1,721,195 research outputs found
Engineered surface for high performance electrodes on paper
No full textFlexible electronics have become widespread in the last decades. Due to the environmental crisis that our planet is facing, the use of sustainable materials, and less time and energy-consuming methods for the fabrication of flexible and light weight devices, have become crucial. In this context, the present study proposes a low environmental impact and scalable method for producing large-area PEDOT:PSS electrodes on standard copy paper through its surface modification. Specifically, the paper substrate is treated (through blade-coating technique) with a cellulose-based polymeric coating to close its porousness and homogenize its surface prior to the deposition of the conductive material. This cellulose-based interface allows the subsequent effective deposition of the conductive PEDOT:PSS layer, achieving an improved electrode in terms of both conductive stability and electromechanical performance. The stability of the electrode was monitored over a six-month period, and the electrodes did not suffer any ageing effects, showing stable resistance values (within the experimental error). The electrodes fabricated on engineered paper display lower (−80 %) electrical resistance. They also showed increased breaking point during strain tests (17 ± 1 % vs 9 ± 1 %) and a minor increase in resistance after 1000 bending cycles (4 % vs 9 % increase). Thus, their increased performance, stability and reproducibility opens new possibilities for wearable electronic devices
Design of graphene based PVA composites for biomedical devices
Full text linkThis work conducted within Prof. Paradossi’s group at the Department of Chemical Science and Technology in the University of Rome Tor Vergata aimed to develop an easily applicable strategy enabling functionalization of graphene, suspended in an aqueous medium in its pristine form, to biocompatible polymeric surfaces, in particular “poly(vinylalcohol)”platforms, designed for biomedical applications. Nowadays graphene, this new two-dimensional material with fascinating properties, is emerging in many scientific fields. Exploitation of graphene propertieshas been one of the motivations to implement biomedical applications of interest for our laboratory. Ourinvestigations are aboutwhat kind of functionalities can be introduced ina polymeric platform, such as hydrogel sponges for anti-tumor drug delivery or the surface of microbubbles, still inthedevelopment phase as multimodal imaging contrast agents mainly for ultrasoundsand photoacoustics. To this regard, photoacoustic imaging is a high-resolution preclinical fast developing diagnostic tool. Evolution of this imaging methodology can bring to a new clinical tool designed for human investigationandis a major challenge that can be tackled by ad hocengineered contrast agents. To this aiman optimized selection of advanced hybrid platforms is needed. Graphene derivatives, mainly graphene oxide (GO) and reduced graphene oxide (RGO),exhibiting depleted properties with respect to pristine graphene, but chemically more versatile, have beenhighlighted in the recent literature. These forms derive from the chemical modifications of the 2D structure of graphene in very harsh conditions, which introduce kinks and irregularities in the carbonic material. Such modifications make GO and RGO more reactive and more processable than pristine graphene, but jeopardize the electrical, optical and mechanical properties of this material. Despite this fact, we have not found a study thatreports theincorporation of pristine graphene into biomedical devicesstarting from its suspended form in aqueous media. The challenge herein was to preserve the graphene original properties which are important for the applications we address;and find the intermediate key to adequately tether graphene on our studied poly(vinylalcohol) composites. For this, Prof. Paradossi’s group strong background about poly(vinylalcohol) hydrogels and microbubbles was a great advantage.The first chapter of the thesis is a brief general introduction about graphene and poly(vinylalcohol) providing the necessary details of why these materials could be interesting candidates for our research, taking into accountthe main problems concerning the separate materials as well as their assembly and formulatinghypothesis regarding the efficiency and biocompatibilityof the hybrid systems.The second chapter