Non-invasive and controlled release of bioactive compounds is an important goal in the development of drug delivery systems and novel biomaterials for tissue engineering. This project aims to exert spatio-temporal control over the release of bioactive compounds from phospholipid vesicle carriers by crosslinking them with superparamagnetic iron oxide nanoparticles to form a magnetic release nanostructure. The magnetic properties of the nanoparticles allow release to be triggered by an alternating magnetic field (AMF), which induces localised heating and “melts” the vesicle membranes. The aggregates can also be manipulated in space by a static magnetic field to create patterned materials. Incorporation of these aggregates into hydrogels has created novel responsive biomaterials. Controlled release of ascorbic acid-2-phosphate has been used to induce collagen production by chondrocytes, demonstrating an AMF triggered cellular response in vitro. The existing system has been redesigned after detailed characterisation and assessment of the performance of each component. Magnetic release has been extensively assessed using fluorescence techniques to quantify release, and optimised through the development of new silica-derived nanoparticle coatings and aggregate formulations informed by quantitative characterisation of nanoparticle functionalisation. The replacement of calcium alginate hydrogels as a 3D cell culture matrix with hyaluronic acid- based hydrogels was found to eliminate gel-induced leakage of vesicle contents and also improves the compatibility of the system with a greater range of cell types. Recently the effective encapsulation and AMF-triggered release of proteins including enzymes has been demonstrated and released enzymes have been demonstrated to retain their activity. Released trypsin was shown to retain proteolytic activity while hyaluronidase released into hyaluronan-derived hydrogels has been demonstrated to influence the rheological properties of the gel. A galactose-terminated lipid has been synthesised that enables specific targeting of the asialoglycoprotein (ASGPR) cell surface receptor receptor found in human hepatocytes, demonstrating the potential for customisation of the MNPV system to particular requirements.

Orientador: Fauze Ahmad Aouada / Resumo: Neste trabalho, primeiramente foram desenvolvidos hidrogéis nanocompósitos baseados em poli(ácido metacrílico) (PMAA) e nanoargilas cloisita-Na+, laponitas RD (Lpt RD) e RDS (Lpt RDS) por meio de polimerização via radical livre. A formação do nanocompósito e o grau de dispersão das nanoargilas junto a matriz polimérica foram investigados por análise de FTIR, MEV e DRX. A presença do argilomineral se apresentou um fator importante no que diz respeito ao aumento da capacidade de absorver água (Q) dos hidrogéis, atingindo um máximo em 5% de incorporação das Lpts no PMAA, além de uma melhora na estabilidade térmica dos nanocompósitos comprovada por TG. Assim como as nanocargas, o pH do meio também é um fator determinante para o controle do intumescimento. Pois, os grupos carboxílicos do PMAA sofrem ionização dependendo do pH da solução, aumentando assim o intumescimento do hidrogel. Segundo, foi realizado um estudo relativo à eficiência da adsorção pelos nanocompósitos (nanoargilas Lpt RD, Lpt RDS e cloisita-Na+) do herbicida paraquat (PQ) e sua posterior liberação em solução aquosa. Mais uma vez a presença do argilomineral se mostrou relevante, aumentando para 100% de eficiência no carregamento para nanocompósitos constituídos por 20% de nanoargilas. As adsorções em todas as formulações dos nanocompósitos se ajustaram à isoterma de Langmuir. Enquanto o modelo de isoterma de Freundlich foi o melhor modelo para a matriz sem nanoargila. Todas as isotermas apresentaram perfil de ads... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, initially, nanocomposite hydrogels based on poly(methacrylic acid) (PMAA), closite-Na+, laponite RD (Lpt RD) and laponite RDS (Lpt RDS) nanoclays were synthesized from free radical polymerization. The formation of the nanocomposite and the degree of dispersion of the nanoclays into polymeric matrices were investigated by FTIR, SEM, and XRD techniques. The presence of the clay mineral was a significant factor because it increased the capacity of water absorption (SD) of the hydrogels, reaching a maximum of 5% of Lpts into PMAA. Besides, the thermal stability of the nanocomposites, confirmed by TG, was increased by clay presence. As the nanofillers, the pH of the environment is also a determinant factor for the control of swelling. Because the carboxyl groups of the PMAA undergo ionization depending on the pH of the solution, increasing the swelling of the hydrogel. Then, a study was carried out on the adsorption efficiency of the herbicide paraquat (PQ) using hydrogel nanocomposites (with Lpt RD, Lpt RDS, and cloisite-Na+ nanoclays) as adsorbent materials. After, its release properties were investigated in aqueous solution. The presence of nanoclay was again relevant, increasing to 100% its loading efficiency for nanocomposites made up of 20% nanoclays. Adsorption in all nanocomposite formulations fitted the Langmuir isotherm. Already, the paraquat sorption results followed the Freundlich isotherm model. All isotherms had favorable adsorption profiles, and it pre... (Complete abstract click electronic access below) / Doutor

