Contents
Fully compliant

FDA 510(k) premarket notification guidance for contact lens care: CMC and surface tension

FDA's 510(k) guidance for contact lens care products asks daily cleaner submissions with surfactant ingredients to report surface tension and critical micelle concentration (CMC). Its Chem-Appendix B measures surface tension with a tensiometer across a dilution series. The Dropometer is a pendant drop tensiometer, so it runs that method as written.

What brings you here?

Who this is for
Regulatory, analytical and formulation teams at contact lens care and ophthalmic medical device manufacturers.
Compliance tier
Fully compliant: Chem-Appendix B asks for surface tension by tensiometer and a least squares fit. It names no ring, plate or drop geometry, so the Dropometer pendant drop tensiometer runs it as written.
Measurement
Pendant drop surface tension up to 75 mN/m, ±0.03 mN/m accuracy, static and dynamic (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, on the bench.
Last updated
October 20, 2026
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Free one page checklist for CMC by surface tension: dilution series, settings to lock, replicates, the two line fit and what to record for a submission file.

Talk to an expert

Book a 15 minute demo on your cleaner

Tell us your surfactant, medium and current method. We will run a pendant drop live and tell you plainly where the Dropometer fits your validation plan and where it does not.

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View the FDA guidance
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against FDA 510(k) Guidance: Determining CMC by Surface Tension
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box

Guidance

FDA CDRH, Premarket Notification (510(k)) Guidance Document for Contact Lens Care Products, issued May 1, 1997. For daily cleaners with surfactant active ingredients, the chemistry section should include the solution's surface tension and the surfactant's micelle concentration, using the method in Chem-Appendix B or another scientifically valid method. Contact lens care products are Class II medical devices, so a new cleaner reaches the market through a 510(k) premarket notification that shows it is substantially equivalent to a legally marketed predicate device.

Compliance tier

Fully compliant. Chem-Appendix B dilutes the surfactant system in the cleaner's own medium, measures surface tension with a tensiometer, and fits least squares lines against log concentration. It does not specify a ring, plate or drop geometry. The Dropometer is a pendant drop tensiometer.

Instrument performance

Surface tension up to 75 mN/m, accuracy ±0.03 mN/m, resolution 0.01 mN/m, Young-Laplace fit, static and dynamic pendant drops, from the Dropometer product specification.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Published research

Researchers used the Dropometer as a pendant drop tensiometer to measure polymer and surfactant mixtures. Read our analysis of the paper.

Customer evidence

A university rheology lab put surface tension next to every flow curve and reported it in seven publications. Read the case study.

What it does not tell you

Surface tension and CMC support a cleaning claim. They do not prove cleaning effectiveness on their own. The guidance also asks for other chemistry, microbiology and clinical data.

Executive summary

What the guidance asks for, who uses it and how the Dropometer fits

FDA's 1997 510(k) guidance for contact lens care products asks daily cleaners with surfactant ingredients to report the solution's surface tension and the surfactant's critical micelle concentration (CMC). Regulatory, analytical and formulation teams use the data to support cleaning effectiveness. Chem-Appendix B measures surface tension with a tensiometer, and the Dropometer pendant drop tensiometer runs it as written. The results go into the chemistry section of the premarket submission, next to the comparison with the predicate device.

You find the CMC by measuring surface tension across a dilution series. Surface tension falls as surfactant is added, then levels off. The break between the two parts of the curve is the CMC.

The Dropometer pendant drop tensiometer reads each drop with a Young-Laplace fit. For the full workflow, see CMC assessment and surfactant efficiency. A university rheology lab has reported Dropometer surface tension data in seven publications. Background reading: our pharmaceutical guide, the surface tension measurement guide and the guide to surfactants.

Further reading: what critical micelle concentration means, what to look for in a tensiometer for surfactant and CMC research, how to show repeatability with repeatability, reproducibility and Gage R&R and our Gage R&R calculator, a classroom version in the effect of surfactants on surface tension, and reference values in CMC of common surfactants.

How the Dropometer fits the submission process

CMC by surface tension, step by step, in our own words

From dilution series to a CMC value

These steps follow the order of Chem-Appendix B, in our own words. Read the guidance itself before you write your SOP.

±0.03 mN/m

Surface tension accuracy

From the Dropometer product specification. Resolution is 0.01 mN/m.

About 2 min

Setup

Base plate, phone holder, LED and Hamilton syringe. No PC needed.

5.29 µL

Per dropper rotation

Manual dropper volume per rotation, so each drop uses very little solution.

1

Plan the dilution series

Make Solution 1, the cleaner's medium without surfactants. Make Solution 2, a stock of the surfactant system in the product's ratio. Dilute Solution 2 with Solution 1 to make the Solution 3 series, spaced on a log scale from well below to well above the expected CMC.

