Cycling of the relative humidity (RH) levels in the reactant streams of polymer electrolyte membrane (PEM) fuel cells has been reported to decay fuel cell performance. This study focuses on the accelerated durability testing to examine different modes of membrane failure via RH cycling. A single PEM fuel cell with an active area of 42.25 cm2 was tested. A Greenlight G50 test station was used to establish baseline cell (Run 1) performance with 840 hours of degradation under high-humidity idle conditions at a constant current density of 10 mA cm-2. Under the same conditions, two other experiments were conducted by varying the RH. For the H2-air RH cycling test (Run 2), anode and cathode inlet gases were provided as dry and humidified gases. Another RH cycling experiment was the H2 RH cycling test (Run 3): the anode inlet gas was cycled whereas keeping the other side constantly at full humidification. These two RH cycling experiments were alternated in dry and 100% humidified conditions every 10 and 40 minutes, respectively. In the experiments, the fuel cells contained a GoreTM 57 catalyst coated membrane (CCM) and 35 BC SGL gas diffusion layers (GDLs). The fuel cell test station had been performed under idle conditions at a constant current density of 10 mA cm-2. Under the idle conditions, operating at very low current density, a low chemical degradation rate and minimal electrical load stress were anticipated. However, the membrane was expected to degrade due to additional stress from the membrane swelling/contraction cycle controlled by the RH. In this work the performance of the 100% RH humidified cell (Run 1) was compared with that of RH cycling cells (Run 2 and Run 3). Chemical and mechanical degradation of the membrane were investigated using in-situ and ex-situ diagnostic methods. The results of each measurement during and after fuel cell operation are consistent. They clearly show that changing in RH lead to an overall PEM fuel cell degradation due to the increase in membrane degradation rate from membrane resistance, fluoride ion release concentration, hydrogen crossover current, membrane thinning, and hot-spot/pin-hole formation.

Cycling of the relative humidity (RH) levels in the reactant streams of polymer electrolyte membrane (PEM) fuel cells has been reported to decay fuel cell performance. This study focuses on the accelerated durability testing to examine different modes of membrane failure via RH cycling. A single PEM fuel cell with an active area of 42.25 cm2 was tested. A Greenlight G50 test station was used to establish baseline cell (Run 1) performance with 840 hours of degradation under high-humidity idle conditions at a constant current density of 10 mA cm-2. Under the same conditions, two other experiments were conducted by varying the RH. For the H2-air RH cycling test (Run 2), anode and cathode inlet gases were provided as dry and humidified gases. Another RH cycling experiment was the H2 RH cycling test (Run 3): the anode inlet gas was cycled whereas keeping the other side constantly at full humidification. These two RH cycling experiments were alternated in dry and 100% humidified conditions every 10 and 40 minutes, respectively. In the experiments, the fuel cells contained a GoreTM 57 catalyst coated membrane (CCM) and 35 BC SGL gas diffusion layers (GDLs). The fuel cell test station had been performed under idle conditions at a constant current density of 10 mA cm-2. Under the idle conditions, operating at very low current density, a low chemical degradation rate and minimal electrical load stress were anticipated. However, the membrane was expected to degrade due to additional stress from the membrane swelling/contraction cycle controlled by the RH. In this work the performance of the 100% RH humidified cell (Run 1) was compared with that of RH cycling cells (Run 2 and Run 3). Chemical and mechanical degradation of the membrane were investigated using in-situ and ex-situ diagnostic methods. The results of each measurement during and after fuel cell operation are consistent. They clearly show that changing in RH lead to an overall PEM fuel cell degradation due to the increase in membrane degradation rate from membrane resistance, fluoride ion release concentration, hydrogen crossover current, membrane thinning, and hot-spot/pin-hole formation.

