In this study, a new concept is introduced into physics - gravitational cells. The gravitational cell hypothesis was organically integrated into string theory. As a result, using the Schwarzschild radius formula and the Coulomb formula, a gravitational formula in the region of black holes was obtained on the basis of two fundamental constants, and its exact value was determined. The value of the "usual" gravitational constant was also confirmed and the mass of the gravitational cell was obtained. The introduction of the gravitational cell hypothesis into string theory made it possible to apply Planck's constant to gravitational interaction. As a result, a formula for the energy of a gravitational quantum and a formula for the vibrational velocity of a gravitational string were obtained. On this basis, the formula for the mass of the electron was obtained and its value was calculated, which coincided with the experimental mass of the electron. According to the formula for the vibrational velocity of the gravitational string, the formula for the minimum distance of the gravitational interaction was obtained and this distance was calculated. This minimum distance of the gravitational interaction with absolute accuracy coincided with the known experimental data obtained when determining the Casimir effect (force). Another great scientific result is the determination by a new formula of the minimum distance of the onset of the action of Coulomb forces between electric 3 charges and obtaining the minimum length of a standing electric wave between charges.