No description available.

This review concentrates on findings described in the recent literature on the response of cells and tissues to electromagnetic fields (EMF). Models of the causal interaction between different forms of EMF and ions or biomolecules of the cell will be presented together with our own results in cell surface recognition. Naturally occurring electric fields are not only important for cell-surface interactions but are also pivotal for the normal development of the organism and its physiological functions. A further goal of this review is to bridge the gap between recent cell biological studies (which, indeed, show new data of EMF actions) and aspects of EMF-based therapy, e.g., in wounds and bone fractures. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

No description available.

No description available.

Surfactants, polymers, and their mixtures are widely used in commercial formulations of paints, water-based adhesives, detergents, food, and other products. This thesis describes measurements of the forces acting on colloidal particles in surfactant and polymer solutions. The change in force on addition of surfactants and polymers is usually caused by adsorption to an interface. In this thesis, I also describe the effect of surface charge density, surface crystallinity, surface heterogeneity, and preadsorbed polymer on surfactant adsorption. A new method for the stabilization of colloidal particles is introduced via the synthesis and adsorption of unnatural proteins. Unnatural proteins can be synthesized using the natural "machinery" of a bacterial cell with almost any primary sequence, and provide an environmentally friendly route to colloidal stabilization. As a model system, we study the stabilization of alumina, because alumina has a high Hamaker constant and is therefore difficult to stabilize. An unnatural protein with the sequence, thioredoxin-Pro39Glu10 is used. The Glu10 is anionic (pH > 3) and is designed to adsorb to positively charged alumina (pH<9). The thioredoxin-Pro39 is hydrophilic so it should remain in solution, thereby providing a steric barrier to the approach of two particles in a range of salt and pH conditions. Ellipsometry experiments show that thioredoxin-Pro39Glu10 adsorbs to alumina. Force measurements with the Atomic Force Microscopy (AFM) colloid probe technique show that adsorption of the unnatural protein leads to repulsive forces that decay exponentially with the separation between the surfaces, and are independent of salt concentration. The loss of a salt-dependent force shows that adsorption of the unnatural protein has effectively neutralized the charge on the alumina. Thus, I have shown that an unnatural protein can be used to control the stability of a colloidal system. In general, the same hydrophilic block can probably be added to a variety of anchoring blocks to stabilize different colloidal particles. Electrostatic forces are frequently responsible for the stabilization of colloidal particles. The decay length of these forces is dictated by the electrolyte concentration. The relationship between the decay length and the concentration is well understood for fully dissociated 1:1 electrolytes. Here, I examine the decay-length in solutions where the ions associate strongly. The forces are measured between silica surfaces in aqueous carboxylic acid and surfactant solutions. The decay lengths of the electrostatic double-layer force in both these solutions are well described by the usual expression for decay length when the concentration of ions is obtained from an activity measurement. The effect of the surface properties of the solid substrate on surfactant adsorption is also described in this thesis. The adsorption characteristics of a charged surfactant onto fixed charged surfaces as a function of surface charge density is reported. This is the first time that a method has been introduced for making a series of known fixed charged surfaces. Investigating surfactant adsorption to these surfaces has improved our understanding of the role of charge density in surfactant adsorption and desorption. The desired surface charge density is achieved by the use of gold-thiol self-assembled monolayers (SAMs) of different Ï -groups ("OH and "N+(CH3)3). The mole fraction of "N+(CH3)3 on the mixed SAM dictates the surface charge density. The charge on "N+(CH3)3 is fixed and does not self-regulate. The adsorption of sodium dodecyl sulfate (SDS) to the interface between these model surfaces and aqueous solutions of SDS is investigated. Atomic Force