Indiana University-Purdue University Indianapolis (IUPUI) / Calcium phosphate-filled restorative materials were developed to provide calcium (Ca) and phosphate (PO4) ions, which have been proposed to enhance remineralization of demineralized tooth structure. Recently, tricalcium phosphate (TCP)-filled restorative materials were introduced as an alternative to amorphous calcium phosphate. The TCP filler has a more crystalline structure than ACP and is therefore potentially stronger. The aim of the present study was to examine TCP-filled restorative resins at different concentration levels at different time intervals to characterize the concentrations of Ca and PO4 ions released, and to measure the water sorption (WS) of these resins. An in vitro study was conducted by formulating resin composite using TCP as the filler mixed with EBPADMA, HmDMA, and HEMA as the resin matrix. One-hundred- sixty samples were prepared, 40 samples of each filler concentration (30 percent, 40 percent, 50 percent, and 60 percent) by weight. From each filler concentration, 5 samples of each of the 8 time points (time intervals of 4 h, 8 h, 12 h, 24 h, 3 d, 7 d, 14 d, and 21 d) were immersed in 100-ml deionized water. Calcium and PO4 ions were measured using atomic absorption spectroscopy and light spectroscopy, respectively. Water sorption (WS) was measured according to ISO 4049 specification and then the WS and the diffusion coefficient were calculated. The significance level was set at p = 0.001. The results indicated that Ca and PO4 ion release increased with increasing filler level at a rate faster than being linear. In addition, WS results were very high and failed to meet the ISO 4049 specification requirement. Diffusion coefficient results were also high. One-way ANOVA test for only 21-day data revealed that there is a statistically significant difference in filler level percent, and two-way ANOVA testing revealed that there is a statistically significant interaction between time and filler level percent on the Ca, PO4 released and WS. It can be concluded that the concentrations of Ca and PO4 released and WS were affected by composition of the monomers, filler level and type, dispersion, and the absence of coupling agent. Although this TCP-filled restorative material may release Ca and PO4, it cannot serve as a restorative material due to high WS values. Further study is needed to improve the material and evaluate its ability in promoting remineralization of the tooth structure in order for it to serve its purpose.

Besides osteoconductivity and a high degradation rate, mesoporous bioactive glasses (MBGs) are specific for their highly ordered channel structure and high specific surface area, making them suitable as drug and/or growth factor delivery systems. On the other hand, the mesoporous channel structure and MBG composition can have an effect on common cell evaluation assays, leading to inconclusive results. This effect is especially important when MBG is mixed in composite bioinks, together with cells. Additionally, the hydrogel component of the ink can influence the degradation of MBG, leading to different ion releases, which can additionally affect the analyses. Hence, our aim here was to show how the MBG structure and composition influence common cell viability and differentiation assays when calcium (Ca)- or magnesium (Mg)-containing glass is part of an alginate-based composite bioink. We suggested pre-labeling of cells with DiI prior to bioprinting and staining with calcein-AM to allow identification of metabolically active cells expressing signals in both green and red channels, allowing the use of fluorescence imaging for cell viability evaluations in the presence of high amounts (7 wt %) of MBGs. The release and uptake of ions during degradation of CaMBG and MgMBG were significantly changed by alginate in the composite bioinks, as confirmed by higher release and uptake from bulk glasses. Additionally, we detected a burst release of Mg²⁺ from composites only after 24 h of incubation. Furthermore, we demonstrated that released ions and the mesoporous channel structure affect the measurement of lactate dehydrogenase (LDH) and alkaline phosphatase activity (ALP) in bioprinted composite scaffolds. Measured LDH activity was significantly decreased in the presence of CaMBG. On the other hand, the presence of MgMBG induced increased signal measured for the ALP. Taken together, our findings show how composite bioinks containing MBGs can interfere with common analyses, obtaining misleading results.

Previous studies of short DNA hairpins have revealed that loop and stem sequences can significantly affect the thermodynamic stability of short DNA hairpins. Nevertheless, there has not been sufficient investigation into the pressure-temperature stability of DNA hairpins, and the current thermodynamic knowledge of DNA hairpins’ stability is limited to the temperature domain. In this work, we report the effect of hydrostatic pressure on the helix-coil transition temperature (TM) for eleven short DNA hairpins at different salt concentrations by performing UV-monitored melting. The studied hairpins form by intramolecular folding of 16-base self-complementary DNA oligo¬deoxy¬ribonucleotides. Model dependent (van’t Hoff) transition parameters such as ΔHvH and transition volume (ΔV) were estimated from analysis of optical melting transitions. Experiments revealed the ΔV for denaturation of these molecules range from -2.35 to +6.74 cm3mol-1. The difference in the volume change for this transition is related to differences in the hydration of these molecules.

