Microcrystalline cellulose as a sponge as an alternative concept to the crystallite-gel model for extrusion and spheronization

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.

Optimization of granular formulations of Metarhizium humberi microsclerotia with humectants

Granular microsclerotial formulations of entomopathogenic fungi deserve attention because of their post-application, in situ production of new conidia that enhance and prolong mycoinsecticidal efficacy against a target pest insect. Because high ambient moisture is a crucial condition to induce fungal development and conidiogenesis on granules, we tested the impacts of the additions of three humectants-glycerin, propylene glycol, and polyethylene glycol 400-on water absorption by pellets incorporating microsclerotia of Metarhizium humberi IP 46 with microcrystalline cellulose or vermiculite carriers, and on the production of infective conidia of IP 46 microsclerotia in ambient humidities suboptimal for routine conidiogenesis. Glycerin facilitated greater and faster absorption of water than the other humectants. Microcrystalline cellulose absorbed low quantities of water without any added humectant whereas vermiculite did not. IP 46 did not grow or sporulate on pellets prepared with or without glycerin at 86% relative humidity (RH) or on control pellets without glycerin at 91% RH; conidial production on pellets prepared with vermiculite or microcrystalline cellulose and 10% glycerin reached 1.1 × 10⁵  conidia/mg and 1 × 10⁵  conidia/mg, respectively, after 20 days of exposure at 91% RH. Hence, these results strongly support glycerin as a suitable humectant for granular microsclerotial formulations of this fungus.

Fibrillated Cellulose via High Pressure Homogenization: Analysis and Application for Orodispersible Films

Powdered cellulose (PC) and microcrystalline cellulose (MCC) are common excipients in pharmaceuticals. Recent investigations imply that particle size is the most critical parameter for the different performance in many processes. High-pressure homogenization (HPH) was used to reduce fiber size of both grades. The effect of the homogenization parameters on suspension viscosity, particle size, and mechanical properties of casted films was investigated. PC suspensions showed higher apparent viscosities and yield stresses under the same process conditions than MCC. SLS reduced shear viscosity and thixotropic behavior of both cellulose grades probably due to increased electrostatic repulsion. Homogenization reduced cellulose particle sizes, but re-agglomeration was too strong to analyze the particle size correctly. MCC films showed a tensile strength of up to 16.0 MPa and PC films up to 4.1 MPa. PC films disintegrated within 30 s whereas MCC films did not. Mixtures of MCC and PC led to more stable films than PC alone, but these films did not disintegrate anymore. Diclofenac sodium was incorporated in therapeutic dose with drug load of 47% into orodispersible PC films. The content uniformity of these films fulfilled requirements of Ph.Eur and the films disintegrated in 12 s. In summary, PC and MCC showed comparable results after HPH and most differences could be explained by the smaller particle size of MCC suspensions. These results confirm the hypothesis that mainly the fiber size during processing is responsible for the existing differences of MCC and PC in pharmaceutical process, e.g., wet-extrusion/spheronization.

Formulation and evaluation of sustained release enteric-coated pellets of budesonide for intestinal delivery

Introduction:

The aim of present work was to develop intestinal-targeted pellets of Budesonide, a potent glucocorticoid, used for the treatment of ulcerative colitis and Crohn's disease by extrusion and spheronization method. Current available oral formulations of Budesonide have low efficacy because of the premature drug release in the upper part of the gastrointestinal tract. In this study, a pH-controlled intestinal-targeted pellet of budesonide was established using 3² full factorial design by giving an enteric coating with Eudragit S100.

Materials and Methods:

Budesonide-sustained release pellets were prepared by extruder and spheronization technique using a combination of water-soluble and permeable polymers by applying 3² full factorial design. The pellets were coated by spray coating technique using Eudragit S100 as an enteric polymer. The pellets were characterized for its flowability, sphericity, friability, and in vitro drug release. Release behaviour was studied in different pH media. The release profile was studied for the mechanism of drug release.

Result:

The optimized formulation showed negligible drug release in the stomach followed by release for 12 h in the intestinal pH. Differential scanning calorimetry and Fourier Transform Infrared Spectroscopy studies indicated no interaction between drug and polymer. Scanning Electron Microscopy image of coated pellets suggested a uniform and smooth coat over the surface of pellets. Accelerated stability studies showed a stable nature of drug in the formulation. All evaluation parameter showed that pellets were good in spherocity and flowability.

