Advice on Tablet Compression and Coating for Food Supplements

It sounds like you're working on a challenging tablet formulation with a high concentration of active ingredient (66%). Tablet brittleness is a common issue, and coating requires specific materials and techniques. Based on your description and the properties of common excipients, here's some advice:

Addressing Tablet Brittleness

Your current formula uses Microcrystalline Cellulose (MCC), Corn Starch, and Magnesium Stearate. Let's look at their roles and potential issues:

• Microcrystalline Cellulose (MCC): MCC, such as Microcrystalline Cellulose (PH101, 50micron, Direct Compression Tableting) and Microcrystalline Cellulose (PH102, 100micron, Direct Compression Tableting), is an excellent binder and filler for direct compression. It contributes significantly to tablet hardness. However, at very high active ingredient loads, the proportion of MCC might not be sufficient to provide adequate binding for the entire tablet structure.
• Corn Starch: Corn starch primarily functions as a disintegrant, helping the tablet break apart in the body. While it can have some binding properties, it's generally less effective as a primary binder compared to MCC or other dedicated binders.
• Magnesium Stearate: This is a lubricant essential for preventing the powder from sticking to the punches and dies and ensuring smooth tablet ejection. However, Magnesium Stearate (Food Grade / Tableting) is hydrophobic. Using too much can interfere with particle-to-particle bonding during compression, leading to weaker, more brittle tablets. It can also slow down disintegration.

Recommendations for Brittleness:

• Optimize Binder: Given the high active ingredient percentage, you may need a stronger binder or a higher proportion of binder relative to the lubricant. Consider if the grade of MCC you are using is optimal for direct compression at this concentration. You might also explore other binders. Pregelatinized Maize Starch (USP/BP, For Direct Compression) is another excipient known for its binding properties in direct compression. For wet granulation, Fully Pregelatinized Maize Starch (For Wet granulation Binder) is a suitable binder. Hydroxypropyl Methylcellulose (HPMC), such as HPMC For Tablet Binding/Coating, can also function as a binder, often used in wet granulation or as a dry binder.
• Adjust Lubricant Level: Carefully evaluate the amount of Magnesium Stearate. Use the minimum effective concentration needed to prevent sticking. Excessive lubricant is a frequent cause of reduced tablet strength.
• Consider Granulation: If direct compression continues to yield brittle tablets, switching to a granulation method (wet or dry) can improve powder flow and compressibility, often resulting in stronger tablets. Using a binder like Fully Pregelatinized Maize Starch (For Wet granulation Binder) or certain grades of HPMC in a wet granulation process can significantly enhance tablet strength.
• Evaluate Process Parameters: Ensure your compression force is optimized. Too little force results in soft tablets, but excessively high force can cause capping or lamination, which are also forms of breakage. Particle size distribution and homogeneity of your powder blend are also critical.

Tablet Coating

Coating tablets can improve their appearance, mask taste/odor, and provide protection. For food supplements, film coating is common for aesthetic purposes and ease of swallowing.

• Coating Material: Hydroxypropyl Methylcellulose (HPMC) is a widely used polymer for film coating food supplements due to its water solubility, safety, and ability to form a smooth film. Products like HPMC For Tablet Binding/Coating or Hydroxypropyl Methylcellulose (HPMC, 50cP, 55C Gel, Food) are suitable types. There are also specific grades like HPMC For Sustain Release Coating (4,000cps) if controlled release is desired, but for general aesthetic coating, a standard HPMC grade is appropriate.
• Coating Process: Film coating is typically done in a tablet coater (e.g., pan coater or fluid bed coater). A solution containing the HPMC polymer, plasticizer (to make the film flexible), and optionally colorants/opacifiers (like Titanium Dioxide) is sprayed onto the tumbling tablets while warm air is passed through to evaporate the solvent (usually water).
• Proportions: The amount of coating applied is usually expressed as a percentage weight gain of the tablet, often 2-5% for aesthetic coatings. The exact formulation of the coating solution (polymer concentration, plasticizer ratio, etc.) will depend on the specific HPMC grade and desired film properties, and usually requires some experimental optimization.

In summary, to address brittleness, focus on optimizing your binder system and lubricant level, potentially exploring granulation. For coating, HPMC is a good choice, applied using standard film coating equipment and techniques.