Contents
Material Wettability, Wicking and Microfluidics

Hydrogel and Biomaterial Wettability for Tissue Engineering: Contact Angle That Survives Drying and Absorption

Wettability shapes protein adsorption and cell adhesion on hydrogels, scaffolds and coated implants. Measure water contact angle with a fixed swelling, blotting and read time, so drying and absorption do not decide the number, and compare formulations like with like.

Who this is for: Tissue engineering, biomaterials and medical device R&D labs working with hydrogels, scaffolds, films and coated implants.

Where it fits: Formulation screening, surface treatment and coating checks, lot comparison and the surface section of a characterization package.

What it does not do: It does not measure cell adhesion, protein adsorption or biocompatibility, and no standard we checked prescribes a hydrogel contact angle method.

Method
Sessile drop water contact angle at a fixed early read time after controlled swelling and blotting
Standard
No standard method for hydrogel contact angle found; ASTM F2150 lists surface properties among scaffold characterization areas
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Transparent vase with hydrogel isolated on white — Photo
Why it matters

Why biomaterial wettability needs careful measurement

40° and 50°

water contact angles at which adhesion of endothelial cells and HeLa cells peaked on mixed self assembled monolayers in one controlled study.

Arima and Iwata, Biomaterials 28(20):3074, 2007

65°

water contact angle that separates surfaces with long range attractive forces from those with repulsive forces, later called the Berg limit for bioadhesion.

Vogler, Adv. Colloid Interface Sci. 74:69, 1998

32.1° to 89°

rise in water contact angle on one silicone hydrogel contact lens after 16 hours of repeated short air exposure, showing how drying changes the result.

Eftimov et al., Int. J. Mol. Sci. 20(6):1313, 2019

Sources: Arima Y., Iwata H., Biomaterials, 2007; Vogler E. A., Structure and reactivity of water at biomaterial surfaces, Advances in Colloid and Interface Science, 1998; Eftimov P. et al., Impact of air exposure time on the water contact angles of daily disposable silicone hydrogels, International Journal of Molecular Sciences, 2019. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this hydrogel wettability check does and what it does not

A quick reference for biomaterials labs checking fit before reading further.

Evidence Box

Problem this solves

Hydrogel and scaffold contact angles that change with drying, absorption and handling, so formulations cannot be compared or results reproduced.

Standards

No standard we checked prescribes a hydrogel contact angle method. ASTM F2150 lists surface properties among scaffold characterization areas; ISO 18369-4 does not cover wettability.

Peer reviewed method

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

Customer case study

A shared facility at Harvard University supported seven publications from five labs on one Dropometer, including regenerative hydrogels.

Customer publication

A Bioactive Materials (2025) study measured GelMA and GelTA hydrogels on the Dropometer with 16 µL drops read after 1 s, n = 3, and reported about 50 to 70°.

Honest limit

Wettability is one factor in cell response, not the only one. One chitosan study found no link between contact angle and cell attachment.

Who this is for

What biomaterial wettability question are you trying to answer?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Tissue engineering researcher

You compare hydrogel formulations, crosslinking or added biologics. Contact angle under a fixed swelling and read time shows whether a change altered the surface cells will meet.

Report swelling, blotting, drop volume and read time with every value.

Biomaterials or device engineer

You plasma treat scaffolds or coat implants and films. Contact angle before and after treatment shows the surface changed and whether it stays changed in storage.

Porous scaffolds can wick drops; read early and treat values as comparative.

Core facility manager

Many groups bring hydrogels, films and scaffolds to one instrument. A shared method lock makes their numbers comparable and their methods sections complete.

Post the method lock beside the instrument.
Fit check

Is this the right check for your biomaterial?

It measures water contact angle on the hydrated surface at a fixed time. It does not measure biology.

Good fit if

You compare hydrogel formulations or crosslinking conditions.
You plasma treat or coat scaffolds, films or implants.
You need a surface result for a paper or characterization package.
Your samples can be cast flat in a fixed mould.
Several labs share one instrument and need one method.

Less relevant if

You need cell adhesion or protein data; use biological assays.
Your gel must stay fully immersed; consider captive bubble.
Your scaffold wicks drops at once; report wicking, not an angle.
Your sample is too soft or curved to hold a drop.
Summary

How contact angle supports hydrogel and biomaterial work

The answer in under a minute.

