USP <1062> tablet characterization is one of the most integral chapters to understanding the tablet characterization process; it helps to understand the compactibility, tabletability, and compressibility of the material. USP <1062> profiles are impacted by any adjustments to the material and tablet tooling.
In the present study, Natoli has mainly focused on the impact of different punch cup depths on the USP <1062> profiles and its possible implication in the behavior of model acetaminophen tablets. The punches with different cup depths were used for this study:
- Flat face (FF)
- Flat face beveled edge (FFBE)
- Flat face radius edge (FFRE)
- Standard concave (SCC)
- Shallow concave (SHCC)
- Compound concave (CCC)
- Deep concave (DCC)
- Extra deep concave (XDCC)
The model acetaminophen formulation was compressed using these tools at a compression pressure of 100, 150, 200, 250, 300 MPa with a speed of 20 RPM. The USP <1062> profile (compressibility, tabletability, compactibility, and manufacturability) profile was generated for each tool.
The result suggests that tablets compressed with FF tooling showed maximum tensile strengh compared to other tooling types (Figure 1). Tablet compressed with DCC and XDCC tools at 200, 250, 300 MPa compression pressures were capped during the tablet breaking force test. The punches’ rank order for a better tabletability at 150 MPa compression pressure with 20 RPM turret speed is as follows:
FF ≻ FFRE ≻ FFBE ≻ SHCC ≻ CCC ≻ SCC ≻ DCC ≻ XDCC
The uniform pressure distribution on FF tablet designs, when compression pressure is applied, explains this observation. It indicates that the strength will be the same at all points (center and edges) in these tablet designs. In the case of convex tablet designs, however, compression pressure distribution will not be equal when applied. The center part of the tablet will be weaker compared to the edges. Hence, tablet tensile strength decreases with increases in the punch cup depth in the present study. This phenomenon may change with the material or formulation in focus. If material is highly compressible, then an FF tablet design may exhibit over-compression compared to convex tablet when the same compression pressure is applied. Over-compression may lead to tablet capping.
Isotropic index was defined as the ratio of axial and radial breaking force, while anisotropic index was determined by the ratio of axial and radial young modulus. Capping index data are presented in figure 3. A quantitative Partial Least Square model (PLS) (figure 4) was computed [Unscrambler® 10.4.1, Trondheim, Norway] to understand the effect of punch cup depths and compression parameters on the capping index. A PLS model exhibited a positive impact of the punch cup designs such as DCC and XDCC on the tablet capping index. The model suggests that an increase in punch cup depth will contribute to a higher possibility of tablet capping.
Tablet capping is one of the most prominent tablet defects in the tableting industry. There are no standardized procedures to determine the capping tendency of the material. Natoli has developed an in-house technique called “Capping Index” to determine the capping propensity of the material. This defect is a function of anisotropic and isotropic properties of the tablet. Young modulus and breaking force of the tablet has been considered anisotropic and isotropic properties of the tablets, respectively. Capping index was determined as the ratio of isotropic to anisotropic indices (Figure 2).
In the present study, compression pressure and an ejection force displayed positive and negative impacts on the tablet capping index, respectively. A high cup depth correlated negatively with weaker tablets, which in turn yielded a higher capping index (Figure 4). This study revealed that tablet capping is a direct function of an increment in the punch cup depth and cup volume of punches in addition to the intrinsic material properties of the formulation blend.