Advancing Microwave Technology for Dehydration Processing of Biologics

Abstract

Our prior work has shown that microwave processing can be effective as a method for dehydrating cell-based suspensions in preparation for anhydrous storage, yielding homogenous samples with predictable and reproducible drying times. In the current work an optimized microwave-based drying process was developed that expands upon this previous proof-of-concept. Utilization of a commercial microwave (CEM SAM 255, Matthews, NC) enabled continuous drying at variable low power settings. A new turntable was manufactured from Ultra High Molecular Weight Polyethylene (UHMW-PE; Grainger, Lake Forest, IL) to provide for drying of up to 12 samples at a time. The new process enabled rapid and simultaneous drying of multiple samples in containment devices suitable for long-term storage and aseptic rehydration of the sample. To determine sample repeatability and consistency of drying within the microwave cavity, a concentration series of aqueous trehalose solutions were dried for specific intervals and water content assessed using Karl Fischer Titration at the end of each processing period. Samples were dried on Whatman S-14 conjugate release filters (Whatman, Maidestone, UK), a glass fiber membrane used currently in clinical laboratories. The filters were cut to size for use in a 13 mm Swinnex Ò syringe filter holder (Millipore TM , Billerica, MA). Samples of 40 mL volume could be dehydrated to the equilibrium moisture content by continuous processing at 20% with excellent sample-to-sample repeatability. The microwave-assisted procedure enabled high throughput, repeatable drying of multiple samples, in a manner easily adaptable for drying a wide array of biological samples. Depending on the tolerance for sample heating, the drying time can be altered by changing the power level of the microwave unit.

Resilience of Oocyte Germinal Vesicles to Microwave-Assisted Drying in the Domestic Cat Model

“…26 In subsequent work, an analytical grade microwave was used to enable continuous heating at a lower power setting. 21 This system was the preferred choice for the current studies. This analytical grade unit uses the same 2.45 GHz magnetron as a conventional household microwave system, but the instrument is designed to enable more precise control over the power delivered.…”

“…Samples were sealed into bags at a moisture content of *0.12 gH 2 O/gDW, which was predicted to result in a T g in the range of *10°C, based on a binary best fit curve to multiple data sets. 20,21 Given the difficulty in measuring T g in situ, and a lack of information regarding the optimal storage temperature with respect to T g , the existence or non-existence of the glassy state in these samples is somewhat speculative. Storage in the Dri-shield bags resulted in moderate additional drying, as the bags themselves were found to absorb some amount of moisture.…”

“…capacity = 12 filters) of samples contained in these filter holders. 21 A set of up to 5 oocytes, along with 40 mL of trehalose solution, were transferred onto each conjugate-release filter paper and dehydrated with the SAM 255 microwave. A control filter without oocytes was processed with each batch at each time point to assess the moisture contents immediately after microwaving or storage.…”

Determination of the relaxation characteristics of sugar glasses embedded in microfiber substrates

“…In order to investigate the effect of processing conditions on the relaxation characteristics of amorphous glasses formed by drying dilute sugar solutions, we used a microwave-assisted drying approach [16]. When using this approach to process samples, the moisture content in the sample can be decreased, within 30 minutes, to an end-point moisture level that enables the formation of a glassy state at room temperature.…”

“…This drying approach is recognized as a fast, uniform and reproducible method to dehydrate biomaterials into the glassy state [15, 16]. The microwave-assisted technique has been successfully applied to dehydrate viruses and cat germinal vesicles [13, 14].…”