Extensive tests have been carried out to assess the impact of fluid-dynamic-generated stress during alkaline lysis of Escherichia coli cells (host strain DH1 containing the plasmid pTX 0161) to produce a plasmid DNA (pDNA) solution for gene therapy. Both a concentric cylinder rheometer and two stirred reactors have been used, and both the alkaline addition and neutralization stages of lysis have been studied. Using a range of shear rates in the rheometer, stirrer speeds in the reactors, and different periods of exposure, their impact on chromosomal DNA (chDNA) and pDNA was assessed using agarose gel electrophoresis, a Qiagen Maxiprep with a polymerase chain reaction (PCR) assay, and a Qiagen Miniprep purification with a UV spectrophotometer. Comparison has been made with unstressed material subjected to similar holding times. These tests essentially show that under all these conditions, <2% chDNA was present in the pDNA solution, the pDNA itself was not fragmented, and a yield of 1 mg/g cell was obtained. These results, together with studies of rheological properties, have led to the design of a 60-L, stirred lysis reactor and the production of high-quality pDNA solution with <1% chDNA after further purification.
ObjectiveThe aim of the current study was to assess the puncture resistance and stiffness of nitrile and latex dental examination gloves. Methods Puncture resistance was measured by employing an adapted version of ASTM F1342-91 using both a 316 stainless steel puncture probe (0.8 mm diameter) and a dental injection needle (0.45 mm diameter) interfaced to a tensile testing apparatus. Glove specimens (12 cm length, 1.5 cm breadth) were removed for modulus (M100) evaluation by assessing the force required to elongate the specimen to 100% of the original length. Glove samples were also aged to investigate whether puncture resistance and M100 values varied with aging at 70°C for 7 days in an air-circulating oven. Results The nitrile glove types were assessed to have significantly higher puncture resistance compared with the latex glove type when the steel puncture probe was the pentrometer when using the one way analysis of variance (ANOVA) at the 95% significance level. Interestingly the puncture resistance for the latex glove type was significantly higher (P < 0.001) when a dental injection needle was used as the pentrometer compared with the nitrile glove types. The M100 values were significantly higher for the nitrile glove types for which the stiffness increased when the gloves were aged (P < 0.001). Conclusions The higher stiffness values resulted in increased puncture resistance when the nitrile glove specimens were aged irrespective of the pentrometer type. However, the ability of latex to re-seal itself on puncture may be beneficial when considering the protection potential of each glove type against breaches in cross infection. For clinicians that have experienced an adverse reaction to natural latex gloves, the results of the current study indicate that nitrile gloves are available at reasonable cost and offer the clinician comparable resistance to puncture with latex gloves.
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