Measure water contact angle on hydrogels and biomaterials only after a fixed swelling and blotting step, with a fixed drop volume and an early fixed read time. Then compare formulations, treatments and lots under the same conditions. A real difference shows the surface changed; a drifting value usually shows drying or absorption.

The Dropometer contact angle kit runs the measurement. A Bioactive Materials study of regenerative hydrogels used it with 16 µL drops read after 1 s, and the Harvard University case study shows a shared facility serving hydrogel, film and implant labs. Our contact angle measurement guide and biotechnology guide explain more.

Expert Quote

Expert perspective on what a drop sees

“

Wettability is set by the top five to ten ångström of a surface: what the liquid actually sees. It doesn't matter what lies beneath; that outermost layer is what you are really measuring.

Dr. Alidad Amirfazli

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

The problem

Why hydrogel contact angles are hard to trust

Cells do not meet a biomaterial directly; they meet the proteins that adsorb to its surface in the first minutes, and wettability shapes that layer. Controlled studies on model surfaces found cell adhesion peaked at moderate water contact angles, for example 40° for endothelial cells and 50° for HeLa cells on mixed monolayers, and 53 to 55° on a PLGA wettability gradient. A water contact angle of about 65° is widely cited as the boundary between hydrophilic and hydrophobic behaviour for bioadhesion. Not every study agrees: one chitosan film study found no link between contact angle and cell attachment, so wettability is one factor among several. Measuring hydrogels adds its own problems. They lose water within minutes in room air, which raises the angle. Drops soak into the gel, so the angle falls with time. The surface depends on the mould it was cast against: one hydrogel chemistry read about 35° or up to about 120° depending on the mould. Sessile drop and captive bubble methods can even rank the same lenses differently. Without a fixed method, a contact angle on a hydrogel says more about timing and handling than about the material.

The angle changes every few seconds while you watch.
Repeat samples of one formulation disagree.
Values differ from published ones for the same material.
Plasma treated scaffolds read zero because the drop wicks in.
Reviewers ask how the hydrogel was conditioned before measuring.
Troubleshooting

Why hydrogel readings vary and what to check

Why:

  • Hydrogels lose water in room air, and the surface becomes less hydrophilic as it dries.

How to detect:

  • The angle rises with the time between blotting and the drop.

Corrective action:

  • Lock the time from blotting to drop, measure quickly and record humidity.

Why:

  • Water diffuses into the gel, so the drop shrinks and the angle falls over seconds to minutes.

How to detect:

  • The angle falls steadily during the read.

Corrective action:

  • Read at a fixed early time and report it, as published hydrogel work does.

Why:

  • Swelling time and how surface liquid is removed change the surface the drop meets.

How to detect:

  • Spread between samples is large while the formulation is the same.

Corrective action:

  • Fix the swelling medium and time and blot the same way each time.

Why:

  • The mould material can change which groups sit at the hydrogel surface.

How to detect:

  • The same formulation reads differently from different moulds.

Corrective action:

  • Cast all samples against the same mould material and geometry.

Why:

  • Drops soak into porous or plasma treated scaffolds, so the reading is wicking, not a true angle.

How to detect:

  • The drop disappears within moments and reads near zero.

Corrective action:

Report wicking time and treat values as comparative only. Our page on paper microfluidic wicking control covers wicking.

Why:

Drop volume and read time change the result. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

  • A reference formulation reads differently between sessions.

Corrective action:

Measure a reference each session and check a flat control against our contact angle reference values.

Not sure your hydrogel readings are comparable?

Send two formulations and your current method, and we will compare them on a call.

Book a 15 minute demo
Lab records

What a hydrogel wettability record contains

Each check produces a record you can file with the formulation and cite in a methods section.

Material

Formulation, concentration, crosslinking, additives and lot.

Conditioning

Mould, swelling medium and time, blotting method and time to drop.

Method settings

Drop volume, read time, temperature and humidity.

Readings

Contact angle per sample, median and spread, with n.

Context

Linked SEM, AFM or cell results for the same samples.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure on hydrogels and biomaterials

Surface

Water contact angle at a fixed early read time

Why it matters: It shows the hydrophilicity of the surface cells and proteins will meet.

How to interpret: Compare formulations under the same conditions. Published model surface studies found adhesion peaks between about 40° and 70° depending on cell type; your own cell results decide.

