Granule Porosity Research Articles

Evaluation of the influence of material properties and process parameters on granule porosity in twin-screw wet granulation

In recent years, continuous twin-screw wet granulation (TSWG) is gaining increasing interest from the pharmaceutical industry. Despite the many publications on TSWG, only a limited number of studies focused on granule porosity, which was found to be an important granule property affecting the final tablet quality attributes, e.g. dissolution. In current study, the granule porosity along the length of the twin-screw granulator (TSG) barrel was evaluated. An experimental set-up was used allowing the collection of granules at the different TSG compartments. The effect of active pharmaceutical ingredient (API) properties on granule porosity was evaluated by using six formulations with a fixed composition but containing APIs with different physical–chemical properties. Furthermore, the importance of TSWG process parameters liquid-to-solid (L/S) ratio, mass feed rate and screw speed for the granule porosity was evaluated. Several water-related properties as well as particle size, density and flow properties of the API were found to have an important effect on granule porosity. While the L/S ratio was confirmed to be the dictating TSWG process parameter, granulator screw speed was also found to be an important process variable affecting granule porosity. This study obtained crucial information on the effect of material properties and process parameters on granule porosity (and granule formation) which can be used to accelerate TSWG process and formulation development.

In situ wet pharmaceutical granulation captured using synchrotron radiation based dynamic micro-CT.

Synchrotron radiation based dynamic micro-computed tomography (micro-CT) is a powerful technique available at synchrotron light sources for investigating evolving microstructures. Wet granulation is the most widely used method of producing pharmaceutical granules, precursors to products like capsules and tablets. Granule microstructures are known to influence product performance, so this is an area for potential application of dynamic CT. Here, lactose monohydrate (LMH) was used as a representative powder to demonstrate dynamic CT capabilities. Wet granulation of LMH has been observed to occur on the order of several seconds, which is too fast for lab-based CT scanners to capture the changing internal structures. The superior X-ray photon flux from synchrotron light sources makes sub-second data acquisition possible and well suited for analysis of the wet-granulation process. Moreover, synchrotron radiation based imaging is non-destructive, does not require altering the sample in any way, and can enhance image contrast with phase-retrieval algorithms. Dynamic CT can bring insights to wet granulation, an area of research previously only studied via 2D and/or ex situ techniques. Through efficient data-processing strategies, dynamic CT can provide quantitative analysis of how the internal microstructure of an LMH granule evolves during the earliest moments of wet granulation. Here, the results revealed granule consolidation, the evolving porosity, and the influence of aggregates on granule porosity.

Modelling the effect of L/S ratio and granule moisture content on the compaction properties in continuous manufacturing

The pharmaceutical field is currently moving towards continuous manufacturing pursuing reduced waste, consistency, and automation. During continuous manufacturing, it is important to understand how both operating conditions and material properties throughout the process affect the final properties of the product to optimise and control production. In this study of a continuous wet granulation line, the liquid to solid ratio (L/S) and drying times were varied to investigate the effect of the final granule moisture content and the liquid to solid ratio on the properties of the granules during tabletting and the final tensile strength of the tablets. Both variables (L/S and granule moisture) affected the tablet tensile strength with the moisture content having a larger impact. Further analysis using a compaction model, showed that the compactability of the granules was largely unaffected by both L/S and moisture content while the compressibility was influenced by these variables, leading to a difference in the final tablet strength and porosity. The granule porosity was linked to the L/S ratio and used instead for the model fitting. The effect of moisture content and granule porosity was added to the model using a 3d plane relationship between the compressibility constant, the moisture content and porosity of the granules. The tablet tensile strength model, considering the effect of moisture and granule porosity, performed well averaging a root mean squared error across the different conditions of 0.17 MPa.

The Architecture, Nature, and Mystery of Starch Granules. Part 1: A Concise History of Early Investigations and Certain Granule Parts

AbstractA review with 303 references. Part 1 of a summarized history of investigations into the structures of starch granules. It has been a little more than three centuries since scientific studies of starch granules began. During the first 200 years after the microscope is first used to study them, many ideas are put forth about the makeup, properties, and behaviors of starch granules and how they are formed. This review of the unraveling of the mystery of the architecture of starch granules presents the progression of these ideas during this period and aspects of granule structural analysis since then. It is divided into seven sections: Introduction; Overview of early history, The outer layer, Inner layers/growth rings, Granule growth, Granule crystallinity, and Granule porosity.

