Wide Range of Functionalized Poly(N-alkyl acrylamide)-Based Amphiphilic Polymer Conetworks via Active Ester PrecursorsPublished: 11 July 2018 by American Chemical Society (ACS) in Macromolecules
A versatile strategy for the fabrication of functional and nanostructured poly(N-alkyl acrylamide)-based amphiphilic polymer conetworks (APCNs) from hydrophobic precursor networks is presented. The active ester monomer pentafluorophenyl acrylate (PFPA) fulfills a dual role: it provides miscibility with hydrophobic macromonomer cross-linkers and activates the acrylate for amidation reactions. Thereby, it acts as a general hydrophobic masking group for N-alkyl acrylamides, and enables the transformation of PFPA-based hydrophobic precursor networks into a multitude of different poly(N-alkyl acrylamide)-l-PDMS APCNs. These optically transparent APCNs possess nanophase-separated morphologies with domain sizes in the nanometer range. Variation of the amide results in different types of APCNs, despite them being derived from the same precursor network and having identical network structures. Accordingly, the properties of these APCNs can be tailored to the desired application by simple variation of the amide functionality. Furthermore, the combination of PFPA with another hydrophobically masked monomer allows for the fabrication of APCNs with small yet precisely defined amounts of functional amide units in the hydrophilic phase. A controlled functionalization of APCNs with pendant groups such as pH-responsive imidazole, fluorescent dyes, and biotin for specific protein binding is achieved, greatly expanding the functionality of the APCNs. Such functionalized APCNs could find application as stimuli-responsive drug delivery membranes, smart hydrogels, biosensors, or matrices for biocatalysis.
Transient activation of biochemical reactions by visible light and subsequent return to the inactive state in the absence of light is an essential feature of the biochemical processes in photoreceptor cells. To mimic such light-responsiveness with artificial nanosystems, polymersome nanoreactors were developed that can be switched on by visible light, and self-revert fast in the dark at room temperature to their inactive state. Donor-Acceptor Stenhouse Adducts (DASAs), with their ability to isomerize upon irradiation with visible light, were employed to change the permeability of polymersome membranes by switching polarity from a non-polar triene form to a cyclopentenone with increased polarity. To this end, amphiphilic block copolymers containing poly(pentafluorophenyl methacrylate) in their hydrophobic block were synthesized by reversible addition fragmentation chaintransfer (RAFT) radical polymerization and functionalized either with a DASA that is based on Meldrum’s acid, or with a novel fast switching pyrazolone-based DASA. These polymers were self-assembled into vesicles. Release of hydrophilic payload could be triggered by light and stopped as soon as the light was turned off. The encapsulation of enzymes yielded photo-responsive nanoreactors that catalyzed reactions only if they were irradiated with light. A mixture of polymersome nanoreactors, one that switches in green light, the other switching in red light, permitted to specifically control the individual reactions of a reaction cascade in one pot by irradiation with varied wavelengths, thus enabling light-controlled wavelength-selective catalysis. The DASA-based nanoreactors demonstrate the potential of DASAs to switch permeability of membranes, and could find application to switch reactions on and off on demand, e.g. in microfluidics or in drug delivery.
Polymer optical fibers are increasingly being used for medical applications, e.g. as wearable devices for diagnostics or therapeutics. Due to the multitude of applications and the corresponding restrictions and prerequisites, the properties of these optical fibers are fine-tuned to their specific application.Regarding wearables and continuous, unobtrusive long-term monitoring, a very low burden is reached when the integration into textiles is complete and the wearer's comfort is ensured. Here, we will discuss a selection of recent solutions within wearable photonic sensors. Integration processes are highlighted as to provide insight for further development.Finally, implications of long-term monitoring are discussed including data mining. The effect of knowing one's vitals on society is highlighted as a relevant influence on medical care. If ubiquitous monitoring were realized for a high percentage of the population, concerns can arise regarding the long-term reliability of the photonic sensors as well as ethical use of patient data.
