Guilherme M. Pereira

Albumin release from a brain-resembling superabsorbent magnetic hydrogel based on starch

Brain-resembling superabsorbent hydrogel composites were developed via UV-induced copolymerization-crosslinking of vinyl-modified starch with acrylic acid (AAc) and N,N-dimethylacrylamide (DMAAm) in the presence of Fe3O4 particles. The iodine test revealed the actual 3D network structure of starch within the swollen hydrogel composite. FTIR spectra of the hydrogel composites indicated interaction between the carboxyl groups from a hydrogel and the iron ions from Fe3O4. The formation of the hydrogel composites also was evidenced by wide-angle X-ray diffraction (WAXD) and energy dispersive X-ray (EDS) spectroscopies. Scanning electron microscopy (SEM) images revealed a homogeneous material since no phase separation between the hydrogel and the Fe3O4 phases could be observed. Minimal fragments of the swollen composite allowed the study of its actual morphology by TEM imaging. Stick-type structures were observed in the composite, as a result of a water-equilibrated structural configuration (obtained in a swollen state) of carboxyl groups of AAc coordinated to iron ions of Fe3O4. The albumin release mechanism of the hydrogel without Fe3O4 is governed by macromolecular relaxation. In the hydrogel composites, the albumin release was driven by macromolecular relaxation, but with a strong tendency to anomalous transport, because of both the tortuosity effect and attenuation of the anion–anion electrostatic repulsion forces. On the other hand, the albumin release became more dependent on anomalous transport with an applied magnetic field, which intensified the tortuosity effect. The proposed hydrogels are more appropriate for use as oral drug delivery systems because they provide a better sustention of the drug over the in vitro release experiment.

From ionic liquid-modified cellulose nanowhiskers to highly active metal-free nanostructured carbon catalysts for the hydrazine oxidation reaction

Ionic liquid (or [C4mim][CH3SO3])-modified cellulose nanowhiskers (CNWs) are synthesized and successfully used as precursors to make heteroatom (N and S)-doped nanostructured carbon catalysts. The catalysts can efficiently electrocatalyze the hydrazine oxidation reaction (HOR) with an onset potential close to the reactions thermodynamic value, or with a value better than those obtained for other related materials. The synthesis of these metal-free carbon electrocatalysts generally involves only a few, relatively less demanding synthetic steps. Based on relevant control experiments, the outstanding catalytic activity of the materials is attributed to the heteroatom dopants and defect sites in the materials, which form during carbonization due to the [C4mim][CH3SO3] placed around the CNWs. However, it is not necessarily the density of heteroatom dopant species introduced into the nanostructured carbon materials by the ILs that directly affect the electrocatalytic activity of these materials; it is rather the specific type of dopant-associated chemical moiety and vacancy site created in the materials, which are the main factors positively affecting the electrocatalytic activity of the materials toward the reaction. The surface areas of the materials play a relatively lesser role in affecting the electrocatalytic properties of the materials toward the HOR as well.

Hydroxyapatite nanowhiskers embedded in chondroitin sulfate microspheres as colon targeted drug delivery systems

An inorganic/organic hybrid material with a triggering mechanism for specific drug delivery at the colon was synthesized. First, hydroxyapatite nanowhiskers (n-HA) with a high aspect ratio, narrow particle size distribution and high surface area, ca. 67 m2 g-1, are prepared. As proof-of-concept, terbinafine, a fungicidal agent, was loaded onto the n-HA, obtaining a drug loading of 40.63 mg of terbinafine per gram of n-HA. Hydroxyapatite nanowhiskers loaded with terbinafine were encapsulated with chondroitin sulfate (CS) microspheres, using chemically modified glycidyl methacrylate by performing ultrasonic microemulsion polymerization. The obtained hybrid materials were characterized by TEM, SEM, FTIR, and NMR. Dispersed n-HA in CS microspheres was obtained for different n-HA contents, from 1 to 10% (w/w). In vitro studies have been carried out to investigate terbinafine release from hybrid microspheres in simulated gastric fluid and simulated intestinal fluid. The studies demonstrated that sustained drug release can be obtained using the developed hybrid material.

