Projects /MEng Final Year Project — DCU 2026

Microfluidics Soft Lithography Mechanical Design SolidWorks · FDM PDMS · Centrifugal LoD

PDMS Microfluidic Chip
for Sequential Cell Capture

A centrifugal microfluidic chip that captures individual mammalian cells in trap pocket and relocates them into shared co-location chamber via 90° mechanical indexing — no on-chip valves required.

Why this matters: Studying how a cancer cell and an immune cell interact requires placing them one-to-one inside a confined micro-chamber and observing what happens. Existing approaches either rely on random loading — leaving most chambers empty or over-filled — or require complex on-chip valves that are expensive to fabricate. This platform solves both problems using only centrifugal force and a single 90° mechanical rotation: simple, low-cost, and valve-free.

2025 – 2026 Individual Project DCU Microfluidics Lab Supervised by Dr. Eadaoin Carthy

How It Works

Key concept — two distinct locations

A trap pocket (24.55 µm aperture) is the capture site — it holds exactly one cell during spinning. A co-location chamber (57.83 µm diameter) is the shared storage site downstream. After 90° indexing, the centrifugal force re-aligns with a 30 µm transfer channel connecting the two — cells are driven by centrifugal sedimentation from the trap pocket through the transfer channel into the co-location chamber. The trap pocket is then empty and ready for a second cell population.

Fig 1.1 – Rotation-assisted sequential capture concept (a–h)

Fig 1.1 — Sequential three-population capture workflow. (a–b) Red cells (Pop. 1) loaded at 0°, captured in trap pockets, then platform rotates 90° — red cells driven through the transfer channel into co-location chambers. Platform returns to 0°. (c–e) Yellow cells (Pop. 2) loaded at 0°, captured in the now-empty trap pockets, then indexed 90° into co-location chambers alongside red cells. Platform returns to 0°. (f–h) Blue cells (Pop. 3) loaded at 0°, captured in trap pockets, then relocated into co-location chambers — all three populations co-located.

Primary Capture

Platform at 0°. 5 Hz centrifugal force (≈ 5.4 g) drives cells into the 24.55 µm trap pocket. A lodged cell acts as a hydrodynamic plug, steering subsequent cells to neighbouring empty trap pockets.

Mechanical Indexing

Spring-loaded latch actuates the 86:22 gear train, rotating the chip carrier exactly 90° and aligning the centrifugal vector with the internal transfer channels.

Cell Relocation

The same body force pushes captured cells through the 30 µm transfer channel into the 57.83 µm co-location chamber — trap pockets are now empty for a second cell population.

Methodology

Two parallel workstreams: PDMS soft lithography and custom rotational platform design.

PDMS Chip Fabrication

Sylgard 184 (10:1) cast against a laser-engraved Ni master, vacuum degassed, cured at 70 °C for 2.5 h, demoulded, and oxygen-plasma bonded to glass. A 45-min vacuum priming cycle wets all dead-end features before cell loading.

PDMS gravimetric mixing (13.11 g base + 1.35 g curing agent)

Step 1 — Gravimetric mixing: 13.11 g base + 1.35 g curing agent

Step 2 — Vacuum desiccator degassing until optically clear; pour onto master

Step 3 — Thermal curing at 70 °C for 2.5 h (Mason convection oven)

Step 4 — Perimeter cut → controlled peel → biopsy punch inlet holes

Step 5 — Plasma activation (60 s, 100 W) → roller seal → 70 °C bake → 45 min vacuum prime

Rotational Indexing Platform

Iterative SolidWorks design FDM-printed in PLA. V1 used a full-coverage retainer plate; the final version introduced a spring-loaded latch and local chip covers, enabling tool-free 90° indexing with four locating pins to eliminate backlash.

V1 CAD — circular carrier with cross-shaped optical windows for in-situ monitoring

Final design — spring-loaded latch + local retaining cover; 86:22 gear train (r = 54 mm)

Assembled — operated inside transparent safety enclosure at 5 Hz (≈ 5.4 g at 54 mm)

Protocol — static prime → 0° capture spin (12 min) → 90° index → relocation spin (12 min)

Key Results

Fixed mammalian cells (15–20 µm) in PBS, spun at 5 Hz (≈ 5.4 g) for 12 minutes per loading phase.

In short: Single-cell capture was confirmed in the distal region of the array — occupancy above the Poisson-random baseline. After 90° indexing, captured cells were successfully transferred into the co-location chambers, providing proof-of-concept for valve-free, deterministic cell routing on a centrifugal platform.

Single-Cell Capture in Trap Pocket

Fig 6.3c Distal region – single-cell capture confirmed

Distal region — traps flooded; single cells lodged in 24.55 µm trap pockets ✓

Fig 6.3b Medial region – sporadic capture

Medial region — sporadic captures in transitional wet/dry zone

Proximal region — dry-out due to limited reservoir volume

Individual cells lodged in the trap pocket act as hydrodynamic plugs, diverting subsequent cells to neighbouring empty pockets — confirming deterministic single-cell capture above Poisson-loading occupancy in the wetted distal region.

Cell Relocation into Co-Location Chamber

Fig 6.4a Cell relocated into 57.83 µm co-location chamber

Magnified — cell transferred from pocket into 57.83 µm chamber after 90° index ✓

Fig 6.4b Array survey – red successful, green clusters, orange failed

Distal array survey — successful (red), clusters (green), failed (orange)

Fig 5.7 Keyence metrology – master vs PDMS replica

Keyence metrology — master aperture 21.50 µm vs. PDMS replica 24.55 µm (+14% dimensional expansion due to PDMS replication)

After 90° indexing, cells were driven through the 30 µm transfer channel and remained stably confined in the low-shear co-location chamber — a proof-of-concept for deterministic, valve-free cell routing on a centrifugal platform.

Reflection

"This project gave me end-to-end research experience: translating a vague brief into measurable engineering objectives, owning a complete soft-lithography fabrication workflow, and using quantitative metrology to interpret experimental results. Designing the 3D-printed indexing platform through two full iterations — identifying a kinematic symmetry limitation and implementing a practical manual workaround — was a direct lesson in pragmatic engineering decision-making under real project constraints."

Tools & Skills Applied

SolidWorks CAD

Platform design & drawings

FDM 3D Printing

PLA structural components

Soft Lithography

PDMS chip fabrication

Keyence Microscopy

Planar metrology (ImageJ)

Gear Mechanism Design

86:22 spur gear indexing

Plasma Bonding

PDMS-to-glass sealing

Risk Assessment

BSL-1, COSHH, rotating safety

Technical Writing

MEng thesis, DCU 2026

PDMS Microfluidic Chip for Sequential Cell Capture