PubMed · 1217507
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E R Gaughran, A J Goudie. 1975. The heat sterilization methods.. https://pubmed.ncbi.nlm.nih.gov/1217507/
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A general design for a thermal test object (TTO) is proposed. A number of novel features make the design particularly suitable for use as a standardised device for assessing the heating capability of diagnostic ultrasound beams. To assess performance, soft-tissue TTOs have been made containing thin-film thermocouples sandwiched between discs of tissue-mimicking gel. Installed in an appropriate measurement system, these TTOs exhibit excellent thermal and spatial resolution, allowing the ultrasound beam to be located rapidly and reproducibly. The measured temperature rise after 3 minutes of heating has been compared with theoretical predictions based on measured pressure distributions, and agreement is within 10%. Other studies have shown that soft-tissue- and bone-mimicking TTOs can be used to evaluate a wide range of ultrasound fields and that different physical tissue models can be simulated. It is concluded that this design would be suitable for providing reference assessments of the thermal hazard posed by diagnostic ultrasound under standardised conditions.
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In the previous study (part I), heat-denatured RNase A aggregation was shown to depend on the solution pH. Interestingly, at pH 3.0, the protein did not aggregate even when exposed to 75 degrees C for 24 h. In this study, electrostatic repulsion was shown to be responsible for the absence of aggregates at that pH. While RNase A aggregation was prevented at the extremely acidic pH, this is not an environment conducive to maintaining protein function in general. Therefore, attempts were made to confer electrostatic repulsion near neutral pH. In this study, heat-denatured RNase A was mixed with charged polymers at pH 7.8 in an attempt to provide the protein with excess surface cations or anions. At 75 degrees C, SDS and dextran sulfate were successful in preventing RNase A aggregation, whereas their cationic, nonionic, and zwitterionic analogs did not do so. We believe that the SO3- groups present in both additives transformed the protein into polyanionic species, and this may have provided a sufficient level of electrostatic repulsion at pH 7.8 and 75 degrees C to prevent aggregation from proceeding.