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Team:Evry/Pill design
From 2013.igem.org
Capsule design
Abstract
For an optimum efficiency of our iron chelating bacteria, the purpose is to enhance its growth at the distal area of the duodenum and the proximal area of the jejunum. To target this region, we designed a capsule suited for bacteria delivery and improved its galenic formulation to optimize growth.
Our first step was to create a novel capsule following the actual norms from the European Pharmacopeoa concerning gastro-enteric resistant formulations.
In a second step, our goal is to make the bacteria survive right after the dissolution tests of our capsule.
Posology
For a treatment based on bacteria as an medically active entity, we thought of the posology of such a capsule. The patient has to take the capsule on an empty stomach. Thus, beside reducing the exposure to gastric acidity, it also gives the bacteria enough time to grow once delivered in the duodenum and jejunum. Our strategy focuses on preparing the duodenum of the patient for the next meal and let the bacteria sufficient time to settle and produce sufficient chelators to reduce the iron absorption.
Barriers to overcome and conditions to fulfill
The challenge here is double. First, we need to overcome the acidity of the stomach which is lethal for most living forms. Secondly, our capsule must dissolve right in the duodenum to deliver the containment at the distal duodenum and the proximal jejunum. Additionnally, we added HPMC (Hydroxypropylmethylcellulose) among the components for the capsule design to optimize bacterial growth. More in detail, right after the split into the duodenum, the obstruction caused by the HPMC in contact of water has been evaluated to have the right viscosity to allow a stagnant growth of the bacteria and also the passage of food.
Design of the capsule, step by step
Which galenic formulation suits the best our purpose?
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 not only requires a heavy and dry compression but also the bacteria in a lyophilized form. This last step consists of extreme variations of temperature and pression which are not favorable for living beings. However, the 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 softer environment for bacteria transport. Additionnaly, lyophilized bacteria have a delayed recovery before starting any metabolic activity in comparison to a dessicated form.
How to store the bacteria in the capsule?
The design of a capsule requires every component to be in a powder form. Thus, we tested which one was able to absorb the most LB medium saturated with bacteria. In galenic research, this is called a moisture absorbent and has the right chemical properties to keep our drug (here our bacteria in LB medium) in a dry environment. We experimented
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 the pharmaceutical world, and more precisely in galenical research, to overcome the acidity of the stomach and to target the duodenum/jejunum for the delivery of the capsule. By a simple saoking of one side of the capsule in an ethanol-based solution of methacrylic acid and followed by a drying process (hot air), we managed to surround our capsule with a double-enveloppe resistant that confers resistance to gastric acidity. The capsule has to resist as long as possible to the gastric content, but not to much otherwise we miss its dissolution in the duodenum. To conclude, a double-coating is sufficient to fulfill this criteria.
How to deliver the bacteria in the jejunum?
the target delivery in the duodenum/jejunum is possible thanks to the gelatine-based composition of the capsule. By a simple dissolution in water, it delivers its containment.
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:
Additionnally, beside the moisture absorbent, we need to have a sufficient volume of powder to be able to make our capsules (in our case, 50 at a time). This is called a diluent. In galenic formulations, we have the choice between a lot of different diluents, but one particularly has some interesting properties: HPMC (HydroxyPropylMethylCellulose). It is able to swell in the presence of water and, depending on its density, is more or less viscuous. This process creates an environment where bacteria can statically proliferate. So, when the capsule splits into the duodenum, the swelling of the HPMC occurs in the jejunum and creates a temporary obstruction. In this situations, our bacteria will be able to proliferate in the obstruction area, thus optimizing growth. We had to choose the right viscosity to have a sufficient stability in the jejunum and to have the right amount for an optimal penetrance of the water. Thus, HPMC, beside its properties as a diluent, is also a bio-adhesive for its ability to stick to the membranes of the intestin and form an obstruction.
Norms of the European Pharmacopeoa
Figure 1 and 2 show the material required to test the resistance of our capsule to the acidity. At the left side of the machine, a lever repeatedly moves the basket with the capsules inside the solution (figure 1). In the basket,
