Measuring tissue back-pressure--in vivo injection forces during subcutaneous injection

Area of Science:

• Pharmacology
• Biomedical Engineering
• Drug Delivery Systems

Background:

• Parenteral injections are common drug delivery routes.
• Understanding in vivo injection forces is crucial for safe and effective drug administration.
• Limited data exists on the contribution of subcutaneous tissue to injection forces.

Purpose of the Study:

• To investigate the role of subcutaneous (sc) tissue in determining injection forces during in vivo administration.
• To quantify the relationship between viscosity, injection rate, and sc tissue back-pressure.

Main Methods:

• In vivo injections were performed on Göttingen minipigs.
• Isotonic dextran solutions with varying viscosities (1-100 mPas) were used.
• Different injection rates (0.025-0.2 mL/s) and volumes (2.5 vs. 4.5 mL) were tested.

Main Results:

• Subcutaneous tissue back-pressure increased linearly with viscosity and injection rate.
• Injection forces ranged from 0.6 ± 0.5 N to 4.7 ± 3.3 N across tested conditions.
• Maximum force reached 12.9 N at 20 mPas and 0.2 mL/s; 6.9 ± 0.3 N at 100 mPas and 0.025 mL/s.
• No significant difference in forces was observed between injection volumes.
• Local warming of the sample in the needle partially compensated for tissue resistance.

Conclusions:

• Subcutaneous tissue contribution must be considered when estimating in vivo injection forces.
• Local warming of the injected substance within the needle influences measured forces.
• Accurate modeling of injection forces requires accounting for both tissue resistance and thermal effects.