Rapid prototyping for biomedical engineering: current capabilities and Challenges

A new set of manufacturing technologies has emerged in the past decades to address market requirements in a customized way and to provide support for research tasks that require prototypes. These new techniques and technologies are usually referred to as rapid prototyping and manufacturing technologies, and they allow prototypes to be produced in a wide range of materials with remarkable precision in a couple of hours. Although they have been rapidly incorporated into product development methodologies, they are still under development, and their applications in bioengineering are continuously evolving. Rapid prototyping and manufacturing technologies can be of assistance in every stage of the development process of novel biodevices, to address various problems that can arise in the devices' interactions with biological systems and the fact that the design decisions must be tested carefully. This review focuses on the main fields of application for rapid prototyping in biomedical engineering and health sciences, as well as on the most remarkable challenges and research trends

Ask yeast how to burn your fats: lessons learned from the metabolic adaptation to salt stress

[EN] Here, we review and update the recent advances in the metabolic control during the adaptive response of budding yeast to hyperosmotic and salt stress, which is one of the best understood signaling events at the molecular level. This environmental stress can be easily applied and hence has been exploited in the past to generate an impressively detailed and comprehensive model of cellular adaptation. It is clear now that this stress modulates a great number of different physiological functions of the cell, which altogether contribute to cellular survival and adaptation. Primary defense mechanisms are the massive induction of stress tolerance genes in the nucleus, the activation of cation transport at the plasma membrane, or the production and intracellular accumulation of osmolytes. At the same time and in a coordinated manner, the cell shuts down the expression of housekeeping genes, delays the progression of the cell cycle, inhibits genomic replication, and modulates translation efficiency to optimize the response and to avoid cellular damage. To this fascinating interplay of cellular functions directly regulated by the stress, we have to add yet another layer of control, which is physiologically relevant for stress tolerance. Salt stress induces an immediate metabolic readjustment, which includes the up-regulation of peroxisomal biomass and activity in a coordinated manner with the reinforcement of mitochondrial respiratory metabolism. Our recent findings are consistent with a model, where salt stress triggers a metabolic shift from fermentation to respiration fueled by the enhanced peroxisomal oxidation of fatty acids. We discuss here the regulatory details of this stress-induced metabolic shift and its possible roles in the context of the previously known adaptive functions.The work of the authors was supported by grants from Ministerio de Economía y Competitividad (BFU2011- 23326 and BFU2016-75792-R).Pascual-Ahuir Giner, MD.; Manzanares-Estreder, S.; Timón Gómez, A.; Proft ., MH. (2017). Ask yeast how to burn your fats: lessons learned from the metabolic adaptation to salt stress. Current Genetics. 