Vacuum Induced Surface Freezing (VISF) and surface treatment of containers

In the present work, the effect of surface treatments on the feasibility of controlled nucleation using the Vacuum-Induced Surface Freezing technique has been investigated. There are evidences that the application of VISF, in its current form, to aqueous solutions leads to sub-optimal results in presence of hydrophobic coatings. The experimental tests compared untreated and sulphate treated vials with containers having hydrophobic surfaces such as siliconized and TopLyo ® vials. The tested formulations were demineralized water, demineralized water + 0,02% w/v Tween 80, 5% w/w sucrose, 5% w/w sucrose + 0,02% w/v Tween 80, 5% w/w mannitol and 5% w/w mannitol+ 0,02% w/v Tween 80. The results obtained indicate that there is no marked influence of the type of vials on the nucleation pressure of the solution. Depending on the type of solutions selected have been observed boiling and bubbling phenomena at pressure values much higher than those generally used to trigger nucleation (i.e., 1-2 mbar). Both bubbling and boiling lead to obtain products with an unacceptable morphology, therefore should be avoided. The inhibition of the boiling phenomenon by the presence Tween 80 and the effectiveness of the degassing in eliminating the bubbling have been proven. Finally, it was possible to implement VISF through an automatic mode without the need for manual pressure adjustments by visual inspection of the samples.