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KAJEESAN

CPNBCATHETER THESIS

Joint masters thesis: Developed and tested a catheter-anchoring concept designed to keep a nerve-block catheter within 2 mm of its intended position, without disrupting the anesthesiologists existing workflow or introducing additional patient risk.

Project question

How might an anchor resist movement during use while still allowing intended removal?

Outcome
One documented ex-vivo session under defined but not fully matched conditions.
Joint activities
Workflow synthesis · concept selection · physical engineering · test design
Joint authors
Kajeesan Jeevendra and Tobias Sebastian Bernhardt

JOINT MSc THESIS · FIVE MONTHS · EXPLORATORY / NON-CLINICAL

OBSERVE PROCEDURE

THE PROBLEM WAS MOVEMENT WITHIN A PROCEDURE.

Catheter behaviour depended on insertion, ultrasound guidance, needle removal, activation, infusion and intended removal—not one isolated mechanism state.

Evidence inputs

  • Four observed single-shot procedures
  • Clinician conversations
  • Jelly insertion exercise
  • Literature & benchmarking
  1. Dark clinical reconstruction panel showing a needle inserted through tissue under ultrasound guidance.
    01

    Insertion

    Insert the needle under ultrasound guidance.

  2. Dark clinical reconstruction panel showing a blue catheter advanced through a needle toward a target nerve.
    02

    Catheter advance

    Advance the catheter near the target nerve.

  3. Dark clinical reconstruction panel showing the needle being withdrawn while a blue catheter remains in tissue.
    03

    Needle removal

    Withdraw the needle, leaving the catheter in place.

  4. Dark clinical reconstruction panel showing a catheter connector and an illustrated deployed anchor near the target.
    04

    Activate & infuse

    Deploy the anchor and connect the infusion line.

  5. Dark clinical reconstruction panel showing the catheter moving away from the target in an intended-removal scenario.
    05

    Intended removal

    Retract the catheter and anchor when treatment is complete.

What the synthesis changed

Procedure first

The mechanism had to work inside the full clinical workflow.

Interfaces mattered

Insertion, ultrasound guidance, needle removal and intended removal could not be designed separately.

A shared sequence

The evidence was synthesized into one reviewable CPNB procedure storyboard.

Problem defined

UNDERSTAND THE WHOLE SEQUENCE BEFORE DEFINING THE DEVICE.

KEEP OBSERVATIONS, SOURCE STORYBOARDS AND EXPLANATORY FLOWS DISTINCT.

The team combined procedure observations, clinician conversations, a jelly insertion exercise, literature and benchmarking into a shared view of the problem.

Separating what was observed from what was later synthesized keeps the clinical context useful without converting four single-shot blocks into evidence for an anchor procedure that was not observed.

Source Pajunk CPNB storyboard · 11 steps

Portrait crop of the source Pajunk CPNB storyboard containing eleven illustrated procedure steps.

Source Flower storyboard · 11 steps

Portrait crop of the source Flower catheter storyboard containing eleven illustrated steps.

Condensed explanatory reconstruction

Flower catheter · anchor activation included

  1. 01

    Receive patient

    Bring the patient into the anaesthetic room and explain the procedure.

    Patient arriving in the procedure room with a clinician.
  2. 02

    Set up ultrasound

    Prepare the ultrasound device and brief the patient.

    Ultrasound equipment being prepared beside the patient.
  3. 03

    Prepare anaesthesia

    Prepare the anaesthetic and sterile equipment.

    Clinicians preparing anaesthetic equipment on a sterile table.
  4. 04

    Unpack catheter

    Remove the Flower catheter from its sterile package.

    Flower catheter being unpacked from a sterile tray.
  5. 05

    Connect backend

    Connect the backend to the tube and syringe.

    Syringe being connected to the catheter backend.
  6. 06

    Locate target

    Apply gel and identify the target nerve with ultrasound.

    Clinician locating the target with an ultrasound probe.
  7. 07

    Insert needle

    Clean the site and insert the needle with the outer catheter.

