Calculations

Single-Use Bioprocess Assembly Calculations: Formulas and Worked Examples

The five calculations that govern a single-use assembly build, run step by step with real units and worked numbers so you can reproduce them on your own kits.

Single-use bioprocess assemblies combine film bags, tubing, connectors, and filters into sterile, gamma-irradiated kits. Five calculations govern the build: film yield, tubing cut length, assembly labor, sterilization or dose loading, and rolled throughput yield. Each pulls inputs from the bill of materials, the drawing, and time studies. Getting them right separates a quote that holds from one that bleeds margin. This guide runs the math with real units and worked numbers so you can reproduce it on your own kits. Tools like Bag Film Yield and Tubing Cut Length Cost automate the arithmetic once you understand where the inputs come from.

Start with film yield, the ratio of usable bag area to film consumed. Take a 1500 mm web and a 2D bag blank measuring 600 mm by 800 mm nested two across. Two across uses 1200 mm, leaving 300 mm edge waste, or 20 percent across the web. Add a 30 mm seal and index margin, so the length pitch is 830 mm. A 2D bag needs two film layers, so film consumed per bag equals 1.245 m2 while finished bag area is 0.96 m2. Yield is 0.96 divided by 1.245, or 77 percent. Feed that into Bag Film Yield to convert rolls into part counts.

Tubing cut length drives both material and scrap. Sum every segment on the drawing, then add trim and kerf. A manifold with segments of 300, 450, 600, and 250 mm totals 1600 mm. Add a 5 mm trim at each of the 8 cut faces, or 40 mm, giving 1640 mm, which is 1.64 m per assembly. At $6.50 per meter for platinum-cured silicone, material is $10.66. If offcuts below 150 mm are unusable and you average 90 mm of drop per build, effective consumption climbs to 1.73 m, or $11.25. Tubing Cut Length Cost captures both the net length and the drop penalty.

Assembly labor is standard time per operation multiplied by counts, plus setup. Say aseptic connector installation runs 90 seconds each and a build has 6 connectors, that is 540 seconds. Add two tube welds at 120 seconds and a 180 second kitting setup, totaling 960 seconds, or 16.0 minutes per unit. In an ISO 7 cleanroom, apply a gowning and break overhead. If gowning is 20 minutes twice per shift and effective time is 6.5 of 8.0 paid hours, the labor inflation factor is 1.23, pushing effective build time to 19.7 minutes. Connector Assembly Labor and Cleanroom Labor split these out.

Two paths sterilize the kit. For gamma, dose is fixed by validation, commonly 25 kGy to 40 kGy, and cost scales with mass and dwell. If a contract irradiator charges by density-adjusted volume and your kit fills 0.012 m3 at 95 kg per m3, and a tote holds 40 kits, the per-unit dose cost falls as you pack tighter. Gamma Dose Cost converts a pallet rate to per-unit. For autoclave or E-beam batches, Sterilization Load gives pieces per cycle: chamber usable volume divided by part envelope volume times a 0.55 packing efficiency. A 0.4 m3 chamber holding 0.012 m3 kits yields about 18 units per load.

Quality throughput hinges on test cycle time. A pressure decay leak test with a 30 second fill, 20 second stabilize, and 25 second decay measure is 75 seconds, plus 15 seconds to load and unload, or 90 seconds total. Capacity is 3600 divided by 90, or 40 units per hour per station. Leak Test Capacity sizes how many stations you need for a 500 unit day, which at 40 per hour is 12.5 station-hours. Packaging Integrity Yield tracks the pass rate of dye or bubble integrity checks, feeding the rolled number computed next.

Rolled throughput yield multiplies first-pass yields across every step. If film forming is 0.97, welding 0.98, leak test 0.96, and packaging integrity 0.99, RTY equals 0.97 times 0.98 times 0.96 times 0.99, or 0.903, so 90.3 percent of kits pass clean. Starting 500 kits yields 451 sellable, meaning 49 need rework or scrap. Scrap Cost turns those losses into dollars by layering material and accumulated labor at the step where the unit failed. Traceability Workload then counts the lot and serial records each surviving unit carries, typically 8 to 20 line entries per device history record.

Published 2026-07-02.