Imperial College London

DrIainDunlop

Faculty of EngineeringDepartment of Materials

Reader in Biomaterials and Cell Engineering
 
 
 
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Contact

 

+44 (0)20 7594 6731i.dunlop

 
 
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Location

 

1.02Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

35 results found

Güney TG, Herranz AM, Mumby S, Dunlop IE, Adcock IMet al., 2021, Epithelial-stromal cell interactions and ECM mechanics drive the formation of airway-mimetic tubular morphology in lung organoids, iScience, Pages: 103061-103061, ISSN: 2589-0042

Complex human airway cellular organisation where extracellular matrix (ECM), epithelial and stromal lineages interact present challenges for organ study in vitro. Current in vitro lung models, that focus on the lung epithelium do not represent complex airway morphology and cell-ECM interactions seen in vivo.Models including stromal populations often separate them via a semipermeable barrier precluding cell-cell interaction or the effect of ECM mechanics. We investigated the effect of stromal cells on basal epithelial cell-derived bronchosphere structure and function through a triple culture of human bronchial epithelial, lung fibroblast and airway smooth muscle cells. Epithelial-stromal cross-talk resulted in epithelial cell-driven branching tubules with stromal cells surrounding epithelial cells termed bronchotubules. Agarose-matrigel scaffold (Agrigel) formed a mechanically tuneable ECM, with adjustable viscoelasticity and stiffness enabling long-term tubule survival. Bronchotubule models may enable research into how epithelial-stromal cell and cell-ECM communication drive tissue patterning, repair and development of disease.

Journal article

Hopkins T, Bemmer V, Franks S, Dunlop C, Hardy K, Dunlop Iet al., 2021, Micromechanical mapping of the intact ovary interior reveals contrasting mechanical roles for follicles and stroma, Biomaterials, ISSN: 0142-9612

Follicle development in the ovary must be tightly regulated to ensure cyclical release of oocytes (ovulation). Disruption of this process is a common cause of infertility, for example via polycystic ovary syndrome (PCOS) and premature ovarian insufficiency (POI). Recent ex vivo studies suggest that follicle growth is mechanically regulated, however, crucially, the actual mechanical properties of the follicle microenvironment have remained unknown. Here we use atomic force microscopy (AFM) spherical probe indentation to map and quantify the mechanical microenvironment in the mouse ovary, at high resolution and across the entire width of the intact (bisected) ovarian interior. Averaging over the entire organ, we find the ovary to be a fairly soft tissue comparable to fat or kidney (mean Young’s Modulus 3.3 +/-2.5 kPa). This average, however, conceals substantial spatial variations, with the overall range of tissue stiffnesses from c. 0.5 –10 kPa, challenging the concept that a single Young’s Modulus can effectively summarize this complex organ. Considering the internal architecture of the ovary, we find that stiffness is low at the edge and centre which are dominated by stromal tissue, and highest in an intermediate zone that is dominated by large developmentally-advanced follicles, confirmed by comparison with immunohistology images. These results suggest that largefollicles are mechanically dominant structures in the ovary, contrasting with previous expectations that collagen-rich stroma would dominate. Extending our study to the highest resolutions (c. 5 μm) showed substantial mechanical variations within the larger zones, even over very short (sub-100 μm) lengths, and especially within the stiffer regions of the ovary. Taken together, our results provide a new, physiologically accurate, framework for ovaria

Journal article

Ramadan S, Lobo R, Zhang Y, Xu L, Shaforost O, Tsang DKH, Feng J, Yin T, Qiao M, Rajeshirke A, Jiao LR, Petrov PK, Dunlop IE, Titirici M-M, Klein Net al., 2021, Carbon-dot-enhanced graphene field-effect transistors for uitrasensitive detection of exosomes, ACS Applied Materials and Interfaces, Vol: 13, Pages: 7854-7864, ISSN: 1944-8244

Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.