Physical characterization of oxygenic photogranules

This study investigated hydrodynamic properties of oxygenic photogranules (OPGs) generated in a sequencing batch reactor (SBR) treating wastewater without aeration and OPGs cultivated under hydrostatic conditions and used to seed an SBR reactor. Using isopycnic centrifugation the average density of OPGs was found to be 1037 kg/m3 and 1050 kg/m3 for the reactor OPGs and hydrostatic OPGs, respectively. The reactor OPGs had measured settling velocities in the range of 0.001–0.021 m/s while the hydrostatic OPGs had higher velocities, up to 0.07 m/s. The estimated porosity of reactor granules was 86 % while that of hydrostatic granules was 81 %. The porosity and settling velocities of reactor OPGs showed a general decrease with increasing granular size. In contrast, the porosity of the hydrostatic OPGs showed low correlations with granular size while their settling velocities decreased with increasing diameter (0.6–1.4 mm). These physical parameters reflect OPGs amenability to rapid solids separation during wastewater treatment. Moreover, the high porosity and low permeability reflect the microbial mobility with increasing size to optimize functionality especially related to motile filamentous cyanobacteria. Strategies utilizing size based bioreactor operations for different treatment objectives and optimized agitation minimizing energy use towards environmental stewardship in treatment can also be achieved.

The effect of granules characters on mechanical properties of press-coated tablets: A comparative study

The aim of this study was to investigate the correlation between critical granules characters (including particle size, surface roughness, and apparent porosity) and mechanical properties of press-coated tablets. Granules of a model formulation were prepared through Roll Compaction Granulation (RCG), High Shear Granulation (HSG), and Fluidized Bed Granulation (FBG) to prepare granules with different surface roughness and apparent porosity. The surface roughness and porosity of granules had a significantly greater effect on mechanical properties than the particle size of granules. Whether for brittle or plastic materials, FBG granules with the roughest surface and the greatest apparent porosity exhibited the best compression properties. The elastic recovery test, the interlayer adhesion forces study, the break pattern test, and the X-ray microcomputed tomography investigation suggested that granules with great apparent porosity and rough surfaces could contribute to the production of stable press-coated structures. Moreover, for press-coated tablets prepared using granules, the proper granules in the coat layer could eliminate the side effect of the rigid core on the mechanical strength. The above understandings will be conducive to the selection of compatible and appropriate granules characters, which can enhance mechanical properties and extend the application of press-coated tablets.

Surface microstructure of rice starch is altered by removal of granule-associated proteins

The morphological characteristics and surface structure of waxy, low-amylose and high-amylose rice starches before and after extraction of granule-associated proteins (SGAPs), especially surface-proteins and channel-proteins, were systematically investigated. Removal of SGAPs on surfaces and in channels of granules without significant change in morphological structure was evidenced by microscope images of granules and confocal laser scanning microscope images of fluorescamine-stained and 8-amino-1,3,6-pyrenetrisulfonic acid-stained granules. For nano-scale surface features, atomic force microscopy showed that a more roughened surface occurred on granules after removal of SGAPs, meanwhile, specific surface area, total pore volume, surface and average diameter of pores increased in granules. The results gave direct evidence that extraction of SGAPs induced larger surface area and increased size of channels (pores) in starch granules. Once SGAPs have been removed, dextran-probes could quickly diffuse into channels and cavities, thus probe-diffusion of the granular matrix was accelerated. Although waxy rice starch had the lowest SGAPs content, the change of dextran diffusion into its granule was the greatest of three tested rice starches when SGAPs were removed. The surface texture and porosity of the starch granules before and after removal of SGAPs were significantly correlated to the pasting properties of starch, providing a new insight into the SGAPs-surface microstructure-function relationship of starch granules.