    Needle and outer catheter being inserted at the target site.
  8. 08

    Withdraw needle

    Unlock the needle and withdraw it while holding the catheter steady.

    Needle being withdrawn while the catheter remains in place.
  9. 09

    Activate anchor

    Push the clip to deploy the Flower anchor.

    Flower catheter anchor being activated at the patient interface.
  10. 10

    Connect infusion

    Connect the anaesthetic supply tube to the catheter.

    Anaesthetic supply line connected to the catheter.
  11. 11

    Observe block

    Observe the patient and check the efficacy of the nerve block.

    Patient being observed by a clinician after catheter placement.

Swipe, scroll or use the arrows to follow the sequence.

Workflow synthesized

TURN THE SHARED WORKFLOW INTO EXPLICIT OBJECTIVES.

MOVE FROM PRIOR EVIDENCE TO FUNCTIONS, FOCUS AND SPECIFICATION.

Function-means trees isolated four critical functions. After doctor discussions, catheter fixation became the primary development focus.

A requirement was treated as essential for viability; a criterion was a desirable attribute that could improve the product without being strictly necessary.

01

Prior evidence

02

Function-means trees

03

Four critical functions

04

Doctor discussion

05

Fixation focus

06

Product specification

07

Concept evaluation next

Regenerated function-means tree for catheter-on-the-needle, showing four critical functions in the design focus.
CON function-means tree · four critical functions isolatedOpen full-size
Requirements & criteria defined

GENERATE 25 CONCEPTS.

OPEN THE SOLUTION SPACE BEFORE EVALUATING IT.

Four ideation approaches fed a morphology chart and a catalogue of 25 catheter concepts.

Breadth came before screening. These drawings record ideation—not proof that the mechanisms would work.

Ideation methods

Biomimicry & bio cards

Industry inspiration

KJ technique + negative brainstorming

Stakeholder concept workshop

Morphology chart
Generated morphology chart with five rows of catheter mechanism sketches organized under anchoring, anchor actuation, release, release actuation, needle configuration and compliance.

Idea catalogue

25 contextualized catheter concepts
01 / 25
  1. 01Generated catheter anchoring concept 01.
  2. 02Generated catheter anchoring concept 02.
  3. 03Generated catheter anchoring concept 03.
  4. 04Generated catheter anchoring concept 04.
  5. 05Generated catheter anchoring concept 05.
  6. 06Generated catheter anchoring concept 06.
  7. 07Generated catheter anchoring concept 07.
  8. 08Generated catheter anchoring concept 08.
  9. 09Generated catheter anchoring concept 09.
  10. 10Generated catheter anchoring concept 10.
  11. 11Generated catheter anchoring concept 11.
  12. 12Generated catheter anchoring concept 12.
  13. 13Generated catheter anchoring concept 13.
  14. 14Generated catheter anchoring concept 14.
  15. 15Generated catheter anchoring concept 15.
  16. 16Generated catheter anchoring concept 16.
  17. 17Generated catheter anchoring concept 17.
  18. 18Generated catheter anchoring concept 18.
  19. 19Generated catheter anchoring concept 19.
  20. 20Generated catheter anchoring concept 20.
  21. 21Generated catheter anchoring concept 21.
  22. 22Generated catheter anchoring concept 22.
  23. 23Generated catheter anchoring concept 23.
  24. 24Generated catheter anchoring concept 24.
  25. 25Generated catheter anchoring concept 25.
25 concepts generated

SCREEN 25 CONCEPTS AGAINST SIX HARD CRITERIA.

ELIMINATE WHAT CANNOT BE BUILT BEFORE ASKING WHAT PEOPLE PREFER.

Six non-negotiable engineering checks removed 14 of the 25 concepts. Combining and developing the survivors then produced seven candidates for stakeholder evaluation.

With 25 directions on the table, the team switched from divergence to elimination. Every concept had to pass the same six engineering checks: manufacturability, independent anesthesia flow, confidence in the anchoring principle, feasibility at a 1 mm diameter, material availability and passive anchoring without continuous energy.

The screen removed 14 concepts and left 11 viable directions. Only after that gate were related ideas combined and developed into seven candidates for stakeholder review. This was a decision-making step—not evidence that any surviving mechanism had already been validated.

