Time to get in the lab !

You've sourced your components: tubes, markers, tips, adhesives, and connectors are sitting on your bench. Now comes the critical question: how do you actually assemble these parts into a functional catheter delivery system?

This isn't about production-line precision or cleanroom protocols. This is about building a testable prototype that will survive 50-100 deployment cycles on your U-Handle testing platform, generate meaningful performance data, and help you validate your design specifications.

What you'll learn in this guide:

• Essential equipment setup (costs under €300 total)
• Four fundamental bonding techniques every catheter builder needs
• How to calculate total tube length including U-Handle mounting allowance
• Step-by-step assembly sequence from distal tip to proximal connector
• Realistic time estimates (first build: 90-120 minutes, subsequent builds: 50-70 minutes)
• Common mistakes that waste hours and how to avoid them

The goal: By the end of this article, you'll have a clear assembly workflow that takes you from loose components to a mounted, testable catheter on your U-Handle in one afternoon.

Let's get started.

Essential Equipment: Your Assembly Workstation

Before touching any components, set up a proper workspace. You don't need a cleanroom, but you do need organization and the right tools.

Core Equipment (€150-200 total investment)

UV Curing Lamp:

• Wavelength: 365nm or 405nm
• Power: 3-10W sufficient for prototyping
• Purpose: Curing UV-activated adhesives (Bostik UV1540)

Precision Applicators:

• 27-30 gauge blunt-tip needles
• Purpose: Controlled adhesive application (tiny drops, thin beads)
• Quantity: Buy 50-pack (they're disposable)

Mandrels/Wire:

• Stainless steel wire: 1-3mm diameter
• Purpose: Support tubes during bonding, prevent collapse
• Length: 1.5-2 meters (longer than your catheter)

Digital Calipers:

• Resolution: 0.01mm
• Purpose: Verify component dimensions, measure marker positions

Cleaning Supplies:

• Isopropyl alcohol (IPA) 99%: €10 for 1 liter
• Acetone: €8 for 500ml (use sparingly—attacks some plastics)
• Lint-free wipes:

Work Surface Protection:

• Silicone mat or PTFE sheet
• Purpose: Adhesive won't stick to it, easy cleanup

Optional but Helpful:

Heat gun (low setting):

• Purpose: Accelerate adhesive cure, apply heat-shrink

Stereoscope or magnifying lamp:

• Purpose: Precise marker positioning, visual inspection

Total basic setup: €150-200

This equipment lasts for hundreds of catheter builds.

The Fundamental Bonding Techniques

Every catheter assembly involves combinations of four bonding scenarios. Master these, and you can build virtually any delivery system configuration.

Technique 1: Bonding Marker Bands to Catheter Shafts

Application: Radiopaque markers for fluoroscopic visibility

Adhesive: Bostik 7452 (fast-cure cyanoacrylate)

Why this adhesive: Markers don't flex, so rigid bond is fine. Fast cure (10-30 seconds) speeds assembly.

Step-by-step process:

1. Calculate marker position:

• Measure from distal end
• Typical positions: 5-10mm from tip, or at specific device positions
• Mark position lightly with marker pen on tube exterior

2. Surface preparation:

• Wipe tube exterior with IPA-soaked lint-free cloth
• Wipe marker band interior with IPA
• Let both dry completely (30 seconds)
• Critical: Any contamination (oils, dust, moisture) weakens bond

3. Insert mandrel:

• Slide stainless steel wire through tube interior
• Extends beyond where marker will be placed
• Purpose: Prevents tube collapse when you slide marker on and apply pressure

4. Apply adhesive:

• Attach 27-gauge needle tip to Bostik 7452 bottle
• Apply tiny ring of adhesive to tube exterior at marked position
• Amount: Thin, continuous ring—not a blob
• Too much adhesive = oozing and mess; too little = weak bond

5. Slide marker band:

• Quickly (adhesive cures in 10-30 sec) slide marker band over tube end
• Position at marked location
• Press gently to ensure contact all around circumference
• Don't twist—rotational movement spreads adhesive unevenly

6. Hold position:

• Maintain light pressure for 30 seconds
• Support tube with mandrel inside to prevent deformation
• Watch for adhesive "flash" (tiny bead appearing at marker edges)—this confirms good coverage

7. Cure and inspect:

• Full cure: 2-5 minutes
• Check: Marker should not rotate or slide on tube
• Visual: Clean joint, no excess adhesive pooling
• If excess adhesive present: Carefully wipe with IPA before full cure

Common mistakes:

❌ Too much adhesive: Oozes out, creates rough surface, wastes material ✓ Correct amount: Thin ring, slight flash at edges, clean appearance

❌ Applying adhesive to marker band: Hard to control amount and placement ✓ Apply to tube: Easier to control, more consistent

❌ Sliding marker before adhesive applied: Must reposition after adhesive, causes uneven coverage ✓ Position marker immediately after adhesive application

Technique 2: attaching distal tips

You have three options for distal tips, each with different attachment methods.

