Engaging the Public with Your Research

Effectively communicating science and linking it to the 'real world' has important benefits for both scientists and society. Here we share our experience at Pint of Science, an initiative that encourages researchers to discuss their findings with the public and to engage in conversation in a relaxed setting. We discuss strategies towards organizing a scientific outreach event - big or small - and encourage you to get involved in a science festival near you.

High resolution and dynamic imaging of biopersistence and bioreactivity of extra and intracellular MWNTs exposed to microglial cells

Multi-walled carbon nanotubes (MWNTs) are increasingly being developed both as neuro-therapeutic drug delivery systems to the brain and as neural scaffolds to drive tissue regeneration across lesion sites. MWNTs with different degrees of acid oxidation may have different bioreactivities and propensities to aggregate in the extracellular environment, and both individualised and aggregated MWNTs may be expected to be found in the brain. Before practical application, it is vital to understand how both aggregates and individual MWNTs will interact with local phagocytic immune cells, the microglia, and ultimately to determine their biopersistence in the brain. The processing of extra- and intracellular MWNTs (both pristine and when acid oxidised) by microglia was characterised across multiple length scales by correlating a range of dynamic, quantitative and multi-scale techniques, including: UV-vis spectroscopy, light microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy. Dynamic, live cell imaging revealed the ability of microglia to break apart and internalise micron-sized extracellular agglomerates of acid oxidised MWNTs, but not pristine MWNTs. The total amount of MWNTs internalised by, or strongly bound to, microglia was quantified as a function of time. Neither the significant uptake of oxidised MWNTs, nor the incomplete uptake of pristine MWNTs affected microglial viability, pro-inflammatory cytokine release or nitric oxide production. However, after 24 h exposure to pristine MWNTs, a significant increase in the production of reactive oxygen species was observed. Small aggregates and individualised oxidised MWNTs were present in the cytoplasm and vesicles, including within multilaminar bodies, after 72 h. Some evidence of morphological damage to oxidised MWNT structure was observed including highly disordered graphitic structures, suggesting possible biodegradation. This work demonstrates the utility of dynamic, quantitative and multi-scale techniques in understanding the different cellular processing routes of functionalised nanomaterials. This correlative approach has wide implications for assessing the biopersistence of MWNT aggregates elsewhere in the body, in particular their interaction with macrophages in the lung.

The effect of particle agglomeration on the formation of a surface-connected compartment induced by hydroxyapatite nanoparticles in human monocyte-derived macrophages

Agglomeration dramatically affects many aspects of nanoparticle–cell interactions. Here we show that hydroxyapatite nanoparticles formed large agglomerates in biological medium resulting in extensive particle uptake and dose-dependent cytotoxicity in human macrophages. Particle citration and/or the addition of the dispersant Darvan 7 dramatically reduced mean agglomerate sizes, the amount of particle uptake and concomitantly cytotoxicity. More surprisingly, agglomeration governed the mode of particle uptake. Agglomerates were sequestered within an extensive, interconnected membrane labyrinth open to the extracellular space. In spite of not being truly intracellular, imaging studies suggest particle degradation occurred within this surface-connected compartment (SCC). Agglomerate dispersion prevented the SCC from forming, but did not completely inhibit nanoparticle uptake by other mechanisms. The results of this study could be relevant to understanding particle–cell interactions during developmental mineral deposition, in ectopic calcification in disease, and during application of hydroxyapatite nanoparticle vectors in biomedicine.

Selenium-enhanced electron microscopic imaging of different aggregate forms of a segment of the amyloid β peptide in cells

The aggregation of misfolded proteins is a common feature underlying a wide range of age-related degenerative disorders, including Alzheimer's and Parkinson's diseases. A key aspect of understanding the molecular origins of these conditions is to define the manner in which specific types of protein aggregates influence disease pathogenesis through their interactions with cells. We demonstrate how selenium-enhanced electron microscopy (SE-EM), combined with tomographic reconstruction methods, can be used to image, here at a resolution of 5-10 nm, the interaction with human macrophage cells of amyloid aggregates formed from Aβ(25-36), a fragment of the Aβ peptide whose self-assembly is associated with Alzheimer's disease. We find that prefibrillar aggregates and mature fibrils are distributed into distinct subcellular compartments and undergo varying degrees of morphological change over time, observations that shed new light on the origins of their differential toxicity and the mechanisms of their clearance. In addition, the results show that SE-EM provides a powerful and potentially widely applicable means to define the nature and location of protein assemblies in situ and to provide detailed and specific information about their partitioning and processing.