Illustrative concept-screening process: a broad set of catheter concept sheets enters six repeated engineering checks, rejected sheets drop away, and fewer surviving concepts are combined into a smaller developed set.
Illustrative reconstruction of the screening sequence · counts and criteria remain live textOpen full-size

Six hard criteria

  1. 01

    Mass-producible with current manufacturing technologies

  2. 02

    Anesthesia flow remains independent of anchoring

  3. 03

    Certainty that the anchoring principle works

  4. 04

    Feasible to produce at 1 mm diameter

  5. 05

    Required materials available at the necessary scale

  6. 06

    No active energy required to remain anchored

11 concepts passed · 7 developed for stakeholder review

COMBINE, REVIEW AND WEIGHT BEFORE SELECTING WHAT TO PROTOTYPE.

STAKEHOLDER RANKING ALONE DID NOT RESOLVE THE DECISION.

Seven developed concepts were reviewed through doctor, manufacturing-expert and supervisor lenses, then compared with a weighted Pugh method.

Different stakeholder rankings made a second comparison method necessary. Flower and Cone moved forward because the decision process selected them—not because either had already demonstrated a validated performance result.

19

Flower

Selected
Technical marker sketch of the Flower catheter concept with rectilinear support ribs connecting a perforated front collar to the rear sleeve.
Concept 19 · Flower
22

Cone

Selected
Technical marker sketch of the Cone catheter concept with a transparent expanding sleeve around the central tube.
Concept 22 · Cone

Weighted comparison

Review lensesDoctors · Manufacturing expert · Supervisor

7 concepts compared across 4 weighted Pugh criteria. Selected candidates are marked in the column headers.
Weighted Pugh criteria09Screw15Vacuum deactivated anchor16Magnetic deactivated anchor19FlowerSelected22ConeSelected23String Folder25Sponge
1Stakeholder rankingWeight 6
6
5
6
9
8
5
4
2Potential to transition from CTN to CONWeight 5
4
5
5
8
9
4
3
3ManufacturabilityWeight 8
7
4
5
7
8
5
4
4Anchoring-size potentialWeight 10
6
4
5
8
8
4
3
Weighted score (Σ)172127151230237130101
Flower + Cone selected

USE THE LOWEST-EFFORT MODEL THAT CAN ANSWER THE QUESTION.

LET PHYSICAL FAILURE OVERRULE A PROMISING PAPER CONCEPT.

The first prototype phase used scaled-up anchor-tip models, simple available materials and quick processes rather than attempting complete catheters.

Cone stopped within the project scope after demoulding and folding failures. Flower earned the next development cycle because the principle model demonstrated the intended deploy-and-release motion at enlarged scale.

Raster prototype image of the flexible Cone principle model that could not fold flush to the catheter.
Cone principle modelOpen full-size

Branch stopped

Silicone dip moulding failed during demoulding and was too soft for the anticipated snap behaviour. The Flexible 80A SLA version could not fold flush or reach the required minimum diameter.

Raster prototype image of the large Flower principle model with longitudinal petals deployed.
Flower principle modelOpen full-size

Branch continued

A PVC tube and inner cable were joined at the tip. Relative movement opened the longitudinal slots and the folding structure deployed as intended.

Flower branch continued

LET PHYSICAL FAILURE DEFINE THE MANUFACTURING WORKFLOW.

MOVE FROM AN ENLARGED PRINCIPLE TO CATHETER-SCALE TUBING.

Doctor-provided catheters, spare tubing and manufacturer samples exposed cutting, rotation and support problems that the next fixtures had to control.

The manufacturing problem became part of the mechanism problem: a cut that wandered changed the rib geometry, and a tube without internal support could not be cut consistently enough for the next test stage.

Flower mechanism

Wide technical sketch showing one continuous transparent catheter tube whose four longitudinal slits stay collapsed in the deactivated state and bow outward in the activated state.

Physical learning route

  1. 01

    Scale down

    Test doctor-provided catheters, spare tubing and manufacturer samples.

