Date of Completion


Embargo Period



Protein formulation, high concentration, lyophilization, freeze drying, reconstitution, formulation, processing, viscosity, crystalline, porous structure

Major Advisor

Robin Bogner

Associate Advisor

Devendra Kalonia

Associate Advisor

Joseph Rinella

Field of Study

Pharmaceutical Science


Doctor of Philosophy

Open Access

Open Access


Highly concentrated therapeutic protein products stabilized by lyophilization often have undesirably long and variable reconstitution times. The overall objective of this work was to identify factors governing the reconstitution times of these formulations. Fundamental understanding of these factors will reduce the barrier to efficient formulation and process design presented by poorly reconstituting drug products.

Properties of the lyophilized “cake” that have been previously implicated in influencing reconstitution are cake wettability, liquid penetration into cake, cake disintegration, and cake porous structure. Methods to quantify these properties of intact cakes in vials were refined and further developed. The effects of formulation and processing on each of these properties were investigated to understand their role in mediating reconstitution times. Additionally, the role of viscosity near the surface of the dissolving cake (“concentrated formulation viscosity”) in influencing reconstitution time was also examined.

While “concentrated formulation viscosity” was the key factor governing reconstitution of amorphous cakes, crystallinity and larger pores governed reconstitution of partially crystalline cakes. Cake hydration results in a viscous region at the dissolving cake surface in contact with the reconstitution fluid. This viscous layer provides resistance to the diffusion of the reconstitution fluid through the layer into the remaining undissolved cake, delaying wetting and hydration of the cake core and prolonging the reconstitution time. Dissolution of amorphous cakes proceeded via hydration followed by gradual surface erosion. Partial crystallinity and larger pores tremendously improved wettability and liquid penetration in partially crystalline cakes, ultimately resulting in small, well dispersed cake pieces. Thus, cake dissolution involved wetting, disintegration followed by hydration. The “concentrated formulation viscosity” is expected to influence reconstitution of both amorphous and partially crystalline cakes. However, in the latter case, there is an increase in surface area of the dispersed solids, lowering the barrier provided by the viscous layer.

Based on these findings, both formulation and processing conditions can be tailored to achieve faster reconstitution. Including a crystallizable excipient and incorporating an annealing step to facilitate its crystallization and to promote larger pores were beneficial. A viscosity lowering excipient may be advantageous but this approach needs to be explored further.

Overcoming Long Reconstitution Times of High Concentration Lyophilized Protein Formulations

12 May, 2019

Shreya Shashank Kulkarni, B.Pharm Bombay College of Pharmacy (Mumbai University)

M.S., University of Colorado

Ph.D., University of Connecticut

Directed by: Professor Robin Bogner

Available for download on Thursday, April 23, 2020