Heckel Analysis Research Articles

Compaction behavior and optimization of spray-dried lactose with various amorphous content

The purpose of this study was to investigate the influence of amorphous content in spray-dried lactose on tableting characteristics. To obtain different amorphous contents, spray-dried lactoses were prepared at various lactose concentrations in distilled water. Plain spray-dried lactose and hydrochlorothiazide-lactose based tablets were compressed on an instrumented tablet press. Heckel analysis indicated that relative density (D B ) and yield pressure (P y ) correlated with both the degree of crystallinity and particle size and shape. The compactibility of the tablets was found to increase with amorphous content up to 20 % and then decreased and leveled off as the amorphous content was greater than 30 %. At 30 % amorphous and higher the spray-dried lactose tablets exhibited dissolution and erosion rather than disintegration in distilled water which was observed with lower amorphous lactose. The results indicated that tablet disintegration was influenced by compaction pressure and amorphous level (p

Compressional characteristics and drug release profile of tablets of the crude leaves extract of Vernonia galamensis

Tablet formulation of the crude aqueous extract of the leaves of Vernonia galamensis (Asteraceae), used for the treatment of diabetes in folk medicine was carried out using the wet granulation method. The dried extract is deliquescent in nature; therefore, efflorescent diluents were carefully selected for the formulation. The purpose of this study was to establish suitable diluents for the formulation of Vernonia galamensis tablets and to study the compressional characteristics and drug release profile. The efflorescent diluents were; calcium phosphate (Hopkins and Williams, UK), Aerosil® 200 (GmbH, Meggle, Germany) and Avicel® PH 101 (FMC Corporation, USA). The dissolution times of tablets were determined as specified in BP 2007. Heckel analysis was used for compaction studies, tensile strength for mechanical strength and dissolution time for drug release studies. GraphPad Prism® version 5.03 software was used for statistical analysis. Negative intercepts were a major limitation to the use of Heckel analysis, but good quality tablets of the deliquescent crude extract of Vernonia galamensis (Asteraceae) with acceptable release profile could be formulated using calcium phosphate as diluent and polyvinylpyrrolidone (5%, w/v) as binder at a compression pressure of 290 MNm–2. Key words: Compressibility, dissolution, Heckel equation

Negative intercepts in the Heckel analysis of the crude extract of Vernonia galamensis: A major setback of the equation

Introduction: The dry powdered leaf of Vernonia galamensis (Asteraceae) has been used by traditional herbalists in northern Nigeria to treat diabetes mellitus. However, medicinal plants used in folk medicine have no standard dose or acceptable method of formulation. In this study therefore, the leaves of Vernonia galamensis (Asteraceae) were extracted, evaluated for pharmacological activity and formulated into tablets. Materials and Methods: The extract was found to be highly hygroscopic and deliquescent, therefore the following efflorescent diluents; aerosil® 200 (GmbH, Meggle, Germany), avicel PH 101 (Honey Well and Stein, UK), and anhydrous calcium phosphate (BDH chemicals, England) were used. The wet granulation method was employed for the tablet formulation and the compaction characteristics of the granules were determined using the Heckel equation. Results and Conclusions: Negative intercepts were a setback to the use of the Heckel equation due to the resulting negative values of D A and D B . This makes it difficult to explain the compaction characteristics of the crude extract.

The effect of spray drying on the compaction properties of hypromellose acetate succinate

Background: The aim of this study was to evaluate the compaction behavior of a model two-component amorphous spray-dried dispersion system compared with the unprocessed excipients, using simulated rotary tablet press production conditions. Method: In this study, the stabilizing polymer, hypromellose acetate succinate (HPMCAS), was solubilized and spray dried with and without sodium lauryl sulfate (SLS). The impact of compression force and speed on the tabletting process was quantified by means of tablet tensile strength, compaction energy, and Heckel analysis. Results: Addition of the surfactant SLS, spray dried or as a physical mix, reduced the tablet strength. However, a lesser impact on the unprocessed excipients was observed in comparison with the spray-dried excipients. In the presence of 1% (w/w) SLS, tablets displayed a tendency to cap when compressed at higher speeds, supported by high elastic energy values indicating high uniaxial stress upon decompression. In the presence of 3% (w/w) SLS, tablets could not be produced at high speeds. Heckel analysis revealed a greater strain rate sensitivity of HPMCAS when spray dried in the presence of surfactant. Exposure of samples to a range of relative humidities before compaction had no effect on tablet strength. Conclusion: This study has shown that spray drying of HPMCAS in the presence of a surfactant affects the compressibility of the material, resulting in decreased tablet strength, increased elastic deformation, and capping.

