Co-reporter:Isabel Schlegel, Rafael Muñoz-Espí, Patricia Renz, Ingo Lieberwirth, George Floudas, Yasuhito Suzuki, Daniel Crespy, and Katharina Landfester
Macromolecules June 27, 2017 Volume 50(Issue 12) pp:4725-4725
Publication Date(Web):June 8, 2017
DOI:10.1021/acs.macromol.7b00667
Permeability is the key property of nanocapsules because it dictates the release rate of encapsulated payloads. Herein, we engineer the crystallinity of polymers confined in the shell of nanocapsules. Nanocapsules with crystalline shells are formed from polyurea and polyphosphoester. The thermal properties, such as crystallization temperature and degree of crystallinity, are different from the bulk. The degree of crystallinity is used to control the shell permeability and, therefore, the release of encapsulated payloads, such as fluorescent dyes, typically used as model components for biomedical applications.
Co-reporter:Shuai Jiang, Wei He, Katharina Landfester, Daniel Crespy, Steven E. Mylon
Polymer 2017 Volume 127(Volume 127) pp:
Publication Date(Web):3 October 2017
DOI:10.1016/j.polymer.2017.08.061
•Electrospinning of nanoparticles dispersed in a hydrophilic polymer.•DLS and electron microscopy investigations of dispersions and nanofibers.•Dispersion of particles in fibers depends on electrospinning conditions, polymer Mw and concentration, and particles concentration.Colloid-electrospinning is a technique widely used to immobilize nanoparticles in nanofibers. Such hierarchical structures are advantageous because they benefit from the properties of both nanoparticles and nanofibers. Controlling the aggregation state of nanoparticles in nanofibers is essential for the properties of the resulting materials. We investigate here the relationship between the aggregation state of nanoparticles in dispersion before spinning and in electrospun nanofibers. The aggregation state of nanoparticles in nanofibers was found to depend on the aggregation state of the nanoparticles in dispersion.Download high-res image (176KB)Download full-size image
Co-reporter:Li-Ping Lv;Shuai Jiang;Alper Inan;Katharina Landfester
RSC Advances (2011-Present) 2017 vol. 7(Issue 14) pp:8272-8279
Publication Date(Web):2017/01/23
DOI:10.1039/C6RA24796B
The difference in the reactivity of two monomers, aniline (ANI) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT), was employed to design nanoparticles with completely different nanostructures. The monomers were simultaneously polymerized by tandem oxidative polymerization occurring in the miniemulsion droplets. DMcT is also a corrosion inhibitor and its polymer can be depolymerized by reduction, which avoids the unwanted release of the payload DMcT when the capsules are not activated. The redox-responsive release profile of DMcT from the composite particles is controlled by the morphology of the particles and it was investigated for monolithic, multi-hollow, and yolk–shell structures. These PANI/PDMcT composite particles may find potential application in Li–S batteries or in the self-healing systems for corrosion protection.
Co-reporter:Shuai Jiang, Li-Ping Lv, Katharina Landfester, and Daniel Crespy
Accounts of Chemical Research 2016 Volume 49(Issue 5) pp:816
Publication Date(Web):May 2, 2016
DOI:10.1021/acs.accounts.5b00524
Hierarchical structure is a key feature explaining the superior properties of many materials in nature. Fibers usually serve in textiles, for structural reinforcement, or as support for other materials, whereas spherical micro- and nanoobjects can be either highly functional or also used as fillers to reinforce structure materials. Combining nanocontainers with fibers in one single object has been used to increase the functionality of fibers, for example, antibacterial and thermoregulation, when the advantageous properties given by the encapsulated materials inside the containers are transferred to the fibers. Herein we focus our discussion on how the hierarchical structure composed of nanocontainers in nanofibers yields materials displaying advantages of both types of materials and sometimes synergetical effects. Such materials can be produced by first carefully designing nanocontainers with defined morphology and chemistry and subsequently electrospinning them to fabricate nanofibers. This method, called colloid-electrospinning, allows for marrying the properties of nanocontainers and nanofibers. The obtained fibers could be successfully applied in different fields such as catalysis, optics, energy conversion and production, and biomedicine.The miniemulsion process is a convenient approach for the encapsulation of hydrophobic or hydrophilic payloads in nanocontainers. These nanocontainers can be embedded in fibers by the colloid-electrospinning technique. The combination of nanocontainers with nanofibers by colloid-electrospinning has several advantages. (1) The fiber matrix serves as support for the embedded nanocontainers. For example, through combining catalysts nanoparticles with fiber networks, the catalysts can be easily separated from the reaction media and handled visually. This combination is beneficial for the reuse of the catalyst and the purification of products. (2) Electrospun nanofibers containing nanocontainers offer the active agents inside the nanocontainers a double protection by both the fiber matrix and the nanocontainers. Since the polymer of the fibers and the polymer of the nanocontainers have usually opposite polarities, the encapsulated substance, for example, catalysts, dyes, or drugs, can be protected against a large variety of environmental influences. (3) Electrospun nanofibers exhibit unique advantages for tissue engineering and drug delivery that are a structural similarity to the extracellular matrix of biological tissues, large specific surface area, high and interconnected porosity which enhances cell adhesion, proliferation, drug loading, and mass transfer properties, as well as the flexibility in selecting the raw materials. Moreover, the nanocontainer-in-nanofiber structure allows multidrug loading and programmable release of each drug, which are very important to achieve synergistic effects in tissue engineering and disease therapy.The advantages offered by these materials encourage us to further understand the relationship between colloidal properties and fibers, to predict the morphology and properties of the fibers obtained by colloid-electrospinning, and to explore new possible combination of properties offered by nanoparticles and nanofibers.
Co-reporter:Shahed Behzadi, Christine Rosenauer, Michael Kappl, Kristin Mohr, Katharina Landfester and Daniel Crespy
Nanoscale 2016 vol. 8(Issue 26) pp:12998-13005
Publication Date(Web):30 May 2016
DOI:10.1039/C6NR01882C
The encapsulation of payloads in micro- to nano-scale capsules allows protection of the payload from the surrounding environment and control of its release profile. Herein, we program the release of hydrophilic payloads from nanocontainers by co-encapsulating simple inorganic salts for adjusting the osmotic pressure. The latter either leads to a burst release at high concentrations of co-encapsulated salts or a sustained release at lower concentrations. Osmotic pressure causes swelling of the nanocapsule's shell and therefore sustained release profiles can be adjusted by crosslinking it. The approach presented allows for programing the release of payloads by co-encapsulating inexpensive salts inside nanocontainers without the help of stimuli-responsive materials.
