Drug injection

Micropyrotechnics is of great interest in the administration of drugs, offering simple and inexpensive solutions. Since the 1990s, therapeutic research has used microtechnologies to find and implement new solutions in order to increase the efficiency of treatments while improving the comfort and security of patients. Beyond the miniaturization of systems, the interest lies in the « smart» and automatic administration of the injection. Many teams are working on implantable drug delivery systems. In the case of non-implantable, simple, low cost devices that require a single or limited number of injection doses, micropyrotechnics is an interesting solution. It offers pneumatic microactuators or very inexpensive pyrotechnic gas generators, allowing the administration of programmed injections. The over pressure (DP) that they are able to generate is a function of the ratio Vp/Vo, where Vo represents the initial volume of the system in which the energetic material is integrated, and Vp is the volume of the energetic material. Figure below shows that it is possible to regulate the pressure, from a few to dozens of bars, by adjusting the proportions of the volumes of energetic material and initial one.

Figure. Generated pressure (DP)

§ First pyrotechnical drug injection device : automatic transdermal patch - Project 1994-1995

In 1994, a system for rehydration of transdermal patches has been designed based on 3 pyrotechnic actuators: two one-shot microvalves and one gas generator. The microvalves are activated first, unsealing the reservoir; the gas generator then pushes the drug through the opened microvalves to rehydrate the transdermal patch. The system is flexible so as not to decrease the adherence of the patch to the patient.

It also allows the fabrication of one-shot microvalves by breaking a fine membrane with the combustion gases as shown in figure below.

Pyrotechnic Valve concept Pyrotechnic gas generator concept

Schematic view of a pyrotechnic transdermal patch

This type of system was particularly attractive because it may be activated by an electrical control without the patient’s manual intervention. It is inexpensive and well adapted to the current demand for disposable systems.

§ Pyrotechnically driven microsyringe – ESA project 2001-2003

We have proposed a system of microinjection via a pyrotechnic gas generator that can be integrated on silicon micro machined microsyringe arrays. The operating principle is as follows: once the injection has been programmed, a pyrotechnic gas generator is activated and generates a pressure in the combustion chamber. When the pressure reaches 20MPa, a specifically dimensioned membrane ruptures and transmits the pressure to the drug that then goes through the microneedles.

A schematic of the injection microsystem based on pyrotechnics is given in figure below.

- The top level is the pyrotechnic gas microgenerator.

- The intermediate level is the injection component that contains a gas expansion chamber, a membrane and the drug reservoir.

- The bottom level is the microsyringe array.

Figure. Schematic view of a pyrotechnic injection microsystem adaptable to a microsyringe array (Puig et al)

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