Mechanistic investigation on pressure dependency of Heckel parameter

This work proposed to study the influence of varying compaction pressure on the plastic energy, elasticity (Young's modulus), particle yield strength, strain hardening, and applied pressures on derived Heckel parameter using material with different densification and deformation mechanisms: ibuprofen (IBN), paracetamol (PCM) (elastic behavior), methyl cellulose (Me-Cel), microcrystalline cellulose (MCC), sodium chloride (NaCl) (plastic behavior), and dicalcium phosphate (DCP) (brittle fracture). Force–displacement data were captured during in-die compaction for all materials having different deformation behavior. The apparent mean yield pressure (Py), plastic energy, Young's moduli, strain hardening parameter and rate of increase in Py were calculated from force–displacement compaction profiles obtained across a pressure range of 65–260 MPa. Materials under confined compression loading showed pressure dependent biphasic behavior in Py upon increasing pressure from 65 MPa to 260 MPa. IBN and PCM showed pressure dependency due to simultaneous elasticity and strain hardening upon increasing applied pressure. Me-Cel, MCC, and NaCl showed lower pressure dependency while DCP showed higher change in Py upon increasing pressure as a result of higher yield strength of DCP particles. Apparent mean yield pressure from Heckel analysis was significantly affected by the applied pressure, viscoelastic behavior, particle yield strength, and strain hardening. The simultaneously occurring events of elastic deformation and strain hardening give a false increase in Py at higher applied pressures.

Standarization and optimization of micromeretic properties of nimesulide for processing into a tablet dosage form by crystalo-co-agglomeration technology

The present study was undertaken to prepare direct compressible tablets of nimesulide by altering its physical properties with the help of the method crystallo-co-agglomeration technology. Nimesulide is a widely used nonsteroidal anti- inflammatory drugs type of drug and is very useful in the treatment of arthritis. Because of its poor flowability character, tablets of nimesulide cannot be prepared by direct compression. An attempt has been taken to improve the tableting property by altering the micromeretic properties, like flow rate, Carr index, Hausner ratio and angle of repose. Conformation of improvement of compressibility and other processing problems was studied by Heckel analysis and Kawakita constant using a hydraulic press under a pressure of 0.5, 1, 2 and 4 tonnes for 10 s. The tablets were prepared by direct compression of nimesulide agglomerates using two different types of polymers, polyethelene glycol (PEG6000) and ethyl cellulose (EC) in different ratios (50, 100 and 200 mg).The drug release shows different patterns for the various percentages of PEG and EC.

Evaluation of the mechanical properties of extrusion-spheronized beads and multiparticulate systems

Background: The mechanical properties of extrusion-spheronized beads as part of multiparticulate systems has not been adequately studied. Aim: The purpose was to study the mechanical properties of such drug beads and blends of drug beads and glycerol monostearate (GMS)-placebo beads. Method: Heckel analysis (mean yield pressure, Py), strain rate sensitivity (SRS), elastic recovery (ER), and total work of compression (TWC) studies were conducted using a PressterTM linear rotary tablet machine simulator operating at several combinations of speed and force. Results: The GMS-placebo beads exhibited the lowest Py values (9.1 ± 1.6 MPa) and TWC (1.9 ± 0.3 J) overall and these values steadily increased with increases in both applied speed and force. Although the placebo beads had the lowest ER values of 3.8 ± 0.7%, these beads showed significant time-dependent deformation behavior based on their SRS value of 70.2%. Heckel analysis showed that uncoated theophylline beads containing 58% ethylcellulose were more compressible than control beads containing 58% dicalcium phosphate dihydrate, the latter having the highest overall Py of 79.3 ± 3.8 MPa for the low speed/low force condition. Heckel plots also showed that 50:50 ratios of blends containing drug beads coated with either Surelease® or Eudragit® NE30D behaved similarly under increasing force and speed. Surelease®-coated cimetidine beads gave the highest Py, TWC, and ER values and these values were higher than Eudragit® NE30D-coated beads. The 50:50 blend ratios containing coated cimetidine beads showed higher Py, TWC, and ER values than the 60:40 ratios. Conclusion: Variation in the compressibility of different beads and blends can be attributed to excipients used in their formulation as well as to the drug bead-to-placebo bead ratio.

