An evaluation of three-dimensional modeling of compaction cycles by analyzing the densification behavior of binary and ternary mixtures

Characterization of acid modified Dioscorea starches as direct compression excipient

Starches obtained from four different Dioscorea species namely White (D. rotundata), Bitter (D. dumetorum), Chinese (D. oppositifolia) and Water yam (D. alata), were modified by acid hydrolysis and the physicochemical, material and tablet formation properties of the starches were investigated with the aim of determining their usefulness as a direct compression excipient in pharmaceutical tablets. The results obtained indicate that the physicochemical, material and tablet properties of the acid modified Dioscorea starches varied considerably among the various species. Acid hydrolysis led to an increase in solubility but decrease in swelling of the starches. Acid modification also led to an increase in the compressibility of the starches when compared with the native forms of the starches. Acid modified Water and White formed intact stable tablets only at higher rho(rel,) (max), while acid modified Chinese and Bitter formed tablets at all relative densities which could already be predicted from the deformation behaviour as analyzed by 3-D modeling. The result indicates that acid modified starch tablets showed higher crushing force and acceptable disintegration time and could therefore be useful as directly compressible excipient.

Evaluation of Tableting and Tablet Properties of Kollidon SR: The Influence of Moisture and Mixtures with Theophylline Monohydrate

The aim of the study was firstly to investigate the influence of moisture on the tableting and tablet properties of Kollidon SR and secondly to investigate the influence of theophylline monohydrate on the tableting behavior and tablet properties produced from binary mixtures with Kollidon SR. In comparison to Kollidon SR, microcrystalline cellulose (MCC) was used. The glass transition temperature (Tg) of the powder over the whole range of RH (0-90%), and in addition, the Tg of tablets of Kollidon SR were measured. Densities and flowability of the powders were analyzed. The tablets were produced at five different maximum relative densities (rho(rel), max) on an instrumented eccentric tableting machine. They were produced at three different relative humidities (RH), 30%, 45%, and 60% RH for the pure substances and binary mixtures with different ratios of drug and excipient were tableted at 45% RH. The tableting properties were analyzed by 3D modeling, force-displacement profiles, and compactibility plots. First, the Tg of the powder decreased with increasing RH and the Tg of the tablet was 4-8 K lower than the powder. The predominant deformation of Kollidon SR is plastic deformation and Kollidon SR showed a higher compactibility than MCC. The parameters of the 3D model showed an extreme change between 45 and 60% RH, and at higher RH more and more particles deformed elastically. This was confirmed by analysis of force-displacement profiles. At 60% RH, the radial tensile strength of the Kollidon SR tablets was half of the radial tensile strength at 45% RH. The reason is a higher relative energy of plastic deformation than for MCC. This results in a better utilization of the energy to deform the powder into a tablet and the exceeding of the glass transition temperature at higher RH. In conclusion, at 60% RH at the same rho(rel, max), tableting and tablet properties of Kollidon SR are extremely changed since plasticity is significantly higher. In the second part of the study, the insufficient flowability of theophylline monohydrate can be compensated by using Kollidon SR in a mixture with up to 20% theophylline. Further, pressure plasticity e of MCC and Kollidon SR was lowered in the mixture with theophylline monohydrate. The same is valid for the compactibility. The influence of theophylline monohydrate on the pressure plasticity e of the mixtures was better compensated in the mixture with MCC than in a mixture with Kollidon SR. This compensation was also visible by analyzing the force-displacement-profiles. However, hardly any influence on the radial tensile strength could be detected. Kollidon SR and Kollidon SR mixtures exhibited a higher compactibility than MCC and MCC mixtures. The differences became smaller with increasing theophylline content.

Evaluation of Tablet Formation of Different Lactoses by 3D Modeling and Fractal Analysis

The aim of this study was to use 3D modeling to differentiate not only among the four different types of lactose alpha-lactose monohydrate, spray-dried lactose, agglomerated lactose and lactose anhydrous but also between products from different manufacturers. Further "box-counting" fractal analysis of SEM images was done to gain additional information on tableting characteristics and tablet properties which can be found in the fractal structure. Twelve different materials from different manufacturers were analyzed for their powder-technological and physicochemical properties. They were tableted on an eccentric tableting machine at graded maximum relative densities and the recorded data, namely force, time, and displacement were analyzed by the 3D modeling technique. Tablet properties such as, elastic recovery, crushing force and morphology were analyzed. The results show that 3D modeling can precisely distinguish deformation behavior for different types of lactose and also for the same type of material produced with a slightly different technique. Furthermore, the results showed that the amorphous content of the lactose determined the compactibility of the material, which is due to a reversible exceeding of the glass transition temperature of the material. The three fractal dimensions DBW (box surface dimension), DWBW (pore/void box mass dimension), and DBBW (box solid mass dimension) are capable of describing morphological differences in lactose materials. Multivariate regression analysis showed that the fractal surface structure of the lactose-based materials is strongly correlated to tableting characteristics and tablet properties. Especially with regards to 3D modeling, it was found that the fractal indices can describe the parameters time plasticity d, pressure plasticity e, and fast elastic decompression, which is the inverse of omega. In addition, the 3D parameters are able to describe the powder and tablet fractal indices. In conclusion, the 3D modeling is not only able to characterize the compression process but it can also provide information on the final tablet morphology.