Conclusion:

Sustained release pellets of Budesonide could be prepared by extrusion and spheronization which released the drug in intestinal pH for an intestine to treat inflammatory bowel disease. A ratio of polymer combination could be decided using a full factorial design.

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.

The change in characteristics of microcrystalline cellulose during wet granulation using a high-shear mixer

The objective of this study was to investigate the mechanism of hard granule formation and to demonstrate the applicability of X-ray diffraction methods for studying the polymeric pharmaceutical excipients. Using a high-shear mixer, microcrystalline cellulose (MCC) was granulated with water as the granulating liquid. The hardness of the MCC granules increased with granulation time and the amount of water added. The specific surface area measured by the N2 adsorption method was reduced during the process. Crystallite size of cellulose, calculated by Scherrer's equation adapted for wide angle X-ray diffraction method, decreased with granulation time and with increasing amounts of water added. Debye plots for X-ray small scattering patterns suggested that the average magnitude of the continuous solid region in MCC granules became significantly greater, whereas the specific surface area of the MCC granules, calculated from Debye plots, became smaller in comparison with that of intact MCC. These findings suggested that the long-chain structures in MCC were disrupted, resulting in smaller units with shorter chain lengths due to the strong shear force of the impeller. These smaller units then form a network within the granules. Thus, MCC granules are strengthened with longer granulation time and greater amounts of water, resulting in a more intricate network. The change in MCC chain length and physical structure can be experimentally detected using the small-angle X-ray scattering and wide-angle powder X-ray diffraction methods.

Formulation of rate-modulating pellets for the release of ibuprofen: an extrusion-spheronization process

PURPOSE

To develop a stable and reproducible modified release pellet formulation containing ibuprofen.

METHODS

Using extrusion-spheronization technology to produce pellets.

RESULTS

The percentage yield, size distribution and overall pellet shape within the desired size range of 1000-1400 microm was found to be dependent on various process variables. These include extrusion and spheronization speed, spheronization time and composition of the granulation fluid. Formulation factors such as viscosity grade of hydroxypropylmethylcellulose and concentration of microcrystalline cellulose were shown to influence the drug release rate of the pellets. In vitro dissolution studies revealed that the pellets behaved in a pH-dependent manner. Pellets exposed to different drying techniques exhibited an increase in drug release rate in the order corresponding to oven-dried, vacuum-dried, fluid bed-dried and freeze-dried pellets. In conjunction with scanning electron microscopy, kinetic modelling and statistical treatment of dissolution data, it was confirmed that the predominant release rate-controlling mechanism was diffusion, as evidenced from the power law expressions incorporating Fickian and relaxational parameters (M(t) /M(infinity) = K(1)t(n); M(t) /M(infinity) = K(1)t(2n)). Matrix swelling and erosion were not significant factors in modulating the drug release rate.

CONCLUSIONS

The pH-dependent property of the pellets may be strategically employed towards development of a site-specific drug delivery system for non-steroidal anti-inflammatory agents. In general, targeting the delivery of an agent with potential for gastric irritation to the proximal intestine/colon may effectively reduce its ulcerogenic effect and ultimately contribute towards improved patient compliance.

The effect of the amount of binder liquid on the granulation mechanisms and structure of microcrystalline cellulose granules prepared by high shear granulation

The structure of granules changes during the high shear granulation process. The purpose of this research was to investigate the effect of the amount of binder liquid on the structure of the granules and the structural changes which occur during the granulation process, using microcrystalline cellulose (MCC) and water as the model system. The structure is the result of the granulation mechanism; therefore, conclusions can be drawn about the latter by studying the former. X-ray microtomography and scanning electron microscopy (SEM) were applied in order to visualise the densification process of granules, which were first freeze dried in order to preserve their structure. Variations in their porosity were quantified by applying image analysis to the tomography results. In order to link the granule mechanical properties to their structural differences, a micromanipulation technique was used to measure granule resistance to deformation. MCC granules granulated with 100% (w/w) water showed increased densification with time, as expected; detailed examination showed that densification is more pronounced in the core of the granule; whereas the outer part remained more porous. Increased densification reduces deformability, so that granules become more resistant to breakage. The lower deformability of the densified granules in the final stages of granulation might result in establishment of equilibrium between attrition and growth, without substantial gross breakage. On the other hand, when more water was used (125%, w/w), densification was hardly observed; the porosity of the granule core was still high even after prolonged granulation times. This may be explained by the fact that higher water content increases the ease of deformation of granules. This increased deformability led to significant granule breakage even during the final phases of the granulation process. Therefore, for these granules a final equilibrium between breakage and coalescence might be established. This also explains why more granules produced with 125% granulation liquid were composed of fragments of irregular shape. Our results establish the link between the granulation behaviour of MCC in the latter stages and the material structure of these granules, which is determined by their liquid content. The process conditions (amount of liquid) to be chosen depend largely on the final purpose for which the granular material is produced.