is a proof of concept on the method allowing pristine graphene entrapment into a poly(vinylalcohol) hydrogel matrix with potential in drug release at physiological temperature by using thermosensitive moieties.The third chapter of this thesisis a general introduction to the photoacoustic imaging. It provides the basic theoretical foundation for understanding this method and the physical mechanisms related to photoacoustic generation in biological tissues. First, we describe light propagation mechanisms in tissues, and the deposition of heat via optical absorption. Assimilating the biological tissue to a liquid medium, wethen introduce the fundamental equations describing the photoacoustic issue, and the assumptions used in imaging to improve diagnosis. We also introduce ultrasound imaging and its inherent clinical approach for diagnostic and therapy. Finally, the contrast agents used in both ultrasound and photoacoustic imaging modalities are discussed through two important examples: microbubbles and NIR absorbing agents. The chapter IV details the state of the art in the context of the objectives we pursued during this thesis regarding hybrid contrast agents for photoacoustic imaging based pristine graphene and poly(vinylalcohol) microbubbles. Details on the microdevice fabrication as well as its physico-chemical characterization are provided. Finally, the potential of the graphene poly(vinylalcohol) microbubbles in enhancing the photoacoustic signal is assessed in vitro and in vivo. In the chapter V, we present a study on the influence of diamine intermediates and PEGylation used as links between graphene and the PVA microbubbles on the colloidal behavior, acoustic properties, and cytotoxicity of the overall system.An appendix is presented at the end of the thesis describing a preliminarywork carried recently on the realization of new “phase-change”ultrasound contrast agents with a photo-polymerized surfactant monolayer shell structureencapsulating perfluorocarbon. These systems are in normal conditions droplets and upon ultrasound irradiation,they convert into microbubbles by “acoustic droplet vaporization”. The phase change efficiency is studied and the experimental setup and operating conditionsaredetailed
Studio sulla struttura e sul comportamento dinamico di idrogel polisaccaridici per la formulazione di nuovi dispositivi biomedicali
Full text linkHyadd4-G è un derivato dell’acido ialuronico avente l’ 1÷3% di gruppi carbossilici legati a catene laterali di esadecilammina. L’introduzione di catene laterali esadeciliche sull’acido ialuronico (HA) porta alla formazione di un polisaccaride con nuove proprietà in grado di formare idrogel fisici, stabili a concentrazioni di polimero molto basse, mentre l’ HA nativo forma soluzioni viscose anche a concentrazioni dieci volte maggiori. Il comportamento strutturale e dinamico dell’idrogel Hyadd4-G riguarda diverse scale temporali e spaziali. Il fattore dinamico di struttura, f(Q,t), ottenuto con misure di DLS, è stato usato per ricavare i tempi microscopici caratteristici e le dimensioni della maglia del network. La metodologia del recupero di fluorescenza dopo photobleaching, FRAP, è stata usata per misurare i coefficienti di diffusione di sonde fluorescenti con diverse dimensioni. Le dimensioni idrodinamiche delle sonde, evidenziando un effetto di setaccio degli idrogel con gli esperimenti di FRAP, possono essere comparate con le dimensioni di maglia, δ, degli idrogel Hyadd4-G studiati con DLS. Misure di reologia nel regime viscoelastico lineare hanno mostrato che Hyadd4-G è un gel “soffice” viscoelastico. Tali misure hanno mostrato inoltre un particolare meccanismo di ricostituzione (“recupero di struttura”) dopo la distruzione del network del gel con misure in flusso e l’iniettabilità dell’idrogel è supportata da un pronunciato comportamento di “shear-thinning” sotto una deformazione non-lineare. La tecnica dello scattering dei neutroni ha fornito informazioni sulla microstruttura e sulle proprietà di diffusione dell’acqua nel network. La caratterizzazione dello Hyadd4-G ha mostrato che la formazione del gel è dovuta all’interazione tra le catene laterali idrofobiche che stabilizzano il network 3D con un’architettura di dimensioni nanoscopiche, nonostante il basso grado di sostituzione. Questa rappresentazione fornisce il necessario background per considerare Hyadd4-G come un potenziale nuovo idrogel utilizzabile per trattamenti di malattie osteoarticolari.
