Freeze-Dry Microscopy: Impact of Nucleation Temperature and Excipient Concentration on Collapse Temperature Data

Abstract

Abstract. The objective of this study was to investigate the impact of nucleation temperature (T n ) and excipient concentration on the collapse temperature data obtained from freeze-dry microscopy (FDM) experiments. T n , the temperature of the onset of collapse (T oc ), and the full collapse temperature (T fc ) were determined for aqueous solutions of polyvinylpyrrolidone (PVP) 40 kDa and 2-(hydroxypropyl)-ß-cyclodextrin. Concentrations were varied from 1% to 20% (w/w) for PVP and from 1% to 30% (w/w) for the 2-(hydroxypropyl)-ß-cyclodextrin. Mutual correlation coefficients were calculated for the observed T n , T oc , and concentrations of the solutions. In addition, outliers were detected and eliminated by applying the leaving-one-out routine and calculating correlation coefficients without it. T n was found to be non-correlated with concentrations and only weakly correlated with T oc . The correlation between these two temperatures was particularly poor for the solutions of the highest and lowest concentrations. In contrast, T oc correlated much better with the corresponding concentrations, resulting in a quadratic fit for PVP and a linear fit for 2-(hydroxypropyl)-ß-cyclodextrin.

Development of highly stabilized curcumin nanoparticles by flash nanoprecipitation and lyophilization

“…A similar 759 observation has also been reported for PS-PEO polymer films, 760 where PEO was found to be embedded in the PS domain by phase 761 contrast analysis [49]. Consequently, the current AFM data accord Kleptose is a collapse temperature modifier [51]. The high concen- The redispersibility data of various freeze-dried samples are 807 summarized in Table 4.…”

“…Long-term storage stability (>1 year) could be achieved by 49 lyophilization of the optimized nanosuspension with Kleptose (hydroxypropyl-b-cyclodextrin), which 50 was shown to be the only effective lyoprotectant among all the ones tested for the CUR nanoparticles. 51 At an optimal concentration of Kleptose (1.25% w/v), the redispersibility (S f /S i ; ratio of the final and initial 52 particle sizes) and encapsulation efficiency of lyophilized CUR nanoparticles were about 1.22% and 94%, 53 respectively. tems for specific biological applications [1,2].…”

“…To select a suitable protectant for lyophilizing the CUR nanosuspension, four sugars 787 (lactose, trehalose, glucose, mannitol) and one sugar compound 788 (Kleptose; hydroxypropyl-b-cyclodextrin) were each assessed at a 789 concentration of 10% w/v in the dialyzed nanosuspension for effectiveness in maintaining the integrity of the nanoparticles during 791 lyophilization. These protectants are sometimes grouped collectively under the category of ''cryoprotectant'' [50] although the 793 term cryoprotectant should normally be reserved for those agents 794 that are truly capable of protecting the nanoparticles from freezing 795 damage (i.e., for lactose, trehalose dihydrate, and glucose in this 796 case)[51]. Similarly, the remaining two protectants should also 797 be referred to by their proper technical names based on their actual 798 protective mechanisms; thus mannitol is a bulking agent, and…”

Collapse temperature of solutions important for lyopreservation of living cells at ambient temperature

“…It is clear from the table that for both trehalose concentrations, no significant difference in the collapse temperature is observable between the samples frozen without seeding, with ice seeding at À48C, and with ice seeding at À78C. Similar effect of ice nucleation (in an uncontrolled spontaneous manner though) at much lower temperatures (from À16 to À228C) on collapse temperature has been reported in the literature (Meister et al, 2009) for simple binary aqueous solutions, where PVP (40 kDa) and 2-(hydroxypropyl)-b-cyclodextrin rather than trehalose were used as the lyoprotectants. Although ice seeding does not affect the collapse temperature significantly, it could greatly affect the primary drying rate (Searles et al, 2001a,b) and should be carefully optimized to ensure high cell viability without compromising drying rate significantly.…”

“…When a small amount of ice nuclei are seeded at a high subzero temperature, the growth of the ice nuclei dominates ice nucleation with further freezing to lower temperatures, leading to the formation of large ice crystals with the apparent dendritic structure in the frozen region. In the absence of ice seeding, however, water in the sample is subcooled to a deep subzero temperature (usually À158C or lower) that favors the formation of much more ice nuclei and growth of the ice nuclei is limited due to the limited availability of space, resulting in the formation of much more homogeneous small ice crystals in the frozen sample shown in Figures 1, 2, and 4 (Kashchiev, 2000;Meister et al, 2009;Toner, 1993).…”