2

Set up for pendant drop

Fit a clean needle to the Hamilton syringe and mount the phone and LED. Enter the density difference between the solution and air for the Young-Laplace fit.

3

Measure each concentration

Form a fresh pendant drop and read it at the same age every time. Surfactants take time to reach the surface, so use the dynamic mode to see when the value settles.

4

Replicate and avoid carryover

Measure several drops per concentration. Run from the lowest to the highest concentration, and rinse the syringe and needle between solutions.

5

Plot and find the CMC

Plot surface tension against log concentration. Fit one straight line to the falling part and one to the plateau. The point where they meet is the CMC.

6

Record for the submission

Record room temperature, drop age, needle size, density values, replicates, fit quality and the regression rule. Keep the drop images with the data.

7

Watch the full measurement

This video shows a complete Dropometer pendant drop surface tension measurement, from setup to result. Repeat it at each concentration in your series.

Dropometer pendant drop surface tension, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A.

Read the validation papers

Published client paper

Researchers used the Dropometer as a pendant drop tensiometer at room temperature to measure polymer solutions with added surfactants, reporting the average surface tension of repeated drops.

Read our analysis of the paper

Check the method before your 510(k) submission

Pendant drop · CMC · method validation

Chem-Appendix B sets the steps but not the checks around them. Add your own: measure pure water against its reference value at your room temperature, run a reference surfactant with a published CMC, and repeat with two operators on different days.

The appendix notes that pH, tonicity and other inactive ingredients can shift the CMC. That is why the dilutions use the cleaner's own medium, not plain water.

Write the least squares rule into your SOP before you test the product, so the break point is not chosen by eye.

Example output

Example data for illustration only. These are not measured results. Your surfactant, medium and temperature decide the numbers.

Example: nonionic surfactant dilution series in buffer, 22 °C room

Concentration (% w/v) Drops (n) Mean γ (mN/m) Std dev (mN/m) Region Note
0.0001568.120.08FallingNear water
0.001554.600.11Falling
0.003542.000.09Falling
0.01536.210.07PlateauJust above the break
0.03535.940.06Plateau
0.1535.710.06PlateauTypical use level sits here

How to read this table

Each row is the mean of five pendant drops. Surface tension falls steeply, then flattens. In this example, straight lines fitted to the two parts meet near 0.008% w/v, the estimated CMC.

Example output chart

The same example data as the table, plotted on a log scale with the two fitted lines.

Example plot of surface tension against log surfactant concentration with two fitted lines meeting at the critical micelle concentration

Example data, not measured results. Dashed lines are straight line fits to the falling part and the plateau.

Business impact

What changes when surface tension runs on your own bench

Metric Before Dropometer With Dropometer Results
Where the test runs Ring or plate tensiometer, often at a contract lab Pendant drop on your own bench No published benchmark
Solution per reading A vessel of liquid per reading One pendant drop; the manual dropper gives 5.29 µL per rotation Dropometer product specification
Result format A value per concentration A value per drop, ±0.03 mN/m, with the drop image Dropometer product specification
Record Lab report Drop images, fits and settings kept with the data No published benchmark

See a pendant drop on your own solution

Bring your cleaner and its surfactant. We will measure a short dilution series live.

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ROI estimate

Estimate the cost of the quality failures this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings

Lock these in your SOP before you test the product

Parameter Recommended Setting Technical Rationale
Mode Pendant drop, Young-Laplace fit The Dropometer surface tension method. The model is in the software.
Density difference Measured density of each solution The fit needs it. Dilute solutions are close to water, but check it.
Drop age at reading The same for every drop, set in the SOP Surfactants adsorb over time, so an early reading reads high.
Concentration range Well below to well above the expected CMC, log spaced You need enough points on both lines to fit them.
Replicates Several fresh drops per concentration Shows repeatability and catches a bad drop.
Order Lowest to highest, rinse between Carryover from a strong solution lowers the next reading.
CMC rule Two line regression, written before testing Stops the break point being picked by eye.
Temperature Record it, and keep the room steady CMC shifts with temperature. The Dropometer runs at 10 to 45 °C and has no temperature control.

Is this FDA guidance the right reference for your submission?

Pick the reference by what you need to show

Start: What do you need to report?

Surface tension and CMC for a lens cleaner 510(k)

Signals:

Your daily cleaner has surfactant active ingredients.

Rule-out:

Follow Chem-Appendix B. The Dropometer pendant drop tensiometer runs it as written.

A published CMC method by surface tension

Signals:

You want a standard method name to cite for CMC.

Rule-out:

See ISO 4311.

Surface tension of a solution by ring or plate

Signals:

Your SOP or customer names a ring or plate method.