Microscopy (AFM) of the adsorbed surfactant reveals no surface micelles above the critical micelle concentration, cmc, over a wide variety of "N+(CH3)3 densities. This shows that the lateral mobility of ions other than surfactant at the interface is important for the formation of surface micelles of ionic surfactants. Adsorption isotherms of SDS (with no added salt) measured by Surface Plasmon Resonance (SPR) show a plateau region in which the surface excess of SDS is equal to the known fixed surface charge. This demonstrates that the adsorption is electrostatically driven. There is no critical surface charge density at which adsorption rises rapidly. Thus there appears to be no 'hemimicelle concentration'. My work suggests that the formation of hemimicelles depends on the lateral mobility of the surface ions. Desorption experiments starting above the cmc show rapid desorption of SDS into water until the surface excess is equal to the surface charge density. The rapid desorption is followed by a much slower desorption. The elucidation of this fast-slow desorption pattern based on charge density is made possible by the preparation of a set of constant charge surfaces. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do presente trabalho foi estudar o comportamento dos potenciais superficiais e do perfil de potencial atraves da membrana de eritr ocito em func ao da forca i onica e das cargas superficiais, usando um modelo que leva em conta as cargas el etricas do glicoc alix e das prote&#305;nas citoplasm aticas, al em das cargas superficiais da bicamada lip&#305;dica e os efeitos dos eletr olitos divalentes. Programas espec&#305;ficos em linguagem C foram elaborados para o c alculo desses potenciais, tomando como dados num ericos resultados experimentais de medidas de mobilidade eletrofor etica de eritr ocitos para diferentes valores de forca i onica. Neste c alculo, o metodo para tratamento dos dados eletrofor eticos indicado por Hsu et al.[57] foi inclu&#305;do em nosso modelo. A equac ao de Poisson-Boltzmann nao linear foi resolvida por computac ao num erica, usando o metodo de Runge-Kutta de quarta ordem, obtendo-se os perfis de potencial. Os resultados mostraram que a estimativa da densidade de carga el etrica na superf&#305;cie de c elulas usando a equac ao cl assica de Helmholtz-Smoluchowski conduz a valores que nao conseguem refletir as forcas que regem o comportamento eletrofor etico das mesmas. O presente modelo gerou valores de potenciais superficiais e perfis de potencial para a membrana do eritr ocito bem distintos daqueles obtidos anteriormente para um modelo descrito por uma equac ao de Poisson-Boltzmann linear. Nossos resultados confirmam que a avaliac ao de parametros el etricos superficiais da membrana de eritr ocito, envolvendo dados oriundos de eletroforese, deve incluir c alculos hidrodin amicos al em de eletroest aticos, como sugerido por Hsu et al. [57]. / The aim of present work was to study the behavior of the surface potentials and the potential profile across erythrocyte membrane in function of ionic strength and surface charge, using a model which takes into account electrical charges on glycocalyx and citoplasmatic proteins, in addition surface charges on lipid bylayer and effects due to mono and divalent electrolytes. Programs in C language were build to estimate the surface potentials, and experimental values of electrophoretic mobilities of erythrocytes for different ionic strength were applied. For this calculation, the method indicated by Hsu et al. [57] for treating electrophoretic data was included in our model. The non linear Poisson-Boltzmann equation was solved by numerical computation, using the forth order Range-Kutta method, to give the potential profiles. Results showed that values of electric charge on cellular surface obtained by applying the classical Helmholtz-Smoluchowski equation were not able to represent the forces involved in the electrophoretic behavior of cells. The present model generate values for surface potentials and potential profiles different from those obtained in previous work for a model described by linear Poisson- Boltzmann equation. According to our results, the estimation of surface electric parameters for the erythrocyte membrane from electrophoretic data must ese hydrodynamics and electrostatics calculations, as suggested by Hsu et al. [57]

