Time dependence of elastic recovery for characterization of tableting materials

A modified mechanistic approach for predicting ribbon solid fraction at different roller compaction speeds

This research investigates the modeling of the pharmaceutical roller compaction process, focusing on the application of the Johanson model and the impact of varying roll speeds from 1 to 15 RPM on predictive accuracy of ribbon solid fraction. The classical Johanson's model was integrated with a dwell time parameter leading to an expression of a floating correction factor as a function of roll speed. Through systematic analysis of the effect of different roll speeds on the solid fraction of ribbons composed of microcrystalline cellulose, lactose, and their blends, corrective adjustment to the Johanson model was found to depend on both roll speed and formulation composition. Interestingly, the correction factor demonstrated excellent correlation with the blend's mechanical properties, namely yield stress (Py) and elastic modulus (E0), representative of the deformability of the powder. Validated by a multicomponent drug formulation with ±0.4-1.3 % differences, the findings underscore the utility of this modified mechanistic approach for precise prediction of ribbon solid fraction when Py or E0 is known for a given blend. Hence, this work advances the field by offering early insights for more accurate and controllable roller compaction operations during late-stage pharmaceutical manufacturing.

Towards simultaneous determination of tablet porosity and height by terahertz time-domain reflection spectroscopy

The quality control of pharmaceutical tablets is still based on testing small sample numbers using at- and off-line testing methods. Traditional in-process controls, such as tablet mass, height, mechanical strength, and disintegration time are time- and resource-consuming and poorly suited to support an effective transition towards continuous manufacturing. Another suitable parameter to monitor during production would be tablet porosity. Porosity can be linked to mechanical strength and disintegration but typically requires knowledge of tablet dimensions and mass. Tablet porosity measurements based on terahertz time-domain spectroscopy (THz-TDS) offer a fast and non-destructive approach to in-process control testing for physical tablet properties. This study presents THz-TDS reflection measurements as an alternative to the previously reported transmission setup. It is shown that the proposed method can determine porosity based on the reflected amplitude from the tablet surface, but also allows for precise determination of tablet height in the same measurement. The tablet mass can be estimated by combining the height and porosity measurements. This opens up for the opportunity to determine the tablet's mechanical strength by using the possible correlation to the determined porosity.

Leveraging a multivariate approach towards enhanced development of direct compression extended release tablets

Extended release formulations play a crucial role in the pharmaceutical industry by maintaining steady plasma levels, reducing side effects, and improving therapeutic efficiency and compliance. One commonly used method to develop extended release formulations is direct compression, which offers several advantages, such as simplicity, time savings, and cost-effectiveness. However, successful direct compression-based extended release formulations require careful assessment and an understanding of the excipients' attributes. The scope of this work is the characterization of the compaction behavior of some matrix-forming agents and diluents for the development of extended release tablets. Fifteen excipients commonly used in extended release formulations were evaluated for physical, compaction and tablet properties. Powder properties (e.g., particle size, flow properties, bulk density) were evaluated and linked to the tablet's mechanical properties in a fully integrated approach, and data were analyzed by constructing a principal component analysis (PCA). Significant variability was observed among the various excipients. The present work successfully demonstrates the applicability of PCA as an effective tool for comparative analysis, pattern and clustering recognition and correlations between excipients and their properties, facilitating the development and manufacturing of direct compressible extended release formulations.

Design of experiments approach on the compaction properties of co-amorphous tablets

Co-amorphous systems are an evolving strategy to stabilize the amorphous form of a drug molecule with the aim of overcoming its poor water-solubility. With research focussing on the molecular level of co-amorphous systems, little is known about their downstream processing. In this study, tablets of co-amorphous carvedilol and aspartic acid (CAR-ASP) with calcium hydrogen phosphate and croscarmellose sodium as excipients were produced using a compaction simulator. The amorphous form of spray dried CAR-ASP and the subsequently produced tablets was confirmed with XRPD. Over the storage time of 12 weeks, no recrystallization of the amorphous material was observed. A central composite face-centred design with three factors was set up to investigate the interplay of formulation and processing variables with the tablet characteristics elastic work, tensile strength and disintegration time. As a result, increasing the amount of co-amorphous material led to a decrease in elastic work and an increased tensile strength. These effects were beneficial for tablet properties, namely harder tablets and reduced elasticity. Disintegration time was prolonged by amounts of up to 25-30% co-amorphous material, while larger amounts induced faster tablet disintegration. While showing the feasibility of compacting co-amorphous material with calcium hydrogen phosphate, this study also gives insight into how tablet characteristics are affected by co-amorphous material and relevant process parameters.