Option A: Bonded 3D-Printed Tips

Adhesive: Bostik UV1540 (UV-cure adhesive)

Why UV-cure: Allows precise positioning before cure. You can adjust tip orientation, verify alignment, then cure in seconds with UV lamp.

Process:

1. Prepare tube end:

• Clean with IPA
• Ensure cut is perpendicular (use sharp tubing cutter, not scissors)
• Deburr interior and exterior with fine sandpaper

2. Prepare 3D-printed tip:

• Ensure tip is fully post-cured per Formlabs specifications
• Clean any uncured resin residue with IPA
• Check fit: Tip should slide onto tube OD with slight resistance

3. Apply UV adhesive:

• Apply thin ring of Bostik UV1540 to tube OD (distal end)
• Amount: Enough to create small fillet when tip is pressed on

4. Position tip:

• Slide tip onto tube
• Critical: Align tip orientation correctly (if tip has directional geometry)
• Verify no air gaps at joint
• You have 3-5 minutes to adjust before curing

5. UV cure:

• Position UV lamp 5-10cm from joint
• Expose for 30-60 seconds
• Rotate catheter slowly to cure all sides of joint
• Verify cure: Joint should be hard, not tacky

6. Final cure:

• Some UV adhesives benefit from additional ambient cure (10-20 minutes)
• Check manufacturer specifications
• 
  

Option B: injected molded tips (Bonded)

Same process as 3D-printed tips, use Bostik UV1540 or Bostik 7475.
Injected tips typically have better mechanical properties but same attachment method.

Option C: Protobrix threaded atraumatic tips

The game-changer for prototyping.

Process:

1. Bond thread :

Our threaded atraumatic tips comes with a thread that is glued on the central tube.

2. Thread tip onto catheter:

• Screw threaded tip clockwise into prepared threads
• Hand-tight, don't over-torque (polyurethane threads can strip)
• Advantage: Takes 30 seconds

3. Swap tips:

• Unscrew current tip (counterclockwise)
• Screw on different durometer or geometry tip (clockwise)

Technique 3: Attaching Proximal Connectors (Luers)

Application: Connecting proximal end to handle, flush ports, or pressure monitoring

Adhesive: Bostik 2720 (two-part epoxy)

Why epoxy: Proximal connections experience pulling forces during actuation. Epoxy provides maximum bond strength. 24-hour cure is acceptable since this is last assembly step.

Process:

1. Prepare tube proximal end:

• Cut perpendicular
• Deburr interior and exterior
• Clean with IPA

2. Prepare luer connector:

• Verify fit: Luer barb should fit snugly into tube ID
• Clean luer with IPA

3. Mix epoxy:

• Bostik 2720 is 1:1 ratio (equal parts resin and hardener)
• Mix small amount on disposable surface (use popsicle stick)
• Mix thoroughly for 30-60 seconds
• Working time: 5-10 minutes

4. Apply epoxy:

• Thin coating on luer barb
• Insert luer into tube ID
• Push until fully seated
• Small fillet of epoxy should appear at joint

5. Wipe excess:

• Use IPA-dampened wipe to clean excess epoxy before it cures
• Smooth fillet around joint for clean appearance

6. Support during cure:

• Position catheter so luer/tube joint is horizontal
• Support both sides to prevent sagging
• Avoid moving or stressing joint

7. Cure time:

• Workable: 5-10 minutes
• Handling strength: 4-6 hours
• Full cure: 24 hours
• Plan this as your final assembly step—leave overnight before testing
• 
  

Critical Planning Step: calculating total tube length

This is where most first-time builders make expensive mistakes.

Your catheter tubes aren't just the working length (shaft extending outside the U-Handle). A portion of tube sits inside the U-Handle mechanism, bonded to internal components that connect to the actuation system.

Formula:

Total tube length = Working length + U-Handle mounting length

Working length

This is the catheter shaft length needed for your application:

• Cardiovascular (femoral access to aortic valve): 1000-1200mm
• Neurovascular (femoral/carotid to cerebral): 1400-1600mm
• Peripheral (varies widely): 800-1400mm

Add 50-100mm safety margin to account for:

• Trim adjustments during assembly
• Testing setup variations
• Handling damage to tube ends

U-Handle mounting length

This varies by your U-Handle configuration. Reference table:

Configuration	Outer Tube Mounting Length	Inner Tube Mounting Length
80mm stroke, non-steerable	120mm	120mm
100mm stroke, non-steerable	140mm	140mm
120mm stroke, non-steerable	160mm	160mm
80mm stroke, steerable	120mm	130mm
100mm stroke, steerable	140mm	150mm
120mm stroke, steerable	160mm	170mm

Note: Steerable configurations require extra length on inner tube for pull-wire mechanism attachment.