Chemische und physikalische Eigenschaften von Polymeren können verschiedene Zelltypen unterschiedlich, z. B. hinsichtlich Adhärenz oder Funktionalität, beeinflussen. Die Elastizität eines Polymers beeinflusst vor allem, welche Zugkräfte eine Zelle gegenüber ihrem Substrat entwickeln kann. Das Zellverhalten wird dann über intrazelluläre Rückkopplungsmechanismen reguliert. Die Oberflächenladung und/oder Hydrophilie eines Polymers beeinflusst zunächst die Adsorption von Ionen, Proteinen und anderen Molekülen. Vor allem über die Zusammensetzung, Dichte und Konformation der adsorbierten Komponenten werden anschließend die Wechselwirkungen mit den Zellen vermittelt. Des Weiteren können verschiedene Zelltypen unterschiedliche membranassoziierte Proteine, Zucker und Lipide aufweisen, so dass Polymereigenschaften zellspezifische Effekte bewirken können. Für biotechnologische Anwendungen und für den Einsatz in der regenerativen Medizin gewinnen Polymere, die spezifische Zellreaktionen regulieren können, immer weiter an Bedeutung. Die Isolierung und Kultur von primären Keratinozyten ist noch immer anspruchsvoll und die adäquate Heilung von Hautwunden stellt eine fortwährende medizinische Herausforderung dar. Ein Polymer, das eine bevorzugte Adhärenz von Keratinozyten bei gleichzeitig verminderter Anheftung dermaler Fibroblasten ermöglicht, würde erhebliche Vorteile für den Einsatz in der Keratinozyten-Zellkultur und als Wundauflage bieten. Um den potentiell spezifischen Einfluss bestimmter Polymereigenschaften auf primäre humane Keratinozyten und dermale Fibroblasten zu untersuchen, wurde in der vorliegenden Arbeit ein Zellkultursystem für die Mono- und Cokultur beider Zelltypen entwickelt. Das Testsystem wurde als Screening konzipiert, um den Einfluss unterschiedlicher Polymereigenschaften in mehreren Abstufungen auf die Zellen zu untersuchen. Folgende Parameter wurden untersucht: 1. Vitalität und Dichte adhärenter und nicht-adhärierter Zellen, 2. Schädigung der Zellmembran, 3. selektive Adhärenz von Keratinozyten in Cokultur durch die spezifische immunzytochemische Färbung von Keratin14 und Vimentin. Für die Polymere mit variabler Elastizität wurden zusätzlich die Ablagerung extrazellulärer Matrixkomponenten und die Sekretion löslicher Faktoren durch die Zellen untersucht. Als Modellpolymere für die Variation der Elastizität wurden vernetzte Poly(n-butylacrylate) (cPnBA) verwendet, da deren Elastizität durch den Anteil des Vernetzers eingestellt werden kann. Auf dem weniger elastischen cPnBA zeigte sich in der Cokultur ein doppelt so hohes Verhältnis von Keratinozyten zu Fibroblasten wie auf dem elastischeren cPnBA, so dass ein leichter zellselektiver Effekt angenommen werden kann. Acrylnitril-basierte Copolymere wurden als Modellpolymere für die Variation der Oberflächenladung und Hydrophilie verwendet, da die Eigenschaften durch Art und molaren Anteil des Comonomers eingestellt werden können. Durch Variation des molaren Anteils der Comonomere mit positiver bzw. negativer Ladung, Methacrylsäure-2-aminoethylester-hydrochhlorid (AEMA) und N-3-Aminopropyl-methacrylamid-hydro-chlorid (APMA) bzw. Natriumsalz der 2-Methyl-2-propen-1-sulfonsäure (NaMAS), wurde der Anteil der positiven bzw. negativen Ladung im Copolymer variiert. Durch die Erhöhung des molaren Anteils des hydrophilen Comonomers N-Vinylpyrrolidon (NVP) wurde die Hydrophilie des Copolymers gesteigert. Die Erhöhung des molaren Anteils an positiv geladenem Comonomer AEMA im Copolymer führte tendenziell zu einer höheren Keratinozytendichte, wobei die Fibroblastendichte unverändert blieb. Durch die Erhöhung des molaren Anteils des positiv geladenen Comonomers APMA ergaben sich keine deutlichen Unterschiede in Dichte, Vitalität oder Selektivität der Zellen. Durch die stufenweise Erhöhung des molaren Anteils des negativ geladenen Comonomers NaMAS konnte, wie im Falle von AEMA, eine Tendenz zur verbesserten Keratinozytenadhärenz beobachtet werden. Die Steigerung der Hydrophilie der Copolymere führte sowohl für Keratinozyten als auch für Fibroblasten zu einer reduzierten Adhärenz und Vitalität. In der vorliegenden Doktorarbeit wurde ein Testverfahren etabliert, das die Untersuchung von primären humanen Keratinozyten und primären humanen Fibroblasten in Monokultur und Cokultur auf verschiedenen Polymeren ermöglicht. Die bisherigen Ergebnisse zeigen, dass sich durch die gezielte Modifizierung verschiedener Polymereigenschaften die Adhärenz und Vitalität beider Zelltypen beeinflussen lässt. Die Reduktion der Elastizität sowie die Erhöhung des molaren Anteils geladener Comonomere führten zu einer Zunahme der Keratinozytenadhärenz. Da die Fibroblasten unbeeinflusst blieben, zeigte sich für einige der untersuchten Polymere eine leichte Zellselektivität. Diese