1.4.3 Profilometry
To determine the final solids distribution, the profiles of the dried
samples can also be generated using a profilometer. This is a physical analog to SWLI, implementing a mechanical stylus instead of
light to profile the sample. In this approach a diamond stylus is
moved vertically until it contacts with the sample, and then it is
moved laterally across the sample for a specified distance and specified contact force. A scanning velocity of 0.3 mm/s was used to
generate the profiles in our earlier work [9]. As shown in the
example illustration in Fig. 2, profilometry results can discriminate
between processing conditions that lead to the characteristic
“rings” associated with passive drying techniques, compared to
the more homogeneous profiles that we observe with energy delivery drying methods.
Fig. 1 SWLI height profiles of a representative LAD processed sample
Before drying
Microwave/laser
assisted drying
Passive drying
Profilometry
Profilometry
Profilometer
stylus
Profilometer
stylus
Height (mm)
Distance (mm)
Height (mm)
Distance (mm)
sample
Fig. 2 An example illustration of profilometry of droplets dried by energy delivery drying (upper) and passive
drying (bottom)
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209
To determine the final solids distribution, the profiles of the dried
samples can also be generated using a profilometer. This is a physical analog to SWLI, implementing a mechanical stylus instead of
light to profile the sample. In this approach a diamond stylus is
moved vertically until it contacts with the sample, and then it is
moved laterally across the sample for a specified distance and specified contact force. A scanning velocity of 0.3 mm/s was used to
generate the profiles in our earlier work [9]. As shown in the
example illustration in Fig. 2, profilometry results can discriminate
between processing conditions that lead to the characteristic
“rings” associated with passive drying techniques, compared to
the more homogeneous profiles that we observe with energy delivery drying methods.
Fig. 1 SWLI height profiles of a representative LAD processed sample
Before drying
Microwave/laser
assisted drying
Passive drying
Profilometry
Profilometry
Profilometer
stylus
Profilometer
stylus
Height (mm)
Distance (mm)
Height (mm)
Distance (mm)
sample
Fig. 2 An example illustration of profilometry of droplets dried by energy delivery drying (upper) and passive
drying (bottom)
Drying Technology for Preservation of Biologics
209