The pyranine-benzalkonium ion pair: A promising fluorescent system for the ratiometric detection of wound pHPublished: 01 October 2017 by Elsevier BV in Sensors and Actuators B: Chemical
Neonatal jaundice (hyperbilirubinaemia) is common in neonates and, often, intensive blue-light phototherapy is required to prevent long-term effects. A photonic textile can overcome three major incubator-related concerns: Insulation of the neonate, human contact, and usage restraints. This paper describes the development of a homogeneous luminous textile from polymer optical fibres to use as a wearable, long-term phototherapy device. The bend out-coupling of light from the POFs was related to the weave production, e.g. weave pattern and yarn densities. Comfort, determined by friction against a skin model and breathability, was investigated additionally. Our textile is the first example of phototherapeutic clothing that is produced sans post-processing allowing for faster commercial production.
Carbon Dots and Fluorescein: The Ideal FRET Pair for the Fabrication of a Precise and Fully Reversible Ammonia SensorPublished: 07 August 2017 by MDPI in Proceedings
Monitoring of ammonia in the human breath is of paramount importance to monitor diseases link to liver and kidney mulfunctioning. The present paper describes a solid-state optical ammonia sensor based on Förster resonance energy transfer (FRET) between narrowly dispersed blue-emitting carbon nanodots (CNDs) as FRET donor and fluorescein as FRET acceptor. The fluorophores were physically entrapped in a close to superhydrophobic sol-gel matrix, in turn deposited on a PVDF-HFP electrospun fiber membrane. The sensor shows a linear calibration with a remarkably low limit of detection, i.e., 110 ppb, and adequate reproducibility up to six N2/NH3 cycles.
Correction to 'Body-monitoring with photonic textiles: a reflective heartbeat sensor based on polymer optical fibres'.Published: 03 May 2017 by The Royal Society in Journal of The Royal Society Interface
Body-monitoring with photonic textiles: a reflective heartbeat sensor based on polymer optical fibres.Published: 08 March 2017 by The Royal Society in Journal of The Royal Society Interface
Knowledge of an individual's skin condition is important for pressure ulcer prevention. Detecting early changes in skin through perfusion, oxygen saturation values, and pressure on tissue and subsequent therapeutic intervention could increase patients' quality of life drastically. However, most existing sensing options create additional risk of ulcer development due to further pressure on and chafing of the skin. Here, as a first component, we present a flexible, photonic textile-based sensor for the continuous monitoring of the heartbeat and blood flow. Polymer optical fibres (POFs) are melt-spun continuously and characterized optically and mechanically before being embroidered. The resulting sensor shows flexibility when embroidered into a moisture-wicking fabric, and withstands disinfection with hospital-type laundry cycles. Additionally, the new sensor textile shows a lower static coefficient of friction (COF) than conventionally used bedsheets in both dry and sweaty conditions versus a skin model. Finally, we demonstrate the functionality of our sensor by measuring the heartbeat at the forehead in reflection mode and comparing it with commercial finger photoplethysmography for several subjects. Our results will allow the development of flexible, individualized, and fully textile-integrated wearable sensors for sensitive skin conditions and general long-term monitoring of patients with risk for pressure ulcer.
Optimization of novel melt-extruded polymer optical fibers designed for pressure sensor applicationsPublished: 01 March 2017 by Elsevier BV in European Polymer Journal
We report on the production, characterization, and textile integration of polymer optical fibers (POF) to develop a flexible photonic sensor. Mono-component POFs were produced continuously by melt-extrusion. Advantageously for pressure sensing, the un-clad fibers are more susceptible to macro-bending. The fibers’ mechanical and optical properties and their dependence on production parameters were investigated, allowing for tuning of the pressure sensitivity. The fibers also withstood cyclic loading with a linear, quick response. We produced and successfully tested a demonstrator with a matrix of intersecting fibers secured on a textile substrate. A possible application of this textile pressure sensor would be supervision of pressure on tissue as part of pressure ulcer prevention. Pressure ulcers are prevalent in paraplegics and bedbound sick. The lack of data at skin level still makes prevention difficult. Novel flexible sensors could deliver data while preventing further injury. When combined with a photoplethysmograph, the discussed matrix is foreseen to give information on the relationship between pressure and ceasing oxygen supply in the skin.
Aging population and longer life expectancy are the main reasons for an increasing number of patients with wound problems. Although the interest in wound care increases continuously, wound management still remains a challenge mainly due to the higher occurrence of chronic wounds, which require intensive care and constant monitoring. Here, we demonstrate a fluorescent sensing system to monitor the wound status and to distinguish between an autonomously healing and a chronic wound at an early stage. The system allows monitoring two of the most relevant fluctuating wound parameters during the healing process which are pH and glucose concentration. A fluorescent pH indicator dye, carboxynaphthofluorescein, and a metabolite-sensing enzymatic system, based on glucose oxidase and horseradish peroxidase, were immobilized on a biocompatible polysaccharide matrix to develop a functional hydrogel coating for wound monitoring. The changes in metabolite and enzyme concentration in artificial wound extract were converted into a fluorescent signal.
