3D-printed Laponite/Alginate hydrogel-based suppositories for versatile drug loading and release.

Traditional approaches to solid rectal therapies have halted progress, leading to a continual decline in the use of conventional suppositories. Additive manufacturing techniques have been recently explored as a suitable innovative tool for suppository fabrication. However, little advancement has been made in composition materials for 3D-printed suppository (3DPS) manufacturing and still, conventional vehicles are often used for construct fabrication, hindering the growth in the field. As a novelty, this study unveils a ground-breaking Laponite-alginate hydrogel-based 3DPS. Interestingly, this study proposes a novel approach for loading drugs into the 3DPS employing for the first time the post-printing loading. Thus, a passive loading strategy of molecular models is developed, demonstrating the versatility and capacity to load molecules of different charges and molecular sizes within the matrix systems. This novel strategy allows adapting the load of a wide range of drugs into a single ink, which simplifies and speeds up the 3DPS technological development process for drugs with different physico-chemical properties. Additionally, in this research, a displacement strategy of the three-dimensional Laponite matrices is developed in order to enhance the drug release capacity through the 3DPS and their disintegration capacity, resulting in a significant improvement of the drug diffusion through the hydrogel matrix and a rapid disintegration of the 3DPS. Finally, our study demonstrates that the obtained 3DPS have a suitable in vivo behavior, being non-obstructive and allowing the normal motility of the rats intestine.

Highly Sensitive DNA Sensor Based on Upconversion Nanoparticles and Graphene Oxide.

In this work we demonstrate a DNA biosensor based on fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er nanoparticles and graphene oxide (GO). Monodisperse NaYF4:Yb,Er nanoparticles with a mean diameter of 29.1 ± 2.2 nm were synthesized and coated with a SiO2 shell of 11 nm, which allowed the attachment of single strands of DNA. When these DNA-functionalized NaYF4:Yb,Er@SiO2 nanoparticles were in the proximity of the GO surface, the π-π stacking interaction between the nucleobases of the DNA and the sp(2) carbons of the GO induced a FRET fluorescence quenching due to the overlap of the fluorescence emission of the NaYF4:Yb,Er@SiO2 and the absorption spectrum of GO. By contrast, in the presence of the complementary DNA strands, the hybridization leads to double-stranded DNA that does not interact with the GO surface, and thus the NaYF4:Yb,Er@SiO2 nanoparticles remain unquenched and fluorescent. The high sensitivity and specificity of this sensor introduces a new method for the detection of DNA with a detection limit of 5 pM.

Synthesis and characterization of biocatalytic γ-Fe2O3@SiO2 particles as recoverable bioreactors.

In this work, we present a suitable methodology to produce magnetically recoverable bioreactors based on enzymes, which are covalently attached on the surface of iron oxide@silica nanoparticles. In order to produce this system, iron oxide clusters with a mean diameter of 68 nm were covered with silica. This strategy yields spherical γ-Fe2O3@SiO2 cluster@shell nanoparticles with a mean diameter of 200 nm which present magnetic responsiveness and enhanced stability. The surface of these nanoparticles was modified into two steps with the aim to obtain carboxylic functional groups, which were activated to react with the enzyme glucose oxidase (GOx) that was thus immobilized on the surface of the nanoparticles. The objective of this chemistry at the nanoparticles interface is to produce magnetic-responsive bioreactors. The enzymatic activity was evaluated by using the recoverable bioreactors as part of an amperometric biosensor. These measurements allowed determining the stability, catalytic activity and the amount of enzyme immobilized on the surface of the nanoparticles. Furthermore, the functionalized nanoparticles can be recovered by applying an external magnetic field, which allows them to be employed in chemical processes where the recovery of the biocatalyst is important.

Fluorescence decrease of conjugated polymers by the catalytic activity of horseradish peroxidase and its application in phenolic compounds detection.

We report the fluorescence decrease of the water-soluble π-π-conjugated polymer poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene, MPS-PPV) by the catalytic activity of horseradish peroxidase in the presence of H(2)O(2). MPS-PPV acts as a donor substrate in the catalytic cycle of horseradish peroxidase where the electron-deficient enzymatic intermediates compounds I and II can subtract electrons from the polymer leading to its fluorescence decrease. The addition of phenolic drug acetaminophen to the former solution favors the decrease of the polymer fluorescence, which indicates the peroxidase-catalyzed co-oxidation of MPS-PPV and acetaminophen. The encapsulation of horseradish peroxidase within polyacrylamide microgels allows the isolation of intermediates compound I and compound II from the polymer, leading to a fluorescence decrease that is only due to the product of biocatalytic acetaminophen oxidation. This system could be used to develop a new device for phenolic compounds detection.

