Micro-Bioreactor Shear Stress Optimization

ISEF Category: Biomedical Engineering

Subcategory: Cell and Tissue Engineering  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Tiny changes in flow can decide whether cells grow evenly or get stressed in the wrong spots. In tissue engineering, that matters a lot, because cells respond to mechanical cues as much as they respond to chemicals. Your project lets you test how scaffold shape changes those cues before anyone prints or seeds a real device.

What Is It?

A micro-bioreactor scaffold is a tiny support structure that can guide fluid through a 3D space where cells would grow. Think of it like a maze for water. If the maze is too narrow in one spot and too open in another, the fluid pushes harder in some places and barely moves in others. That uneven push shows up as different shear stress levels, which is the rubbing force fluid makes on a surface.

Computational fluid-structure interaction, or FSI, means you model both the moving fluid and the scaffold that shapes it. SimVascular is one software package that can help you do that. You can build a virtual scaffold, run flow through it, and map where shear stress rises or falls. Pareto optimization then helps you compare tradeoffs, such as uniform shear stress versus pressure drop, so you can choose designs that balance competing goals instead of chasing one metric alone.

Why This Is a Good Topic

This makes a strong science fair topic because you can change geometry, flow conditions, and design goals, then measure the effect in a clear numerical way. The project connects to real tissue engineering problems, since cells in bioreactors need the right mechanical environment to behave well. You can learn modeling, optimization, and data analysis, and you can still make the final result visual with 3D-printed parts.

Research Questions

• How does scaffold pore size affect the uniformity of wall shear stress in a simulated micro-bioreactor?
• What is the effect of channel branching angle on peak shear-stress hotspots in the scaffold?
• Does changing scaffold porosity reduce the variation between low-flow and high-flow regions?
• To what extent does inlet flow rate change the Pareto frontier for shear-stress uniformity versus pressure drop?
• Which scaffold geometry gives the best balance between average shear stress and spatial uniformity?
• How does adding curved channels instead of straight channels change flow recirculation zones?

Basic Materials

• Computer with enough memory to run 3D simulation software.
• SimVascular or a comparable open-source modeling workflow.
• 3D modeling software such as Blender or Fusion 360 for simple scaffold shapes.
• Spreadsheet software for tracking design variables and outputs.
• Graphing software for plotting shear-stress maps and Pareto fronts.
• Sub-$300 SLA 3D printer for visual prototypes.
• Resin or filament for prototype prints.
• Digital calipers for checking printed dimensions.
• Notebook or lab journal for design notes and model assumptions.

Advanced Materials

• Access to a workstation with a dedicated GPU or strong multi-core CPU.
• University-level CFD or FSI software access, such as SimVascular plus supporting meshing tools.
• High-resolution imaging or micro-CT data for importing realistic scaffold geometry.
• Pressure sensor or flow sensor data for model validation.
• Microfluidic pump system for comparison experiments.
• Biocompatible scaffold materials for experimental follow-up.
• Mesh refinement tools for convergence testing.
• Statistical software for multi-objective optimization and sensitivity analysis.

Software & Tools

• SimVascular: Builds vascular and flow models, runs simulations, and maps shear-stress patterns in complex geometries.
• Blender: Helps you create and edit custom scaffold shapes before simulation or printing.
• ImageJ: Measures geometric features from images or prints and checks dimensional accuracy.
• Python: Handles parameter sweeps, Pareto plots, and summary statistics for multiple designs.
• ParaView: Visualizes 3D flow fields and makes shear-stress maps easier to compare.

Experiment Steps

1. Define the design variables you will change, such as pore size, branching angle, or channel curvature.
2. Build a small set of scaffold geometries that vary one feature at a time, plus one or two combined designs.
3. Set your performance metrics before you run any models, such as shear-stress uniformity, peak stress, and pressure drop.
4. Run a baseline simulation first, then compare every new design against the same reference conditions.
5. Plot the results as both heat maps and Pareto fronts so you can see tradeoffs, not just one best number.
6. Choose the top designs for a 3D print and check whether the physical prototype matches the digital geometry.

Common Pitfalls

• Using a mesh that is too coarse, which hides shear-stress hotspots and makes designs look more uniform than they are.
• Comparing models with different boundary conditions, which turns design changes into a fake result.
• Changing several geometry features at once, which makes it hard to tell which feature caused the shear-stress shift.
• Ignoring pressure drop while optimizing for uniform flow, which can produce a design that looks good in simulation but would be impractical to pump.
• Printing a prototype that does not match the CAD model, which breaks the link between the simulated scaffold and the visual demo.

What Makes This Competitive

A stronger version of this project does more than compare a few shapes. You can test many designs, keep the simulation settings consistent, and use a clear optimization method with real tradeoffs. A top-level project also validates the model, at least in part, with print measurements or simple flow tests, so the results do not stay trapped on a screen. If you add sensitivity analysis or compare two different objective functions, your work starts to look like engineering research instead of a class exercise.

Project Variations

• Compare straight and curved scaffold channels to see which one gives more even shear stress.
• Test how changing only porosity alters pressure drop and flow uniformity in the same base geometry.
• Use a patient-inspired or organ-inspired scaffold shape and compare it with a simple grid design.

Learn More

• SimVascular documentation: Official guides for geometry creation, meshing, and flow simulation, found through the SimVascular project site.
• NIH 3D Print Exchange: Free models and background on biomedical 3D printing, found by searching the NIH 3D Print Exchange site.
• NCBI PubMed: Search for review articles on bioreactor scaffold design, shear stress, and mechanotransduction.
• NASA Open Courseware and university CFD lectures: Look for free lectures on fluid dynamics and finite element modeling from university OpenCourseWare pages.
• Nature Reviews Materials: Search the journal for review articles on scaffolds, tissue engineering, and mechanical cues.