64(1):63-69. https://doi.org/10.1007/s00294-017-0724-5S6369641Aguilera J, Prieto JA (2001) The Saccharomyces cerevisiae aldose reductase is implied in the metabolism of methylglyoxal in response to stress conditions. Curr Genet 39:273–283Albertyn J, Hohmann S, Thevelein JM, Prior BA (1994) GPD1, which encodes glycerol-3-phosphate dehydrogenase, is essential for growth under osmotic stress in Saccharomyces cerevisiae, and its expression is regulated by the high-osmolarity glycerol response pathway. Mol Cell Biol 14:4135–4144Alepuz PM, Jovanovic A, Reiser V, Ammerer G (2001) Stress-induced map kinase Hog1 is part of transcription activation complexes. Mol Cell 7:767–777Alepuz PM, de Nadal E, Zapater M, Ammerer G, Posas F (2003) Osmostress-induced transcription by Hot1 depends on a Hog1-mediated recruitment of the RNA Pol II. EMBO J 22:2433–2442Ansell R, Granath K, Hohmann S, Thevelein JM, Adler L (1997) The two isoenzymes for yeast NAD+-dependent glycerol 3-phosphate dehydrogenase encoded by GPD1 and GPD2 have distinct roles in osmoadaptation and redox regulation. EMBO J 16:2179–2187Babazadeh R, Lahtvee PJ, Adiels CB, Goksor M, Nielsen JB, Hohmann S (2017) The yeast osmostress response is carbon source dependent. Sci Rep 7:990Bender T, Pena G, Martinou JC (2015) Regulation of mitochondrial pyruvate uptake by alternative pyruvate carrier complexes. EMBO J 34:911–924Berry DB, Gasch AP (2008) Stress-activated genomic expression changes serve a preparative role for impending stress in yeast. Mol Biol Cell 19:4580–4587Bilsland-Marchesan E, Arino J, Saito H, Sunnerhagen P, Posas F (2000) Rck2 kinase is a substrate for the osmotic stress-activated mitogen-activated protein kinase Hog1. Mol Cell Biol 20:3887–3895Brewster JL, Gustin MC (2014) Hog 1: 20 years of discovery and impact. Sci Signal 7:re7Clotet J, Posas F (2007) Control of cell cycle in response to osmostress: lessons from yeast. Methods Enzymol 428:63–76Clotet J, Escote X, Adrover MA, Yaakov G, Gari E, Aldea M, de Nadal E, Posas F (2006) Phosphorylation of Hsl1 by Hog1 leads to a G2 arrest essential for cell survival at high osmolarity. EMBO J 25:2338–2346Cook KE, O’Shea EK (2012) Hog1 controls global reallocation of RNA Pol II upon osmotic shock in Saccharomyces cerevisiae. Genes Genomes Genetics 2:1129–1136de Nadal E, Posas F (2015) Osmostress-induced gene expression—a model to understand how stress-activated protein kinases (SAPKs) regulate transcription. FEBS J 282:3275–3285de Nadal E, Alepuz PM, Posas F (2002) Dealing with osmostress through MAP kinase activation. EMBO Rep 3:735–740de Nadal E, Casadome L, Posas F (2003) Targeting the MEF2-like transcription factor Smp1 by the stress-activated Hog1 mitogen-activated protein kinase. Mol Cell Biol 23:229–237de Nadal E, Zapater M, Alepuz PM, Sumoy L, Mas G, Posas F (2004) The MAPK Hog1 recruits Rpd3 histone deacetylase to activate osmoresponsive genes. Nature 427:370–374Duch A, de Nadal E, Posas F (2013a) Dealing with transcriptional outbursts during S phase to protect genomic integrity. J Mol Biol 425:4745–4755Duch A, Felipe-Abrio I, Barroso S, Yaakov G, Garcia-Rubio M, Aguilera A, de Nadal E, Posas F (2013b) Coordinated control of replication and transcription by a SAPK protects genomic integrity. Nature 493:116–119Escote X, Zapater M, Clotet J, Posas F (2004) Hog1 mediates cell-cycle arrest in G1 phase by the dual targeting of Sic1. Nat Cell Biol 6:997–1002Ferreira C, van Voorst F, Martins A, Neves L, Oliveira R, Kielland-Brandt MC, Lucas C, Brandt A (2005) A member of the sugar transporter family, Stl1p is the glycerol/H+ symporter in Saccharomyces cerevisiae. Mol Biol Cell 16:2068–2076Gonzalez R, Morales P, Tronchoni J, Cordero-Bueso G, Vaudano E, Quiros M, Novo M, Torres-Perez R, Valero E (2016) New genes involved in osmotic stress tolerance in Saccharomyces cerevisiae. Front Microbiol 