Erick Sarmiento-Gómez

Sodium alginate was extracted from beach-cast Sargassum spp. collected along the coast of Puerto Progreso, Yucatán, Mexico, using two established pretreatment routes based on formaldehyde and ethanol. This study evaluates how extraction methodology controls alginate recovery, molecular structure, hydrogel rheology, macroscopic integrity, swelling behavior, and preliminary inorganic contaminant profiles. The ethanol-based route provided the highest extraction yield, reaching 19.87 ± 0.79% w/w for AE-5, whereas the formaldehyde route reached a maximum of 15.60 ± 0.62% w/w for AF-12; statistical analysis confirmed significant differences among extraction conditions (ANOVA, p < 0.05). Despite its lower yield, the formaldehyde route produced alginate with higher intrinsic viscosity (2.13 dL/g) and viscosity-average molecular weight (1.00 × 105 g/mol) than the ethanol-derived sample (1.33 dL/g and 0.62 × 105 g/mol), indicating better preservation of polymer chain length. ¹H NMR analysis showed that AE-5 had higher guluronic acid content (F_G = 0.60), lower M/G ratio (0.67), and higher G-block fraction (F_GG = 0.54), favoring Ca²⁺-mediated junction zone formation. Consequently, AE-5-derived hydrogels exhibited the highest storage modulus at 1 Hz (G′ = 23,650 Pa), compared with AF-12-derived hydrogels (13,160 Pa) and the commercial reference (14,480 Pa). However, visual inspection and swelling analysis showed that the higher small-amplitude stiffness of AE-5 did not translate into superior macroscopic integrity; these hydrogels showed greater fragmentation during handling and higher long-term swelling. In contrast, AF-12-derived hydrogels showed lower stiffness but better apparent cohesion and a more restricted swelling profile, consistent with enhanced long-range network connectivity derived from higher molecular weight. FTIR confirmed preservation of the characteristic functional groups of sodium alginate, whereas XRD provided qualitative evidence of residual crystalline inorganic phases. Selected-metal analysis by MP-AES detected Cu in both extracted alginates, while As was detected but not quantified only in AF-12; Cd and Pb were not detected under the analytical conditions employed. Overall, the results establish a route-dependent structure-property relationship in which extraction conditions govern yield, chain preservation, block architecture, viscoelastic response, swelling behavior, and preliminary contaminant profile. These findings support beach-cast Sargassum as a promising source of research-grade sodium alginate, while emphasizing that further purification, expanded contaminant profiling, arsenic speciation, biological evaluation, and direct mechanical testing are required before any food, biomedical, pharmaceutical, or environmental application can be proposed.

Sodium alginate was extracted from beach-cast Sargassum spp. collected along the coast of Puerto Progreso, Yucatán, Mexico, using two established pretreatment routes based on formaldehyde and ethanol. The study was designed to determine how extraction methodology influences alginate molecular structure and, consequently, its rheological performance. The ethanol-based route provided the highest extraction yield (up to 19.87%), whereas the formaldehyde route afforded alginate with higher intrinsic viscosity and viscosity-average molecular weight. Structural characterization by ¹H NMR revealed clear differences in monomer composition and sequence distribution, with ethanol-extracted alginate showing higher guluronic acid content, lower M/G ratio, and greater abundance of G-rich blocks. These structural differences were directly reflected in the viscoelastic behavior of Ca²⁺-crosslinked hydrogels. Alginate obtained by the ethanol route produced stiffer gels with the highest storage modulus, consistent with enhanced ionic crosslinking promoted by G-block-rich sequences, although with limited macroscopic cohesion due to lower molecular weight. In contrast, alginate obtained by the formaldehyde route showed a more balanced mechanical response associated with improved chain connectivity and network integrity. FTIR analysis confirmed the preservation of the characteristic functional groups of alginates in all samples. Overall, the results demonstrate that beach-cast Sargassum from the Yucatán coast is a viable source of sodium alginate and that extraction route is a key parameter governing its microstructure and rheological performance. These findings provide a structure–property framework for the valorization of stranded Sargassum biomass as a source of functional polysaccharides.

The transport properties of colloids in external potentials are often studied at low concentrations to avoid particle-particle interactions. The transport properties of colloids in external potentials are often studied at low concentrations to avoid particle-particle interactions. However, the impact of concentration on colloidal dynamics under external potentials has received limited attention. We examine the effect of concentration on the diffusivity of a quasi-$2D$ colloidal dispersion subjected to a light-induced sinusoidal potential (interference fringes). By measuring particle diffusivity perpendicular to the fringes at various concentrations and laser powers, we find how the particle transport is governed by concentration and the structural organization induced by the external potential. Specifically, we introduce the concept of modulated-crowding for this physical scenario and characterize its influence on the long-time self-diffusion coefficient. These findings are confirmed using Brownian dynamics simulations.

