Assessing the Impact of Punch Geometries on Tablet Capping Using a Newly Proposed Capping Index.

PURPOSE: Increased tablet anisotropy could lead to increased tablet capping propensity. Tooling design variables such as cup depth could serve as a key player for inducing tablet anisotropy. METHODS: A new capping index (CI) consisting of the ratio of compact anisotropic index (CAI) and material anisotropic index (MAI) is proposed to evaluate tablet capping propensity as a function of punch cup depth. CAI is the ratio of axial to radial breaking force. MAI is the ratio of axial to radial Young's modulus. The impact of various punch cup depths [flat face, flat face beveled edge, flat face radius edge, standard concave, shallow concave, compound concave, deep concave, and extra deep concave] on the capping propensity of model acetaminophen tablets was studied. Tablets were manufactured at 50, 100, 200, 250, and 300 MPa compression pressure at 20 RPM on different cup depth tools using Natoli NP-RD30 tablet press. A partial least squares model (PLS) was computed to model the impact of the cup depth and compression parameters on the CI. RESULTS: The PLS model exhibited a positive correlation of increased cup depth to the capping index. The finite elemental analysis confirmed that a high capping tendency with increased cup depth is a direct result of non-uniform stress distribution across powder bed. CONCLUSIONS: Certainly, a proposed new capping index with multivariate statistical analysis gives guidance in selecting tool design and compression parameters for robust tablets.

Compression-decompression modulus (CDM) - an alternative/complementary approach to Heckel's analysis.

The novel modulus-based approach was developed to characterize the compression behavior of the materials and how it results into tablet mechanical strength (TMS) of the final tablet. The force-displacement profile for the model materials (Vivapur® 101, Starch 1500®, Emcompress®, and Tablettose® 100) was generated at different compression pressures (100, 150, and 200 MPa) and speeds (0.35, 0.55, and 0.75 m/s) using compaction emulator (Presster™). A generated continuous compression profile was evaluated with Heckel plot and the proposed material modulus method. The computed compression parameters were qualitatively and quantitatively correlated with TMS by principal component analysis and principal component regression, respectively. Compression modulus has negatively correlated, while decompression modulus is positively correlated to TMS. Proposed modulus descriptors are independent of particle density measurements required for the Heckel method and could overcome the limitations of the Heckel method to evaluate the decompression phase. Based on the outcome of the study, a two-dimensional compression and decompression modulus classification system (CDMCS) was proposed. The proposed CDMCS could be used to define critical material attributes in the early development stage or to understand reasons for tablet failure in the late development stage.

Negative porosity issue in the Heckel analysis: A possible solution.

A parameterization of compaction simulator generated dynamic compression profile with a few grams of powder provides important information about the material deformation and compact elasticity. The Heckel equation is by far the most popular choice among pharmaceutical scientists for such parametrization. A general approach of Heckel analysis uses pycnometric powder density (ρP0) for relative density calculation. However, as 'in-die' tablet bulk density at applied compression pressure (ρBP) becomes greater than or equal to the measured ρP0, the general approach typically poses a negative porosity challenge at high compression pressure regions. It is only theoretically possible to have a tablet with zero or negative porosity. Negative porosity may be detected during 'in-die' compression analysis, but it will not exist after ejection of the tablet in practical aspect. Thus, the present work proposes a new approach to using pycnometric tablet density (ρPP) in the relative density calculations of Heckel analysis. This ρPP may be a better representation of actual tablet particle volume, as it is composed of non-accessible intra-particulate pores, which are broken under applied compression pressure. A new approach showed its immunity for Heckel high-pressure negative porosity. It enables the utilization of the compression and decompression phases of dynamic compression profiles to evaluate macroscopic compaction performance. The proposed approach was validated with a reported modified Heckel approach. The Heckel parameters computed with both methodologies for microcrystalline cellulose and lactose were not statistically different. However, a modified Heckel approach was unable to compute Heckel parameters of poorly compacting starch unlike the new approach. A modified Heckel approach became invalid during starch compaction at low compression pressures (below 400 MPa), where starch was forming weaker but still intact tablets. Certainly, a complete Heckel profiling with a new approach could save time and costs in an early development stage for designing and screening scientifically based lead prototype formulations.

A Mechanistic Approach To Model the Compression Cycle of Different Toolings Based on Compression Roller Interactions.

The aim of the current work was to model and understand the mechanical interactions of tooling heads with compression rollers during tableting. Binary direct compression blends of Prosolv® SMCC with 0.5% w/w magnesium stearate and ternary blends with 30% w/w acetaminophen were used. Tablet compression was performed using an instrumented Riva Piccola press with 10 mm round flat face D- and B-type TSM domed punches. Five punches were used for the study with varying dimensions of head flats. Strain rate studies were carried out at 12.5, 25, 50, and 75 revolutions of turret per minute (RPM) and a compaction profile was performed at compression pressures of 50, 100, 150, and 200 MPa. Tablet weight, thickness, and tensile strength were evaluated. Compression raw data was used to model the punch interactions. A MATLAB program was created to model the head profiles based on their dimensions, punch tip separation, vertical velocity, and pitch circle diameter of the press. Tablets compressed with no head flats were the weakest and showed less strain rate sensitivity. Tensile strengths increased linearly with the head flat dimensions. Also, difference in loading times due to roll movement during compression was evaluated. Capping was observed in tablets compressed at 75 RPM from the ternary blend containing 30% acetaminophen. However, punches with zero head flat showed no capping at these speeds. Also, B-type tooling showed relatively less capping tendency. This work shows that dwell time effect on tablet properties is based on the punch head flat region and the punch head interactions with the rollers.

Compression-Induced Polymorphic Transformation in Tablets: Role of Shear Stress and Development of Mitigation Strategies.

Our goals were to evaluate the effects of (i) hydrostatic pressure alone and (ii) its combined effect with shear stress during compaction, on the polymorphic transformation (form C → A) of a model drug, chlorpropamide. The powder was either subjected to hydrostatic pressure in a pressure vessel or compressed in a tablet press, at pressures ranging from 25 to 150 MPa. The overall extent of phase transformation was determined by powder X-ray diffractometry, whereas 2D-X-ray diffractometry enabled quantification of the spatial distribution of phase composition in tablets. Irrespective of the pressure, the extent of transformation following compaction was higher than that because of hydrostatic pressure alone, the difference attributed to the contribution of shear stress experienced during compaction. At a compression pressure of 25 MPa, there was a pronounced gradient in the extent of phase transformation when monitored from radial tablet surface to core. This gradient decreased with increase in compression pressure. Four approaches were attempted to minimize the effect of compression-induced phase transformation: (a) site-specific lubrication, (b) use of a viscoelastic excipient, (c) ceramic-lined die, and (d) use of cavity tablet. The ceramic-lined die coupled with site-specific lubrication was most effective in minimizing the extent of compression-induced phase transformation.