When it is not enough: It does not measure protein adsorption or cell response.

Time

Angle over the first seconds

Why it matters: Hydrogels absorb drops, so the curve shows absorption as well as wettability.

How to interpret: Report the value at the locked read time and note how fast it falls.

When it is not enough: Very fast absorption can leave too few frames for a value.

Treatment

Angle before and after plasma or coating

Why it matters: It shows the treatment reached the surface.

How to interpret: Published plasma treatment of PLGA cut the angle from 92° to about 30°, with more cell adhesion.

When it is not enough: On porous scaffolds a near zero value is wicking, not a contact angle.

Storage

Angle after storage

Why it matters: Treated and coated surfaces can change before use.

How to interpret: Repeat on stored samples measured the same way.

When it is not enough: It does not show sterilisation effects unless you test after sterilising.

Validation

Validated measurement approach for hydrogels

How the Dropometer itself has been validated, and how a customer measured hydrogels with it.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

Customer evidence on regenerative hydrogels

A Bioactive Materials (2025) study cast GelMA and GelTA hydrogels in a 500 µm PDMS mould, swelled them in DPBS for 3 hours, blotted them and measured 16 µL water drops after 1 s on the Dropometer, n = 3. GelTA hydrogels read about 50 to 70°, a range the authors link to cell adhesion.

Read the citation analysis
QC Protocol

How to measure contact angle on hydrogels

Six steps per sample set. Keep every step identical between formulations.

1

Cast

Cast each hydrogel in the same mould material and geometry on a flat support.

2

Swell

Swell in a fixed medium for a fixed time, such as DPBS for 3 hours.

3

Blot

Remove surface liquid the same way every time and start a timer.

4

Measure

Place the drop within the locked time and read at the locked read time, such as 1 s. Our captive bubble entry covers the immersed alternative.

5

Repeat

Use fresh spots or fresh samples and record n.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the hydrogel contact angle SOP

A two page SOP you can adapt for your materials, with the conditioning and method lock, comparison rules, a troubleshooting table and a record sheet.

Contact angle measurement with the Dropometer

Example output

Example hydrogel wettability log

Example data only. Your values will differ and depend on your own conditioning and read time.

How to read this log

All samples were swelled, blotted and read the same way, so the differences are real. Formulation B with an added biologic read the same as A. The plasma treated film fell sharply. The last row shows the same gel left in air for 10 minutes: drying alone raised the angle. Our medical device guide covers coated devices.

Example hydrogel wettability log

Sample Conditioning Read time (s) Contact angle (°) Spread (°) Note
Hydrogel A Swelled, blotted, measured within 30 s 1 58 3 Reference
Hydrogel B (with biologic) Same 1 60 4 Same as A
PLGA film, untreated Dry film 1 88 2 Baseline
PLGA film, plasma treated Dry film 1 34 3 Treatment reached surface
Hydrogel A Left in air 10 min after blotting 1 74 6 Drying artefact

Example data, not customer data. Hydrogels cast in a 500 µm mould, swelled 3 h in buffer; 16 µL water drops read at 1 s; n = 3.

Signal order

The order to check signals on hydrogel readings

Check these in order. Each one rules out a cause before you look at the next.

1

Conditioning

Rules out swelling and blotting differences.

2

Timing

Rules out drying before the drop and absorption during it.

3

Reference formulation

Confirms the session reads as before.

4

Formulation difference

Shows a real change in the surface.

5

Biological result

Confirms what the surface change means. Our page on implant surface QC covers implants.

FAQ

Common questions about hydrogel and biomaterial wettability

Questions biomaterials labs ask about contact angle on hydrated surfaces.

What contact angle is best for cell adhesion?

There is no single value. Controlled studies found peaks at 40° for endothelial cells and 50° for HeLa cells on model monolayers, about 53 to 55° on a PLGA gradient and about 70° for fibroblasts on plasma treated polymers. Cell type, surface chemistry and adsorbed proteins all matter, so test your own cells.

What is the Berg limit?

A water contact angle of about 65° that separates hydrophilic from hydrophobic behaviour for bioadhesion. Vogler reported long range attractive forces only between surfaces above about 65° and repulsive forces below it, and the threshold was later named the Berg limit. It is a useful guide, not a rule for every material.