Solutes are often most efficiently deployed in discrete pulses, for example in the delivery of herbicides or drugs. Manual application of each pulse can be labor-intensive, automated application of each pulse can be capital intensive, and both are often costly and impractical. Barrier-Mediated Pulsatile Release (BMPR) systems offer a materials-based alternative for automated pulsatile drug delivery, without pumps, power supplies, or complex circuitry. While earlier materials-based approaches such as delayed-release microcapsules are limited to two or three pulses due to the independent nature of each pulse’s timing control, BMPR systems link the timing of each pulse to the previous pulse. Each dose of drug is sequestered in its own stimuli-sensitive depot, releasing only upon contact with the stimulant. These depots are stacked with sacrificial barriers in between, each of which block the stimulant for a predetermined time. For instance, layers of soluble drug may be separated by degradable polymer layers. Water, as the stimulant, will erode the polymer layer over a fixed period of time, followed by quick dissolution and release of the underlying drug and the start of degradation for the next polymer layer. This example, however, is quickly limited by irregular polymer erosion, a single stimulant (water), and difficulty in scaling delay times. The research work presented in this thesis reports the development of a generalized BMPR system which overcomes those limitations. Model drugs (methylene blue and methyl orange) were immobilized in a pH-sensitive polymer [poly(methyl methacrylate-co-dimethylaminoethyl methacrylate)] which released only at low pH. Zinc oxide (ZnO) nanoparticles immobilized in a pH-insensitive matrix [poly(vinyl alcohol)] served as the barrier layer. The time required for acid to penetrate the barrier layer scaled with the ZnO concentration and with the square of the polymer thickness, allowing wide scaling of the delay time with only minor changes to the barrier layer. Harnessing the swelling pressure of the acid-sensitive hydrogel, each barrier/depot bilayer can delaminate upon solute release, directly exposing the next bilayer to the stimulant source. This system has demonstrated tuned release using a citric acid stimulant to produce up to ten pulses of model drug (methylene blue) over various preset timescales. This system has also demonstrated the alternate release of multiple solutes (methylene blue and methyl orange) at regular time intervals up to five pulses from a single BMPR device. For non-delaminating BMPR systems, spent bilayers impede stimulant diffusion to the inner layers and solute diffusion from the inner layers, increasing the delay time and the pulse width. To predict these changes, a computational model was constructed in FORTRAN. This model was extensively explored over a wide range of parameter space to understand the release behavior of various kinds of non-delaminating BMPR systems. The computer model also validates the performances of experimental delaminating BMPR system. This model can be used to guide the physical modeling of BMPR systems. The model also allows to incorporate variety of stimulants other than just acid. BMPR technology introduces efforts to further generalize the delivery strategy by incorporating glucose as a stimulant.

Metallo-supramolecular hydrogels have interesting dynamic properties for many applications. We report a simple method for synthesizing copper-based polymer hydrogels made from nontoxic poly(methyl vinyl ether-alt-maleic anhydride) (PVM-alt-MA) in the absence or presence of added dicarboxylates, such as adipate and terephthalate. We utilize metal-polycarboxylate backbone and carboxylate spacer ligands between polymers strands engineered via non-covalent metal ion coordination. Rheological measurements revealed that the mechanical stability of the hydrogels was enhanced by the addition of supplementary dicarboxylate ligands. The optimal ratio of polymer to dicarboxylate to Cu2+ was 10:4:2.5. Our scanning electron microscope (SEM) and Cryo-SEM imaging and physical adsorption measurements revealed the formation of pores. The Brunauer–Emmett–Teller (BET) surface area of the dried hydrogels increased from 177.96 m2 g−1 in a dried hydrogel without added dicarboxylate to 646.90 and 536.44 m2 g−1 with the addition of adipate and terephthalate, respectively. The pore volume increased as well. Separation of CO2 from post-combustion flue gases is important for environmental and economic sustainability. The PVM-alt-Na-MA:adipate:Cu2+ hydrogels are promising material for post-combustion CO2 separation. At normal conditions (298 K and 1 bar), the PVM-alt-Na-MA:adipate:Cu2+ hydrogel samples with 10:4:2.5 ratio, showed notable CO2/N2 selectivity of 78.46 and a high CO2/CH4 selectivity reaching 26.09 at 1 bar. Additionally, we investigated in detail the effect of transition metal ion on the rigidity and structure of hydrogels using Al3+, Fe3+, Cu2+, Ni2+, Zn2+, and Co2+. We also studied the effect of using tricarboxylate spacer ligands such as nitrilotriacetic (NTA) and trisodium citrate or tetracarboxylate such as ethylenediaminetetraacetic acid (EDTA). It is important to mention that one of the main advantages of our facile synthesis method is being simple and can be scaled up for commercial applications. For scaling up the synthesis of hydrogels, we utilized a filling machine that is able to increase the amount of hydrogel aliquots with variable volume. Silver-based hydrogels showed significant antibacterial activity, due to the presence of silver nanoparticles. We utilized a filling machine for application of amorphous wound dressing. The optimization of the conditions of the filling enabled us to scale up the synthesis and the filling process.

