Drop Penetration into Porous Powder Beds

Model of drop infiltration into a thin amphiphilic porous medium

HYPOTHESIS

Water drop infiltration into a thin amphiphilic porous medium is influenced by wettability. Due to the reorganization of amphiphilic matter in contact with water, polar interaction changes the wettability in the bulk porous medium and at the liquid/porous substrate interface. To model out of equilibrium water transfer, we propose a thermodynamics approach derived from Onsager's principle.

MODELING

A 2D macroscopic gradient-dynamics model coupling the drop infiltration and the water dynamic into an amphiphilic porous medium is developed and applied to rhizospheric soil in presence of exopolysaccharides (EPS) as an example. The free energy of the entire drop and porous medium system is defined by taking into account the free surface energy of the water and the effective interaction between the porous matrix and the amphiphilic matter.

FINDINGS

The temporal evolution of the 2D drop volume and contact angle are studied during infiltration using the new formulation. Depending on amphiphilic concentrations and initial water saturation, numerical simulation captures similar scenarios to those described in the literature for powder media, as well as a latency phenomenon occurring in dry soil. The latter has been until now poorly modeled.

Experimental study of liquid drop impact on granular medium: Drop spreading/splashing and particle ejection

The impact of a liquid drop on a granular medium is a common phenomenon in nature and engineering. The possible splashing droplets and ejected particles could pose a risk of pathogen transmission if the water source or granular medium is contaminated. This work studies the liquid drop impact on the granular medium using high-speed photography and considers the effects of liquid properties, drop impact characteristics, and granular medium properties. Four flow regimes, including direct penetration, prompt splashing, spreading, and corona splashing, are observed and a regime map is created to identify their thresholds. The spreading regime can eject a large number of particles, and the corona splashing regime can produce splashing droplets in addition to the ejected particles. For the splashing droplets, their median diameters and velocities are in the ranges 0.11 to 0.21 and 0.15 to 0.37 of the diameter and velocity of the impact drop, and their median splashing angles range from 14° to 27°. Two particle ejection mechanisms are observed, falling squeeze and forward collision, driven by the collapsing and forward spreading of the liquid lamella, respectively. The particles ejected by the latter mechanism have larger ejection velocities, angles and distances from the impact center, which can facilitate their long-range transmission. In addition, the process of spreading and retracting of the lamella formed by the drop impact is also studied, and it is found that the maximum spreading diameter of the lamella is proportional to the crater diameter. These results improve the understanding of the phenomenon after the drop impact on the granular medium and the characteristics of the splashing droplets and ejected particles, contributing to the prediction and risk assessment of contaminated particle transmission.

Perspectives on the Wetting of Solids in Pharmaceutical Systems

PURPOSE

The ability of water and aqueous solutions to wet relatively nonpolar pharmaceutical solids during the processing and administration of solid dosage forms is an important part of development.

RESULTS

Various factors, both fundamental and technological, which are important to wettability are reviewed and analyzed. Initially, the ideal thermodynamic importance of liquid surface tension and solid surface energetics, determined by the contact angle and the polarity of the solid surface, are established. Then, emphasis is placed on various factors that change the surface energetics due to crystal defects, polymorphism, varying Miller Indices, crystal habit, amorphous structure, variable surface concentration of components in a formulation mixture, surface roughness, and complex pore structure. Case studies cover single component systems (APIs and excipients), binary mixtures (amorphous solid dispersions and physical mixtures), multicomponent systems (granules and tablets), as well as disintegration and dissolution of solid oral dosage forms.

CONCLUSIONS

This perspective and analysis indicates the primary importance of understanding and modifying solid surface energetics, surface chemical and physical heterogeneities, and pore structure to promote wettability in pharmaceutical systems.