Ammonium Nitrate/Fuel Oil Vapour Detection with Conducting Polymer Percolation Network Sensors

Ammonium nitrate mixed with fuel oil (ANFO) is one of the most commonly used materials for improvised explosive devices (IEDs). ANFO detection is challenging because ANFO itself is not volatile. However, ammonium nitrate (AN) slowly decomposes into NH3 and HNO3.1 Additionally, fuel oils such as diesel are omnipresent and can cause a high false positive rate. Existing detection methods often require large pieces of equipment and are therefore impractical for many safety, security, and humanitarian applications. Conductive polymer (CP) based chemiresitive vapour sensors offer a potential solution because they can be used for stand-off detection, are small scale, relatively cheap, and operate at room temperature.2 Here we use percolation networks of conducting polymers to detect ANFO, instead of the more traditional thin films, to increase the sensitivity.3-5 Using a custom made sensor testing chamber, sensors based on a percolation network of polypyrrole (PPy) were exposed to a series of vapours emitted by 7 different fertilisers and ANFOs made with those fertilisers (Figure 1). The sensor responses to the fertiliser and ANFO samples were rapid and reversible. It is likely that the sensor responses measured are responses to the NH3 emitted by the fertiliser in the sample. For this reason a calibration curve based on known NH3 concentrations can be used to determine the NH3 concentration detected as a result of an unknown fertiliser or ANFO sample. Ammonia vapour concentrations emitted by the fertiliser and ANFO samples of 13-180 ppb were detected.Exposing the sensors to all 7 fertilisers and their ANFOs results in different sensor responses for the different fertilisers (Figure 1). Although one might expect that the sensor response is directly related to the nitrogen content of the fertiliser, we found that this is not the case. It is possible that other components such as additives or internal desiccants play a role. Even in small quantities around 0.1% of common additives such as magnesium nitrate play an important role in the stability of the fertiliser.6 Additionally, the porosity of the fertiliser granules or prills might affect the measured NH3 concentration because the pores may store NH3 and thus influence the amount of available NH3. The relationship between sensor response and granule porosity could provide valuable information for sensing applications because porosity is known to be one of the most important factors determining explosives properties such as detonation velocity.7 Furthermore, it was shown that our sensors do not respond to diesel alone, and that there is no significant difference between the sensor responses to the fertiliser and ANFO made with the same fertiliser. This eliminates false positives due to the presence of diesel vapours in the environment.At the end of each series of exposures the sensor was exposed to the first fertiliser from the series for a second time. This control experiment demonstrates that the sensor has good stability and reproducibility, and doesn’t degrade over time or after repeated exposures.Our sensor responses were validated by comparison to gas chromatography/mass spectroscopy (GCMS) measurements conducted for the same fertilisers and ANFOs. Although our sensors detected much smaller NH3 concentrations, the pattern of different NH3 concentrations detected for the different fertilisers was similar for the two methods. Furthermore, in both methods the fuel oil component did not affect the detection of the fertiliser or ANFO.Figure 1: Top: Schematic of custom made sensor testing chamber. The testing chamber has 2 gas inlets, allowing for gases directly from a cylinder as well as vapours emitted by solid or liquid samples carried into the chamber by an N2 flow. Bottom: Vapour concentrations measured by our conducting polymer percolation network sensors for 7 different fertilisers and ANFOs made with those fertilisers. Ammonia vapour concentrations emitted by the fertiliser and ANFO samples of 13-180 ppb were detected.

PRODUCTION OF LIME-AMMONIUM NITRATE BASED ON CHALK, NITRATE AND AMMONIUM SULFATE

The article studies the process of obtaining carbonate-ammonium nitrate (CAN) based on the mixing of melt ammonium nitrate (NH4NO3) with chalk (СаСО3) and ammonium sulfate (NH4)2SO4). For the granulation of nitrate-sulfate-carbonate melt the prilling method is applied using a granulation tower. Determined the composition and properties of new types of fertilizers. It is shown that with the ratio NH4NO3 : СаСО3 : (NH4)2SO4 = 100 : 24 : 1 the product contains 28,03% N, SO3 – 0,50%, 10% СаО and has a granule strength of 6,03 MPa, which is much higher than the strength of pure NH4NO3 granules (1,32 MPa). Porosity and absorption of pure AN granules is 22,0% and 4,82 g. With an increase in the proportion of chalk and ammonium sulfate to the NH4NO3 : СаСО3 : (NH4)2SO4 = 100 : 24 : 1 ratio, the porosity and absorbency of the LAN granules is 6,11% and 2,57g, respectively. It was revealed that the use of the (NH4)2SO4, СаСО3 additive in the NH4NO3 melt at a mass ratio of NH4NO3 : СаСО3 : (NH4)2SO4 = from 100 : 2 : 0,5 to 100 : 58 : 2 allows to increase the strength and temperature of the onset of decomposition of the nitrate granules by 2-6,7 and 1-1,3 times and reduce the porosity by 2,7-4,8 2 times.