Předložená diplomová práce se zabývá přípravou hydrogelů odvozených od polyakrylonitrilu a charakterizací jejich fyzikálních a chemických vlastností. Teoretická část shrnuje základní poznatky z oblasti hydrogelů, a také o polyakrylonitrilu. Dále se zabývá možností zpracování polyakrylonitrilu do reaktivní formy, takzvaného aquagelu a jeho zásadité hydrolýzy za účelem přípravy multi-blokových kopolymerů schopných tvořit 3D síť (gel). Experimentální část prezentuje výsledky charakterizace hydrogelů z polyakrylonitrilu neboli HYPANů, které byly připraveny bazicky katalyzovanou hydrolýzou aquagelu. Aquagel byl připraven rozpuštěním a následnou extruzí polyakrylonitrilu. Vzniklé vlákno bylo zpracováno do formy pelet, které byly dále užity pro zmiňovanou hydrolýzu. Hydrolýza byla prováděna za různých podmínek (teplota, NaOH koncentrace, reakční čas) za účelem přípravy produktů s různým stupněm konverze -CN skupiny. Hydrolýzou vytvořené hydrofóbní a hydrofilní bloky, mohou zformovat 3D síť o různých vlastnostech, závisejících na poměru mezi počtem a délkou bloků. Z hydrolyzátů byly připraveny hydrogely jejichž visko-elastické a optické vlastnosti byly dále charakterizovány. Optimalizací přípravy bylo dozaženo multi-blokového kopolymeru schopného vytvořit gel s vhodnými fyzikálními vlastnostmi. Tento gel může najít uplatnění v medicíně, například jako implantáty v oftamologii.

This diploma thesis is focused on development and characterization of hydrogel materials for agricultural use. In the experimental section, different methods of preparing these materials were designed and optimized according to previous literature review. In the characterization of resulting materials, the main attention was paid to the kinetics of swelling, to the solubility, the leaching of nitrate and of humic compounds. Thermogravimetric analysis represented another important characterization technique, which provided information about the content and form of water bound in the material. The development of the material aimed mainly at an agricultural application providing the delivery of nutrients to soil and regulation of water content in soil.

This diploma thesis is focused on foliar fertilization. It is nowadays one of the most widespread types of application of commercial fertilizers. Concern of this thesis is the study of plant cuticles as a thin layer on the leaves. These thin membranes are responsible for regulation of water transport and nutrients. Further function of plant cuticles is the mechanical protection of the outer part of the plant. Plant cuticles were characterized by fluorescence spectroscopy, classical optical microscopy and profilometry. The main aim of this thesis is the optimization and verification of experimental methodology aimed to the transport of commercial humic product through plant cuticles by simple diffusion techniques. The results obtained by presented diffusion techniques of humic product through plant cuticles were correlated with the same diffusion experiments through synthetic membranes with defined pore size and density. The study on transport of commercial humic product was realized in hydrogel medium by two different diffusion methods – non-stationary diffusion technique and diffusion couple. The important part of this diploma thesis is the characterization of supported hydrogel matrix by rheology tests, mercury intrusion porosimetry and scanned electron microscopy. Conclusions of this diploma thesis could be used for improving of efficiency of foliar fertilization.

