Aerogel Rafts Allowing for the Comparison of Novel Solvent-Based Biological Formulations During the Primary Drying Phase of Lyophilisation

Abstract

Silica aerogels (SA) are comprised of up to 90% air. As such, they are useful for many different techniques and delivery systems. In the present study, SA were successfully synthesised using the novel solvent tetraethyl butrane (TEB) as a reaction solvent via sol-gel formation and aging followed by a freezedrying (lyophilisation) process. Although the TEB solvent is expensive, it could still be a suitable alternative to traditional solvents for the synthesis of SA. The TEB solvent has a relatively short required gelation time that eliminates the need for the solvent exchange process, thereby allowing for a shorter synthesis time. Moreover, TEB solvent could be recycled. The lyophilisation process is one of the most common processes in pharmaceutical production; however, it is a relatively expensive technique due to the length of time it takes to complete. To reduce the cost of this process, the sublimation time should be minimised, as this is the longest of the three phases of lyophilisation. This is why it is very important to determine the end point of the sublimation phase. The second part of this study therefore involved producing SA combined with different substances. These were monitored by several sensors to determine the end point of their primary drying. Some successful formulations were synthesised when the SA was combined with agarose (AG), mannitol (MAT), polyvinyl alcohol (PVA) and ethyl cellulose (EC). SA/AG was the basic formula that monitored by thermocouple temperature, Corillonite V.2.3 and the microbalance sensors. The remaining formulations hardened the structure of the SA and significantly affected the sublimation time when measured by thermocouple sensor only. These findings suggest that SA produced by those substances (AG, MAT, PVA and EC) could decrease the end point of primary drying in the lyophilisation process and producing a better shape than pure SA.