What Factors Should Be Considered When Designing Sheet Shapes Based on Uniform Pressure Distribution?

Avoid sharp edges and corners

1. Principle of rounded corner design:

1. Try to use basic shapes such as circles, ellipses, etc. without sharp edges and corners. If it is necessary to design irregular pieces, such as square or triangular pieces, the corners should be designed as larger radius rounded corners. For example, when designing a square shape, set the radius of curvature of the four corners to about 1/10 to 1/8 of the edge length of the shape. In this way, during the compression process, the pressure can be evenly distributed along the rounded corners, avoiding stress concentration on sharp corners and reducing the risk of cracking.

For some special shaped tablets, such as cartoon characters or irregular shaped tablets with comp

lex patterns, soft curved transitions should also be used at the edges of the pattern. For example, when designing a children's medication tablet in the shape of an animal, the animal's ears, tail, and other parts should have a rounded shape rather than sharp edges.

2. Pressure distribution simulation and verification:

During the design phase, computer-aided design (CAD) software can be used to simulate the pressure distribution of the wafer. By inputting the geometric shape of the tablet, physical properties of the drug and excipients (such as elastic modulus, Poisson's ratio, etc.), and compression pressure parameters, the software can predict the pressure distribution in various parts of the tablet. For example, for a newly designed tablet with grooves, the pressure concentration area at the edge of the groove can be discovered through simulation, and the tablet shape can be optimized accordingly.

2. Produce a small amount of samples for actual compression testing to verify the simulation results. Pressure sensors can be used to measure the pressure changes in different parts of the tablet during the compression process. For example, placing micro pressure sensors at the center, edges, and corners of tablets, comparing the pressure differences in these areas under different shapes of tablets, and further adjusting the tablet design based on actual test results.

Consider the pressure balance of multi-layer and special pattern film types

1. Inter layer pressure transmission in multi-layer films:

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For double-layer or multi-layer sheets, the thickness and shape of each layer of the sheet should be matched with each other to ensure uniform transmission of pressure between each layer. Generally speaking, the thickness ratio of each layer should be determined based on the drug dosage and physical properties. For example, in designing a bilayer film, one layer is a rapid release layer and the other is a sustained release layer. The thickness of the rapid release layer can be relatively thin, accounting for about 1/3 of the total thickness, while the sustained release layer accounts for about 2/3.

The shape design of the interface between layers is also important. In order to effectively transmit pressure, the interface can be designed in a nested shape, such as a convex concave structure. In this way, during compression, the pressure from the upper layer can be better transmitted to the lower layer through the convex and concave parts, avoiding delamination. For example, in a double-layer gastric tablet, the bottom of the upper rapid release layer is designed with small protrusions, and the top of the lower sustained release layer has corresponding grooves. During compression, the protrusions are embedded in the grooves to ensure even pressure transmission.

2. Uniformity of pressure on special pattern sheets (such as scratch sheets):

For tablets with scratches, the depth and width of the scratches should be appropriate. Scratches that are too shallow may not achieve the expected segmentation effect, while those that are too deep can lead to pressure concentration at the scratch site, making it easy to crack. Generally, a depth of 1/5-1/3 of the tablet thickness is more suitable for scoring. For example, when designing a blood pressure reducing pill that can be divided and taken, the depth of the indentation is about 1/4 of the tablet thickness, and the width is 1-2mm.

The shape of the scratch can also affect the pressure distribution. Linear scoring is relatively simpler in pressure distribution than curved scoring, but if curved scoring (such as wavy) is used, pressure can be balanced by adjusting the curvature and spacing of the curve. In the design process, it is necessary to consider the relationship between the direction of the indentation and the direction of the compression force, and try to evenly distribute the pressure at the indentation to avoid the tablet from breaking at the indentation.

Use mold structure to improve pressure distribution (for complex shapes)

1. Design of mold buffer structure:

For tablets with complex shapes, such as circular, hollow, or those with internal structures, a cushioning structure can be designed inside the mold. For example, for annular sheet shapes, elastic buffer layers can be installed on the inner and outer rings of the mold. During the compression process, pressure is first applied to the buffer layer, which can undergo appropriate deformation according to the magnitude and direction of the pressure, thereby ensuring a more uniform transmission of pressure to the tablet material.

The material selection for the buffer structure is also crucial. You can choose rubber or polymer materials with certain elasticity and hardness. The elastic modulus of these materials should be determined based on the properties of the drug and excipients. For example, for drug components with higher hardness, the elastic modulus of the buffering material can be appropriately higher to provide sufficient reaction force to evenly distribute pressure.

2. Design of compatibility between molds and sheet shapes:

The shape of the mold should be closely adapted to the sheet shape. For tablets with special shape requirements, such as those with protrusions or indentations, the corresponding parts of the mold should be precisely designed. For example, when designing a tablet with a central depression, the punch part of the mold should be able to accurately press out the depression and ensure that the pressure around the depression is uniform throughout the entire compression process. Uniform pressure distribution can be achieved by adjusting the shape and size of the mold punch, as well as the coordination with the mold cavity.