Fabrication and Evaluation of Layered Double Hydroxide-Enriched ß-Tricalcium Phosphate Nanocomposite Granules for Bone Regeneration: In Vitro Study.

One of the most important challenges facing tissue engineering researches is the scaffold design with optimum physical and mechanical properties for growth and proliferation of cells, and tissue formation. The aim of this study was to produce a novel nanocomposite containing β-tricalcium phosphate and layered double hydroxide (β-TCP-LDH) and analyzing the capacity of its osteogenic activity in vitro. In this paper, β-tricalcium phosphate and layered double hydroxide powders were synthesized by co-precipitation processes. Then, the porous nanocomposite granules were prepared by the polyurethane sponge replication method. In this study, four kinds of β-TCP granules containing LDHs nanoparticles (ranging from 0.1 to 10wt%) have been prepared. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) analyses were selected to study the phase structure, morphology, and phase distribution, respectively. Physicochemical characterizations demonstrated that the granules were synthesized successfully. Interconnected macro pores ranging over 200-500μm were observed for all kinds of granules. SEM micrographs showed that human mesenchymal stem cells (hMSCs) were attached to the surfaces of the granules and proliferated in good shape. The results warranted that the synthesized granules exhibited good biocompatibility and mineralization. Based on the results of compressive strength and porosity tests, the most suitable type of granule is β-TCP/LDH 10wt% with 77% porosity and compressive modulus of 231.4MPa, which can be utilized in bone tissue engineering. To our knowledge, layered double hydroxides have not previously been incorporated into tricalcium phosphate granules for bone grafting. Also, this study is the first report on the effects of LDH on the mechanical properties and porosity of β-TCP granules. Our results demonstrated that β-TCP/LDH nanocomposite granule has a great potential for bone defects regeneration and tissue engineering applications.

A moving-boundary model of dissolution from binary drug-excipient granules incorporating microstructure

Accurate mechanistic in vitro dissolution models can deliver insight into drug release behaviour and guide formulation development. Drug release profiles from drug-excipient granules can be impacted by variation of porosity and drug load within granules, which may arise from inherent variability in granulation processes. Here, we analyse and validate a recent model of drug release from a single spherical granule with a matrix of insoluble excipient, incorporating radial variation of porosity and drug load. The model is presented and specialised to the case where the initial drug load is large compared to the capacity of the granule’s pores at solubility. In this limit, the model reduces to a single ordinary differential equation describing depletion of a shrinking, drug-saturated core. Model validation is performed using drug release data from the literature for a granule system consisting of acetaminophen and microcrystalline cellulose. A new extended model to describe dissolution from a polydisperse collection of granules is derived. The performance is compared to single particle models using equivalent spherical diameters. The developed model provides a new tool to explore the dissolution parameter space for these systems and for considering the impact of radial variation of granule porosity and drug load arising from manufacturing processes.

Granulated apatite filters for phosphorous retention in treatment wetlands: Experience from full-scale applications

Since natural apatite has shown a great capacity for phosphorus retention from wastewater, a granulated apatite product was developed to control the particle size distribution of the filter material and avoid premature clogging. Since 2012, twenty full-scale granulated apatite filters have been installed in France, with the primary aim to remove phosphorus from domestic wastewater. Measurement campaigns concerning four of these full-scale filters were carried out over two years (2017-2018) to assess their performance, the maximum retention capacity and phosphorus removal kinetics after several years of operation. The filters were selected according to their age and their hydraulic characteristics (horizontal flow, vertical down flow, vertical up flow). The maximum phosphorus retention capacity was found to be approximately 7.4 g PO4-P/kg of granulated apatite. The study revealed low kinetic removal rate coefficients. It is believed that phosphorus retention occurred by adsorption and precipitation within the porosity of granules since precipitation on the granules surface was not observed by the Scanning Electron Microscopy images. Therefore, under the specific environmental conditions tested, the substrate behaves exclusively as an adsorptive-like media. The increase in pH due to alkalinity release requires the implementation of pH correction for a significant period after the commissioning of the filter (0.5–1.2 years).

