Osmotic Bolus Injector Reduces Injection Frequency

A novel osmotic drive powers low-cost bolus injection technology that can be applied to a broad range of drugs.

The Subcuject (Hellebaek, Denmark) Osmotic Wearable Bolus Injector (WBI) is a low-cost, patient-friendly, prefilled bolus injector that utilizes forward osmosis technology to deliver three ml of a fluid drug of choice. In simplified terms, the osmotic drive module contains two chambers of liquid separated by a semipermeable membrane. Controlled addition of salt to one chamber draws in liquid from the other chamber, generating hydraulic/mechanical pressure that drives the plunger in the primary drug container.

Feature of the single use, disposable WBI device include invisible, automatic thin needle insertion and retraction; small size (76 mm) and low weight 55 grams); thin needles; and noiseless operation, as there are no electronics or batteries involved. To activate the Osmotic WBI, it is affixed to the skin, activated by a single button press, and discarded after use. Total injection time is between 245 and 349 seconds, depending on the viscosity of the drug and needle gauge. No assembly is required, and there are no settings to be adjusted.

“Subcuject has developed a purely mechanical wearable injector for single use, using forward osmosis as the drive mechanism and using a standard glass primary container. This achieves significant economic advantage, with the device cost expected to be in the range of a single-use autoinjector,” said Claus Schmidt Moeller, CTO of Subcuject. “As pressure needs to be built up before the plunger starts moving, there is a soft injection start for increased patient comfort and minimized risk of impact damage in the primary container.”

Osmosis is a spontaneous process, where water molecules cross a membrane in both directions without spending any external energy (Brownian movements). When an osmotic agent (such as salt) is dissolved in the water on one side of the membrane, each ion of a dissolved salt crystal attracts and binds several water molecules. The permeability of these hydrated ions through the membrane is much lower than for the free water molecules, and they stay on one side of the membrane due to a combination of their size and the complex hydrophilic/hydrophobic properties of the membrane. This results in spontaneous flow of water molecules from the freshwater side to the saltwater side of the membrane, building up pressure.

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