Dominic Walsh

Microstructure, mechanical, and biomimetic properties of fish scales from Pagrus major

The fish scale of Pagrus major has an orthogonal plywood structure of stratified lamellae, 1-2 microm in thickness, consisting of closely packed 70- to 80-nm-diameter collagen fibers. X-ray diffraction, energy-dispersive X-ray analysis, and infrared spectroscopy indicate that the mineral phase in the scale is calcium-deficient hydroxyapatite containing a small amount of sodium and magnesium ions, as well as carbonate anions in phosphate sites of the apatite lattice. The tensile strength of the scale is high (approximately 90 MPa) because of the hierarchically ordered structure of mineralized collagen fibers. Mechanical failure occurs by sliding of the lamellae and associated pulling out and fracture of the collagen fibers. In contrast, demineralized scales have significantly lower tensile strength (36 MPa), indicating that interactions between the apatite crystals and collagen fibers are of fundamental importance in determining the mechanical properties. Thermal treatment of fish scales to remove the organic components produces remarkable inorganic replicas of the native orthogonal plywood structure of the fibrillary plate. The biomimetic replica produced by heating to 873 K consists of stratified porous lamellae of c-axis-aligned apatite crystals that are long, narrow plates, 0.5-0.6 microm in length and 0.1-0.2 microm in width. The textured inorganic material remains intact when heated to 1473 K, although the size of the constituent crystals increases as a result of thermal sintering.

Crystal Tectonics: Construction of Reticulated Calcium Phosphate Frameworks in Bicontinuous Reverse Microemulsions

The chemical construction of organized architectures is an important aspect of innovative materials synthesis. Bicontinuous water-filled microemulsions can be used as preorganized systems for the fabrication of crystalline calcium phosphate materials with extended reticulated microstructures. These macroporous materials are formed by mineralization reactions located within the interconnecting water channels of the bicontinuous network. The resulting materials represent replicas of the microemulsion architecture, but the pore sizes are incommensurate, suggesting that secondary modifications in the bicontinuous microstructure occur during crystal growth. Synthetic macroporous calcium phosphates could have uses in biomaterial implants.

Influence of monosaccharides and related molecules on the morphology of hydroxyapatite

The influence of monosaccharides and related molecules on the crystal morphology of hydroxyapatite (HAP) precipitated from chloride-containing supersaturated solutions has been studied by transmission electron microscopy. Pulse addition of aliquots of CaCl2 to Na2HPO4 solutions resulted in the formation of plate-like HAP crystals. In contrast, the presence of the monosaccharides D-glucose, D-galactose, D-mannose, glucuronic acid, N-acetyl glucosamine and D-fructose (phosphate:additive = 6:1) induced the precipitation of needle-shaped HAP crystals elongated along the c-axis. Other molecules, such as sorbitol and 1,2-butanediol, also showed this morphological effect. The order of decreasing aspect ratios was; sorbitol = 1,2-butanediol (25:1)> fructose (20:1)> glucose = galactose = mannose = glucuronic acid = N-acetyl glucosamine (10:1). Expression of the needle-like morphology is discussed in terms of kinetic factors involving nucleation and growth. The former is dependent on the exclusion of Cl- from HAP nuclei due to additive interactions with an amorphous calcium phosphate precursor phase. The latter is related to the strength of additive binding with the subsequent development of {100} HAP crystal faces.

Stimulation of human bone marrow stromal cells using growth factor encapsulated calcium carbonate porous microspheres

The fabrication of self-assembling biomineral-related complexes for cell growth and gene/biomolecule delivery offers important opportunities for skeletal repair. In this work, 5–30 µm-sized calcium carbonate (vaterite) spheroids with elaborate sponge-like macroporous architectures were prepared by passive evaporation of water-in-oil microemulsions, and investigated as potential vehicles for the delivery of skeletal growth factors to human bone marrow stromal cells maintained in culture. The spheroids spontaneously form within dispersed droplets of supersaturated calcium bicarbonate, and become patterned in situ by entrapped micro-bubbles of carbon dioxide. Water-soluble biomolecules such as proteins (collagen type I, haemoglobin), cell growth factors (dexamethasone, pleiotrophin), bone morphogenetic proteins (rhBMP-2, SaOS ‘retentate’), and plasmid DNA were incorporated into the microspheres during synthesis or by soaking pre-washed spheroids. Primary human bone marrow stromal cells labelled with cell tracker green and ethidium homodimer-1 or transfected with an adenoviral vector expressing green fluorescent protein were co-cultured with the vaterite microspheres over three weeks without loss of function and viability. At three weeks, microspheres were encapsulated and integrated with the human bone marrow stromal cells. Histological analysis confirmed the expression of alkaline phosphatase, synthesis of extracellular matrix, and capacity for extensive mineralization. Use of vaterite microspheres to adsorb and deliver active growth factors such as pleiotrophin and an admixture of bone morphogenetic proteins derived from an osteosarcoma (SaOS ‘retentate’) was demonstrated using human bone marrow stromal cells. Ex vivo chorioallantoic membrane culture of pelleted vaterite spheres and human bone marrow cells placed into a chick femur defect resulted in the secretion of an organised collagen matrix. Vaterite spheres containing bioactive proteins induced osteogenesis in promyoblast C2C12 cells. These studies demonstrate the development of facile techniques for the generation of inorganic scaffolds constructed from porous microspheres that are biocompatible, aid mineralization, and offer potential for growth factor delivery through entrapment of functional biomolecules.