Development and characterization of ibuprofen co-crystals granules prepared via fluidized bed granulation in a one-step process – a design of experiment approach

Objective The focus of this study was to investigate the possibility of producing ibuprofen-nicotinamide (IBU-NIC) and ibuprofen-isonicotinamide (IBU-INA) cocrystal-containing granules, using a one-step fluidized bed dryer granulation manufacturing process, and evaluate their mechanical properties. Significance Pharmaceutical cocrystals represent a suitable strategy to improve properties of active pharmaceutical ingredients (APIs), such as solubility and processability. Ibuprofen (IBU) is a small molecule API which can form cocrystals with different coformers, including NIC and INA. An improvement in mechanical properties for IBU-NIC cocrystals relative to IBU was previously reported but, to date, the formulation of IBU cocrystals in a solid dosage form has not been investigated. Methods In situ cocrystallization and granulation were achieved concurrently by processing in a lab-scale fluidized bed granulator following a design of experiment (DoE) approach using a two-level factorial design with both process and formulation variables. Solid-state, micrometric, dissolution, and mechanical (tabletability) characteristics of granules were assessed post-processing. Results Granules containing cocrystals were successfully prepared for 11 of 16 DoE runs. Parameters with a significant effect on granule drug loading, flow function, porosity, and size could be identified from the DoE model. Process yield was increased by using a high inlet temperature at high solution feed rate. To avoid the formation of sticky particles, caking and over-wetting of the powder during the process, the utilization of high inlet temperature, low API + coformer:filler ratio, low API concentration in solution and low solution feed rate were suggested by the model. Conclusion The multivariable model developed enables accurate optimization of the granulation process for IBU cocrystals.

EVALUATION OF MECHANICAL STRENGTH AFTER COMPRESSION OF METFORMIN 500MG TABLETS PRODUCED BY DIFFERENT WET ROUTES

Objective: This work evaluated the post-compression hardness gain of Metformin tablets made from two granulates of the same formulation, but with different formation principles, one by the fluidized bed and the other in a V-shaped mixer.
 Methods: The base granulate for the production of the tablets was prepared using Metformin HCL as the main active ingredient. After compression, the prepared tablets were tested with different evaluation parameters like relative humidity, apparent and compacted density, granulometric dispersion, hardness, moisture content, and friability for complete characterization.
 Results: All prepared samples were within the pre-established humidity ranges (MT1 = 3.31%, MT2 = 2.72%, MT3 = 1.73%, LF1 = 3.25%, LF2 = 2.43% and LF3 = 1.79%). The density determination showed that the granules produced in the fluidized bed are less dense than those of the V mixer. LF2 sample had an apparent density of 0.525 g/ml and a compacted density of 0.546 g/ml, while the MT2 sample had an apparent density of 0.711 g/ml and a compacted density of 0.738 g/ml, corroborating the greater porosity of granules produced in a fluidized bed. It was found that there is a difference in the increase in hardness between the two granulation methods. The tablets manufactured from the granules elaborated in a V-shaped mixer showed a greater gain in comparison with those produced in the fluid bed. The MT1 sample had the highest gain percentage, reaching 99.47%, 48 h after compression. The MT2 sample obtained, for the same time, 76.34%, at a much slower speed than MT1. As for the other samples, all increased between 24 and 42%. These results are justified by the migration of agglutination liquid that occurs during the drying step.
 Conclusion: This work demonstrated that the product Metformin 500 mg tablet has increased hardness after compression, with most significance in the first hour after the procedure. It was possible to verify that the tablets made from the granules produced in a V-shaped mixer have a greater increase in hardness than those produced by the fluidized bed, in the same humidity range.