Rule-out:

See ASTM D1331.

Wetting of hydrophobic lenses in a conditioning solution

Signals:

Your product is a conditioning solution, not a cleaner.

Rule-out:

The same guidance lists wetting angle against soaking time. That is a contact angle measurement, which the Dropometer also runs.

Decision tree at a glance

Start from what you need to report. Blue boxes are measurements the Dropometer runs.

Decision tree for choosing FDA Chem-Appendix B on the Dropometer, ISO 4311, ASTM D1331 or a contact angle soaking test

Pick the reference by what you need to report.

Interpreting results

What the curve tells you, and what it does not

Steep fall, then a plateau: Surface tension drops as surfactant fills the surface, then levels off once micelles form. The break is the CMC.
Product concentration above the CMC: Chem-Appendix B treats a surfactant level above the CMC as in vitro evidence of cleaning effectiveness. The 510(k) summary of a previously cleared device, K050729, makes the same point.
A dip near the break: A minimum just below the plateau often points to an impurity in the surfactant. Check the raw material.
Medium and temperature move the CMC: Salts, buffers and temperature all shift it, so measure in the product's own medium and record the room.
Expert perspective

Read the whole curve

Surface tension versus concentration is one of the few measurements that lets you watch a surfactant reorganise an interface in real time: read the curve, not just the endpoint.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits

Honest limits of the method and of the Dropometer

The Dropometer has no temperature control. Record room temperature and keep it steady, or the CMC will drift.
Reading a drop too early gives a high value. Fix the drop age and check the dynamic trace.
Surfactant carryover in the syringe lowers the next reading. Run low to high and rinse.
Very low surface tension or viscous solutions can give unstable drops. Check fit quality on every drop.
The guidance dates from 1997. Check FDA's current expectations, and consider a pre submission meeting.
FAQ

Frequently asked questions

Does FDA ask for surface tension data on contact lens cleaners?

For daily cleaners with surfactant active ingredients, FDA's 1997 510(k) guidance lists the solution's surface tension and the surfactant's micelle concentration in the chemistry section. Check the current FDA guidance documents for your product type before you plan the testing.

Which surface tension method does the guidance describe?

Chem-Appendix B dilutes the surfactant system in the cleaner's medium, measures surface tension with a tensiometer, plots it against log concentration and uses least squares regressions to find the CMC. It does not name a ring, plate or drop method, and the guidance also accepts another scientifically valid method.

Can the Dropometer determine CMC?

It measures the surface tension at each concentration by pendant drop. You then plot surface tension against log concentration and fit two straight lines. The point where they meet is the CMC. Write that regression rule into your SOP before testing.

Why does temperature matter for CMC?

CMC and surface tension both change with temperature. The Dropometer has no temperature control, so keep the room steady, record the temperature for every series, and compare products only at matching conditions.

How long should a drop age before reading?

Long enough for the value to settle. Surfactant molecules take time to reach a fresh surface, so an early reading is too high. Use the dynamic mode to see when the trace flattens, then fix that drop age in your SOP.

Does the guidance cover contact angle too?

Yes, for conditioning solutions. It lists the wetting angle of hydrophobic lenses in the solution as a function of soaking time. That is a contact angle measurement, which the Dropometer also runs.

Where does this data fit in the 510(k) submission process?

A 510(k) premarket notification asks FDA to find that a new device is substantially equivalent to a legally marketed predicate device: as safe and effective, with the same intended use. For a daily cleaner with surfactant ingredients, the 1997 guidance lists surface tension and CMC in the chemistry section, alongside microbiology and clinical data. FDA's review goal for a 510(k) is 90 days, counted in FDA review days. A device that is not substantially equivalent may need a De Novo request, and Class III medical devices need premarket approval (PMA) instead. The Dropometer produces the surface tension data only: FDA clearance applies to your product, not to the instrument.

Legal note

This page summarises FDA guidance in our own words. It is not regulatory advice. Check FDA's current guidance and talk to FDA before you rely on a method in a submission. Droplet Lab does not certify compliance. Your own method validation does.

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How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

FDA's 1997 contact lens care 510(k) guidance, FDA 510(k) summary K050729, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the guidance, and this is not regulatory advice.

04

Last checked

October 2026

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References

1. US FDA, CDRH. Premarket Notification (510(k)) Guidance Document for Contact Lens Care Products, May 1, 1997. fda.gov guidance page
2. US FDA. 510(k) summary K050729, Alcon multi purpose disinfecting solution, cleared September 14, 2005. accessdata.fda.gov K050729
3. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
4. Droplet Lab. Analysis of a client paper on surfactants in polymer solutions. dropletlab.com/validation/citations/analysis/
5. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/