7:1545Ho YH, Gasch AP (2015) Exploiting the yeast stress-activated signaling network to inform on stress biology and disease signaling. Curr Genet 61:503–511Hohmann S (2015) An integrated view on a eukaryotic osmoregulation system. Curr Genet 61:373–382Hohmann S, Krantz M, Nordlander B (2007) Yeast osmoregulation. Methods Enzymol 428:29–45Hong SP, Carlson M (2007) Regulation of snf1 protein kinase in response to environmental stress. J Biol Chem 282:16838–16845Li SC, Diakov TT, Rizzo JM, Kane PM (2012) Vacuolar H+-ATPase works in parallel with the HOG pathway to adapt Saccharomyces cerevisiae cells to osmotic stress. Eukaryot Cell 11:282–291Maeta K, Izawa S, Inoue Y (2005) Methylglyoxal, a metabolite derived from glycolysis, functions as a signal initiator of the high osmolarity glycerol-mitogen-activated protein kinase cascade and calcineurin/Crz1-mediated pathway in Saccharomyces cerevisiae. J Biol Chem 280:253–260Manzanares-Estreder S, Espi-Bardisa J, Alarcon B, Pascual-Ahuir A, Proft M (2017) Multilayered control of peroxisomal activity upon salt stress in Saccharomyces cerevisiae. Mol Microbiol 104:851–868Mao K, Wang K, Zhao M, Xu T, Klionsky DJ (2011) Two MAPK-signaling pathways are required for mitophagy in Saccharomyces cerevisiae. J Cell Biol 193:755–767Martinez-Montanes F, Pascual-Ahuir A, Proft M (2010) Toward a genomic view of the gene expression program regulated by osmostress in yeast. OMICS 14:619–627Martinez-Pastor M, Proft M, Pascual-Ahuir A (2010) Adaptive changes of the yeast mitochondrial proteome in response to salt stress. OMICS 14:541–552Mas G, de Nadal E, Dechant R, Rodriguez de la Concepcion ML, Logie C, Jimeno-Gonzalez S, Chavez S, Ammerer G, Posas F (2009) Recruitment of a chromatin remodelling complex by the Hog1 MAP kinase to stress genes. EMBO J 28:326–336Mettetal JT, Muzzey D, Gomez-Uribe C, van Oudenaarden A (2008) The frequency dependence of osmo-adaptation in Saccharomyces cerevisiae. Science 319:482–484Molin C, Jauhiainen A, Warringer J, Nerman O, Sunnerhagen P (2009) mRNA stability changes precede changes in steady-state mRNA amounts during hyperosmotic stress. RNA 15:600–614Nadal-Ribelles M, Conde N, Flores O, Gonzalez-Vallinas J, Eyras E, Orozco M, de Nadal E, Posas F (2012) Hog1 bypasses stress-mediated down-regulation of transcription by RNA polymerase II redistribution and chromatin remodeling. Genome Biol 13:R106Pastor MM, Proft M, Pascual-Ahuir A (2009) Mitochondrial function is an inducible determinant of osmotic stress adaptation in yeast. J Biol Chem 284:30307–30317Petelenz-Kurdziel E, Kuehn C, Nordlander B, Klein D, Hong KK, Jacobson T, Dahl P, Schaber J, Nielsen J, Hohmann S, Klipp E (2013) Quantitative analysis of glycerol accumulation, glycolysis and growth under hyper osmotic stress. PLoS Comput Biol 9:e1003084Posas F, Chambers JR, Heyman JA, Hoeffler JP, de Nadal E, Arino J (2000) The transcriptional response of yeast to saline stress. J Biol Chem 275:17249–17255Proft M, Struhl K (2002) Hog1 kinase converts the Sko1-Cyc8-Tup1 repressor complex into an activator that recruits SAGA and SWI/SNF in response to osmotic stress. Mol Cell 9:1307–1317Proft M, Struhl K (2004) MAP kinase-mediated stress relief that precedes and regulates the timing of transcriptional induction. Cell 118:351–361Proft M, Pascual-Ahuir A, de Nadal E, Arino J, Serrano R, Posas F (2001) Regulation of the Sko1 transcriptional repressor by the Hog1 MAP kinase in response to osmotic stress. EMBO J 20:1123–1133Proft M, Mas G, de Nadal E, Vendrell A, Noriega N, Struhl K, Posas F (2006) The stress-activated Hog1 kinase is a selective transcriptional elongation