António J. Guiomar

Biofunctionalized magnetic hydrogel nanospheres of magnetite and κ-carrageenan

Magnetic hydrogel kappa-carrageenan nanospheres were successfully prepared via water-in-oil (w/o) microemulsions combined with thermally induced gelation of the polysaccharide. The size of the nanospheres (an average diameter of about 50 and 75 nm) was modulated by varying the concentration of surfactant. The nanospheres contained superparamagnetic magnetite nanoparticles (average diameter 8 nm), previously prepared by co-precipitation within the biopolymer. Carboxyl groups, at a concentration of about 4 mmol g(-1), were successfully grafted at the surface of these magnetic nanospheres via carboxymethylation of the kappa-carrageenan. The carboxylated nanospheres were shown to be thermo-sensitive in the 37-45 degrees C temperature range, indicating their potential as thermally controlled delivery systems for drugs and/or magnetic particles at physiological temperatures. Finally, preliminary results have been obtained for IgG antibody conjugation of the carboxylated nanospheres and the potential of these systems for bio-applications is discussed.

Immobilization of glucose oxidase onto a Langmuir-Blodgett ultrathin film of a cellulose derivative deposited on a self-assembled monolayer

Abstract Glucose oxidase was immobilized on a Langmuir-Blodgett film of cellulose acetate propionate deposited on a self-assembled monolayer coated substrate. These layers were characterized in terms of their ellipsometric thickness, wettability and infra-red spectra. Glucose oxidase was immobilized on this composite layer by physisorption. The presence of the enzyme on the surface was confirmed by ellipsometry, infra-red spectroscopy and by detecting its activity electrochemically. An enzyme population remained active after adsorption onto this assembly.

Biofunctionalized ferromagnetic CoPt3/polymer nanocomposites

Magnetic latexes were prepared by the encapsulation of organically capped CoPt3 nanoparticles via miniemulsion in situ radical polymerization of tert-butyl acrylate (tBA). This is the first example of a CoPt3 based polymer nanocomposite showing ferromagnetic behaviour at room temperature. Each nanocomposite particle contains a magnetic core composed of CoPt3 nanoparticles (d~7 nm, a0 = 3.848 A) encapsulated by poly(t-butyl acrylate). The CoPt3/PtBA latexes contain polyester groups that can be readily hydrolysed, rendering the surface with carboxylic functionalities and hence allowing bioconjugation. Complementary to such surface modification experiments, we report that bovine IgG antibodies can bind to the magnetic latexes, and the potential of the nanocomposites for in vitro specific bioapplications is discussed.

Functionalization of nickel nanowires with a fluorophore aiming at new probes for multimodal bioanalysis

This work reports research on the development of bimodal magnetic and fluorescent 1D nanoprobes. First, ferromagnetic nickel nanowires (NiNW) have been prepared by Ni electrodeposition in an anodic aluminum oxide (AAO) template. The highly ordered self-assembled AAO nanoporous templates were fabricated using a two-step anodization method of aluminum foil. The surface of the NiNW were then modified with polyethyleneimine (PEI) which was previously labeled with an organic dye (fluorescein isothiocyanate: FITC) via covalent bonding. The ensuing functionalized NiNW exhibited the characteristic green fluorescence of FITC and could be magnetically separated from aqueous solutions by using a NdFeB magnet. Finally, the interest of these bimodal NiNW as nanoprobes for in vitro cell separation and biolabeling was preliminary assessed in a proof of principle experiment that involved the attachment of biofunctionalized NiNW to blood cells.

Changes in glucose uptake rate and in the energy status of PC-12 cells acutely exposed to hexavalent chromium, an established human carcinogen

In the 1920s, Otto Warburg reported a striking metabolic shift in solid tumors: contrary to their normal counter parts, which exhibited a nearly pure respiratory metabolism, where cancer cells relied strongly on lactic fermentation for energy production, even in the presence of ample oxygen. This metabolic shift, later named the Warburg effect, is now viewed as a nearly universal cancer phenotype. To investigate whether it is operating in hexavalent chromium (Cr(VI))-induced carcinogenesis, PC-12 cells were exposed to low Cr(VI) concentrations and effects determined on the rates of glucose uptake, lactate production and oxygen consumption, critical indicators of the type of energy metabolism adopted by the cells. Further, the influence on the cells’ energy charge, an important parameter in the evaluation of the cellular physiological state was assessed. In the presence of ample oxygen, concentration-dependent, statistically significant decreases in the energy charge were detected, which were accompanied by an increased glucose uptake rate. This enhanced uptake may constitute the first step in a compensatory mechanism aimed at counteracting the decrease in energy charge. Although these changes may be too small to exert an impact in the cellular functions, they may provide insight into the initial steps of Cr(VI)-induced carcinogenesis.

Controlled release of moxifloxacin from intraocular lenses modified by Ar plasma-assisted grafting with AMPS or SBMA: An in vitro study

Intraocular lenses (IOLs) present an alternative for extended, local drug delivery in the prevention of post-operative acute endophthalmitis. In the present work, we modified the surface of a hydrophilic acrylic material, used for manufacturing of IOLs, through plasma-assisted grafting copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) or [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), with the aim of achieving a controlled and effective drug release. The material was loaded with moxifloxacin (MFX), a commonly used antibiotic for endophthalmitis prevention. The characterization of the modified material showed that relevant properties, like swelling capacity, wettability, refractive index and transmittance, were not affected by the surface modification. Concerning the drug release profiles, the most promising result was obtained when AMPS grafting was done in the presence of MFX. This modification led to a higher amount of drug being released for a longer period of time, which is a requirement for the prevention of endophthalmitis. The material was found to be non-cytotoxic for rabbit corneal endothelial cells. In a second step, prototype IOLs were modified with AMPS and loaded with MFX as previously and, after sterilization and storage (30days), they were tested under dynamic conditions, in a microfluidic cell with volume and renovation rate similar to the eye aqueous humour. MFX solutions collected in this assay were tested against Staphylococcus aureus and Staphylococcus epidermidis and the released antibiotic proved to be effective against both bacteria until the 12th day of release.

Polyurethane-Polyurea Membranes for Blood Oxygenation

The structural versatility of polyurethane based membranes is enhanced through the introduction of two soft segments to obtain new membranes with improved hemocompatibility. Crosslinked polyurethane/urea membranes with two soft segments were prepared by extending a polypropylene oxide-based tri-isocyanate terminated prepolymer (PU) with polybutadiene diol (PBDO). The ratio of PU to PBDO was 100/0 and 90/10. The membranes were characterised in terms of permeation towards O2 and CO2 and their hemocompatibility was evaluated through hemolysis and thrombosis experiments. It was found that the membrane with PBDO had the highest permeability to O2 and CO2 and it was non-hemolytic and less thrombogenic.

Modelling the Release of Moxifloxacin from Plasma Grafted Intraocular Lenses with Rotational Symmetric Numerical Framework

A rotational symmetric finite element model is constructed to simulate the release of moxifloxacin from different types of plasma-grafted intraocular lenses, utilizing general discontinuous boundary conditions to describe the interface between lens and outside medium. Such boundary conditions allow for the modelling of partitioning and interfacial mass transfer resistance. Due to its rotational symmetry, the shape of the optical part of the intraocular lens is fully taken into account.