Project undertaken in course year 2022-23 with Gilead

Project Goal

To develop a method / system that allows clinicians to manually inject 1.5mL of high viscosity (300 cP) medications throuhg standard 3mL syringes within 15 seconds.

Project Motivation

The medical industry is shifting from daily pills to long-term injectables to administer medications in order to increase patient compliance and mental health.  Gilead Sciences is currently in the clinical evaluation stage of an HIV drug, Lenacapavir, which requires the use of a standard syringe to inject.

The issue with developing long-acting injectables is that there is a much higher concentration of medication in the solution, which leads to very viscous solutions that require forces too high for clinicians to manually inject through standard syringes.  Therefore, there is a need for hte development of a device to provide the mechanical advantage needed to make the manual injection possible. 


Gilead Sciences is a biopharmaceutical company that focuses on the development of medications and are trying to make a more sustainable transition to long-acting injectables to improve patient compliance. However, these kinds of drugs are difficult to produce since they typically require high volumes and a higher drug concentration, which leads to the development of more viscous medications. 

With the Lenacapavir drug in clinical development, Gilead want to enable easy and quick injections for that evaluation.  AutoInjectors are commonly used for this type of application but take considerable time to develop; so Gilead wanted an all-mechanical solution that would enable use of a standard syringe to inject the medicine. 

Annotated diagram of a syringe. The force applied to the syringe is described by the Hagen-Poiseuille equation. For a 23 gage needle on a 3mL syringe, 1.5ml of 300 cP medication to be injected in 15 seconds through a subcutaneous needle (5/8") results in needing 127 N of force to be applied (Approx 29 lbf).

High Priority Requirements

Ethical Considerations


We designed an made the Viscoject 300 which amplifies the user's input force by 8x, requiring on average 33.67 N of force to inject the syringe contents to inject in 15 seconds.  

Viscoject 300

The device with a standard syringe inserted in the long arm of the left side.  You can see the red-tipped luer of the 23gage needle on the left of the image.  The device works similarly to a caulk gun, where a draw on the handle will push on the syringe plunger, with an 8:1 mechanical advantage. 


The Viscoject 300 being used to subcutaneously inject 1.5 mL of a viscous solution into artificial skin

Viscosity testing

The team made a honey-water mixture to desired viscosities and measured the resulting viscosity with a size 3 Zahn cup

Syringe Force testing

Measurement method used to measure the actual force required to depress the syringe, to confirm mechanical advantage of the system

System test

Setup showing how device force tests were measured.  The syringe was filed with the desired viscosity liquid, placed in the device, and the handle pulled.  Handle force measurements made using force gage to pull on the handle, and time to dispense was measured. 

Expected and Measured Syringe Force for 280 cP Fluid

For a given flow rate, the measured force to depress the syringe was less than that predicted by the Hagen-Poiseuille equation.  A flow rate of 0.10 mL/s is our target flow rate (1.5 mL over 15 seconds)

Device force and time results for 320 cP fluid

Testing with 320 cP fluid, over three trials, resulted in an average force at the handle to dispense the fluid of 33. 7N


The syringe plunger was seen to buckle under the loads. The polypropylene syringe was not designed to handle these high loads; the team switch to a ABS plunger to resolve this issue.

Other testing conducted

Student team

Future Work