We developed a paper coating for the potential application in food packaging based on polylactide and montmorillonite. It is applied to the paper in the form of a stable, water-based latex with a solid content of 25–28 wt %. The latex is prepared from a commercially available polylactide, surfactants, montmorillonite, a plasticizer, chloroform (to be removed later) and water by an emulsion/solvent evaporation procedure. This coating formulation is applied to the paper substrate by bar-coating, followed by hot-pressing at 150 °C. The coated papers achieved up to an 85% improvement in water vapor transmission rates when compared to the pristine papers. The coating latex is prepared from inexpensive materials and can be used for a solvent-free coating process. In addition, the ingredients of the latex are non-toxic; thus, the coated papers can be safely used for food packaging.
2,2′:6′,2′′-Terpyridine-functionalized redox-responsive hydrogels as a platform for multi responsive amphiphilic polymer...Published: 01 January 2016 by Royal Society of Chemistry (RSC) in RSC Advances
Amphiphilic polymer co-networks were functionalized with spyropiran and terpyridine yielding multi-responsive membranes with switchable properties and potential applications in drug delivery and medical sensors. Nanophase-separated amphiphilic polymer co-networks are ideally suited as responsive membranes due to their stable co-continuous structure. Their functionalization with redox-responsive 2,2′:6′,2′′-terpyridine–metal complexes and light-responsive spiropyran derivatives leads to a novel material with tunable optical, redox and permeability properties. The versatility of the system in complexing various metal ions, such as cobalt or iron at different concentrations, results in a perfect monitoring over the degree of crosslinking of the hydrophilic poly(2-hydroxyethyl acrylate) channels. The reversibility of the complexation, the redox state of the metal and the isomerization to the merocyanine form upon UV illumination was evidenced by cyclic voltammetry, UV-Vis and permeability measurements under sequential conditions. Thus, the membrane provides light and redox addressable functionalities due to its adjustable and mechanically stable hydrogel network.
Preparation of ellipsoid-shaped supraparticles with modular compositions and investigation of shape-dependent cell-uptak...Published: 01 January 2016 by Royal Society of Chemistry (RSC) in RSC Advances
Hybrid ellipsoid-shaped supraparticles consisting of different nanomaterials are fabricated and the influence of the supraparticle shape on cell-uptake is investigated. Hybrid colloidal supraparticles often show a superior performance in catalysis, optics and biomedicine thanks to the synergistic effect of the ensemble of their single nanoparticle building blocks. Despite the emerging importance of shape-dependent properties of nanostructures, the synthesis of supraparticles is generally limited to a spherical shape. Here, a broadly applicable method is presented for the fabrication of ellipsoid supraparticles from one or several types of inorganic nanoparticles in various compositions. The method is highly versatile and modular, allowing free choice of hydrophobic nanoparticles to combine desired properties in the resulting supraparticles. A representative series of ellipsoid-shaped supraparticles is fabricated and their morphology, hybrid structure and composition as well as their functional properties are investigated. All employed nanoparticle types are successfully incorporated resulting in ellipsoid-shaped supraparticles with largely homogeneous intra- and interparticular distribution of the different nanoparticle building blocks. A biological assessment of iron oxide ellipsoid supraparticles reveals no safety issues but a pronounced lower cellular uptake compared to spherical ones. This distinct shape–property relationship illustrates the importance of the supraparticle shape as a parameter for the rational design of nanosystems for biomedical applications.
