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BackgroundTo isolate and characterization of human spermatogonial stem cells from stem spermatogonium.MethodsThe disassociation of spermatogonial stem cells (SSCs) were performed using enzymatic digestion of type I collagenase and trypsin. The SSCs were isolated by using Percoll density gradient centrifugation, followed by differential surface-attachment method. Octamer-4(OCT4)-positive SSC cells were further identified using immunofluorescence staining and flow cytometry technques. The purity of the human SSCs was also determined, and a co-culture system for SSCs and Sertoli cells was established.ResultsThe cell viability was 91.07% for the suspension of human spermatogonial stem cells dissociated using a two-step enzymatic digestion process. The cells isolated from Percoll density gradient coupled with differential surface-attachement purification were OCT4 positive, indicating the cells were human spermatogonial stem cells. The purity of isolated human spermatogonial stem cells was 86.7% as assessed by flow cytometry. The isolated SSCs were shown to form stable human spermatogonial stem cell colonies on the feeder layer of the Sertoli cells.ConclusionsThe two-step enzyme digestion (by type I collagenase and trypsin) process is an economical, simple and reproducible technique for isolating human spermatogonial stem cells. With little contamination and less cell damage, this method facilitates isolated human spermatogonial stem cells to form a stable cell colony on the supporting cell layer.

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A model of Ni-yttria stabilized zirconia (YSZ)-gas triple phase boundary (TPB) is built to simulate the oxygen transfer and hydrogen oxidation processes in solid oxide fuel cell anodes by using density functional theory. The highest barrier in the anodic processes is found in the step of oxygen transfer from the YSZ surface to the TPB site, where the oxygen is connected with nickel and yttrium/zirconium atoms. Three TPB sites and associated reaction paths, near Y or Zr atoms, and one nickel site on the Ni terrace are compared for the hydrogen oxidation reaction. Depending on the local structures of TPB sites, the reaction barrier of the (O + H)* → OH* reaction varies from 0.46 to 0.57 eV, and the reaction barrier of (OH + H)* → H2O* varies from 0.83 to 1.05 eV. When O or OH is on the Ni site, which is only 3 Å from the Y at TPB site, the reaction barriers of the above reactions are 1.15 and 1.02 eV, respectively.

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