A Simplified Model Structure for Compression Characterization of Pharmaceutical Tablets

Despite, or maybe because of, many shortcomings, Heckel's equation is by far the most investigated compressibility model for decades. The somewhat overlooked Gurnham equation is proposed as a more stable and better fitting compressibility model. Combining this equation with a linear model for the strength/pressure relation provides a composite function identical with the often-used Ryshkewitch equation for the relation between strength and porosity. It is thus questioned whether the three-dimensional compression characterization presented in USP monograph 1062 is correct. Substantial errors in computed parameters are revealed with consequences for reproducibility or inter-lab assessments. Elastic recovery is proposed as a more interesting and relevant characteristic in relation to pharmaceutical tablet formulation.

On the complexity of predicting tablet capping

Predicting tablet defects, such as capping, that might occur during manufacturing, is a challenge in the pharmaceutical industry. In the literature, different parameters were presented to predict capping but no general consensus seems to have been reached yet. In this article, we chose to study a wide range of products (18 formulations, 8 of which presenting capping) to predict capping on biconvex tablets using the properties characterized on defect-free flat-faced tablets (tensile strength, solid fraction, elastic recovery, etc.), made using the same process parameters. Single parameters and predictive indices presented in the literature were evaluated on this set of formulations and were found not suitable to predict capping. A predictive model was then developed using a decision tree analysis and was found to depend only on three in-die tablet properties: the plastic energy per volume, the in-die elastic recovery and the residual die-wall pressure. This model was tested on another set of 13 formulations chosen to challenge it. The capping behavior of 29 out of the 31 formulations studied in total was well estimated using the developed model with only two products which were predicted to cap and did not. This shows the potential of the used approach in terms of risk analysis and assessment for capping occurrence.

Breaking patterns of press-coated tablets during the diametral compression test: Influence of the product, geometry and process parameters

Press-coated tablets are a high-interest technology in chronopharmaceutics, for modified release applications. As for any kind of tablet, the test of the mechanical resistance is of primary importance at the industrial level during both the development and production steps. For this purpose, the diametral compression test is commonly used in the industry for press-coated tablets. Nevertheless, the result of this test can be much more complex compared to the case of single layer tablets. This work aims to study the applicability of this test to press-coated tablets. Diametral compression tests were performed on press-coated tablets obtained with different products (shell/core), shell sizes and compaction pressures. Four types of breaking profiles were found: total diametral, shell diametral, around the core and laminated depending on the process parameters/products used to obtain the tablet. Digital image correlation was used in order to understand the breaking patterns especially in terms of failure initiation and propagation. The kind of breaking pattern obtained is dependent on the final structure of the tablet in terms of density distribution and thus of elastic properties. To confirm the findings, numerical simulations by the finite element method was used to visualize the stress distribution inside the tablet and confirm the influence of the process parameters. The multiple failure profiles obtained imply that the output value of the diametral compression test applied to press-coated tablets should be taken with caution.

Monitoring the weight and dimensional expansion of pyridostigmine bromide tablets under dynamic vapor sorption and impact of deliquescence on tablet strength and drug release

Changes of weight and axial expansion of tablets of the deliquescent drug pyridostigmine bromide with Kollidon SR were followed with relative humidity (RH) using dynamic vapor sorption and displacement transducer. The effects of RH on placebo and drug containing (API) tablets prepared at low and high compression were related to tablet strength and molecular changes. Tablet weight and expansion increased with RH, especially above RH 40%. Tablet rigidity and strength decreased linearly with moisture for placebo tablets whereas for API tablets there was decrease up to 50% followed by large drop at 60%. Raman spectra of tablets did not show chemical interactions due to moisture, but decreased intensity of drug peak at 2370 cm^-1 indicating solid state changes. Decrease of polymer peak intensities at 805 and 1740 cm^-1 occurred only in API tablets implicating drug deliquescence in polymer moisture sorption. X-ray diffraction and thermal analysis of tablets indicated complete drug liquefaction after exposure at 60% RH, which impacted great loss of strength but did not affect the sustained release profile. In conclusion, monitoring of the physical properties of tablets during production of deliquescent drugs is necessary to avoid pitfalls during downstream processes such as coating, packaging and storage.