ATRP-based synthesis and characterization of light-responsive coatings for transdermal delivery systemsPublished: 08 May 2015 by IOP Publishing in Science and Technology of Advanced Materials
The grafting of poly(hydroxyethylmethacrylate) on polymeric porous membranes via atom transfer radical polymerization (ATRP) and subsequent modification with a photo-responsive spiropyran derivative is described. This method leads to photo-responsive membranes with desirable properties such as light-controlled permeability changes, exceptional photo-stability and repeatability of the photo-responsive switching. Conventional track etched polyester membranes were first treated with plasma polymer coating introducing anchoring groups, which allowed the attachment of ATRP-initiator molecules on the membrane surface. Surface initiated ARGET–ATRP of hydroxyethylmethacrylate (where ARGET stands for activator regenerated by electron transfer) leads to a membrane covered with a polymer layer, whereas the controlled polymerization procedure allows good control over the thickness of the polymer layer in respect to the polymerization conditions. Therefore, the final permeability of the membranes could be tailored by choice of pore diameter of the initial membranes, applied monomer concentration or polymerization time. Moreover a remarkable switch in permeability (more than 1000%) upon irradiation with UV-light could be achieved. These properties enable possible applications in the field of transdermal drug delivery, filtration, or sensing.
For the long-time monitoring of electrocardiograms, electrodes must be skin-friendly and non-irritating, but in addition they must deliver leads without artifacts even if the skin is dry and the body is moving. Today's adhesive conducting gel electrodes are not suitable for such applications. We have developed an embroidered textile electrode from polyethylene terephthalate yarn which is plasma-coated with silver for electrical conductivity and with an ultra-thin titanium layer on top for passivation. Two of these electrodes are embedded into a breast belt. They are moisturized with a very low amount of water vapor from an integrated reservoir. The combination of silver, titanium and water vapor results in an excellent electrode chemistry. With this belt the long-time monitoring of electrocardiography (ECG) is possible at rest as well as when the patient is moving.
Effect of plasticizers on the barrier and mechanical properties of biomimetic composites of chitosan and clayPublished: 01 January 2015 by Elsevier BV in Carbohydrate Polymers
Biomimetic composites of polymer and clay are known to possess high mechanical strength and excellent barrier properties. However, the ductility of these composites is always low. One way to overcome this limitation consists on the incorporation of plasticizers which work effectively for the pure polymer. It is shown here that an imidazolium-based ionic liquid is a more effective plasticizer for chitosan, in terms of suppression of the glass transition temperature and mechanical properties, than the more commonly used glycerol. This might result from the ionic interaction between both species that is not present when glycerol is used as the plasticizer. Biomimetic composites of chitosan and clay were also prepared containing these two plasticizers. A similar effect on the mechanical properties was observed as for the pure polymer, that is, even at a very low (∼12%) final concentration, the ionic liquid was a better plasticizer than glycerol, being able to double the ductility of the composites. Regarding barrier properties, no difference was observed between the original and the plasticized composites. This study thus shows that the incorporation of plasticizers is an effective method to improve the flexibility of biomimetic composites without deleterious effect on their excellent barrier properties.
Ellipsoid-shaped nanoclusters composed of single superparamagnetic nanoparticles and possessing a high saturation magnetization can be generated by emulsion electrospinning. Ellipsoid-shaped nanoclusters composed of single superparamagnetic nanoparticles can be generated by emulsion electrospinning. Stretching and subsequent solvent evaporation of iron oxide loaded emulsion droplets during the emulsion electrospinning process enables the creation of such structures embedded in polymer nanofibers. Dissolution of the polymer fibers yields an aqueous dispersion of the inorganic clusters which are the first example of ellipsoid-shaped superparamagnetic nanoclusters with a high saturation magnetization (∼47 emu g −1 ).
Incorporation of a FRET dye pair into mesoporous materials: a comparison of fluorescence spectra, FRET activity and dye ...Published: 01 January 2015 by Royal Society of Chemistry (RSC) in The Analyst
The incorporation of fluorescent dyes into mesoporous silicates was investigated as potential FRET based systems for gas sensing applications with better response than non-particulate systems. Fluorescein and rhodamine B modified mesoporous silica particles were synthesized by post-grafting and co-condensation approaches. The materials exhibited different pore size distributions, particle shapes and sizes. The materials were characterized by nitrogen sorption, scanning electron microscopy and fluorescence spectroscopy. The Förster resonance energy transfer between the selected dye pair was explored for the different materials by exposure to various concentrations of gaseous ammonia. A logarithmic increase in rhodamine B emission with increasing ammonia concentration was observed for both post-grafted and co-condensed materials. The dye accessibility by ammonia gas in the silica framework of mesoporous materials was evaluated by using a flow cell gas sensor setup built in-house. Response to ammonia gas and recovery with nitrogen gas are explained by comparing the structure properties and dye loading of the materials. The post-grafted dye modified silica showed better performance in terms of reversibility and recovery.