The aim of this diploma thesis was to study the structure and to evaluate the properties of the hydrogel prepared by the interaction of the aminolclay with the biopolymer. Representatives of the biopolymers were selected from low to medium molecular weight sodium hyaluronate and sodium polystyrenesulfonate. On the basis of the experiments carried out, it was found that phase separation takes place only when the aminolclay interacts with medium molecular weight hyaluronan (MMW). In the experimental part, analyzes of this sample were carried out in order to determine the formation of phase-separated hydrogel by influencing the solution by ionic strength, investigation of hydrogel extinction in various organic solvents, stability of hydrogel under extreme temperature conditions, the effect of storage on its degradation, etc. Viscoelastic properties were experimentally proven by rheology and thermal analysis detected binding water. Inhibition of microorganisms was confirmed by antibacterial diffusion assays. All experiments were carried out for the use of the Aj-HyA hydrogel (MMW) in the field of medical applications, specifically for the modern method of wet wound healing of the skin.

This diploma thesis deals with the use of fluorescence correlation spectroscopy technique for microrheological characterization of hydrogel in a system of hyaluronate-cetyltrimethylammonium bromide. Fluorescently labelled particles were used for microrheological FCS analysis. To optimize the method the most appropriate size of particles was chosen on the basis of Newtonian glycerol solutions analysis. Among other things, the discussion was focused on the influence of refractive index change of analysed solutions on analysis results. After hyaluronate solutions analysis it was possible to assess the biopolymer concentration and molecular weight impact on the FCS microrheology results, which could then be compared with analysis results of model hydrogels of hyaluronate and CTAB. Finally, usability and limitations of FCS microrheology have been discussed.

