator during simultaneous Raman microscopy imaging. The method enables experiments probing the molecular response of micro-fibers to external stress. This set-up was applied to biomimetic non-mineralized and mineralized collagen micro-fibers revealing that above 30% mineralization the proline-related Raman band shows a pronounced response to stress, which is not observed in non-mineralized collagen. This molecular response coincides with a strong increase in the Young’s modulus from 0.5 to 6 GPa for 0% and 70% mineralized collagen, respectively. Our results are consistent with a progressive interlocking of the collagen triple-helices by apatite nanocrystals as the degree of mineralization increases

Human glabrous skin contains crystallized urea dendriform structures in the stratum corneum which affect the hydration levels

Glabrous skin is hair-free skin with a high density of sweat glands, which is found on the palms, and soles of mammalians, covered with a thick stratum corneum. Dry hands are often an occupational problem which deserves attention from dermatologists. Urea is found in the skin as a component of the natural moisturizing factor and of sweat. We report the discovery of dendrimer structures of crystalized urea in the stratum corneum of palmar glabrous skin using laser scanning microscopy. The chemical and structural nature of the urea crystallites was investigated in vivo by non-invasive techniques. The relation of crystallization to skin hydration was explored. We analysed the index finger, small finger and tenar palmar area of 18 study participants using noninvasive optical methods, such as laser scanning microscopy, Raman microspectroscopy and two-photon tomography. Skin hydration was measured using corneometry. Crystalline urea structures were found in the stratum corneum of about two-thirds of the participants. Participants with a higher density of crystallized urea structures exhibited a lower skin hydration. The chemical nature and the crystalline structure of the urea were confirmed by Raman microspectroscopy and by second harmonic generated signals in two-photon tomography. The presence of urea dendrimer crystals in the glabrous skin seems to reduce the water binding capacity leading to dry hands. These findings highlight a new direction in understanding the mechanisms leading to dry hands and open opportunities for the development of better moisturizers and hand disinfection products and for diagnostic of dry skin

“On demand” triggered crystallization of CaCO3 from solute precursor species stabilized by the water-in-oil microemulsion

Can we control the crystallization of solid CaCO3 from supersaturated aqueous solutions and thus mimic a natural process predicted to occur in living organisms that produce biominerals? Here we show how we achieved this by confining the reaction between Ca2+ and CO32- ions to the environment of nanosized water cores of water-in-oil microemulsions, in which the reaction between the ions is controlled by the intermicellar exchange processes. Using a combination of in situ small-angle X-ray scattering, high-energy X-ray diffraction, and low-dose liquid-cell scanning transmission electron microscopy, we elucidate how the presence of micellar interfaces leads to the formation of a solute CaCO3 phase/species that can be stabilized for extended periods of time inside micellar water nano-droplets. The nucleation and growth of any solid CaCO3 polymorph, including the amorphous phase, from such nano-droplets is prevented despite the fact that the water cores in the used microemulsion are highly supersaturated with respect to all known calcium carbonate solid phases. On the other hand the presence of the solute CaCO3 phase inside of the water cores decreases the rigidity of the micellar surfactant/water interface, which promotes the aggregation of micelles and the formation of large (>2 μm in diameter) globules. The actual precipitation and crystallization of solid CaCO3 could be triggered “on-demand” through the targeted removal of the organic-inorganic interface and hence the destabilization of globules carrying the CaCO3 solute

Trends in the analysis and monitoring of organotins in the aquatic environment

AbstractOrganotin compounds are toxic and have long-term persistence in the environment. Consequently very low environmental quality standards are set internationally for tributyltin, the major of substance of concern in water. The fulfilment of these regulatory demands has necessitated the development of highly sensitive and selective analytical techniques for the measurement of these compounds. These developments have been coupled with novel extraction and pre-concentration methods that have the potential to be used with automated on-line procedures. Quantification using isotopically enriched tin standards in mass spectrometric-based techniques have allowed for improvements in robustness and precision of analytical methods. In parallel to these laboratory techniques, there have also been enhancements in monitoring methods, particularly the use of passive samplers. This review gives an overview of organotin compounds in the aquatic environment and current trends for their analysis and monitoring within the context of meeting the statutory regulatory environmental standards for tributyltin

The Characteristics and Biological Relevance of Inorganic Amorphous Calcium Carbonate (ACC) Precipitated from Seawater

The importance of amorphous calcium carbonate (ACC) as a precursor phase in the biomineralization of marine calcifiers is increasingly being reported, particularly as the presence of ACC has been observed or inferred in several major groups. Here, we investigate the structure of ACC and the conditions required for its precipitation from seawater-based solutions, with an emphasis on the coinfluence of the carbonate system (pH, dissolved inorganic carbon (DIC) concentration), seawater Mg/Ca ratio, and presence of amino acids. We find that Mg2+ and the presence of aspartic acid, glutamic acid, and glycine strongly inhibit ACC precipitation. Moreover, we were unable to precipitate ACC from seawater with a carbonate chemistry within the range of that thought to characterize the calcification site of certain marine calcifiers (i.e., DIC < 6 mM, pH < 9.3), although substantial modification of the seawater Mg/Ca ratio (Mg/Casw) allowed precipitation at a reduced DIC with the implication that this could be an important component of utilizing an ACC pathway. In addition, the degree to which Mg/Casw and the presence of amino acids influences the structure of ACC and the necessary seawater [CO3 2-] for precipitation is strongly pH dependent. At lower, more biologically relevant pH than that typical of much inorganic work, decreasing Mg/Casw can result in greater long-range order and less water of crystallization but facilitates precipitation at a considerably lower [CO3 2-] than at higher pH