Magnetocaloric properties of spheroidal La(Fe,Mn,Si)13H[formula omitted] granules and their performance in epoxy-bonded active magnetic regenerators

Magnetic cooling has been researched as an alternative near room-temperature refrigeration technology for the past two decades. However, one of its greatest limitations is the lack of materials which can be properly shaped for optimal thermal-hydraulic performance while maintaining a substantial magnetocaloric effect at moderate fields (i.e., between 1 and 2 T) and remaining mechanically (and chemically) stable. In this paper, we thoroughly characterized a commercially accessible La(Fe,Mn,Si)13Hy material (available as spheroidal granules), in terms of its magnetocaloric properties and thermal-hydraulic performance in an Active Magnetic Regenerator (AMR) device. The regenerator bed built from epoxy-bonded spheroidal particles endured dozens of hours of operation in AMR cycles without any noticeable degradation of their mechanical integrity, thanks to a comparatively larger α−Fe content and granule porosity. As for the magnetic cooling performance, the AMR reached zero-span specific cooling capacities as high as 300 W kg−1. A 1-D two-temperature approach AMR model predicted the performance data with average deviations smaller than 7% for the zero-span specific cooling capacity and 5% for the AMR pressure drop.

Exploring the wet granulation growth regime map – validating the boundary between nucleation and induction

A methodological approach to define the regime map boundaries does not exist, and while some experimental data has been reported previously the boundaries have not been “validated”. The present study explored and quantified the boundary between the nucleation and induction growth regimes for a model high drug load formulation. It was postulated that the induction period could be decreased by increasing the liquid saturation of the system, with the effect of introducing additional binder liquid to the surface of the granules, which facilitates consolidation and growth. An increase in liquid saturation was achieved by increasing the liquid to solid ratio, or by densifying the granules to squeeze intragranular liquid to the surface. The densification was achieved by subjecting the granules to an extended wet massing period and by varying the impeller speed. By characterizing the response in granule porosity as a function of liquid to solid ratio, wet massing time and impeller speed the boundary between the nucleation and induction growth regimes was defined. Granules formed in the induction growth regime were shown to suffer significantly reduced compactibility. Further analysis of liquid saturation and compactibility data allows a critical granule porosity to be established as a basis for developing a control strategy. The attention to granule porosity allows a mechanistic interpretation of the growth behavior, rather than simply relying upon size measurements. The porosity based approach was successfully superimposed onto the existing growth regime map framework, and established that the boundary between regimes is a gradual transition rather than the conventionally visualized abrupt binary state.

Effects of heat‐moisture and alkali treatment on the enzymatic hydrolysis of porous sago ( Metroxylon sagu ) starch

Pretreatment(s) of heat-moisture treatment (HMT) and alkali treatment was tested for the enzymatic hydrolysis of sago (Metroxylon sagu) starch. HMT was undergone by autoclaving the sago starch at 120°C for 60 min. While sodium hydroxide pellets (0.60% [w/w starch dry basis (d.b.)] to 50 g of sago starch) were applied as the alkali treatment. Dual pretreatments were also evaluated. The dextrose equivalent values of porous starch with alkali pretreatment (31%), HMT (37%), and dual pretreatments (42%) were significantly higher than those of non-pretreated porous sago starch (21%). Greater porosity of pretreated starch granules (0.91–5.19 µm) was also obtained. The thermal properties (gelatinization temperature) of porous starch with pretreatments were improved compared to the non-pretreated porous sago starch. In addition, the pretreatment(s) also improved the oil adsorption capacity of the porous starch. Dual pretreatments were an efficient way to facilitate enzymatic hydrolysis in preparing porous sago starch. Practical applications Porous starch is in high demand as a natural carrier for food applications such as flavor retention, food structure improvement, and extension of food shelf life. The porosity of the starch provides higher surface area and better immobilization to food ingredients, especially as a functional food. The abundance and lower cost of sago starch added the preference. Hence, the main purpose of the study is to produce highly porous sago starch granules with enhanced surface area to fulfill the processing requirement of food industries. Thus, the effect of pretreatment(s) on sago starch using heat-moisture and alkali treatments prior to enzymatic hydrolysis was evaluated. Both heat-moisture and alkali pretreatment(s) enhanced the enzymatic hydrolysis of sago starch and formed the intended porous structure. Porous sago starch has better absorption capacity and efficient oil adsorption. Besides, the thermal properties of pretreated sago starch were improved compared to the non-pretreated porous sago starch. Hence, the pretreated sago starch is the potential to be an excellent adsorbent. Overall, the outcome shows that the objective is positively achieved via the dual of the pretreatment(s).

