Emulsion-derived (PolyHIPE) foams for structural materials applications

The simplest type of sandwich composite consists of two, thin, stiff strong sheets of dense material separated by a thick layer of low density material. The first major structure to incorporate sandwich panels was the Second World War "Mosquito aircraft" which consisted of a balsa wood core with plywood faces. The cellular materials used for sandwich core applications can generally be divided into two categories; honeycomb structures and polymer foams. Other cellular cores which exist are balsa wood and corrugated cores. Honeycomb materials generally have a hexagonal cellular shape, and are the core material of choice for advanced composites, In this thesis it was the aim to prepare open-cellular PolyHIPE foam core materials by the polymerisation of the continuous phase of a high internal phase emulsion (HIRE). To assess whether PolyHIPE materials are viable as core materials their flexural, compressive and shear properties were evaluated against the current commercially used core materials. It was shown that it was possible to improve the flexural, compressive and shear properties of a styrene/DVB PolyHIPE material by the addition of fibres to the material and the use of an optimised surfactant system (OSS). It was also shown that by the addition of monomers such as; butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate and methyl methacrylate to the monomer phase that the compressive properties of the S/DVB material could be varied. It was also possible to prepare a fibre-free and fibre-reinforced resorcinol- formaldehyde-based material, which had greater compressive and shear properties compared to the styrene/DVB material. Also a PolyHIPE material containing poly (ϵ-caprolactone) diacrylate showed shape-memory properties and an elongated cell structure after deformation and cooling. This elongated cell structure could lead to possible anisotropic behaviour. Finally it was concluded that the best mechanically performing PolyHIPE materials prepared competed well with the shear and compressive strength of the commercial honeycomb and foam core materials examined

Highly permeable macroporous polymers synthesized from pickering medium and high internal phase emulsion templates

Open porous poly-Plckerlng-M/HIPEs with permeabilities of up to 2.6 D were prepared by polymerisation of PickeringM/HIPEs to which small amounts of surfactant were added. The permeability of these poly-Pickering-M/HIPEs is more than 5 times that of conventional polyHI PEs. This approach allows the synthesis of a novel class of permeable particle reinforced macroporous polymers with significant potential for practical exploitation. (Figure Presented) © 2010 WILEY-VCH VerlagGmbH S.Co. KCaA, Weinheim

Ferulic acid is bound to the primary cell walls of all gymnosperm families

Abstract Unligni"ed primary cell walls containing ester-linked ferulic acid #uoresce blue in ultraviolet radiation which changes to green with increased intensity on treatment with ammonium hydroxide. Using this #uorescence behaviour, we detected ester-linked ferulic acid in the primary cell walls of all 41 species of gymnosperms we examined. These species were in 17 families representing all four extant classes of gymnosperms. In addition, we obtained cell-wall preparations containing '95% primary cell walls from nine gymnosperm species in nine families, representing all four extant classes. These preparations were analysed for ester-linked monomeric phenolic acids. We found ferulic acid (mostly trans) (88-1,561 g/g cell walls) in all of the preparations and p-coumaric acid (mostly trans) (0}106 g/g cell walls) in all except one of them. Ferulic acid ester-linked to primary cell walls has previously been found in angiosperms: in the commelinoid monocotyledons and in the dicotyledon order Caryophyllales, both monophyletic groups. From the present results, we postulate that the extant classes of gymnosperms are monophyletic and no class is sister to the angiosperms

Kiwifruit fermentation drives positive gut microbial and metabolic changes irrespective of initial microbiota composition