Insights on the role of excipients and tablet matrix porosity on aspirin stability

Excipient-moisture interaction can be a critical attribute in determination of product stability. This study aimed to investigate influence of integrating excipients having different moisture interaction into moisture sensitive drug formulations. Aspirin was formulated with maize starch (MS), microcrystalline cellulose (MCC) and calcium hydrogen phosphate dihydrate (DCP). The excipients were evaluated for their inherent moisture content and water activity. Tablets fabricated at different compression pressures were exposed to 40 °C, 75% relative humidity for a stipulated period before analyzing for aspirin degradation. The results revealed that while MS had higher moisture content, the water activity was relatively low. Consequently, MS tablets had lower aspirin degradation than MCC and DCP tablets. In contrast, high water activity of DCP resulted in greater aspirin degradation. This was despite the low moisture content of DCP. Influence of tablet porosity on aspirin degradation was minimal. This illustrated the fugacity of moisture, possessing high thermodynamic activity and physical spatial delimitation would not suppress its distribution. The findings suggested that excipients possessing high water retentive capacity could potentially be useful as internal tablet desiccants by acting as a moisture scavenger. This study also highlights the importance of water activity in preformulation studies related to the choice of excipients.

Elastic recovery in roll compaction simulation

Roll compaction/dry granulation is a widely used granulation method in the pharmaceutical industry. The simulation of the process is of great interest, especially in the early phase of formulation development of solid dosage forms. The hybrid modeling approach allows to predict the roll compaction process parameters to produce ribbons with a desired solid fraction. Based on the process parameters, compacts (ribblets) of the same solid fraction are produced on a single punch press. So far, the prediction accuracy for the solid fraction of the ribbons was not satisfactory. It was found that the lack in prediction accuracy was due to the elastic recovery, which was not considered in the model. In this study, the fast in-die and the slow out-of-die elastic recovery of different excipients with varying compaction properties were investigated. A method was established to compensate for the elastic recovery of compacts in roll compaction simulation and to improve the prediction accuracy of the solid fraction considerably. The results were successfully implemented into the model through an additional learning step. Moreover, the findings were transferred to the mimicking of an API containing formulation. By modeling, it was possible to accurately predict the process settings to obtain ribbons with the desired solid fraction using only a small amount of material.

Challenges in technology of bilayer and multi-layer tablets: a mini-review

Bilayer and multi-layer tablets are enjoying growing popularity among original drug and generic product manufacturers. Multi-layer tablets have many key benefits compared to classic immediate-release tablets. The use of such solid oral dosage forms simplifies dosing regimens in combination therapy, and thus improves patient compliance. However, the technology of multilayer tablets is demanding and requires precise choice of excipients and production parameters with regard to each technological step. The main benefits of multi-layer tablets, certain aspects of their production and the challenges encountered during the compression process are reviewed in this paper.

The influence of core tablets rheology on the mechanical properties of press-coated tablets

Press-coating (also called compression coating or dry coating) consists of a second compression of an outer layer of material over a preformed tablet core. Despite being old, this technology has returned to popularity due to its widespread use in preparation of chronotherapeutic dosage forms. The literature available on press-coated tablets has mainly investigated drug release kinetics, while there is a lack of information about their mechanical properties. Here we study, for the first time, the effect of material properties and manufacturing parameters on the mechanical characteristics of press-coated tablets. Firstly, we show that the stiffness of the bare core tablets depends on the material type and, in case of viscoelastic materials, also depends on the compression pressure. We then demonstrate that less stiff (i.e. more viscoelastic) core tablets deform to a greater extent upon the second compression and thus allow the formation of less porous, harder coats and with a more homogenous density distribution. Finally, we find that changes in the mechanical properties of press-coated tablets over one month storage are almost negligible. Our data suggest that viscoelastic rather than stiff cores should be used in dry coating, as they promote the formation of more homogenous coats and with better mechanical properties.

Predicting tablet tensile strength with a model derived from the gravitation-based high-velocity compaction analysis data

In the present study, a model was developed to estimate tablet tensile strength utilizing the gravitation-based high-velocity (G-HVC) method introduced earlier. Three different formulations consisting of microcrystalline cellulose (MCC), dicalcium phosphate dihydrate (DCP), hydroxypropyl methylcellulose (HPMC), theophylline and magnesium stearate were prepared. The formulations were granulated using fluid bed granulation and the granules were compacted with the G-HVC method and an eccentric tableting machine. Compaction energy values defined from G-HVC data predicted tensile strength of the tablets surprisingly well. It was also shown, that fluid bed granulation improved the compaction energy intake of the granules in comparison to respective physical mixtures. In addition, general mechanical properties and elastic recovery were also examined for all samples. In this study it was finally concluded, that the data obtained by the method was of practical relevance in pharmaceutical formulation development.

