Bioenergetic shifts during transitions between stem cell states

Two defining characteristics of stem cells are their multilineage differentiation potential (multipotency or pluripotency) and their capacity for self-renewal. Growth factors are well-established regulators of stem cell differentiation and self renewal, but less is known about the influence of the metabolic state on stem cell function. Recent studies investigating cellular metabolism during the differentiation of adult stem cells, human embryonic stem cells (ESCs), and induced pluripotent stem cells have demonstrated that activation of specific metabolic pathways depends on the type of stem cells as well as the lineage cells are differentiating into and that these metabolic pathways can influence the differentiation process. However, some common patterns have emerged, suggesting that undifferentiated stem cells primarily rely on glycolysis to meet energy demands. Our own data indicate that undifferentiated ESCs not only exhibit a low mitochondrial membrane potential but also express high levels of the mitochondrial uncoupling protein 2 and of glutamine metabolism regulators when compared with differentiated cells. More importantly, interventions that target stem cell metabolism are able to either prevent or enhance differentiation. These findings suggest that the metabolic state of stem cells is not just a marker of their differentiation status but also plays an active role in regulating stem cell function. Regulatory metabolic pathways in stem cells may thus serve as important checkpoints that can be modulated to direct the regenerative capacity of stem cells

Thermal Transport Properties of β‑Ga₂O₃ Thin Films on Si and SiC Substrates Fabricated by an Ion-Cutting Process

Integrating β-Ga2O3 films onto a highly thermally conductive substrate is regarded as a promising method to remove the heat from β-Ga2O3 high-power devices, ultimately increasing their reliability and performance. In this work, we fabricated three wafer-scale heterogeneous integration materials (HIMs), i.e., β-Ga2O3–SiC (GaOSiC), β-Ga2O3–Al2O3–SiC (GaOISiC), and β-Ga2O3–Al2O3–Si (GaOISi), by using ion-cutting and surface-activated bonding techniques. The heat block effect of the intermediate amorphous Al2O3 layer from β-Ga2O3 to SiC is significantly relieved by employing a post-annealing process. Furthermore, the Al2O3 layer blocks the interfusion of elements between β-Ga2O3 and the host substrate, avoiding the degradation of thermal conductivity of β-Ga2O3 films after post-annealing. Benefited from this, a relatively high thermal conductivity (9.3 W/m·K) is achieved among β-Ga2O3 thin films with the same thickness and the effective thermal boundary conductance was improved in all β-Ga2O3 HIMs. One to two orders of magnitude reduction in the junction-to-package device thermal resistance is revealed by the thermal modeling of β-Ga2O3 HIM metal-oxide-semiconductor field-effect transistors, which demonstrates that extremely high heat dissipation can be realized by optimizing the TBReff value and integrating with thermally conductive substrates (SiC and diamond). These results give key guidelines to engineer the thermal transport properties of β-Ga2O3 HIMs for device thermal management