RESUMO
A volatile sessile liquid droplet or a sublimating solid manifests levitation on its own vapor when placed on a sufficiently heated surface, illustrating the Leidenfrost phenomenon. In this study, we introduce a non-invasive capacitance method for investigating this phenomenon, offering a potentially simpler alternative to existing optical techniques. The designed sensor features in-plane miniaturized electrodes forming a double-comb structure, also known as an interdigitated capacitor. Initially, the sensor's capacitance is characterized for various distances between the sensor and a dielectric material. The influence of the sensor substrate material and the spacing between the electrodes on the sensor's capacitance is also investigated. To demonstrate the feasibility of the method, a sublimating dry ice pellet is placed on the capacitive sensor, and its performance is evaluated. We present results for the dimensionless vapor layer thickness and the pellet's lifetime at different substrate temperatures, derived from the capacitance output. The results are compared with Optical Coherence Tomography (OCT) data, serving as a benchmark. While the temporal evolution of the sensor's output, variation in the dimensionless vapor layer thickness, and the lifetime of the dry ice pellet align with expected results from OCT, notable quantitative deviations are observed. These deviations are attributed to practical experimental limitations rather than shortcoming in the sensor's working principle. Although this necessitates further investigation, the methodology presented in this paper can potentially serve as an alternative for the detection and measurement of Leidenfrost vapor layers.
RESUMO
Cryogenic liquids such as liquid nitrogen are of relevance for numerous processes in engineering, and the food and pharmaceutical industries. However, as a result of its strong evaporation at ambient conditions, its handling for laboratory purposes and experimentation is so far cumbersome. In the present work an original design approach for a supply device for liquid nitrogen is developed and characterized in detail. With the device pure liquid nitrogen is supplied from a pressurized dewar flask to a hypodermic needle without contamination of the liquid with its own vapor or frost, finally enabling to generate a free liquid jet or single droplets in a way comparable to the handling of non-cryogenic liquids using a syringe and a hypodermic needle. Compared to previous approaches for the generation of liquid nitrogen droplets in scientific studies which mostly rely on a reservoir for liquid nitrogen from which droplets form at a bottom outlet due to gravity, the present design allows generation of droplets and free liquid jets in a significantly better controlled and more flexible way. The device is experimentally characterized for varying operational conditions during generation of a free liquid jet, and its versatility for laboratory research purposes is further briefly demonstrated.
RESUMO
PURPOSE: In precision oncology, tumor molecular profiles guide selection of therapy. Standardized snap freezing of tissue biospecimens is necessary to ensure reproducible, high-quality samples that preserve tumor biology for adequate molecular profiling. Quenching in liquid nitrogen (LN2 ) is the golden standard method, but LN2 has several limitations. We developed a LN2 -independent snap freezer with adjustable cold sink temperature. To benchmark this device against the golden standard, we compared molecular profiles of biospecimens. METHODS: Cancer cell lines and core needle normal tissue biopsies from five patients' liver resection specimens were used to compare mass spectrometry (MS)-based global phosphoproteomic and RNA sequencing profiles and RNA integrity obtained by both freezing methods. RESULTS: Unsupervised cluster analysis of phosphoproteomic and transcriptomic profiles of snap freezer versus LN2 -frozen K562 samples and liver biopsies showed no separation based on freezing method (with Pearson's r 0.96 (range 0.92-0.98) and >0.99 for K562 profiles, respectively), while samples with +2 h bench-time formed a separate cluster. RNA integrity was also similar for both snap freezing methods. Molecular profiles of liver biopsies were clearly identified per individual patient regardless of the applied freezing method. Two to 25 s freezing time variations did not induce profiling differences in HCT116 samples. CONCLUSION: The novel snap freezer preserves high-quality biospecimen and allows identification of individual patients' molecular profiles, while overcoming important limitations of the use of LN2 . This snap freezer may provide a useful tool in clinical cancer research and practice, enabling a wider implementation of (multi-)omics analyses for precision oncology.
Assuntos
Criopreservação , Neoplasias , Humanos , Criopreservação/métodos , Neoplasias/genética , Medicina de Precisão , Congelamento , RNARESUMO
A fresh and frozen high-quality patient bio-sample is required in molecular medicine for the identification of disease-associated mechanism at molecular levels. A common cooling procedure is immersing the tissue enclosed in a vial in a coolant such as liquid nitrogen. This procedure is not user friendly and is laborious as reducing the lag time from excision time to freezing depends on the logistic organizational structure within a hospital. Moreover snapfreezing must be done as soon as possible after tissue excision to preserve the tissue quality for molecular tests. Herein, we report an electrically powered snap freezing device as an alternative to quenching the vial in liquid nitrogen and therefore can be used directly at the location where the tissue is acquired. This device also facilitates the study of the effect of freezing conditions on the various molecular processes in the samples. Cooling experiments of a vial in the snap freezing device show that the cooling rates similar to or faster than quenching in liquid nitrogen are feasible. We performed experiments with several set point conditions and compared the results with a mathematical model.
