= Michel Vert
{c}
\b[Michel Vert] chaired IUPAC's project on terminology for biorelated <polymers> and coauthored the resulting 2012 recommendations. The project explicitly addressed materials intended to function for a limited time in biomedical applications.<Terminology for biorelated polymers and applications project by IUPAC>[chairman and project description]{ref} Its scientific motivation is to distinguish what happens to a material from what an application hopes it will do.
For example, <hydrolysis> of susceptible backbone bonds, diffusion of water into a specimen and escape of soluble fragments need not occur on the same timescale. A decrease in molecular size is not identical to complete removal of a device or its products from the body.
An original scale estimate compares water <diffusion> over distance $L$ with a first-order cleavage model. The characteristic times are
$$
t_D\sim\frac{L^2}D,\qquad t_R\sim\frac1k.
$$
Choose $L=1\,\mathrm{mm}$, $D=10^{-10}\,\mathrm{m^2\,s^{-1}}$ and $k=10^{-6}\,\mathrm{s^{-1}}$. Then $t_D\sim10^4\,\mathrm s$ while $t_R\sim10^6\,\mathrm s$. Water can penetrate this idealized length before extensive cleavage. Reducing $D$ by a factor of $10^4$ reverses that ordering. The model neglects swelling, changing transport and reaction products; it illustrates why specimen dimensions and transport can alter degradation patterns even at a fixed reaction rate.
Testing a temporary <biomaterial> therefore needs separately defined observations: changes in molecular structure, retained mass, mechanical function and the fate of released products. These model comparisons explain the project motivation and are not clinical predictions or experimental values attributed to Vert.
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