Co-reporter:Diego Estupiñán, Markus B. Bannwarth, Steven E. Mylon, Katharina Landfester, Rafael Muñoz-Espí and Daniel Crespy
Nanoscale 2016 vol. 8(Issue 5) pp:3019-3030
Publication Date(Web):12 Jan 2016
DOI:10.1039/C5NR08258G
Silica nanoparticles are versatile materials whose physicochemical surface properties can be precisely adjusted. Because it is possible to combine several functionalities in a single carrier, silica-based materials are excellent candidates for biomedical applications. However, the functionality of the nanoparticles can get lost upon exposure to biological media due to uncontrolled biomolecule adsorption. Therefore, it is important to develop strategies that reduce non-specific protein–particle interactions without losing the introduced surface functionality. Herein, organosilane chemistry is employed to produce magnetic silica nanoparticles bearing differing amounts of amino and alkene functional groups on their surface as orthogonally addressable chemical functionalities. Simultaneously, a short-chain zwitterion is added to decrease the non-specific adsorption of biomolecules on the nanoparticles surface. The multifunctional particles display reduced protein adsorption after incubation in undiluted fetal bovine serum as well as in single protein solutions (serum albumin and lysozyme). Besides, the particles retain their capacity to selectively react with biomolecules. Thus, they can be covalently bio-functionalized with an antibody by means of orthogonal click reactions. These features make the described multifunctional silica nanoparticles a promising system for the study of surface interactions with biomolecules, targeting, and bio-sensing.
Co-reporter:Shuai Jiang, Beatriz Chiyin Ma, Jonas Reinholz, Qifeng Li, Junwei Wang, Kai A. I. Zhang, Katharina Landfester, and Daniel Crespy
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 44) pp:29915
Publication Date(Web):October 18, 2016
DOI:10.1021/acsami.6b09165
Materials with a hierarchical structure often demonstrate superior properties with combined and even synergistic effects of multiple functions. Herein, we report the design of a new class of material with a multicompartment nanofibrous structure as a promising candidate for antibacterial wound dressing and functional textile applications. The design consists in first synthesizing nanocapsules loaded with functional payloads and subsequently embedding the nanocapsules into polymer nanofibers by using the colloid-electrospinning technique. The nanocontainer-in-nanofiber structure allows for a selective and separate loading of different functional agents with different polarities, and it offers a flexible combination of the properties of nanocontainers and nanofibers. An example of the potential for these multicompartment materials is demonstrated here, in which the synergistic antibacterial effect against E. coli K-12 and B. Subtilis combined with anti-UV property is shown.Keywords: anti-UV; antibacterial; electrospinning; nanofibers; wound dressing
Co-reporter:Shahed Behzadi, Mark Steinmann, Diego Estupiñán, Katharina Landfester, Daniel Crespy
Journal of Controlled Release 2016 Volume 242() pp:119-125
Publication Date(Web):28 November 2016
DOI:10.1016/j.jconrel.2016.08.040
The controlled release of payloads from mesoporous silica nanocapsules (SiNCs) consisting of stimulus-responsive shells is of considerable interest in applications such as self-healing materials and drug delivery. However, the release of payloads from SiNCs before application of external triggers (i.e. non-selective release) remains a formidable challenge. In fact, the non-selective release of payloads from SiNCs occurs because of the mesoporous nature of the silica shell that cannot trap payloads in the core of SiNCs perfectly. We establish an efficient and straightforward strategy based on the encapsulation of a pro-active payload to hinder the non-selective release of small payloads from mesoporous capsules. A pro-active payload is defined as a compound that is converted to an active functional molecule in the environment where it is needed. In this sense, it is a generalization of a prodrug. Encapsulating a pro-active payload instead of a payload allowed hindering the non-selective release of the payload from SiNCs. A selective release of the payload could be achieved upon reduction of the encapsulated pro-active payload. Furthermore, the total amount of released substance is significantly enhanced by introducing responsive groups in the silica shell. These results show that the pro-active payload strategy combined with the use of stimulus-responsive materials can be successfully exploited to achieve selective release of cargo from mesoporous nanocapsules.A selective release of the payload can be achieved via combination of the pro-active payload strategy with the responsive behavior of the nanocapsules shell.
Co-reporter:Shahed Behzadi, Markus Gallei, Johannes Elbert, Michael Appold, Gunnar Glasser, Katharina Landfester and Daniel Crespy
Polymer Chemistry 2016 vol. 7(Issue 20) pp:3434-3443
Publication Date(Web):14 Apr 2016
DOI:10.1039/C6PY00344C
Stimuli-responsive micro- to nano-scale containers have gained increasing attention due to their unique potential to selectively release payloads under specific environmental conditions. We report here novel triple stimuli-responsive nanocapsules that selectively respond to changes in temperature, pH value, and redox potential. The nanocapsules were prepared from either a triple responsive triblock terpolymer or a blend of responsive diblock copolymers, both synthesized by sequential anionic polymerization. We then compared the release performance of nanocapsules under oxidative conditions and changes of temperature or pH value. Our results reveal the close correlation between the release properties of stimuli-responsive nanocontainers and the microstructure of the polymer shell. In fact, the microphase separation between the responsive diblock copolymers across the shell significantly hinders the triggered release of the payload from the nanocapsules. These results demonstrate that the fine morphology of triblock terpolymers can be exploited to achieve the triggered release of payloads from polymer nanocontainers upon application of three different external triggers.
