Real-world examples showing how R&D engineers adapt materials, techniques, and assembly strategies for different delivery systems

Reading assembly guides is useful. But nothing beats seeing how real engineers make material choices and assembly decisions for actual clinical applications.

This article walks through three catheter builds that cover the spectrum of delivery system development:

1. 8Fr Coronary Stent Delivery (PCI) — Small diameter, high flexibility, guidewire-based navigation
2. 20Fr TAVR Delivery System — Large bore, long stroke, straight-path deployment
3. 8Fr Neurovascular Thrombectomy — Steerable, tortuous navigation, pull-wire integration

Each example shows the material logic, assembly choices, and why certain techniques matter for that specific application. By the end, you'll understand how to adapt these approaches to your own project.

Case 1: 8Fr Coronary stent delivery system

Clinical Context

Application: Percutaneous coronary intervention (PCI) for treating coronary artery disease

Access: Radial or femoral approach

Target anatomy: Coronary arteries (3-4mm diameter, highly tortuous)

Key challenge: Navigate through tortuous coronary vessels while maintaining pushability over 1000mm+ length

Design specifications

Outer catheter: 8Fr (2.67mm OD)

Inner catheter: 4Fr (1.33mm OD)

Working length: 1200mm (access to distal coronary segments)

Guidewire support: Yes (0.014" guidewire channel integrated)

Steerability: No (guidewire provides navigation)

Material selection logic

Outer tube: Pebax 63D, non-braided

Why this choice?

• Coronary anatomy is highly tortuous (multiple 90°+ curves)
• 63D durometer balances flexibility for curves with enough column strength for pushability
• Non-braided = maximum flexibility (kink resistance less critical with guidewire support)
• Pebax "breathes" through curves better than polyurethane

Alternative considered: Pebax 55D (more flexible) — rejected because pushability over 1200mm would be insufficient

Inner tube: PTFE single-lumen, 4Fr

Why PTFE?

• Extremely low friction against Pebax outer tube
• Smooth guidewire passage through 0.014" lumen
• Maintains 4Fr differential from outer tube (smooth push-pull actuation)

Distal tip: Protobrix threaded tip, Shore 60A (soft)

Why soft tip?

• Coronary vessels are delicate—atraumatic navigation is critical
• Shore 60A compresses slightly at tight curves (reduces vessel trauma risk)
• Threaded attachment allows testing Shore 60A vs. 70A during development

Markers: Dual Pt-Ir bands

Positioning strategy:

• First marker: 5mm from distal tip (tip position reference)
• Second marker: 25mm from distal tip (stent deployment zone indicator)
• Rationale: 20mm spacing matches typical stent lengths (15-30mm)

Assembly strategy

Critical assembly consideration: This catheter will flex constantly through tortuous anatomy. Every bond must remain flexible.

Step 1: Distal markers

• Use Bostik 7452 (fast CA) for marker bonding
• Markers are rigid components—fast CA is appropriate
• Position at 5mm and 25mm with calipers for precision

Step 2: Threaded tip attachment

• Tap M2.5 threads directly into 8Fr Pebax tube (63D is soft enough)
• Thread on Shore 60A tip
• No adhesive required—mechanical threads sufficient

Step 3: Coaxial assembly

• Slide 4Fr PTFE inner tube through 8Fr Pebax outer tube
• Critical: Test smooth sliding before any bonding (this determines catheter performance)
• If friction feels high: inspect for burrs on PTFE tube ends, re-deburr if needed

Step 4: Bond proximal end only

• Apply Bostik 7475 (flexible CA) where inner/outer tubes meet proximally
• This keeps tubes together during handling but leaves distal end free for independent actuation
• Never bond distal end—must remain completely free-sliding

Step 5: Bond to U-Handle internal components

• Use Bostik 7475 (flexible CA) for tube-to-component bonds
• Support horizontally during cure to prevent kinking
• Verify no kinks at bond points (kinks here = permanent performance degradation)

Step 6: Proximal luer attachment

• Mix Bostik 2720 epoxy
• Bond luer to inner tube (4Fr PTFE)
• Leave overnight for full cure

Testing insight: guidewire channel validation

Before mounting on U-Handle, critical check:

• Thread 0.014" guidewire through full catheter length (1200mm)
• Guidewire should pass smoothly with minimal resistance
• If guidewire binds: identify location, inspect for tube misalignment or adhesive intrusion into lumen

This catheter lives or dies on guidewire compatibility—validate before any deployment testing.