The dynamical properties of the local area available per particle and its relationship with the self-diffusion coefficient of colloids in quasi-2D colloidal dispersions are studied using video microscopy, supported by Brownian dynamics simulations. The local area is determined via the well-known Voronoi tessellation technique. Our findings reveal that local areas per particle are highly dispersed, exhibiting slow dynamics over time. Additionally, the evolution of the ensemble-averaged area distribution as a function of concentration shows a long tail at large and small areas for low and high concentrations, respectively, leading to a maximum in information entropy when the distribution becomes symmetric. We introduce and analyze several expressions for local area-weighted diffusion coefficients. Notably, we find that the contribution of the averaged diffusion coefficient can be expressed in terms of local areas, establishing a new framework to determine the weighted influence of each local area on particle dynamics.

Colloidal suspensions may be stable or unstable due to aggregation, which would alter the properties of the suspension and is related to many-body interactions and the delicate balance between repulsive and attractive forces, which also defines the internal structure and its macroscopic properties. Experimental studies about many-body interactions demand a lot of resources and time due to the accumulation of statistics necessary to obtain reliable results. A way to study the colloidal suspension structure is to process a great amount of bright-field images. Taking advantage of the emerging deep generative networks, we propose a method to complement this study to reduce both experimental and computational costs. The method consists of designing and tuning an architecture based on Generative Adversarial Networks (GANs) that learns the static structure of a colloidal suspension from experimental images depending on concentration and generates images to concentrations outside of the experimental data. This allows the exploration of the fully accessible phase space and carry out a visual recognition of regions of interest. The best-performed network was Wasserstein Generative Adversarial Network with Gradient Penalty (WCGAN-GP), trained from bright-field images of a confined colloidal suspension formed by spherical polystyrene particles in water at different area fractions. Experimental results showed that the algorithm generates new images with a high accuracy rate (85%–98%) on the expected particle number at different concentrations; also, it was able to reproduce the static structure of the colloidal suspension, i.e., the pair correlation function ( g ( r ) ) lies within the experimental variation, not only for the trained data set but also for any other intermediate concentration. The correlation coefficient between experimental and generated ( g ( r ) ) was very strong (0.86–0.99) for concentrations of 0.1 and higher. The proposed GAN could be used to construct phase diagrams, identifying stable and unstable zones of colloidal systems with different interaction potentials.

This work presents and validates a methodology to manipulate bubbles in foam. As the bubble has a lower index of refraction than the surrounding media, optical trapping with a single Gaussian profile is impossible. Instead, a circular array of traps is used to effectively confine the bubble. As the bubble does not present Brownian motion, trapping is calibrated using the drag method, finding optical stiffnesses close to pN/mm. We apply the presented method to determine the adhesion force between two bubbles of different sizes and vary the surface tension, which is expected to have a significant effect on the adhesion forces.

Spectroscopy is essential for research in the qualitative and quantitative analysis of samples. In recent years, the need to develop portable and accessible equipment for sample characterization has reduced real-time analysis. The objective is to design and build a prototype of a portable spectrophotometer with an integrating sphere using tools such as Rhinoceros and Trace-Pro for its theoretical design and radiation simulation. The result is an integrating sphere 3D printed with PLA material and an internal coating with a 95% high reflectance paint. The AS7265 Triad module is the detector, along with signal processing to obtain spectra from control samples. The spectral profiles obtained were comparable with commercial equipment, validating the viability of the measurement system as the first spectroscopic instrument in the field, in complement to other spectroscopic techniques. This breakthrough promises to facilitate research in the field and in environments where mobility and accessibility are priorities. Keywords: Integrating sphere, High reflectance coating, simulation Trace Pro, Manufacturing integrating sphere, spectroscopy.

A partir de fontes de distintas naturezas, como a história oral, os processos de expulsão e os periódicos, o artigo objetiva narrar o envolvimento dos galegos no setor terciário, no comércio e na hotelaria, assim como a participação de parte desse grupo no radical Centro Cosmopolita. O envolvimento dos galegos no mundo do trabalho carioca mostra as suas estratégias de sobrevivência, bem como as suas redes de solidariedade e de exploração em ambientes que mesclavam hostilidade e solidariedade. Palavras-chave: Rio de Janeiro; imigração galega; associativismo; Centro Cosmopolita.

Pathological processes often change the mechanical properties of cells. Increased rigidity could be a marker of cellular malfunction. Erythrocytes are a type of cell that deforms to squeeze through tiny capillaries; changes in their rigidity can dramatically affect their functionality. Furthermore, differences in the homeostatic elasticity of the cell can be used as a tool for diagnosis and even for choosing the adequate treatment for some illnesses. More accurate types of equipment needed to study biomechanical phenomena at the single-cell level are very costly and thus out of reach for many laboratories around the world. This study presents a simple and low-cost technique to study the rigidity of red blood cells (RBCs) through the application of electric fields in a hand-made microfluidic chamber that uses a capacitor principle. As RBCs are deformed with the application of voltage, cells are observed under a light microscope. From mechanical force vs. deformation data, the elastic constant of the cells is determined. The results obtained with the capacitor-based method were compared with those obtained using optical tweezers, finding good agreement. In addition, P. falciparum-infected erythrocytes were tested with the electric field applicator. Our technique provides a simple means of testing the mechanical properties of individual cells.