Dynamic-mechanical thermoanalysis test as a high-performance alternative for accelerated freeze-thaw stability testing: a case study of O/W emulsions

D-optimal design of experiments and comprehensive rheological analysis in the development of natural anti-aging creams

“…Compared to at least 12 days typically required for conventional freeze-thaw test in the stability chamber (45 °C/24 h; -5 °C/24 h, minimum 6 cycles), properly programmed DMTA test allowed us to evaluate the thermal stability of the developed anti-aging creams in a significantly shorter time (about 2 h per formulation). Looking closely at the DMTA graph, the trend of the sample structural change during the test can be easily observed through a series of G' peaks corresponding to the temperature plateau at 20 °C, where each peak indicates the change of G' prior to temperature oscillation (initial value) and after each conducted stress test cycle [10,11]. Figure 5b represents an enlarged inset of Figure 5a for narrower storage modulus range (G' 231-241 Pa).…”

“…DMTA test, recently developed as the rheological simulation of the routine freeze-thaw test in the stability chamber [10,11], was also conducted in the LVE region, at deformation values equal to or lower from the γ L value for respective model formulations, while ω was set at 10 rad/s. Briefly, the test was designed to monitor, at thermal equilibrium (20 °C), the change of G' max value of each subsequent cycle of temperature oscillation (G' max , n , n = 1-6) in relation to the G' max value of the initial measurement (before temperature oscillation, G' max,t0 ), thus allowing the calculation of Delta (Δ) value, as a measure of structural change of the investigated sample (Δ = G' max , n / G' max,t0 , n = 1-6) [13], after which Delta difference, as an absolute value, was calculated (Δ difference = |Δ n -Δ t0 |, n = 1-6).…”

“…Briefly, the test was designed to monitor, at thermal equilibrium (20 °C), the change of G' max value of each subsequent cycle of temperature oscillation (G' max , n , n = 1-6) in relation to the G' max value of the initial measurement (before temperature oscillation, G' max,t0 ), thus allowing the calculation of Delta (Δ) value, as a measure of structural change of the investigated sample (Δ = G' max , n / G' max,t0 , n = 1-6) [13], after which Delta difference, as an absolute value, was calculated (Δ difference = |Δ n -Δ t0 |, n = 1-6). Temperature oscillations (20 °C to 45 °C/ 45 °C to -5 °C/ -5 °C to 20 °C) were programed only once and repeated using internal loop in the RheoCompass TM software [10,11]. The rate of the temperature change was 5 °C/min.…”

“…The employed D-optimal design has enabled: (1) to analyze simultaneously the effects of key formulation components (emollient and emulsifier concentration) on the critical quality attributes of developed creams (viscosity, yield point, flow point, storage and loss moduli, loss factor, structural change); (2) to discover and estimate significant interactions between tested variables, and (3) to optimize the formulation of natural anti-aging cream in order to provide desired rheological performance and stability. In order to cut down the time needed for physical stability evaluation of developed creams, an original, previously developed and fully described dynamic-mechanical thermoanalysis (DMTA) test was applied as a rapid rheological simulation of accelerated freeze-thaw stability testing [10,11].…”

‘All‐natural’ anti‐wrinkle emulsion serum with Acmella oleracea extract: A design of experiments (DoE) formulation approach, rheology and in vivo skin performance/efficacy evaluation

“…DMTA test, recently developed as a rapid rheological alternative to the routine freeze-thaw stability test [17,18], was employed to monitor (at 20°C) the change of G' max value of each subsequent temperature oscillation cycle in relation to the G' max value of the initial measurement (before temperature oscillation, t 0 ), thus allowing the calculation of Delta (Δ) as a measure of structural change of the investigated sample (Δ n = G' max,n /G' max,t0 , n = 1-6), after which an absolute value of Delta difference was calculated (Δ dif = |Δ n -Δ t0 |, n = 1-6) [17]. The test was performed by employing MCR 302 air-bearing rheometer, in the LVE region, at γ L value for respective model formulations, while ω was set at 10 rad/s.…”