The effect of punch tilting in evaluating powder densification in a rotary tablet machine

The effect of punch tilting on the mechanism of punch penetration in the die of a rotary tablet machine during the compression cycle was evaluated by installing four displacement transducers on one station of a rotary machine. Two transducers were symmetrically positioned beside the upper punch in the upper turret, and the other two transducers were similarly placed beside the lower punch in the lower turret. Microcrystalline cellulose and dicalcium phosphate dihydrate were compressed at 5, 10, 15 and 20 kN using two different machine speeds, in order to quantify the effect of punch tilting in the evaluation of punch penetration. These compression data served to construct the powder bed reduction curves, from which it was possible to establish that punch tilting is directly proportional to the compression force used. Tilting is maximal at the beginning of the dwell time, disappears at half dwell time, and reaches a new maximum at the end of the dwell time. In latter case, tilting occurred in the direction opposite that of the first maximum. The impact of tilting in powder densification behaviour, evaluated through the construction of Heckel plots, depends on the compression force used in the analysis. Heckel plots are as distorted as the compression force is elevated. Consequently, the calculated Heckel parameters differ from the real values. Unless a very low compression force is used, a proper Heckel analysis can be performed in a rotary machine only if it is fitted with a device that includes the effect of punch tilting in the evaluation of punch penetration.

Influence of dry granulation on compactibility and capping tendency of macrolide antibiotic formulation

The effect of dry granulation (roller compaction and slugging) on compactibility and tablet capping tendency in a formulation with macrolide antibiotic and microcrystalline cellulose (MCC) was investigated. Direct tableting of this formulation revealed a pronounced capping tendency. Both dry granulated systems exhibit better compactibility and significant reductions in capping tendency compared to direct tableting. The capping tendency was also reduced through the use of precompression during direct tableting. The main volume reduction mechanism for macrolide antibiotic is fragmentation; this was confirmed by Heckel analysis, the lubricant sensitivity test, and SEM images. The yield pressure ( P y) of the direct tableting system is lower than the P y of dry granulated systems, which indicates the lower plasticity of dry granulated systems. These findings do not explain the lower capping tendency of dry granulated systems compared to direct tableting. The main differentiating bonding mechanism is attributed to long distance intermolecular bonds due to the intense amorphization of macrolide antibiotic that occurs during dry granulation. Amorphization leads to a significant increase in surface free energy and consequently stronger long distance bonding between particles, which can withstand elastic relaxation and therefore reduce the capping problem. Solid bridges probably do not make a notable contribution to the mechanical strength of tablets, due to the brittle nature of the particles and the complex molecular structure of macrolide antibiotic.

Compaction behavior of roller compacted ibuprofen

The effect of roller compaction pressure on the bulk compaction of roller compacted ibuprofen was investigated using instrumented rotary tablet press. Three different roller pressures were utilized to prepare granules and Heckel analysis, Walker analysis, compressibility, and tabletability were performed to derive densification, deformation, course of volume reduction and bonding phenomenon of different pressure roller compacted granules. Nominal single granule fracture strength was obtained by micro tensile testing. Heckel analysis indicated that granules prepared using lower pressure during roller compaction showed lower yield strength. The reduction in tabletability was observed for higher pressure roller compacted granules. The reduction in tabletability supports the results of granule size enlargement theory. Apart from the granule size enlargement theory, the available fines and relative fragmentation during compaction is responsible for higher bonding strength and provide larger areas for true particle contact at constant porosity for lower pressure roller compacted granules. Overall bulk compaction parameters indicated that granules prepared by lower roller compaction pressure were advantageous in terms of tabletability and densification. Overall results suggested that densification during roller compaction affects the particle level properties of specific surface area, nominal fracture strength, and compaction behavior.