Understanding the multi-scale structure and digestibility of different waxy maize starches

This work concerns different cultivars of waxy maize starch (WMS), from which a significant correlation between the multi-scale structure and the digestibility has been identified. WMSs show a typical A-type crystalline polymorph. The surface porosity of WMS granules facilitates their digestibility. In contrast, the in vitro digestion results indicate that the resistant starch (RS) content increased with higher contents of amylose, single helices, and surface short-range ordered structures. Resistant starch (RS) was found to be made up of single helices and perfect crystallites formed by the fraction of chains with a degree of polymerization (DP) between 13 and 24. Slowly digestible starch (SDS) consists of single helices. Rapidly digestible starch (RDS) is mainly composed of disordered molecular chains in the amorphous regions of starch. This work reveals the relationship between the multiscale structure and digestibility of different WMSs and can provide guidance for the application of WMSs in food or non-food fields.

Deactivation mechanism of calcified anaerobic granule: Space occupation and pore blockage

Calcification and deactivation of high rate sludge bed reactors is a common and serious engineering problem in the application of anaerobic bioreactor. In this study, the characteristics and deactivation mechanism of calcified anaerobic granules were investigated. The results showed that the calcium content of calcified anaerobic granules was ten times higher than that of control anaerobic granules. A large part of the calcium accumulated in the center of anaerobic granules in the form of calcite, and a small part of the calcium distributed in the outer layer of anaerobic granules in the form of Ca-P deposit. The calcium core occupied a large space which was available for the functional microorganisms. The calcium salts deposited in the outer layer of granular sludge which led to the significant reduction of macropore volume. The porosity of calcified anaerobic granules decreased by 13% compared with that of control anaerobic granules, causing generally the decline of methanogenic activity (for example, by 13% at influent organic concentration of 6.6 g COD L−1). The substrate gradient created by methanation of organic salts, including organic calcium salts, was deduced to be the driving force of anaerobic granule calcification, while the gradual accumulation of calcium salts in anaerobic granules was deduced to be the dominant factor for the decline of anaerobic granule activity.

Analysis of Microstructure of Granules Prepared by Continuous Twin Screw Granulator Using X-Ray Micro-computed Tomography.

Granules prepared by a continuous twin screw granulator (TSG) were analyzed by X-ray micro-computed tomography (X-ray μCT) and the relationships between porosity of granules and granule properties were investigated. A model formulation containing ibuprofen, lactose monohydrate, microcrystalline cellulose, and hydroxypropyl cellulose was used. The porosity of granules was measured by X-ray μCT and mercury porosimetry. The data sets obtained by both methods showed linear correlation despite different values, which were attributed to the resolution of X-ray μCT and a low-signal-to-noise ratio of the original cross-sectional images. The porosity of granules measured by X-ray μCT decreased from 11-14 to 6-7% as liquid-to-solid ratio (L/S) increased, while the standard deviation (S.D.) of the porosity of individual granules decreased from 4-5 to 2%. L/S affected the porosity of granules. By contrast, the effect of screw speed was not significant. Pressure transmission, G, which indicates the liquid dispersion in wet kneaded masses, increased as the porosity of granules and the S.D. decreased. The cross-sectional images showed that granules were densified as L/S increased. Based on these results, the effect of L/S on the porosity of granules can be explained by liquid dispersion and densification of the wet granules. The porosity of granules measured by X-ray μCT showed good linear correlation with friability and drug dissolution rate (R2 = 0.9107 and 0.8834, respectively). This study revealed that the drug dissolution rate was regulated by a disintegration step in which the porosity of granules plays an important role.