Why does the angle change while I measure a hydrogel?

Two things happen at once. The gel surface dries in room air, which raises the angle, and the drop soaks into the gel, which lowers it. Lock the time from blotting to drop and read at a fixed early time, such as 1 s, and report both times.

Sessile drop or captive bubble?

Sessile drop is fast and works on blotted, freshly swelled samples. Captive bubble keeps the sample immersed, so it avoids drying, but the two methods can rank the same materials differently. Choose one, keep it fixed and report it. Our captive bubble entry explains the immersed method.

Is there a standard method?

We found none for hydrogel contact angle. ASTM F2150 lists surface properties among the areas to characterize for tissue engineering scaffolds, and ISO 18369-4 for contact lenses does not cover wettability. Report your full method so others can reproduce it.

What about porous scaffolds?

Drops often soak straight into porous or plasma treated scaffolds, so a near zero reading is wicking, not a true contact angle. One study noted values on porous mats are valid only for comparison. Report wicking time and compare scaffolds of the same structure.

Does plasma treatment improve cell attachment?

Often, but not always. Plasma treatment cut the water contact angle of PLGA from 92° to about 30° with more cell adhesion and growth, and electrospun PCL scaffolds showed about 10% higher cell viability after treatment. Measure the angle and the biological result on the same samples.

Which instrument do we need?

One that places small, repeatable drops and reads at early fixed times, with images you can archive. The Dropometer does this at the bench, and a Harvard University shared facility used one across hydrogel, film and implant projects.

Business impact

What changes when you lock the hydrogel method

Typical changes in how labs work. Benchmarks are given only where a published source exists.

Before and with a locked hydrogel method

Metric Before Dropometer With Dropometer Indicative Benchmark
Comparability Values depend on timing and handling Fixed swelling, blotting and read time Silicone hydrogel 32.1° to 89° with air exposure (Eftimov et al., 2019)
Formulation screening Cell assays on every candidate Contact angle first, cells on the shortlist No published benchmark; track on your own projects
Treatment checks Assumed to work Angle before and after treatment PLGA 92° to about 30° after plasma (Khang et al., 1997)
Methods reporting Drop and timing often missing Full method recorded per sample 16 µL, 1 s, n = 3 reported (Bioactive Materials, 2025, Dropometer)

See the measurement on your own hydrogels

Send two formulations. We will show the comparison on a call.

Book a 15 minute demo

Estimate saved screening work on biomaterial formulations

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Biomaterial screening estimate

Estimate saved screening work on biomaterial formulations.

Each Dropometer unit is US$5,000; the default models one unit.
Your own cost to seed, culture and image one formulation.
Casting, swelling, blotting and contact angle measurement and analysis.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Candidates saved per month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What contact angle cannot tell you about a biomaterial

Honest limits, so you know when to reach for another test.

It does not measure cell response.
Drying and absorption change the value within seconds.
Values are only comparable under the same method.
Porous scaffolds give wicking, not true angles.
Sessile drop and captive bubble can disagree.
No standard method exists for hydrogels.

Contact angle shows the wettability of a hydrated surface under a fixed method. Protein adsorption, cell adhesion, biocompatibility and degradation need their own tests.

Book a 15 minute demo Request a quote
Related

Evidence and related biomaterial workflows

These pages cover customer evidence and the wetting checks that sit beside this one.

Case study

Harvard University

One shared Dropometer, seven publications from five labs.

Read case study

Published paper

Bio-adhesive hybrid hydrogels

GelMA and GelTA hydrogels measured on the Dropometer.

Read our analysis

Instrument

Dropometer

Contact angle and surface energy.

View product

Related use case

Material wettability, wicking and microfluidics

All wettability and wicking use cases in one place.

View Page

Related use case

Paper microfluidic wicking control

Wicking in lateral flow and paper devices.

View Page

Related use case

Dental and orthopedic implant QC

Surface checks on implants.

View Page

Guide

Biotechnology guide

Surface science for biotech labs.

