Importance of the fraction of microcrystalline cellulose and spheronization speed on the properties of extruded pellets made from binary mixtures

Croscarmellose Sodium as Pelletization Aid in Extrusion-Spheronization

Only few excipients are known to be suitable as pelletization aids. In this study, the potential use of croscarmellose sodium (CCS) as pelletization aid was investigated. Furthermore, the impact of cations on extrusion-spheronization (ES) of CCS was studied and different grades of CCS were tested. The influence of different cations on the swelling of CCS was investigated by laser diffraction. Mixtures of CCS with lactose monohydrate as filler with or without the inclusion of different cations were produced. The mixtures were investigated by mixer torque rheometry and consequently extruded and spheronized. Resulting pellets were analyzed by dynamic image analysis. In addition, mixtures of different CCS grades with dibasic calcium phosphate anhydrous (DP) and a mixture with praziquantel (PZQ) as filler were investigated. Calcium and magnesium cations caused a decrease of the swelling of CCS and influenced the use of CCS as pelletization aid since they needed to be included for successful ES. Aluminum, however, led to an aggregation of the CCS particles and to failure of extrusion. The inclusion of cations decreased the uptake of water by the mixtures which also reduced the liquid-to-solid-ratio (L/S) for successful ES. This was shown to be dependent on the amount of divalent cations in the mixture. With DP or PZQ as filler, no addition of cations was necessary for a successful production of pellets, however the optimal L/S for ES was dependent on the CCS grade used. In conclusion, CCS can be used as a pelletization aid.

Influence of the surface tension of wet massing liquid on the functionality of microcrystalline cellulose as pelletization aid

This study designed to investigate the impact of surface tension of moistening liquid on the functionality of MCC as pelletization aid. For this purpose, sodium dodecyl sulfate (SDS), poloxamer 188 (PL), di-potassium hydrogen phosphate (K₂HPO₄) and combinations thereof were incorporated into the powder blend comprised of MCC and dicalcium phosphate (DCP) at different levels. Physical mixture (PM) and co-processed composite (Cop) of MCC and sodium carboxymethyl cellulose (SCMC) replaced MCC as pelletization aids. The pellets prepared were characterized for their median diameter (D₅₀), particle size distribution (PSD), sphericity, porosity, tensile strength and disintegration. SDS induced a drop in the surface tension of water from 68.7 to 23.7 mN/m at 0.1% (w/w). In contrast, the surface tension values of PL and K₂HPO₄ solutions were 2.08- and 3.07-fold higher than that of SDS solutions, respectively. MCC based pellets obtained with SDS showed wider PSD and lower sphericity than those made with PL, K₂HPO₄ and their combinations. In addition, the PSD and porosity increased with rise of SDS concentration from 0.05 to 0.25% (w/w). It was thus inferred that a critical surface tension of moistening liquid was essential for functionality of MCC as pelletization aid but not for PM and Cop.

Scale-up of the rounding process in pelletization by extrusion-spheronization

Previously described scaling models for the spheronization process of wet extrudates are incomplete, often concluding with an adjustment of the plate speed according to the spheronizer diameter, but neglecting to give guidelines on the adjustment of the load or the process duration. In this work, existing scaling models were extended to include the load and the process time. By analyzing the final particle size and shape distributions as well as the rounding kinetics for various loads and plate speeds in spheronizers with plate diameters of 0.12 m, 0.25 m and 0.38 m, the found scaling model was validated. The peripheral speed was found to be the main influence on the rounding kinetic, while the load and the plate diameter only showed minor influence. Higher peripheral speeds, higher loads and a larger spheronizer diameter led to an increase in rounding kinetic, allowing for shorter residence times and increased throughput. However, lower peripheral speed, lower loads and lower plate diameters led to particles of increased sphericity.

Use of extrusion aids for successful production of Kollidon® CL-SF pellets by extrusion-spheronization

OBJECTIVE

Fine particle ethylcellulose (FPEC) or poly(ethylene oxide) (PEO) addition to a Kollidon CL-SF was investigated to address low yield and poor sphericity in extruded-spheronized pellets.