Assembly sequence: building your catheter step-by-step

Now let's put all techniques together in logical order.

Step 1: tube preparation

Cut tubes to calculated total length:

• Use sharp tubing cutter (not scissors, they create angled, rough cuts)
• Measure twice, cut once
• Outer tube: Working length + mounting length + 50mm margin
• Inner tube: Same calculation

Deburr tube ends:

• Use 220-grit sandpaper wrapped around mandrel
• Smooth both interior and exterior cut edges
• Remove any plastic shavings or rough spots
• Why critical: Rough edges create stress concentrations and leak paths

Surface cleaning:

• Wipe entire tube lengths with IPA-soaked lint-free cloth
• Pay special attention to areas where components will bond
• Let dry 30-60 seconds

Step 2: distal marker placement 

Calculate marker position:

• Measure from distal end
• Mark lightly with marker pen

Bond first marker (using Technique 1):

• Insert mandrel through tube
• Apply Bostik 7452 thin ring at marked position
• Slide marker band, hold 30 seconds
• Cure 5 minutes

Repeat for additional markers if needed

Step 3: Distal tip attachment

Bonded tip or Protobrix thread

• Apply Bostik UV1540 to tube distal end
• Position tip, align orientation
• UV cure 60 seconds
• 
  

Step 4: mounting on U-Handle 

Please refer to assembly guide for detailed procedure.

1. Prepare U-Handle:

• Unlock carriage positioning
• Open half-handle access panels

2. Install internal components (with bonded tubes):

• Slide assembled components into U-Handle frame
• Follow configuration-specific instructions
• Secure with provided fasteners

3. Position carriage:

• Determine starting position based on your deployment sequence
• Lock carriage positioning mechanism

4. Function check:

• Actuate each half-handle through full range
• Verify smooth motion (no binding)
• Check inner and outer tubes move independently
• Guidewire channel clear (if applicable)

5. Document setup:

• Take photos of configuration
• Record: tube sizes, stroke length, carriage position, tip type
• Critical for DID documentation

Step 5: proximal luer attachment 

Using Technique 4:

• Mix small amount of Bostik 2720 epoxy
• Apply to luer barb
• Insert into tube proximal end
• Wipe excess
• Support horizontally
• Leave overnight (24hr cure)

This is your last assembly step. After luer cure, catheter is complete and ready for U-Handle mounting.

Catheter is now mounted and ready for testing.

Common assembly mistakes and how to avoid them

Mistake 1: Too much adhesive

Problem: Excess adhesive oozes out, creates rough surface, interferes with sliding motion, looks messy

Why it happens: "More is stronger" instinct

Reality: Thin, complete coverage beats thick, uneven globs

Solution:

• ✓ Use precision applicator tips (27-30 gauge)
• ✓ Apply thin beads or rings
• ✓ Watch for slight flash at joint edges (confirms coverage)
• ✓ Wipe excess immediately with IPA

Mistake 2: inadequate surface preparation

Problem: Bonds fail after 20-30 test cycles

Why it happens: Oils, dust, or moisture on bonding surfaces

Solution:

• ✓ Always wipe with IPA before bonding
• ✓ For PTFE: Light abrasion with sandpaper improves adhesion
• ✓ Let surfaces dry completely (30-60 seconds)
• ✓ Don't touch bonding surfaces with bare hands after cleaning

Mistake 3: wrong adhesive for application

Problem: Rigid adhesive on flexing joint → cracks appear. Flexible adhesive on marker → marker rotates.

Solution:

• ✓ Rigid CA (Bostik 7452) for: markers, rigid connectors
• ✓ Flexible CA (Bostik 7475) for: tube-to-tube joints, flex areas
• ✓ UV cure (UV1540) for: tips requiring positioning control
• ✓ Epoxy (2720) for: maximum strength proximal connections

Mistake 4: cutting tubes too short

Problem: Tubes don't reach through U-Handle mounting area—assembly impossible

Why it happens: Forgetting to add mounting length to working length

Solution:

• ✓ Use formula: Working length + Mounting length (see reference table) + 50mm margin
• ✓ Always order tubes slightly longer than calculated minimum
• ✓ Trimming excess is easy; adding length is impossible

Mistake 5: not using mandrels

Problem: Tubes collapse or deform when applying pressure during marker bonding or tight-tolerance assembly

Solution:

• ✓ Always insert mandrel (stainless wire) through tube interior during bonding steps
• ✓ Provides internal support, prevents collapse
• ✓ Cost: €5 for wire that lasts hundreds of builds