Characterization of Mechanical Property Distributions on Tablet Surfaces

Powder densification through uniaxial compaction is governed by a number of simultaneous processes taking place on a reduced time as the result of the stress gradients within the packing, as well as the frictional and adhesive forces between the powder and the die walls. As a result of that, a density and stiffness anisotropy is developed across the axial and radial directions. In this study, microindentation has been applied to assess and quantify the variation of the module of elasticity ( E m o d ) throughout the surface of cylindrical tablets. A representative set of deformation behaviors was analyzed by pharmaceutical excipients ranging from soft/plastic behavior (microcrystalline cellulose) over medium (lactose) to hard/brittle behavior (calcium phosphate) for different compaction pressures. The results of the local stiffness distribution over tablet faces depicted a linear and directly proportional tendency between a solid fraction and E m o d for the upper and lower faces, as well as remarkable stiffness anisotropy between the axial and radial directions of compaction. The highest extent of the stiffness anisotropy that was found for ductile grades of microcrystalline cellulose (MCC) in comparison with brittle powders has been attributed to the dual phenomena of overall elastic recovery and Poisson's effect on the relaxation kinetics. As a reinforcement of this analysis, the evolution of the specific surface area elucidated the respective densification mechanism and its implementations toward anisotropy. For ductile excipients, the increase in the contact surface area as well as the reduction and closing of interstitial pores explain the reduction of surface area with increasing compaction pressure. For brittle powders, densification evolves through fragmentation and the subsequent filling of voids.

Impact of Porous Excipients on the Manufacturability and Product Performance of Solid Self-Emulsifying Drug Delivery Systems

FDA-approved self-emulsifying medicines rely on liquid-based formulations, which can exhibit limited stability and short shelf-lives. Solid self-emulsifying drug delivery systems (SEDDS) can improve such issues, but there is still a great need for identifying suitable porous carriers to convert liquid SEDDS into solids without impairing their mechanical properties, functionality, and industrial feasibility. The impact of SEDDS adsorption on tableting is also poorly understood. Therefore, solid SEDDS were prepared by adsorbing liquid SEDDS onto ten commercially available porous excipients. Products were assessed with respect to mechanical behavior, tabletability, and product performance. Adsorbing SEDDS onto porous excipients led to satisfactory stability, with the exception of Zeopharm® 600 due to its high alkalinity, and Neusilin® US2/UFL2, which caused quercetin to crystallize out of the liquid concentrate. SEDDS adsorption reduced the elastic recovery of most excipients, making tableting achievable using Aeroperl® 300 and Aerosil® 200/300. The impact of SEDDS on elastic recovery provides additional understanding on solid SEDDS manufacture process. Acceptable tablets were made via direct compression but with slow disintegration. Addition of a superdisintegrant (crospovidone 5% w/w) ensured tablet manufacturing without impairment of product performance. Solid SEDDS displayed several technical advantages over their liquid counterparts, but attention must be given to the properties of the porous excipient chosen. Drug-excipient interactions play a significant role in drug degradation and crystallization in solid SEDDS. Improved mechanical behavior upon adsorption led to well-composed tablets that performed satisfactorily in vitro upon addition of a superdisintegrant. This study provides an insight on excipient-oriented rational development of solid SEDDS.

Powder Compression Properties of Paracetamol, Paracetamol Hydrochloride, and Paracetamol Cocrystals and Coformers

The objective was to study the relationship between crystal structure, particle deformation properties, and tablet-forming ability for the monoclinic form of paracetamol (PRA), 2 cocrystals and a salt crystal of PRA in addition to 2 coformers (oxalic acid and 4,4'-bipyridine). Thus, the structure-property-performance relationship was investigated. Analytical powder compression was used for determination of effective plasticity, as inferred from the Heckel yield pressure and the Frenning parameter, and the elastic deformation was determined from in-die tablet elastic recovery. The plasticity could not be linked to the crystal lattice structure as crystals containing zig-zag layers displayed similar plasticity as crystals containing slip planes. In addition, crystals containing slip planes displayed both high and low plasticity. The mechanical properties could not be linked to the tablet-forming ability as the tablet tensile strength, unexpectedly, displayed a tendency to reduce with increased plasticity. Furthermore, the elastic deformation could not explain the tablet-forming ability. It was concluded that no relationship between structure-property-performance for PRA and its cocrystals and salt could be established. Thus, it was indicated that to establish such a relationship, an improved knowledge of crystallographic structure and interparticle bonding during compaction is needed.