Why this configuration works for coronary

Flexibility where it matters:

• Non-braided Pebax 63D negotiates tight coronary curves
• Soft Shore 60A tip minimizes vessel trauma
• Guidewire provides navigation support (reduces need for active steering)

Pushability maintained:

• 63D durometer (not 55D) provides adequate column strength
• PTFE liner minimizes inner/outer friction
• 1200mm length is near upper limit for non-braided design

Trade-offs accepted:

• Kink resistance is lower than braided tubes (acceptable with guidewire support reducing stress on catheter)
• Pushability is moderate (acceptable for guidewire-assisted delivery)

Case 2: 20Fr transfemoral TAVR delivery system

Clinical Context

Application: Transcatheter aortic valve replacement (TAVR)

Access: Femoral artery (large bore access required)

Target anatomy: Descending aorta to aortic valve annulus

Key challenge: Large device delivery (26mm valve) through relatively straight path, precise positioning required

Design specifications

Outer catheter: 20Fr (6.67mm OD)

Inner catheter: 16Fr (5.33mm OD)

Working length: 1100mm (femoral to aortic valve)

Guidewire support: Yes (but large bore means less reliance on guidewire for navigation)

Steerability: No (aortic anatomy relatively straight)

Material selection logic

Outer tube: Pebax 72D, braided reinforcement

Why this choice?

• Large diameter (20Fr) requires stiffer material to maintain pushability
• 72D durometer provides excellent column strength over 1100mm
• Braided reinforcement critical for kink resistance (20Fr tubes kink easily without reinforcement)
• Anatomy is straighter than coronary—can sacrifice some flexibility for pushability

Alternative considered: Polyurethane — rejected because less flexible than Pebax, harder to navigate moderate aortic arch tortuosity

Inner tube: Pebax 55D, non-braided, 16Fr

Why different durometer than outer?

• Inner tube doesn't need same column strength (outer tube provides most push force)
• Softer inner tube (55D) reduces friction against outer tube
• Non-braided maintains 4Fr differential without excessive wall thickness

Distal tip: Protobrix threaded tip, Shore 70A (medium stiffness)

Why medium stiffness?

• Aortic vessels are larger and more robust than coronaries (can tolerate firmer tip)
• Shore 70A provides good column strength for positioning 26mm valve
• Still atraumatic but less compression than Shore 60A

Markers: Single Pt-Ir band

Positioning:

• One marker at 15mm from distal tip
• Rationale: TAVR valves are large (26mm); single marker at deployment zone is sufficient for positioning

Assembly strategy

Critical assembly consideration: This catheter prioritizes pushability and kink resistance over flexibility. Large bore means different assembly priorities.

Step 1: Distal marker (single)

• Position at 15mm using Bostik 7452
• Ensure marker ID fits 20Fr OD snugly (large tubes = risk of marker sliding if bond inadequate)
• Apply slightly thicker adhesive ring than smaller catheters (larger circumference to cover)

Step 2: Threaded tip

• Tap M3 threads into 20Fr Pebax tube (larger thread size for 20Fr vs. M2.5 for 8Fr)
• Thread on Shore 70A tip
• Test thread engagement—should require 3-4 full rotations for secure seating

Step 3: Coaxial assembly with attention to concentricity

• Slide 16Fr inner tube through 20Fr outer tube
• Large diameter tubes = higher risk of eccentricity (inner tube riding against one side of outer tube)
• Check: Rotate inner tube while inside outer tube—should not bind at any rotational position
• If binding occurs: inspect for tube ovality, ensure tubes are truly round

Step 4: Bond proximal end

• Bostik 7475 at proximal junction
• For large diameter tubes: Apply adhesive in two stages (allow first application to wick, then add second thin bead after 30 seconds)
• Ensures complete coverage around large circumference

Step 5: Reinforce stress points

• Large diameter catheters experience higher forces
• Optional: Add small drop of Bostik 7475 at marker locations (bonds marker to tube more securely)
• This reinforcement unnecessary for 8Fr but valuable for 20Fr

Step 6: Bond to U-Handle components

• Use Bostik 7475
• Critical: Support large tubes horizontally during cure (heavy tubes sag more than small diameter)
• Use foam blocks every 200-300mm to prevent sagging/kinking during cure

Assembly challenge unique to large bore

Problem: 20Fr tubes are heavy and less flexible than smaller diameters. During assembly, they want to kink at bond points.