könnte durch die weitere Erhöhung der Steifigkeit oder des Anteils geladener Comonomere möglicherweise weiter gesteigert werden. / Chemical and physical properties of polymers can influence various cell types, e.g. concerning adherence and functionality. For instance, the elasticity of a polymer can influence, which pulling force a cell can generate towards a substrate. According to the cell type, its behavior can be controlled by intracellular feedback mechanisms. The surface charge and/or hydrophilicity of a polymer initially influence the adsorption of ions, proteins and other molecules. In particular, the composition, density, and conformation of the adsorbed components mediate the cell-material interactions. Since different cell types present varying cell membrane associated proteins, sugars and lipids, it is assumed that polymer properties can induce cell specific effects. Polymers, which can regulate specific cell reactions, become more and more important for biotechnological uses and applications in the regenerative medicine. The isolation and culture of primary keratinocytes is still challenging and an adequate wound healing remains a clinical task. A polymer, which enables a preferential adherence of keratinocytes and induces a reduced adherence of dermal fibroblasts, would provide enormous advantages for keratinocyte culture systems as well as for wound dressings. To investigate the specific influence of certain polymer properties on primary human keratinocytes and fibroblasts, a cell culture system for mono- and coculture of both cell types was established. The test system was designed as a screening to investigate the influence of polymers with gradations of different properties on the cells. Thereby, the viability and density of adherent and not adhered cells, as well as the impairment of the cell membranes were analyzed in mono- and cocultures, and the selective adherence of keratinocytes in the coculture was evaluated using a specific immunocytochemical staining for keratin14 and vimentin. Furthermore, the deposition of extracellular matrix components and the secretion of soluble factors were analyzed for the elastic polymers. Since the elasticity of crosslinked poly(n-butylacrylate) (cPnBA) networks can be adjusted by the amount of the crosslinker, they were used as model polymers to investigate the influence of varying elasticity to the cells. On the less elastic cPnBA, the ratio of keratinocytes to fibroblasts was increased compared to the more elastic one. From these results, a slight cell selective effect can be assumed. Acrylonitrile-based copolymers were used as model polymers for the variation of surface charge and hydrophilicity, since their properties can be modified by the type and molar ratio of comonomers. By the variation of the molar ratio of positively charged comonomers (Methacrylic acid-2-aminoethylester hydrochloride (AEMA) and N-3-aminopropyl methacrylamide hydrochloride (APMA)), or a negatively charged comonomer (2-methyl-2-propene-1-sulfonic acid sodium salt (NaMAS)), the amount of positive or negative charges was modified. The hydrophilicity was increased by the molar ratio of the hydrophilic comonomer N-vinylpyrrolidone (NVP). With an increased molar ratio of the positively charged comonomer AEMA, a tendency towards a higher density of adherent keratinocytes could be shown, whereby, the density of adherent fibroblasts remained unaffected. With increasing molar ratios of the positively charged comonomer APMA, no differences between cell densities, viability or selectivity were detectable. Comparable to AEMA, a tendency towards improved keratinocyte adhesion could be shown with an increasing molar ratio of the negatively charged comonomer NaMAS. The increase of the hydrophilicity of the copolymers led to a reduced adherence and viability of the keratinocytes, as well as of the fibroblasts. In conclusion, a test system was established, which enables the evaluation of primary human keratinocytes and fibroblasts in contact with different polymers in monoculture, as well as in coculture. Furthermore, the present thesis shows that directed modifications of polymer properties influenced the adherence and viability of both cell types. The decrease of elasticity and the increase of the molar ratio of charged comonomers led to an increased keratinocyte adherence. Since the fibroblasts remained unaffected, slight cell selectivity was shown. By further increasing the stiffness or the amount of charged comonomers, further enhancement of this effect might be possible.