In-line monitoring of compaction properties on a rotary tablet press during tablet manufacturing of hot-melt extruded amorphous solid dispersions

As the number of applications for polymers in pharmaceutical development is increasing, there is need for fundamental understanding on how such compounds behave during tableting. This research is focussed on the tableting behaviour of amorphous polymers, their solid dispersions and the impact of hot-melt extrusion on the compaction properties of these materials. Soluplus, Kollidon VA 64 and Eudragit EPO were selected as amorphous polymers since these are widely studied carriers for solid dispersions, while Celecoxib was chosen as BCS class II model drug. Neat polymers and physical mixtures (up to 35% drug load) were processed by hot-melt extrusion (HME), milled and sieved to obtain powders with comparable particle sizes as the neat polymer. A novel approach was used for in-line analysis of the compaction properties on a rotary tablet press (Modul P, GEA) using complementary sensors and software (CDAAS, GEA). By combining 'in-die' and 'out-of-die' techniques, it was possible to investigate in a comprehensive way the impact of HME on the tableting behaviour of amorphous polymers and their formulations. The formation of stable glassy solutions altered the formulations towards more fragmentary behaviour under compression which was beneficial for the tabletability. Principal component analysis (PCA) was applied to summarize the behaviour during compaction of the formulations, enabling the selection of Soluplus and Kollidon VA 64 as the most favourable polymers for compaction of glassy solutions.

Diffusion and swelling measurements in pharmaceutical powder compacts using terahertz pulsed imaging

Tablet dissolution is strongly affected by swelling and solvent penetration into its matrix. A terahertz-pulsed imaging (TPI) technique, in reflection mode, is introduced as a new tool to measure one-dimensional swelling and solvent ingress in flat-faced pharmaceutical compacts exposed to dissolution medium from one face of the tablet. The technique was demonstrated on three tableting excipients: hydroxypropylmethyl cellulose (HPMC), Eudragit RSPO, and lactose. Upon contact with water, HPMC initially shrinks to up to 13% of its original thickness before undergoing expansion. HPMC and lactose were shown to expand to up to 20% and 47% of their original size in 24 h and 13 min, respectively, whereas Eudragit does not undergo dimensional change. The TPI technique was used to measure the ingress of water into HPMC tablets over a period of 24 h and it was observed that water penetrates into the tablet by anomalous diffusion. X-ray microtomography was used to measure tablet porosity alongside helium pycnometry and was linked to the results obtained by TPI. Our results highlight a new application area of TPI in the pharmaceutical sciences that could be of interest in the development and quality testing of advanced drug delivery systems as well as immediate release formulations. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:1658–1667, 2015

A material-sparing method for assessment of powder deformation characteristics using data collected during a single compression-decompression cycle

Compressibility profiles, or functions of solid fraction versus applied pressure, are used to provide insight into the fundamental mechanical behavior of powders during compaction. These functions, collected during compression (in-die) or post ejection (out-of-die), indicate the amount of pressure that a given powder formulation requires to be compressed to a given density or thickness. To take advantage of the benefits offered by both methods, the data collected in-die during a single compression-decompression cycle will be used to generate the equivalent of a complete out-of-die compressibility profile that has been corrected for both elastic and viscoelastic recovery of the powder. This method has been found to be both a precise and accurate means of evaluating out-of-die compressibility for four common tableting excipients. Using this method, a comprehensive characterization of powder compaction behavior, specifically in relation to plastic/brittle, elastic and viscoelastic deformation, can be obtained. Not only is the method computationally simple, but it is also material-sparing. The ability to characterize powder compressibility using this approach can improve productivity and streamline tablet development studies.