Solution:

• Always use mandrel wire internally during any bonding step
• For 20Fr, use thicker mandrel (3-4mm diameter stainless wire vs. 1-2mm for 8Fr)
• Support externally with foam blocks
• Never allow unsupported spans >300mm during cure

Why this configuration works for TAVR

Pushability prioritized:

• Pebax 72D braided outer tube provides excellent column strength
• Large 4Fr differential (20Fr/16Fr) reduces friction
• 1100mm length is comfortable for this stiffness

Kink resistance critical:

• Braided reinforcement prevents catastrophic kinking during valve deployment
• 72D durometer adds stiffness that resists kinking under load

Flexibility sufficient:

• TAVR anatomy (femoral to aortic valve) has moderate curves
• 72D Pebax still flexible enough for aortic arch navigation
• Guidewire provides additional support

Trade-offs accepted:

• Less flexible than 63D (acceptable for this anatomy)
• Heavier, more difficult to handle during assembly (acceptable for prototyping)

Case 3: 8Fr Neurovascular thrombectomy catheter (Steerable)

Clinical context

Application: Acute ischemic stroke treatment (mechanical thrombectomy)

Access: Femoral or carotid approach

Target anatomy: Navigate to cerebral vessels (M1/M2 segments, basilar artery)

Key challenge: Extreme tortuosity through carotid siphon, requires active tip deflection

Design specifications

Outer catheter: 8Fr (2.67mm OD)

Inner catheter: 4Fr (1.33mm OD)

Working length: 1500mm (longer access path than coronary)

Guidewire support: Yes, but not continuous (removed for final navigation)

Steerability: Yes (uni-directional pull-wire for tip deflection)

Material selection logic

Outer tube: Pebax 55D, non-braided, WITH pull-wire channel integrated

Why 55D (softer than coronary's 63D)?

• Cerebral vessels are extremely delicate
• 55D provides maximum flexibility for tortuous carotid siphon
• Pull-wire will provide tip control (reduces need for catheter stiffness-based navigation)

Why pull-wire channel integrated?

• Cannot add pull-wire after tube manufacturing
• Must specify "single lumen + pull-wire channel" when ordering tube
• Pull-wire channel runs along outer wall of tube (typically 0.5mm diameter channel)

Inner tube: PTFE 4Fr, standard single-lumen

No pull-wire in inner tube—only outer tube steers

Distal tip: Protobrix threaded tip, Shore 60A, WITH pull-wire attachment point

Critical difference from non-steerable tips:

• Threaded tip must have small eyelet or attachment point for pull-wire
• Pull-wire threads through eyelet, returns through pull-wire channel in outer tube
• When ordering: specify "threaded tip with pull-wire attachment, uni-directional"

Pull-wire: Stainless steel 0.008" diameter

Material choice:

• Stainless provides excellent tensile strength without stretch
• 0.008" fits through typical pull-wire channels
• Alternative: Nitinol wire (more expensive, provides shape memory)

Markers: Dual Pt-Ir bands (similar to coronary)

Positioning at 5mm and 25mm from tip

Assembly strategy: integrating pull-wire

This is where assembly gets significantly more complex.

Step 1: Thread pull-wire BEFORE any bonding

• Cut pull-wire to length: working length + 300mm excess
• Thread pull-wire through pull-wire channel in outer Pebax tube (runs along tube exterior wall inside tube structure)
• Pull-wire exits tube at distal end
• Confirm pull-wire moves freely through channel (no binding)

Step 2: Distal markers

• Position markers at 5mm and 25mm
• Critical: Pull-wire runs UNDER markers (between tube and marker)
• Apply Bostik 7452 to bond markers
• Ensure adhesive doesn't block pull-wire movement

Step 3: Attach pull-wire to threaded tip

• Thread tip onto tube
• Pull-wire threads through eyelet in tip
• Create loop: Pull-wire exits tip eyelet, returns through pull-wire channel
• Secure pull-wire at tip with small crimp or adhesive dot (Bostik 7452)
• Test: Pull on proximal pull-wire end—tip should deflect smoothly

Step 4: Coaxial assembly

• Slide 4Fr inner tube through 8Fr outer tube
• Inner tube must not interfere with pull-wire mechanism
• Verify smooth inner tube sliding even when pull-wire is tensioned (tip deflected)

Step 5: Bond proximal end

• Apply Bostik 7475 where tubes meet
• Pull-wire exits outer tube proximally (will connect to U-Handle steerable mechanism)
• Ensure pull-wire is not bonded or restricted at proximal junction

Step 6: Bond to U-Handle steerable components

• Outer tube bonds to steerable half-handle component
• Pull-wire threads through steerable actuation mechanism
• Inner tube bonds to standard (non-steerable) half-handle component
• This configuration: inner tube = push/pull, outer tube = deflection via pull-wire

Assembly challenge: pull-wire Integration

Problem: Pull-wire must move freely through channel while markers, adhesive, and inner tube are added.

Solution sequence:

1. Thread pull-wire first (before anything else)
2. Test free movement
3. Add markers carefully (don't block pull-wire)
4. Attach pull-wire to tip
5. Test deflection before proceeding (if pull-wire binds now, fix before bonding tubes)
6. Only then proceed with coaxial assembly

Common mistake: Bonding markers or tubes first, then trying to thread pull-wire. Pull-wire won't pass through—catheter ruined.

