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Dynamic versus Static In Vitro Drug Release Testing of Subcutaneous Implants with Distinct Microstructures
Scarlett Zeiringer1, Laura Wiltschko1, Bianca Brandl1,2
1University of Graz, Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology and Biopharmacy, Universitätsplatz 1, 8010 Graz, Austria.
ACS Omega
|July 24, 2026
Summary
This study reveals how physiological factors like fluid flow and tissue firmness impact drug release from subcutaneous implants. Understanding these factors improves long-term in vitro testing for biodegradable drug delivery systems.
Area of Science:
- Biomaterials Science
- Drug Delivery
- Pharmacokinetics
Background:
- Current in vitro release testing for subcutaneous implants often overlooks critical physiological parameters like pH, buffer capacity, flow, and tissue properties.
- Accurate in vitro models are essential for predicting the in vivo performance of long-acting implantable drug delivery systems.
Purpose of the Study:
- To investigate the long-term in vitro release of dexamethasone from biodegradable implants with varying internal structures (dense HME vs. porous FFF).
- To evaluate the influence of physiological parameters, including buffer capacity, fluid flow, and tissue/extracellular matrix (ECM) firmness, on drug release kinetics.
- To establish a framework for improved in vitro testing of subcutaneous implants.
Main Methods:
- Two types of biodegradable dexamethasone-loaded implants (dense HME and porous FFF) were fabricated.
- In vitro release studies were conducted over 8 weeks using various media (phosphate buffers, simulated body fluid, simulated interstitial fluid) and conditions (static vs. USP 4 flow apparatus).
- Korsmeyer-Peppas modeling was used to determine the drug release mechanism, and a gel-based setup mimicked tissue/ECM firmness.
Main Results:
- 100 mM phosphate buffer demonstrated optimal stability for long-term release studies.
- Fluid flow significantly increased drug release from porous FFF implants but not dense HME implants.
- Tissue/ECM firmness reduced overall drug release and altered the release mechanism for both implant types.
Conclusions:
- The internal structure of implants significantly influences their response to physiological flow conditions.
- In vitro release testing must incorporate parameters like fluid flow and tissue/ECM firmness to accurately predict subcutaneous implant performance.
- This research provides a foundation for developing more physiologically relevant in vitro models for long-acting drug delivery systems.
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