1. Development of Nanoscale Water Channels in a Tissue-Engineering Scaffold Material
Sousa, Jaap, Kohn, Libera
Macromolecules 2006
39,
Because of the fine length scales involved and the complex dynamics of hydrolytic degradation and erosion, little is known about the development of morphology as polymers for tissue-engineering and drug-delivery applications undergo bioresorption.
We have studied the nanoscale morphology of random blocky copolymers of PEG and a tyrosine-derived polycarbonate (PDTE) as a function of exposure time to water.
High-Angle Annular-Dark-Field Imaging in the Cryo-STEM (top left) after 12 months immersion in water shows nanoscale features with dark contrast.
Energy-loss spectroscopy can differentiate between PEG, PDTE, and water, and 15 nm resolution spectroscopic imaging shows that water appears as nanosized droplets in specimen regions depleted in PEG (left).
These findings suggest that bulk erosion in these blocky copolymers occurs slowly until a percolated network of nanosized water channels form, at which point fast diffusion paths exist for the rapid removal of small-molecule degradation products (below).
200 nm
HAADF STEM
0.3
0.25
0.2
0.15
0.1
200 nm
Water map
15 nm pixel size
0.2
0.15
0.1
0.05
0.0
PEG map
Flux of water-soluble
degradation products