The sequestration of hydroxyapatite nanoparticles by human monocyte-macrophages in a compartment that allows free diffusion with the extracellular environment

Calcium phosphate and hydroxyapatite nanoparticles are extensively researched for medical applications, including bone implant materials, DNA and SiRNA delivery vectors and slow release vaccines. Elucidating the mechanisms by which cells internalize nanoparticles is fundamental for their long-term exploitation. In this study, we demonstrate that hydrophilic hydroxyapatite nanoparticles are sequestered within a specialized compartment called SCC (surface-connected compartment). This membrane-bound compartment is an elaborate labyrinth-like structure directly connected to the extracellular space. This continuity is demonstrated by in vivo 2-photon microscopy of ionic calcium using both cell-permeable and cell-impermeable dyes and by 3-D reconstructions from serial block-face SEM of fixed cells. Previously, this compartment was thought to be initiated specifically by exposure of macrophages to hydrophobic nanoparticles. However, we show that the SCC can be triggered by a much wider range of nanoparticles. Furthermore, we demonstrate its formation in A549 human lung epithelial cells, which are considerably less phagocytic than macrophages. EDX shows that extensive amounts of hydroxyapatite nanoparticles can be sequestered in this manner. We propose that SCC formation may be a means to remove large amounts of foreign material from the extracellular space, followed by slow degradation, may be to avoid excessive damage to surrounding cells or tissues.

pH-dependent toxicity of high aspect ratio ZnO nanowires in macrophages due to intracellular dissolution

High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl(2). Confocal microscopy on live cells confirmed a rise in intracellular Zn(2+) concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn(2+) rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed.

The mesoporosity of microparticles spray dried from trehalose and nanoparticle hydroxyapatite depends on the ratio of nanoparticles to sugar and nanoparticle surface charge

The ratio of hydroxyapatite (HA) nanoparticles (NP) to trehalose in composite microparticle (MP) vaccine vehicles by determining inter-nanoparticle space potentially influences antigen release. Mercury porosimetry and gas adsorption analysis have been used quantify this space. Larger pores are present in MPs spray dried solely from nanoparticle gel compared with MPs spray dried from nanoparticle colloid which have less inter-nanoparticle volume. This is attributed to tighter nanoparticle packing caused by citrate modification of their surface charge. The pore size distributions (PSD) for MP where the trehalose has been eliminated by combustion generally broaden and shifts to higher values with increasing initial trehalose content. Modal pore size, for gel derived MPs is comparable to modal NP width below 30% initial trehalose content and approximates to modal NP length (approximately 50 nm) at 60% initial trehalose content. For colloidally derived MPs this never exceeds the modal NP width. Pore-sizes are comparable, to surface inter-nanoparticle spacings observed by SEM.

Hydroxyapatite nano and microparticles: correlation of particle properties with cytotoxicity and biostability

Synthetic colloid and gel hydroxyapatite (HA) nanoparticles (NPs) were spray dried to form microparticles (MPs). These are intended for use as slow release vaccine vectors. The physico-chemical properties of gel and colloid NPs and MPs were compared to those of HA obtained commercially. Their cytotoxicity to human monocytes'-derived macrophages (HMMs) was assessed in vitro using a range of techniques. These included the MTT assay, LDH leakage and a confocal based live-dead cell assay. Cytotoxicity differed significantly between preparations, with the suspended gel preparation being the most toxic (31-500 microg/ml). Other preparations were also toxic but only at higher concentrations (>250 microg/ml). Transmission electron microscopy (TEM) and stereology showed variable cellular uptake and subsequent dissolution of the various forms of HA. We have demonstrated that HA particle toxicity varied considerably and that it was related to their physico-chemical properties. Cell death correlated strongly with particle load. The intracellular dissolution of particles as a function of time in HMM suggests that increased cytoplasmic calcium load is likely to be the cause of cell death. Some HA NPs eluded the phagocytic pathway and a few were even seen to enter the nuclei through nuclear pores.

The use of dual beam ESEM FIB to reveal the internal ultrastructure of hydroxyapatite nanoparticle-sugar-glass composites

Microparticles (MP) spray dried from hydroxyapatite (HA) nanoparticle (NP) sugar suspensions are currently under development as a prolonged release vaccine vehicle. Those with a significant sugar component cannot be sectioned by ultramicrotomy as resins are excluded by the sugar. Focused ion beam (FIB) milling is the only method to prepare thin sections that enables the inspection of the MPs ultrastructure by transmission electron microscopy (TEM). Several methods have been explored and we have found it is simplest to encapsulate MPs in silver dag, sandwiched between gold foils for FIB-milling to enable multiple MPs to be sectioned simultaneously. Spray dried MPs containing 80% sugar have an inter-nanoparticle separation that is comparable with NP size (approximately 50 nm). MPs spray dried with 50% sugar or no sugar are more tightly packed. Nano-porosity in the order of 10 nm exists between NPs. MPs spray dried in the absence of sugar and sectioned by ultramicrotomy or by FIB-milling have comparable nanoscale morphologies. Selected area electron diffraction (SAED) demonstrates that the HA remains (substantially) crystalline following FIB-milling.