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Biomedical engineering applies engineering analysis, measurement and design to problems in biology, medicine and health care. It includes instruments for medical imaging, devices that interact mechanically with the body, biomaterials and tissue engineering. The National Library of Medicine's scope connects experimental and analytical engineering methods with devices, materials, processes and systems for biology and medicine.^[ref]

A useful research example combines tensile testing with Raman spectroscopy. A mechanical tester mounted on a Raman microprobe stage held hydrated bone specimens while their mineral spectra were measured during elastic loading. The apparatus connected macroscopic deformation to a molecular-scale observation.^[ref] Neither measurement alone describes every property of the biological system.

For an original device-mechanics example, model a uniform elastic test strip of length $L$, area $A$ and Young's modulus $E$. Under axial force $F$, the small-extension model givesWith $F=10\mathrm{N}$, $L=20\mathrm{mm}$, $A=2\mathrm{m}{\mathrm{m}}^2$ and $E=1\mathrm{GPa}$, the predicted extension is $0.10\mathrm{mm}$. Doubling area halves that extension without changing material stiffness. These stipulated values illustrate a design calculation, not a device recommended for use in a patient.

The model must be tested against relevant biological conditions. Hydration, loading rate, tissue interfaces and biocompatibility can matter alongside stiffness. Bench measurements establish behavior under their test conditions; evidence that a device achieves a clinical benefit requires a separate assessment. A biomedical engineer connects the physical model, the measurement and the intended biological function.

Tissue engineering uses biological cells, engineered environments and material structures to build or restore tissue-like function. A construct must do more than resemble the shape of a tissue: its cells need suitable surroundings, and the resulting structure must perform the intended biological or mechanical task. The field lies within biomedical engineering, whose scope includes engineering methods applied to biological materials and systems.^[ref]

One approach seeds cells onto a tissue-engineering scaffold that provides an initial geometry and attachment environment. The cells can deposit extracellular matrix while the construct is maintained under controlled culture conditions. A bioreactor can supply nutrients and impose a defined mechanical environment. These roles should be distinguished: a scaffold’s initial strength, the matrix produced by the cells and the mature construct’s function need not be identical.

A motivating primary experiment is the 1999 report of arteries grown from vascular smooth muscle cells and endothelial cells. Bovine vessels were cultured under pulsatile conditions, then assessed for rupture strength, suture retention, contraction and cellular differentiation. The study also reported implantation in miniature swine, with a finite follow-up observation. The combination of mechanical and biological measurements illustrates why a tissue-like shape alone is insufficient evidence of function.^[ref]

A simple design calculation shows how size affects cell support. For diffusion with characteristic diffusivity $D$, the diffusion time over distance $L$ scales asFor illustrative $D=10^{-9}{\mathrm{m}}^2{\mathrm{s}}^{-1}$, a $0.1\mathrm{mm}$ distance gives $t_D\sim 10\mathrm{s}$, whereas $1\mathrm{mm}$ gives $t_D\sim 1000\mathrm{s}$. The tenfold increase in distance produces a hundredfold time scale. These chosen values do not establish a survival limit: consumption, binding, boundary concentrations and fluid transport also matter. They explain why scaling up a dense construct introduces a transport problem, rather than merely requiring more cells.

The engineering task is to coordinate transport, cell adhesion, matrix formation, biocompatibility and mechanical demands. An experiment can measure each separately: nutrient conditions, viable-cell distribution, matrix organization and force response. Together those observations test whether the designed environment has produced the intended tissue function.