SIGNIFICANCE

The success of crospovidone as a diluent in extrusion-spheronization was dependent on a small particle size of the polymer. FPEC aided production of rugged and spherical pellets using a large particle size grade, Polyplasdone^® XL. PEO acted as an extrusion-spheronization aid when ethylcellulose was the diluent. These extrusion-spheronization aids could serve in this role when Kollidon^® CL-SF (K CL-SF) is the diluent.

METHODS

The influence of formulation and process variables on pellet properties was investigated using design of experiments. A planetary mixer was used to prepare powder blends and the wetted mass after addition of water. An EXD 60 extruder produced extrudate that was spheronized in a Q230 marumerizer. Wet pellets were dried in a forced-air oven.

RESULTS

FPEC improved rounding up but reduced pellet yield. Poly(ethylene oxide) imparted desired characteristics to the wetted mass, the extrudate, and the spheronized pellets. Pellet average diameter, yield, sphericity, aspect ratio, friability, and dissolution profile were assessed. Equations for pellet characteristics facilitated discussion of the influences of factors and their interactions. Optimization was performed on pellets that included PEO.

CONCLUSIONS

PEO proved to be an exceptional extrusion-spheronization aid in the preparation of pellets using K CL-SF. It facilitated wetted mass extrusion with minimal mass loss to the extruder, and markedly improved the sphericity of the pellets produced by marumerization. Immediate release pellets were obtained.

Small-scale twin-screw extrusion - evaluation of continuous split feeding

OBJECTIVES

The aim of this work was to evaluate a continuous, small-scale extrusion process with a particular focus on powder and liquid-feeding systems, because it is likely that uniformity issues are related to small-scale production.

METHODS

The study is divided into three parts. The first part investigates the uniformity and accuracy of the powder and the liquid feeders. In the second part, a solid polymer and low amounts of liquid plasticizer were combined in hot-melt extrusion. The third part deals with wet extrusion-spheronization using water as the granulation liquid.

KEY FINDINGS

The powder and the liquid feed rate were identified as crucial parameters in small-scale extrusion. With respect to powder feeding, the cohesiveness of the powder and electrostatic charging are the limitations, while liquid feeding is challenging based on particularly low feed rates. The hot-melt extrusion was performed using a powder feed rate of 2 g/min. When small quantities of plasticizer were applied to the hot melt extrusions (from 2.5% to 15% w/w), homogenous plasticizer distribution was found. In wet extrusion, larger quantities of water were used and the extrudates were investigated with respect to their spheronization behaviour. Spherical pellets were obtained at certain water contents.

CONCLUSIONS

These findings demonstrated that the extruder is a useful tool to screen formulations and perform feasibility studies on a small scale in the early stages of product development.

Use of fine particle ethylcellulose as the diluent in the production of pellets by extrusion-spheronization

The effect of small ethylcellulose particle size on the manufacture and properties of pellets produced by extrusion-spheronization was investigated. A factorial design revealed the effects of microcrystalline cellulose (MCC), polyethylene oxide (PEO), water, and spheronization speed and time on pellet properties. Response surface modeling allowed optimization of the responses with expansion to a central composite design. Pellet yield, size, shape, friability and drug release profile were studied, along with surface and interior morphology. Pellets were spherical irrespective of the formulation and process variables and exhibited physical and mechanical characteristics appropriate for further processing. Yield in the 12/20 mesh cut was lower with FPEC than observed with coarse particle ethylcellulose (CPEC), but FPEC-containing pellets were more rugged and the PEO to obtain optimal pellets was lower for FPEC compared to CPEC. Immediate release products were obtained and ethylcellulose particle size was of no consequence to drug release. Observed responses for the optimized product agreed with predicted values, demonstrating the success of the optimization procedure. These results suggest that FPEC is a good diluent for extrusion-spheronization.

Production and characterization of pellets using Avicel CL611 as spheronization aid

PURPOSE

The study looked into the feasibility of producing pellet using Avicel CL611 as spheronization aid by the extrusion/spheronization technique.

METHODS

Pellets were formulated to contain either 20% or 40% Avicel CL611 and lactose monohydrate as the other sole ingredient. Water is used as liquid binder. Quality of pellets and extrudates were analyzed for size distribution, shape, surface tensile strength and disintegration profile.

