Complementarity of mDSC, DMA, and DRS Techniques in the Study of T_g and Sub-T_g Transitions in Amorphous Solids: PVPVA, Indomethacin, and Amorphous Solid Dispersions Based on Indomethacin/PVPVA

Abstract

Recently, glasses, a subset of amorphous solids, have gained attention in various fields, such as polymer chemistry, optical fibers, and pharmaceuticals. One of their characteristic features, the glass transition temperature (T g ) which is absent in 100% crystalline materials, influences several material properties, such as free volume, enthalpy, viscosity, thermodynamic transitions, molecular motions, physical stability, mechanical properties, etc. In addition to T g , there may be several other temperaturedependent transitions known as sub-T g transitions (or β-, γ-, and δ-relaxations) which are identified by specific analytical techniques. The study of T g and sub-T g transitions occurring in amorphous solids has gained much attention because of its importance in understanding molecular kinetics, and it requires the combination of conventional and novel characterization techniques. In the present study, three different analytical techniques [modulated differential scanning calorimetry (mDSC), dynamic mechanical analysis (DMA), and dielectric relaxation spectroscopy (DRS)] were used to perform comprehensive qualitative/quantitative characterization of molecular relaxations, miscibility, and molecular interactions present in an amorphous polymer (PVPVA), a model drug (indomethacin, IND), and IND/PVPVA-based amorphous solid dispersions (ASDs). This is the first ever reported DMA study on PVPVA in its powder form, which avoids the contribution of solvent to the mechanical properties when a selfstanding polymer film is used. A good correlation between the techniques in determining the T g value of PVPVA, IND, and IND/ PVPVA-based ASDs is established, and the negligible difference (within 10 °C) is attributed to the different material properties assessed in each technique. However, the overall T g behavior, the decrease in T g with increase in drug loading in ASDs, is universally observed in all the above-mentioned techniques, which reveals their complementarity. DMA and DRS techniques are used to study the different sub-T g transitions present in PVPVA, amorphous IND, and IND/PVPVA-based ASDs because these transitions are continued...

Continuous Manufacturing of Solvent-Free Cyclodextrin Inclusion Complexes for Enhanced Drug Solubility via Hot-Melt Extrusion: A Quality by Design Approach

“…A polymer concentration below 5% resulted in high torque, halting the extrusion process, while a concentration above 30% w / w did not significantly improve IBU solubility or the dissolution rate compared to a 30% w / w polymer concentration. The extrusion temperature ranged from 115 to 145 °C, since 115 °C is required to liquefy the polymer (for PVP VA-64 the loss tangent (tan δ) = 1 at 115 °C), while 145 °C was chosen as the upper limit because IBU tends to evaporate above 150 °C [ 38 , 39 , 40 , 41 ]. The screw speed was selected between 15 and 45 rpm since the higher screw speed (>50 rpm) resulted in a high torque >70%.…”

Construction of a Viscoelastic Model of Human Cancellous Bone in Alveolar Bone Based on Bone Mineral Density Distribution

“…However, when BMD increased by 53%, the average change rates of storage modulus and loss modulus were about 281% and 82%, respectively. The increase in BMD was the result of the increase in the number of trabecular bones with complex pores in CBAB (Figure 4) and the number and length of its internal molecular chains [11]. Therefore, the storage modulus was increased and the elastic properties were improved.…”

“…The BMD range of CBAB in different tooth regions was measured to be 0.604 g/cm 3 to 0.926 g/cm 3 based on micro-CT scanning. DMA described the properties of materials through the state of molecular motion [11]. Storage modulus was the energy storage capacity of viscoelastic materials under a cyclic alternating load.…”

“…Three basic material parameters were obtained as a function of BMD to develop an isotropic crushable foam (CF) model. Dynamic mechanical analysis (DMA) describes the properties of materials through the state of molecular motion [11]. This has been widely used to characterize the viscoelastic properties of composites and biomaterials [12].…”

Evaluation of Different Thermoanalytical Methods for the Analysis of the Stability of Naproxen-Loaded Amorphous Solid Dispersions

“…Overall, it can be stated about the methods suitable for T g determination that as their operation principles differ, the sensitivity and resolution are also distinct. For this reason, the joint application of more analytical techniques can contribute to an in-depth understanding of complex molecular processes in ASDs [40,41]. The better the behavior of the ASDs under development is known, the better the physical stability of the amorphous phase can be estimated.…”