Influence of crystal structure on the tableting properties of n‐alkyl 4‐hydroxybenzoate esters (parabens)

Certain crystallographic features, such as the existence of slip planes, can greatly facilitate the ability of crystals to deform plastically. An investigation of the relationship between the slip planes and the tableting performance of the crystals of methyl, ethyl, n-propyl, and n-butyl 4-hydroxybenzoate (parabens) was conducted. The absence of slip planes in methyl paraben crystal structure results in significantly poorer tableting performance than the other three parabens. While slip planes are present in the crystal structures of ethyl, propyl, and butyl parabens, they exhibited different plasticity as confirmed by crystal free volume analysis, crystal nano-indentation hardness, and Heckel analysis. Sieved fraction, 150-250 microm, of each paraben powder was compressed into tablets under different conditions. Tablet tensile strength, porosity, and Indices of tableting performance (ITP) were obtained. Under the same compaction pressure, tablet tensile strength was higher for crystals with higher plasticity. Tableting performance, assessed using the ITP, also improved with increasing crystal plasticity. The results confirm that high levels of plasticity, which can result from the presence of slip planes in crystal lattice, plays a critical role in the formation of strong and intact tablets by means of powder compaction.

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.

Mechanistic Study of the Effect of Roller Compaction and Lubricant on Tablet Mechanical Strength

Heckel analysis, tablet tensile strength, and indentation hardness were determined for a series of sieved and roller compacted microcrystalline cellulose mixtures under both unlubricated and lubricated conditions with magnesium stearate. These results have been used to evaluate the loss of reworkability following roller compaction for microcrystalline cellulose and show the extent of impact on tableting properties when magnesium stearate is added intragranularly prior to roller compaction. While results consistent with traditional work-hardening are observed as shown by a modest increase in dynamic hardness and mean yield pressure for unlubricated, roller compacted microcrystalline cellulose, it is overshadowed by the overlubrication effect seen during roller compaction and in particular, the subsequent milling step. The common practice of lubricating the feedstock with magnesium stearate to avoid sticking of the material to the compaction rolls appears to be the major cause of decreased mechanical strength of the final compressed tablets.

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.

Development of directly compressible powders via co-spray drying

Continuous production of directly compressible powders was achieved by coprocessing acetaminophen and carbohydrates via spray drying. Binary and ternary powder mixtures containing drug substance and carbohydrates were prepared by co-spray drying and evaluated on spray drying processibility, powder hygroscopicity, flowability, and compactability. The influence of process parameters during spray drying on the compaction behaviour of drug/excipient mixtures was investigated via Heckel analysis. Erythritol, lactose, maltodextrin, and mannitol were efficient in co-spray drying with acetaminophen. However, lactose mixtures showed poor flowability. Spray dried mixtures containing mannitol and erythritol were characterised as non-hygroscopic, highly dense, and good flowing powders. Mannitol increased tablet tensile strength in contrast with the poor compactability of erythritol. Maltodextrin was selected for further experiments because it provided excellent tablet tensile strength. The use of erythritol, maltodextrin and mannitol in binary drug/excipient mixtures resulted in high process yields. Compacts of erythritol, mannitol, and maltodextrin were characterised by higher tablet tensile strength at higher spray drying temperatures due to the increased particle fragmentation of erythritol and mannitol mixtures and to the increased plastic deformation of maltodextrin formulations. A combination of erythritol, maltodextrin, and mannitol was selected for further formulation and process optimisation of co-spray dried powders for direct compression.