Development of an acetaminophen amperometric biosensor based on peroxidase entrapped in polyacrylamide microgels.

In this work, horseradish peroxidase (HRP) has been entrapped in cross-linked polyacrylamide microparticles using the concentrated emulsion polymerization method. The feasibility of amperometric detection of acetaminophen (APAP) in a biosensor using this HRP immobilized system as the biological material in the presence of hydrogen peroxide was investigated. We found that the optimum microgel cross-linking degree required to retain the protein and to allow the diffusion of the phenolic drug onto the microparticles was 8%. The apparent diffusion coefficients of APAP across the different microparticles have been calculated using the Cottrell equation. The diffusion coefficients decrease as the microgel cross-linking increases, and the data fit an uniexponential equation well. Those microparticles with a cross-linking degree lower than 5% operated under kinetic control, whereas those whose cross-linking degree was above this value operated under diffusion control. Biosensor response was also optimized to investigate the effect of H(2)O(2) concentration and enzyme loading on the current intensity. Under optimal conditions, the sensitivity of this biosensor for APAP was 74.9 mA M(-1) cm(-2), the detection limit was 3.1×10(-6) M based on S/N=3 and the response time was 135 s. The linear range goes from 1.0×10(-5) to 4.9×10(-4) M APAP, and can be extended using the Hill equation to 5.7×10(-3) M. The biosensor is selective for APAP and was applied to determine the APAP concentration in three commercial pharmaceutical formulations.

Investigation of the relationship between hydrogen bonds and macroscopic properties in hybrid core-shell gamma-Fe2O3-P(NIPAM-AAS) microgels.

We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe(2)O(3) and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe(2)O(3) increases. The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures as due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse.

Interpenetrated PNIPAM-polythiophene microgels for nitro aromatic compound detection.

In this work, we present a facile and reproducible method to obtain thermally responsive, monodisperse, fluorescent microgels with diameters smaller than 700 nm based on poly(N-isopropyl acrylamide) (PNIPAM) interpenetrated with poly(thiophene-ethyl buthyl sulfonate) (PTEBS). Changing the temperature and inducing the microgel volume phase transition, it is possible to modify the photoluminescence (PL) properties of the microgels. Thus, when the temperature was below the low critical solution temperature (LCST) of PNIPAM, the PL intensity was higher than that above the LCST. Time-resolved fluorescence measurements indicate that, in the swollen state, the increment of cross-linking increases the fluorescence decay time of PTEBS. By contrast, in the collapsed state, variations in the decay time were attributed to higher rigidity of the PNIPAM-PTEBS system, which was confirmed by neutron scattering measurements. Moreover, the shift in the wavelength of the fluorescence emission peak observed above the LCST indicates that the collapsed PNIPAM matrix was able to interact with the PTEBS chains hindering the formation of pi-pi interactions. This property is envisaged for developing a picric acid microsensor based on the formation of pi-pi interactions with the pi-conjugated polymer, thus quenching its PL emission. Above the LCST of PNIPAM-PTEBS microgels, the interactions would be broken and the initial PL emission would be recovered. This property could render reusable microsensors for detection of nitro aromatic compounds.

Gels and microgels for nanotechnological applications.

In recent years, "smart" materials have been the focus of considerable interest, from both fundamental and applied perspectives. Polymer gels are within this category; they respond to specific environmental stimuli by changing their size. Thus, the internal structure, the refractive index, and the mechanical properties of the polymer network change. They are considered super absorbent materials, as they can absorb solvent up to several hundred times their own weight. They respond rapidly to local environmental variations, an important fact in device miniaturization and microsensor developments. As size changes are accompanied by changes in internal dimensions, microgels have found application as carriers of therapeutic drugs and as diagnostic agents. They have also been used as microreactors, optically active materials, for template synthesis of nanoparticles or fabrication of artificial muscle. In this paper we review a set of application based on the special features associated to this systems. Basic concepts on the physical-chemistry of gel swelling is first described, followed by different applications covering drug delivery, composite materials using polymer gels to modulate optical or magnetic and electrical properties, molecular imprinting, gel-based biosensors and polymer sensors and actuators used in the field of artificial muscles.

Switchable photoluminescence of CdTe nanocrystals by temperature-responsive microgels.

