Pro rheometer

In order to detect some criticities in semisolid formulation, such as high pH and silicone presence, an appropriate emulsion was prepared. Silicone chemistry plays a key role in personal care and cosmetic formulations due to a multifunctional set of properties [21 ,22 (link)]. Table 1 shows the qualitative and quantitative composition of the formulation intended to fill the final packaging and used as the simulant. Phases A and B were stirred separately. Phase B was added to phase A using a Silverson SL2T High Shear Laboratory Stirrer Mixer (Silverson Machines Ltd., Chesam, UK) for 10 min, 6700 rpm, and at 50 °C.
The formulation was stored overnight at 25 °C. Successively, pH organoleptic characteristics and rheological properties were evaluated. The pH measurement was performed using a pH meter model 3510 (Jenway, Staffordshire, UK), and viscosity properties were evaluated using a Kinexus Pro+ rheometer (Malvern, Worcestershire, UK), equipped with Peltier Plate Cartridge, with cone geometry CP40/4.

Evaluation of viscoelastic properties was performed using a Kinexus Pro Rheometer (Malvern, UK). Using Parallel-plate geometry (20 mm×65 mm), gels were placed onto the lower plate of the rheometer, while the higher plate oscillated on the sample at a gap size of 1 mm. For each of the samples, small deformation linearity (linear viscoelastic region) was identified via strain measurement under the application of controlled stress sweeps. Optimum conditions such as shear strain at 1.0% of the angular single frequency (1 Hz) were selected. All measurements were performed at a temperature of 37±0.02°C (n = 4, from two independent experiments). Shear modulus (G′) measurements were derived from G′/G″-frequency (ω) plots produced by single frequency measure. Data was analyzed using proprietary software (rSpace).

The investigation of the rheologic behavior was performed through dynamic oscillatory measurements using a Kinexus Pro rheometer equipped with a Peltier element for precise temperature control, performed at 25 °C. Samples of hydrogel hydrated at equilibrium (d = 20 mm, h = 1.5 mm) were placed on the bottom plate of the rheometer, and parallel-plate geometry was used. Sand paper was used on the plates to avoid slipping. Dehydration was prevented using a water lock. The linear viscous region was established through amplitude sweep measurements, and subsequently a frequency sweep analysis was performed in the frequency range of 0.01–100 Hz at a constant stress value of 10 Pa. The storage and loss moduli (G’ and G”, respectively) were plotted in a logarithm graph.

Fully formed hydrogel samples (4 h gelation) were swollen in a sink of PBS and incubated at 37 °C for two days prior to forming rheological measurements. A Kinexus Pro rheometer from Malvern was used to obtain the magnitude of the (complex) dynamic shear modulus (|G*|) at an oscillation frequency of 1 Hz and a strain of 0.5 % at room temperature (21 °C). Parallel plate geometry with a diameter of 20 mm and a sample gap of 1.0 mm was used. All experiments were performed within the linear viscoelastic region.

Rheological and viscoelastic properties of acellular calcium-crosslinked and double crosslinked hydrogels were determined using a Kinexus Pro rheometer (Malvern, Malvern, UK). Rotational shear-viscosity measurements were carried out at 25 °C using a shear ramp test (1–1000 s⁻¹, 2 min) after applying one loading cycle with 2 min intervals, before acquiring the rheological data. The yield stress, which is the minimum shear stress required to initiate flow, was analyzed by applying a shear stress ramp (1–100 Pa, 2 min) with plate–plate geometry (0.5 mm) at 25 °C. Viscoelastic properties of double crosslinked hydrogels equilibrated in culture medium at 5% CO₂ and 37 °C for 24 h were determined by testing 4 mm diameter samples in a humidified environment at 37 °C. Samples were compressed at 20% of their initial height and strain amplitude sweeps were conducted from 0.1 to 100% at 0.1 Hz, while frequency sweeps were carried out from 0.01 to 10 Hz at 1% strain (within the linear viscoelastic region).

Stress relaxation studies were conducted on an ARES/RFS II Rheometer in parallel-plate configuration. The tests were performed in a strain control mode (1%) at specified temperatures. Activation energy of the exchange reaction, E_a,r, was estimated from: $ln{\tau }^{*}\text{=}ln\left(A\right)\text{+}\frac{E_{a,r}}{RT}$ where τ^* is the characteristic relaxation time defined as the time required for G/G₀ = 1/e; G₀, R and T are the initial relaxation modulus, universal gas constant and absolute temperature, respectively.
Dynamic oscillatory frequency sweeps of modulus were carried out under the strain amplitude 1% at 60–140 °C from 100 to 0.0001 or 0.001 Hz by Kinexus pro+ Rheometer.