An assessment of substrate-binder interactions in model wet masses. 1: Mixer torque rheometry

Wet granulation end point prediction using dimensionless numbers in a mixer torque rheometer: Relationship between capillary and Weber numbers and the optimal wet mass consistency

The optimal wet mass consistency during wet granulation is often determined using the hand squeezing test. In this study, torque values recorded inside the wet mass were measured using a mixer torque rheometer (MTR) via multiple additions of liquid. The main objective of this work was to predict the optimal wet mass consistency of pharmaceutical powders using the modified capillary (Ca^∗) and Weber (We^∗) dimensionless numbers. The results show that the optimal wet mass consistency versus Ca^∗ (or We^∗) can be fitted with a power-law function, whereas the improved capillary number Ca^' proposed in this work gives different relationships and behaviors depending on the spreadability and wettability of the blend. The wettability was obtained by measuring the contact angle between the liquids and the pharmaceutical powders. The surface free energy and the polar and dispersive parts of a liquid's surface energy were obtained from Young's equation and the Owens-Wendt-Rabel-Kaelble (OWRK) model. This study demonstrated the importance of the interfacial energy σ_b-s and the pore radius, R_pore in the establishment of a dimensionless number, Ca^∗, that can satisfactorily predict with an R² of 0.80, the optimal wet mass consistency of pharmaceutical powders measured by the MTR.

Formation of Indomethacin-Saccharin Cocrystals during Wet Granulation: Role of Polymeric Excipients

Formulation of a cocrystal into a solid pharmaceutical dosage form entails numerous processing steps during which there is risk of dissociation. In an effort to reduce the number of unit operations, we have attempted the in situ formation of an indomethacin-saccharin (INDSAC) cocrystal during high-shear wet granulation (HSWG). HSWG of IND (poorly water-soluble drug) and SAC (coformer), with polymers (granulating agents), was carried out using ethanol as the granulation liquid and yielded INDSAC cocrystal granules. Therefore, cocrystal formation and granulation were simultaneously accomplished. Our objectives were to (i) evaluate the influence of polymers on cocrystal formation kinetics during wet granulation and (ii) mechanistically understand the role of polymers in facilitating the cocrystal formation. Polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), and polyethylene oxide (PEO) were chosen to investigate the influence of soluble polymers. The cocrystal formation kinetics was influenced by the polymer (PVP < HPC < PEO) and its concentration. The interaction of the polymer with cocrystal components inhibited the cocrystal formation. Complete cocrystal formation was observed in the presence of PEO, a polymer which does not interact with IND and SAC.

Impact of Humidity on Silica Nanoparticle Agglomerate Morphology and Size Distribution

The effect of humidity on flame-made metal oxide agglomerate morphology and size distribution is investigated, for the first time to our knowledge, and compared to that on soot, which has been widely studied. Understanding the impact of humidity on such characteristics is essential for storage, handling, processing, and eventual performance of nanomaterials. More specifically, broadly used agglomerates of flame-made silica nanoparticles are humidified at various saturation ratios, S = 0.2-1.5, and dried before characterization with a differential mobility analyzer (DMA), an aerosol particle mass (APM) analyzer, and transmission electron microscopy. At high humidity, the constituent single and/or aggregated (chemically bonded) primary particles (PPs) rearrange to balance the capillary forces induced by condensation-evaporation of liquid bridges between PPs. Larger agglomerates restructure more than smaller ones, narrowing their mobility size distribution. After humidification at S = 1.5 and drying, agglomerates collapse into compact structures that follow a fractal scaling law with mass-mobility exponent D_fm = 3.02 ± 0.11 and prefactor k_m = 0.27 ± 0.07. This critical S = 1.5 for silica agglomerates is larger than the 1.26 obtained for soot because of the hydrophilic surface of silica that delays water evaporation. The relative effective density, ρ_eff/ρ, of collapsed agglomerates becomes invariant of mobility diameter, d_m, similar to that of fluidized and spray-dried granules. The average silica ρ_eff/ρ = 0.28 ± 0.02 is smaller than the 0.36 ± 0.04 measured for the humidified-dried soot because of the larger size of silica aggregates, d_m/ d_p, and number of constituent primary particles, n_p, of diameter d_p. This is verified by tandem-DMA (TDMA) measurements, yielding maximum d_m = 3 d_p or 5 d_p and n_p = 13 or 36 for the soot or silica aggregates studied here, in good agreement with those reported from microscopy and high-pressure agglomerate dispersion. A scaling law relating the initial d_m,o to d_m, D_fm, and k_m after condensation-drying is developed. The mass-mobility relationship of collapsed silica and soot agglomerates obtained by combining this law with fast TDMA measurements is in excellent agreement with that measured by the direct, but tedious, DMA-APM analysis.