Inhibiting the Leidenfrost Effect by Superhydrophilic Nickel Foams with Ultrafast Droplet Permeation

Inhibiting the Leidenfrost effect has drawn extensive attention due to its detrimental impact on heat dissipation in high-temperature industrial applications. Although hierarchical structures have improved the Leidenfrost point to over 1000 °C, the current performance of single-scale structures remains inadequate. Herein, we present a facile high-temperature treatment method to fabricate superhydrophilic nickel foams that demonstrate ultrafast droplet permeation within tens of milliseconds, elevating the Leidenfrost point above 500 °C. Theoretical analysis based on the pressure balance suggests that these remarkable features arise from the superhydrophilic property, high porosity, and large pore diameter of nickel foams that promote capillary wicking and vapor evacuation. Compared to solid nickel surfaces with a Leidenfrost temperature of approximately 235 °C, nickel foams nucleate boiling at high superheat, triggering an order of magnitude higher heat flux. The effects of the pore diameter and surface temperature on droplet permeation behaviors and heat transfer characteristics are also elucidated. The results indicate that droplet permeation is dominated by inertial and capillary forces at low and high superheat, respectively, and moderate pore diameters are more conducive to facilitating droplet permeation. Furthermore, our heat transfer model reveals that pore diameter plays a negligible role in the heat flux at high surface temperatures due to the trade-off between effective thermal conductivity and specific surface area. This work provides a new strategy to address the Leidenfrost effect by metal foams, which may promise great potential in steel forging and nuclear reactor safety.

Influence of the Resin System and Sand Type on the Infiltration of 3D-Printed Sand Tools

Binder jetting is a highly productive additive manufacturing (AM) method for porous parts. Due to its cost-effectiveness, it is used for large components and quantities ranging from prototyping to series production. Post-processing steps like sintering or infiltration are common in several applications to achieve high density and strength. This work investigates how 3D-printed sand molds can be infiltrated with epoxy resins without vacuum assistance to produce high-strength molds for thermoforming applications. Specimens 3D-printed from different sand types are infiltrated with resins of different viscosity and analyzed for infiltration velocity and depth. The infiltration velocities corresponded well with the correlation described in Washburn's equation: The resins' viscosities and the saturation level were decisive. Amongst the investigated sand types commonly used in foundries, sand type GS19 was found most suitable for infiltration. However, the sand type proved to be a less relevant influencing factor than the resins' viscosities and quantities applied. Infiltration of topology-optimized 3D-printed sand tools up to a wall thickness of 20 mm for thermoforming applications was found to be feasible.

Over-blending effect of lubricants on capsules manufacturing: a simple and fast wettability technique to predict batch dissolution performance

Mixing/blending is a crucial operation in the manufacturing of solid drug products in the pharmaceutical industry. Although usually described and controlled in specific steps, blending is also inherent to other operations such as transference of materials and equipment feeding systems. This study aimed to investigate a simple and fast wettability testing procedure capable to foresee potential over-blending effects of lubricants occurring during manufacturing of solid dosage forms. An industrial batch blend was submitted to two mixing mechanisms studies (diffusion and shear) during increasing time periods, and the developed wettability testing procedure was applied to assess their impact on blend water uptake. Capsules filled with these blends were tested for dissolution and disintegration. The method was applied to capsules with known dissolution results manufactured at industrial scale. Results demonstrated that processes inducing shear stress led to less permeable blends with consequent retardation on capsules dissolution of at least 35% in the tested timepoints and obtained study metrics above 500 s. Moreover, disintegration testing was not able to detect non-compliant dissolutions, while the proposed wettability testing procedure proved to be able to identify performance failures. Wettability results correlate the effect of mixing mechanisms to capsules dissolution performance, evidencing that this technique can be applied in pharmaceutical industry to evaluate possible over-blending effects.

Development of a Granule Growth Regime Map for Twin Screw Wet Granulation Process via Data Imputation Techniques

Twin screw granulation (TSG) is a continuous wet granulation technique that is used widely across different solid manufacturing industries. The TSG has been recognized to have numerous advantages due to its modular design and continuous manufacturing capabilities, including processing a wide range of formulations. However, it is still not widely employed at the commercial scale because of the lack of holistic understanding of the process. This study addresses that problem via. the mechanistic development of a regime map that considers the complex interactions between process, material, and design parameters, which together affect the final granule quality. The advantage of this regime map is that it describes a more widely applicable quantitative technique that can predict the granule growth behavior in a TSG. To develop a robust regime map, a database of various input parameters along with the resultant final granule quality attributes was created using previously published literature experiments. Missing data for several quality attributes was imputed using various data completion techniques while maintaining physical significance. Mechanistically relevant non-dimensional X and Y axis that quantify the physical phenomena occurring during the granulation were developed to improve the applicability and predictability of the regime map. The developed regime map was studied based on process outcomes and granule quality attributes to identify and create regime boundaries for different granule growth regimes. In doing so breakage-dominant growth was incorporated into the regime map, which is very important for TSG. The developed regime map was able to accurately explain the granule growth regimes for more than 90% of the studied experimental points. These experimental were generated at vastly different material, design, and process parameters across various studies in the literature, this further increases the confidence in the developed regime map.

