One is that the amorphous state of P(3HB) in vivo can be
caused by a simple physical-kinetic limitation [153,154]
within granules based on their small size (stabilized by an
amphiphilic shell). This assumes that the rate of P(3HB)
crystallization in vivo is governed by the rate of spontaneous
nucleation events, which depends upon the granule
volume and therefore on the third power of the granule
radius. The upper limitfor the rate constant of spontaneous
crystal nucleation in isolated P(3HB) at 30 ◦C (the temperature
of bacterial growth) is 2.5 events mm−3 s−1 [155,156].
The corresponding rate of nucleation for a typical storage
granule of diameter 0.25 m is 2.0 × 10−11 events s−1. Provided
the granules do not coalesce and are not exposed