# An Intelligent Wired Capsule for the Treatment of Helicobacter pylori
## 2 Materials and Methods
### Overall Characteristics of the Device
#### 2.2.1 Therapeutic Module  
The therapeutic module is presented as the main component of the capsule to eradicate the bacterium. As the name itself suggests, in fact, it is the functional module for administering the treatment of PDT. To ensure effective photodynamic therapy, careful selection of the wavelengths that are optimal for photo-killing is essential. The most effective wavelengths, at least intuitively, should be those at which the endogenous porphyrins of _H. pylori_ show increased sensitivity. The number of ROS generated, in fact, can be considered, as a first approximation, directly proportional to the quantity of photons absorbed by the PS. By analyzing the absorption spectrum of the endogenous porphyrins of _H. pylori_, there is an important peak around 400-410 nm. The spectrum reveals, in reality, other peaks in the visible range, which, however, are clearly lower than the main one and less and less important proceeding in the direction of the infrared. For this reason, it would seem that the most effective wavelength for photo-killing is in the violet range. However, the first therapeutic solutions based on the use of this wavelength have found a high rate of long-term reinfection. Although, in fact, the eradication rate manifested immediately after the administration of the treatment was 99%, the results of the breath test revealed the reappearance of the infection already after 5 days [11]. Additionally, taking into account the 99.9% eradication detected by in vitro experimentation, it is assumed that the reappearance of the infection is due to the rapid proliferation of bacterial colonies nested in the innermost layers of the gastric mucosa that cannot be reached by photons at 400 nm. In fact, if the penetration depth of visible light inside the gastric mucosa is also taken into consideration, the graph on the right in Figure 2, it can be seen that wavelengths around 400 nm have low penetrating power. Penetration is optimal in the red range. A small peak of penetrating power is also recorded near 500 nm. Comparing the two graphs in Figure 2, it is clear that photons at 400 nm are ideal for the excitation of PS but not very suitable for penetrating into tissues. On the other hand, in the red range, characterized by maximum penetrating power within visible light, the absorption spectrum of the porphyrins endogenous to _H. pylori_ has a small spike close to 630 nm. It could, therefore, be assumed that the wavelength of 630 nm, combining the high penetration into the mucosa with the discrete ability to be absorbed by the PS, could somehow compensate for the inefficient penetrating capacity of blue, optimizing the outcome of the therapy. In the same vein, the wavelength of 500 nm attracted attention. At 500 nm, in fact, there is an average penetrating power inside the mucosa and a medium absorption capacity by porphyrins. The combination of the two actions of medium intensity could have an even better effect than that of red and blue, which tend to excel in one aspect but are mediocre in the other. By virtue of the provisions and also taking into account the results obtained in the simulation of [PERSON] et al. on the effectiveness of photo-killing, it was decided to integrate three wavelengths into the therapeutic module: 405 nm, 630 nm and 500 nm. Figure 2: **Left**: absorption spectrum of the endogenous porphyrins of _H. pylori_. **Right**: depth of penetration of visible light inside the gastric mucosa. Having to administer a therapeutic treatment in addition to selecting the wavelengths, it is also essential to consider the emission of the light source. The energy released by the therapeutic module per unit of surface in the unit of time, otherwise identified as a dose, must be suitable for the eradication of the bacterium. It would be preferable to be able to carry out the treatment in the shortest possible time in order to provide an efficient therapy without reducing effectiveness.