Journal article

Ramadan S, Zhang Y, Tsang DKH, Shaforost O, Xu L, Bower R, Dunlop IE, Petrov PK, Klein Net al., 2021, Enhancing structural properties and performance of graphene-based devices using self-assembled HMDS monolayers, ACS Omega, Vol: 6, Pages: 4767-4775, ISSN: 2470-1343

The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.

Journal article

Hopkins T, Bemmer V, Franks S, Dunlop C, Hardy K, Dunlop Iet al., 2021, Mapping the mechanical microenvironment in the ovary, Publisher: Bioarxiv

Follicle development in the human ovary must be tightly regulated to ensure cyclical release of oocytes (ovulation), and disruption of this process is a common cause of infertility. Recent ex vivo studies suggest that follicle growth may be mechanically regulated, however the actual mechanical properties of the follicle microenvironment have remained unknown. Here we map and quantify the mechanical microenvironment in mouse ovaries using colloidal probe atomic force microscope (AFM) indentation, finding an overall mean Young's Modulus 3.3 ± 2.5 kPa. Spatially, stiffness is low at the ovarian edge and centre, which are dominated by extra-follicular ECM, and highest in an intermediate zone dominated by large follicles. This suggests that large follicles should be considered as mechanically dominant structures in the ovary, in contrast to previous expectations. Our results provide a new, physiologically accurate framework for investigating how mechanics impacts follicle development and will underpin future tissue engineering of the ovary.

Working paper

Guney T, Mumby S, Dunlop I, Adcock Iet al., 2020, Epithelial-stromal cell interactions and ECM mechanics drive the formation of airway-mimetic tubular morphology in lung organoids, Publisher: Bioarxiv

The complex cellular organisation of the human airway tract where interaction between epithelial and stromal lineages and the extracellular matrix (ECM) make it a difficult organ to study in vitro. Current in vitro lung models focus on modelling the lung epithelium such as air-liquid interface (ALI) cultures and bronchospheres, do not model the complex morphology and the cell-ECM interaction seen in vivo. Models that include stromal populations often separate them via a semipermeable barrier, which precludes the effect of cell-cell interaction or do not include the ECM or the effect of ECM mechanics such as viscoelasticity and stiffness. Here we investigated the effect of stromal cells on basal epithelial cell-derived bronchosphere structure and function through a triple culture of bronchial epithelial, lung fibroblast and airway smooth muscle cells. Epithelial-stromal cross talk enabled formation of epithelial cell-driven branching tubules consisting of luminal epithelial cells surrounded by stromal cells termed bronchotubules. Addition of agarose to the Matrigel scaffold (Agrigel) created a mechanically tunable ECM, where viscoelasticity and stiffness could be altered to enable long term tubule survival. Bronchotubule models enable the investigation of how epithelial-stromal cell and cell-ECM communication drive tissue patterning, repair and development of disease.

Working paper

Uwagboe I, Mumby S, Dunlop I, Adcock Iet al., 2020, Tissue engineering of lung organoids with advanced biomaterials for in-vitro disease modelling, International Conference of the American-Thoracic-Society (ATS), Publisher: American Thoracic Society, Pages: 1-1, ISSN: 1073-449X

Conference paper

Uwagboe I, Mumby S, Guney T, Dunlop I, Adcock Iet al., 2020, Use of biomaterials to tissue engineer 3D models with lung organoids for in-vitro disease modelling, Publisher: EUROPEAN RESPIRATORY SOC JOURNALS LTD, ISSN: 0903-1936

Conference paper

Scotson CP, Munoz-Hernando M, Duncan SJ, Ruiz SA, Keyes SD, van Veelen A, Dunlop IE, Roose Tet al., 2019, Stabilizing gold nanoparticles for use in X-ray computed tomography imaging of soil systems, Royal Society Open Science, Vol: 6, ISSN: 2054-5703