Co-reporter:Kerstin Malzahn;Sro Ebert;Isabel Schlegel;Oliver Neudert;Manfred Wagner;Gunnar Schütz;Andreas Ide;Farnoosh Roohi;Kerstin Münnemann;Katharina Lfester
Advanced Healthcare Materials 2016 Volume 5( Issue 5) pp:567-574
Publication Date(Web):
DOI:10.1002/adhm.201500748
The enhanced relaxation of hydrogen atoms of surrounding water from suitable contrast agent promotes magnetic resonance imaging as one of the most important medical diagnosis technique. The key challenge for the preparation of performant contrast agents for magnetic resonance imaging with high relaxivity is to ensure a high local concentration of contrast agent while allowing a contact between water and the contrast agent. Both requirements are answered by tailoring a semipermeable confinement for a gadolinium complex used as contrast agent. A locally high concentration is achieved by successfully encapsulating the complex in polymer nanocontainers that serves to protect and retain the complex inside a limited space. The access of water to the complex is achieved by carefully controlling the chemistry of the shell and the core of the nanocontainers. The confinement of the nanocontainers enables an increased relaxivity compared to an aqueous solution of the contrast agent. The nanocontainers are successfully applied in vivo to yield enhanced contrast in magnetic resonance imaging.
Co-reporter:D. Crespy, L. P. Lv and K. Landfester
Nanoscale Horizons 2016 vol. 1(Issue 4) pp:268-271
Publication Date(Web):03 Feb 2016
DOI:10.1039/C5NH00112A
Nanocapsules are key components in new technologies related to biomedicine and materials science. However, their long-term fate after use is still largely ignored. We discuss here a sustainable approach where the products of degradation of the nanoparticles play a significant role in their application because they are also functional molecules. The polymer shell of the nanocapsules is chemically engineered so that the degradation products formed upon chemical damage are useful after their normal use.
Co-reporter:Li-Ping Lv, Yi Zhao, Katharina Landfester and Daniel Crespy
Polymer Chemistry 2015 vol. 6(Issue 31) pp:5596-5601
Publication Date(Web):16 Oct 2014
DOI:10.1039/C4PY01159G
Amphiphilic random copolymers are designed to bear a corrosion inhibitor as cleavable side group, which can be released upon activation by chemical reduction. Polymer nanoparticles are obtained by self-assembly of the copolymers in water. A model dye is encapsulated in the nanoparticles and its release is triggered by reductive cleavage of the copolymer, leading hence to the co-release of the corrosion inhibitor. The present system has the advantage that the cleaved units are functional payloads.
Co-reporter:Yi Zhao, Li-Ping Lv, Shuai Jiang, Katharina Landfester and Daniel Crespy
Polymer Chemistry 2015 vol. 6(Issue 23) pp:4197-4205
Publication Date(Web):14 Apr 2015
DOI:10.1039/C5PY00323G
Stimuli-responsive polymer nanocapsules (PNCs) are smart nanocarriers that encapsulate functional payloads and release them on demand upon external triggers. Stimuli-responsive PNCs are of interest in a wide range of disciplines such as pharmaceutics, agriculture, and materials science. Studies on stimuli-responsive PNCs so far are widely reported but are mainly focused on using only one stimulus to release one payload. However, a nanocarrier is efficient if distinct payloads can be selectively released via different stimuli because unwanted and unspecific release can be avoided. Here, the recent progress of stimuli-responsive PNCs that possess enhanced capabilities for payloads delivery is highlighted, including PNCs that respond to multiple stimuli, stimuli-responsive PNCs that co-encapsulate different payloads, and stimuli-responsive PNCs that release the payloads selectively or in a pulsatile way. Finally, the possible future directions in this area are suggested.
Co-reporter:S. K. Murase, L.-P. Lv, A. Kaltbeitzel, K. Landfester, L. J. del Valle, R. Katsarava, J. Puiggali and D. Crespy
RSC Advances 2015 vol. 5(Issue 68) pp:55006-55014
Publication Date(Web):09 Jun 2015
DOI:10.1039/C5RA06267E
Novel enzyme loaded scaffolds with enzyme-responsive degradable properties for drug delivery are prepared by an original inverse-miniemulsion electrospinning method. Miniemulsions with aqueous nanodroplets containing different enzymes, i.e. lipase or α-chymotrypsin, and a fluorophore are electrospun with a solution of poly(ester amide) and polycaprolactone to fabricate multicompartment nanofibers. The poly(ester amide) contains the two essential amino acids phenylalanine and leucine that promote low cytotoxicity degradation products and makes them suitable for the preparation of drug delivery devices for the biomedical field. The activity of the loaded enzymes in different conditions and a sustained degradation of fibers mechanism with an approximate 20% weight loss within one month are observed. Locating enzymes in degradation medium accelerated the degradation until complete scaffold destruction in less than 5 days. In all cases, a nearly complete release of the loaded fluorophore (from 80% and upwards) was achieved before the complete degradation of fibers occurred, suggesting that the nanofibers are suitable as self-triggered drug release systems with sustained mechanical integrity and a flexible range of degradation rates.
Co-reporter:Li-Ping Lv, Zhong-Shuai Wu, Long Chen, Hao Lu, Yi-Ran Zheng, Tobias Weidner, Xinliang Feng, Katharina Landfester and Daniel Crespy
RSC Advances 2015 vol. 5(Issue 62) pp:50063-50069
Publication Date(Web):28 May 2015
DOI:10.1039/C5RA06697B
We describe the synthesis of hierarchical porous nitrogen-doped carbon nanoparticles with high specific surface area and specific capacitance for supercapacitors. Octapyrrolylnaphthalene (OPN) with eight substituent pyrrolyl groups is used as a reaction precursor and the oxidative product, assigned as POPN, is synthesized in miniemulsion droplets. Further carbonization of POPN at 600 °C (POPN600) and 800 °C (POPN800) provides particles with hierarchical porosity, well-defined nanoparticle structure, and high specific surface area. The obtained nitrogen-doped carbon particles POPN800 exhibit a specific capacitance of 156 F g−1 at the scan rate of 2 mV s−1 and 80 F g−1 when the scan rate increases to 100 mV s−1. The high specific capacitance and excellent rate capability can be attributed to the controlled structure of the nanoparticles, hierarchical micro- and mesoporosity, high surface area (365 m2 g−1), and rich nitrogen-doping. The present method allows therefore for the synthesis of nitrogen-doped carbon materials for supercapacitors in an easy one-pot and template-free miniemulsion procedure followed by carbonization.
