Biosynthesis Brittleness

Crystallinity of articles made of PHA copolymers is another property which can be adjusted by the incoiporation of mcl-3HA units. Crystallinity influences the stiffness of the material. Because of the strict molecular stereoregularity of PHA created by the biosynthesis, the crystallinity of PHB homopolymer is known to become very high, often well in excess of 50%. Such high crystallinity results in the excessively hard and brittle material not well suited for many practical applications. The incorporation of mcl-3HA comonomer units, which cannot be incorporated into the PHB crystal lattice structure, should be an effective disruption to the excessive level of crystallinity. 

Echinod ms can be divided into two groups based on sterol composition. Starfish and sea cucumbers contain predominantly A -sterols while the sea lilies, brittle stars, and sea urchins contain primarily A -sterols (89). Two early studies indicated that sterols are not synthesized in echinoderms (85,90), but later studies demonstrated biosynthesis in most echinoderm species studied (89,91). One of the latter studies (89) also provided data suggesting that echinoderms synthesize Cn sterols, but obtain Cjs and sterols fiom the diet. 

---