RESULTS

More water was needed when higher Avicel CL611 fraction was used during the production of pellets. The pellets of larger size were obtained by increasing the water content. Pellets with aspect ratios of ∼1.1 were produced with high spheronization speed at short residence time. Higher tensile strength was achieved when increasing the water content and the fraction of Avicel CL611 during pellet production. These pellets also took longer time to disintegrate, nonetheless all the pellets disintegrated within 15 min. A positive linear relationship was obtained between the tensile strength and time for pellets to disintegrate.

CONCLUSION

Strong but round pellets that disintegrate rapidly could be produced with Avicel CL611 as spheronization aid using moderately soluble compounds such as lactose.

Stress relaxation test for the characterization of the viscoelasticity of pellets

The characterization of the mechanical properties of single uncoated pellets was performed in order to verify if these parameters could be used to predict the pellets aptitude to be compressed or utilized differently. Different ratios of microcrystalline cellulose and lactose monohydrate were used for the preparation of four batches of pellets by an extrusion/spheronization process. The 0.6-0.71 mm pellet fraction was used for the tests. Crushing strength and stress relaxation tests were carried out on the single pellets. The first test provided information of both the mechanical strength and the fragmentation aptitude. The second test provided information about their deformation ability (viscous flow) and residual elasticity (stress relaxation modulus). The results obtained from these tests were then compared with those obtained from the Heckel analysis. An excellent consistency was discovered between the parameters obtained from both the stress relaxation and crushing strength tests on one side and the Heckel parameters on the other side. Tests performed on single pellets are very useful tools to predict their deformation and fragmentation aptitude under compression and can be used for early insight of the pellet aptitude to be compressed.

Use of Chitosan-Alginate as Alternative Pelletization Aid to mMicrocrystalline Cellulose in Extrusion/Spheronization

Two types of different molecular weight chitosan were investigated as a pelletization aid in extrusion/spheronization using water as granulation liquid. Spherical pellets with a maximum fraction of 60% w/w chitosan could be produced when 1.25-2.5% w/w sodium alginate was included in the formulations with no microcrystalline cellulose (MCC). Chitosan with lower molecular weight of 190 kDa showed a better pellet forming property. The pellets obtained had acceptable physical characteristics and a fast drug release. The results from Fourier transform infrared spectroscopy, differential scanning calorimetry and (13)C CP-MAS nuclear magnetic resonance spectroscopy confirmed the formation of polyelectrolyte complex (PEC) between chitosan and sodium alginate, which might be a reason for successful pelletization by extrusion/spheronization. Moreover, the presence of PEC might influence the physical characteristics and dissolution behavior of chitosan-alginate pellets. The results indicated an achievement in production of pellets by extrusion/spheronization without using MCC. Moreover, chitosan combined with sodium alginate could be used as a promising alternative pelletization aid to MCC in extrusion/spheronization.

A novel fiber-optic photometer for in situ stability assessment of concentrated oil-in-water emulsions

The purpose of this research was to evaluate a novel fiber-optic photometer for its ability to monitor physical instabilities occurring in concentrated emulsions during storage. For this, the fiber-optic photometer was used to measure transmission of oil-in-water emulsions stabilized with hypromellose (HPMC) as a function of oil volume fraction and droplet size distribution (DSD). To detect physical instabilities like creaming and coalescence, the transmissivity of the samples was studied at 2 different height levels over a certain period of time. The corresponding droplet size distributions were determined by laser diffraction with PIDS. Transmissivity was found to depend on the number of dispersed droplets and thus is sensitive to both the variation of phase volume fraction as well as the emulsions droplet size distribution. At constant DSD, light transmission decreased linearly with increasing oil content within a large interval of phase volume fractions from 0.01 to 0.3. At constant phase volume fraction, an increase in droplet size increased light transmission. Investigation of creaming on emulsions with different droplet size distributions showed changes in the initial delay times and creaming velocities. In contrast to creaming phenomenon coalescence can be identified by height independent changes of the transmissivity. In conclusion, transmissivity of oil-in-water emulsions observed by the novel fiber-optic photometer is sensitive to phase volume fraction, droplet size distribution, and thus can be used as a tool for stability studies on concentrated emulsions.

