Bioactive Glass Coatings for PLA Bone Screws Science Fair

ISEF Category: Biomedical Engineering

Subcategory: Biomaterials and Regenerative Medicine  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

Real bioactive glass implants encourage bone to grow right onto them. The recipe is mostly silica, calcium, and phosphate. You can mimic the first two with crushed glass and eggshells. After a soak in simulated body fluid, your homemade coating should grow a layer of bone-like apatite you can detect with aquarium phosphate strips.

What Is It?

Bioactive glass is a class of materials that bonds to bone. Common formulas include silica from soda-lime glass, calcium from carbonate sources like eggshell, and small amounts of phosphate or boron. When dipped into simulated body fluid (SBF), the surface releases ions and pulls phosphate from solution, forming hydroxyapatite, the mineral in bone.

A 3D-printed PLA bone screw is a teaching analog, not a real implant. You coat it with your glass mix, cure it, then submerge it in SBF for days. Each day you measure the phosphate left in solution. Falling phosphate means apatite is forming.

Aquarium phosphate strips give semi-quantitative readings. With careful color calibration on your phone, you can convert the strip color to a numeric concentration and plot uptake over time.

Why This Is a Good Topic

Bioactive coatings are an active orthopedic implant topic. The chemistry is friendly enough for home or school labs and the readout is colorimetric, so no expensive instruments are needed. You will learn dissolution kinetics, surrogate-implant design, and SBF protocols used in the real field.

Research Questions

• How does eggshell-to-glass ratio change phosphate-uptake rate?
• What is the effect of borax content on apatite formation?
• Does coating thickness scale linearly with uptake slope?
• To what extent does SBF refresh frequency shift the curve?
• Which composition forms a visible apatite layer fastest?
• How does PLA surface roughness affect coating adhesion?
• What is the effect of soak temperature on uptake kinetics?

Basic Materials

• FDM 3D printer and PLA filament.
• Crushed soda-lime glass (mortar and pestle).
• Cleaned eggshell powder (calcium source).
• Borax.
• Phosphate aquarium test strips.
• Drugstore salts for Kokubo SBF.
• Smartphone with color-calibration card.
• Sealable glass jars.

Advanced Materials

• Lab-grade silica and calcium hydroxide.
• Inductively coupled plasma optical emission spectrometer.
• X-ray diffraction access.
• Scanning electron microscope.
• Reference bioactive glass 45S5 powder.

Software & Tools

• ImageJ: Converts strip color to numeric phosphate values via calibration.
• Python (SciPy): Fits exponential decay to phosphate-uptake curves.
• Excel or Google Sheets: Logs daily readings.
• OpenSCAD: Designs the printed bone-screw analog.

Experiment Steps

1. Lock a fixed bone-screw geometry and PLA print profile.
2. Decide the composition sweep (eggshell ratio or borax level) and lock the rest.
3. Build a phosphate standard curve before any test starts.
4. Plan controls (uncoated PLA, no SBF, no eggshell) that rule out background effects.
5. Choose sampling timepoints that capture both fast and slow uptake.
6. Compare your uptake slopes to published apatite-formation rates.

Common Pitfalls

• Mixing SBF salts in the wrong order, causing immediate phosphate precipitation.
• Reading aquarium strips under different lighting between days.
• Ignoring evaporation in the jars, which concentrates phosphate without uptake.
• Crushing glass too coarsely so the coating cracks off.
• Failing to refresh SBF, which saturates and masks ongoing uptake.

What Makes This Competitive

A class-level version just confirms phosphate drops. A competitive ISEF entry calibrates strips against a known phosphate standard, runs multiple compositions, reports apatite formation rate as a slope with confidence intervals, and benchmarks against published Kokubo SBF studies on commercial bioactive glasses.

Project Variations

• Swap eggshell for crushed coral and compare ion release.
• Test multiple SBF temperatures to estimate activation energy.
• Add a polylactic-acid degradation tracer and link coating loss to apatite growth.

Learn More

• PubMed: Search Kokubo simulated body fluid review.
• NIH PubMed Central: Open-access papers on bioactive glass 45S5.
• MIT OpenCourseWare: Course 3.051J Materials for Biomedical Applications.
• Journal of Biomedical Materials Research (library access): Foundational SBF protocols.
• NIST WebBook: Reference ionic concentrations for blood plasma.