This investigation establishes a system of gold nanoparticlesthat show good colloidal stability as an X-ray computedtomography (XCT) contrast agent under soil conditions. Goldnanoparticles offer numerous beneficial traits for experiments inbiology including: comparatively minimal phytotoxicity, X-rayattenuation of the material and the capacity for functionalization.However, soil salinity, acidity and surface charges can induceaggregation and destabilize gold nanoparticles, hence inbiomedical applications polymer coatings are commonlyapplied to gold nanoparticles to enhance stability in the in vivoenvironment. Here we first demonstrate non-coatednanoparticles aggregate in soil-water solutions. We then showcoating with a polyethylene glycol (PEG) layer prevents thisaggregation. To demonstrate this, PEG-coated nanoparticleswere drawn through flow columns containing soil and wereshown to be stable; this is in contrast with control experimentsusing silica and alumina-packed columns. We furtherdetermined that a suspension of coated gold nanoparticleswhich fully saturated soil maintained stability over at least 5days. Finally, we used time resolved XCT imaging and imagebased models to approximate nanoparticle diffusion as similar tothat of other typical plant nutrients diffusing in water. Together,these results establish the PEGylated gold nanoparticles aspotential contrast agents for XCT imaging in soil.

Journal article

Kwong Hong Tsang D, Lieberthal T, Watts C, Del Rio Hernandez A, Dunlop I, Ramadan S, Klein Net al., 2019, Chemically functionalised graphene FET biosensor for the label-free sensing of exosomes, Scientific Reports, Vol: 9, ISSN: 2045-2322

A graphene field-effect transistor (gFET) was non-covalently functionalised with 1-pyrenebutyric acid N-hydroxysuccinimide ester and conjugated with anti-CD63 antibodiesfor the label-free detection of exosomes.Using a microfluidic channel, part of a graphene film was exposed to solution. The change in electrical properties of the exposed graphene created anadditional minimum alongside the original Dirac point inthe drain-source current(Ids)-back-gate voltage (Vg) curve. When phosphate buffered saline (PBS) was present in the channel, the additional minimum was present at a Vglower than the original Dirac point and shifted with time when exosomes were introduced into the channel.Thisshift of the minimum from the PBS reference point reached saturationafter 30 minutesand was observed for multiple exosome concentrations. Upon conjugation with an isotype control, sensor responsetothe highest concentration ofexosomes was negligible in comparison to that with anti-CD63antibody, indicatingthat thefunctionalised gFETcan specifically detect exosomes at least down to 0.1μg/mLand is sensitive to concentration. Such a gFET biosensor has not been used before for exosome sensing and could be an effective tool for the liquid-biopsy detection of exosomes as biomarkers for early-stage identification of diseases such as cancer.

Journal article

Constantinou A, Marie-Sainte U, Peng L, Carroll D, McGilvery C, Dunlop I, Georgiou Tet al., 2019, Effect of block copolymer architecture and composition on gold nanoparticle fabrication, Polymer Chemistry, Vol: 10, Pages: 4632-4642, ISSN: 1759-9954

Gold nanoparticles (AuNPs) have many biomedical applications. Their size is a crucial parameter, as it affects cellular uptake. Here, we investigate how the formation of AuNPs is affected by the composition and architecture (AB, BAB and ABA) of the copolymers, which were used as templates for the fabrication of AuNPs.

Journal article

Gonzalez-Carter DA, Ong ZY, McGilvery CM, Dunlop IE, Dexter DT, Porter AEet al., 2019, L-DOPA functionalized, multi-branched gold nanoparticles as brain-targeted nano-vehicles, Nanomedicine: Nanotechnology, Biology and Medicine, Vol: 15, Pages: 1-11, ISSN: 1549-9634

The blood-brain barrier (BBB) is a protective endothelial barrier lining the brain microvasculature which prevents brain delivery of therapies against brain diseases. Hence, there is an urgent need to develop vehicles which efficiently penetrate the BBB to deliver therapies into the brain. The drug L-DOPA efficiently and specifically crosses the BBB via the large neutral amino acid transporter (LAT)-1 protein to enter the brain. Thus, we synthesized L-DOPA-functionalized multi-branched nanoflower-like gold nanoparticles (L-DOPA-AuNFs) using a seed-mediated method involving catechols as a direct reducing-cum-capping agent, and examined their ability to cross the BBB to act as brain-penetrating nanovehicles. We show that L-DOPA-AuNFs efficiently penetrate the BBB compared to similarly sized and shaped AuNFs functionalized with a non-targeting ligand. Furthermore, we show that L-DOPA-AuNFs are efficiently internalized by brain macrophages without inducing inflammation. These results demonstrate the application of L-DOPA-AuNFs as a non-inflammatory BBB-penetrating nanovehicle to efficiently deliver therapies into the brain.