Mechanical characterization of pharmaceutical solids: A comparison between rheological tests performed under static and dynamic porosity conditions

The aim of this work was to verify how and to what extent rheological tests, carried out under dynamic (Heckel) and static (creep, stress/strain) porosity conditions, may serve as a valuable complement to the classic Heckel tests in the characterization of viscoelastic and densification properties of solid materials for pharmaceutical use. Six different modified (pregelatinized) starches were compressed in a rotary tablet machine equipped to measure force and punch displacement. Tablets were obtained using flat-faced 6 mm diameter punches at different compression pressures. Compression cycles performed at the maximal pressure of 200 MPa were used to build the Heckel plots. Ejected tablets at the 10%, 20%, 30%, and 40% porosity levels were used for the stress/strain and creep tests. Parameters obtained with both types of tests were consistent with each other. In particular, among the six starches, lower viscosity values corresponded to lower P Y values, and lower elastic modulus values corresponded to lower elastic recovery of the tablet. Mechanical properties of materials can be better characterized if viscoelastic tests performed under dynamic porosity conditions (Heckel analysis) are supported by classical viscoelastic tests carried out under conditions of static porosity.

Effect of Particle Size and Compression Force on Compaction Behavior and Derived Mathematical Parameters of Compressibility

To analyze the influence of inherent densification and deformation properties of paracetamol on the mathematical parameters derived from Heckel, Walker, Kawakita, and Adams equations and to correlate these with single particle nominal fracture strength and bulk compression parameters using confined compression on a fully instrumented rotary tablet press. Force-displacement data were captured during in-die compression for four different particle size fractions (150-250, 300-450, 500-650, and 700-1,000 microm) of paracetamol each at compression force of 5.2, 8.6, and 17.3 kN. Nominal single particle fracture strength was obtained by micro tensile testing. Apparent mean yield pressure (Py) from Heckel analysis was significantly affected by the applied pressure, and was influenced by elastic energy and Young's modulus. The single particle fracture strength correlated to parameters obtained from Heckel, Walker, Kawakita, and Adams equations. Results obtained from bulk compression and single particle measurements were consistent with, and polynomially related to Py, Kawakita (1/b), and Adams parameter (tau0'). Values of Py, 1/b, and tau0' obtained from Heckel, Kawakita, and Adams equations, respectively, can be interpreted as a measure of single particle nominal fracture strength during confined compression loading. Walker and Adams parameters were less affected, than Heckel and Kawakita parameters, by the applied pressure.

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.

Polyethylene oxides

The aim of this study was to study tablet formation of polyethylene oxides (PEOs) with different molecular masses by means of 3D modeling and comparing the results to those of other more traditional techniques, such as Heckel analysis, analysis by the pressure-time function and energy analysis. The molecular masses ranged between 400,000 and 7,000,000 Da. Material properties, such as water content, particle size and morphology, and glass transition temperature were also studied. To complete this study, elastic recovery dependent on maximum relative density and time were determined. Furthermore, the crushing force of the tablets and their morphology were analyzed. The PEOs consist of smooth edged particles of irregular shape; the particle size is similar to one type of MCC, namely Avicel PH 200. The PEOs are much more ductile during compression than MCC. Elastic recovery after tableting is higher than that for tablets made from MCC and continues for some time after tableting. The crushing force of the resulting tablets is low. In conclusion, with regards to direct compression the PEOs do not appear to be useful as sole tableting excipients.

A material-sparing method for simultaneous determination of true density and powder compaction properties—Aspartame as an example

True density results for a batch of commercial aspartame are highly variable when helium pycnometry is used. Alternatively, the true density of the problematic aspartame lot was obtained by fitting tablet density versus pressure data. The fitted true density was in excellent agreement with that predicted from single crystal structure. Tablet porosity was calculated from the true density and tablet apparent density. After making the necessary measurements for calculating tablet apparent density, the breaking force of each intact tablet was measured and tensile strength was calculated. With the knowledge of compaction pressure, tablet porosity and tensile strength, powder compaction properties were characterized using tabletability (tensile strength versus pressure), compactibility (tensile strength versus porosity), compressibility (porosity versus pressure) and Heckel analysis. Thus, a wealth of additional information on the compaction properties of the powder was obtained through little added work. A total of approximately 4 g of powder was used in this study. Depending on the size of tablet tooling, tablet thickness and true density, 2–10 g of powder would be sufficient for characterizing most pharmaceutical powders.