Biofilm Growth on Surface Coatings

ISEF Category: Cellular and Molecular Biology

Subcategory: Other  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A slimy biofilm can turn a clean surface into a stubborn one fast. That matters in kitchens, hospitals, and water systems. You can test how different coatings change that stickiness using safe microbes, a stain, and your phone camera.

What Is It?

Biofilms are communities of microbes that stick to a surface and to each other. Think of them like a tiny apartment building with glue between the units. Once a biofilm starts, the cells often behave differently than free-floating cells, and they can become harder to remove.

This project looks at how fast a biofilm builds on different coatings. PLA and PET are common plastics, and beeswax is a natural coating. You are testing whether the surface itself changes how well safe microbes attach and grow. Crystal violet staining helps you see the biofilm, and smartphone colorimetry turns that purple signal into data you can compare across surfaces.

Why This Is a Good Topic

This is a strong science fair topic because you can change one clear variable, the surface coating, and measure one clear outcome, biofilm mass or stain intensity. The project connects to real problems in food safety, medical devices, and reusable materials. You can learn experimental design, image analysis, controls, and basic statistics without needing a university lab.

Research Questions

• How does surface coating affect the rate of biofilm formation on PLA, PET, and beeswax?
• What is the effect of surface coating on final crystal violet stain intensity after the same growth period?
• Does a kombucha SCOBY form a denser biofilm than yogurt-derived Lactobacillus on the same coating?
• To what extent does surface roughness change biofilm signal on coated versus uncoated materials?
• Which coating leads to the fastest early attachment signal in smartphone color measurements?
• How does repeated washing change residual biofilm signal on each coating?

Basic Materials

• Kombucha SCOBY culture.
• Plain yogurt with live cultures.
• PLA plastic samples.
• PET plastic samples.
• Beeswax-coated sample strips.
• Sterile or clean clear cups or petri dishes.
• Crystal violet stain solution.
• Distilled water.
• Smartphone with camera.
• White background card or light box.
• Digital kitchen scale with 0.1 g accuracy.
• Timer or stopwatch.
• Disposable gloves.
• Measuring ruler.
• Notebook or spreadsheet for data table.

Advanced Materials

• Biosafety cabinet or clean bench if available.
• Autoclave or pressure sterilization access for media and waste handling.
• Spectrophotometer or plate reader for comparison to phone-based colorimetry.
• Confocal or fluorescence microscope for biofilm structure checks.
• Scanning electron microscope access for surface and attachment imaging.
• Image analysis software for stain quantification and texture measurements.
• Contact angle goniometer for surface wettability testing.
• Profilometer or atomic force microscopy access for surface roughness measurements.

Software & Tools

• ImageJ: Measures stain intensity from photos and helps you compare biofilm coverage across samples.
• Python: Automates image processing, graphing, and statistics for larger data sets.
• Google Sheets: Organizes measurements and makes quick charts for trial comparisons.
• GeoGebra: Helps you fit curves if you compare growth over time.
• RStudio: Runs cleaner statistical tests if you need group comparisons and error bars.

Experiment Steps

1. Define the exact surfaces you will compare and keep the sample shape, size, and cleaning method the same.
2. Choose one microbial inoculum plan and one growth window so your results reflect the coating, not a changing culture.
3. Plan your controls, including a no-inoculum control and a known higher-attachment surface if you can access one.
4. Build a photo workflow with fixed lighting, fixed phone distance, and a single background so color values stay comparable.
5. Decide how you will turn stain images into numbers, then test the method on a few pilot samples before the full run.
6. Map out the statistics you will use to compare coatings, time points, and replicates before you collect the final data.

Common Pitfalls

• Using changing room light for photos, which makes crystal violet intensity look different even when biofilm growth is the same.
• Comparing surfaces with different texture or thickness, which confounds coating effects with simple roughness effects.
• Letting the microbial source vary from trial to trial, which changes attachment behavior and hides the coating effect.
• Rinsing samples too hard after staining, which strips off weak biofilm and destroys the signal you want to measure.
• Skipping replicate samples, which leaves you unable to tell real surface effects from random variation.

What Makes This Competitive

A stronger project will do more than compare three surfaces. You can add time-course measurements, quantify image data with a repeatable method, and test whether roughness or wettability explains the pattern. A good entry also includes proper replicates, strong controls, and a clear statistical test. If you compare phone-based colorimetry with another measurement method, your project looks more analytical and less like a simple demo.

Project Variations

• Compare uncoated PLA with PLA coated in a thin natural wax layer to test whether a single coating change alters attachment.
• Swap the microbial source to a mixed yogurt culture versus a single isolated Lactobacillus colony if your school lab can support it.
• Add a surface texture angle by comparing smooth and sanded samples with the same coating to separate chemistry from roughness.

Learn More

• PubMed: Search review articles on biofilm formation, crystal violet assays, and surface adhesion in safe microbial models.
• NIH NCBI Bookshelf: Find free background chapters on microbial growth, biofilms, and experimental design.
• NOAA National Centers for Coastal Ocean Science: Explore biofilm and surface fouling concepts in aquatic settings and applied microbiology contexts.
• NASA Open Science resources: Look for papers and reports on biofilm control, materials, and spaceflight surface contamination.
• MIT OpenCourseWare: Search for microbiology or biological engineering lecture notes that explain adhesion, growth curves, and data analysis.