Journal article

Wu P-J, Kabovka I, Ruberti J, Sherwood J, Dunlop IE, Paterson C, Torok P, Overby Det al., 2018, Water content, not stiffness, dominates Brillouin spectroscopy measurements in hydrated materials, Nature Methods, Vol: 15, Pages: 561-562, ISSN: 1548-7091

Journal article

Loftus C, Saeed M, Davis D, Dunlop IEet al., 2018, Activation of human Natural Killer cells by graphene oxide-templated antibody nanoclusters, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 18, Pages: 3282-3289, ISSN: 1530-6984

An emerging new paradigm is that immune cell activation is controlled by transient interactions between supramolecular assemblies of receptors and ligands. Current immunotherapy biologic pharmaceuticals that activate or desensitize NK cells are, however, individual molecules that do not replicate this nanoscale organization of proteins. Here, we use nanoscale graphene oxide (NGO) as a template to generate soluble nanoscale clusters of Natural Killer cell-activating antibodies. We control nanocluster size and molecular number to mimic reported values for cell surface proteins. These NGO-templated molecular nanoclusters, used to stimulate NK cells via the CD16 receptor, successfully induced cellular activation, indicated by degranulation of cytolytic granules and IFN-γ secretion. Importantly, activation significantly exceeded that induced by the same antibodies applied as a solution of individual molecules. These results demonstrate that future immunotherapies could be enhanced by assembling immunomodulatory drugs into nanoclusters and establish NGO-templating as a candidate technology.

Journal article

Ong ZY, Chen S, Nabavi E, Regoutz A, Payne DJ, Elson DS, Dexter DT, Dunlop IE, Porter AEet al., 2017, Multibranched Gold Nanoparticles with Intrinsic LAT-1 Targeting Capabilities for Selective Photothermal Therapy of Breast Cancer., ACS Applied Materials and Interfaces, Vol: 9, Pages: 39259-39270, ISSN: 1944-8244

Because of the critical role of the large neutral amino acid transporter-1 (LAT-1) in promoting tumor growth and proliferation, it is fast emerging as a highly attractive biomarker for the imaging and treatment of human malignancies, including breast cancer. While multibranched gold nanoparticles (AuNPs) have emerged as a promising modality in the photothermal therapy (PTT) of cancers, some of the key challenges limiting their clinical translation lie in the need to develop reproducible and cost-effective synthetic methods as well as the selective accumulation of sufficient AuNPs at tumor sites. In this study, we report a simple and direct seed-mediated synthesis of monodispersed multibranched AuNPs using the catechol-containing LAT-1 ligands, L- and D-dopa, to confer active cancer targeting. This route obviates the need for additional conjugation with targeting moieties such as peptides or antibodies. Nanoflower-like AuNPs (AuNF) with diameters of approximately 46, 70, and 90 nm were obtained and were found to possess excellent colloidal stability and biocompatibility. A significantly higher intracellular accumulation of the L- and D-dopa functionalized AuNFs was observed in a panel of breast cancer cell lines (MCF-7, MDA-MB-231, MDA-MB-468, and MDA-MB-453) when compared to the nontargeting control AuNFs synthesized with dopamine and 4-ethylcatechol. Importantly, no significant difference in uptake between the targeting and nontargeting AuNFs was observed in a non-tumorigenic MCF-10A breast epithelial cell line, hence demonstrating tumor selectivity. For PTT of breast cancer, Ag(+) was introduced during synthesis to obtain L-dopa functionalized nanourchin-like AuNPs (AuNUs) with strong near-infrared (NIR) absorbance. The L-dopa functionalized AuNUs mediated selective photothermal ablation of the triple negative MDA-MB-231 breast cancer cell line and sensitized the cells to the anticancer drugs cisplatin and docetaxel. This work brings forward an effective strategy

