Testing & durability: evidence before claims
Endurance, material fatigue and failure analysis are central development tasks. This page shows what is calculated, what is planned — and what has so far been neither measured nor validated.
Lifetime
Lifetime target and test approach
| Topic | State | Status |
|---|---|---|
| Membrane lifetime target | several hundred million load cycles | Design target |
| Accelerated testing | parallel endurance runs at different frequencies | Planned |
| Transferability of time compression | determined experimentally | Open |
| Validated lifetime | does not exist | Open |
The figures describe what is designed and tested for — not what has been proven.
Critical components
What has to last hundreds of millions of cycles
- Membrane and membrane edge
- Drive mechanics, pumps and bearings
- Guides and moving parts
- Motor bearings
- Valves
- Lubrication and particle management
- Sensors
- Electrical insulation and encapsulation
Membrane project
High-cycle polymer membrane system for a pulsatile artificial-heart pump
Separate, documented R&D project in six work packages; the packages partly run in parallel.
- Requirements analysis and membrane designIn progress
Stroke, pressure and installation-space requirements; parametric design of different membrane geometries.
- Material selection, membrane casting and specimen productionIn progress
Selection of suitable elastomers; production and characterisation of single- and multilayer membrane specimens with varied wall thickness, rolling radius and preload.
- CAD design, numerical FE simulation and prototype manufacturingIn progress
Non-linear FE simulation with hyperelastic or viscoelastic material models; local principal strains, stresses and bending radii; iterative prototypes.
- Functional tests and iterative geometry adjustmentIn progress
Functional tests of the prototypes and iterative adjustment of geometry and membrane clamping.
- Development of the multi-station endurance test rigIn progress
Test rig with defined stroke and back pressure plus cycle, pressure, temperature and leakage monitoring.
- Endurance, frequency validation and failure analysisIn progress
Parallel endurance runs at different frequencies; analysis of cracks, creep, abrasion, fatigue and layer failure; comparison with simulation.
Honestly separated
What is measured — and what is not
Status on the existing circulatory bench (earlier architecture stage). All values of the current architecture are design quantities, not measurement results.
| Quantity | Status | Remark |
|---|---|---|
| Pressure | Measured on bench | |
| Temperature | Measured on bench | |
| Runtime and endurance | Measured on bench | |
| Volumetric flow | Open | derived by calculation, not measured |
| Pumping at blood-like viscosity | Measured on bench | with model fluid |
| Haemolysis and blood compatibility | Open | no blood testing performed |
| Flow simulation (CFD) | Open | not performed |
| Structural simulation (FEA) | Open | planned in work package 3 of the membrane project |
| Standards-compliant testing | Open |
Validation matrix
Risk, method and open evidence
| Field | Risk | Method | Open evidence |
|---|---|---|---|
| Membrane life | Cracks at edges and curvature, leakage. | Endurance with pressure load, inspection, leakage checks. | Cycle life under realistic load. |
| Drive mechanics | Wear, backlash, lubricant ageing, particles. | Endurance, particle analysis, teardown inspection. | Wear behaviour over the design reserve. |
| Hemocompatibility | Hemolysis, thrombus formation, platelet activation. | Blood/surrogate loops, microscopy, deposits, markers. | Long-duration evidence in the assembled blood path. |
| Pulmonary pulsatility | Too little pulsatility or harmful pressure peaks. | Pressure waves, pulse volume, rate, compliance. | Useful pulse envelope without unsafe peaks. |
| Thermal safety | Heating from motor, electronics or energy transfer. | Thermal maps, load cycles, tissue phantoms. | Temperature limits in continuous operation. |
| Sensor plausibility | Wrong response caused by drift or fouling. | Fault injection and cross-sensor comparison. | Rules for contradictory pressure and flow signals. |
Research clusters
Open validation questions in detail
Each cluster is a separate validation problem with an open requirement.
Hemocompatibility
Blood contact is the primary biological risk. Membrane surface, chamber, valve paths and the continuous-flow pump flow path must be assessed as an assembled hydraulic path, not only as isolated materials. The drive has no blood contact.
Open requirement: define markers, loop conditions, exposure time and acceptance limits before claiming blood compatibility.
Shear forces
Shear is not a single number. It depends on rotor clearance, valve jets, membrane deformation and sudden area changes. Short high-shear bursts and longer moderate exposure both matter.
Open requirement: connect simulated shear zones with measured hemolysis and pressure-flow data.
Residence time and stagnation
Risk zones are chamber corners, membrane edge regions and valve pockets. Good average flow can hide stagnation; PIV or dye tests should show whether each cycle refreshes the chamber volume.
Open requirement: show washout behaviour for normal and pulse operation.
Thrombosis risk
Thrombosis risk emerges from surface, shear history, stagnation and foreign-body response and cannot be solved by a single material choice.
Open requirement: map deposit locations and relate them to geometry and flow state.
Pulmonary pulsatility
The continuous-flow pump supplies continuous baseline flow, the pulse chamber adds pressure and flow impulses. The question is not whether pulses can be generated but which pulse envelope is useful rather than harmful.
Open requirement: define safe pulse amplitude, rate and volume ranges.
Membrane fatigue
The membrane is deformed with every heartbeat. Fatigue may start at clamped edges, high curvature or repeated contact zones.
Open requirement: demonstrate cycle life under realistic pressure loads.
Valve life and timing
Inlet and outlet valves determine filling, ejection and backflow. Small timing errors can cause regurgitation, high shear or incomplete emptying.
Open requirement: verify valve timing and leakage after endurance cycles.
Rotor and bearings of the continuous-flow pump
Rotor and bearing behaviour decide heat, vibration, hemolysis and reliability. A normal speed signal does not prove normal flow.
Open requirement: demonstrate a safe response when rotor speed and measured flow disagree.
Particle management
Drive mechanics, bearings and guides can generate particles. The blood path and the lubricated drive region must stay separated; filters remain a concept until particle size, material and capture efficiency are measured.
Open requirement: measure particle generation and containment after mechanical endurance testing.
Thermal safety
Heat can come from the motor, electronics, battery and energy transfer. In an implantable housing, heat dissipation is limited.
Open requirement: map temperature during combined operation and charging.
Simulation and flow visualisation
CFD helps find candidate high-shear, recirculation and pressure-loss regions but is not final proof. PIV, dye tests or transparent models reveal dead zones and jets that average sensors miss.
Open requirement: link simulation predictions to measured data instead of treating them as proof.
Bench tests and acceptance criteria
Test benches must couple pressure, flow, compliance, resistance, temperature, valve state, particles and hemolysis markers. A friendly single operating point is not enough.
Open requirement: define pass/fail criteria before running validation tests.
Regulatory evidence path
Any path to a medical-device claim would require material validation, a sterilisation strategy, biocompatibility, hemocompatibility, electrical safety, software validation, risk management and long-duration evidence. None of this exists yet.
Open requirement: maintain traceability from hazard to control to verification evidence.