Maykel González Torres

Radiation-induced graft polymerization of chitosan onto poly(3-hydroxybutyrate)

Chitosan is among the most studied biopolymers and offers important advantages, such as biodegradability, biocompatibility and nontoxicity. In this study, this polysaccharide was grafted onto poly(3-hydroxybutyrate) using the simultaneous gamma-irradiation-initiated polymerization method. The polyester was immersed in diverse solvents, which allowed the preparation of graft copolymers with different yields and crystallinities. A successful synthesis and the estimation of the degree of crystallinity were verified by spectroscopic and calorimetric techniques. The most suitable method was found to be the thermoanalytical approach because it displayed a linear relationship between the degree of crystallinity and the increasing degree of grafting. The results also indicated that the lowest degree of grafting was seen for acetic acid (14.27%), while the highest degree corresponded to ethyl acetate (32.11%). The mechanism of grafting was proposed on the basis of the experimental results.

Novel Poly(3-hydroxybutyrate-g-vinyl alcohol) Polyurethane Scaffold for Tissue Engineering.

The design of new synthetic grafted poly(3-hydroxybutyrate) as composite 3D-scaffolds is a convenient alternative for tissue engineering applications. The chemically modified poly(3-hydroxybutyrate) is receiving increasing attention for use as biomimetic copolymers for cell growth. As of yet, these copolymers cannot be used efficiently because of the lack of good mechanical properties. Here, we address this challenge, preparing a composite-scaffold of grafted poly(3-hydroxybutyrate) polyurethane for the first time. However, it is unclear if the composite structure and morphology can also offer a biological application. We obtained the polyurethane by mixing a polyester hydroxylated resin with polyisocyanate and the modified polyhydroxyalkanoates. The results show that the poly(3-hydroxybutyrate) grafted with poly(vinyl alcohol) can be successfully used as a chain extender to form a chemically-crosslinked thermosetting polymer. Furthermore, we show a proposal for the mechanism of the polyurethane synthesis, the analysis of its morphology and the ability of the scaffolds for growing mammalian cells. We demonstrated that astrocytes isolated from mouse cerebellum, and HEK293 can be cultured in the prepared material, and express efficiently fluorescent proteins by adenoviral transduction. We also tested the metabolism of Ca2+ to obtain evidence of the biological activity.

Growth of hydroxyapatite on the cellular membrane of the bacterium Bacillus thuringiensis for the preparation of hybrid biomaterials

This study aimed to grow hydroxyapatite (HAp) crystals on the cellular wall of the Gram-positive bacterium Bacillus thuringiensis using a bio-mimetic method. Several strains were phenotypically and genotypically characterized using multilocus sequence typing (MLST) gene markers to differentiate the strains and confirm the identity of the isolated species to guarantee that the selected species was not harmful to human health or the environment. Three of the analyzed strains were selected because they exhibited the best nucleation and growth of HAp on the bacterial surface. This innovative method to grow HAp crystals on a cellular membrane helps to elucidate the mechanisms by which osseous tissue is formed in nature. The optimum concentration for the simulated physiological fluid (SPF) was 1.5×. The hybrid materials were characterized by optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).

Tribological and Mechanical Properties of Poly[(R)-3-hydroxybutyric acid] Grafted with Vinyl Compounds: Insight into Possible Application

Biodegradable graft copolymers were prepared by gamma radiation-induced graft polymerization of two vinyl monomers, vinyl acetate and vinyl alcohol, onto poly[(R)-3-hydroxybutyric acid]. Success of the grafting reaction was verified by Fourier-transform infrared and nuclear magnetic resonance spectroscopy. Thermal remolding was used to create membranes from the copolymers. We determined tribological and mechanical properties of the membranes obtained. The lowest elongation at break in tensile testing is seen for P(3HB) and the highest for P(3HB-g-VA). Up to 5 N or so, the highest scratch resistance is exhibited by P(3HB-g-VA). Piezoelectric behavior is seen for P(3HB-g-VA) while P(3HB-g-VAc) and plain P(3HB) showed no electric response. Explanation of the piezoelectric behavior in terms of molecular structures is provided.

A new study of the kinetics of curd production in the process of cheese manufacture

We studied the role played by temperature and rennet concentration in the coagulation process for cheese manufacture and the evaluation of their kinetics. We concluded that temperature is the main factor that determines the kinetics. The rennet concentration was unimportant probably due to the fast action of the enzyme chymosin. The Dynamic light scattering technique allowed measuring the aggregates size and their formation kinetics. The volume fraction of solids was determined from viscosity measurements, showing profiles that are in agreement with the size profiles. The results indicate that the formation of the aggregates for rennet cheese is strongly dependent on temperature and rennet concentration. The results revealed that at 35·5 °C the volume fraction of solids has the maximum slope, indicating that at this temperature the curd is formed rapidly. The optimal temperature throughout the process was established. Second-order kinetics were obtained for the process. We observed a quadratic dependence between the rennet volume and the volume fraction of solids (curd), thereby indicating that the kinetics of the curd production should be of order two.

Transformation kinetics of fermented milk using Lactobacillus casei (Lc1) and Streptococcus thermophilus: comparison of results with other Inocula.

Probiotic-based starter cultures are generally used to produce fermented milks with improved characteristics in the final product. In this study, Lactobacillus casei and Streptococcus thermophilus (Lc1-St) were used as the starter inoculum. The transformation kinetics and properties of the final product were compared with systems produced with other inocula. The Lc1-St inoculum delayed the production of lactic acid from 40 to 70 min (depending on temperature and concentration) when compared to Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus (Lb-St) and Lactobacillus johnsonii and Streptococcus thermophilus (La1-St). The Lc1-St inoculum reached the aggregation system faster (30-80 min) than Lb-St (120-210 min) and La1-St (160-220 min), however, the production of exopolysaccharides and organic phosphates was delayed as a consequence of the lack of synergy between Lc1 and St.

Adsorption of lead ions in contaminated water using commercial hydrophilic silica nanoparticles

The adsorption of lead ions from simulated industrial wastewater using hydrophilic commercial silica nanoparticles (Aerosil A130VS) is reported. These results were compared with those obtained using sol-gel silica nanoparticles prepared in our laboratory. Hydrated commercial silica nanoparticles have, on their surface, silanol groups (≡Si-OH) that are appropriated for the adsorption process. The commercial particles are dense because they are produced by a pyrogenic process. The absence of pores means a smaller internal surface area and, consequently, a smaller number of silanol groups available for adsorption; as compared with the highly porous sol-gel silica nanoparticles. This effect is partially compensated by the small particle size that can be obtained from these commercial particles. Different concentrations of lead ions in aqueous solution were added to a suspension of commercial particles until the critical flocculation concentration was reached. The flocculation kinetic was obtained using dynamic light scattering and the amount of adsorbed lead ions using atomic absorption. The lead concentration was reduced from 65.9 ppm to 0.2 ppm using Aerosil A130VS.