4D study of liquid binder penetration dynamics in pharmaceutical powders using synchrotron X-ray micro computed tomography

The properties of pharmaceutical powders, and the liquid binder, directly influence the penetration behavior in the wet granulation process of the pharmaceutical industry. Conventional methods encounter challenges in understanding this fast process. In this work, an emerging synchrotron-based X-ray imaging technique (having fast imaging capability) was employed to investigate the internal process from 2D and 3D to real-time (in-situ with ms time intervals) 3D (also considered 4D) perspectives. Two commonly used excipients (lactose monohydrate (LMH) and microcrystalline cellulose (MCC)) were used to make binary mixtures with acetaminophen (APAP) as the active pharmaceutical ingredient (API). Isopropanol and water were employed as liquid binders in the single droplet impact method. Results showed that for most of the mixtures, the porosity increased at higher fractions of APAP. MCC mixtures experienced less agglomeration and more uniform pore distribution than LMH ones, resulting in a faster droplet penetration with isopropanol. Moreover, the imbibition-spreading studies showed that isopropanol penetration in MCC powders followed more unidirectional vertical movement than horizontal spreading. Our results also demonstrated that simultaneous granulation of LMH with water resulted in much slower penetration. This study revealed that synchrotron X-ray imaging can investigate 3D internal pore structures and how they affect the quantitively real-time internal penetration dynamics.

Physicochemical Limitations of Capillary Models Applied to High-Concentration Polymer Solutions

Advances in binder jet printing (BJP) require the development of new binder-powder systems, for example, to increase compatibility with better performance metal alloys or to increase the strength of parts using stronger binders. The dynamics of binder absorption are principally understood through capillary models. However, validation of these models in BJP has focused on variation of powder properties. Using a design-of-experiments approach and an optical observation method to track absorption of droplets, this study tests the influence of fluid properties on absorption time against the predictions of capillary models. Properties specific to polymeric binders, such as molecular weight and entanglement state, are also considered. Capillary models are found to be generally accurate in predicting absorption time in dilute systems; however, these predictions are not accurate for highly concentrated binder solutions. The effect of polymer entanglement becomes prevalent as the solution concentration increases, which can also potentially occur as a result of increased evaporation due to powder bed heating. Specifically, concentrated solutions close to the onset of entanglement will absorb much more slowly than predicted. Future models of BJP systems must account for the possibility of polymer entanglement throughout the absorption process. Improved models will provide a more accurate understanding of the flow and solidification of the binder in the powder, allowing faster development of new binders for improved performance in printing.

The Study of Biological Glue Droplet Impact Behavior of Bioceramic Powders Applied in 3D Printing of Bone Scaffolds

This paper aims to develop a reliable and effective model to investigate the behavior of micron-sized biological glue droplets impacting micron-sized bioceramic powder beds applied to the 3D printing process. It also endeavours to explore the common rules of droplet impact affected by particle size and the wettability of powder, which are supposed to provide process parameters guidance for the application of new materials in 3D printing. Firstly, based on the low impulse impact model, the simplified model was proposed. Then, the observation and simulation experiments of millimeter-scale droplet impacting were carried out under the same conditions to prove the effectiveness of the model. Furthermore, the characterization of a parametric experiment of a 3D printing practice was used to verify the significance and effectiveness of the simulation study method. Lastly, the method was performed to investigate the effect of wettability and particle size of the micron powder on the micron droplet impact. The results showed that the binder powder’s wettability and particle size could directly influence the droplet spreading behavior. The characterization results of samples printed in the simulation-predicted parameter showed that the amount of binder used could be reduced by 38.8~50.1%, while the green strength only lost 17.9~20%. The significance of this simulation method for prediction of 3D printing process parameters was verified.