The 3-D model: Experimental Testing of the Parameters d, e, and ω and Validation of the Analysis

The aim of the study was to evaluate the parameters d, e, and omega for their significance in compression data analysis. Materials with predominantly different compression properties were used and tableting data were obtained with an instrumented eccentric and rotary tableting machine. The parameters time plasticity (d), pressure plasticity (e), and the twisting angle (omega), an indicator of fast elastic decompression, were derived by 3-D modeling. The Peak-Offset-Time, the pressure-time function parameters, the Heckel slope, normalized compaction (E2(norm)) and elastic energy (E3(norm)), and fast elastic recovery (FER), which are well known tableting parameters, were calculated from the tableting data. The plastic microhardness of the tablets was determined from using microindentation. The results revealed that d is influenced by speed, e correlates with microhardness, and omega correlates with the Elastic modulus (E). Thus, for all three 3-D model parameters an experimental basis is given. The validation showed that d correlates with the Peak-Offset-Time and the pressure-time function parameters, e correlates with the Heckel slope and E2(norm), and omega correlates with E3(norm) and FER of the tablets. The significance of the three parameters is fully given. It is no longer necessary to use two separate methods to differentiate between time- and pressure-dependent deformations.

“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 3D Model: Explaining Densification and Deformation Mechanisms by Using 3D Parameter Plots

The aim of the study was to analyze very differently deforming materials using 3D parameter plots and consequently to gain deeper insights into the densification and deformation process described with the 3D model in order to define an ideal tableting excipient. The excipients used were dicalcium phosphate dihydrate (DCPD), sodium chloride (NaCl), microcrystalline cellulose (MCC), xylitol, mannitol, alpha-lactose monohydrate, maltose, hydroxypropyl methylcellulose (HPMC), sodium carboxymethylcellulose (NaCMC), cellulose acetate (CAC), maize starch, potato starch, pregelatinized starch, and maltodextrine. All of the materials were tableted to graded maximum relative densities (rhorel, max) using an eccentric tableting machine. The data which resulted, namely force, displacement, and time, were analyzed by the application of 3D modeling. Different particle size fractions of DCPD, CAC, and MCC were analyzed in addition. Brittle deforming materials such as DCPD exhibited a completely different 3D parameter plot, with low time plasticity, d, and low pressure plasticity, e, and a strong decrease in omega values when densification increased, in contrast to the plastically deforming MCC, which had much higher d, e, and omega values. e and omega values changed only slightly when densification increased for MCC. NaCl showed less of a decrease in omega values than DCPD did, and the d and e values were between those of MCC and DCPD. The sugar alcohols, xylitol and mannitol, behaved in a similar fashion to sodium chloride. This is also valid for the crystalline sugars, alpha-lactose monohydrate, and maltose. However, the sugars are more brittle than the sugar alcohols. The cellulose derivatives, HPMC, NaCMC, and CAC, are as plastic as MCC, however, their elasticity depends on substitution indicated by lower (more elastic) or higher (less elastic) omega values. The native starches, maize starch and potato starch, are very elastic, and pregelatinized starch and maltodextrine are less elastic and exhibited higher omega values. Deformation behavior as shown in 3D parameter plots depends on particle size for polymers such as CAC and MCC; however, it does not depend on particle size for brittle materials such as DCPD. An ideally deforming tableting excipient should exhibit high e, d, and omega values with a constant ratio of e and omega at increasing densification.

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.

The 3-D model: comparison of parameters obtained from and by simulating different tableting machines

The aim of this study is to apply 3-D modeling to data obtained from different tableting machines and for different compression wheels on a linear rotary tableting machine replicator. A new analysis technique to interpret these data by 3-D parameter plots is presented. Tablets were produced on an instrumented eccentric tableting machine and on a linear rotary tableting machine replicator. The materials used were dicalcium phosphate dihydrate (DCPD), spray-dried lactose, microcrystalline cellulose (MCC), hydroxypropyl methylcellulose (HPMC), and theophylline monohydrate. Tableting was performed to different maximum relative densities (rho (rel, max)). Force, time, and displacement were recorded during compaction. The 3-D data plots were prepared using pressure, normalized time, and porosity according to Heckel. A twisted plane was fitted to these data according to the 3-D modeling technique. The resulting parameters were analyzed in a 3-D parameter plot. The results show that the 3-D modeling technique can be applied to compaction cycles from different tableting machines as different as eccentric and rotary tableting machines (simulated). The relation of the data to each other is the same even when the absolute values are different. This is also true for different compression wheels used on the linear rotary tableting machine replicator. By using compression wheels of different sizes on this simulator, mainly time plasticity changes. By using bigger compression wheels for simulation, the materials deform slower at lower densification and they deform faster at higher densification. For brittle materials, the stages of higher densification are influenced; for plastically deforming materials, the stages of lower and higher densification can be influenced.