factor for genes responding to osmotic stress. Mol Cell 23:241–250Ratnakumar S, Young ET (2010) Snf1 dependence of peroxisomal gene expression is mediated by Adr1. J Biol Chem 285:10703–10714Regot S, de Nadal E, Rodriguez-Navarro S, Gonzalez-Novo A, Perez-Fernandez J, Gadal O, Seisenbacher G, Ammerer G, Posas F (2013) The Hog1 stress-activated protein kinase targets nucleoporins to control mRNA export upon stress. J Biol Chem 288:17384–17398Rep M, Krantz M, Thevelein JM, Hohmann S (2000) The transcriptional response of Saccharomyces cerevisiae to osmotic shock. Hot1p and Msn2p/Msn4p are required for the induction of subsets of high osmolarity glycerol pathway-dependent genes. J Biol Chem 275:8290–8300Rep M, Proft M, Remize F, Tamas M, Serrano R, Thevelein JM, Hohmann S (2001) The Saccharomyces cerevisiae Sko1p transcription factor mediates HOG pathway-dependent osmotic regulation of a set of genes encoding enzymes implicated in protection from oxidative damage. Mol Microbiol 40:1067–1083Rienzo A, Poveda-Huertes D, Aydin S, Buchler NE, Pascual-Ahuir A, Proft M (2015) Different mechanisms confer gradual control and memory at nutrient- and stress-regulated genes in yeast. Mol Cell Biol 35:3669–3683Romero-Santacreu L, Moreno J, Perez-Ortin JE, Alepuz P (2009) Specific and global regulation of mRNA stability during osmotic stress in Saccharomyces cerevisiae. RNA 15:1110–1120Roy A, Hashmi S, Li Z, Dement AD, Cho KH, Kim JH (2016) The glucose metabolite methylglyoxal inhibits expression of the glucose transporter genes by inactivating the cell surface glucose sensors Rgt2 and Snf3 in yeast. Mol Biol Cell 27:862–871Ruiz-Roig C, Noriega N, Duch A, Posas F, de Nadal E (2012) The Hog1 SAPK controls the Rtg1/Rtg3 transcriptional complex activity by multiple regulatory mechanisms. Mol Biol Cell 23:4286–4296Saito H, Posas F (2012) Response to hyperosmotic stress. Genetics 192:289–318Sekito T, Thornton J, Butow RA (2000) Mitochondria-to-nuclear signaling is regulated by the subcellular localization of the transcription factors Rtg1p and Rtg3p. Mol Biol Cell 11:2103–2115Silva RD, Sotoca R, Johansson B, Ludovico P, Sansonetty F, Silva MT, Peinado JM, Corte-Real M (2005) Hyperosmotic stress induces metacaspase- and mitochondria-dependent apoptosis in Saccharomyces cerevisiae. Mol Microbiol 58:824–834Sole C, Nadal-Ribelles M, de Nadal E, Posas F (2015) A novel role for lncRNAs in cell cycle control during stress adaptation. Curr Genet 61:299–308Tamas MJ, Luyten K, Sutherland FC, Hernandez A, Albertyn J, Valadi H, Li H, Prior BA, Kilian SG, Ramos J, Gustafsson L, Thevelein JM, Hohmann S (1999) Fps1p controls the accumulation and release of the compatible solute glycerol in yeast osmoregulation. Mol Microbiol 31:1087–1104Teige M, Scheikl E, Reiser V, Ruis H, Ammerer G (2001) Rck2, a member of the calmodulin-protein kinase family, links protein synthesis to high osmolarity MAP kinase signaling in budding yeast. Proc Natl Acad Sci USA 98:5625–5630Timon-Gomez A, Proft M, Pascual-Ahuir A (2013) Differential regulation of mitochondrial pyruvate carrier genes modulates respiratory capacity and stress tolerance in yeast. PLoS One 8:e79405Vanacloig-Pedros E, Bets-Plasencia C, Pascual-Ahuir A, Proft M (2015) Coordinated gene regulation in the initial phase of salt stress adaptation. J Biol Chem 290:10163–10175Warringer J, Hult M, Regot S, Posas F, Sunnerhagen P (2010) The HOG pathway dictates the short-term translational response after hyperosmotic shock. Mol Biol Cell 21:3080–3092Wei CJ, Tanner RD, Malaney GW (1982) Effect of sodium chloride on bakers’ yeast growing in gelatin. Appl Environ Microbiol 