Testing steerable configuration

Before mounting on U-Handle:

• Pull proximal pull-wire manually
• Tip should deflect smoothly to ~45-90° (depends on catheter stiffness and pull-wire routing)
• Release pull-wire—tip should return to straight (Pebax 55D has shape memory)
• Cycle 10 times to verify no pull-wire binding

After mounting on U-Handle:

• Steerable half-handle actuates pull-wire via mechanical advantage
• Test full deflection range
• Inner tube (non-steerable half-handle) should still push/pull independently

Why this configuration works for neurovascular

Extreme flexibility:

• Pebax 55D navigates carotid siphon tortuosity
• Softest durometer used in these examples

Active steering:

• Pull-wire provides tip deflection when guidewire removed
• Critical for reaching M1/M2 segments in tortuous anatomy

Atraumatic:

• Shore 60A soft tip minimizes cerebral vessel trauma
• Delicate vessels require maximum care

Trade-offs accepted:

• Pushability is lowest of three examples (55D softest durometer, 1500mm longest)
• Acceptable because pull-wire steering reduces need for pushing force
• Assembly complexity highest (pull-wire integration adds steps and failure modes)

Comparing the three builds

Aspect	Coronary (8Fr)	TAVR (20Fr)	Neuro Steerable (8Fr)
Outer tube material	Pebax 63D, non-braided	Pebax 72D, braided	Pebax 55D with pull-wire channel
Design priority	Flexibility + pushability balance	Pushability + kink resistance	Maximum flexibility + steering
Tip stiffness	Shore 60A (soft)	Shore 70A (medium)	Shore 60A (soft)
Assembly complexity	Moderate	Moderate (heavy tubes)	High (pull-wire integration)
Testing focus	Guidewire compatibility	Kink resistance under load	Deflection range, pull-wire durability
Anatomy challenges	Tortuous small vessels	Large bore, moderate curves	Extreme tortuosity, delicate vessels

Universal principles across all three

Material selection is anatomy-driven:

• More tortuous anatomy → softer durometer
• Longer working length → consider stiffer durometer for pushability
• Larger diameter → add reinforcement (braiding)

Adhesive choice matters:

• Fast CA (7452) for rigid components: markers, rigid connectors
• Flexible CA (7475) for anything that will flex: tube joints, stress points
• Epoxy (2720) for maximum strength: proximal luers

Assembly sequence is non-negotiable:

• Thread pull-wires FIRST (if steerable)
• Bond distal components before coaxial assembly
• Test critical functions before final bonding (guidewire passage, pull-wire deflection)
• Bond to U-Handle components last
• Proximal luer overnight cure is final step

Threaded tips enable iteration:

• All three examples use threaded tips
• Testing reveals optimal stiffness (60A vs. 70A)
• Swap in minutes instead of rebuilding catheter

Adapting these approaches to your project

Start with the closest analog:

• Small diameter, tortuous anatomy, guidewire-based? → Follow coronary approach
• Large bore, straight path, high forces? → Follow TAVR approach
• Need active steering? → Follow neurovascular approach

Adjust materials based on your specifics:

• More flexibility needed? → Drop durometer 10-20 points (72D → 63D → 55D)
• More pushability needed? → Increase durometer or add braiding
• Different diameter? → Scale tube sizes, maintain ~4Fr differential

Assembly techniques transfer:

• Marker bonding technique identical across all diameters
• Coaxial assembly principles same (test smooth sliding before bonding)
• Pull-wire integration approach works for any steerable catheter

Test what matters for your application:

• Coronary: Guidewire compatibility, flexibility through curves
• TAVR: Kink resistance, positioning stability under load
• Neuro: Deflection range, atraumatic tip performance

Conclusion: three applications, same fundamentals

These three catheter builds look different:

• 8Fr flexible coronary vs. 20Fr stiff TAVR vs. 8Fr steerable neuro
• 63D vs. 72D vs. 55D durometers
• Non-braided vs. braided vs. pull-wire integrated

But the fundamentals are identical:

• Choose materials that match anatomy (flexibility where needed, pushability where required)
• Follow logical assembly sequence (distal → proximal, test critical functions early)
• Use appropriate adhesives for each joint type
• Validate performance before moving to next development phase

The goal isn't perfect first builds—it's rapid iteration to optimal design. Build, test, learn, refine. Threaded tips let you iterate tip stiffness in minutes. Modular U-Handle lets you test multiple diameters without custom hardware for each.

This is modern catheter development: Fast, data-driven, in your control.

Questions about your specific application?

📧 Engineering support: contact@protomed.fr

📞 Technical guidance: +33 367 176 721

🛒 Components & U-Handle: protobrix.fr/shop