Previous studies of short DNA hairpins have revealed that loop and stem sequences can significantly affect the thermodynamic stability of short DNA hairpins. Nevertheless, there has not been sufficient investigation into the pressure-temperature stability of DNA hairpins, and the current thermodynamic knowledge of DNA hairpins’ stability is limited to the temperature domain. In this work, we report the effect of hydrostatic pressure on the helix-coil transition temperature (TM) for eleven short DNA hairpins at different salt concentrations by performing UV-monitored melting. The studied hairpins form by intramolecular folding of 16-base self-complementary DNA oligo¬deoxy¬ribonucleotides. Model dependent (van’t Hoff) transition parameters such as ΔHvH and transition volume (ΔV) were estimated from analysis of optical melting transitions. Experiments revealed the ΔV for denaturation of these molecules range from -2.35 to +6.74 cm3mol-1. The difference in the volume change for this transition is related to differences in the hydration of these molecules.

[ES] Las aleaciones biomédicas de alta entropía (Bio-HEA) con propiedades no tóxicas, sintetizadas mediante métodos de pulvimetalurgia, han recibido una atención limitada a pesar de su potencial para un rendimiento mecánico y biológico favorable. Este estudio tuvo como objetivo investigar sistemáticamente las características microestructurales, mecánicas, electroquímicas y de liberación de iones de distintas composiciones de aleaciones porosas organizadas en tres grupos. El grupo uno consta de cuatro aleaciones porosas de TNZT EB con distintas proporciones de Ti/Ta, mientras que el grupo dos consta de dos aleaciones porosas de TNZTM EB con diferentes proporciones de Ti/Mo. Por último, el grupo tres incluye dos aleaciones más densas de TNZT SPS con diferentes proporciones de Ti/Ta. En el análisis de la microestructura de las aleaciones TNZT EB, es evidente la presencia de fase (matriz) BCC semiequiaxial y micrométrica con un pequeño contenido de fase HCP. Propiedades mecánicas, que abarcan módulos elásticos (83-100 GPa), dureza (373-430 HVN), flexión máxima (225-476 MPa), resistencia a la tracción (120-256 MPa) y compresión (713-1410 MPa); además, la velocidad de corrosión electroquímica (4,5-9,6 ¿m año-1) y la liberación de iones (toxicidad, 0,04-1,1 ¿m año-1), se encuentran dentro de los límites aceptables para los biomateriales de implantes. Sorprendentemente, aumentar el contenido de Ti (y disminuir Ta) muestra ventajas en la mejora de la resistencia mecánica y reduce el módulo elástico. La microestructura del grupo dos, específicamente las aleaciones Ti20 EB TNZTM, exhibe fases (matriz) BCC semiequiaxiales y micrométricas con proporciones disminuidas de fases Zr FCC y HCP. Por el contrario, en Ti25 EB TNZTM, la microestructura comprende fases FCC (matriz) micrométricas y semiequiaxiales con cantidades reducidas de fases HCP y BCC. Es digno de mención subrayar el desafío de la débil homogeneidad que conduce a una heterogeneidad evidente en las aleaciones TNZTM EB. Las propiedades mecánicas, incluidos módulos elásticos (78-80 GPa), dureza (257-294 HVN), flexión máxima (186-210 MPa), resistencia a la tracción (121-144 MPa), compresión (661-774 MPa), corrosión electroquímica. (5-6,6 ¿m año-1) y la liberación de iones (toxicidad, 0,3-0,8 ¿m año-1) están también dentro de rangos aceptables para biomateriales de implantes. La reducción ventajosa del módulo elástico y la liberación de iones se logra disminuyendo el contenido de Ti (y aumentando el Mo), mientras que la mejora del fortalecimiento mecánico se facilita al aumentar el contenido de Ti (y disminuyendo el Mo). El grupo tres, aleaciones TNZT SPS, exhibe una microestructura con fases BCC (matriz) micrométricas y semiequiaxiales y un menor contenido de fases HCP y FCC. Los módulos elásticos (85-88 GPa), dureza (268-349 HVN), flexión máxima (225-476 MPa) y corrosión electroquímica (4,7-5,1 ¿m año-1) resultan ligeramente inferiores que en las aleaciones de polvos elementales. El aumento del contenido de Ti (y la disminución de Ta) muestran ventajas en cuanto a la reducción del módulo elástico y mejoran la dureza. El valor