Daniel M. Horowitz

PHA APPLICATIONS: ADDRESSING THE PRICE PERFORMANCE ISSUE: I. TISSUE ENGINEERING

This paper describes the development of medical applications for polyhydroxyalkanoates (PHAs), a class of natural polymers with a wide range of thermoplastic properties. Methods are described for preparing PHAs with high purity, modifying these materials to change their surface and degradation properties, and methods for fabricating them into different forms, including tissue engineering scaffolds. Preliminary reports characterizing their in vivo behavior are given, as well as methods for using the natural polymers in tissue engineering applications.

Phase separation within artificial granules from a blend of polyhydroxybutyrate and polyhydroxyoctanoate: biological implications

Abstract A recently developed in vitro procedure for preparing artificial granules of microbial polyesters has been applied to a blend of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyoctanoate) (PHO). Density gradient analysis showed that these granules formed a single, uniform population; n.m.r. showed that the polymers retained their amorphous elastomeric state; and thermal analysis indicated that the polymers formed separate phases within these granules. These results contrast strongly with the observation that a recombinant bacterial strain simultaneously expressing PHB and PHO stores the two polymers in separate cellular granules. The implications of the in vitro findings for granule formation in vivo are discussed.

Nuclear magnetic resonance relaxation studies of poly(hydroxybutyrate) in whole cells and in artificial granules

The physical state of poly(hydroxybutyrate) (PHB) in whole cells and in the form of artificial biomimetic granules has been probed using 13C nuclear magnetic resonance (NMR) spectroscopy. Studies on varying concentrations of whole cells of Alcaligenes eutrophus show that changes in the line widths of PHB in whole cells do not correlate with changes in transverse relaxation times. Solid-state magic-angle spinning NMR studies demonstrate that the line broadening results from a reduction in the static field homogeneity rather than from intrinsic properties of the PHB within the cells. Transverse and longitudinal relaxation times of PHB in whole cells and in artificial granules are similar, indicating similarities in structure and mobility.