Elucidation of spheroid formation with and without the extrusion step

Spheroid formation mechanisms were investigated using extrusion-spheronization (ES) and rotary processing (RP). Using ES (cross-hatch), ES (teardrop), and RP (teardrop), spheroids with similar mass median diameter (MMD) and span were produced using equivalent formulation and spheronization conditions. During spheronization, the teardrop-studded rotating frictional surface, with increased peripheral tip speed and duration, produced spheroids of equivalent MMD and span to those produced by the cross-hatch rotating frictional plate surface. The roundness of these spheroids was also similar. RP required less water to produce spheroids of MMD similar to that of spheroids produced by ES. However, these RP spheroids were less spherical. Image analysis of 625 spheroids per batch indicated that the size distribution of RP spheroids had significantly greater SD, positive skewness, and kurtosis. Morphological examination of time-sampled spheroids produced by ES indicated that spheroid formation occurred predominantly by attrition and layering, while RP spheroids were formed by nucleation, agglomeration, layering, and coalescence. RP produced spheroids with higher crushing strength than that of ES-produced spheroids. The amount of moisture lost during spheronization for spheroids produced by ES had minimal influence on their eventual size. Differences in process and formulation parameters, in addition to size distribution and observed morphological changes, enabled a greater understanding of spheroid formation and methods to optimize spheroid production.

Water Distribution Studies Within Microcrystalline Cellulose and Chitosan using Differential Scanning Calorimetry and Dynamic Vapor Sorption Analysis

The objective of the study was to assess and compare the interaction and distribution of water within microcrystalline cellulose (MCC) and chitosan by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. After accounting for the percent crystallinity of MCC and chitosan, no statistically significant difference was observed in their ability to bind water molecules per repeating unit at the minimum water content at which freezing water is evident. Exposure of chitosan to water for 30 min was sufficient to achieve equilibration at 61% w/w actual water content. The moisture sorption profiles were analyzed according to the GAB and Young and Nelson equations. The adsorbed monolayer, externally adsorbed moisture, and internally absorbed moisture were not statistically different for MCC and chitosan after accounting for the amorphous content of the polymers. These studies suggest that chitosan can act as a "molecular sponge," and thus aid in the production of beads by extrusion and spheronization.

Extruded and Spheronized Beads Containing No Microcrystalline Cellulose: Influence of Formulation and Process Variables

The purposes of this study were to investigate the use of chitosan in the manufacture of beads by extrusion-spheronization without inclusion of microcrystalline cellulose, and to study the effect of formulation and process variables on the characteristics of the beads. Beads containing chitosan, fine particle ethylcellulose, hydroxypropyl methylcellulose (HPMC), and caffeine as the model drug were manufactured. Bead size, yield, shape, friability, density, porosity, and release studies were determined. Spherical beads with good mechanical properties could be manufactured without microcrystalline cellulose. Release studies showed that there was immediate release of drug from the beads. A five factor, half fraction screening design was employed to study the effect of formulation variables and process variables on the properties of the beads. Statistical analysis indicated that formulation variables such as the chitosan content, HPMC content, and water content, and process variables such as the spheronizer speed and extruder speed significantly affected the physical properties of the beads. The bead size decreased with an increase in chitosan content. Significant two-factor interactions exist between the variables for several of the measured responses. Beads with high percentage yield and high sphericity can be obtained at high chitosan content, and low HPMC content, water content, spheronizer speed, and extruder speed. Less friable beads can be obtained at high levels of studied formulation variables and low levels of studied process variables. Beads of high density and low porosity can be manufactured at high levels of the studied formulation and process variables. Regression equations were generated using Statgraphics Plus software that can be used to develop formulations with desired bead properties. Chitosan was useful to provide beads of acceptable physical properties using water as a granulating fluid in the extrusion-spheronization process.