moderado del módulo elástico tiene beneficios potenciales para aliviar el efecto de apantallamiento de tensiones entre los implantes y el tejido orgánico. Sin embargo, en el caso del grupo uno (TNZT EB), la velocidad de corrosión mostró una tendencia ascendente, mientras que la liberación de iones metálicos disminuyó con el aumento del contenido de Ti. Por el contrario, para el grupo dos (TNZTM EB), tanto la velocidad de corrosión como la liberación de iones metálicos disminuyeron en respuesta al aumento del contenido de Ti. Dentro del grupo tres (TNZT SPS) hubo un aumento en la velocidad de corrosión a medida que aumentaba el contenido de Ti. Con base en lo anterior, las aleaciones porosas de TNZT EB con contenidos de Ti medios y altos (Ti30 EB y Ti35 EB) resultan los candidatos más prometedores para aplicaciones de implantes biomédicos. / [CA] Els aliatges biomèdics d'alta entropia (Bio-HEA) amb propietats no tòxiques, sintetitzats mitjançant mètodes de pulvimetal·lúrgia, han rebut una atenció limitada malgrat el seu potencial per a un rendiment mecànic i biològic favorable. Aquest estudi te com a objectiu investigar sistemàticament les característiques microestructurals, mecàniques, electroquímiques i d'alliberament d'ions de diferents composicions d'aliatges porosos organitzats en tres grups. El grup u consta de quatre aliatges porosos de TNZT EB amb diferents proporcions de Ti/Ta, mentre que el grup dos consta de dos aliatges porosos de TNZTM EB amb diferents proporcions de Ti/Mo. Finalment, el grup tres inclou dos aliatges més denses de TNZT SPS amb diferents proporcions de Ti/Ta. A l'anàlisi de la microestructura dels aliatges TNZT EB, és evident la presència de fase (matriu) BCC semiequiaxial i micromètrica amb un petit contingut de fase HCP. Propietats mecàniques, que abasten mòduls elàstics (83-100 GPa), duresa (373-430 HVN), flexió màxima (225-476 MPa), resistència a la tracció (120-256 MPa) i compressió (713-1410 MPa); a més, la velocitat de corrosió electroquímica (4.5-9.6 ¿m any-1) i l'alliberament d'ions (toxicitat, 0.04-1.1 ¿m any-1), es troben dins dels límits acceptables per als biomaterials d'implants. Sorprenentment, augmentar el contingut de Ti (i disminuir Ta) mostra avantatges en la millora de la resistència mecànica i redueix el mòdul elàstic. La microestructura del grup dos, específicament els aliatges Ti20 EB TNZTM, exhibeix fases (matriu) BCC semiequiaxials i micromètriques amb proporcions disminuïdes de fases Zr FCC i HCP. Per contra, a Ti25 EB TNZTM, la microestructura comprèn fases FCC (matriu) micromètriques i semiequiaxials amb quantitats reduïdes de fases HCP i BCC. És digne de menció subratllar el desafiament de la feble homogeneïtat que condueix a una heterogeneïtat química evident en els aliatges TNZTM EB. Les propietats mecàniques, inclosos mòduls elàstics (78-80 GPa), duresa (257-294 HVN), flexió màxima (186-210 MPa), resistència a la tracció (121-144 MPa), compressió (661-774 MPa), corrosió electroquímica. (5-6.6 ¿m any-1) i l'alliberament d'ions (toxicitat, 0,3-0,8 ¿m any-1) estan també dins de rangs acceptables per a biomaterials d'implants. La reducció avantatjosa del mòdul elàstic i l'alliberament d'ions s'aconsegueix disminuint el contingut de Ti (i augmentant el Mo), mentre que la millora de l'enfortiment mecànic es facilita en augmentar el contingut de Ti (i disminuint el Mo). El grup tres, aliatges TNZT SPS, exhibeix una microestructura amb fases BCC (matriu) micromètriques i semiequiaxials i un menor contingut de fases HCP i FCC. Els mòduls elàstics (85-88 GPa), duresa (268-349 HVN), flexió màxima (225-476 MPa) i corrosió electroquímica (4.7-5.1 ¿m any-1) resulten lleugerament inferiors que en els aliatges de pols elementals. L'augment del contingut de Ti (i la disminució de Ta) mostren avantatges quant a la reducció del mòdul elàstic i milloren la duresa. El valor moderat del mòdul elàstic té beneficis potencials per alleujar l'efecte d'apantallament de tensions entre els implants i el teixit orgànic. Tot i això, en el cas del grup u (TNZT EB), la velocitat de corrosió va mostrar una tendència ascendent, mentre que l'alliberament d'ions metàl·lics va disminuir amb l'augment