Strongly Bound Surface Water Affects the Shape Evolution of Cerium Oxide Nanoparticles

The surface structure and composition of functional materials are well-known to be critically important factors controlling the surface reactivity. However, when doped the surface composition will change, and the challenge is to identify its impact on important surface processes and nanoparticle morphologies. We have begun to address this by using a combination of density functional theory and potential-based methods to investigate the effect of surface dopants on water adsorption and morphology of the technologically important material, CeO$_2$, which finds application as electrolyte in SOFCs, catalyst in soot combustion, and enzyme mimetic agents in biomedicine. We show that by mapping CeO$_2$ surface phase diagrams we can predict nanoparticle morphologies as a function of dopant, temperature, and water partial pressure. Our results show that low-temperature, undoped CeO$_2$ nanocubes with active {100} surface sites are thermodynamically stable, but at the typical high temperature, operating conditions favor polyhedra where {100} surfaces are replaced by less active {111} surfaces by surface ion migration. However, doping with trivalent cations, such as Gd$^{3+}$, will increase binding of water on the {100} surfaces and hence act to preserve the cuboidal architecture by capping the active surfaces. As surfaces tend to be decorated by impurities and dopants it is clear that their role should receive more attention and the approach we describe can be routinely applied to nanomaterials, morphologies, and associated active/inactive surfaces

Regulation of mesenchymal stem cell morphology using hydrogel substrates with tunable topography and photoswitchable stiffness

Cell function can be directly influenced by the mechanical and structural properties of the extracellular environment. In particular, cell morphology and phenotype can be regulated via the modulation of both the stiffness and surface topography of cell culture substrates. Previous studies have highlighted the ability to design cell culture substrates to optimise cell function. Many such examples, however, employ photo-crosslinkable polymers with a terminal stiffness or surface profile. This study presents a system of polyacrylamide hydrogels, where the surface topography can be tailored and the matrix stiffness can be altered in situ with photoirradiation. The process allows for the temporal regulation of the extracellular environment. Specifically, the surface topography can be tailored via reticulation parameters to include creased features with control over the periodicity, length and branching. The matrix stiffness can also be dynamically tuned via exposure to an appropriate dosage and wavelength of light, thus, allowing for the temporal regulation of the extracellular environment. When cultured on the surface of the hydrogels, the morphology and alignment of immortalised human mesenchymal stem cells can be directly influenced through the tailoring of surface creases, while cell size can be altered via changes in matrix stiffness. This system offers a new platform to study cellular mechanosensing and the influence of extracellular cues on cell phenotype and function

Controlling the rheology of gellan gum hydrogels in cell culture conditions

Successful culturing of tissues within polysaccharide hydrogels is reliant upon specific mechanical properties. Namely, the stiffness and elasticity of the gel have been shown to have a profound effect on cell behaviour in 3D cell cultures and correctly tuning these mechanical properties is critical to the success of culture. The usual way of tuning mechanical properties of a hydrogel to suit tissue engineering applications is to change the concentration of polymer or its cross-linking agents. In this study sonication applied at various amplitudes was used to control mechanical properties of gellan gum solutions and gels. This method enables the stiffness and elasticity of gellan gum hydrogels cross-linked with DMEM to be controlled without changing either polymer concentration or cross-linker concentration. Controlling the mechanical behaviour of gellan hydrogels impacted upon the activity of alkaline phosphatase (ALP) in encapsulated MC3T3 pre-osteoblasts. This shows the potential of applying a simple technique to generate hydrogels where tissue-specific mechanical properties can be produced that subsequently influence cell behaviour

Analysis of conserved microRNAs in floral tissues of sexual and apomictic Boechera species

