Abstract
Recent advances in molded vial manufacturing enabled manufacturers to use a new manufacturing technique to achieve superior homogeneity of the vial wall thickness. This study evaluated the influence of the different manufacturing techniques of molded vials and glass compositions on vial heat transfer in freeze-drying. Additionally, the influence of using empty vials as thermal shielding on thermal characteristics of edge and center vials was investigated. The vial heat transfer coefficient Kv was determined gravimetrically for multiple vial systems. The results showed superior heat transfer characteristics of the novel manufacturing technique as well as differences in heat transfer for the different glass compositions. Empty vials on the outside of the array did not influence center vial Kv values compared to a full array. The direct contact area and vial bottom curvature and their correlation to heat transfer parameters were analyzed across multiple vial systems. A new approach based on light microscopy to describe the vial bottom curvature more accurately was described. The presented results for the contact area allowed for an approximation of the pressure-independent heat transfer parameter KC. The results for the vial bottom curvature showed a great correlation to the pressure-dependent heat transfer parameter KD. Overall, the results highlighted how a thorough geometrical characterization of vials with known heat transfer characteristics could be used to predict thermal characteristics of new vial systems as an alternative to a time-consuming gravimetric Kv determination. Primary drying times were simulated to show the influence of Kv on drying performance.
Highlights
Glass vials are the most common primary packaging material used in pharmaceutical freeze-drying [1]
The manufacturing process for molded vials is routinely performed in two steps: first, the molten glass is formed into an initial parison with a defined opening and a hollow inside
Comparison of the 20-mL BB and 20-mL PB1 vials showed that while the PB process had a clear effect on Kv and KD, the differences observed between the two manufacturing processes were likely not practically relevant for drying performance
Summary
Glass vials are the most common primary packaging material used in pharmaceutical freeze-drying [1]. The manufacturing process for molded vials is routinely performed in two steps: first, the molten glass is formed into an initial parison with a defined opening and a hollow inside. This parison is transferred into a second mold where the final shape of the vial is formed by blowing the parison with compressed air. The formation of the initial parison in the first mold can either be performed by blowing the molten glass with compressed air (“blow-blow,” further abbreviated as BB) or pressing it with a metal plunger (“press-blow,” further abbreviated as PB). Recent advances in vial manufacturing have allowed manufacturers to produce smaller PB molded vials down to a size of 15-mL injection vials [4]
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