Journal article

Luongo G, Perez JE, Kosel J, Georgiou TK, Regoutz A, Payne DJ, Stevens MM, Porter AE, Dunlop IEet al., 2017, Scalable high-affinity stabilization of magnetic iron oxide nanostructures by a biocompatible antifouling homopolymer, ACS Applied Materials and Interfaces, Vol: 9, Pages: 40059-40069, ISSN: 1944-8244

Iron oxide nanostructures have been widely developed for biomedical applications, due to their magnetic properties and biocompatibility. In clinical application, the stabilization of these nanostructures against aggregation and non-specific interactions is typically achieved using weakly anchored polysaccharides, with better-defined and more strongly anchored synthetic polymers not commercially adopted due to complexity of synthesis and use. Here, we show for the first time stabilization and biocompatibilization of iron oxide nanoparticles by a synthetic homopolymer with strong surface anchoring and a history of clinical use in other applications, poly(2-methacryloyloxyethy phosphorylcholine) (poly(MPC)). For the commercially important case of spherical particles, binding of poly(MPC) to iron oxide surfaces and highly effective individualization of magnetite nanoparticles (20 nm) are demonstrated. Next-generation high-aspect ratio nanowires (both magnetite/maghemite and core-shell iron/iron oxide) are furthermore stabilized by poly(MPC)-coating, with nanowire cytotoxicity at large concentrations significantly reduced. The synthesis approach is exploited to incorporate functionality into the poly(MPC) chain is demonstrated by random copolymerization with an alkyne-containing monomer for click-chemistry. Taking these results together, poly(MPC) homopolymers and random copolymers offer a significant improvement over current iron oxide nanoformulations, combining straightforward synthesis, strong surface-anchoring and well-defined molecular weight.

Journal article

Delcassian D, Sattler S, Dunlop IE, 2017, T cell immunoengineering with advanced biomaterials, Integrative Biology, Vol: 9, Pages: 211-222, ISSN: 1757-9694

Recent advances in biomaterials design offer the potential to actively control immune cell activation and behaviour. Many human diseases, such as infections, cancer, and autoimmune disorders, are partly mediated by inappropriate or insufficient activation of the immune system. T cells play a central role in the host immune response to these diseases, and so constitute a promising cell type for manipulation. In vivo, T cells are stimulated by antigen presenting cells (APC), therefore to design immunoengineering biomaterials that control T cell behaviour, artificial interfaces that mimic the natural APC-T cell interaction are required. This review draws together research in the design and fabrication of such biomaterial interfaces, and highlights efforts to elucidate key parameters in T cell activation, such as substrate mechanical properties and spatial organization of receptors, illustrating how they can be manipulated by bioengineering approaches to alter T cell function.

Journal article

Perez JE, Contreras MF, Vilanova E, Felix LP, Margineanu MB, Luongo G, Porter AE, Dunlop IE, Ravasi T, Kosel Jet al., 2016, Cytotoxicity and intracellular dissolution of nickel nanowires., Nanotoxicology, Vol: 10, Pages: 871-880

The assessment of cytotoxicity of nanostructures is a fundamental step for their development as biomedical tools. As widely used nanostructures, nickel nanowires (Ni NWs) seem promising candidates for such applications. In this work, Ni NWs were synthesized and then characterized using vibrating sample magnetometry, energy dispersive X-Ray analysis, and electron microscopy. After exposure to the NWs, cytotoxicity was evaluated in terms of cell viability, cell membrane damage, and induced apoptosis/necrosis on the model human cell line HCT 116. The influence of NW to cell ratio (10:1 to 1000:1) and exposure times up to 72 hours was analyzed for Ni NWs of 5.4 μm in length, as well as for Ni ions. The results show that cytotoxicity markedly increases past 24 hours of incubation. Cellular uptake of NWs takes place through the phagocytosis pathway, with a fraction of the dose of NWs dissolved inside the cells. Cell death results from a combination of apoptosis and necrosis, where the latter is the outcome of the secondary necrosis pathway. The cytotoxicity of Ni ions and Ni NWs dissolution studies suggest a synergistic toxicity between NW aspect ratio and dissolved Ni, with the cytotoxic effects markedly increasing after 24 hours of incubation.