    Technical sketch comparing a large blue tube, a smaller clear catheter tube and a slender needle to show the move toward catheter scale.
  2. 02

    Cut the ribs

    Razor and scalpel cuts were possible but drifted from the tube centre and produced uneven slits.

    Close technical sketch of a catheter tube with four evenly spaced longitudinal slits and a scalpel beside it.
  3. 03

    Control rotation

    A fixture was needed to rotate the tube through four defined 90-degree positions.

    Technical sketch of a clear indexing fixture holding a catheter tube in a collar with four quarter-turn detents.
  4. 04

    Support the tube

    The tubing needed internal support during cutting, so it was fed over a needle.

    Technical sketch of a hand holding the needle hub while the needle runs through and supports the clear catheter tube.
  5. 05

    Adaptation

    Doctors favored catheter on the needle due to easier control.

    Technical sketch of the final catheter-on-the-needle assembly with blue clip, locking adapter and needle handle.

BUILD THE TEST INFRASTRUCTURE

WHEN THE SETUP CHANGES THE RESULT, THE SETUP BECOMES PART OF THE DESIGN.

The third prototype phase moved from hand-pulled gelatin tests to a motorized rig and revised locking system, so the anchor could be compared under more defined conditions.

  1. 01

    V1 · handheld pull

    Pull speed varied with counterforce, and the shallow 4 × 4 cm gelatin specimen left too little material above the anchor for the intended pull-out setup.

    Technical illustration of a handheld Newton-meter pull above a shallow gelatin specimen.
    V1 handheld pull illustration
  2. 02

    V2 · motorized linear pull

    A geared rig moved the Newton meter along one defined axis, while a deeper holder constrained specimen movement and enabled observation through acrylic windows.

    Technical illustration of the motorized vertical pull-test rig above a deeper specimen holder.
    V2 motorized linear pull illustration
  3. 03

    Load-path correction

    The one-way clip loaded only the inner tube and progressively activated the anchor, creating an unrepresentative pull-out load case.

    Technical illustration showing the one-way clip loading the inner catheter tube and activating the anchor.
    One-way load-path illustration
  4. 04

    Two-way lock

    The revised clip held the inner and outer tubes relative to one another in both deployed and undeployed positions.

    Technical illustration showing the revised two-way lock holding the inner and outer catheter tubes.
    Two-way lock illustration

V2 rig callouts

Technical illustration of the V2 vertical test rig, geared motor, Newton meter, pulley line and specimen holder.
V2 test-rig technical illustration
  1. 12 V DC motor
  2. 5:1 gear reduction
  3. Pulley + double-layer line
  4. Additional 2:1 speed reduction
  5. Measured pull speed · 6.5 mm/s at 8 V
  6. 60 mm specimen depth
  7. Acrylic observation windows

Real-project rig evidence

The V2 rig reduced important sources of handheld variation. Its measured 6.5 mm/s pull speed is a rig setting—not the separate 6.5 N maximum recorded later in one ex-vivo session.

  1. Project photograph of the first handheld pull setup with a Newton meter above a shallow gelatin specimen.
    V1 · handheld gelatin pull setupProject test photograph cropOpen full-size
  2. Project photograph of the motorized vertical pull-test rig and specimen holder.
    V2 · motorized linear pull rigProject test-rig photograph cropOpen full-size
  3. Project photograph of the deeper gelatin specimen held inside the rig's transparent observation fixture.
    Deeper gelatin holder · acrylic observation windowsProject test photograph cropOpen full-size
01

Defined pull axis

The geared line moved the Newton meter vertically instead of relying on a hand-pulled path.

02

Deeper specimen support

The acrylic holder constrained the gelatin and made the pull-out path observable.

03

Bounded interpretation

More-controlled mechanics improved comparison, but did not turn the setup into a validated test standard.

TEST AND INTERPRET

LET THE METHOD, RESULT AND LIMITS TRAVEL TOGETHER.

The Flower moved through a more-controlled gelatin comparison before one final ex-vivo tissue session with doctors at Hillerød Hospital.