43:757–763Westfall PJ, Patterson JC, Chen RE, Thorner J (2008) Stress resistance and signal fidelity independent of nuclear MAPK function. Proc Natl Acad Sci USA 105:12212–12217Ye T, Garcia-Salcedo R, Ramos J, Hohmann S (2006) Gis4, a new component of the ion homeostasis system in the yeast Saccharomyces cerevisiae. Eukaryot Cell 5:1611–1621Yoshida A, Wei D, Nomura W, Izawa S, Inoue Y (2012) Reduction of glucose uptake through inhibition of hexose transporters and enhancement of their endocytosis by methylglyoxal in Saccharomyces cerevisiae. J Biol Chem 287:701–71

Influence of the chemical structure on the kinetics of the structural relaxation process of acrylate and methacrylate polymer networks

The enthalpy relaxation of poly(hydroxyethyl methacrylate) (PHEMA), poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) networks, obtained by DSC, are compared. The temperature interval of the glass transition broadens in the sequence PEA-PEMA-PHEMA. The plots of the enthalpy loss during the annealing for 200 min at different temperatures below T g show that the structural relaxation process also takes place in PHEMA in a broader temperature interval than in PEA or PEMA. The modelling of the structural relaxation process using a phenomenological model allows determining the temperature dependence of the relaxation times concluding that the fragility in PHEMA is significantly lower than in PEMA. Both features are ascribed to the connectivity of the polymer chains in PHEMA via hydrogen bonding. The role of the presence of the methyl group bonded to the main chain is analysed by comparing the results obtained in PEA and PEMA

Dielectric relaxation spectrum of poly (ε-caprolactone) networks hydrophilized by copolymerization with 2-hydroxyethyl acrylate

The dielectric relaxation spectrum of polycaprolactone (PCL) networks hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) is investigated. PCL is a semicrystalline polyester with a complex relaxation spectrum that includes the main α relaxation and two secondary modes (β, γ) at lower temperatures. The overlapping of the different relaxational modes was split by using several Havriliak-Negami functions. Crosslinking the material modifies the dynamics of the main relaxation process as reflected by the parameters that characterize the Vogel behavior of the process and the dynamic fragility. The incorporation of HEA units in the network results in a material with microphase separation: two α processes are detected, the one corresponding to the PCL chains and the new one associated to nanometric regions that contain different amount of both comonomers. The incorporation of the HEA units in the system involves the presence of a new βsw relaxation due to the link of two side chains by water molecules through hydrogen bonding

Structure and dynamics in poly(L-lactide) copolymer networks

Poly(L-lactide) networks (PmLA) hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) were investigated by dielectric relaxation spectroscopy, thermally stimulated depolarization currents, and differential scanning calorimetry. The incorporation of HEA units in the PmLA network, with the aim of modulating the water sorption capacity of the system, results in a material with a complex behavior. The system consists of phase-separated microdomains richer in one or the other comonomers that constitute the network. Initially, the addition of smalls amount of HEA units in the network gives rise to a one-phase, two-component system; however, when the amount of HEA in the system increases, a new phase (HEA-rich one) is formed containing some mLA chains that modify the main relaxation mode of these domains and the local dynamics of the system. The structure of the system has been analyzed by comparing the relaxational modes in the PmLA and PHEA homonetworks with those in the copolymer networks

