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Multi-Lumen Core

Many catheters are not built on a simple round bore: dialysis and infusion catheters, distal-access aspiration designs, and multi-channel delivery systems start from a multi-lumen extruded core — a solid polymer rod with shaped internal lumens — with the wall stack (jackets, braid, coil, pullwire layers) laminated on top.

VirtuCath models these designs directly. The core drives the cross-section mechanics, including anisotropic bending for asymmetric profiles (a double-D bends differently across the septum than along it), and flows through every downstream tool — simulation, analysis, flowdown, and reports.

Enabling a core​

On the wizard's General Properties step, set Design Mode to Multi-Lumen Core. This:

  • Adds a Core Profile step to the wizard, where the inner geometry is defined (the Step-1 diameter inputs are hidden — the core owns the inner dimension).
  • Builds the catheter inside-out: walls stack outward from the core OD, and the final OD is a computed result.

The Core Profile step​

Templates​

Pick a profile from the template gallery, then shape it with its parametric dimensions. Every dimension is unit-aware and live-previewed:

TemplateProfile
N Lumens1–8 round lumens evenly spaced on a pitch circle.
Central + N LumensA central lumen with 0–8 satellite lumens around it.
Multi-D2–4 D-shaped lumens separated by straight septa, with area-balance controls to size the lumens unequally.
Pie Sectors3–6 wedge-shaped sectors, with or without a central hub.
Round + CrescentA round lumen tangent to the outer wall, with a crescent filling the remaining bore. The crescent can be split in two.
Central + CrescentsA central lumen ringed by 2–4 crescent-shaped sections.
OvalA single horizontal oval lumen, optionally with one or two satellite lumens above/below.
Custom (Measured)Enter measured section properties (area and moments of inertia) directly when the profile comes from a supplier drawing or a measured part.

Templates with same-size lumen groups have an "All lumens are equal size" checkbox — uncheck it to dial individual lumen diameters (for example, one large aspiration lumen and smaller wire lumens on the same pitch circle).

Core material and guardrails​

  • Core Outer Diameter and Core Material set the rod itself; the material comes from the Materials Library.
  • A status line continuously reports the minimum outer wall and minimum web (the thinnest polymer between lumens, and between lumens and the surface) — the two numbers an extrusion vendor will ask about.
  • Geometry errors — overlapping lumens, or lumens escaping the core — block the Next button until fixed. Warnings (thin but manufacturable webs) do not block.

Per-section opt-out​

Each section has a "Use multi-lumen core in this section" checkbox (on by default). Uncheck it to build that one section on a plain bore at the core OD instead — for example, a soft distal tip in front of a multi-lumen shaft.

Pullwires and the core​

Pullwires are never routed through the core. They are defined as usual on the Pullwire Settings step and run in the wall stack above the core — the wizard keeps the pullwire offset clear of the core OD automatically.

On core designs the Pullwire Settings step also gains:

  • Core preview: the cross-section visualization shows the core inside the bore, so you can see how the pullwires sit relative to the lumens.
  • Core Rotation: rotates the core about the catheter axis in 90° steps to align its lumens with the pullwire layout. This is real assembly geometry — the rotation flows to the computed bending axes, all cross-section views, the 3D model, and the report.

How the core changes the analysis​

  • Anisotropic bending: asymmetric profiles report separate EIx / EIy bending stiffnesses on the Catheter Analysis tab and in the reports (plus the principal min/max range on the Review page and reports), and the dynamic simulation bends with the same independent X and Y stiffness.
  • Min. Bend Radius (first yield): the bend radius at which the core polymer first yields (onset of permanent set) — the meaningful bend limit for a solid core, reported with its yield moment. Conservative: it ignores stress concentration at the lumen webs.
  • Round-bore KPIs show N/A: burst pressure, crush pressure, and the elastic instability radius assume a thin-walled round tube and are not reported for core sections.
  • Flowdown: the core is the reflow boundary — the stackup builds outward from the core OD, and the core itself never reflows. It appears (statically) in the flowdown 3D view.
  • Response Surface Analysis: the core is treated as fixed tooling — its OD is shown read-only and cannot be swept. Sweep wall-stack parameters instead.
  • Reports: PDF and Excel document the core as authored — template, parametric dimensions, and manufacturability minima — with a cross-section image.