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

The role of Laplace pressure in the maximal weight of pendant drops

HYPOTHESIS

The value of the maximal weight of a pendant drop formed at the end of a syringe needle is lower than the intensity of the corresponding capillary force. The balance of the external forces applied to the maximal pendant drop must be completed by the overpressure generated by the piston of the syringe. Inside the drop, the Laplace pressure corresponds to this overpressure.

EXPERIMENTS

Pendant drops are made with three liquids and five different needle diameters. The influence of Laplace pressure on the maximal weight is experimentally highlighted by modulating the drop curvatures thanks to glass beads placed at the apex of the pendant drop. Their maximal weight and curvatures are measured by image analysis.

FINDINGS

Experiments confirm that the balance of external forces must be completed by the force acting on the syringe piston. The overpressure on the piston has an impact on the drops via the Laplace pressure. A master curve between the mean curvature and the maximal volume of the pendant drops is observed. This result allows to validate an expression of the maximal weight which integrates the Laplace pressure. This work contributes to a better understanding of the maximal pendant drop properties and beyond, of the capillary phenomenon.

Pharmaceutical applications of powder-based binder jet 3D printing process - A review

Pharmaceutical applications of the 3D printing process have recently matured, followed by the FDA approval of Spritam, the first commercial 3D printed dosage form. Due to being a new technology in the conventional dosage formulation field, there is still a dearth of understanding in the 3D printing process regarding the effect of the raw materials on the printed dosage forms and the plausibility of using this technology in dosage development beyond the conventional ways. In this review, the powder-based binder jet 3D printing (BJ3DP) process and its pharmaceutical applications have been discussed, along with a perspective of the formulation development step. The recent applications of BJ3DP in pharmaceutical dosage development, the advantages, and limitations have further been discussed here. A discussion of the critical formulation parameters that need to be explored for the preformulation study of the solid oral dosage development using the BJ3DP process is also presented.

Using a material database and data fusion method to accelerate the process model development of high shear wet granulation

High shear wet granulation (HSWG) has been wildly used in manufacturing of oral solid dosage (OSD) forms, and process modeling is vital to understanding and controlling this complex process. In this paper, data fusion and multivariate modeling technique were applied to develop a formulation-process-quality model for HSWG process. The HSWG experimental data from both literature and the authors' laboratory were fused into a single and formatted representation. A material database and material matching method were used to compensate the incomplete physical characterization of literature formulation materials, and dimensionless parameters were utilized to reconstruct process variables at different granulator scales. The exploratory study on input materials properties by principal component analysis (PCA) revealed that the formulation data collected from different articles generated a formulation library which was full of diversity. In prediction of the median granule size, the partial least squares (PLS) regression models derived from literature data only and a combination of literature data and laboratory data were compared. The results demonstrated that incorporating a small number of laboratory data into the multivariate calibration model could help significantly reduce the prediction error, especially at low level of liquid to solid ratio. The proposed data fusion methodology was beneficial to scientific development of HSWG formulation and process, with potential advantages of saving both experimental time and cost.

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.

Key factors governing the reconstitution time of high concentration lyophilized protein formulations

Lyophilized protein formulations containing highly concentrated proteins often have long and variable reconstitution times. Reconstitution time is dependent on a number of factors in a complex manner. Furthermore, factors influencing the reconstitution of partially crystalline cakes are reportedly different from those of amorphous cakes. The objectives of this work were to identify the key factors governing reconstitution and understand the mechanisms involved in reconstitution of both amorphous and partially crystalline cakes. Partial crystallinity in the final cake, larger pores and low "concentrated formulation viscosity" (i.e., viscosity near the surface of the dissolving cake) were identified as desirable characteristics for expediting reconstitution. Crystallinity and larger pores dramatically improved wettability and liquid penetration into partially crystalline cakes, ultimately resulting in well dispersed small pieces of partially dissolved cake. The smaller disintegrated cake pieces dissolved faster because of the increased surface area. The amorphous cakes exhibited poorer wettability than partially crystalline cakes. Moreover, the ability of the reconstitution fluid to penetrate the pores, and the resulting cake disintegration was much lower than that observed for partially crystalline cakes. In fact, for some of the amorphous cakes, the reconstitution fluid did not penetrate the cake at all. As a result, the undissolved intact cake or a large cake chunk floated on the reconstitution fluid amidst foam or bubbles generated during reconstitution. Dissolution of the floating cake appeared to proceed via gradual surface erosion where reconstitution time was found to be highly correlated with the viscosity near the surface of the dissolving cake solids. A higher viscosity prolonged reconstitution. Thus, both formulation and processing conditions can be tailored to achieve faster reconstitution. Including a crystallizable excipient proved to be beneficial. Incorporating an annealing step to facilitate crystallization of the crystallizable excipient and to promote larger pores was also found to be advantageous. A viscosity lowering excipient in the formulation could potentially be helpful but needs to be explored further.