Co-reporter:Diego Estupiñán;Markus B. Bannwarth;Katharina Lfester
Macromolecular Chemistry and Physics 2015 Volume 216( Issue 21) pp:2070-2079
Publication Date(Web):
DOI:10.1002/macp.201500239
Co-reporter:Markus B. Bannwarth, Stefanie Utech, Sandro Ebert, David A. Weitz, Daniel Crespy, and Katharina Landfester
ACS Nano 2015 Volume 9(Issue 3) pp:2720
Publication Date(Web):February 19, 2015
DOI:10.1021/nn5065327
The assembly of nanoparticles into polymer-like architectures is challenging and usually requires highly defined colloidal building blocks. Here, we show that the broad size-distribution of a simple dispersion of magnetic nanocolloids can be exploited to obtain various polymer-like architectures. The particles are assembled under an external magnetic field and permanently linked by thermal sintering. The remarkable variety of polymer–analogue architectures that arises from this simple process ranges from statistical and block copolymer-like sequencing to branched chains and networks. This library of architectures can be realized by controlling the sequencing of the particles and the junction points via a size-dependent self-assembly of the single building blocks.Keywords: colloidal polymers; controlled sequencing; magnetic self-assembly; nanoparticles;
Co-reporter:Wei He, Maria Parowatkin, Volker Mailänder, Marion Flechtner-Mors, Robert Graf, Andreas Best, Kaloian Koynov, Kristin Mohr, Ulrich Ziener, Katharina Landfester, and Daniel Crespy
Biomacromolecules 2015 Volume 16(Issue 8) pp:
Publication Date(Web):July 10, 2015
DOI:10.1021/acs.biomac.5b00500
The hydrophilic peptide YY (PYY) is a promising hormone-based antiobesity drug. We present a new concept for the delivery of PYY from pH-responsive chitosan-based nanocarriers. To overcome the drawbacks while retaining the merits of the polyelectrolyte complex (PEC) method, we propose a one-pot approach for the encapsulation of a hydrophilic peptide drug in cross-linked PEC nanocarriers. First, the hydrophilic peptide is encapsulated via polyelectrolyte complexation within water-in-oil miniemulsion droplets. In a second step, the PEC surface is reinforced by controlled interfacial cross-linking. PYY is efficiently encapsulated and released upon pH change. Such nanocarriers are promising candidates for the fight against obesity and, in general, for the oral delivery of protein drugs.
Co-reporter:Markus B. Bannwarth, Thomas Weidner, Evelyn Eidmann, Katharina Landfester, and Daniel Crespy
Chemistry of Materials 2014 Volume 26(Issue 3) pp:1300
Publication Date(Web):January 21, 2014
DOI:10.1021/cm4040769
Co-reporter:Li-Ping Lv, Katharina Landfester, and Daniel Crespy
Chemistry of Materials 2014 Volume 26(Issue 11) pp:3351
Publication Date(Web):May 14, 2014
DOI:10.1021/cm500923d
Co-reporter:Yi Zhao, Rüdiger Berger, Katharina Landfester and Daniel Crespy
Polymer Chemistry 2014 vol. 5(Issue 2) pp:365-371
Publication Date(Web):12 Sep 2013
DOI:10.1039/C3PY01096A
Patchy particles (PPs) are considered as interesting building blocks for the fabrication of novel structures with enhanced complexity and functionality. However, their development is primarily limited by the fact that there is no reliable method to prepare PPs on a large scale. Herein, a one-pot strategy to prepare PPs relying on polymerization-induced phase separation in monomer-embedded polymer nanoparticles is demonstrated. The surface is found to be composed of sticky patches embedded in a hard matrix by adhesion and force–distance measurements performed by atomic force microscopy. The patch sizes could be easily tuned by controlling the monomer conversion or varying the composition between the polymer and the monomer. This study presents the possibility to develop a simple, low-cost and scalable method for preparing large quantities of PPs from homopolymers. It may also pave the way to new PPs for functional materials and devices.
Co-reporter:Roland H. Staff, Jochen Willersinn, Anna Musyanovych, Katharina Landfester and Daniel Crespy
Polymer Chemistry 2014 vol. 5(Issue 13) pp:4097-4104
Publication Date(Web):19 Mar 2014
DOI:10.1039/C4PY00085D
Janus nanoparticles presenting one face functionalized with azide and one face functionalized with alkyne groups were prepared in water. The surface density of the functional groups could be adjusted by controlling the functional group density in the polymers used to generate the Janus particles. The control was achieved by the preparation of copolymers in which the ratio of the functional monomer was varied by free-radical polymerization and by the use of atom transfer radical polymerization (ATRP) with functional initiators. Furthermore, reagents and methods were developed to quantify the alkyne and azide groups on the surface of the Janus particles. Thus, the activity of the groups was also proven.
Co-reporter:Daejune Joe;Florian E. Golling;Kathrin Friedemann;Markus Klapper;Klaus Müllen
Macromolecular Materials and Engineering 2014 Volume 299( Issue 10) pp:1155-1162
Publication Date(Web):
DOI:10.1002/mame.201300435
Abstract
The formation of polyethylene fibers via metallocene-catalyzed polymerization using anisotropic organic supports as templates is presented. The supports are obtained by electrospinning a mixture of polyvinyl alcohol and functionalized polystyrene nanoparticles. After loading the MAO-activated metallocene on the support and olefin polymerization, the obtained catalyst system yields polyethylene fibers displaying a core-sheath structure with a controlled diameter in the range of 0.3–2 μm. This strategy represents a direct method to fabricate well-defined polyolefin fibers and mats during the polymerization without any further processing.
Co-reporter:Yi Zhao;Diana Döhler;Li-Ping Lv;Wolfgang H. Binder;Katharina Lfester
Macromolecular Chemistry and Physics 2014 Volume 215( Issue 2) pp:198-204
Publication Date(Web):
DOI:10.1002/macp.201300558
Co-reporter:Li-Ping Lv, Yi Zhao, Hai-Xin Zhou, Katharina Landfester, Daniel Crespy
Polymer 2014 Volume 55(Issue 3) pp:715-720
Publication Date(Web):12 February 2014
DOI:10.1016/j.polymer.2013.12.061
Titanium dioxide nanoparticles are precisely segregated in or on polymer submicron particles domains by phase separation between a polymer and a hydrophobic liquid or between two different polymers. The inorganic nanoparticles can be located either in the core, as a patch on the surface of the polymer particle, as a disk, or in the middle of Janus polymer particles. In the latter case, tricompartment submicron particles arranged in a linear triblock fashion are fabricated.