Development of fast-disintegrating pellets in a rotary processor

The aim of the present work was to formulate fast-disintegrating pellets by direct pelletization in a rotary processor. Formulations containing kaolin or bentonite and lactose were agglomerated with or without the addition of crospovidone in an instrumented rotary processor. The effects of the excipients on the amount of wall adhesion, the size and size distribution, the disintegration time, and the shape of the agglomerates, as well as the content of agglomerates > 2800 microns, were investigated. Further, pellets containing a model drug having a low aqueous solubility were prepared, and the drug dissolution profile was compared to that of pellets containing microcrystalline cellulose (MCC). Formulations containing kaolin resulted in fast-disintegrating pellets. Pellets containing bentonite eroded, but did not disintegrate, and the formulations gave rise to large amounts of wall adhesion. The addition of crospovidone increased the water content at the end of liquid addition for all formulations, and resulted in slightly more spherical agglomerates. When comparing formulations containing kaolin and MCC, kaolin gave rise to wider size distributions and a higher amount of agglomerates > 2800 microns, but the drug dissolution rate was much faster. Complete (100%) drug release was seen after 8 min with the kaolin formulation, whereas only 40% was released after 2 hr from the MCC formulation.

Microcrystalline cellulose-water interaction--a novel approach using thermoporosimetry

PURPOSE

To study the physical state of water in microcrystalline cellulose (MCC) and in silicified microcrystalline cellulose wet masses and the effect of granulation on different water fractions.

METHODS

Thermoporosimetry, together with the solute exclusion technique, was used to measure different water fractions and pore size distributions of wet granules. To understand the effect of granulation on the physical state of water, both ungranulated and granulated wet masses were studied. In addition, dynamic and isothermal step melting procedures were compared.

RESULTS

Four distinct fractions of water (nonfreezing, freezing bound, free, and bulk water) could be detected in MCC wet masses. Granulation decreased the volume of bulk water and increased the volume of freezing bound and free water. Consequently, granulated wet masses were able to hold more water inside the particles compared to ungranulated wet masses. Thus, granulation had a similar effect on MCC as beating has on cellulose fibers in the papermaking proces

CONCLUSIONS

Thermoporosimetry and solute exclusion increased the understanding of MCC-water interaction and showed how the physical state of water in MCC wet masses changes during granulation.

Characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a powder rheometer

A powder rheometer has been used to study the properties of wet powder masses and the results have been compared to the mixer torque rheometer (MTR). Two different microcrystalline cellulose (MCC) grades (Avicel and Emcocel) and silicified microcrystalline cellulose (SMCC, Prosolv) were used as model powders. The wet massing behaviour of one material (Prosolv) was studied by the powder rheometer using liquid addition experiments, while the rheological properties of wet granules were studied using both the powder rheometer and the MTR. In water addition measurements the torque behaved in a similar way to MTR measurements and the maximum value of ZTL (zero torque limit) was achieved at the capillary state of wet mass. The wet granules exhibited different behaviour in the powder rheometer and the MTR experiments, which indicates that these rheometers involve different shear forces or they measure different properties of the wet granules. Emcocel wet masses achieved the capillary state at lower liquid amount than Avicel and Prosolv masses, which indicates that Emcocel is not able to hold as much water in the internal structure as Avicel and Prosolv. The powder rheometer proved to be a sensitive piece of equipment, which can be used to study both dry and wet powder masses. It was able to distinguish wet granules from wet powder masses after liquid addition, whereas the MTR could not. However, before the powder rheometer can be properly utilised in wet powder mass studies, the problem of torque overload requires resolution.

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.