Since single nanopores were firstly proposed as a potential rapid and low-cost tool for DNA sequencing in 1990s (PNAS, 1996, 93, 13770), extensive studies on both biological and synthetic nanopores and nanochannels have been reported. Nanochannel based stochastic sensing at single molecular level has been widely reported through the detection of transient ionic current changes induced by geometry blockage due to analytes translocation. Novel properties, including ion current rectification (ICR), memristive and memcapacitive behaviors were reported. These fundamental properties of nanochannels arise from the nanoscale dimensions and enables applications not only in single molecule sensing, but also in drug delivery, electrochemical energy conversion, concentration enrichment and separation, nanoprecipitation, nanoelectronics etc. Electrostatic interactions at nanometer-scale between the fixed surface charges and mobile charges in solution play major roles in those applications due to high surface to volume ratio. However, the knowledge of surface charge density (SCD) at nanometer scale is inaccessible within nanoconfinement and often extrapolated from bulk planar values. The determination of SCD at nanometer scale is urgently needed for the interpretation of aforementioned phenomena. This dissertation mainly focuses on the determination of SCD confined at a nanoscale device with known geometry via combined electroanalytical measurements and theoretical simulation. The measured currents through charged nanodevices are different for potentials with the same amplitude but opposite polarities, which deviates away from linear Ohm's behavior, known as ICR. Through theoretical simulation of experiments by solving Poisson and Nernst-Planck equations, the SCD within nanoconfinement is directly quantified for the first time. An exponential gradient SCD is introduced on the interior surface of a conical nanopre based on the gradient distribution of applied electric field. The physical origin is proposed based on the facilitated deprotonation of surface functional groups by the applied electric field. The two parameters that describe the non-uniform SCD distribution: maximum SCD and distribution length are determined by fitting high- and low-conductivity current respectively. The model is validated and applied successfully for quantification and prediction of mass transport behavior in different electrolyte solutions. Furthermore, because the surface charge distribution, the transport behaviors are intrinsicaly heterogeneous at nanometer scale, the concept is extended to noninvasively determine the surface modification efficacy of individual nanopore devices. Preliminary results of single molecule sensing based on streptavidin-iminobiotin are included. The pH dependent binding affinity of streptavidin-iminobiotin binding is confirmed by different current change signals ("steps" and "spikes") observed at different pHs. Qualitative concentration and potential dependence have been established. The chemically modified nanopores are demonstrated to be reusable through regenerating binding surface.

