Preparation of hybrid thiol-acrylate emulsion-templated porous polymers by interfacial copolymerization of high internal phase emulsions

Emulsion-templated highly porous polymers (polyHIPEs), containing distinct regions differing in composition, morphology, and/or properties, are prepared by the simultaneous polymerization of two high internal phase emulsions (HIPEs) contained within the same mould. The HIPEs are placed together in the mould and subjected to thiol-acrylate photopolymerization. The resulting polyHIPE material is found to contain two distinct semicircular regions, reflecting the composition of each HIPE. The original interface between the two emulsions becomes a copolymerized band between 100 and 300 μm wide, which is found to be mechanically robust. The separate polyHIPE layers are distinguished from one another by their differing average void diameter, chemical composition, and extent of contraction upon drying.

Graft copolymers of hydroxyethyl cellulose by a ‘grafting to’ method: 15N labelling as a powerful characterisation tool in ‘click’ polymer chemistry

The use of ¹⁵N labeling demonstrates the success of ‘grafting to’ preparation of cellulose graft copolymers by ‘click’ coupling.

The preparation of graft copolymers of cellulose and cellulose derivatives using ATRP under homogeneous reaction conditions

Atom transfer radical polymerisation (ATRP) is used to modify cellulose and cellulose derivatives under homogeneous conditions, yielding novel materials for application in areas such as drug delivery.

Galactose-functionalized polyHIPE scaffolds for use in routine three dimensional culture of mammalian hepatocytes

Three-dimensional (3D) cell culture is regarded as a more physiologically relevant method of growing cells in the laboratory compared to traditional monolayer cultures. Recently, the application of polystyrene-based scaffolds produced using polyHIPE technology (porous polymers derived from high internal phase emulsions) for routine 3D cell culture applications has generated very promising results in terms of improved replication of native cellular function in the laboratory. These materials, which are now available as commercial scaffolds, are superior to many other 3D cell substrates due to their high porosity, controllable morphology, and suitable mechanical strength. However, until now there have been no reports describing the surface-modification of these materials for enhanced cell adhesion and function. This study, therefore, describes the surface functionalization of these materials with galactose, a carbohydrate known to specifically bind to hepatocytes via the asialoglycoprotein receptor (ASGPR), to further improve hepatocyte adhesion and function when growing on the scaffold. We first modify a typical polystyrene-based polyHIPE to produce a cell culture scaffold carrying pendent activated-ester functionality. This was achieved via the incorporation of pentafluorophenyl acrylate (PFPA) into the initial styrene (STY) emulsion, which upon polymerization formed a polyHIPE with a porosity of 92% and an average void diameter of 33 μm. Histological analysis showed that this polyHIPE was a suitable 3D scaffold for hepatocyte cell culture. Galactose-functionalized scaffolds were then prepared by attaching 2'-aminoethyl-β-D-galactopyranoside to this PFPA functionalized polyHIPE via displacement of the labile pentafluorophenyl group, to yield scaffolds with approximately ca. 7-9% surface carbohydrate. Experiments with primary rat hepatocytes showed that cellular albumin synthesis was greatly enhanced during the initial adhesion/settlement period of cells on the galactose-functionalized material, suggesting that the surface carbohydrates are accessible and selective to cells entering the scaffold. This porous polymer scaffold could, therefore, have important application as a 3D scaffold that offers enhanced hepatocyte adhesion and functionality.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

'Multicopy multivalent' glycopolymer-stabilized gold nanoparticles as potential synthetic cancer vaccines

Mucin-related carbohydrates are overexpressed on the surface of cancer cells, providing a disease-specific target for cancer immunotherapy. Here, we describe the design and construction of peptide-free multivalent glycosylated nanoscale constructs as potential synthetic cancer vaccines that generate significant titers of antibodies selective for aberrant mucin glycans. A polymerizable version of the Tn-antigen glycan was prepared and converted into well-defined glycopolymers by Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization. The polymers were then conjugated to gold nanoparticles, yielding 'multicopy-multivalent' nanoscale glycoconjugates. Immunological studies indicated that these nanomaterials generated strong and long-lasting production of antibodies that are selective to the Tn-antigen glycan and cross-reactive toward mucin proteins displaying Tn. The results demonstrate proof-of-concept of a simple and modular approach toward synthetic anticancer vaccines based on multivalent glycosylated nanomaterials without the need for a typical vaccine protein component.

Macrostructuring of emulsion-templated porous polymers by 3D laser patterning

Micro-stereolithography (μSL) is used to produce 3D porous polymer structures by templating high internal phase emulsions. A variety of structures are produced, including lines, squares, grids, and tubes. The porosity matches that of materials produced by conventional photopolymerization.