Application of near-infrared spectroscopy to optimize dissolution profiles of tablets according to the granulation mechanism

We developed a method for the optimization of dissolution properties of solid oral dosage forms manufacturing using high shear wet granulation (HSWG) by using near-infrared spectroscopy (NIRS) with chemometrics in small-scale experiments. The changes in rheology and NIR spectra of the granules were monitored to verify the granulation mechanism and determine the suitable water amount for model formulation during the HSWG. Tablets were manufactured by altering the added water amount to investigate the impact of the granulation mechanism on drug product qualities. Model formulation granules were prepared with 10-20% w/w water in a funicular state, corresponding to the plateau region in score plots obtained by principal component analysis (PCA). The dissolution rate of model formulation tablets manufactured with more than 20% w/w of water was significantly delayed while tablets manufactured with 15% w/w water showed 100% dissolution at 15 min. NIRS and PCA are applicable to the optimization of dissolution properties via the process understanding of HSWG at the early formulation development stage and could facilitate drug development.

A quality by design approach to scale-up of high-shear wet granulation process

High-shear wet granulation is a complex process that in turn makes scale-up a challenging task. Scale-up of high-shear wet granulation process has been studied extensively in the past with various different methodologies being proposed in the literature. This review article discusses existing scale-up principles and categorizes the various approaches into two main scale-up strategies - parameter-based and attribute-based. With the advent of quality by design (QbD) principle in drug product development process, an increased emphasis toward the latter approach may be needed to ensure product robustness. In practice, a combination of both scale-up strategies is often utilized. In a QbD paradigm, there is also a need for an increased fundamental and mechanistic understanding of the process. This can be achieved either by increased experimentation that comes at higher costs, or by using modeling techniques, that are also discussed as part of this review.

Interaction between Binder and Powder in Injection Moulding of 316L Stainless Steel

Owing to several steps involved in metal injection moulding (MIM) process, it is important to understand the interactions between metal powder and binder mixture particularly during mixing, injection moulding and debinding. A polar organic compound generally forms hydrogen bonds more readily with metal powder because of acid-base interactions. In this study, the interaction of local binder system comprised of; palm stearin (PS) and thermoplastic natural rubber (TPNR) with conventional binder; polyethylene (PE), polypropylene (PP) and paraffin wax (PW) and mixed with 316L stainless steel powder were investigated. The results showed that all the binder have high interaction with 316L stainless steel that make, the resulting the bonding sufficiently strong and suitable for MIM process. Keywords: Chemical interaction, Injection Moulding, Binder, Rheology

Upgrading wet granulation monitoring from hand squeeze test to mixing torque rheometry

With over 50 years of research in granulation technology, however more research is required to elucidate this widely applicable technology. Wetting phenomena could influence redistribution of individual ingredients within a granule according their solubility and also could affect the drying processes. Binder selection for a particular system is quite often empirical and dependent on the skills and experience of the formulator. Hand squeeze test was and still the main way for determination of wet granulation end point, but it is subjected to individual variation. It depends mainly on operator experience, so it is not possible to be validated. Literature reveals a variety of advanced monitoring techniques following up different wet massing stages. Torque measurement has been proved to be the most reliable control method as its tight relation to mass resistance. Many reports showed successful applications of mixing torque rheometer (MTR) for monitoring the wet massing procedure and scale up in addition to some preformulation applications. MTR as a new approach allows formulators to select a liquid addition range where the granule growth behavior is more predictable.

The effect of the physical states of binders on high-shear wet granulation and granule properties: a mechanistic approach toward understanding high-shear wet granulation process. Part II. Granulation and granule properties

The objective is to provide mechanistic understanding of a preferred wet granulation process that a binder is added in a dry state. Blends of CaCO(3) and binders were prepared and used as model systems, and they were exposed to either 96% RH (rubbery/solution state) or 60% RH (glassy state) at room temperature to control the physical state of the binders, followed by high-shear granulation and particle size measurement. The blends of PVP K12, PVP K29/32, and HPC showed a significant increase in particle size after exposure to 96% RH. An increase of aspect ratio was also observed for the blend of HPC. In contrast, the blends being exposed to 60% RH did not exhibit any increase in particle size or aspect ratio. Regarding the effect of binder molecular weight on the mechanical strength of granules, granules of PVP K29/32 had higher strength than granules of PVP K12. This can be explained using polymer entanglement theory, in which the degree of polymerization (DP) of (N ∼ 440-540) of PVP K29/32 is above the critical value (N(c)  ∼ 300-600) for entanglement; while DP of PVP K12 (N ∼ 20-30) is below it. Finally, a water sorption-phase transition-diffusion induced granule growth model for granulation has been suggested.