In the present study, we report a method for preparing a fluorescent thermosensitive hybrid material based on monodisperse, thermosensitive poly( N-isopropyl acrylamide) (PNIPAM) microgels covered with CdTe nanocrystals of 3.2 nm diameter. The CdTe nanocrystals were covalently immobilized on the surface of PNIPAM microgels. The chemical environment around the CdTe nanocrystals was modified by changing the temperature and inducing the microgel volume-phase transition. This change provoked a steep variation in the nanocrystal photoluminescence (PL) intensity in such a way that when the temperature was under the low critical solution temperature (LCST) of the polymer (36 degrees C) the PL of the nanocrystals was strongly quenched, whereas above the LCST the PL intensity was restored.

Synthesis and characterization of poly(magnesium acrylate) microgels.

In this work, we present the synthesis of a novel poly(magnesium acrylate) microgel, its microstructural characterization, and its application as an enzyme immobilization system. The variation of the monomer concentration employed in the synthesis permitted to tune up the shape of the microgels in such a way that using 1.5 mol L(-1) we produced microgels of average size 40 microm formed by smaller subunits of around 1 microm. This fact confers the microgels a pomegranate-like structure that increases the specific surface of the system. Glucose oxidase (GOx) from Aspergillus niger was immobilized within the microgels with the aim of using them as bioreactors. The microgels were characterized by scanning electron microscopy and by neutron scattering. The incorporation of the enzyme results in an increment in the network mesh size and the appearance of a new correlation length in the neutron scattering pattern. Finally, the enzymatic activity of the microgels with GOx entrapped was studied as a function of the microgel cross-linking content.

Enzymatic biodegradable micro-reactors for therapeutic applications.

Poly(epsilon-caprolactone) is a well known biocompatible polymer, widely used as drug immobilization systems. In this work poly(epsilon-caprolactone) microparticles with average size between 5 and 25 microm have been prepared by O/W emulsion evaporation method. Inside the microparticles, we have encapsulated Glucose Oxidase with the aim of preparing micro-reactors for enzymatic therapy. These microparticles were structurally characterized and its enzymatic activity analyzed in order to improve the enzyme entrapment. Thus, at the optimum synthesis conditions the enzyme entrapped in the microparticles showed an enzymatic activity of (29.9 +/- 2.1)% comparing with the same amount of free enzyme. Moreover the microparticles maintained a (70.4 +/- 3.2)% of their initial enzymatic activity after placing them in buffer solution for two weeks.

Biosensors based on acrylic microgels: a comparative study of immobilized glucose oxidase and tyrosinase.

Acrylic microgels are proposed as enzyme immobilizing support in amperometric biosensors. Two enzymes, glucose oxidase and tyrosinase, were entrapped in this matrix and their behaviour is compared. The optimum cross-linking of the polymeric matrix required to retain the enzyme, and to allow the diffusion of the substrate is different for each enzyme, 3.2% for glucose oxidase and 4.5% for tyrosinase. The effect of pH and temperature on the biosensor responses has been studied by experimental design methodology and predictions have been compared with independently performed experimental measurements. A quadratic effect of the variables studied (pH and T) on the biosensor response and the small or null interaction between them was confirmed. The pH results obtained with both methods are coincident revealing an reversible effect on the enzyme. However, the temperature optimum value obtained by experimental design was 10 degrees C lower as a result of an activity decay due to irreversible thermal denaturation of both enzymes.

Design of an amperometric biosensor using polypyrrole-microgel composites containing glucose oxidase.

A new material consisting of a water-dispersed complex of polypyrrole-polystyrensulfonate (PPy) embedded in polyacrylamide (PA) has been prepared and tested as enzyme immobilizing system for its use in amperometric biosensors. Glucose oxidase (GOx) and the water-dispersed polypyrrole complex were entrapped within polyacrylamide microgels by polymerization of acrylamide in the dispersed phase of concentrated emulsions containing GOx and PPy. Polymerization of the dispersed phase provides microparticles whose size lies between 3.5 and 7 microm. The aim of incorporating polypyrrole into the polyacrylamide microparticles was to facilitate the direct transfer of the electrons released in the enzymatic reaction from the catalytic site to the platinum electrode surface. The conductivity of the microparticles was measured by a four-point probe method and confirmed by the successful anaerobic detection of glucose by the biosensor. Thus, the polyacrylamide-polypyrrole (PAPPy) microparticles combine the conductivity of polypyrrole and the pore size control of polyacrylamide. The effects of the polyacrylamide-polypyrrole ratio and cross-linking on the biosensor response have been investigated, as well as the influence of analytical parameters such as pH and enzymatic loading. The PAPPy biosensor is free of interferences arising from ascorbic and uric acids, which allows its use for quantitative analysis in human blood serum.