Evaluating Atmospheric pressure Solids Analysis Probe (ASAP) mass spectrometry for the analysis of low molecular weight synthetic polymers

Atmospheric pressure Solids Analysis Probe (ASAP) mass spectrometry has facilitated the ionisation of oligomers from low molecular weight synthetic polymers, poly(ethylene glycol) (PEG: M(n) = 1430) and poly(styrene) (PS: M(n) = 1770), directly from solids, providing a fast and efficient method of identification. Ion source conditions were evaluated and it was found that the key instrument parameter was the ion source desolvation temperature which, when set to 600 °C was sufficient to vapourise the heavier oligomers for ionisation. PS, a non-polar polymer that is very challenging to analyse by MALDI or ESI without the aid of metal salts to promote cationisation, was ionised promptly by ASAP resulting in the production of radical cations. A small degree of in-source dissociation could be eliminated by control of the instrument ion source voltages. The fragmentation observed through in-source dissociation could be duplicated in a controlled manner through Collision-Induced Dissociation (CID) of the radical cations. PEG, which preferentially ionises through adduction with alkali metal cations in MALDI and ESI, was observed as a protonated molecular ion by ASAP. In-source dissociation could not be eliminated entirely and the fragmentation observed resulted from cleavage of the C-C and C-O backbone bonds, as opposed to only C-O bond cleavage observed from tandem mass spectrometry.

Enzyme-degradable self-assembled hydrogels from polyalanine-modified poly(ethylene glycol) star polymers

The generation of a range of star-shaped block copolymers composed of a biocompatible poly(ethylene glycol) (PEG) core tethered to a polyalanine (PAla) shell that possesses the capability to (reversibly) self-assemble in water is described. The hydrogels formed offer a hydrophilic environment ideal for biological processes involving proteins and are able to withhold albumin for prolonged periods before its triggered release following the targeted material degradation by the proteolytic enzyme elastase. Consequently, the materials formed offer significant promise for the delivery of proteins, and possibly inhibitors, in response to a proteolytic enzyme overexpressed in chronic wounds.

A Nitroxide for Effecting Controlled Nitroxide-Mediated Radical Polymerization at Temperatures ≤90 °C

Factors underlying design of a new nitroxide, 2,2,5-trimethyl-4-tert-butyl-3-azahexane-3-oxyl (TITNO), and its styrene alkoxyamine (Styryl-TITNO) for effecting nitroxide-mediated polymerization (NMP) at temperatures ≤90 °C are described. The rate coefficient, k_d, for thermal dissociation of Styryl-TITNO was determined in the range 70-100 °C, giving Arrhenius parameters A_d = 2.9 × 10¹² s^-1 and E_d = 104.1 kJ mol^-1. Due to the low value of E_d, values of k_d and the activation-deactivation equilibrium constant for NMP of n-butyl acrylate (BA) and styrene are much lower at any given temperature than for alkoxyamines of more established nitroxides. Good control of molecular weight and dispersity, with negligible contributions from termination, is achieved at 90 °C for BA and at 70 °C for styrene, thus, eliminating the complicating contributions from styrene thermal initiation. Hence, TITNO and Styryl-TITNO offer new opportunities for controlled NMP at temperatures much lower than has previously been attainable.

Synthetic polymers for simultaneous bacterial sequestration and quorum sense interference

Double agents: dual-action polymers are able to sequester rapidly the marine organism Vibrio harveyi from suspension, while at the same time quenching bacterial quorum sense (QS) signals. The potency of the polymers is assessed by cell aggregation experiments and competitive binding assays against a QS signal precursor, and their effect on bacterial behavior is shown by means of bioluminescence.

Cellular integration and vascularisation promoted by a resorbable, particulate-leached, cross-linked poly(ε-caprolactone) scaffold

Flexible, strong scaffolds were created by crosslinking PCL with 1,6-hexamethylenediisocyanate, using paraffin beads as a porogen. Particulate leaching generated homogeneous scaffolds with interconnected spherical pores of 5-200 µm. Subcutaneous implantation in rats for 3 months resulted in minimal scaffold resorption and a non-inflammatory regenerative host response, with complete infiltration by alternatively-activated CD68(+) macrophages. In addition, scaffolds were populated extensively along microfractures by a stromal matrix, which was highly vascularised and contained a subset of stromal cells that expressed the anti-inflammatory CD163 antigen. Such microfractures may be an important physical feature for directing stromal integration and vascularisation events.