Journal article

Podhorska L, Delcassian D, Goode AE, Agyei M, McComb DW, Ryan MP, Dunlop IEet al., 2016, Mechanisms of polymer-templated nanoparticle synthesis: contrasting ZnS and Au, Langmuir, Vol: 32, Pages: 9216-9222, ISSN: 0743-7463

We combine solution small-angle X-ray scattering (SAXS) and high-resolution analytical transmission electron microscopy (ATEM) to gain a full mechanistic understanding of substructure formation in nanoparticles templated by block copolymer reverse micelles, specifically poly(styrene)-block-poly(2-vinyl pyridine). We report a novel substructure for micelle-templated ZnS nanoparticles, in which small crystallites (~4 nm) exist within a larger (~20 nm) amorphous organic-inorganic hybrid matrix. The formation of this complex structure is explained via SAXS measurements that characterize in situ for the first time the intermediate state of the metal-loaded micelle core: Zn2+ ions are distributed throughout the micelle core, which solidifies as a unit on sulfidation. The nanoparticle size is thus determined by the radius of the metal-loaded core, rather than the quantity of available metal ions. This mechanism leads to particle size counter-intuitively decreasing with increasing metal content, based on the modified interactions of the metal-complexed monomers in direct contrast to gold nanoparticles templated by the same polymer.

Journal article

Gonzalez-Carter D, Goode AE, Fiammengo R, Dunlop IE, Dexter DT, Porter AEet al., 2016, Inhibition of Leptin-ObR Interaction Does not Prevent Leptin Translocation Across a Human Blood-Brain Barrier Model., J Neuroendocrinol, Vol: 28

The adipocyte-derived hormone leptin regulates appetite and energy homeostasis through the activation of leptin receptors (ObR) on hypothalamic neurones; hence, leptin must be transported through the blood-brain barrier (BBB) to reach its target sites in the central nervous system. During obesity, however, leptin BBB transport is decreased, in part precluding leptin as a viable clinical therapy against obesity. Although the short isoform of the ObR (ObRa) has been implicated in the transport of leptin across the BBB as a result of its elevated expression in cerebral microvessels, accumulating evidence indicates that leptin BBB transport is independent of ObRa. In the present study, we employed an ObR-neutralising antibody (9F8) to directly examine the involvement of endothelial ObR in leptin transport across an in vitro human BBB model composed of the human endothelial cell line hCMEC/D3. Our results indicate that, although leptin transport across the endothelial monolayer was nonparacellular, and energy- and endocytosis-dependent, it was not inhibited by pre-treatment with 9F8, despite the ability of the latter to recognise hCMEC/D3-expressed ObR, prevent leptin-ObR binding and inhibit leptin-induced signal transducer and activator of transcription 3 (STAT-3) phosphorylation in hCMEC/D3 cells. Furthermore, hCMEC/D3 cells expressed the transporter protein low-density lipoprotein receptor-related protein-2 (LRP-2), which is capable of binding and endocytosing leptin. In conclusion, our results demonstrate that leptin binding to and signalling through ObR is not required for efficient transport across human endothelial monolayers, indicating that ObR is not the primary leptin transporter at the human BBB, a role which may fall upon LRP-2. A deeper understanding of leptin BBB transport will help clarify the exact causes for leptin resistance seen in obesity and aid in the development of more efficient BBB-penetrating leptin analogues.

