2024 - SILVA, RODRIGO da; BARONI, LUIS F.S.; MARTINS JUNIOR, CLAUDIO B.; MAGALHAES, DANIELLE C.C.; VACCHI, GUILHERME S.; KLIAUGA, ANDREA M.; LIMA, NELSON B.; OTUBO, JORGE; DELLA ROVERE, CARLOS A.

The addition of rare earth elements, such as cerium, to austenitic Fe-Mn-Si-based shape memory alloys has been shown to improve both corrosion resistance and shape recovery. However, the mechanisms underlying the effect of Ce on shape recovery are still unclear. This study investigates the influence of the addition of small amounts of Ce (0.18, 0.42, and 0.96 wt%) on the microstructure and shape recovery of an austenitic Fe-13.50Mn-3.98Si-9.54Cr-4.51Ni alloy. Ce additions induce the formation of a large number of Ce-rich particles, which act as austenitic grain refiners. Both grain refinement and the formation of Ce-rich particles contribute to the strengthening of the matrix at 0.42 wt% Ce addition. In addition, Ce additions alter the MS temperature, which increases with Ce additions. Total shape recovery improves with 0.18 and 0.42 wt% Ce additions, but decreases with 0.96 wt% Ce addition. The beneficial effect of Ce addition in improving the shape recovery of the austenitic Fe-Mn-Si-Cr-Ni alloy is related to the enhancement of the elastic shape recovery component of the total shape recovery. However, the shape memory recovery due to the shape memory effect always decreases with the increase of the Ce content.

2024 - BARBOSA, INGRID A.B.; MARCUZZO, JOSSANO S.; COSENTINO, IVANA C.; FARIA JUNIOR, RUBENS N. de

Amidst different types of energy storage systems, electrochemical supercapacitors have received considerable attention as they close the gap between electrolytic capacitors and batteries. This work addresses electric double-layer capacitors (EDLCs), a type of electrochemical supercapacitor, and has been divided into two parts. In the former, the synthesis and characterization of activated carbon fiber-felt (ACFF) electrodes, derived from textile PAN-based fiber, have been provided. In the latter, the electrochemical characterization of EDLCs in potassium hydroxide solutions ( aqueous electrolytes) and in potassium hydroxide-glycerol hybrid electrolytes (glycerol-based electrolytes) have been investigated. The synthesis of ACFF electrodes via two-step oxidation, carbonization, and physical activation resulted in low-cost and binder-free electrodes containing 87% of the total volume of pores as micropores (maximum pore width of 3 nm) and a high specific surface area of 1875 m(2) g(-1). Electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques were carried out in a symmetric two-electrode setup at room temperature. The results showed that ACFF electrodes are suitable for aqueous electrolytes, particularly 2 M KOH, and KOH:GLY (3:1), a glycerol-based electrolyte. Although KOH:GLY (3:1) exhibited high electrolyte resistance (34 +/- 3 Omega), this hybrid green-electrolyte supports a potential window that is twice greater than that of aqueous electrolytes. In addition, glycerol, commonly called glycerin, is a by-product of FAME (fatty acid methyl ester) biodiesel, which is the major source of glycerol. Glycerol-based electrolytes are promising green electrolytes for EDLCs. Therefore, it is necessary to decrease its viscosity and resistance.

2024 - MASSIMINO, LIVIA C.; MARTINS, VIRGINIA da C.A.; VULCANI, VALCINIR A.S.; OLIVEIRA, EVERTON L. de; ANDREETA, MARIANE B.; BONAGAMBA, TITO J.; KLINGBEIL, MARIA F.G.; MATHOR, MONICA B.; PLEPIS, ANA M. de G.

The aim of this study was the development of collagen and collagen/auricular cartilage scaffolds for application in dermal regeneration. Collagen was obtained from bovine tendon by a 72 h-long treatment, while bovine auricular cartilage was treated for 24 h and divided into two parts, external (perichondrium, E) and internal (elastic cartilage, I). The scaffolds were prepared by mixing collagen (C) with the internal part (CI) or the external part (CE) in a 3:1 ratio. Differential scanning calorimetry, scanning electron microscopy (SEM) analysis, microcomputed tomography imaging (micro-CT) and swelling degree were used to characterize the scaffolds. Cytotoxicity, cell adhesion, and cell proliferation assays were performed using the cell line NIH/3T3. All samples presented a similar denaturation temperature (Td) around 48 degrees C, while CE presented a second Td at 51.2 degrees C. SEM micrographs showed superficial pores in all scaffolds and micro-CT exhibited interconnected pore spaces with porosity above 60% (sizes between 47 and 149 mu m). The order of swelling was CE < CI < C and the scaffolds did not present cytotoxicity, showing attachment rates above 75%-all samples showed a similar pattern of proliferation until 168 h, whereas CI tended to decrease after this time. The scaffolds were easily obtained, biocompatible and had adequate morphology for cell growth. All samples showed high adhesion, whereas collagen-only and collagen/external part scaffolds presented a better cell proliferation rate and would be indicated for possible use in dermal regeneration.

2024 - GERALDES, ADRIANA N.; ROSERO, WILMMER A.A.; ROSTELATO, MARIA E.C.M.; SARKIS, JORGE E.S.

Accurate nanoparticle characterization is essential since it can significantly affect its physicochemical and biological properties. Among physicochemical properties used to characterize nanomaterials, size and size distribution are essential and should be assessed before surveying poisonousness or biocompatibility. Several methods are suitable to evaluate these characteristics including the dynamic light scattering. The aims of the present paper were to propose a methodology to measure nanoparticle size and present the estimation of the particle size uncertainty using the dynamic light scattering technique. The reliability of measurements was ensured by a series of handling precautions and quality criteria for good measurements to be applied for methodology validation using reference material polyvinylpyrrolidone coated silver nanoparticles. The identification and quantification of input quantities to the measurement uncertainties were estimated. The uncertainty concerning the equipment was 1.2% while the repeatability obtained was 1.4%, within the range of values stipulated in the reference standard (less than 5%). The relative standard uncertainties of trueness and repeatability were below the thresholds defined by the International Organization for Standardization. The result of the expanded uncertainty was 3.9% with 95% coverage probability for the reference material.