del contingut de Ti. Per contra, per al grup dos (TNZTM EB), tant la velocitat de corrosió com l'alliberament d'ions metàl·lics van disminuir en resposta a l'augment del contingut de Ti. Dins el grup tres (TNZT SPS) hi va haver un augment en la velocitat de corrosió a mesura que augmentava el contingut de Ti. Amb base a això, els aliatges porosos de TNZT EB amb continguts de Ti mitjans i alts (Ti30 EB i Ti35 EB) resulten els candidats més prometedors per a aplicacions d'implants biomèdics. / [EN] Biomedical high entropy alloys (Bio-HEAs) with non-toxic properties, synthesized through powder metallurgy methods, have received limited attention despite their potential for favorable mechanical and biological performance. This study aimed to systematically investigate the microstructural, mechanical, electrochemical, and ion release features of distinct porous alloy compositions organized into three groups. Group one consisted of four porous TNZT EB alloys with varied Ti/Ta ratios, while group two comprised two porous TNZTM EB alloys with different Ti/Mo ratios. Lastly, group three included two porous TNZT SPS alloys with varying Ti/Ta ratios. In the microstructure analysis of TNZT EB alloys, the presence of semi-equiaxed and micrometric BCC phases (matrix) with lower HCP phase content was evident. Mechanical properties, encompassing elastic moduli (83-100 GPa), hardness (373-430 HVN), ultimate bending (225-476 MPa), tensile (120-256 MPa) strength, and compression (713-1410 MPa), in addition to electrochemical corrosion (4.5-9.6 ¿m year-1) and ion release (toxicity, 0.04-1.1 ¿m year-1), fell within acceptable limits for implant biomaterials. Remarkably, augmenting the Ti content (and decreasing Ta) exhibited advantages in improving mechanical strength and reducing the elastic modulus. The microstructure of group two, specifically the Ti20 EB TNZTM alloys, exhibited semi-equiaxed and micrometric BCC phases (matrix) with diminished proportions of FCC and HCP phases. Conversely, in Ti25 EB TNZTM, the microstructure comprised semi-equiaxed and micrometric FCC-phases (matrix) with reduced quantities of HCP and BCC phases. It is noteworthy to underscore the challenge of weak homogeneity leading to evident heterogeneity in TNZTM EB alloys. The mechanical properties, including elastic moduli (78-80 GPa), hardness (257-294 HVN), ultimate bending (186-210 MPa), tensile (121-144 MPa) strength, compression (661-774 MPa), electrochemical corrosion (5-6.6 ¿m year-1), and ion release (toxicity, 0.3-0.8 ¿m year-1), fell within acceptable ranges for implant biomaterials. The advantageous reduction of elastic modulus and ion releases was achieved by decreasing the Ti content (and increasing Mo), whereas enhancing mechanical strengthening was facilitated by increasing the Ti content (and decreasing Mo). Group three, TNZT SPS alloys, exhibited a microstructure with semi-equiaxed and micrometric BCC-phases (matrix) and lower HCP and FCC phase content. The elastic moduli (85-88 GPa), hardness (268-349 HVN), and ultimate bending (225-476 MPa), and electrochemical corrosion (4.7-5.1 ¿m year-1). Increasing Ti content (and decreasing Ta) were advantageous for reducing the elastic modulus and improving hardness. The moderate elastic modulus value holds potential benefits in alleviating the mechanical incongruence between the implant and organic tissue. Nevertheless, in the case of group one (TNZT EB), the corrosion rate exhibited an upward trend, while the metallic ion release declined with increasing Ti content. In contrast, for group two (TNZTM EB), both the corrosion rate and metallic ion release diminished in response to escalating Ti content. Within group three (TNZT SPS) there was increase in the corrosion rate as the Ti content escalated. Based on the above, porous TNZT EB alloys with medium and highest Ti contents (Ti30 EB and Ti35 EB) emerged as promising candidates for biomedical implant applications / Kamel Mohammad Al-Hawajreh, G. (2024). Performance Effect of the Content of Alloying Elements in the Development of High Entropy Alloys of the Ti-Nb-Zr-Ta-Mo Family for Biomedical Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/208235