Tablet fracture

The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these microcap tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily... 

Fig. 3—Scanning electron micrograph of the tablet fracture surface from a matrix tablet. Compressive force, 2 kN core coat ratio, 1 1.

Hardness is determined using a hardness tester, where the tablet is placed between two jaws that crush the tablet. The instrument measures the force applied to the tablet and detects when the tablet fractures. Usually 10-20 tablets are tested and the mean value is calculated. Test results can be affected by speed of the testing, the geometry of the tablet contact points, and debris in the testing area, as well as by variation in temperature, humidity, and the age of the tablets. Therefore, the tablets must be oriented consistently in the hardness tester. 

Hiestand Tableting Indices Likelihood of failure during decompression depends on the abihty of the material to relieve elastic-stress by plastic deformation without undergoing brittle fracture, and this is time dependent. Those which relieve stress rapidly are less... 

One should note that BC represents a highly elastic material as little plastic deformation or brittle fracture has occurred. Also, sharp differences between the slope CD and DE are indicative of weak, or failed, tablet structures. The RDWF estimated from these plots can provide a good indication of the ejection force. More detailed treatments of such studies are now in the open literature, to which the interested reader is referred [118-120],... 

Just as metals can be ductile or brittle, so can organic materials. The Brittle Fracture Index is a measure of the brittleness of a material. It is a measure of the ability of a compact of material to relieve stress by plastic deformation. The Brittle Fracture Index (BFI) is determined [29,31] by comparing the tensile strength of a compact, stress concentrator) in it, o-T0, using the tensile test we have described. A hole in the center of the compact generally weakens a tablet. If a material is very brittle, theoretical considerations show that the tensile strength of a tablet with a hole in it will be about one-third that of a solid tablet. If, however, the material can relieve stress by plastic deformation, then the strength of the compact with a hole in it will approach that of a compact with no hole. The Brittle Fracture... 

Additionally, the fracture energy for a zero extension rate can be defined as the bioadhesion work to the initial surface between the bioadhesive material (in a form of a tablet or disk) and the biological support of a surface Aq, which allows for calculation of the fracture energy (e) using Eq. (8). 

The crystallites of (VO)2P207 and Si02/(V0)2P207 were fractured by applying pressure (630 Kg cm 2) with a tablet molding machine. The location of Si on the surface of (VO)2P207 was analyzed by a TEM-EDX (JEM 2000 FXII, JEOL). SEM (TSM-T20, JEOL) and XRD (MXP-3, MAC Science) were used for the characterization of the catalysts. 

In the old, sedatives and hypnotics are best avoided. When mental capacity or reserve is already reduced, these medicines can only reduce it further. In some people memory is worsened and control of the limbs impaired by as little as half a tablet of nitrazepam at night. Its withdrawal may restore their liberty. Confusion, falls, fractures, fear, urinary incontinence, antisocial behavior, and aggression are all seen at times to be due to sedatives and hypnotics. 

Hiestand has developed many indices that are useful for tablet formulations (16 18). These include the frequently cited brittle fracture index (BFI), the best-case bonding index (Bib), the worse-case bonding index (BI ), and the viscoelastic index (VI) (15,16). 

Strain rate sensitivity of (or the effect of press speed on) the formulation is of primary concern in scale-up. Whether the product development work was performed on a single-stroke press or a smaller rotary press, the objective in operations will be to increase efficiency, in this case the tablet output rate and, therefore, the speed of the press. For a material that deforms exclusively by brittle fracture, there will be no concern. Materials that exhibit plastic deformation, which is a kinetic phenomenon, do exhibit strain rate sensitivity, and the effect of press speed will be significant. One must be aware that although specific ingredients (such as calcium phosphate and lactose) may exhibit predominately brittle fracture behavior, almost everything has some plastic deformation component, and for some materials (such as microcrystalline cellulose) plastic deformation is the predominant behavior. The usual parameter indication is that target tablet hardness cannot be achieved at the faster press speed. Slowing the press may be the only option to correct the problem. 

Figure 19 Environmental SEM image of (a) Eudragit LlOO-55 and (b) Advantose 100 tablet in the fracture region after diametrical compression (reproduced from Yap et al., 2006). Permitted by Elsevier.

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