Impact of powder-binder interactions on 3D printability of pharmaceutical tablets using drop test methodology

In this study, a pre-screening test has been developed for the binder-jet 3D printing process (BJ3DP) which has been validated using statistical analysis. The pre-screening test or drop test has been adapted from the wet granulation field and modified later on to be used for tablet manufacturing in BJ3DP. Initially, a total of eight powders and ten water-based binder solutions have been introduced in the preliminary test to understand the powder-binder interactions. Afterward, based on the preliminary test results, three blends were developed which had undergone the same drop test. All these powder and binder combinations were then used for 3D printing. The key parameters such as mechanical strength and shape factors of the drop test agglomerates and 3D printed tablets were then compared using multiple linear regressions. Few dimensionless parameters were introduced in this study such as binding capacity and binding index to capture the printability properties of the powders used in this study. Significant relations (p<0.05) were found between the drop test and the BJ3DP process. Application of drop test was carried out to establish a prescreening test, ii) to develop new blend formulations as well as iii) to develop a fundamental understanding of powder-binder interaction during BJ3DP process.

Application of Aquasolv Lignin in ibuprofen-loaded pharmaceutical formulations obtained via direct compression and wet granulation

AS (Aquasolv) Lignin produced via Liquid Hot Water Pretreatment and Enzymatic Hydrolysis has shown potential as an active pharmaceutical ingredient and/or excipient in solid dosage forms. Moreover, lignin is safe to consume and presents antioxidant and antidiabetic capacity, properties that can add to solid dosage forms in pharmaceuticals. This work aimed to evaluate the performance of tablets produced via direct compression and wet granulation when lignin is used in combination with commercial excipients. In order to find optimal tablet performance, different lignin formulations were assessed, and the concentrations were given by extreme vertices mixture design (13 formulations). The blends were composed of AS Lignin, Microcrystalline Cellulose, and Lactose monohydrate and the optimized blend was found to be 14.53 w/w% of disintegrant, 26.57 w/w% of binder and 58.9 w/w% of AS lignin. This proportion was further used to evaluate the performance of lignin-based tablets in drug release, using Ibuprofen as a drug model (50 w/w% and 70 w/w%) and for comparison of direct compression with wet granulation. Direct compressed tablets resulted in higher drug dissolution rates when compared with wet granulation, nevertheless; both tableting techniques showed promising results for lignin. More than 5 formulations tested in this work are compliant with International Pharmacopoeia regulations for solid dosage pharmaceutical forms, thus AS Lignin shows potential to be used as an excipient in pharmaceutical formulations. INDUSTRIAL RELEVANCE: Industrially, AS Lignin appears as promising excipient in the pharmaceutical technologies as well as boost in the biorefining technologies in the following years. Lignin produced is free of sulfur, can be labelled as clean and environmentally-friendly and in this study, was proven this non-cytotoxic AS lignin can be used for excipients and drug carriers. The findings in this paper showed the use of product formulation for life science purposes, thus stressing one of possibilities for lignin valorization in biorefineries.

