Tissues, materials and temperature

Companion to Human Biology for the Medical Maker — Tissues and contact, Bones, joints and movement, Infection control and materials, Making technologies and the reference figures. Educational only — not a medical device, and not for diagnosis, treatment, monitoring or dosing.

Every figure is orientation, not a design value (chapter 6): it tells you which decade you are in. And no material here is ever rated "hospital safe", suitable, or anything else — chapter 13: the infection prevention team specifies the process, the process constrains the material, and the intended use determines the process.

How to use it

Stiffness and strength. Elastic modulus on a log scale from fat (~1–10 kPa) to 316L stainless (~190–200 GPa), tissues in red and materials in blue; switch to ultimate strength for the chapter 6 table. Bars span the literature range (book chapter 5, chapter 6 and appendix C). Below, pick a device material and a bone: the stiffness ratio (316L is about 10× cortical bone, aluminium about 4×) and, for two parts side by side strained equally, the share of the load each carries — the mechanism behind stress shielding.

Temperature. Published glass-transition, heat-deflection (1.8 MPa), upper-working, softening and melting temperatures for printing and engineering polymers, drawn against hospital laundry thermal disinfection (65 °C for 10 minutes or 71 °C for 3 minutes, UK guidance) and steam sterilisation (~121 °C gravity displacement, ~132–135 °C pre-vacuum) from chapter 13 and appendix C. Pick a process to list each figure minus the process temperature — a distance, not a verdict — beside the evidence gaps that the figure leaves open: repeated cycles, chemical compatibility, additives, creep under load, and whether the process owner accepts it. TPU and photopolymer resins have no single figure; use the grade’s datasheet.

Sources: book chapter 13 (PLA, PETG, ABS, acrylic, acetal, UHMWPE, PEEK, polypropylene); Wikipedia articles Polylactic acid, ABS, ASA, Polycarbonate, Nylon 6, Polypropylene, PEEK and Silicone rubber. Hover a bar to see its source.

Thermal expansion. ΔL = α·L·ΔT for a chosen material, and the difference in free expansion between two joined materials (glass to metal, a printed part around a steel insert). The glass calculator compares the surface stress E·α·ΔT ÷ (1 − ν) in borosilicate (α ≈ 3.3 × 10⁻⁶/K) and soda-lime glass (≈ 9 × 10⁻⁶/K, chapter 14) after the same sudden temperature step — the fully constrained upper bound used in thermal-shock analysis (W. D. Kingery, J. Am. Ceram. Soc. 38, 1955). Borosilicate’s 63 GPa is from appendix C; soda-lime’s 72 GPa from Wikipedia’s Soda–lime glass. Expansion coefficients are from the book, the Wikipedia thermal-expansion table and the Engineering ToolBox; where sources differ (polypropylene: 72–90 against 150 × 10⁻⁶/K) the range covers both.

Limits

Literature ranges, not measurements of your material, your grade or anyone’s tissue. Bone and soft tissue vary with site, direction, strain rate, age and donor; printed parts are weakest between layers.
A temperature figure is not a process result. Nothing here establishes that a part survives a cleaning or sterilisation process once, let alone repeatedly — that is the evidence chapter 13 asks you to collect.
The load-sharing and thermal-shock calculations are idealised (parallel springs; instantaneous step on a fully constrained surface) and give no pass or fail.

Related: levers, moment arms and contact, batch, tolerance and shelf life, print tolerances and fits, physics calculators (thermal expansion of other materials).

Share link (under the title) copies a URL that reopens this tool with your selections. Each tab has its own address: #temperature or #expansion opens that tab.

How to use it

Limits

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