Predictive and correlative techniques for the design, optimisation and manufacture of solid dosage forms

There is much interest in predicting the properties of pharmaceutical dosage forms from the properties of the raw materials they contain. Achieving this with reasonable accuracy would aid the faster development and manufacture of dosage forms. A variety of approaches to prediction or correlation of properties are reviewed. These approaches have variable accuracy, with no single technique yet able to provide an accurate prediction of the overall properties of the dosage form. However, there have been some successes in predicting trends within a formulation series based on the physicochemical and mechanical properties of raw materials, predicting process scale-up through mechanical characterisation of materials and predicting product characteristics by process monitoring. Advances in information technology have increased predictive capability and accuracy by facilitating the analysis of complex multivariate data, mapping formulation characteristics and capturing past knowledge and experience.

Starch–dextrin mixtures as base excipients for extrusion–spheronization pellets

Extrusion-spheronization pellets are generally produced with microcrystalline cellulose (MCC) as the principal excipient, giving rise to particles of very high quality. A number of alternative excipients have been proposed and evaluated, mostly other cellulose derivatives (e.g. different grades of Avicel), or mixtures of MCCs and other excipients. In the present study, we evaluated the possible use of starch+agglutinant mixtures as principal excipients for extrusion-spheronization pellets, with the aim of producing pellets with more suitable properties for certain types of release. We first characterized the different excipients in terms of morphometry and basic physical properties. Subsequently, torque-rheometry was used to characterize the rheology of wetted masses of the different excipients and excipient mixtures, with the aim of determining optimal amount of wetting agent (water). We also evaluated the water absorption and water retention capacities of each excipient. In view of the results obtained, we produced pellets with the different starch+agglutinant mixtures (but without drug), and used image analysis to characterize pellet morphology. Our results show that some of the mixtures-notably starch (corn starch or wheat starch)+20% white dextrin-gave high-quality pellets with good size and shape distributions. In addition, the properties of the different materials tested suggest that it may be possible to obtain pellets with very different properties.

Study of effect of excipient source variation on rheological behavior of diltiazem HCl-HPMC wet masses using a mixer torque rheometer

In the wet massing of powders and powder blends, the rheological behavior of the wet powder masses not only plays a critical role in the unit process but also influences the attributes of the product. The physical properties of the powder excipients, such as particle size and size distribution, shape, surface area, bulk and tapped density and surface morphology, are a major source of variability in the rheological behavior of wet powder masses and the quality attributes of the final product. The objective of the present investigations was to study the rheological behavior of wet masses containing hydroxypropyl methylcellulose (HPMC) obtained from two sources (Methocel from Dow and Pharmacoat from Shin-Etsu) using a mixer torque rheometer. In order to simulate a real formulation, diltiazem HCl (DTZ) (40% loading) was used as part of the substrate powder mass. Hydroxypropyl cellulose (HPC) was used as the binder. Since HPMC is water-soluble, isopropyl alcohol (IPA) was used as the wet massing liquid. The rheological behavior of the wet powder masses was studied as a function of mixing time and amount of wet massing liquid (IPA). The rheological profiles obtained for DTZ-Methocel and DTZ-Pharmacoat exhibited same magnitude for mean torque, however, for DTZ-Pharmacoat the peak was more extended than that for DTZ-Methocel. The extended peak for DTZ-Pharmacoat indicated that the wet mass will stay suitable during the process for larger quantities of the wet massing liquid before turning into paste and becoming unsuitable for the process as compared with the DTZ-Methocel system. The mixing kinetics of the two powder systems appeared to be quite different. These differences in the rheological behavior of the wet masses may be attributed to the difference in the particulate and surface properties of the two HPMCs. Some of the properties of the two HPMCs, such as particle size and size distribution, surface area, surface morphology and DSC thermograms, explain the difference observed in their rheological behavior. The difference in the rheological profiles of the two DTZ-HPMC systems indicated superiority of Pharmacoat over Methocel considering their wet massing behavior.

