Painless injections using jet power

Most people find needles painful, not to say frightening. Needle-free injections were invented a long time ago, using jet power to insert proteins such as insulin or hormones into the body. However, this method is not commonly used mainly because of the pain and bruises it causes. A new implementation of jet injection was developed by Samir Mitragotri from the University of California, Santa Barbara and his colleagues. The new strategy uses pulse microjets to inject liquid beneath the while preventing it from penetrating too deep. The new pulse microjet is claimed to cause no pain.

Liquid jet injectors were invented more than fifty years ago. The jet injector was supposed to replace the commonly used needle in injecting proteins to the body. The method utilizes a high pressure stream of liquid able to penetrate the skin. This method is not commonly used for some reasons, among them the pain and bruises caused by the liquid’s deep penetration. The new strategy developed uses microjets to deal with this issue.

Microjets are small jet injectors, with about half the nozzle diameter of conventional jet injectors (50-100 micrometers compared to 75-200 micrometers). Microjet injectors also contain much less liquid – 2–15 nanolitres (compared to 30,000-100,000 nanolitres). This small amount of liquid allows the injector to control the depth of penetration, a parameter that had not been controlled until now. With a microjet injector, the depth of penetration can be as small as 200 micrometres, compared to 2-20 millimeters in the conventional jet injector.

The liquid streams of jet injectors are created using pulsed electrical power. The power is translated into mechanical pressure using a method called piezoelectric, transduction of electrical power into movement of crystals. The electricity, given in pulses, generates energy for the streams penetrating the skin.

The new injector is composed of two separable components, a disposable part and a durable one in order to keep costs down. The disposable component contains the liquid container and the nozzle. The durable part contains the “brain” and the battery. In this way, the user can purchase one “expensive” part and use it with multiple disposable “cheap” parts.

The injector was tested on diabetic rats and found useful. It was able to insert a sufficient amount of insulin to the rat’s blood-cycle. Further tests are pending for the new device in order to be approved for general use. The fact that the injector is activated by electricity makes it easy to control the injection dosage and activation times. This new method for needle-free injections may replace common injection methods, bringing relief to billions of people around the world, especially to those who receive injections on a regular basis (e.g. diabetics).

More information on the research can be found on the University of California Santa Barbara website.

Image: Illustration of Pulsed Microjet System delivering protein drugs Into the Skin without pain or bruising (Credit: UC Santa Barbara).

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