<p>Abstract</p> <p>Background</p> <p>Apomixis or asexual seed formation represents a potentially important agronomic trait whose introduction into crop plants could be an effective way to fix and perpetuate a desirable genotype through successive seed generations. However, the gene regulatory pathways underlying apomixis remain unknown. In particular, the potential function of microRNAs, which are known to play crucial roles in many aspects of plant growth and development, remains to be determined with regards to the switch from sexual to apomictic reproduction.</p> <p>Results</p> <p>Using bioinformatics and microarray validation procedures, 51 miRNA families conserved among angiosperms were identified in <it>Boechera</it>. Microarray assay confirmed 15 of the miRNA families that were identified by bioinformatics techniques. 30 cDNA sequences representing 26 miRNAs could fold back into stable pre-miRNAs. 19 of these pre-miRNAs had miRNAs with <it>Boechera</it>-specific nucleotide substitutions (NSs). Analysis of the Gibbs free energy (ΔG) of these pre-miRNA stem-loops with NSs showed that the <it>Boechera</it>-specific miRNA NSs significantly (p ≤ 0.05) enhance the stability of stem-loops. Furthermore, six transcription factors, the Squamosa promoter binding protein like SPL6, SPL11 and SPL15, Myb domain protein 120 (MYB120), RELATED TO AP2.7 DNA binding (RAP2.7, TOE1 RAP2.7) and TCP family transcription factor 10 (TCP10) were found to be expressed in sexual or apomictic ovules. However, only SPL11 showed differential expression with significant (p ≤ 0.05) up-regulation at the megaspore mother cell (MMC) stage of ovule development in apomictic genotypes.</p> <p>Conclusions</p> <p>This study constitutes the first extensive insight into the conservation and expression of microRNAs in <it>Boechera </it>sexual and apomictic species. The miR156/157 target squamosa promoter binding protein-like 11 (SPL11) was found differentially expressed with significant (p ≤ 0.05) up-regulation at the MMC stage of ovule development in apomictic genotypes. The results also demonstrate that nucleotide changes in mature miRNAs significantly (p ≤ 0.05) enhance the thermodynamic stability of pre-miRNA stem-loops.</p

Structure and dynamics of the pan-genome of Streptococcus pneumoniae and closely related species

Background Streptococcus pneumoniae is one of the most important causes of microbial diseases in humans. The genomes of 44 diverse strains of S. pneumoniae were analyzed and compared with strains of non-pathogenic streptococci of the Mitis group. Results Despite evidence of extensive recombination, the S. pneumoniae phylogenetic tree revealed six major lineages. With the exception of serotype 1, the tree correlated poorly with capsular serotype, geographical site of isolation and disease outcome. The distribution of dispensable genes, genes present in not all, but more than one strain, was consistent with phylogeny, although horizontal gene transfer events attenuated this correlation in the case of ancient lineages. Homologous recombination, involving short stretches of DNA, was the dominant 13 evolutionary process of the core genome of S. pneumoniae. Genetic exchange occurred both within and across the borders of the species, and S. mitis was the main reservoir of genetic diversity of S. pneumoniae. The pan-genome size of S. pneumoniae increased logarithmically with the number of strains and linearly with the number of polymorphic sites of the sampled genomes, suggesting that acquired genes accumulate proportionately to the age of clones. Most genes associated with pathogenicity were shared by all S. pneumoniae strains, but were also present in S. mitis, S. oralis and S. infantis, indicating that these genes are not sufficient to determine virulence. Conclusion Genetic exchange with related species sharing the same ecological niche is the main mechanism of evolution of S. pneumoniae. The open pan genome guarantees the species a quick and economical response to diverse environments

Biopolymers as wound healing materials

Biopolymers are polymers produced from natural sources either chemically synthesized from a biological material or entirely biosynthesized by living organisms. The use of biopolymers from different sources has been investigated for many years for pharmaceutical and biomedical applications. This has resulted in a multitude of healthcare products on the market that use biopolymers in the formulation as a functional excipient or even as an active ingredient. The diverse compositions, tuneable physical behavior, and wide variety from which to choose have fueled the interest in biopolymers. In addition, the relatively low cost of and renewable nature make this class of material particularly attractive to in high-value sectors such as the pharmaceutical and biomedical industries. The most frequently used types of biopolymer in such applications are polysaccharides and proteins, the main focus of this chapter. This chapter intends to provide an overview on the chemical and physical properties of biopolymers used as wound healing materials and how these properties are exploited as dressings

Response to “re: a systematic review and meta-analysis of the association between C-reactive protein and major cardiovascular events in patients with peripheral artery disease”

We appreciate the author’s comments regarding our article. We agree that the studies included in our meta-analysis reported the association between C-reactive protein (CRP) and cardiovascular events using different methods. Hence, we separated studies reporting this association in terms of quantiles of CRP from those reporting in terms of unit increase in CRP