Probing Ink-Powder Interactions during 3D Binder Jet Printing Using Time-Resolved X-ray Imaging

Capillary-driven ink infiltration through a porous powder bed in three-dimensional (3D) binder jet printing (inkjet printing onto a powder bed) controls the printing resolution and as-printed "green" strength of the resulting object. However, a full understanding of the factors controlling the kinetics of the infiltration remains incomplete. Here, high-resolution in situ synchrotron radiography provides time-resolved imaging of the penetration of an aqueous solution of eythylene glycol through a porous alumina powder bed, used as a model system. A static drop-on-demand inkjet printer was used to dispense liquid droplets onto a powder surface. The subsequent migration of the liquid front and its interactions with powder particles were tracked using fast synchrotron X-radiography in the Diamond Synchrotron, with phase-contrast imaging at a frame rate of 500 Hz. Image processing and analysis reveal that both the time-dependent increment in the wetting area and the propagation of the "interface leading edge" exhibit heterogeneous behavior in both temporal and spatial domains. However, mean infiltration kinetics are shown to be consistent with existing infiltration models based on the Washburn equation modified to account for the spreading of the liquid drop on the powder surface and using a modified term for the bed porosity.

In-line temperature measurement to improve the understanding of the wetting phase in twin-screw wet granulation and its use in process development

Wetting is the initial stage of wet granulation processes during which the first contact between the powder and the liquid occurs. Wetting is a critical step to allow granule growth and consolidation, but also to ensure uniform active pharmaceutical ingredient (API) distribution over all granule size fractions. A physical understanding of the wetting stage is therefore crucial to design a robust granulation process. In twin-screw granulation, wetting is physically separated from granule consolidation, growth, breakage and attrition. The present study used this particularity to investigate the wetting step in such a way that the fundamental mechanisms governing the wetting can be linked and understood. A modified granulator barrel was used allowing the collection of granules immediately after the wetting. A low drug-loaded pharmaceutical formulation containing a poorly soluble and poorly wettable API was used for this investigation. Granules obtained after the wetting zone were analysed for granule size distribution, API distribution over the different size fractions and granule temperature. It was found that "wetting efficiency" (i.e., fraction of powder being nucleated during the wetting stage) could be predicted using an energy balance based on in-line measurement of the granule temperature. Wetting efficiency could moreover be linked to final granule quality attributes (i.e., granule size distribution) at the outlet of the granulator. It was further demonstrated that granule growth and consolidation could only be achieved when complete wetting was achieved in the wetting zone of the granulator. This study suggested a methodology based on in-line temperature measurements to quickly determine wetting efficiency. The described methodology could therefore be used as a tool to gain more fundamental understanding of the wetting stage during twin-screw granulation as well as to define suitable formulation and process ranges for further granulation process development.

Droplet Impact on Suspended Metallic Meshes: Effects of Wettability, Reynolds and Weber Numbers

Liquid penetration analysis in porous media is of great importance in a wide range of applications such as ink jet printing technology, painting and textile design. This article presents an investigation of droplet impingement onto metallic meshes, aiming to provide insights by identifying and quantifying impact characteristics that are difficult to measure experimentally. For this purpose, an enhanced Volume-Of-Fluid (VOF) numerical simulation framework is utilised, previously developed in the general context of the OpenFOAM CFD Toolbox. Droplet impacts on metallic meshes are performed both experimentally and numerically with satisfactory degree of agreement. From the experimental investigation three main outcomes are observed—deposition, partial imbibition, and penetration. The penetration into suspended meshes leads to spectacular multiple jetting below the mesh. A higher amount of liquid penetration is linked to higher impact velocity, lower viscosity and larger pore size dimension. An estimation of the liquid penetration is given in order to evaluate the impregnation properties of the meshes. From the parametric analysis it is shown that liquid viscosity affects the adhesion characteristics of the drops significantly, whereas droplet break-up after the impact is mostly controlled by surface tension. Additionally, wettability characteristics are found to play an important role in both liquid penetration and droplet break-up below the mesh.

Strategies to Reduce Reconstitution Time of Lyophilized Biotherapeutics

Lyophilized biotherapeutics with high protein concentration may have long reconstitution times, which pose an inconvenience to the end user. This report describes 2 approaches that lead to reduction of reconstitution time: (1) incorporation of tert-butyl alcohol (TBA) in the prelyophilization formulation and (2) decreased headspace pressure in the final lyophilized vial. Cakes made from prelyophilization formulations containing a range of TBA concentrations were physically characterized. The stability of antibodies with TBA in the liquid and lyophilized states was evaluated under stress conditions. Reconstitution time was minimized (>50% reduction) at a TBA concentration of 5% w/v. Reduced headspace pressure in the lyophilized vial demonstrated greater than 50% reduction in reconstitution time at headspace pressures of less than 50 Torr.