Co-reporter:Dr. Markus Bannwarth ;Dr. Daniel Crespy
Chemistry – An Asian Journal 2014 Volume 9( Issue 8) pp:2030-2035
Publication Date(Web):
DOI:10.1002/asia.201402316
Abstract
The preparation and applications of nanoparticles and nanofibers are widely described in the literature. Both types of materials have specific advantages but also drawbacks. We discuss here the methods to fabricate nanofibers from nanoparticles and vice versa by template-free methods and colloid-electrospinning. Nanoparticles and nanofibers can be also synergistically combined to yield nanostructured constructs that display highly advantageous properties such as good mechanical integrity, double protection of encapsulated substances, or the possibility to co-encapsulate payloads with different polarities.
Co-reporter:Roland H. Staff, Markus Gallei, Katharina Landfester, and Daniel Crespy
Macromolecules 2014 Volume 47(Issue 15) pp:4876-4883
Publication Date(Web):July 18, 2014
DOI:10.1021/ma501233y
The preparation of nanocontainers with a hydrophilic core from water-in-oil emulsions and their subsequent transfer to aqueous medium is crucial because it enables the efficient encapsulation of hydrophilic payloads in large quantities. However, major challenges are associated with their synthesis including low colloidal stability, leakage of encapsulated payloads due to osmotic pressure, and a demanding transfer of the nanocontainers from apolar to aqueous media. We present here a general approach for the synthesis of polymer nanocontainers that are colloidally stable, not sensitive to osmotic pressure, and responsive to environmental stimuli that trigger release of the nanocontainer contents. Additionally, the nanocontainers can selectively deliver one or two different payloads upon oxidation and changes of pH or temperature. Our approach uniquely enables the synthesis of nanocontainers for applications in which aqueous environments are desired or inevitable.
Co-reporter:Li-Ping Lv ; Yi Zhao ; Nicole Vilbrandt ; Markus Gallei ; Ashokanand Vimalanandan ; Michael Rohwerder ; Katharina Landfester
Journal of the American Chemical Society 2013 Volume 135(Issue 38) pp:14198-14205
Publication Date(Web):August 20, 2013
DOI:10.1021/ja405279t
Redox-responsive nanocapsules consisting of conductive polyaniline and polypyrrole shells were successfully synthesized by using the interface of miniemulsion droplets as a template for oxidative polymerizations. The redox properties of the capsules were investigated by optical spectroscopies, electron microscopy, and cyclic voltammetry. Self-healing (SH) chemicals such as diglycidyl ether or dicarboxylic acid terminated polydimethylsiloxane (PDMS-DE or PDMS-DC) were encapsulated into the nanocapsules during the miniemulsion process and their redox-responsive release was monitored by 1H NMR spectroscopy. The polyaniline capsules exhibited delayed release under oxidation and rapid release under reduction, which make them promising candidates for anticorrosion applications.
Co-reporter:Christian Wohnhaas, Kathrin Friedemann, Dmitry Busko, Katharina Landfester, Stanislav Baluschev, Daniel Crespy, and Andrey Turshatov
ACS Macro Letters 2013 Volume 2(Issue 5) pp:446
Publication Date(Web):May 6, 2013
DOI:10.1021/mz400100j
We present a method for the fabrication of ultralight upconverting mats consisting of rigid polymer nanofibers. The mats are prepared by simultaneously electrospinning an aqueous solution of a polymer with pronounced oxygen-barrier properties and functional nanocapsules containing a sensitizer/emitter couple optimized for triplet–triplet annihilation photon upconversion. The optical functionality of the nanocapsules is preserved during the electrospinning process. The nanofibers demonstrate efficient upconversion fluorescence centered at λmax = 550 nm under low intensity excitation with a continuous wave laser (λ = 635 nm, power = 5 mW). The pronounced oxygen-barrier property of the polymer matrix may efficiently prevent the oxygen penetration so upconversion fluorescence is registered in ambient atmosphere. The demonstrated method can be used for the production of upconverting ultralight porous coatings for sensors or upconverting membranes with freely variable thickness for solar cells.
Co-reporter:Johannes Fickert, Christian Wohnhaas, Andrey Turshatov, Katharina Landfester, and Daniel Crespy
Macromolecules 2013 Volume 46(Issue 3) pp:573-579
Publication Date(Web):January 22, 2013
DOI:10.1021/ma302013s
Copolymers of styrene and various hydrophilic monomers were synthesized by anionic and free-radical polymerizations, and by polymer–analogue reactions. The copolymers were subsequently used in an emulsion–solvent evaporation process to yield core–shell nanoparticles. We describe here the influence of the copolymer structure on the morphology of the nanocapsules. The core–shell nanoparticles were found to be suitable for the encapsulation of monomers and catalysts for self-healing materials.
Co-reporter:Stefanie Zuber;Katharina Lfester;Ana-Maria Popa
Journal of Polymer Science Part A: Polymer Chemistry 2013 Volume 51( Issue 15) pp:3308-3313
Publication Date(Web):
DOI:10.1002/pola.26727
ABSTRACT
Poly(N-vinylcaprolactam) (PVCL) and poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) are well known for their thermoresponsive behavior in aqueous solutions. Indeed, they display lower critical solution temperatures (LCST) in the physiological range, which makes them interesting for biomedical devices and use in drug delivery systems. Homopolymers of N-vinylcaprolactam and di(ethylene glycol) methyl ether methacrylate as well as copolymers thereof were synthesized by solution and direct miniemulsion polymerizations. The cloud points of the copolymers in aqueous solution were investigated as a function of temperature, comonomer ratio, and in the presence of model pharmaceutical ingredients. By variation of the comonomer ratio, it was possible to control the cloud point temperature between 26 and 35 °C, which was found to be beneficial to attenuate the effect of the drugs that also altered the cloud points. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3308–3313
Co-reporter:Anika Hamberger, Ana-Maria Popa, Rene M. Rossi, Daniel R. Kattnig, Dariush Hinderberger, Katharina Landfester and Daniel Crespy
Journal of Materials Chemistry A 2012 vol. 22(Issue 19) pp:9909-9920
Publication Date(Web):13 Apr 2012
DOI:10.1039/C2JM30333G
Nano-gas generators were synthesized by encapsulating azo-components into hydrophobic polymer particles. The dispersions of azo-components were subsequently thermally decomposed and could be reacted with either hydrophilic or hydrophobic dyes, which were located in the continuous and dispersed phases, respectively. Both systems displayed an irreversible switch in color upon temperature increase, yielding a new class of thermochromic materials. The mechanism and kinetics of the reaction between the azo-component and copper(II) phthalocyanine were monitored by EPR spectroscopy. The dispersions were also spin-coated on glass substrates and a significant change of turbidity occurred upon heating due to the gas generation in the films.