Controlling cell growth with tailorable 2D nanoholes arrays

A facile and reproducible route that can lead to two-dimensional arrays of nanopores in thin polymer films is demonstrated. The formation of the pores in the polymer films involves breath figure phenomenon and occurs during the film deposition by spin coating. The formation of nanoporous thin films takes only few seconds, and the method does not require complex equipment or expensive chemicals. This method also constitutes a straightforward approach to control the size of the pores formed in thin films. Besides allowing control over the average pore size of the porous films, the use of dynamic deposition with the breath figure phenomenon causes the reduction in the pore size to nanometer scale. The nanoporous arrays obtained by the breath figure are applied as substrates for cell growth, and the effect of their nanopore size on cell growth was evaluated. Notably, it is found that cell viability is related to pore size, where 2D nanoporous structure is more beneficial for cell culture than 2D microporous structures. The change in the average pore size of the polymer films from 1.22 μm to 346 nm results in a threefold increase in cell viability.

Hosted formation of PbS crystals on polyethylene modified surface

Supported and stable inorganic crystals in nanometric size, such as PbS or other quantum dots, are very desired materials in the form of thin films for the application in technological areas. Herein, an approach to the growth of PbS crystals in poly(acrylic acid) (PAA) ultrathin film covalently immobilized in the polyethylene (PE) surface is described. The method used allows the obtaining of materials with different shapes and sizes by the adjustment of experimental variables. The more homogenous composites with the smallest particles were obtained at pH 6 due to the slower removal of Pb2+ ions from PAA ultrathin film. Hence, the PbS is formed in situ inside of PAA. A direct relationship between Pb2+ and thioacetamide (TAA) concentrations was observed by the analysis of the composite morphologies. More homogenous composites with the smallest particles were obtained in the lowest Pb2+ condition and the highest TAA concentration condition or in the intermediate Pb2+ condition and the lowest TAA concentration condition.

Synthesis of a thermosensitive surface by construction of a thin layer of poly (N-isopropylacrylamide) on maleimide-immobilized polypropylene.

Thermosensitive surfaces were developed by the grafting of a thin layer of PNIPAAm through an UV-induced photopolymerization reaction of vinyl monomers with a free radical-activated polypropylene (PP) surface. PNIPAAm layer covering the PP surface corrected, to some extension, both depressions and fissures of the previously modified PP surfaces. The layered surfaces have morphological characteristic different from those of the non-layered surfaces, and their thickness was dependent on irradiation time. Water contact angles of the layered surfaces revealed a transition at approximately 33.5-36.5 °C as a result of a response to the variation of temperature. There was an increase in the values of the contact angles with an increase in temperature from 26 °C to 44 °C, revealing the nature both hydrophilic and hydrophobic of the surfaces due to a conformational rearrangement of PNIPAAm exposing its isopropyl groups to the liquid drop. This work offers a chemically stable thermosensitive surface (because it is covalently structured) with great potential for use as sensors and actuators.

Covalently-layers of PVA and PAA and in situ formed Ag nanoparticles as versatile antimicrobial surfaces

The in situ synthesis of silver nanoparticles (AgNPs) within covalently-modified poly(ethylene terephthalate) (PET) films possessing ultra-thin layer of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) is successfully demonstrated. The resulting polymeric films are shown to exhibit antimicrobial activities toward Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and fungus (Candida albicans). To make the films, first PET surfaces were subject to photo-oxidation and subsequent solid-state grafting to attach a PVA layer, followed by a PAA layer. To synthesize the AgNPs inside the films, the PVA and PAA-modified PET was soaked in AgNO3 solution and the polymeric film was modified with the Ag(+) ions via Ag(+)-carboxylate interaction, and then the Ag(+) ions-containing polymer film was subject to either photo-reduction or thermal reduction processes. The PVA and PAA thin layers attached by covalent bonds to the PET surface uniquely promoted not only the in situ synthesis but also the stabilization of AgNPs. The formation of the AgNPs was confirmed by UV-vis spectroscopy or by monitoring the surface plasmon resonance (SPR) peak associated with AgNPs. The resulting PVA and PAA ultrathin layers modified and AgNPs containing PET served as bactericide and fungicide, inhibiting the growth of bacteria and fungi on the surfaces. Given PETs versatility and common use in many commercial processes, the method can be used for producing plastic surfaces with versatile antimicrobial and antibacterial properties.