Lo xantano e il konjac glucomannano accoppiati forniscono uno dei sistemi di idrogel sinergici maggiormente studiati. Le zone di giunzione che stabilizzano una struttura 3D sono rappresentate da complessi macromolecolari in soluzione formati da catene polisaccaridiche parzialmente depolimerizzate. Le interazioni non-covalnti che stabilizzano la struttura del complesso polisaccaridico causano la distruzione di una struttura ordinata del complesso in soluzione e dell’idrogel. L’introduzione di legami chimici nella struttura 3D dell’idrogel sinergico rimuove questo comportamento, aggiungendo nuove caratteristiche al rigonfiamento e alle proprietà viscoelastiche dell’idrogel. L’utilizzo di epicloridrina come agente reticolante a basso peso molecolare non influisce sulla vitalità di fibroblasti NIH 3T3.Hyadd4-G is a derivatized hyaluronic acid having 1÷3% of the carboxyl groups grafted with a hexadecylic amide side-chains. The introduction of a hexadecyl side chain onto hyaluronic acid (HA) chains yields a polysaccharide with new properties, capable of forming physical hydrogels, stable at very low polymer concentrations, whereas native HA forms viscous solutions at ten times higher concentrations. We addressed the structural and dynamic behavior of Hyadd4-G hydrogels at different time and length scales. Dynamic structural factor, f(Q,t), obtained by DLS, was used to extract the microscopic characteristic times and pore size of the network. Fluorescence recovery after photobleaching methodology, FRAP, was used to measure diffusion coefficients of fluorescent probes with different size. The hydrodynamic coil dimensions of dextrans evidencing a sieving effect of the hydrogels by FRAP experiments can be compared with the mesh size, δ, of Hyadd4-G hydrogels studied by DLS. Rheology measurements in the linear viscoelastic regime show that Hyadd4-G is a soft viscoelastic gel. Rheological measurements showed an unusual self-healing mechanism (structure recovery) after destruction of the gel network in a shear flow and the injectability of the hydrogel is supported by a pronounced shear-thinning behavior under nonlinear deformations. Neutron scattering techniques can provide information about the microstructure and the diffusional properties of water within the pores of the network. Characterization of Hyadd4-G showed that the driving force for its gel-like behavior is the occurrence of hydrophobic interactions involving hydrophobic side-chains stabilizing a 3D-network with nano-sized architecture, despite the low degree of substitution. This picture provides the necessary background to assess Hyadd4-G as one of the potential new hydrogel systems suitable for treatment of osteoarticular diseases.
Xanthan and konjac glucomannan pair provides one of the most studied synergistic hydrogels. The junction zones stabilizing the 3D structure of this gel are present as macromolecular complexes in solution formed by the partially depolymerised polysaccharidic chains. The non-covalent interactions stabilizing the structure of the polysaccharidic complex cause the melting of the ordered structure of the complex in the solution and of the hydrogels. Introduction of chemical cross-links in the 3D structure of the synergistic hydrogel removes this behaviour, adding new features to the swelling and to the viscoelastic properties of the cured hydrogel. The use of epichlorohydrin as low molecular weight cross-linker does not impact on the viability of NIH 3T3 fibroblasts
Echogenic polymer platforms: toward a versatile diagnostic tool
No full textUltrasound contrast agents (UCAs) have been used routinely in clinical diagnostics. The most used UCA is a saline suspension of lipid shells with a stabilizing hydrophobic gas core. However, focus on other UCAs have been also considered so far, including shells made of high molecular weight moieties. Polymer based shells1 provide a unique platform supporting multimodality2 (US, MRI for example) and multifunctionality3 (targeting, theranostics). The endurance of the polymer shells allows a long circulation life, although this feature can decrease the microbubble echogenicity. Bearing in mind such hurdles, this contribution will highlight the potentialities of polymer shelled microbubbles in supporting fast developing new methodologies such as photoacoustic imaging. It will also illustrate how “crosslinked polymer shells” concept can be advantageously used in the field of the “phase shift” microsystems.4 Insonification can transform microdroplets having crosslinked polymer shell into ultrasound active microbubbles via acoustic droplet vaporization (ADV). The viscoelasticity of the shell controls the expansion of the microbubble shell and is responsible for its return to the original droplet state in a time lapse of some minutes. The analysis of the time dependence of this retraction process provides an insight of the microrheology parameters of the polymer shell.5
References:
1 F. Cavalieri, A. El Hamassi, E. Chiessi, G. Paradossi. Langmuir, , 21, 8758-8764 (2005)
2 T. B. Brismar, D. Grishenkov, B. Gustafsson, J. Härmark, Å. Barrefelt, S. V. V. N. Kothapalli, S. Margheritelli, L. Oddo, K. Caidahl, H. Hebert and G. Paradossi. Biomacromolecules 13 (5), 1390–1399 (2012)
3 R. Villa, B. Cerroni, L. Viganò, S. Margheritelli, G. Abolafio, L. Oddo, G. Paradossi, N. Zaffaroni
Colloids and Surfaces B: Biointerfaces 110, 434 – 442 (2013)
4 S. Capece, E. Chiessi, R. Cavalli, P. Giustetto, D. Grishenkov, G. Paradossi. Chem. Commun., 49, 5763 - 5765 (2013)
5 S. Capece, F. Domenici, F. Brasili, L. Oddo, B. Cerroni, A. Bedini, F. Bordi, E. Chiessi, G. Paradossi, to be submitted (2015
Injectable peptidic hydrogels for bone tissue repair and regeneration.