Journal article

Harrison RH, Steele JAM, Chapman R, Gormley A, Chow L, Mahat M, Podhorska L, Palgrave R, Payne D, Hettiaratchy S, Dunlop IE, Stevens Met al., 2015, Modular and versatile spatial functionalization of tissue engineering scaffolds through fiber-initiated controlled radical polymerization, Advanced Functional Materials, Vol: 25, Pages: 5748-5757, ISSN: 1616-301X

Native tissues are typically heterogeneous and hierarchically organized, and generating scaffolds that can mimic these properties is critical for tissue engineering applications. By uniquely combining controlled radical polymerization (CRP), end‐functionalization of polymers, and advanced electrospinning techniques, a modular and versatile approach is introduced to generate scaffolds with spatially organized functionality. Poly‐ε‐caprolactone is end functionalized with either a polymerization‐initiating group or a cell‐binding peptide motif cyclic Arg‐Gly‐Asp‐Ser (cRGDS), and are each sequentially electrospun to produce zonally discrete bilayers within a continuous fiber scaffold. The polymerization‐initiating group is then used to graft an antifouling polymer bottlebrush based on poly(ethylene glycol) from the fiber surface using CRP exclusively within one bilayer of the scaffold. The ability to include additional multifunctionality during CRP is showcased by integrating a biotinylated monomer unit into the polymerization step allowing postmodification of the scaffold with streptavidin‐coupled moieties. These combined processing techniques result in an effective bilayered and dual‐functionality scaffold with a cell‐adhesive surface and an opposing antifouling non‐cell‐adhesive surface in zonally specific regions across the thickness of the scaffold, demonstrated through fluorescent labelling and cell adhesion studies. This modular and versatile approach combines strategies to produce scaffolds with tailorable properties for many applications in tissue engineering and regenerative medicine.

Journal article

Dunlop IE, Ryan MP, Goode AE, Schuster C, Terrill NJ, Weaver JVMet al., 2014, Direct synthesis of PEG-encapsulated gold nanoparticles using branched copolymer nanoreactors, RSC Advances, Vol: 4, Pages: 27702-27707

Journal article

Delcassian D, Depoil D, Rudnicka D, LIu M, Davis DM, Dustin ML, Dunlop IEet al., 2013, Nanoscale ligand spacing influences receptor triggering in T cells and NK cells, Nano Letters

Bioactive nanoscale arrays were constructed to ligate activating cell surface receptors on T cells (the CD3 component of the TCR complex) and NK cells (CD16). These arrays are formed from biofunctionalized gold nanospheres with controlled interparticle spacing in the range 25 – 104 nm. Responses to these nanoarrays were assessed using the extent of membrane-localized phosphotyrosine in T cells stimulated with CD3-binding nanoarrays, and the size of cell contact area for NK cells stimulated with CD16-binding nanoarrays. In both cases, the strength of response decreased with increasing spacing, falling to background levels by 69 nm in the T cell/anti-CD3 system and 104 nm for the NK cell/anti-CD16 system. These results demonstrate that immune receptor triggering can be influenced by the nanoscale spatial organization of receptor/ligand interactions.

Journal article

Leo BF, Chen S, Kyo Y, Herpoldt KL, Terrill NJ, Dunlop IE, McPhail D, Shaffer MS, Schwander S, Gow A, Zhang J, Chung KF, Tetley T, Porter AE, Ryan MPet al., 2013, The Stability of Silver Nanoparticles in a Model of Pulmonary Surfactant., Environ Sci Technol, Vol: 47, Pages: 11232-11240