A study on in-line tablet coating--the influence of compaction and coating on tablet dimensional changes

Prior to coating, tablets are usually stored for a definite period to enable complete strain recovery and prevent subsequent volumetric expansion-related coating defects. In-line coating is defined as the coating of tablets immediately after compaction. In-line coating will be expected to improve manufacturing efficiencies. In this study, the possibility of in-line coating was studied by evaluating the influence of compaction and coating on tablet dimensional changes. The use of tapered dies for compaction was also evaluated. Two types of tablet coaters which presented different coating environments, namely the Supercell™ coater and pan coater, were employed for coating. The extent of tablet dimensional changes was studied in real time using optical laser sensors in a controlled environment. After compaction, tablet dimensional changes were found to be anisotropic. In contrast, coating resulted in isotropic volume expansion in both the axial and radial directions. Pan coating resulted in significantly greater tablet dimensional changes compared to Supercell™ coating. There was no significant difference in dimensional changes of tablets coated in line or after complete viscoelastic strain recovery for Supercell™ coating. However, significantly different dimensional changes were observed for pan coating. The use of tapered dies during compaction was found to result in more rapid viscoelastic strain recovery and also significantly reduced tablet dimensional changes when tablets were immediately coated after compaction using the pan coater. In conclusion, the Supercell™ coater appeared to be more suitable for in-line tablet coating, while tapered dies were beneficial in reducing tablet dimensional changes when the pan coater was employed for in-line coating.

The reality of in-line tablet coating

The possibility of continuous processing in pharmaceutical tablet manufacturing is hampered by the viscoelastic recovery of tablets post-compaction. Compacted tablets are typically aged before coating to allow complete viscoelastic recovery so as to avoid subsequent coating defects. There has been little attempt to overcome tablet recovery in order to enable continuous processing and improve manufacturing efficiency. However, with the introduction of improved or newly developed types of tablet-coating equipment, there is renewed interest in the coating of tablets in-line. In-line tablet coating is defined as the coating of tablets immediately after compaction. It is a one-step highly integrated system that circumvents the delay in processing time typically given to allow viscoelastic recovery of tablets. This review aims to summarize the requirements of an in-line tablet-coating system. The possibility of carrying out in-line tablet coating in the near future will also be discussed.

Optimization of process parameters for a quasi-continuous tablet coating system using design of experiments

The aim of this study was to identify and optimize the critical process parameters of the newly developed Supercell quasi-continuous coater for optimal tablet coat quality. Design of experiments, aided by multivariate analysis techniques, was used to quantify the effects of various coating process conditions and their interactions on the quality of film-coated tablets. The process parameters varied included batch size, inlet temperature, atomizing pressure, plenum pressure, spray rate and coating level. An initial screening stage was carried out using a 2(6-1(IV)) fractional factorial design. Following these preliminary experiments, optimization study was carried out using the Box-Behnken design. Main response variables measured included drug-loading efficiency, coat thickness variation, and the extent of tablet damage. Apparent optimum conditions were determined by using response surface plots. The process parameters exerted various effects on the different response variables. Hence, trade-offs between individual optima were necessary to obtain the best compromised set of conditions. The adequacy of the optimized process conditions in meeting the combined goals for all responses was indicated by the composite desirability value. By using response surface methodology and optimization, coating conditions which produced coated tablets of high drug-loading efficiency, low incidences of tablet damage and low coat thickness variation were defined. Optimal conditions were found to vary over a large spectrum when different responses were considered. Changes in processing parameters across the design space did not result in drastic changes to coat quality, thereby demonstrating robustness in the Supercell coating process.

Effects of thermal curing conditions on drug release from polyvinyl acetate-polyvinyl pyrrolidone matrices

This study aimed to investigate the effects of dry and humid heat curing on the physical and drug release properties of polyvinyl acetate-polyvinyl pyrrolidone matrices. Both conditions resulted in increased tablet hardness; tablets stored under humid conditions showed high plasticity and deformed during hardness testing. Release from the matrices was dependent on the filler's type and level. Release profiles showed significant changes, as a result of exposure to thermal stress, none of the fillers used stabilized matrices against these changes. Density of neat polymeric compacts increased upon exposure to heat; the effect of humid heat was more evident than dry heat. Thermograms of samples cured under dry heat did not show changes, while those of samples stored under high humidity showed significant enlargement of the dehydration endotherm masking the glass transition of polyvinyl acetate. The change of the physical and release properties of matrices could be explained by the hygroscopic nature of polyvinyl pyrrolidone causing water uptake; absorbed water then acts as a plasticizer of polyvinyl acetate promoting plastic flow, deformation, and coalescence of particles, and altering the matrices internal structure. Results suggest that humid heat is more effective as a curing environment than dry heat for polyvinyl acetate-polyvinyl pyrrolidone matrices.