Agglomeration state and migration of drugs in wet granulations during drying

Migration of drugs was studied during drying of wet granules, agglomerated at pendular and funicular state (S(3) and S(4)). Granulating liquids of different viscosity (2.5 and 7.5 mPa s) and drugs and diluents of different solubility and wettability were employed and correlation was sought between distribution of the liquid, wet kneading parameters (torque and liquid consumption S%), solid-liquid interactions (work of adhesion and spreading coefficients) and the migration of drugs. It was found that drug migration, expressed as CV% of its content, was strongly dependent on the type of diluent. Also, the type of diluent exerted the strongest effect on torque and liquid consumption during wet kneading and a significant one on moisture content of the final granulations. Viscosity of the granulating liquid and molecular weight of the binder had no effect on liquid consumption but viscosity had a significant one on drug migration. Significant linear relationships were found between spreading coefficients and the liquid consumption (S%) at the mid-state of funicular agglomeration (S(3)+S(4))/2 or the torque at the capillary state S(5). Migration of drug was remarkably lower for drying in the microwave oven and increased from the pendular (S(3)) to the funicular (S(4)) agglomeration state when drying in conventional oven was applied. Linear relationships were found between migration (CV%) and the spreading coefficient of liquid on solid, lambda(LS), for the low and the high viscosity levels of the granulating liquid, with r=0.965, P=0.05 and r=0.901, P=0.10, respectively. Also, a general linear relationship (r=0.903 and P=0.002) accommodating all experimental data was found between migration (CV%) and the ratio lambda(LS)/viscosity. Drug migration increases with solubility and may become a problem in a range higher than 1 g in 148-400 ml of granulating liquid.

Effects of physical properties of powder particles on binder liquid requirement and agglomerate growth mechanisms in a high shear mixer

A study was performed in order to elucidate the effects of the physical properties of small powder particles on binder liquid requirement and agglomerate growth mechanisms. Three grades of calcium carbonate having different particle size distribution, surface area, and particle shape but approximately the same median particle size (4-5 microm), were melt agglomerated with polyethylene glycol (PEG) 3000 or 20,000 in an 8-l high shear mixer at three impeller speeds. The binder liquid requirement was found to be very dependent on the packing properties of the powder, a denser packing resulting in a lower binder liquid requirement. The densification of the agglomerates in the high shear mixer could be approximately predicted by compressing a powder sample in a compaction simulator. With the PEG having the highest viscosity (PEG 20,000), the agglomerate formation and growth occurred primarily by the immersion mechanism, whereas PEG 3000 gave rise to agglomerate growth by coalescence. Powder particles with a rounded shape and a narrow size distribution resulted in breakage of agglomerates with PEG 3000, whereas no breakage was seen with PEG 20,000. Powder particles having an irregular shape and surface structure could be agglomerated with PEG 20,000, whereas agglomerate growth became uncontrollable with PEG 3000. When PEG 20,000 was added as a powder instead of flakes, the resultant agglomerates became rounder and the size distribution narrower.

Power consumption profiles in high-shear wet granulation. II: Predicting the overwetting point from a spreading energy

Granulation is an important process in the pharmaceutical industry for the preparation of solid dosage forms. For high-shear wet granulation, the process endpoint is monitored using the device power consumption. However, granulation is very sensitive to variations in the feed product physicochemical properties and, in some cases, power consumption profiles can not be used for process control. In this paper, a model is proposed to predict the granulation overwetting point from the spreading energy of the liquid binder on the powder. This energy is independently calculated from measurements of the powder true surface area, liquid binder surface tension, and liquid contact angle on the powder surface.

Evaluation of melt agglomeration properties of polyethylene glycols using a mixer torque rheometer

Lactose was melt agglomerated in a mixer torque rheometer with polyethylene glycol (PEG) 2000, 3000, 6000, 8000, 10 000, or 20 000 as meltable binder. A longer massing time caused an increase in mean torque until a maximum value after which the torque decreased. A smaller particle size of the PEG gave rise to a faster initial rise in mean torque. The higher viscosity of the PEG 20 000 resulted in a higher mean torque, whereas no clear difference in mean torque was obtained with the other PEGs. The binder concentration could be varied within a rather wide range without causing overwetting, the range being wider with PEG 3000 than with PEG 20 000. The mean torque values obtained were found to be related to the liquid saturation of the agglomerates. The reproducibility of the experiments was found to be very dependent on the experimental conditions, the highest binder viscosities and binder concentrations giving rise to a poor reproducibility. The results were compared with a few melt agglomeration experiments with PEG 3000 in a high shear mixer. The mixer torque rheometer was found not to be suitable for predicting melt agglomeration properties in the high shear mixer because of a marked difference in the shear forces in the two mixers.

Characterization of wet powder masses with a mixer torque rheometer. 3. Nonlinear effects of shaft speed and sample weight

We used mixer torque rheometry to examine the effects of shaft speed and sample weight on the rheological behavior of a model wet mass consisting of microcrystalline cellulose and water. Both variables contribute differently to the measured parameters of mean torque and torque range (amplitude). For small weights, the effect of shaft speed is small, but for large weights, shaft speed has a greater effect. For large sample weights, the effect of shaft speed on measured mean torque can be modeled by the Herschel-Buckley model originally developed for concentrated dispersions, enabling yield stresses and viscosities to be calculated. The data generated compare favorably with those measured previously by capillary rheometry.