Thermal transitions and dynamics in nanocomposite hydrogels

Hydrogels based on nanocomposites of statistical poly(hydroxyethyl acrylate-co-ethyl acrylate) and silica, prepared by simultaneous copolymerization and generation of silica nanoparticles by sol-gel process at various copolymer compositions and silica contents, characterized by a fine dispersion of filler, were investigated with respect to glass transition and polymer dynamics by dielectric techniques. These include thermally stimulated depolarization currents and dielectric relaxation spectroscopy, covering together broad ranges of frequency and temperature. In addition, equilibrium water sorption isotherms were recorded at room temperature (25 A degrees C). Special attention was paid to the investigation of effects of silica on glass transition, polymer dynamics (secondary gamma and beta (sw) relaxations and segmental alpha relaxation), and electrical conductivity in the dry systems (xerogels) and in the hydrogels at various levels of relative humidity/water content. An overall reduction of molecular mobility is observed in the nanocomposite xerogels, in particular at high silica contents. Analysis of the results and comparison with previous work on similar systems enable to discuss this reduction of molecular mobility in terms of constraints to polymeric motion imposed by interfacial polymer-filler interactions and by the formation of a continuous silica network interpenetrated with the polymer network at filler contents higher than about 15 wt%.The research leading to these results has received support from the program for basic research PEBE 2010 funded by the National Technical University of Athens.Kyritsis, A.; Spanoudaki, A.; Pandis, C.; Hartmann, L.; Pelster, R.; Shinyashiki, N.; Rodríguez Hernández, JC.... (2012). Thermal transitions and dynamics in nanocomposite hydrogels. Journal of Thermal Analysis and Calorimetry. 108(3):1067-1078. doi:10.1007/s10973-011-2093-5S106710781083Peppas NA, editor. Hydrogels in medicine and pharmacy, vol. I. Boca Raton, FL: CRC Press; 1986.Stoy V, Kliment C. Hydrogels: speciality plastics for biomedical and pharmaceutical applications. Basel: Technomic; 1996.Kyritsis A, Pissis P, Gomez Ribelles JL, Monleon Pradas M. Depolarization thermocurrent studies in poly(hydroxyethyl acrylate)/water hydrogels. J Polym Sci Part B Polym Phys. 1994;32:1001–8.Kyritsis A, Pissis P, Grammatikakis J. Dielectric relaxation spectroscopy in poly(hydroxyethyl acrylate)/water hydrogels. J Polym Sci Part B Polym Phys. 1995;33:1737–50.Kyritsis A, Pissis P, Gomez Ribelles JL, Monleon Pradas M. Polymer-water interactions in poly(hydroxyethyl acrylate) hydrogels studied by dielectric, calorimetric and sorption isotherm measurements. Polym Gels Netw. 1995;3:445–69.Gallego Ferrer G, Monleon Pradas M, Gomez Ribelles JL, Pissis P. Swelling and thermally stimulated depolarization currents in hydrogels formed by interpenetrating polymer networks. J Non-Cryst Solids. 