Poly(4-hydroxybutyrate) (P4HB) is a bacterial polyhydroxyalkanoate with interesting biological and physico-chemical properties for the use in biomedical applications. The synthesis of P4HB through a fermentation process often leads to a polymer with a too high molecular weight, making it difficult to process it further by solvent- or melt-processing. In this work P4HB was degraded to obtain polymers with a molecular weight ranging from 1.5×10(3)g/mol to 1.0×10(6)g/mol by using a method established in our laboratory. We studied the effect of the change in molecular weight on thermal and mechanical properties. The decrease of the molecular weight led to an increase in the degree of crystallinity of the polymer. Regarding the tensile mechanical properties, the molecular weight played a more prominent role than the degree of crystallinity in the evolution of the properties for the different polymer fractions. The method presented herein allows the preparation of polymer fractions with easier processability and still adequate thermal and mechanical properties for biomedical applications.
Body-Monitoring and Health Supervision by Means of Optical Fiber-Based Sensing Systems in Medical TextilesPublished: 30 October 2014 by Wiley in Advanced Healthcare Materials
Long‐term monitoring with optical fibers has moved into the focus of attention due to the applicability for medical measurements. Within this Review, setups of flexible, unobtrusive body‐monitoring systems based on optical fibers and the respective measured vital parameters are in focus. Optical principles are discussed as well as the interaction of light with tissue. Optical fiber‐based sensors that are already used in first trials are primarily selected for the section on possible applications. These medical textiles include the supervision of respiration, cardiac output, blood pressure, blood flow and its saturation with hemoglobin as well as oxygen, pressure, shear stress, mobility, gait, temperature, and electrolyte balance. The implementation of these sensor concepts prompts the development of wearable smart textiles. Thus, current sensing techniques and possibilities within photonic textiles are reviewed leading to multiparameter designs. Evaluation of these designs should show the great potential of optical fibers for the introduction into textiles especially due to the benefit of immunity to electromagnetic radiation. Still, further improvement of the signal‐to‐noise ratio is often necessary to develop a commercial monitoring system.
In this paper, a textile-based respiratory sensing system is presented. Highly flexible polymeric optical fibres (POFs) that react to applied pressure were integrated into a carrier fabric to form a wearable sensing system. After the evaluation of different optical fibres, different setups were compared. To demonstrate the feasibility of such a wearable sensor, the setup featuring the best performance was placed on the human torso, and thus it was possible to measure the respiratory rate. Furthermore, we show that such a wearable system enables to keep track of the way of breathing (diaphragmatic, upper costal and mixed) when the sensor is placed at different positions of the torso. A comparison of the results with the output of some commercial respiratory measurements devices confirmed the utility of such a monitoring device.
In this paper, a textile-based sensing principle for long term photopletysmography (PPG) monitoring is presented. Optical fibers were embroidered into textiles such that out-coupling and in-coupling of light was possible. The “light-in light-out” properties of the textile enabled the spectroscopic characterization of human tissue. For the optimization of the textile sensor, three different carrier fabrics and different fiber modifications were compared. The sample with best light coupling efficiency was successfully used to measure heart rate and SpO2 values of a subject. The latter was determined by using a modified Beer-Lambert law and measuring the light attenuation at two different wavelengths (632 nm and 894 nm). Moreover, the system was adapted to work in reflection mode which makes the sensor more versatile. The measurements were additionally compared with commercially available system and showed good correlation.
Composites of poly(lactic acid) (PLA) and organoclays with clay loadings of up to 80% were prepared as self‐supporting films using a doctor‐blading approach. Depending on the properties of the used organoclay, either intercalated nanocomposites or conventional composites were obtained. The incorporation of such high amounts of clay resulted in up to 10‐fold decrease in the water vapor transmission rate when compared to the pristine polymer. The effect of clay platelets on the crystallization of PLA chains was also studied; it was found that high amounts of clay hinder only the melt crystallization of the polymer, whereas cold crystallization proceeds as usual. On the other hand, the crystallization of PLA also influenced the composite structure by increasing the extent of intercalation of polymer between clay layers. This study thus shows that the change in the extent of clay‐polymer interactions is also an important factor in controlling nanocomposite structure, especially for high loading. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013