Preparation of a bone-like apatite foam cement.

The preparation of a porous bone-like calcium deficient apatite implant material was investigated. A novel cement system composed of an equimolar mixture of Ca4(PO4)2O, Ca(H2PO4)2{H2O, and CaCO3 was used. At a liquid/powder ratio of 0.83 ml/g low density open framework foam cements were formed due to the rapid evolution of CO2. The initial product of the reactants was CaHPO4{2H2O which then reacted with Ca4(PO4)2O, forming a calcium deficient carbonated apatite, upon soaking of the cement blocks in SBF. Foam-like cements were composed of a plate-like apatite due to epitaxial overgrowth and conversion of the brushite plate precursor. Cylinders of the foam cement were reinforced with an outer layer of a solid apatite cement to form a material suitable for application as a bone-section implant.

Synthesis of tri-calcium phosphate sponges by interfacial deposition and thermal transformation of self-supporting calcium phosphate films

Porous films of β- or α-tri-calcium phosphate (TCP) were prepared by thermal transformation at 1000 °C or 1200 °C, respectively, of thin calcium phosphate/calcium carbonate precursor films precipitated at the air/water interface of a supersaturated carbonic acid solution containing 60 ppm sodium polyaspartate and a [PO43−] : [CO32−] ratio of ca. 2 : 1. The β-Ca3(PO4)2 and α-Ca3(PO4)2 films were typically 10 µm in thickness, consisted of sponge-like interiors with 0.5–1 µm sized macropores, and exhibited surface areas of 10 and 12 m2 g−1 respectively. The thickness and morphology of the TCP flakes were related to the time-dependent structure of the self-supporting composite precursor films, which ranged from highly porous 2-D networks to densely packed agglomerates. Similar films consisting only of calcium phosphate, as well as calcium carbonate films of more complex architecture and up to 150 µm in thickness, were also prepared by polyaspartate-mediated controlled crystallization at the air/water interface. The novel combination of carbonic acid solution and bulk-precipitation inhibitor is described in the preparation of porous minerals that have potential applications as supports for catalysts, for drug delivery, protein adsorption and release, or as bone implant materials.

Data set for: Mo-doped TiO2 photoanodes using [Ti4Mo2O8(OEt)10]2 bimetallic oxo cages as a single source precursor

The data provided in this data set includes all the raw data collected during the characterization of Mo:TiO2 films: raw data of X-Ray photoelectron spectroscopy (XPS), Electrochemically active surface area (ECSA), X-Ray Diffraction, Raman spectroscopy, Electron Paramagnetic Resonance (EPR), UV-Vis spectroscopy, Photocurrent–Potential curves (J-V), Photocurrent–Time (J-t), Nyquist plots, IPCE (Incident photon-to-current efficiency) and Faradaic efficiency.

Synthesis of Well-Defined, Surfactant-Free Co3O4 Nanoparticles: The Impact of Size and Manganese Promotion on Co3O4 Reduction and Water Oxidation Activity

AbstractA surfactant-free synthetic route has been developed to produce size-controlled, cube-like cobalt oxide nanoparticles of three different sizes in high yields. It was found that by using sodium nitrite as salt-mediating agent, near-quantitative yields could be obtained. The size of the nanoparticles could be altered from 11 to 22xa0nm by changing the cobalt concentration and reaction time. These surfactant-free nanoparticles form ideal substrates for facile deposition of further elements such as manganese. The effect of size of the cobalt oxide nanoparticles and the presence of manganese on the reducibility of cobalt oxide to metallic cobalt was investigated. Similarly, the effect of these parameters was investigated with a visible light promoted water oxidation system with cobalt oxide as catalyst, together with [Ru(bpy)3]2+ light harvester dye and an electron acceptor.Graphical AbstractA novel surfactant-free synthetic route has been developed to produce size-controlled, cube shaped cobalt oxide nanoparticles in high yields.n