Read guide

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
Combinational regenerative inductive effect of bio-adhesive hybrid hydrogels conjugated with hiPSC derived myofibers and its derived EVs for volumetric muscle regeneration. Bioactive Materials, 2025. See our citation analysis. https://dropletlab.com/validation/citations/analysis/combinational-regenerative-inductive-effect-of-bio-adhesive-hybrid-hydrogels-conjugated-with-hipsc-derived-myofibers-and-its-derived-evs-for-volumetric-muscle-regeneration/
2.
Arima, Y., Iwata, H. Effect of wettability and surface functional groups on protein adsorption and cell adhesion using well defined mixed self assembled monolayers. Biomaterials 28(20):3074 to 3082, 2007. https://doi.org/10.1016/j.biomaterials.2007.03.013
3.
Vogler, E. A. Structure and reactivity of water at biomaterial surfaces. Advances in Colloid and Interface Science 74:69 to 117, 1998. https://doi.org/10.1016/S0001-8686(97)00040-7
4.
Kanduc, M., Schneck, E., Netz, R. R. Understanding the Berg limit: the 65° contact angle as the universal adhesion threshold of biomatter. Physical Chemistry Chemical Physics, 2024. https://pubs.rsc.org/en/content/articlehtml/2024/cp/d3cp05084j
5.
Tamada, Y., Ikada, Y. Cell adhesion to plasma treated polymer surfaces. Polymer 34(10):2208 to 2212, 1993. https://cpsm.kpi.ua/polymer/1993/10/2208-2212.pdf
6.
Khang, G. et al. Interaction of different types of cells on poly(L-lactide-co-glycolide) surface with wettability chemogradient. Macromolecular Research 8(6):276 to 284, 2000. https://koreascience.or.kr/article/JAKO200011921692360.page?&lang=en
7.
Khang, G. et al. Bio-Medical Materials and Engineering 7(6):357 to 368, 1997. https://pure.jbnu.ac.kr/en/publications/cell-and-platelet-adhesions-on-plasma-glow-discharge-treated-poly/
8.
Hamilton, V. et al. Characterization of chitosan films and effects on fibroblast cell attachment and proliferation. Journal of Materials Science: Materials in Medicine 17(12):1373 to 1381, 2006. https://doi.org/10.1007/s10856-006-0613-9
9.
In vitro water wettability of silicone hydrogel contact lenses determined using the sessile drop and captive bubble techniques. Journal of Biomedical Materials Research A 83A(2):496 to 502, 2007. https://research.manchester.ac.uk/en/publications/in-vitro-water-wettability-of-silicone-hydrogel-contact-lenses-de-2/
10.
Eftimov, P., Yokoi, N., Peev, N., Georgiev, G. A. Impact of air exposure time on the water contact angles of daily disposable silicone hydrogels. International Journal of Molecular Sciences 20(6):1313, 2019. https://doi.org/10.3390/ijms20061313
11.
Kashani, A., Cho, H. J. The role of poroelastic diffusion in the transient wetting behavior of hydrogels. Soft Matter, 2024. https://doi.org/10.1039/d3sm01472j
12.
Yi, B. et al. Surface hydrophobization of hydrogels via interface dynamics induced network reconfiguration. Nature Communications 15:239, 2024. https://doi.org/10.1038/s41467-023-44646-5
13.
Pappa, A. M. et al. Oxygen plasma modified biomimetic nanofibrous scaffolds for enhanced compatibility of cardiovascular implants. Beilstein Journal of Nanotechnology 6, 2015. https://doi.org/10.3762/bjnano.6.24
14.
Rahmati, M. et al. Biological responses to physicochemical properties of biomaterial surface. Chemical Society Reviews 49:5178 to 5224, 2020. https://doi.org/10.1039/d0cs00103a
15.
Menzies, K. L., Jones, L. The impact of contact angle on the biocompatibility of biomaterials. Optometry and Vision Science 87(6):387 to 399, 2010. https://doi.org/10.1097/opx.0b013e3181da863e
16.
Application report AR255, methods for wettability determination on hydrogels, 2006 (instrument maker application note). https://www.kruss-scientific.com/files/kruss-ar255-en.pdf
17.
ASTM F2150-19. Characterization and testing of biomaterial scaffolds used in tissue engineered medical products. https://store.astm.org/f2150-19.html
18.
ISO 18369-4:2017. Ophthalmic optics, contact lenses, part 4: physicochemical properties of contact lens materials. https://www.iso.org/standard/66341.html
19.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
20.
Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects. https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
21.
Droplet Lab validation papers
22.
Customer publications that cite the Dropometer
23.
Contact angle measurement guide
24.
Medical device guide