Biocompatible xanthan/polypyrrole scaffolds for tissue engineering.

Polypyrrole (PPy) was electropolymerized in xanthan hydrogels (XCA), resulting in electroactive XCAPPy scaffolds with (15 ± 3) wt.% PPy and (40 ± 10) µm thick. The physicochemical characterization of hybrid XCAPPy scaffolds was performed by means of cyclic voltammetry, swelling tests, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM) and tensile tests. XCAPPy swelled~80% less than XCA. FTIR spectra and thermal analyses did not evidence strong interaction between PPy and XCA matrix. XCAPPy presented a porous stratified structure resulting from the arrangement of PPy chains parallel to XCA surface. Under stress XCAPPy presented larger strain than neat XCA probably due to the sliding of planar PPy chains. The adhesion and proliferation of fibroblasts onto XCA and XCAPPy were evaluated in the absence and in the presence of external magnetic field (EMF) of 0.4T, after one day, 7 days, 14 days and 21 days. Fibroblast proliferation was more pronounced onto XCAPPy than onto XCA, due to its higher hydrophobicity and surface roughness. EMF stimulated cell proliferation onto both scaffolds.

Synthesis and characterization of xanthan-hydroxyapatite nanocomposites for cellular uptake.

In this work xanthan-nanohydroxyapatite (XnHAp) and its equivalent strontium substituted (XnHApSr) were synthesized by the precipitation of nanohydroxyapatite in xanthan aqueous solution, characterized and compared to conventional hydroxyapatite particles (HAp). XnHAp and XnHApSr were less crystalline than HAp, as revealed by X-ray diffraction. Xanthan chains enriched the surface of XnHAp and XnHApSr particles, increasing the zeta potential values from -(7±1)mV, determined for HAp, to -(17±3)mV and -(25±3)mV, respectively. This effect led to high colloidal stability of XnHAp and XnHApSr dispersions and acicular particles (140±10)nm long and (8±2)nm wide, as determined by scanning electron microscopy and atomic force microscopy. XnHAp and XnHApSr particles were added to xanthan hydrogels to produce compatible nanocomposites (XCA/XnHAp and XCA/XnHApSr). Dried nanocomposites presented surface energy, Young's modulus and stress at break values comparable to those determined for bare xanthan matrix. Moreover, adding XnHAp or XnHApSr nanoparticles to xanthan hydrogel did not influence its porous morphology, gel content and swelling ratio. XCA/XnHAp and XCA/XnHApSr composites proved to be suitable for osteoblast growth and particularly XCA/XnHapSr composites induced higher alkaline phosphatase activity.

Xanthan hydrogel films: molecular conformation, charge density and protein carriers.

In this article the molecular conformation of xanthan chains in hydrogel films was investigated by means of circular dichroism, showing substantial differences between xanthan hydrogel prepared in the absence (XNT) and in the presence of citric acid (XCA). The xanthan chains in XNT hydrogels films presented ordered conformation (helixes), while in XCA they were in the disordered conformation (coils), exposing a larger number of carboxylate groups than XNT. The large charge density in XCA hydrogels was evidenced by their behavior under variable ionic strength. Studies about the application of XNT and XCA for loading and delivering of bovine serum albumin (BSA) and lysozyme (LYZ) showed that both events are controlled by hydrogels and proteins net charge, which can be triggered by pH. The preservation of LYZ native conformation after hydrogel loading explained the substantial bactericidal activity of LYZ loaded hydrogels and enables their use as active wound dressings.

Hybrid composites of xanthan and magnetic nanoparticles for cellular uptake.

We describe a fast and simple method to prepare composite films of magnetite nanoparticles and xanthan networks. The particles are distributed close to hybrid film surface, generating a coercivity of 27 ± 2 Oe at 300 K. The proliferation of fibroblast cells on the hybrid composites was successful, particularly when an external magnetic field was applied.

Synthesis and swelling behavior of xanthan-based hydrogels.

In this work xanthan chains were crosslinked by esterification reaction at 165 °C either in the absence or in the presence of citric acid. Higher crosslinking density was obtained using citric acid, as evidenced by its lower swelling degree. Tensiometry, a very precise and sensitive technique, was applied to study swelling rates and diffusion mechanisms of water, which was initially quasi-Fickian, controlled by wicking properties, changing to Fickian or Anomalous, depending on hydrogel composition. Hydrogels swelling degree increased at high pH values, due to electrostatic repulsion and ester linkages rupture. Equilibrium swelling degree was affected by salts, depending on gel composition and kind of salt. Effects could be explained by interaction between ions and polymeric chains, EPA/EPD ability of water or osmotic gradient.

N1-acetyl-N2-formyl-5-methoxykynuramine modulates the cell cycle of malaria parasites.

We previously reported that intraerythrocytic malaria parasites have their development synchronized by melatonin and other products of tryptophan catabolism (i.e. serotonin, N-acetylserotonin and tryptamine). Here, we show that N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), a product of melatonin degradation, synchronizes Plasmodium chabaudi and Plasmodium falciparum. The synchronization is abrogated with a melatonin receptor antagonist, luzindole. We established quantitatively that a differential AFMK production occurred within the intraerythrocytic stages of rodent malaria parasite Plasmodium chabaudi (ring, trophozoite and schizont), when the infected erythrocytes were previously incubated with melatonin. Measurement of AFMK formation in P. chabaudi after incubation with melatonin at a concentration of 500 nmol/L revealed the following values for AFMK production: ring 0.1 +/- 0.1 nmol/L, trophozoite 22.9 +/- 0.5 nmol/L, schizont 29 +/- 5 nmol/L. Confocal and spectrofluorophotometer experiments with isolated parasites and infected-RBC, loaded with calcium indicator Fluo-4 showed that AFMK elicits an increase in the cytosol calcium concentration in these parasites. Our data suggest that AFMK could have an important role in modulating the cell cycle of malaria parasites mainly in the late stages (trophozoite and schizont).