New Method for Monitoring the Process of Freeze Drying of Biological Materials

Abstract

Abstract. A capacitive sensor was proposed and tested for the monitoring and control of a freeze drying process of a vaccine against the Newcastle disease of birds. The residual moisture of the vaccine was measured by the thermogravimetric method. The vaccine activity was determined by titration in chicken embryos. It was shown that, at the stages of freezing and primary drying, a capacitive sensor measured the fraction of unfrozen liquid phase in a material and allowed one to control the sublimation stage of drying in an optimal way. This prevented the foaming of the material and shortened the total drying time approximately twice. The control range at the sublimation stage of drying expanded up to −70°C. It was found at the final stage of drying that the signal of a capacitive sensor passed through a maximum value. We supposed that this maximum corresponds to the minimum of intramolecular mobility of biological macromolecules and hence to the optimal residual moisture of the material, which ensures long-term preservation of its activity. We also suppose that using the capacitive sensor at the final stage of drying allows one to more precisely detect the time when the residual moisture of dried material reaches the optimal value.KEY WORDS: biological materials; capacitive sensor; freeze drying; optimal residual moisture.At present, most biological materials containing live viruses or bacteria are exposed to lyophilization (i.e., drying from the frozen state); this ensures long-term preservation of their activity. Typically, this process consists of preliminary freezing and subsequent freeze drying. The latter process, in turn, consists of two stages: primary drying and secondary drying. During primary drying or sublimation, frozen water is removed from a biological product under vacuum and at temperatures below 0°C. At this stage, the drying rate is limited because of the foaming of a product that occurs due to its high temperature and the excess amount of liquid phase in it. The secondary drying, or final stage, begins after the end of the sublimation stage and occurs at temperatures above 0°C. The goal of the secondary drying is to bring the residual moisture of a biological product to an optimum level, which provides longterm preservation of its activity. Note that the moisture content both above and below the optimum value reduces the effective life of biological materials (1,2)To increase the shelf life of biological products, the following should be investigated: (1) the influence of the composition of the dried biological product and the residual moisture on the change in its activity over the time (3); (2) it is needed to optimize the sublimation drying process for different types of biological products (4). For the investigation of the of the state of water in the dried biologic drugs and the influence of the humidity of the biological on the change in their activity during shelf life, different physical methods are used such as neutron scattering (5), nuclear magnetic resonance (NMR) (6,7), Raman spec...

Gradient Mechanical Properties Facilitate Arabidopsis Trichome as Mechanosensor

“…It should be noted that SEM analysis requires dry tissue, which may not be the same as the fully hydrated leaves in vivo . The freeze-drying step used to prepare the samples for SEM–EDS has been shown to have no significant influence on cell wall structures and material properties. − We also observed no significant change of the trichome structure after processing.…”

A Novel Biodegradable Tubular Stent Prevents Pancreaticojejunal Anastomotic Stricture

“…Antibiotics were administered after the operation (0.06 ml of 50 mg/ml ceftriaxone per 100 g of body weight) and Biodegradable behavior of the BTS. Each rBTS was removed from the rat duodenum after sacrifice and freeze dried as described previously 28,29 (Christ freeze dryer type Alpha 1-4 LSC; Martin Christ Gefriertrock-nungsanlagen GmbH, Osterode am Harz, Germany). The surface morphologies of the removed rBTS samples were then assessed using scanning electron microscopy (SEM, Hitachi S4800, Tokyo, Japan) prior to stent placement and at 1, 2, 3, 4, 6, 8 and 12 weeks after rBTS placement.…”

An overview of process intensification and thermo stabilization for upscaling of Peste des petits ruminants vaccines in view of global control and eradication

“…Viruses exhibit varying degree of thermo lability at different storage temperatures and stabilization conditions. Preservation of live vaccines by freeze drying has become the accepted method for long term preservation and maintenance of stability [1]. The stability of the vaccine depends upon the thermo stability of the virus, the pH of culture system in which the virus is grown, property of the chemical stabilizer, freeze drying conditions optimal for a virus and reconstitution buffers for long-term storage, transportation and use of viral vaccine under field conditions or other viral preparations under extended time of handling in laboratory settings [71].…”