Morphology control in polymerized high internal phase emulsion templated via macro-RAFT agent composition: visualizing surface chemistry

A series of polymerized high internal phase emulsion (polyHIPE) materials have been prepared by using a water in oil emulsion stabilized by a macro-RAFT agent, 2-(butylthiocarbonothioylthio)-2-poly(styrene)-b-poly(acrylic acid), acting as a polymeric surfactant. The pore structures of the formed polyHIPEs were closed. By removing the RAFT-endgroup of the amphiphilic macro-RAFT agent, the obtained polyHIPEs possessed an open structure with voids. The effect of the RAFT-endgroup of the amphiphilic macro-RAFT agent on the surface chemistry of the polyHIPEs is discussed. The obtained polyHIPEs via this surfactant-assisted functionalization strategies were characterized by FTIR spectroscopy, FTIR mapping, SEM, SEM-EDX, TEM, XPS as well as synchrotron-based scanning transmission X-ray microscopy (STXM). The latter technique revealed the surface chemistry of the obtained polyHIPEs and macro-RAFT agent multicomponents with a surface spatial resolution of the order of 30–100 nm.A. Khodabandeh, R. D. Arrua, B. R. Coad, T. Rodemann, T. Ohigashi, N. Kosugi, S. C. Thickett and E. F. Hilde

Robust open cellular porous polymer monoliths made from cured colloidal gels of latex particles

The coagulation of oppositely charged latexes, prepared from the soap-free emulsion polymerisation of styrene using water as the reaction medium, resulted in the obtainment of colloidal gels that were porous in nature and held together by electrostatic interactions. Chemical crosslinking, involving the introduction of a water-soluble crosslinker, resulted in the obtainment of stronger chemical bonds between particles affording a rigid porous material known as a monolith. It was found that, in a simpler approach, these materials could be prepared using a single latex where the addition of ammonium persulfate both resulted in the formation of the colloidal gel and initiated the crosslinking process. The pore size of the resulting monoliths was predictable as this was observed to directly correlate to the particle diameter, with larger pores achieved using particles of increased size. All gels obtained in this work were highly mouldable and retained their shape, which allowed for a range of formats to be easily prepared without the requirement of a mould

Characterization of oligo(acrylic acid)s and their block co-oligomers

Oligo (acrylic acid), oligoAA are important species currently used industrially in the stabilization of paints and also for the production of self-assembled polymer structures which have been shown to have useful applications in analytical separation methods and potentially in drug delivery systems. To properly tailor the synthesis of oligoAA, and its block co-oligomers synthesized by Reversible-Addition Fragmentation chain Transfer (RAFT) polymerization to applications, detailed knowledge about the chemical structure is needed. Commonly used techniques such as Size Exclusion Chromatography (SEC) and Electrospray Ionization-Mass Spectrometry (ESI-MS) suffer from poor resolution and non-quantitative distributions respectively. In this work free solution Capillary Electrophoresis (CE) has been thoroughly investigated as an alternative, allowing for the separation of oligoAA by molar mass and the RAFT agent end group. The method was then extended to block co-oligomers of acrylic acid and styrene. Peak capacities up to 426 were observed for these 1D CE separations, 10 times greater than what has been achieved for Liquid Chromatography (LC) of oligostyrenes. To provide a comprehensive insight into the chemical structure of these materials 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy was used to provide an accurate average chain and reveal the presence of branching. The chain length at which branching is detected was investigated with the results showing a degree of branching of 1 % of the monomer unit in oligoAA with an average chain length of 9 monomer units, which was the shortest chain length at which branching could be detected. This branching is suspected to be a result of both intermolecular and intramolecular transfer reactions. The combination of free solution CE and NMR spectroscopy is shown to provide a near complete elucidation of the chemical structure of oligoAA including the average chain length and branching as well as the chain length and RAFT agent end group distribution. Furthermore, the purity in terms of the dead chains and unreacted RAFT agent was quantified. The use of free solution CE and 1H NMR spectroscopy demonstrated in this work can be routinely applied to oligoelectrolytes and their block co-oligomers to provide an accurate characterization which allows for better design of the materials produced from these oligomers

Review: Synthetic scaffolds to control the biochemical, mechanical, and geometrical environment of stem cell-derived brain organoids

Stem cell-derived brain organoids provide a powerful platform for systematic studies of tissue functional architecture and the development of personalized therapies. Here, we review key advances at the interface of soft matter and stem cell biology on synthetic alternatives to extracellular matrices. We emphasize recent biomaterial-based strategies that have been proven advantageous towards optimizing organoid growth and controlling the geometrical, biomechanical, and biochemical properties of the organoid's three-dimensional environment. We highlight systems that have the potential to increase the translational value of region-specific brain organoid models suitable for different types of manipulations and high-throughput applications

Preparation of inverse polymerized high internal phase emulsions using an amphiphilic macro-RAFT agent as sole stabilizer

Oil-in-water (‘inverse’) High Internal Phase Emulsions (HIPEs) have been prepared using an amphiphilic macro-RAFT agent with toluene as the internal dispersed phase (∼80 vol%) and an aqueous monomer solution as the continuous phase. The water phase consisted of the monomers acrylamide (AM) and N,N′-methylenebisacrylamide (MBAM), an initiator as well as the amphiphilic macro-RAFT agent, that is 2-(butylthiocarbonothioylthio)-2-poly(n-butyl acrylate)-b-poly(acrylic acid), which was used as an anionic polymeric surfactant. The presence of these amphiphilic species allowed the successful preparation of a polyHIPE upon polymerization. The effect of concentration of macro-RAFT agent, pH, initiator, hexadecane as an organic modifier and the polymerization temperature on the morphology of the resulting porous materials was investigated. Varying the lengths of the hydrophilic and hydrophobic blocks of the macro-RAFT agent resulted in polyHIPEs with different porous structures. The presence of RAFT functionality in the polyHIPE was confirmed by elemental analysis, EDX-SEM, Raman and FT-IR spectroscopies. Raman mapping revealed full coverage of the void walls with dithiocarbamate groups

Preparation of highly interconnected hydrophilic polymers from emulsion templates with improved mechanical properties

Highly interconnected hydrophilic polymers were prepared through the polymerisation of (paraffin-oil)-in-water emulsion templates using internal phases below 74 vol%. These were stabilised by Tween 85 and contained acrylamide and N,N/-methylene bisacrylamide, as monomers, in the continuous water phase. The emulsification energy was increased, resulting in increased contact between emulsion droplets, allowing open cellular and highly interconnected structures to be achieved. This was coupled with a reduction in the internal phase volume allowing the obtainment of highly interconnected materials with excellent mechanical properties under compression, producing a Young’s modulus of 490 ± 90 MPa for a material with 36 ± 3% porosity. It was also found that the morphology of these materials could be altered through variations in the internal phase volume, the surfactant level and the emulsification energy. These porous polymers also possessed quite different behaviours in different solvent environments suggesting applications in controlled release or as rigid absorbents