Dissolution testing of soft biomaterials, and where USP <711> fits
Dissolution testing asks how fast the drug leaves the dosage form. For a tablet, that answer is well understood, and the basket and paddle in USP <711> were built to measure it. For a soft biomaterial that swells, floats, or degrades, the same apparatus starts to measure something it was never designed for.
What does dissolution testing measure?
A dissolution test puts a dosage form in a known volume of fluid at body temperature, agitates it, and tracks how much active ingredient enters the medium over time. The result is a release curve: percent released against time. FDA’s guidance on immediate-release oral forms names three uses: assessing lot-to-lot quality, guiding new formulations, and confirming quality and performance after a change.
The method rests on a few assumptions. The dosage form stays intact enough to behave predictably. It sits where the apparatus expects it. And what you sample from the medium reflects what the form is doing.
How is dissolution testing different from in vitro release testing?
The measurement is the same idea, and the terms mark different products and time scales. Dissolution usually means oral solids under USP <711>. In vitro release usually means injectables and implants, the subject of USP <1001>. The line is loose: a 2026 review of PLGA injectables writes “dissolution or in vitro release testing” as one phrase.
| Feature | Dissolution testing | In vitro release testing |
|---|---|---|
| Typical product | Tablets and capsules | Depots, microparticles and implants |
| USP chapter | <711>, with compendial apparatus | <1001>, general chapter with examples |
| Example time scale | 85% in 15 minutes for a rapidly dissolving product, in FDA’s oral guidance | 84 days for one implant entry in FDA’s database, reproduced in the 2026 review |
| Standard methods | Compendial | “Still no standardized compendial” methods, the review says |
Release testing for depots has its own page: in vitro release testing for long-acting injectable depots.
Where does USP <711> fit, and where does it strain?
USP <711> defines four apparatus. The basket and paddle are what most labs reach for with oral solids, and for tablets and capsules they work well. Soft biomaterials break their assumptions in three ways:
- They change shape. A hydrogel swells and can float, so it leaves the defined hydrodynamic position the apparatus assumes. The European Pharmacopoeia’s dissolution text allows a wire helix or other sinker on a unit that would float. A sinker holds the form down. It doesn’t stop it swelling.
- They degrade. As the network breaks down, fragments shed and the surface area changes, so the release rate is no longer a clean function of a stable form.
- They release slowly. A long-acting form releases over weeks to months, far longer than a standard dissolution run, so a short test sees only the opening.
None of this makes the standard useless. It means a soft biomaterial needs its release measured alongside what the material itself is doing. The USP expert panel describes <711> as guidance for oral dosage forms, and builds its own view of injectables and implants on <1001>.
What does weighing the material add?
Sampling the medium tells you how much drug has come out. Weighing the sample tells you what the material is doing. In a gravimetric method, the sample stays in its chamber and is weighed at set timepoints through the run.
That measurement follows the material’s own behavior:
- Uptake. How much fluid the material takes up as it swells.
- The peak. When mass tops out, and how fast it gets there.
- The set. When the network stabilizes into a plateau.
- Degradation. When the hydrated mass starts to fall as the material breaks down.
Release still comes from the medium: a sample of fluid, measured for dissolved drug at each timepoint. The mass curve shows what the material was doing over the same weeks, whether it was swelling, setting or losing mass. Weighing by hand means lifting and blotting the sample at each reading, and every handling step disturbs it. The release curve and the depot behind it follows this for depots.
What are the limits of a dissolution test?
A dissolution curve can’t show the body. FDA’s oral guidance treats dissolution as one part of the record, submitted with bioavailability and manufacturing data. For a depot, the USP panel warns that a discriminating method isn’t necessarily clinically relevant.
It can’t show the material either. A flat release curve doesn’t say whether the form has set, stalled or begun to erode. A hydrated mass curve doesn’t identify the drug, and for PLGA, molecular weight falls before mass is lost, so it needs its own measurement.
Which method should you use?
Use the basket or paddle when the dosage form is an oral solid, a tablet or capsule that stays intact. When the form swells, degrades, floats, or releases over weeks, sample release on a schedule that fits it, with a flow-through cell or a sample-and-separate method, and track the material’s mass alongside. For most soft biomaterials in drug delivery, that second case is the one you’re in. The depot release methods comparison covers those methods, and sink conditions covers how much medium they need.
What GelTech reports
GelTech tracks the material on Carousel, which weighs each sample to 1 mg in its chamber, unattended for minutes to months. Integrated instruments such as UV-Vis and mass spectrometry read the drug released into the sampled medium, so the mass curve and the release curve come from the same run.
GelTech doesn’t run animal or clinical studies, or accredited biocompatibility or sterility testing. From here, plan an in vitro release study scoped to your formulation, or see how a pilot study works.
Sources
- USP. General chapter <711> Dissolution
- USP. General chapter <1001> In vitro release test methods for parenteral drug preparations
- European Pharmacopoeia 7.0. 2.9.3 Dissolution test for solid dosage forms
- FDA. Guidance for industry: Dissolution testing of immediate release solid oral dosage forms. 1997
- D'Arcy DM, Wacker MG, Klein S, et al. In-vitro product performance of parenteral drug products: view of the USP expert panel. Dissolution Technologies. November 2022
- Lusina Kregar M, Krtalić I, Šagud I. An overview of in vitro release methods for long-acting injectable products based on PLGA. Methods Protoc. 2026;9(3):87
Related reading
Questions
What is dissolution testing?
Dissolution testing measures how quickly an active ingredient releases from its dosage form into a test fluid over time. Oral products rely on it to check lot-to-lot quality and to confirm a product still performs after a change.
Which USP chapter covers release testing for injectables and implants?
USP <1001> is the general chapter on in vitro release test methods for parenteral products such as injectables and implants. USP <711> covers dissolution of oral dosage forms.
Why weigh the sample as well as sampling the medium?
Weighing a soft biomaterial sample, as well as sampling the dissolution medium, shows what the material itself is doing. Sampling the medium tells you how much drug has come out, and weighing the sample tells you how much fluid it takes up, when it peaks, when it sets, and when its hydrated mass starts to fall.
Which standards are GelTech's methods aligned with?
GelTech Labs' methods are aligned with EN 13726, NWSP 240 and 242, USP <711> and ISO 37, and USP <711> applies to its dissolution methods. GelTech's methods are aligned with these standards rather than certified.