Compressional behavior of a mixture of granules containing high load of Phyllanthus niruri spray-dried extract and granules of adjuvants: comparison between eccentric and rotary tablet machines

The purpose of this paper was to evaluate the compressional behavior of granules containing high load of a Phyllanthus niruri spray-dried extract in eccentric (ETM) and rotary (RTM) tablet presses. Tablets were constituted by spray-dried extract granules (SDEG, 92%), excipient granules (EXCG, 7.92%), and magnesium stearate (0.08%). SDEG was obtained by dry granulation and EXCG, composed of microcrystalline cellulose (62.9%) and sodium starch glycolate (37.1%), by wet granulation. Particle size distribution was fixed between 0.250 and 0.850 mm. Tablets did not evidence any mechanical failures, such as lamination or capping, or anomalous weight variation in either tablet machine types. Upper and lower tablet surface photomicrographs from ETM and RTM tablets showed differences in porosity and texture. Different RTM speeds suggested the visco-plastic behavior of the formulation, since, by slowing down rotation speeds, the tensile strength of the tablets increased significantly, but the porosity and disintegration time were not affected. Tablets produced in RTM showed lower friability and porosity than ETM tablets, which did not reflect on higher tensile strength. The EXCG distribution at upper and lower surfaces from ETM and RTM tablets was quantified by image analysis and evaluated through statistical methods. Spray-dried extract release was not influenced by the type of equipment or operational conditions to which the compacts were submitted. Construction and operation differences between both tablet presses influenced the final product, since tablets with similar tensile strength, made by distinct tablet machines, exhibited different quality parameters.

Evaluation of the compaction of sulfathiazole polymorphs

The aim of this study was to relate the tableting performance assessed by an instrumented tableting machine to the mechanical properties measured by nanoindentation. Three different polymorphic forms of sulfathiazole were prepared by recrystallization, and the density and X-ray powder diffraction patterns were measured and compared with theoretical density and simulated powder patterns, respectively. Tablets were prepared using a series of applied pressures, and the results were subjected to energy analysis, three dimensional (3D) modeling, and the traditional Heckel analysis. With these approaches, form I was found to be consistently the most brittle material, but the subtle differences between forms II and III were only revealed by 3D modeling. The rank order of the crushing force was found to be I is congruent to II < III. From nanoindentation, form III was found to be much harder than forms I and II, and III also had a much higher Young's modulus. The energy calculations of the nanoindentation curves showed that form III was distinct from forms I and II, which is consistent with the presence of slip planes that are only present in form III. However, in this system, there was little correspondence between the macroscopic and microscopic measurements, and thus particle-particle interactions may to be of paramount importance.

Evaluation of powder and tableting properties of chitosan

The aim of this study was to analyze the process of tablet formation and the properties of the resulting tablets for 3 N-deacetylated chitosans, with a degree of deacetylation of 80%, 85%, or 90%. Material properties, such as water content, particle size and morphology, glass transition temperature, and molecular weight were studied. The process of tablet formation was analyzed by 3-D modeling, Heckel analysis, the pressure time function, and energy calculations in combination with elastic recovery dependent on maximum relative density and time. The crushing force and the morphology of the final tablets were analyzed. Chitosans sorb twice as much water as microcrystalline cellulose (MCC), the particle size is comparable to Avicel PH 200, a special type of MCC, the particles look like shells, and the edges are bent. Molecular weight ranges from 80,000 to 210,000 kDa, the glass transition temperature (Tg) was not dependent on molecular weight. The chitosans deform ductilely as MCC; however, plastic deformation with regard to time and also pressure plasticity are higher than for MCC, especially for Chit 85, which has the lowest crystallinity and molecular weight. At high densification, fast elastic decompression is higher. 3-D modeling allowed the most precise analysis. Elastic recovery after tableting is higher than for MCC tablets and continues for some time after tableting. The crushing force of the resulting tablets is high owing to a reversible exceeding of Tg in the amorphous parts of the material. However, the crushing force is lower compared with MCC, since the crystallinity and the Tg of the chitosans are higher than for MCC. In summation, chitosans show plastic deformation during compression combined with high elasticity after tableting. Highly mechanically stable tablets result.