1998;235–237:692–6.Gomez Ribelles JL, Monleon Pradas M, Gallego Ferrer G, Peidro Torres N, Perez Gimenez V, Pissis P, Kyritsis A. Poly(methyl acrylate)/poly(hydroxyethyl acrylate) sequential interpenetrating polymer networks. Miscibility and wáter sorption behavior. J Polym Sci Part B Polym Phys. 1999;37:1587–99.Campillo-Fernandez AJ, Salmeron Sanchez M, Sabater i Serra R, Meseguer Duenas JM, Monleon Pradas M, Gomez Ribelles JL. Water-induced (nano) organization in poly(ethyl acrylate-co-hydroxyethyl acrylate) networks. Eur Polym J. 2008;44:1996–2004.Kyritsis A, Spanoudaki A, Pandis C, Hartmann L, Pelster R, Shinyashiki N, Rodríguez Hernández JC, Gómez Ribelles JL, Monleón Pradas M, Pissis P. Water and polymer dynamics in poly(hydroxyl ethyl acrylate-co-ethyl acrylate) copolymer hydrogels. Eur Polym J. 2011;47:2391–2402.Haraguchi K. Nanocomposite hydrogels. Curr Opin Solid State Mater Sci. 2007;11:47–54.Janovák L, Varga J, Kemény L, Dékány I. Swelling properties of copolymer hydrogels in the presence of montmorillonite and alkylammonium montmorillonite. Appl Clay Sci. 2009;43:260–70.Janovák L, Varga J, Kemény L, Dékány I. The effect of surface modification of layer silicates on the thermoanalytical properties of poly(NIPAAm-co-AAm) based composite hydrogels. J Therm Anal Calorim. 2009;98:485–93.Rodriguez Hernandez JC, Salmeron Sanchez M, Gomez Ribelles JL, Monleon Pradas M. Polymer-silica nanocomposites prepared by sol–gel technique: nanoindentation and tapping mode AFM studies. Eur Polym J. 2007;43:2775–83.Rodriguez Hernandez JC, Monleon Pradas M, Gomez Ribelles JL. Properties of poly(2-hydroxyethyl acrylate)-silica nanocomposites obtained by the sol–gel process. J Non-Cryst Solids. 2008;354:1900–8.Pandis C, Spanoudaki A, Kyritsis A, Pissis P, Rodriguez Hernandez JC, Gomez Ribelles JL, Monleon Pradas M. Water sorption characteristics of poly(2-hydroxyethyl acrylate)/silica nanocomposite hydrogels. J Polym Sci Part B Polym Phys. 2011;49:657–68.Stathopoulos A, Klonos P, Kyritsis A, Pissis P, Christodoulides C, Rodriguez Hernandez JC, Monleon Pradas M, Gomez Ribelles JL. Water sorption and polymer dynamics in hybrid poly(hydroxyethyl-co-ethyl acrylate)/silica hydrogels. Eur Polym J. 2010;46:101–11.Kremer F, Schoenhals A, editors. Broadband dielectric spectroscopy. Berlin: Springer; 2002.Donth E. The glass transition: relaxation dynamics in liquids and disordered materials. Berlin: Springer; 2001.Havriliak S Jr, Havriliak SJ. Dielectric and mechanical relaxation in materials. Munich: Hanser; 1997.Kripotou S, Pissis P, Savelyev YV, Robota LP, Travinskaya TV. Polymer dynamics in polyurethane/clay nanocomposites studied by dielectric and thermal techniques. J Macromol Sci Phys. 2010;49:86–110.Pelster R, Spanoudaki A, Kruse T. Microstructure and effective properties of nanocomposites: ferrofluids as tunable model systems. J Phys D Appl Phys. 2004;37:307–17.Pissis P, Kyritsis A. Electrical conductivity studies in hydrogels. Solid State Ionics. 1997;97:105–13.Angell CA. Relaxation in liquids, polymers and plastic crystals—strong/fragile patterns and problems. J Non-Cryst Solids. 1991;131–133:13–31.Fragiadakis D, Pissis P. Glass transition and segmental dynamics in poly(dimethylsiloxane)/silica nanocomposites studied by various techniques. J Non-Cryst Solids. 2007;353:4344–52.Kourkoutsaki Th, Logakis E, Kroutilova I, Matejka L, Nedbal J, Pissis P. Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsequioxanes nanocomposites. J Appl Polym Sci. 2009;113:2569–82.Fragiadakis D, Bokobza L, Pissis P. Dynamics near the particle surface in natural rubber–silica nanocomposites. Polymer. 2011;52:3175–3182.Klonos P, Panagopoulou A, Bokobza L, Kyritsis A, Peoglos V, Pissis P. Comparative studies on effects of silica and titania nanoparticles on crystallization and complex segmental dynamics in poly(dimethylsiloxane). Polymer. 2010;51:5490–9.Napolitano S, Wuebbenhorst M. The lifetime of the deviations from bulk behavior in polymers confined at the nanoscale. Nat Commun. 2011;2:260. doi: 10.1038/incomms1259