Synchrotron-based X-ray in-situ imaging techniques for advancing the understanding of pharmaceutical granulation

Wet granulation of powders is a key unit operation in the pharmaceutical industry. Due to the complexity of the granulation process taking place in a short time, observing and measuring the granulation process is challenging with conventional experimental methods. In this study, synchrotron-based X-ray imaging techniques were, for the first time, employed to capture the dynamic granulation process with a single drop impacting method in pharmaceutical powder beds. Five common pharmaceutical excipients, two active pharmaceutical ingredients (APIs) and their mixtures were used as the powder beds. The dynamic interaction between the liquid binder and solid powders were observed from high resolution X-ray images captured. Results show that pharmaceutical powder properties, including particle size, hydrophilicity, and morphology, have significant influence on the dynamic granulation process and the final granular product.

Cratering response during droplet impacts on granular beds

This experimental work focuses on the cratering response of granular layers induced by liquid droplet impacts. A droplet impact results in severe granular layer deformation, crater formation and deposits in the vicinity of the impact center. High-precision three-dimensional imaging of the granular layer surface revealed important characteristics of liquid impacts on granular matter, such as singular asymmetric deformations of the layer. Our analysis also demonstrated that the impact energy and the granular packing, and its inherent compressibility, are not the unique parameters controlling the bed response, for which granular fraction heterogeneities may induce strong variations. Such heterogeneous conditions primarily influence the magnitude but not the dynamics of liquid impacts on granular layers. Finally, a general equation can be used to relate the enery released during cratering to both the impact energy and the compressibility of the granular matter. However, our results do not support any transition triggered by the compaction-dilation regime. Hence, higly detailed numerical simulations could provide considerable insights regarding the remaining questions related to heterogeneous packing conditions and its influence over the bulk compressibility and the compaction-dilation phase transition.

Effect of Biodegradable Binder Properties and Operating Conditions on Growth of Urea Particles in a Fluidized Bed Granulator

Granulation is an important step during the production of urea granules. Most of the commercial binders used for granulation are toxic and non-biodegradable. In this study, a fully biodegradable and cost-effective starch-based binder is used for urea granulation in a fluidized bed granulator. The effect of binder properties such as viscosity, surface tension, contact angle, penetration time, and liquid bridge bonding force on granulation performance is studied. In addition, the effect of fluidized bed process parameters such as fluidizing air inlet velocity, air temperature, weight of primary urea particles, binder spray rate, and binder concentration is also evaluated using response surface methodology. Based on the results, binder with higher concentration demonstrates higher viscosity and higher penetration time that potentially enhance the granulation performance. The viscous Stokes number for binder with higher concentration is lower than critical Stokes number that increases coalescence rate. Higher viscosity and lower restitution coefficient of urea particles result in elastic losses and subsequent successful coalescence. Statistical analysis indicate that air velocity, air temperature, and weight of primary urea particles have major effects on granulation performance. Higher air velocity increases probability of collision, whereby lower temperature prevents binder to be dried up prior to collision. Findings of this study can be useful for process scale-up and industrial application.

Influence of granulation temperature on particle size distribution of granules in twin-screw granulation (TSG)

This study investigated an influence of granulation temperature during twin-screw granulation (TSG) on particle size distributions (PSDs). The influence of the granulation temperature on granule size distributions varied, depending on the liquid to solid (L/S) ratio, the kind of binders, the method of binder addition, and the filler material. The PSD of granules was broad and bimodal at a barrel temperature of 30 °C. Granules size distributions became narrow and second height decreased at high barrel temperature. While the L/S ratio had an effect on the sharpness of granule size distributions, this effect was minor compared to the granulation temperature. Granule size distributions were influenced by binder addition methods. When the binder was added as solution, PSD became broad. In formulations using lactose as filler, PSD became broad and bimodal at 90 °C. Much lactose was dissolved in granulation solution at high temperature, because the solubility of lactose rises significantly with the solution temperature leading to higher effective L/S ratio in the granulator. Hence, granulation was proceeded and large granules were formed. From these results, the granulation temperature is one of important parameters to obtain mono-modal PSD in TSG.