Optimization and characterization of controlled release multi-particulate beads formulated with a customized cellulose acetate butyrate dispersion

The objectives of the present investigation were: (1) to model the effect of process and formulation variables viz., coating weight gain, duration of curing, and plasticizer concentration on in-vitro release profile of verapamil HCl from multi-particulate beads formulated with a novel aqueous-based pseudolatex dispersion; (2) to optimize the formulation by response surface methodology (RSM) and artificial neural network (ANN); and (3) to characterize the optimized product by thermal and X-ray analyses. Inert beads (Nupareil) were loaded with verapamil HCl and subsequently coated with a custom designed aqueous-based pseudolatex dispersion of cellulose acetate butyrate (CAB). Experiments were designed and data was collected according to a three factor, three level face centered central composite design. Data was analyzed for modeling and optimizing the release profile using both RSM and ANN. Model fitted the data and explained 90% of variability in response in the case of RSM and at least 70% in the case of ANN. Release profile was optimized for a zero-order model. Optimized formulations were prepared according to the factor combinations dictated by RSM and ANN. In each case, the observed drug release data of the optimized formulations was close to the predicted release pattern. However, the modeling and optimization abilities of RSM as evaluated by the R-squared values, were found to be higher than that of ANN. X-ray and drug content analysis suggested the absence of any degradation of verapamil HCl and excipients incorporated in the formulation.

Evaluation of bioadhesive glipizide spheres and compacts from spheres prepared by extruder/marumerizer technique

The objective of this study was to attempt to deliver glipizide from spheres and compacts containing the natural polymer Carrageenan (Gelcarin, GP 812) and prepared by extruder/marumerizer technique. A second objective was to evaluate the mucoadhesive strength of the bioadhesive spheres onto the mucus membrane of rabbit. The effects of polymer, drug level, and type of spheronizing material were evaluated. All sphere formulations were compacted into tablets using a rotary Manesty B-3B machine equipped with 12/32 flat face tooling. Results show drug release from spheres and compacts decreased as the level of Carrageenan was increased. However as the level of drug was increased drug release also increased. Spheres containing Avicel PH-101 gave higher drug release than spheres of the same composition but prepared with Avicel RC-581. In general, the drug release from tablets was higher than its corresponding spheres and drug release from spheres and tablets containing Carrageenan was higher than control spheres and tablets of the same composition but without Carrageenan. Tablet formulations compacted from spheres containing Avicel RC-581 gave higher release rate constants than tablet formulations of the same composition but prepared with Avicel PH-101. The bioadhesion study showed that mucoadhesion strength between spheres and mucus membrane of the rabbit depends on the levels of polymer, drug, and type of spheronizing material. Developed bioadhesive spheres and tablets increase the solubility of glipizide which may increase its bioavailability and also increased the adherence of the bioadhesive systems to the mucous membrane so that once daily dose can be administered.

Interaction of microcrystalline cellulose and water in granules prepared by a high-shear mixer

Microcrystalline cellulose (MCC) granules were prepared by wet granulation using a high-shear mixer. Physical characteristics of the granules were investigated using near IR spectrometry, thermogravimetry and isothermal water vapor adsorption. Near IR spectra of dried MCC granules prepared for various granulation times exhibited different peak intensities at 1428, 1772, and 1920 nm, which were assigned to functional groups of cellulose or water. On isothermogravimetric analysis, the rate of dehydration of water was shown to decrease with granulation time. These results suggest that the physical structure of MCC could change during the granulation process, and the interaction between MCC and water was gradually strengthened. The isothermal water vapor adsorption curves suggested that the amorphous region of MCC would be divided by the strong shear force of the impeller, because the high adsorption ability of intact MCC in the low humidity region was diminished in granules collected following 5 and 10 min of granulation. It was suggested that MCC formed a network which caught water within its structure during the wet granulation process.

Direct pelletization in a rotary processor controlled by torque measurements. II: effects of changes in the content of microcrystalline cellulose

In the present study we investigated the effect of changes in the content of microcrystalline cellulose (MCC) on a direct pelletization process in a rotary processor in which the liquid addition was terminated once a certain increase in torque was produced. Nine different mixtures of MCC and lactose with MCC contents varying from 10% to 100% (w/w) were pelletized using 6 different torque increase levels, and the changes in pellet characteristics were investigated. The pellet characteristics investigated were pellet shape, size, and size distribution as well as the water content of the pellets at the end of liquid addition. To produce spherical agglomerates with suitable characteristics in a reproducible way, a content of at least 20% (w/w) MCC was found necessary. Linear correlations were found between the MCC content and the water content and between the torque increase and the water content, showing that the torque increase is suitable to control the process. A higher torque increase or a higher MCC content was found to increase the water content independently of each other.