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- Wessman, Per, et al.
(author)
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Formulations for freeze-drying of bacteria and their influence on cell survival
- 2013
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In: Journal of Visualized Experiments. - : MyJove Corporation. - 1940-087X. ; :78
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Journal article (peer-reviewed)abstract
- Cellular water can be removed to reversibly inactivate microorganisms to facilitate storage. One such method of removal is freeze-drying, which is considered a gentle dehydration method. To facilitate cell survival during drying, the cells are often formulated beforehand. The formulation forms a matrix that embeds the cells and protects them from various harmful stresses imposed on the cells during freezing and drying. We present here a general method to evaluate the survival rate of cells after freeze-drying and we illustrate it by comparing the results obtained with four different formulations: the disaccharide sucrose, the sucrose derived polymer Ficoll PM400, and the respective polysaccharides hydroxyethyl cellulose (HEC) and hydroxypropyl methyl cellulose (HPMC), on two strains of bacteria, P. putida KT2440 and A. chlorophenolicus A6. In this work we illustrate how to prepare formulations for freeze-drying and how to investigate the mechanisms of cell survival after rehydration by characterizing the formulation using of differential scanning calorimetry (DSC), surface tension measurements, X-ray analysis, and electron microscopy and relating those data to survival rates. The polymers were chosen to get a monomeric structure of the respective polysaccharide resembling sucrose to a varying degrees. Using this method setup we showed that polymers can support cell survival as effectively as disaccharides if certain physical properties of the formulation are controlled.
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- Wätjen, J. Timo, et al.
(author)
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Cu out-diffusion in kesterites : A transmission electron microscopy specimen preparation artifact
- 2013
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:5, s. 051902-
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Journal article (peer-reviewed)abstract
- Solar cells based on Cu2ZnSn(S,Se)(4) absorber layers have received a growing amount of interest. Typically a Mo(S,Se)(2) layer is formed at the Cu2ZnSn(S,Se)(4)/Mo interface during processing. Transmission electron microscopy (TEM) analyses showed the presence of Cu in the Mo(S,Se)(2) which was thought to cause secondary phase formation at the back contact. However, preparing TEM samples can induce artifacts leading to false conclusions. It is therefore of great importance to identify such artifacts. In this work, we show that the Cu presence in the Mo(S, Se) 2 stems solely from TEM sample preparation and does not occur as part of the synthesis process.
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