In first-line chemotherapy trials for MCRC, improvements in PFS are strongly associated with improvements in OS. In this patient population, PFS may be an appropriate surrogate for OS. As a clinical end point, PFS offers increased statistical power at a given time of analysis and a significant lead time advantage compared with OS.
Powders with varying degrees of corrugation were successfully obtained by spray drying with their surface roughness quantified by fractal analysis. It was shown that only a relatively small degree of surface corrugation was sufficient to accomplish a considerable improvement in the aerosol performance of the powder.
Surface fractal dimensions, D
S, of smooth and corrugated bovine serum albumin particles were obtained
from N2 adsorption isotherms using modified Frenkel−Halsey−Hill (FHH) theory. It was found that for
different particles, the correct D
S values depended on the number of adsorbed layers, n. For corrugated
particles, when 1 ≤ n ≤ 10, the value of D
S is equal to 2.39, which agrees with the value obtained from
light scattering (2.39 ± 0.05). Unlike the corrugated particles, the adsorption isotherm for the smooth
particles generated the correct value of D
S (2.12) only for 1.0 ± 0.5 ≤ n ≤ 2.0 ± 0.5 (i.e., around monolayer
coverage). Determination of D
S in the multilayer region (n > 2) produced a higher value than the one
obtained from monolayer coverage. This was because the smooth particles were in closer contact with each
other; at higher coverage the gas molecules probed the surface of the aggregates instead of the single
particles. As there were fewer contact points between the corrugated particles compared to the smooth
particles, this effect took place at higher coverage (pressure) causing deviation from the expected values.
This finding is supported by the fact that for corrugated particles, the value of D
S started to deviate at
higher n and increased to 2.58 when n > 10. The use of modified FHH theory is thus limited by the number
of adsorbed layers on the particles. The closer the particles come in contact, the thinner is the coverage
region describing the correct D
S. To ensure reliable determination of D
S, it is therefore recommended to
determine D
S only around monolayer coverage.
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