In the framework of this thesis, a study was conducted dealing with a strategy to change the mechanical properties of microgel particles using inwards-interweaving self-assembly post-synthesis. This technique was invented by my cooperation partners of the Trau group, and they prepared all particles studied. Exemplarily, agarose microparticles were used to interweave a defined shell of complexed poly(allylamine) (PA) and poly(styrenesulfonic acid) (PSS) into such particles. Thereby, the shell thickness can be well-defined. Adjusting the concentration of PA and the incubation time, the filling of the particles can be readily controlled up to complete filling. By adding excessive PSS, the diffusion-controlled shell formation stops by complexation. The shell thickness of individual particles was determined through fluorescence-labeled PA and confocal laser scanning microscopy. The mechanical properties of single particles were inferred by AFM with an attached colloidal probe (CP). Here, a non-linear increase of the elastic modulus (E-modulus) from 10 to 190 kPa was determined while the shell thickness increased from 10 to 24 µm. After adding a second shell, a further gain to 520 kPa on average can be realized. Furthermore, a new concept was developed by Mr. Fery and me to change the surface mechanical properties of mircogel particles by applying a thermal trigger. Meanwhile, a particular focus was laid to maintain constant adhesive properties at every temperature. First, crosslinked poly(N-isopropyl acrylamide) (PNIPAM) particles are prepared by droplet microfluidics. These gelled particles are injected into a second microfluidic device and surrounded by an aqueous solution of uncrosslinked poly(acrylamide) (PAAM). At a second junction, droplets are formed via the cut-off effect of the continuous organic solvent. The droplets now contain the crosslinked PNIPAM core and a thin uncrosslinked PAAM liquid shell. After a short diffusion of PAAM polymers into the core they are crosslinked by UV-light. These experiments were performed by our cooperation partners of the Seiffert group. I applied temperature-controlled CP-AFM to obtain the resulting adhesive and mechanical properties of individual particles. Here, the core-shell particles behaved similarly to plain PNIPAM particles displaying the typical increase in E-modulus at temperatures above 34°C, however lower in magnitude. Further, no temperature effect on the interfacial interaction for these core-shell particles was detected. While one focus of the study above was on constant adhesion, in the following section, a new synthetic approach for mussel inspired underwater adhesives, and their characterization is presented. Based on a peptide sequence of ten amino acids, which is found frequently in natural mussel foot proteins, a new polymerization route was developed by my cooperation partners of the Börner group. Possible reaction pathways were investigated with specifically designed model reaction and analyzed using mass spectroscopy and gel permeation chromatography. The resulting polymers were further characterized using high-performance liquid chromatography and SDS-page. Nanometer thick coatings of these synthetic polymers revealed an excellent persistence even against highly concentrated salt solutions measured by quartz crystal microbalance with dissipation experiments. My contribution was the investigation of the work of adhesion necessary to detach a microparticle from such a coating by CP-AFM in an aqueous environment. Here, the newly developed synthetic polymer provided higher adhesive strength, up to 10.9 mJ m- 2, compared to comparable natural mussel foot proteins. / Im Rahmen dieser Arbeit, wurde eine Studie durchgeführt, welche die Möglichkei¬ten der nachträglichen Elastizitätsveränderung von Mikrogelpartikeln mittels „nach Innen gerichteter, verwebender Selbstassemblierung“ (engl. inwards-interweaving self-as¬sembly) beleuchtet. Diese Technik wurde von meinen Kooperationspartnern aus der Gruppe von Herrn Trau entwickelt. Am Bespiel von Agarose Mikropartikeln, kann mittels dieser Technik eine definierte Schale aus Polyallylamin (PA) und Polystyrolsulfonsäure (PSS) in das Partikel verwoben werden. Die Schalendicke kann dabei kontrolliert variiert werden, bis hin zur vollständigen Ausfüllung des Partikels, in dem die Konzentration von PA und die Inkubationszeit angepasst werden. Durch Zugabe eines Überschusses an PSS wird der diffusionsgesteuerte Schalenaufbau durch Komplexierung beendet. Die Schalendicke der individuellen Partikel wurde mittels Fluoreszenzmarkierung und konfokaler Laser Raster¬mikroskopie (engl. confocal laser scanning microscopy) ermittelt. Die mechanische Cha¬rakterisierung einzelner Partikel durch AFM und kolloidaler Sonde (engl. colloidal probe, CP) ergab eine nicht lineare Erhöhung des Elastizitätsmoduls (E-Modul) von 10 auf 190 kPa bei einem Schalendicken Zuwachs von 10 auf 24 µm. Durch eine zweite Schale, in der Ersten, konnte der E-Modul auf im Mittel 520 kPa gesteigert werden. Weiterführend, wurde von mir und Herrn Fery ein neues Konzept entwickelt, um eine mechanische, oberflächliche Verhärtung von Mikrogelpartikel durch Temperaturver¬änderung zu induzieren mit einem Augenmerk, dass sich die Adhäsionseigenschaften nicht verändern. Zunächst wurden von meinen Kooperationspartnern aus der Gruppe von Herrn Seiffert vernetzte Poly-N-isopropylacrylamid (PNIPAM) Partikel mittels Tropfenmikroflu¬idik hergestellt. In einem zweiten Mikrofluidik Experiment wurde diese Partikel mit einer wässrigen Lösung von Polyacrylamid (PAAM, unvernetzt) umgeben bevor es zu einer Tropfenbildung in der organischen Phase kommt. Nach kurzer Diffusionszeit der PAAM Polymerketten in die Kernpartikel, wurde die PAAM Schale mittels UV-Licht querver-netzt. In temperaturkontrollierten CP-AFM Untersuchungen habe ich die resultierenden Adhäsions- und mechanischen Eigenschaften auf der Einzelpartikel Ebene bestimmt. Hier¬bei konnte bei den Kern-Schale Partikeln der für bloße PNIPAM Partikel typische E-Modul anstieg oberhalb von 34°C nachgewiesen werden, jedoch mit verminderten Absolutwerten. Eine begleitende Veränderung der adhäsiven Eigenschaften der Kern-Schale Partikel konnte dabei nicht beobachtet werden. Lag ein Fokus der vorherigen Arbeit auf konstanten Wechselwirkungen, behandelt der dritte Teil der Ergebnisse, einen neuen Synthese Ansatz zur Herstellung Muschel in¬spirierter Unterwasser Adhäsiva und deren Charakterisierung. Basierend auf einer natürli¬chen Peptidsequenz, wurde eine enzymatische Polymerisationsroute von meinen Koopera¬tionspartner aus der Börner Gruppe entwickelt. Der Reaktionsverlauf wurde durch neu de¬signte Modelreaktion untersucht und mittels Massenspektroskopie und GPC analysiert, das resultierende Polymer zusätzlich mit HPLC und SDS-page. Nanometer dicke Beschichtun¬gen dieser Muschel inspirierten Polymer wiesen eine sehr gute Beständigkeit gegen hoch konzentrierten Salzlösung in QCM-D Experimenten auf. Die Adhäsionsarbeit, welche nö¬tig ist um eine Mikropartikel von diesen in wässeriger Lösung zu entfernen, wurde von mir mittels CP-AFM bestimmt. Nach meiner Erweiterung einer bekannten Adhäsionstheorie, konnten für das synthetische Polymer höhere Werte als für vergleichbare Natürliche von bis zu 10.9 mJ m-2 bestimmt werden.