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Tablets & Capsules January 2020 21 Table 2 shows a summary of the technical require- ments for VSC production and compares the pros and cons of VSCs and GSCs. Items in red show processing differences compared to GSCs due to new equipment, adaptations to existing equipment, or additional process- ing steps, such as heated transfer and curing. In recent years, modified starch suppliers have offered materials with viscosities of about 40,000 to 50,000 centipoise that can be handled in GSC equipment. In contrast, C-MS formulations can have viscosities as high as 90,0 0 0 centipoise. As the table shows, such polymer masses req uire mixing, heating, t ransfer, and spreading systems designed to handle high-viscosit y materials. In general, starch formulations require moisture control, because the film is sensitive to RH values higher than 20 to 30 percent. For GSCs, the sealing process occur s by sol-gel t ransition (also called gelation), but for VSCs, sealing occurs through gelatinization of the starches. The sealing quality is deter- mined by the film quality, the design of the die roll, the pressure force, and in some cases by processing steps after encapsulation. During encapsula- tion, heating the wedge is not required since sealing is not dependent on temperature. VSC manufacturing As previously mentioned, the properties of the mate- rials used to make VSCs differ from gelatin. Raw mate- rial and equipment suppliers have had to learn how to work with these new materials to overcome challenges related to the resulting capsules' physical, chemical, and functional properties, such as soft- ness, leaking, poor dissolution, and increased dissolution times at stability conditions. Also, VSC polymers have higher viscosities and require higher processing temperatures than gelatin, which makes mixing, deaeration, and transfer processes challenging. With gelatin, film formation is due to the tertiary structure of the gelatin induced below the gelation tempera- ture (30° to 40°C). With starch formu- lations, film formation proceeds mainly by the swelling and gelatinization of the starch (at 90° to 95°C). Gelatiniza- tion refers to irreversible gel formation due to the release of amylose in the starch granules when they are heated and cooled. G elat in f ilms c a s t e a sily a nd quickly, are highly elastic and resistant to strain, and dry quickly. Carrageenan-starch films cast slowly under con- trolled conditions, are elastic and resistant to strain, and dry slowly. Starch films cast slowly, are highly suscep- tible to relative humidity (RH), have low elasticity and resistance to strain, and dry slowly. Raw material and equipment suppliers have had to learn how to work with these new materials to overcome challenges related to the resulting capsules' physical, chemical, and functional properties. Figure 1 Characterization of VSCs at accelerated stability conditions (40°C, 75% RH) 300.0 250.0 200.0 150.0 100.0 50.0 0.0 Hardness/Mechanical resistance (newtons) 6.8 5.1 45% 50% 65% 134.2 107.6 115.8 153.5 71% 79% 307.7 87% 83% 71% 234.8 231.4 248.7 231.3 5 3% 3.4 2.0 5.6 2.1 2.0 2.1 5.1 2.5 2.8 2.5 5.2 2.7 57% 54% 60% 5 3% 52% 227.8 207.5 203.2 210.5 49% 71.8 288.8 241.6 60% 58% 86.4 4.7 3.0 3.7 S1 S2 S4 S5 S6 S7 Products Hardness M0 M1 M2 100 90 80 70 60 50 4 0 30 20 10 0 Seal thickness (%) Mechanical resistance M0 M1 M2 Seal thickness M0 M1 M2