Mistake 6: rushing cure times

Problem: Bonds fail because adhesive wasn't fully cured before next step or handling

Why it happens: Impatience, tight timelines

Reality: Adhesive manufacturers specify cure times for good reasons

Solution:

• ✓ Respect minimum cure times:

  • Fast CA (7452): 2-5 minutes
  • Flexible CA (7475): 5-10 minutes
  • UV cure (UV1540): 30-60 seconds UV + 10-20 minutes ambient
  • Epoxy (2720): 24 hours
• ✓ Plan assembly sequence so you're working on other parts while something cures
• ✓ Don't stress joints until fully cured

Quality checks before testing

Before mounting your catheter on the U-Handle for the first time, verify:

Visual inspection:

• ✓ All adhesive joints clean (no excess blobs)
• ✓ Markers positioned correctly and secure
• ✓ Tip aligned properly (if directional)
• ✓ No kinks or sharp bends in tubes
• ✓ Luer fully seated and straight

Mechanical checks:

• ✓ Markers don't rotate or slide on tube
• ✓ Inner tube slides smoothly through outer tube
• ✓ Distal tip secure (bonded) or threads smoothly (threaded)
• ✓ Luer connection solid (gentle pull test)

Dimensional verification:

• ✓ Total length matches design spec
• ✓ Marker positions within ±2mm of target
• ✓ Tube diameters correct (verify with calipers)

Functional test (before U-Handle mounting):

• ✓ Slide inner tube through outer tube full range
• ✓ No binding or excessive friction
• ✓ Guidewire passes through if applicable
• ✓ Tubes return to position smoothly

Document for DID:

• ✓ Photograph catheter from multiple angles
• ✓ Record all dimensions and component specifications
• ✓ Note any deviations from design intent

If all checks pass → proceed to U-Handle mounting

If issues found → address before mounting (saves time vs. troubleshooting on the handle)

Next Steps: from assembly to testing

You've now built a functional catheter delivery system. Your next workflow steps:

Day 1 (assembly):

• Complete all bonding steps except proximal luer
• Attach luer with epoxy
• Leave overnight for cure

Day 2 (mounting):

• Mount catheter on U-Handle (20 minutes)
• Perform dry-run actuation (no load)
• Verify smooth operation
• Document baseline setup with photos

Day 3-7 (initial testing):

• Start with simple straight-path pushability tests
• Document baseline forces
• Verify carriage positioning meets deployment needs
• Identify any friction or binding points
• If using threaded tips: This is when you'll discover if different tip stiffness would help—swap in 2 minutes

Week 2-4 (iterative testing):

• Progress to complex tortuous path models
• Test in anatomical phantoms
• Generate performance data for DID
• If diameter change needed: Order new internal component set, build new catheter using skills from this guide

The assembly techniques you've learned here are the foundation. You'll build 5, 10, maybe 20 catheters during your development process. Each build gets faster. Each iteration gets you closer to optimal specifications.

Educational resources

Damian Carr / Eyedea MedTech Education:

• "The Catheter R&D Handbook": Visual guide showing 70+ post-processing methods and assembly techniques
• Hands-on workshops: Global schedule at eyedeamedtech.com
• Philosophy: "Start with simplest form possible—don't over-engineer before testing"

Chamfr.com Webinar Series:

• "Concept to Prototype" series covers component selection, assembly best practices, troubleshooting
• Features component suppliers demonstrating optimal techniques

YouTube channels:

• Search "catheter assembly techniques"
• Search "medical device prototyping adhesives"
• Visual learning complements written guides

Conclusion: from components to testable device in one afternoon

Assembly isn't magic. It's:

• Right adhesives for each application
• Clean surfaces and proper preparation
• Respecting cure times
• Following logical sequence
• Building in quality checks

Your first build will feel slow and uncertain. That's normal. By your third build, you'll wonder why it seemed hard.

The reward: Complete control over your catheter prototyping. Change a design parameter? Rebuild in under an hour. Test new tip geometry? Swap threaded tip in 2 minutes. Iterate based on real testing data instead of waiting weeks for supplier revisions.

This is how modern medical device development works: Fast iteration, data-driven decisions, continuous improvement.

Ready to build your first catheter?

📧 Assembly questions: contact@protomed.fr

📞 Technical support: +33 367 176 721

🛒 Order adhesive kit: protobrix.fr/shop

Download: Assembly Techniques Checklist PDF

Step-by-step assembly workflow, adhesive selection guide, cure time reference table, quality check list, troubleshooting flowchart.

Download Assembly Checklist →

Part 2 of 3 in the DIY Catheter Prototyping series.

Previous: Where to Source Components Without Breaking the Bank

Next: Case Study—Building a 10Fr Cardiovascular Delivery Catheter for €100