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Updated: Jun 2, 2026
04:46
The Quantification of Injectability by Mechanical Testing
Published on: May 13, 2020
Injectability evaluation: an open issue.
Francesco Cilurzo1, Francesca Selmin, Paola Minghetti
1Department of Pharmaceutical Sciences "Pietro Pratesi", Università degli Studi di Milano, Milan, Italy. francesco.cilurzo@unimi.it
AAPS Pharmscitech
|May 10, 2011
Summary
This study developed a scoring system to select optimal needle size and length for injections. It found that maximum force (Fmax) below 125 mPa ensures smooth injections, guiding better device selection.
Area of Science:
- Pharmaceutical Technology
- Biomedical Engineering
- Materials Science
Background:
- Selecting appropriate needle-syringe-formulation systems is critical for effective drug delivery.
- Quantifying injection forces and tissue resistance is essential for patient comfort and successful administration.
- Existing methods lack a standardized scoring system to guide optimal needle selection.
Purpose of the Study:
- To propose a novel scoring system for rationalizing the selection of optimal needle diameter and length.
- To correlate quantitative force measurements with subjective human assessment of injectability.
- To consider the pressure exerted at the injection site during needle selection.
Main Methods:
- Evaluated four formulations with varying viscosities using needles from 21 to 26 G and 16 to 40 mm in length.
- Measured plunger-stopper breakloose force, maximum force (Fmax), and dynamic glide force using a texture analyzer at 1 mm/s crosshead speed.
- Conducted tests in air and human subcutaneous tissue, including manual injectability assessment by ten evaluators.
Main Results:
- Established force thresholds for injection feasibility: Fmax > 250 mPa (impossible), 160-250 mPa (very difficult), 125-160 mPa (feasible with difficulty), <125 mPa (smooth).
- Correlated quantitative force measurements with subjective panel test scores.
- Demonstrated the influence of needle size, formulation viscosity, and tissue interaction on injectability.
Conclusions:
- A scoring system based on Fmax provides a rational basis for selecting optimal needle-syringe-formulation combinations.
- The proposed system accounts for injection forces and subcutaneous pressure, enhancing device selection.
- This approach supports the optimization of needle parameters for improved drug delivery performance.
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