To test nanosize surface patterning for application as implant material, a suitable titanium composition has to be found first. Therefore we investigated the effect of surface chemistry on attachment and differentiation of osteoblast-like cells on pure titanium prepared by pulsed laser deposition (TiPLD) and different Ti alloys (Ti6Al4V, TiNb30 and TiNb13Zr13). Early attachment (30 min) and alkaline phosphatase (ALP) activity (day 5) was found to be fastest and highest, respectively, in cells grown on TiPLD and Ti6Al4V. Osteoblasts seeded on TiPLD produced most osteopontin (day 10), whereas expression of this extracellular matrix protein was an order of magnitude lower on the TiNb30 surface. In contrast, expression of the corresponding receptor, CD44, was not influenced by surface chemistry. Thus, TiPLD was used for further experiments to explore the influence of surface nanostructures on osteoblast adhesion, differentiation and orientation. By laser-induced oxidation, we produced patterns of parallel Ti oxide lines with different widths (0.2–10 μm) and distances (2–20 and 1,000 μm), but a common height of only 12 nm. These structures did not influence ALP activity (days 5–9), but had a positive effect on cell alignment. Two days after plating, the majority of the focal contacts were placed on the oxide lines. The portion of larger focal adhesions bridging two lines was inversely related to the line distance (2–20 μm). In contrast, the portion of aligned cells did not depend on the line distance. On average, 43% of the cells orientated parallel towards the lines, whereas 34% orientated vertically. In the control pattern (1,000 μm line distance), cell distribution was completely at random. Because a significant surplus of the cells preferred a parallel alignment, the nanosize difference in height between Ti surface and oxide lines may be sufficient to orientate the cells by contact guiding. However, gradients in electrostatic potential and surface charge density at the Ti/Ti oxide interface may additionally influence focal contact formation and cell guidance. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do presente trabalho foi estudar o comportamento dos potenciais superficiais e do perfil de potencial atraves da membrana de eritr ocito em func ao da forca i onica e das cargas superficiais, usando um modelo que leva em conta as cargas el etricas do glicoc alix e das prote&#305;nas citoplasm aticas, al em das cargas superficiais da bicamada lip&#305;dica e os efeitos dos eletr olitos divalentes. Programas espec&#305;ficos em linguagem C foram elaborados para o c alculo desses potenciais, tomando como dados num ericos resultados experimentais de medidas de mobilidade eletrofor etica de eritr ocitos para diferentes valores de forca i onica. Neste c alculo, o metodo para tratamento dos dados eletrofor eticos indicado por Hsu et al.[57] foi inclu&#305;do em nosso modelo. A equac ao de Poisson-Boltzmann nao linear foi resolvida por computac ao num erica, usando o metodo de Runge-Kutta de quarta ordem, obtendo-se os perfis de potencial. Os resultados mostraram que a estimativa da densidade de carga el etrica na superf&#305;cie de c elulas usando a equac ao cl assica de Helmholtz-Smoluchowski conduz a valores que nao conseguem refletir as forcas que regem o comportamento eletrofor etico das mesmas. O presente modelo gerou valores de potenciais superficiais e perfis de potencial para a membrana do eritr ocito bem distintos daqueles obtidos anteriormente para um modelo descrito por uma equac ao de Poisson-Boltzmann linear. Nossos resultados confirmam que a avaliac ao de parametros el etricos superficiais da membrana de eritr ocito, envolvendo dados oriundos de eletroforese, deve incluir c alculos hidrodin amicos al em de eletroest aticos, como sugerido por Hsu et al. [57]. / The aim of present work was to study the behavior of the surface potentials and the potential profile across erythrocyte membrane in function of ionic strength and surface charge, using a model which takes into account electrical charges on glycocalyx and citoplasmatic proteins, in addition surface charges on lipid bylayer and effects due to mono and divalent electrolytes. Programs in C language were build to estimate the surface potentials, and experimental values of electrophoretic mobilities of erythrocytes for different ionic strength were applied. For this calculation, the method indicated by Hsu et al. [57] for treating electrophoretic data was included in our model. The non linear Poisson-Boltzmann equation was solved by numerical computation, using the forth order Range-Kutta method, to give the potential profiles. Results showed that values of electric charge on cellular surface obtained by applying the classical Helmholtz-Smoluchowski equation were not able to represent the forces involved in the electrophoretic behavior of cells. The present model generate values for surface potentials and potential profiles different from those obtained in previous work for a model described by linear Poisson- Boltzmann equation. According to our results, the estimation of surface electric parameters for the erythrocyte membrane from electrophoretic data must ese hydrodynamics and electrostatics calculations, as suggested by Hsu et al. [57]