Test sequence

  1. 01

    More-controlled gelatin comparison

    Two 12 mm-cut catheters—one beveled and one unbeveled—were each used at 45°, 60° and 75°. Three pull measurements were recorded per tip/angle condition using two catheters total. These were not independent specimens and do not establish repeatability.

    Raster schematic of the deployed 60-degree anchor aligned with a vertical pull fixture.
  2. 02

    One ex-vivo tissue session

    The 60° and 75° anchors were compared with a straight control and Pajunk CON under ultrasound observation.

    Raster schematic of a straight catheter control aligned with a vertical pull fixture.
  3. 03

    Bounded interpretation

    The largest recorded value came from the 60° anchor at complete pull-out in this documented setup.

    Raster schematic of the deployed 60-degree anchor aligned with a vertical pull fixture.

What the results support

6.5 N

Maximum recorded

12 mm anchor · 60° deployment

1.5 N

Straight control

Maximum recorded in this setup

One documented ex-vivo comparison

The anchor deployed beneath fascia under ultrasound observation. Complete pull-out occurred suddenly; the anchor was deformed and partly broken afterward.

What the result does not establish

  • Not initial-displacement or sustained holding force
  • Not an average
  • Not a clinical claim
  • Not proof of repeatability
  • Not production validation

Conditions were not fully matched

  • 60°, straight control and Pajunk CON behind fascia
  • 75° in flesh after insertion difficulties and pre-cutting; began activating during insertion
  • Beef chuck roast without bone
  • Water used instead of anesthesia
  • Handheld 5 N and 10 N Newton meters
  • Ultrasound observation

Documented issues

  • Tip-glue connection failed on a 45° / 9 mm catheter
  • 60° anchor deformed and partly broke after sudden pull-out
  • Possible tissue ripping or cutting remained unresolved
  • One-handed clip activation remained difficult

Real-project test evidence

Real-project photographs document the specimens, handheld Newton meters and ultrasound observation. The deeper record keeps the unmatched 75° condition, control gliding, failures and unresolved tissue interaction visible beside the four recorded maxima.

  1. Project test composition showing catheter anchor states used during gelatin pull measurements.
    More-controlled gelatin comparison · anchor states and pull setupOpen full-size
  2. Project ex-vivo photograph of the 12 mm Flower anchor configured at 60 degrees.
    12 mm anchor · 60° configurationOpen full-size
  3. Project ex-vivo photograph of the 12 mm Flower anchor configured at 75 degrees.
    12 mm anchor · 75° configurationOpen full-size
  4. Project photograph of a handheld Newton meter used during the ex-vivo pull-out session.
    Handheld 5 N and 10 N Newton metersOpen full-size
  5. Project photograph of ultrasound observation during the ex-vivo beef-tissue session.
    Ultrasound observation during placementOpen full-size
Four recorded maxima and their test boundaries
ConditionMaximumWhat was documented
12 mm anchor · 60°6.5 NThe anchor was behind fascia. Complete pull-out occurred suddenly; the anchor was deformed and partly broken afterward.
12 mm anchor · 75°4.5 NThis condition was placed in flesh, required several insertion attempts and pre-cutting, and began activating during insertion.
Straight control1.5 NBehind fascia; the catheter began gliding at about 1 N before reaching its maximum.
Pajunk CON1.5 NBehind fascia; the catheter began gliding at about 1 N before reaching its maximum.

Additional limits: the 45° / 9 mm tip-glue connection failed; possible tissue ripping or cutting remained unresolved; and the gelatin pulls used two catheters total, not independent specimens.

Result interpreted

WHAT THIS PROJECT DEMONSTRATES.

Frame

Workflow synthesis

Turn observations, clinician input, a jelly exercise, literature and benchmarking into a reviewable problem sequence.

Explore

Concept selection

Open the solution space, apply hard criteria, compare stakeholder preferences and let physical failures change direction.

Build

Physical engineering

Move from scaled principles to catheter-scale cuts, concentric tubes, locks and dedicated fixtures.

Test

Test design and interpretation

Make variables more controlled while keeping the result, setup and unresolved confounds together.