The growing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about their potential impact on the environment and human health. Whether AgNPs dissolve and release Ag+ ions, or coarsen to form large aggregates, is critical in determining their potential toxicity. In this work, the stability of AgNPs in dipalmitoylphosphatidylcholine (DPPC), the major component of pulmonary surfactant, was investigated as a function of pH. Spherical, citrate-capped AgNPs with average diameters of 14 ± 1.6 nm (n=200) were prepared by a chemical bath reduction. The kinetics of Ag+ ion release was strongly pH-dependent. After 14 days of incubation in sodium perchlorate (NaClO4) or perchloric acid (HClO4) solutions, the total fraction of AgNPs dissolved varied from ~10 % at pH 3, to ~2 % at pH 5, with negligible dissolution at pH 7. A decrease in pH from 7 to 3 also promoted particle aggregation and coarsening. DPPC (100 mg.L-1) delayed the release of Ag+ ions, but did not significantly alter the total amount of Ag+ released after two weeks. In addition, DPPC improved the dispersion of the AgNPs and inhibited aggregation and coarsening. TEM images revealed that the AgNPs were coated with a DPPC layer serving as a semi-permeable layer. Hence, lung lining fluid, particularly DPPC, can modify the aggregation state and kinetics of Ag+ ion release of inhaled AgNPs in the lung. These observations have important implications for predicting the potential reactivity of AgNPs in the lung and the environment.

Journal article

Dunlop IE, Thomas RK, Titmus S, Osborne V, Edmondson S, Huck WTS, Klein Jet al., 2012, Structure and Collapse of a Surface-Grown Strong Polyelectrolyte Brush on Sapphire, LANGMUIR, Vol: 28, Pages: 3187-3193, ISSN: 0743-7463

Journal article

Shahal T, Geiger B, Dunlop IE, Spatz JPet al., 2012, Regulation of Integrin Adhesions by Varying the Density of Substrate-Bound Epidermal Growth Factor, Biointerphases: an open access journal for the biomaterials interface community

Substrates coated with specific bioactiveligands are important for tissue engineering, enabling the local presentation of extracellular stimulants at controlled positions and densities. In this study, we examined the cross-talk between integrin and epidermal growth factor (EGF) receptors following their interaction with surfaceimmobilized Arg-Gly-Asp (RGD) and EGF ligands, respectively. Surfaces of glass coverslips, modified with biotinylated silane-polyethylene glycol, were functionalized by either biotinylated RGD or EGF (or both) via the biotin–NeutrAvidin interaction. Fluorescent labeling of the adhering A431 epidermoid carcinoma cells for zyxin or actin indicated that EGF had a dual effect on focal adhesions (FA) and stress fibers: at low concentrations (0.1; 1 ng/ml), it stimulated their growth; whereas at higher concentrations, on surfaces with low to intermediate RGD densities, it induced their disassembly, leading to cell detachment. The EGF- dependent dissociation of FAs was, however, attenuated on higher RGD density surfaces. Simultaneous stimulation by both immobilized RGD and EGF suggest a strong synergy between integrin and EGFR signaling, in FA induction and cell spreading. A critical threshold level of EGF was required to induce significant variation in cell adhesion; beyond this critical density, the immobilized molecule had a considerably stronger effect on cell adhesion than did soluble EGF. The mechanismsunderlying this synergy

Journal article

Dunlop IE, Briscoe WH, Titmuss S, Jacobs RMJ, Osborne VL, Edmondson S, Huck WTS, Klein Jet al., 2009, Direct Measurement of Normal and Shear Forces between Surface-Grown Polyelectrolyte Layers, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 113, Pages: 3947-3956, ISSN: 1520-6106

Journal article

Dunlop IE, Zorn S, Richter G, Srot V, Kelsch M, van Aken PA, Skoda M, Gerlach A, Spatz JP, Schreiber Fet al., 2009, Titanium-silicon oxide film structures for polarization-modulated infrared reflection absorption spectroscopy, THIN SOLID FILMS, Vol: 517, Pages: 2048-2054, ISSN: 0040-6090

Journal article

Dunlop IE, Spatz JP, Dustin ML, 2009, Degenerative diseases: manipulating the micro- and nanoscale architecture regulates immunological synapse function, Nanotechnolgy, Editors: Vogel, Weinheim, Publisher: Wiley-VCH

Book chapter

Sugiharto AB, Johnson CM, Dunlop IE, Roke Set al., 2008, Delocalized surface modes reveal three-dimensional structures of complex biomolecules, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 112, Pages: 7531-7534, ISSN: 1932-7447

Journal article

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