Co-reporter:Johannes Fickert, Patrick Rupper, Robert Graf, Katharina Landfester and Daniel Crespy
Journal of Materials Chemistry A 2012 vol. 22(Issue 5) pp:2286-2291
Publication Date(Web):16 Dec 2011
DOI:10.1039/C2JM15151K
Silica nanocapsules functionalized with thiol or amine groups with sizes between 100 and 400 nm could be successfully synthesized using the interface of direct miniemulsion droplets for the hydrolysis and condensation of silicon alkoxides. We show that healing agents such as monomers and catalysts can be successfully encapsulated in the silica shell. The catalyst was encapsulated as a solution to allow a better mobility when released for a self-healing reaction. The functional groups were quantified by 29Si MAS-NMR, XPS, and chemical titration. Therefore a precise picture for the gradient of concentration of functional groups inside the shell could be given. The encapsulated reagents were found to be still active and the self-healing reaction could be successfully monitored by solid-state NMR spectroscopy and thermogravimetry.
Co-reporter:Nesrin Horzum, Rafael Muñoz-Espí, Gunnar Glasser, Mustafa M. Demir, Katharina Landfester, and Daniel Crespy
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 11) pp:6338
Publication Date(Web):October 23, 2012
DOI:10.1021/am301969w
We present herein a new concept for the preparation of nanofibrous metal oxides based on the simultaneous electrospinning of metal oxide precursors and silica nanoparticles. Precursor fibers are prepared by electrospinning silica nanoparticles (20 nm in diameter) dispersed in an aqueous solution of poly(acrylic acid) and metal salts. Upon calcination in air, the poly(acrylic acid) matrix is removed, the silica nanoparticles are cemented, and nanocrystalline metal oxide particles of 4–14 nm are nucleated at the surface of the silica nanoparticles. The obtained continuous silica fibers act as a structural framework for metal oxide nanoparticles and show improved mechanical integrity compared to the neat metal oxide fibers. The hierarchically nanostructured materials are promising for catalysis applications, as demonstrated by the successful degradation of a model dye in the presence of the fibers.Keywords: catalysis; ceria; electrospinning; lithium cobalt oxide; metal oxide; nanoparticles;
Co-reporter:Christine Herrmann, Andrey Turshatov, and Daniel Crespy
ACS Macro Letters 2012 Volume 1(Issue 7) pp:907
Publication Date(Web):July 3, 2012
DOI:10.1021/mz300245b
Electrospinning is used to deform originally spherical polymer nanoparticles into ellipsoidal nanoparticles. The polymer nanoparticles are swollen and the dispersion is then electrospun. Under certain conditions, the stretching generated in the electrospinning jet is enough to generate elongated nanoparticles embedded in fibers. The formation of the anisotropic particles is observed by stimulated emission depletion (STED) microscopy performed on fluorescent nanoparticles and by electron microscopy measurements on the nanoparticles recovered after removal of the fiber matrix.
Co-reporter:Daniel Crespy;Kathrin Friedemann;Ana-Maria Popa
Macromolecular Rapid Communications 2012 Volume 33( Issue 23) pp:
Publication Date(Web):
DOI:10.1002/marc.201290081
Co-reporter:Daniel Crespy;Kathrin Friedemann;Ana-Maria Popa
Macromolecular Rapid Communications 2012 Volume 33( Issue 23) pp:1978-1995
Publication Date(Web):
DOI:10.1002/marc.201200549
Abstract
Solution-, melt-, and co-axial electrospinning are well-known methods for producing nano- and microfibers. The electrospinning of colloids (or colloid-electrospinning) is a new field that offers the possibility to elaborate multicompartment nanomaterials. However, the presence of colloids in the electrospinning feed further complicates theoretical predictions in a system that is dependent on chemical, physical, and process parameters. Herein, we give a summary of recent important results and discuss the perspectives of electrospinning of colloids for the synthesis and characterization of multicompartment fibers.
Co-reporter:Yi Zhao, Katharina Landfester and Daniel Crespy
Soft Matter 2012 vol. 8(Issue 46) pp:11687-11696
Publication Date(Web):27 Sep 2012
DOI:10.1039/C2SM26440D
We report the use of commercially available long-chain tertiary amines as smart switchable surfactants or hydrophobic oils in miniemulsions. Miniemulsion droplets were stabilized by employing the charged tertiary amine as surfactants to prevent coalescence. PMMA and PS nanoparticles were obtained by polymerizing the monomer droplets. Furthermore, the dispersions could be aggregated by bubbling argon (Ar) at 60 °C or by increasing their pH. In both cases, the nanoparticles could be re-dispersed by charging the dispersions with CO2 at room temperature. The same tertiary amines in their neutral form were used as soft liquid templates in miniemulsion droplets. Core–shell nanoparticles, with the hydrophobic tertiary amine as the core and polyvinylformal (PVF) as the shell, were prepared by the emulsion-solvent evaporation technique. By charging the nanocapsules with CO2, the hydrophobic core was transformed to the water soluble ammonium bicarbonate salt. Thus, aqueous dispersions of polymer nanocapsules with a hydrophilic core could be prepared without the conventional transfer of capsules from oil to aqueous dispersions. This method provides a direct pathway to synthesize polymer nanocapsules mimicking natural compartmentalized systems such as liposomes and cells, with aqueous media present inside and outside the compartments.
Co-reporter:Daniel Crespy;Rol Hinrich Staff;Tanja Becker;Katharina Lfester
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 12) pp:1183-1189
Publication Date(Web):
DOI:10.1002/macp.201200124
Abstract
The search for mimicking natural living and non-living systems with synthetic products leads to the fabrication of advanced colloidal morphologies with hierarchical micro- and nanostructures. Different chemical routes toward the synthesis of colloids with complex morphologies are presented and a tentative analogy between these routes and the four basic arithmetic operations is proposed.
