Issue link: http://www.e-digitaleditions.com/i/769284
mechanical properties but not so high that it degrades processability. It's also known that subjecting gelatin to excessive heat for too long can cause the polymer chains to fragment, which reduces their molecular weight and diminishes cap- sule performance due to brittleness. Therefore, in processes that require the gelatin to be heated, keep the heating period as short as possible. When making capsules, the gelatin is usually dissolved in 70º to 80ºC demineralized water in jacketed stainless steel tanks. That process typi- cally lasts about 1 hour. Quality control Reputable manufacturers have a set of procedures to ensure that capsules are of high quality when they reach consumers. The capsules should not have cracks, break when extracted from the package, or—even worse—rup- ture and allow the ingredients to spill out. To ensure your products won't suffer from those prob- lems, assess the strength of the capsules to determine whether they can withstand the forces to which they will be subjected. Compression and tension tests offer a techni- cal approach with quantifiable results. However, be sure to vary the force applied when you conduct your analysis. Don't just subject the capsules to the same amount of force the entire time. Figure 7 shows two approaches to force testing. The results in Figure 7a represent the force applied to a capsule extracted from a blister, while Figure 7b represents the force applied if the capsules crashed into one another in a container. For quality control, use the force profile that best represents the conditions that the capsules must endure. Another way to nondestructively assess the mechanical properties of capsules is to measure their refractive index. As discussed above, the index correlates to how radiation passes through a medium, and any changes in it can be cor- related to changes in the mechanical properties of the gelatin capsules. The results shown in Figure 8 illustrate how the refractive index relates to a capsule's resistance to breakage, which decreases as the RH of the storage envi- ronment decreases. Conclusion Extensive experience in the field of capsule manufactur- ing is needed to identify the fundamental properties that affect capsule performance. Therefore, seek manufacturers who have that experience. At the same time, recognize that the manufacturing process and storage conditions are not the only factors that can cause brittleness. T&C References 1. Empty capsules market by product: Global forecast to 2021. Report by Markets and Markets, May 2016. Online: http://bit.ly/ShellTC117. Accessed December 12, 2016. 2. M.E. Aulton (Ed.) Pharmaceutics: The science of dosage form design. 2002. Churchill Livingstone, Philadelphia. 3. Kontny M.J. et al. Gelatin capsule brittleness as a function of relative humidity at room temperature. Int J Pharm 54(1) 1989, 79-85. 18 January 2017 Tablets & Capsules Figure 6 UV-Vis spectra for gelatin capsules with different TiO 2 concentration [8] 1.2 1 0.8 0.6 0.4 0.2 0 2% TiO 2 3.5% TiO 2 4.5% TiO 2 5.5% TiO 2 0 100 200 300 400 500 600 700 800 900 Wavelength (nm) % light transmission Figure 8 Refractive index of gelatin capsules at different RH exposures Refractive index 2 1.95 1.9 1.85 1.75 1.7 1.65 1.6 0 10 20 30 40 50 60 70 80 90 RH (%) Figure 7 Force profiles 12 10 8 6 4 2 0 0 2 4 6 8 10 12 14 Time a. Strength testing of capsules to be extracted from a blister b. Strength testing of capsules that may collide in a container Force 12 10 8 6 4 2 0 2 4 6 8 10 Time Force Source: Adopted from Sun [9]