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Team:Evry/Pill design
From 2013.igem.org
Capsule design
Abstract
To effectively treat iron over-absorption, our engineered bacteria need to be delivered to the distal area of the duodenum and the proximal area of the jejunum. We thus designed 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.
First, we create a novel capsule following the actual norms from the European Pharmacopeoa concerning gastro-enteric resistant formulations.
Second, we ensure that the bacteria survive following dissolution of the capsule.
Capsule design requirements
We see three main challenges. 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
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 a heavy and dry compression and the bacteria in a lyophilized form, entailling high temperatures and pressures that would result in significant bacterial mortality. We decided a a capsule is more suited for our purpose because it offers the possibility to contain a non-compressed powder and avoids a lyophilization step, thus representing a more favorable environment for bacteria storage. In addition, a capsule avoids lyophilizing the bacteria, which would delay their metabolic activity after being released.
How to store the bacteria in the capsule?
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
For the next step, we want to increase the volume to 35 mL which is the sufficient amount to make 50 capsules (standard for one rack, figure 3). Thus, a diluent is required and we opted for HPMC (hydroxypropylmethylcellulose). The entire volume of powder has to be equally distributed in the capsules (figure 4).
Finally, the 50 capsules contain all together 11 ml of colloidal silica (where 4 mL of saturated bacteria have been dissolved in) and 24 mL of HPMC. The last step is the closing of the capsules (figure 5 and 6).
How to overcome the acidity of the stomach?
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 delivery in the duodenum/jejunum is already possible due to the gelatine-based composition of the capsule. In contact to water, the capsule dissolves and delivers its containment in the duodenum. This is only feasable when the capsule has already resisted to the gastric acidity. Moreover, we added a HPMC as a diulent. In the presence of water, right after the dissolution of the gelatine capsule, it is able to swell. Depending on its density, the polymere forms a more or less 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:
- No dissolution of the capsule after 2 hours of exposure to gastric acid (solution at pH = 2)
- Dissolution of the capsule within 1 hour of exposure to water (Phosphate Buffer solution, pH = 7) right afterwards
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.
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).
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).
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.
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).
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).
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).
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).
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).
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).