Co-reporter:Rol H. Staff;Ingo Lieberwirth;Katharina Lfester
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 3) pp:351-358
Publication Date(Web):
DOI:10.1002/macp.201100529
Abstract
The synthesis of colloidally stable submicron particles of syndiotactic polystyrene (sPS) and isotactic polystyrene (iPS) is reported. Model particles based on poly-L-lactic acid (PLLA), atactic polystyrene (aPS), sPS, and iPS are prepared by the evaporation of a solvent present in miniemulsion droplets. The degree of crystallinity of the particles is found to decrease with their size, as shown by DSC and WAXS measurements. Remarkably, nonspherical particles can be formed in the dispersed state with sPS and iPS, whereas PLLA and aPS particles always display spherical morphologies.
Co-reporter:Christine Herrmann;Markus B. Bannwarth;Katharina Lfester
Macromolecular Chemistry and Physics 2012 Volume 213( Issue 8) pp:829-838
Publication Date(Web):
DOI:10.1002/macp.201100644
Abstract
Anisotropic nanoparticles in comparison to spherical nanoparticles show significant differences in cellular interactions and cellular uptake. In order to enable the use of non-spherical nanoparticles for biomedical application, their synthesis as well as their re-dispersion in aqueous media is crucial. We show here the synthesis of a wide variety of differently functionalized anisotropic nanoparticles and capsules. Non-spherical nanocapsules, functionalized magnetic nanoparticles as contrast agents, and shape changing nanoparticles were synthesized and their re- dispersibility in water investigated.
Co-reporter:Daniel Crespy;Stefanie Zuber;Andrey Turshatov;Katharina Lfester;Ana-Maria Popa
Journal of Polymer Science Part A: Polymer Chemistry 2012 Volume 50( Issue 6) pp:1043-1048
Publication Date(Web):
DOI:10.1002/pola.25875
Co-reporter:Roland H. Staff, Markus Gallei, Markus Mazurowski, Matthias Rehahn, Rüdiger Berger, Katharina Landfester, and Daniel Crespy
ACS Nano 2012 Volume 6(Issue 10) pp:9042
Publication Date(Web):September 28, 2012
DOI:10.1021/nn3031589
Nanocapsules composed of a poly(vinylferrocene)-block-poly(methyl methacrylate) shell and a hydrophobic liquid core are prepared in water. The nanocapsule shells display a patchy structure with poly(vinylferrocene) patches with sizes of 25 ± 3 nm surrounded by poly(methyl methacrylate). The functional nanopatches can be selectively oxidized, thereby influencing the colloidal morphology and introducing polar domains in the nanocapsule shell. The hydrophobic to hydrophilic transition in the redox-responsive nanopatches can be advantageously used to release a hydrophobic payload encapsulated in the core by an oxidation reaction.Keywords: ferrocene; nanocapsules; patchy; redox-responsive; stimuli-responsive
Co-reporter:Johannes Fickert, Marcin Makowski, Michael Kappl, Katharina Landfester, and Daniel Crespy
Macromolecules 2012 Volume 45(Issue 16) pp:6324-6332
Publication Date(Web):August 13, 2012
DOI:10.1021/ma301013p
An orthogonal polymerization reaction between two monomers partitioned in the two liquid phases of a miniemulsion yielded nanocapsules with various functional groups (sulfonate, amine, carboxylic acid, and poly(ethylene glycol) (PEG). The formation of the nanocapsules could be realized in the presence of a self-healing agent in the liquid core. We present here the conditions for the successful preparation of functional polymer nanocapsules by free-radical polymerization as orthogonal reaction for self-healing materials. The stability of the nanocapsules was assessed by AFM measurements in the dried state as well as in water.
Co-reporter:Rafael Muñoz-Espí, Paolo Dolcet, Torsten Rossow, Manfred Wagner, Katharina Landfester, and Daniel Crespy
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 11) pp:4292
Publication Date(Web):September 28, 2011
DOI:10.1021/am200954e
Tin dioxide coatings are widely applied in glasses and ceramics to improve not only optical, but also mechanical properties. In this work, we report a new method to prepare SnO2 coatings from aqueous dispersions of polymer/organotin hybrid nanoparticles. Various liquid organotin compounds were encapsulated in polymeric nanoparticles synthesized by miniemulsion polymerization. Large amounts of tetrabutyltin and bis(tributyltin) could be successfully incorporated in cross-linked and noncross-linked polystyrene nanoparticles that served as sacrificial templates for the formation of tin oxide coatings after etching with oxygen plasma or calcination. Cross-linked polystyrene particles containing bis(tributyltin)—selected for having a high boiling point—were found to be especially suited for the oxide coating formation. The content of metal in the particles was up to 12 wt %, and estimations by thermogravimetrical indicated that at least 96% of the total organotin compound was converted to SnO2. The resulting coatings were mainly identified as tetragonal SnO2 (cassiterite) by X-ray diffraction, although a coexistence of this phase with orthorhombic SnO2 was observed for samples prepared with bis(tributyltin).Keywords: encapsulation; miniemulsion; nanoparticles; organotin; tin oxide;
Co-reporter:Matthias Georg Schwab;Xinliang Feng;Katharina Lfester ;Klaus Müllen
Macromolecular Rapid Communications 2011 Volume 32( Issue 22) pp:1798-1803
Publication Date(Web):
DOI:10.1002/marc.201100511
Abstract
We report the first example of a successful preparation of a microporous organic polymer within the droplet phase of an inverse non-aqueous miniemulsion. Stable nanoparticles with enhanced specific surface area could be obtained despite the harsh conditions regarding reaction temperature (180 °C) and time (72 h) needed for building melamine-based Schiff base networks. Our new flexible method can in principle be applied to other water-sensitive protocols suitable for the bulk synthesis of MOPs that are based on Friedel-Crafts, Sonogashira-Hagihara or Yamamoto chemistry.