Die wall pressure measurement for evaluation of compaction property of pharmaceutical materials

The aim of this study was to evaluate the compaction property of several pharmaceutical materials by measuring the die wall pressure. The profile of die wall force during tabletting process was measured with the compaction process analyzer (TabAll). Several compaction parameters such as maximum die wall pressure (MDP), residual die wall pressure (RDP) and pressure transmission ratio (PTR) from upper punch to lower punch were calculated. The ejection pressure (EP) of tablet compacted was also measured as a parameter for sticking property of the compacts. The profile of die wall force observed was classified to the typical two types, a small type and a large one. Partly pre-gelatinized starch (PCS), cornstarch and low substituted hydroxypropylcellulose (L-HPC) were the small type, while crystalline lactose, ascorbic acid and potassium chloride were the large type. The die wall force of crystalline lactose remarkably increased at the ejection of tablet and then capping was observed. RDP value of PCS, cornstarch, L-HPC was smaller than that of crystalline lactose, ascorbic acid, potassium chloride. As the higher pressure transmission ratio from upper punch to lower punch means a good compressing property of the powder, we proposed that RDP/MDP is a useful parameter for evaluating the compaction property of powders. Although potassium chloride which is strongly plastic deformable powder showed the highest RDP value among the powders tested, the RDP/MDP value was lower than that of crystalline lactose or ascorbic acid and the tensile strength of resultant tablet of potassium chloride was much higher than these powders.

“Soft Tableting”: A New Concept to Tablet Pressure Sensitive Materials

The aim of this study was to confirm the hypothesis that tableting using excipients with greater elastic deformation results in improved performance of pressure-sensitive drugs relative to the excipients with low elastic deformation. Tableting with highly elastic deforming excipients and the resultant minimization of the process damage is referred to in this article as "soft tableting." Carrageenans, chitosans, and polyethylene oxides were tested as potentially useful tableting excipients. alpha-Amylase, amorphous indomethacin, theophylline monohydrate, and enteric-coated pellets were used as models for pressure-sensitive materials. Three-dimensional modeling of the tableting data and elastic recovery of the tablets were the tools for mechanical characterization. The crushing force of the tablets was analyzed. Inactivation of alpha-amylase was determined by using the starch iodine reaction method. Pseudopolymorphic and polymorphic changes were analyzed using Fourier transform (FT) Raman spectroscopy. The effects of pressure on the integrity of the pellets were tested by release studies and scanning electron microscopy. The process of tablet formation was characterized for potentially useful tableting excipients. The results were compared with the results of traditional excipients as microcrystalline cellulose (MCC), dicalcium phosphate dihydrate, and hydroxypropyl methylcellulose (HPMC). A ranking order for soft tableting was deduced from the mechanical properties. The tableting excipients were ranked according to their general plasticity (GP): GP(carrageenans)<GP(chitosans)<GP(MCC)<GP(HPMC)<GP(polyethylene oxides). This theoretical order of suitability has been experimentally proven to be valid for the pressure-sensitive materials. In conclusion, the new concept for soft tableting is valid.

The 3-D model: does time plasticity represent the influence of tableting speed?

The objective of this study is to test the hypothesis that time plasticity (parameter d from 3-D modeling) is influenced by tableting speed. Tablets were produced at different maximum relative densities (rho(rel, max)) on an instrumented eccentric tableting machine and on a linear rotary tableting machine replicator. Some 3-D data plots were prepared using pressure, normalized time, and porosity according to Heckel. After fitting of a twisted plane, the resulting parameters were analyzed in a 3-D parameter plot. The materials used were dicalcium phosphate dihydrate (DCPD), spray-dried lactose, microcrystalline cellulose (MCC), hydroxypropyl methylcellulose (HPMC), kappa-carrageenan (CAR), and theophylline monohydrate (TheoM). The results show that tableting speed especially influences the parameter d (time plasticity) of the 3-D model for plastically and viscoelastically deforming materials such as MCC, HPMC, CAR, and TheoM. For more plastically deforming materials such as MCC, HPMC, and TheoM, a subtle influence on omega is also visible. The stages of higher densification are affected more than the stages of lower densification. Brittle materials such as DCPD exhibit no influence of tableting speed. The influence of speed on spray-dried lactose is minor. The results are valid for data obtained from an eccentric tableting machine and also for data from a linear rotary tableting machine replicator. Thus, the empirically derived parameter time plasticity d really represents the influence of time.