Modification Degree (MoD): How Much of the Acid Is Cross-Linked
Quick facts
- Definition
- The proportion of hyaluronic acid units that were chemically modified by the cross-linking agent.
- Abbreviation
- MoD, from modification degree.
- What it is not
- It is not the same as concentration in mg/ml or the firmness measured by G prime.
- Where to find it
- In the manufacturer's technical material, not always on the packaging.
The modification degree, or MoD, measures how much of the hyaluronic acid was chemically modified during cross-linking. The cross-linking agent, usually BDDE, attaches to the chains, and the MoD expresses the fraction of units that carry that attachment.
What does the MoD tell you, and what does it not?
It is not a synonym for effective cross-linking. Part of the cross-linking agent may be attached at only one end, without forming a bridge between two chains. Those attachments do not create gel structure. That is why the MoD is a chemical measure, not a mechanical one.
| Measure | What it represents |
|---|---|
| MoD | Fraction of modified units |
| Concentration | Total amount of HA per ml |
| G prime | Gel firmness under deformation |
Two gels with the same MoD can have very different G prime values, because the result also depends on molecular weight, particle size and the manufacturing process. The whole picture is in rheology.
How should you use this information?
For the professional, the MoD is one technical data point among several. It helps compare data sheets from the same manufacturer and talk with technical support, but it does not replace reading the instructions for use or the clinical choice for each area. Nor is it a sales argument to give the patient.
Frequently asked questions
What is the MoD of hyaluronic acid?
It is the modification degree: what share of the hyaluronic acid units received a link from the cross-linking agent. A higher MoD indicates more chemical modification, but does not define gel firmness on its own.