Co-reporter:Roland H. Staff, Patrick Rupper, Ingo Lieberwirth, Katharina Landfester and Daniel Crespy
Soft Matter 2011 vol. 7(Issue 21) pp:10219-10226
Publication Date(Web):06 Sep 2011
DOI:10.1039/C1SM05988B
Nanoparticles consisting of different molecular weight poly(styrene-block-methyl methacrylate) (P(S-b-MMA)) copolymers and nanocapsules consisting of the same copolymers, but additionally with hexadecane as liquid core material were prepared by the miniemulsion process. The dependence of the morphology of block copolymer assemblies on the nanoconfinement was investigated. We introduced two nanoconfinement parameters, that are the nanoparticle diameter D and the shell thickness d; D was controlled by varying the concentration of surfactant in the miniemulsion, while d was controlled by the ratio hexadecane/copolymer. As the diameter D of the high molecular weight (Mw ∼ 203,700 g mol−1) P(S-b-MMA) nanoparticles increased, first Janus-particles (at D < 60 nm), then core-shell structures (60 nm < D < 90 nm), onion-like nanoparticles (90 nm < D < 1800 nm) and finally terrace-like morphologies (D > 1800 nm) were obtained. Nanocapsules with 0 < d < D also showed an onion-like structure. In both cases the outmost layer was PMMA as identified by XPS and the lamellar thickness was in agreement with theoretical considerations. Nanoparticles and nanocapsules prepared with a low-molecular weight (Mw ∼ 19,500 g mol−1) P(S-b-MMA) displayed patchy structures. This is the first time that the morphology of block copolymers was studied under double nanoconfinement in colloids.
Co-reporter:Kathrin Friedemann, Andrey Turshatov, Katharina Landfester, and Daniel Crespy
Langmuir 2011 Volume 27(Issue 11) pp:7132-7139
Publication Date(Web):May 11, 2011
DOI:10.1021/la104817r
A model system for multicompartment nanofibers was fabricated by colloid electrospinning. The obtained nanostructured material consisted of fluorescent polymer nanoparticles that were synthesized in a miniemulsion and then embedded in fluorescently labeled polymer nanofibers. Because of the absence of contrast between both polymers, the immobilized nanoparticles cannot be reliably identified in the nanofibers via electron microscopy or other techniques. Here, we describe investigations on the hybrid material with two-color STED microscopy to localize the nanoparticles and to quantify their distribution along nanofibers with particle and fiber radii down to 50 nm.
Co-reporter:Christine Herrmann;Katharina Landfester
Colloid and Polymer Science 2011 Volume 289( Issue 10) pp:1111-1117
Publication Date(Web):2011 July
DOI:10.1007/s00396-011-2430-z
It is shown that it is possible to synthesize high molecular weight hydrophilic polyurethane particles by reacting either tolylene-2,4-diisocyanate or isophorone diisocyanate and oligoethylene glycol (Mn ∼200 g mol−1) in non-aqueous inverse emulsions. This procedure offers the advantage that the formation of polyurea can be prevented in consequence of the absence of water in the emulsion. Apparent molecular weights of hydrophilic polyurethane as high as 19,000 g mol−1 (Mn) were obtained.
Co-reporter:Daniel Crespy;Anastasia Golosova;Elena Makhaeva;Alexei R Khokhlov;Giuseppino Fortunato;René Rossi
Polymer International 2009 Volume 58( Issue 11) pp:1326-1334
Publication Date(Web):
DOI:10.1002/pi.2668
Abstract
BACKGROUND: Responsive materials are able to respond reversibly to an environmental stimulus. When the stimulus is temperature in the physiological range, the responsive material is particularly interesting for textile applications. We describe here the synthesis and characterization of reactive temperature-responsive copolymers and their subsequent grafting on cotton fabrics.
RESULTS: Copolymers of N-vinylcaprolactam and various reactive monomers were synthesized via free radical polymerization in solution. The copolymers were characterized in terms of chemical structure, molecular weight and temperature-responsive properties. The copolymer of N-vinylcaprolactam and methacrylic acid (11 or 22 wt%) and the hydrolysed copolymer of N-vinylcaprolactam and acryloyl chloride were found to be temperature responsive. They were subsequently grafted on cotton fabrics. The grafting was studied using X-ray photoelectron spectroscopy and scanning electron microscopy measurements and was found to be effective. Finally, the modified cotton fabrics were found to exhibit temperature-responsive water regain and water vapour transmission rates.
CONCLUSION: Temperature-responsive copolymers were synthesized, characterized and successfully grafted on cotton fabrics, yielding responsive fabrics. Such fabrics can hence be used to modulate the skin microclimate under textiles. Copyright © 2009 Society of Chemical Industry
Co-reporter:Anika Hamberger, Ana-Maria Popa, Rene M. Rossi, Daniel R. Kattnig, Dariush Hinderberger, Katharina Landfester and Daniel Crespy
Journal of Materials Chemistry A 2012 - vol. 22(Issue 19) pp:NaN9920-9920
Publication Date(Web):2012/04/13
DOI:10.1039/C2JM30333G
Nano-gas generators were synthesized by encapsulating azo-components into hydrophobic polymer particles. The dispersions of azo-components were subsequently thermally decomposed and could be reacted with either hydrophilic or hydrophobic dyes, which were located in the continuous and dispersed phases, respectively. Both systems displayed an irreversible switch in color upon temperature increase, yielding a new class of thermochromic materials. The mechanism and kinetics of the reaction between the azo-component and copper(II) phthalocyanine were monitored by EPR spectroscopy. The dispersions were also spin-coated on glass substrates and a significant change of turbidity occurred upon heating due to the gas generation in the films.
Co-reporter:Johannes Fickert, Patrick Rupper, Robert Graf, Katharina Landfester and Daniel Crespy
Journal of Materials Chemistry A 2012 - vol. 22(Issue 5) pp:NaN2291-2291
Publication Date(Web):2011/12/16
DOI:10.1039/C2JM15151K
Silica nanocapsules functionalized with thiol or amine groups with sizes between 100 and 400 nm could be successfully synthesized using the interface of direct miniemulsion droplets for the hydrolysis and condensation of silicon alkoxides. We show that healing agents such as monomers and catalysts can be successfully encapsulated in the silica shell. The catalyst was encapsulated as a solution to allow a better mobility when released for a self-healing reaction. The functional groups were quantified by 29Si MAS-NMR, XPS, and chemical titration. Therefore a precise picture for the gradient of concentration of functional groups inside the shell could be given. The encapsulated reagents were found to be still active and the self-healing reaction could be successfully monitored by solid-state NMR spectroscopy and thermogravimetry.
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