No full textThe ongoing growth in the incidence of bone injuries and diseases is producing an increment in the demand of medical and healthcare resources, with an urgent need to identify suitable alternatives to current common clinical treatments. In this context, bone tissue engineering is part of an emerging interdisciplinary field that applies the principles of engineering and life sciences towards the development of biological substitutes. Peptide hydrogels may be used in this context as biocompatible and biodegradable materials suitable for cell encapsulation and for the controlled spatial and temporal delivery of biomolecules (e.g. growth factors) able to direct cell differentiation.
Recently, we developed an enzymatic approach for the preparation of injectable, self-assembling materials based on Fmoc-oligopeptides1. The reaction products (Fmoc peptides) spontaneously self-assemble in water to originate fibrils, that become entangled to form a three-dimensional structure of fibers with a diameter of approximately 7 nm, as evidenced by atomic force microscopy (AFM) measurements. Macroscopically, a stable, self-supporting hydrogel material is produced. These materials can be used as controlled drug delivery systems for a wide spectrum of bioactive molecules2 and may enhance cell production of growth factors3. Our results suggest the possibility of using Fmoc oligopetides as building blocks for a new class of injectable scaffolds that could play an important role in bone regeneration, i.e. to reconstruct anatomical defects caused by cancer surgery, malformations and trauma. We employed such hydrogels for the preparation of composite materials specifically designed for bone tissue regeneration. These tailor-made hydrogel systems contain biopolymeric spheres delivering bioactive molecules, as well as pure and substituted calcium phosphate (CaP) nanoparticles to provide bioactivity, osteoconductivity and improved mechanical properties. The morphological and viscoelastic properties of the synthesized hydrogels were investigated and their biocompatibility with different mammalian cells was assessed. Ongoing work is aimed at investigating the biological properties of the composite hydrogel systems, in terms of adhesion, growth and differentiation of human mesenchymal stem cells
Biofabrication of genipin-crosslinked peptide hydrogels and their use in the controlled delivery of Naproxen
No full textThe synthesis and optimization of peptide-based hydrogel materials have gained growing interest in the last years, thanks to their properties, that make them appealing for diverse biotechnological applications, with a particular focus in the field of biomedicine. The self-assembling abilities of low molecular weight peptides make them ideal for designing advanced materials using mild reaction conditions. In this work, a biocatalytic approach has been used for the synthesis of an Fmoc-tripeptide that is able to self-assemble in water affording a self-supporting hydrogel. The mechanical properties of this material have been enhanced through chemical crosslinking by using a natural compound, genipin, that allows to minimize cytotoxic effects. Moreover, we have tested the potential of the prepared materials to be employed as drug delivery systems using naproxen as an anti-inflammatory model drug, and studying its release kinetics in aqueous medium. The cytotoxicity of the hydrogels has been evaluated, and their mechanical and morphological properties have been studied by rheology and SEM microscopy
Polymeric microbubbles as multifunctional Ultrasound Contrast Agents: Design, Properties, and Ultrasound Behaviour.
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