Capsule design

Abstract

To effectively treat iron over-absorption, we needed a device to deliver our Iron Coli bacteria to the distal area of the duodenum and the proximal area of the jejunum. We thus designed and built a capsule with a methacrylic acid exterior that resists the low pH conditions in the stomach, but will dissolve at intestinal pH. The capsule interior contains colloidal silica and hydroxypropylmethylcellulose (HPMC), which ensures that the bacteria survive in the capsule and have enough time to uptake iron when released in the intestine.

Capsule design requirements

We see three main challenges to construction of a device to deliver bacteria to the intestine. First, the capsule must resist the low pH conditions in the stomach, which are lethal to our bacteria. Second, the capsule must rapidly dissolve in the duodenum to deliver its payload to the distal duodenum and the proximal jejunum. Third, the bacteria must have enough time to effectively uptake iron before being excreted from the intestine.

Capsule design, step by step

Which galenic formulation is best suited for our goals?

The first step in the design of our pill is to determine its galenic formulation. We want a per os administration for our bacteria and had the choice between either a tablet or a capsule. A tablet requires dry compression of its contents, meaning the bacteria would have to be lyophilized. We decided a capsule is more suited for our purpose because it can contain a non-compressed powder and avoids lyophilization, which would result in a significant delay in metabolic activity of the bacteria after being released.

How to store the bacteria in the capsule?

Figure 1: Testing both moisture absorbents.

Figure 2: Hand mortar and pestle, old fashioned but efficient.

A pharmaceutical capsule requires every component to be in powder form. We tested which formulation was able to absorb the most LB medium saturated with bacteria. In galenic research, this is called a moisture absorbent and ensures the proper chemical properties to keep our drug (here our bacteria in LB medium) viable in a dry environment. We experimented with several compositions based on and colloidal silica (Figures 1 and 2). Our final choice was colloidal silica.

Figure 3: Preparing the rack with 50 empty capsules.

Figure 4: Filling the capsule with the total amount of powder.

We produced capsules in batches of 50 (standard for one rack, Figure 3). Here we carefully mix colloidal silica with the HPMC diluent such that the entire volume of powder is equally distributed in the capsules (Figure 4).

Figure 5: Closing the capsules after a filling the rack.

Figure 6: Final result, 50 capsules uniformally filled with the powder mixture.

Finally, the 50 capsules contain a total of 11 ml of colloidal silica in which 4 mL of saturated bacteria have been dissolved and 24 mL of HPMC. The last step is sealing the capsules (Figures 5 and 6).

How to overcome the acidity of the stomach?

Figure 7: Dipping of the capsule in an alcohol-based methacrylic acid polymer solution.

Figure 8: Drying of the capsule by evaporating the alcohol.

It is very common in pharmaceutical galenical research to overcome the acidity of the stomach and to target the duodenum/jejunum for medical delivery. To this end, we soaked the capsule in an ethanol-based solution of methacrylic acid and dried it with hot air. This method produced a capsule with a double envelope that resists gastric acidity.

How to deliver the bacteria in the jejunum?

The gelatine-based composition of the capsule dissolves at neutral pH to deliver its payload to the duodenum. Right after the dissolution of the gelatine capsule, the HPMC swells to form a viscuous obstruction. This process creates an environment in the jejunum where bacteria can statically proliferate. Thus, HPMC, beside its properties as a diluent, is also called a bio-adhesive for its ability to stick to the membranes of the intestins and form an obstruction.

How to prove the real efficiency of our capsule?

As a proof of concept, we fulfilled the two basic requirements of the European Pharmacopeia to make a gastro-enteric resistant capsule which are as follows:

1. No dissolution of the capsule after 2 hours of exposure to gastric acid (solution at pH = 2)
2. Dissolution of the capsule within 1 hour of exposure to water (Phosphate Buffer solution, pH = 7) right afterwards

Figure 9: The dissolution machine.

Figure 10: The basket that dips into the solution.

The dissolution machine is able to lift a basket up and down into a 800mL beaker (figure 9). For every experience, we were able to test 6 capsules spread into 6 apart columns (figure 10). Keep in mind that these columns have the possibility to be closed by a lid on the top to increase the dissolution and mimic different segments of the intestins.

Figure 11: Capsule dissolvement stage after 1 hour of exposure to gastric acid.

Figure 12: Water turbidity after 1 hour of exposure to gastric acid.

We observe that after one hour of exposure to gastric acidity, the capsules are not dissolved. They kept their integrity (figure 11) and didn't deliver its contanment (figure 12).

Figure 13: Capsule dissolvement stage after 2 hours of exposure to gastric acid.

Figure 14: Water turbidity after 2 hours of exposure to gastric acid.

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 15: Final solution color after 2 hours of exposure to gastric acidity.

We observe that the water is very clear (figure 15), thus meaning that the first condition of the European Pharmacopeoa to create a gastro-enteric resistant capsule is fullfilled.

Figure 16: Capsule dissolvement stage after 0 minute of exposure to PBS buffer (pH = 7,2).

Figure 17: Water turbidity after 0 minute of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 18: Capsule dissolvement stage after 15 minutes of exposure to PBS buffer (pH = 7,2).

Figure 19: Water turbidity after 15 minutes of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 20: Capsule dissolvement stage after 30 minutes of exposure to PBS buffer (pH = 7,2).

Figure 21: Water turbidity after 30 minutes of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 22: Capsule dissolvement stage after 40 minutes of exposure to PBS buffer (pH = 7,2).

Figure 23: Water turbidity after 40 minutes of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 16: Capsule dissolvement stage after 50 minutes of exposure to PBS buffer (pH = 7,2).

Figure 17: Water turbidity after 50 minutes of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).

Figure 16: Capsule dissolvement stage after 60 minutes of exposure to PBS buffer (pH = 7,2).

Figure 17: Water turbidity after 60 minutes of exposure to PBS buffer (pH = 7,2).

We observe that after two hours of exposure to gastric acidity, the capsule are still not dissolved. They kept their integrity (figure 13) and didn't deliver its contanment (figure 14).