It is well established that individuals vary greatly in the composition of their core microbiota. Despite differing ecology, we show here that metabolic capacity converges under the pressure of kiwifruit substrates in a model gut system. The impact of pre-digested green and gold kiwifruit on the human colonic microbiota and their metabolic products was assessed using in vitro, pH-controlled, anaerobic batch culture fermenters. Phylogenetic analyses revealed that bacterial composition changed over time, irrespective of whether a substrate was added or not, indicating a natural adjustment period to the gut model environment. Adding kiwifruit substrate caused additional changes in terms of growth of specific bacterial groups, bacterial diversity and metabolite profiles. Relative abundance of Bacteroides spp. increased with both green and gold kiwifruit substrate while Bifidobacterium spp. increased only with green kiwifruit. NMR spectroscopy and GC demonstrated an increase in organic acids (primarily acetate, butyrate, and propionate) and a concomitant decrease in several amino acids and oligosaccharides following addition of green and gold kiwifruit substrate. The experiments demonstrated that despite markedly different baseline profiles in individual donor inoculum, kiwifruit components can induce substantive change in microbial ecology and metabolism which could have consequences for human health

Polypeptide-grafted macroporous polyHIPE by surface-initiated N-Carboxyanhydride (NCA) polymerization as a platform for bioconjugation

A new class of functional macroporous monoliths from polymerized high internal phase emulsion (polyHIPE) with tunable surface functional groups was developed by direct polypeptide surface grafting. In the first step, amino-functional polyHIPEs were obtained by the addition of 4-vinylbenzyl or 4-vinylbenzylphthalimide to the styrenic emulsion and thermal radical polymerization. The obtained monoliths present the expected open-cell morphology and a high surface area. The incorporated amino group was successfully utilized to initiate the ring-opening polymer- ization of benzyl-L-glutamate N-carboxyanhydride (BLG NCA) and benzyloxycarbonyl-L-lysine (Lys(Z)) NCA, which resulted in a dense homogeneous coating of polypeptides throughout the internal polyHIPE surfaces as confirmed by SEM and FTIR analysis. The amount of polypeptide grafted to the polyHIPE surfaces could be modulated by varying the initial ratio of amino acid NCA to amino-functional polyHIPE. Subsequent removal of the polypeptide protecting groups yielded highly functional polyHIPE-g-poly(glutamic acid) and polyHIPE-g- poly(lysine). Both types of polypeptide-grafted monoliths responded to pH by changes in their hydrohilicity. The possibility to use the high density of function (−COOH or −NH2) for secondary reaction was demonstrated by the successful bioconjugation of enhanced green fluorescent protein (eGFP) and fluorescein isocyanate (FITC) on the polymer 3D-scaffold surface. The amount of eGFP and FITC conjugated to the polypeptide-grafted polyHIPE was significantly higher than to the amino- functional polyHIPE, signifying the advantage of polypeptide grafting to achieve highly functional polyHIPEs

Emulsion Templated Scaffolds with Tunable Mechanical Properties for Bone Tissue Engineering

Polymerised High Internal Phase Emulsions (PolyHIPEs) are manufactured via emulsion templating and exhibit a highly interconnected microporosity. These materials are commonly used as thin membranes for 3D cell culture. This study uses emulsion templating in combination with microstereolithography to fabricate PolyHIPE scaffolds with a tightly controlled and reproducible architecture. This combination of methods produces hierarchical structures, where the microstructural properties can be independently controlled from the scaffold macrostructure. PolyHIPEs were fabricated with varying ratios of two acrylate monomers (2-ethylhexyl acrylate (EHA) and isobornyl acrylate (IBOA)) and varying nominal porosity to tune mechanical properties. Young's modulus, ultimate tensile stress (UTS) and elongation at failure were determined for twenty EHA/IBOA compositions. Moduli ranged from 63.01±9.13 to 0.36±0.04MPa, UTS from 2.03±0.33 to 0.11±0.01MPa and failure strain from 21.86±2.87% to 2.60±0.61%. Selected compositions were fabricated into macro-porous woodpile structures, plasma treated with air or acrylic acid and seeded with human embryonic stem-cell derived mesenchymal progenitor cells (hES-MPs). Confocal and two-photon microscopy confirmed cell proliferation and penetration into the micro- and macro-porous architecture. The scaffolds supported osteogenic differentiation of mesenchymal cells and interestingly, the stiffest IBOA-based scaffolds that were plasma treated with acrylic acid promoted osteogenesis more strongly than the other scaffolds