Influence of the degree of polymerization on the behavior of cellulose during homogenization and extrusion/spheronization

The study objective was to investigate the influence of the degree of polymerization (DP) of cellulose materials (microcrystalline cellulose [MCC] and powder cellulose [PC]) on the behavior of these materials during homogenization and extrusion/spheronization processes. Suspensions of the cellulose types with different DP values were homogenized using a high-pressure homogenizer. The particle size, agglomeration index, and apparent viscosity of these suspensions was determined at different times after pouring. Additionally, these different cellulose types were processed into pellets using the extrusion/spheronization method, and the water content and power consumption as a function of the DP were determined. Cellulose types with a high DP value showed greater particle size after homogenization than the types with a low DP value. In contrast, no relevant relationship between the apparent viscosity and DP could be observed. During the extrusion process, water content in the extrudate and pellet porosity were increased as the DP was increased for the extrudates produced at the same level of power consumption. MCC types with various DPs compared with PC provided a novel way of understanding the role of cellulose in the extrusion process. The DP showed a remarkable influence on the physicochemical properties of the cellulose materials and, consequently, on the behavior of these materials during the extrusion/spheronization process. It is postulated that the sponge model is more appropriate for the cellulose type with high DP (PC), whereas the gel model is more applicable to cellulose types with lower DP (MCC).

Microcrystalline cellulose and its microstructure in pharmaceutical processing

Mercury porosimetry and nitrogen adsorption methods were used in pore structure and pore surface area characterisation of microcrystalline cellulose powder, granules and tablets. The effect of compression on pore structure and surface area of tablets compressed with three different compression pressures of powder and granules was determined. Densification of MCC in wet granulation led to decreased compactibility in tableting. Effects of granulation on the microstructure of microcrystalline cellulose and plastic deformation of powder during compression were detected with nitrogen adsorption, at the diameter range 3-200 nm. Structure of granules was destroyed during tableting when compression pressures of 196 MPa were used. Fragmentation and deformation of granules were observed from the results determined using both methods. Due to different measurement ranges, different theoretical basis of the methods and behaviour of the samples during analysis, results obtained with mercury porosimetry and nitrogen adsorption methods are not strictly comparable. Results obtained with mercury porosimetry give information on the behaviour of powder and granule particles in granulation or compression, whereas nitrogen adsorption brings out the changes in intraparticular structure of particles. The results obtained using these methods together can be used in the characterisation of behaviour of materials in granulation and tableting.

Rheological characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a mixer torque rheometer

The rheological properties of silicified microcrystalline cellulose (Prosolv 50) were compared with those of standard grades of microcrystalline cellulose (Emcocel 50 and Avicel PH 101). Cellulose samples were analyzed using nitrogen adsorption together with particle size, flowability, density and swelling volume studies. The rheological behaviour of the wet powder masses was studied as a function of mixing time using a mixer torque rheometer (MTR). Silicified microcrystalline cellulose exhibited improved flow characteristics and increased specific surface area compared to standard microcrystalline cellulose grades. Although the silicification process affected the swelling properties and, furthermore, the mixing kinetics of microcrystalline cellulose, the source of the microcrystalline cellulose had a stronger influence than silicification on the liquid requirement at peak torque.

The use of carrageenan in mixture with microcrystalline cellulose and its functionality for making tablets

The modulation of tableting and release behavior of combinations of kappa-carrageenan Gelcarin((R)) GP 911 NF and microcrystalline cellulose (MCC) Avicel((R)) PH 101 has been evaluated. Graded binary mixtures were tableted to a maximum relative density of 0.850 at the maximum displacement of the upper punch. Additionally, ternary mixtures with the same ratios of kappa-carrageenan and MCC and a constant percentage of theophylline monohydrate (20% (v/v)) were tested for their release behavior. Tablets produced from pure kappa-carrageenan deformed more elastically than pure MCC, the tablets produced were stable but not at the same degree as those made from MCC. Scanning electron microscopy (SEM) pictures showed that for MCC a smooth surface of the tablets resulted, tablets made from kappa-carrageenan showed less 'fusion' and thus more mechanical interlocking is responsible for their stability. Binary mixtures showed a continuous change in compaction properties from plastic to elastic deformation. All ternary mixtures with theophylline deformed more plastically than the binary mixtures, the change in deformation properties remained the same. Theophylline reduced the crushing strength due to its different fracture properties. The ternary mixtures showed different release mechanisms: Fast release up to 20% (v/v) kappa-carrageenan, slower release starting from 30% (v/v). The kinetics of release tended at 70% (v/v) more clearly towards zero-order kinetics. This change in release is in accordance with a change in swelling of tablets made of the binary mixtures.