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PubMed1991

Evaluation of polyphosphates and polyphosphonates as degradable biomaterials.

A series of polymers, bisphenol A-based poly(phosphoesters), were evaluated as degradable biomaterials. Degradation was observed for the four polymers studied under both in vitro and in vivo conditions. The rate of degradation was affected by polymer side-chain structure and correlated with the swelling behavior. The ethyl side-chain polymers absorbed more water than their phenyl counterparts. Among the sterilization methods, UV irradiation followed by antibiotic treatment was the most suitable, as steam autoclave and ethylene oxide treatments altered the properties of several of the poly (phosphoesters). Tissue response to the poly(phosphoesters) in rabbits was characterized by minor encapsulation and slight or no lymphocyte, giant cell, or macrophage activity. No evidence of edema or necrosis was found. The elastic moduli of these materials varied from 488 MPa for poly(bisphenol A-ethylphosphate) (BPA/EOP) to 627 MPa for the more rigid poly(bisphenol A-phenylphosphonate) (BPA/PP). The ultimate strength, modulus, and energy to failure of BPA/PP were lower than those of similarly compression molded high-molecular-weight poly(L-lactic acid) (PLLA).

Animals↗
PubMed1985

Novel method for the preparation of controlled-release theophylline granules coated with a polyelectrolyte complex of sodium polyphosphate-chitosan.

A novel method for the preparation of theophylline granules coated with a polyelectrolyte complex of sodium tripolyphosphate and chitosan was developed. The theophylline granules containing sodium tripolyphosphate were stirred in an HCl solution of chitosan. During the mixing, the dissolved sodium tripolyphosphate in the granule moved to the surface and reacted with the chitosan, resulting in the formation of the polyelectrolyte complex film. The factors affecting the drug content, the particle size, and the coating-film thickness of the resultant coated granules were determined. The theophylline content in the coated granule decreased with increasing content ratio of sodium tripolyphosphate to theophylline in the original granule and with increasing chitosan concentration in the coating solution. The coated granule size increased with increasing chitosan concentration in the coating solution and with decreasing agitation speed. The coating-film thickness increased with an increase in the chitosan concentration, the pH of the coating solution, and the sodium tripolyphosphate to theophylline content ratio in the original granule. The drug-release pattern of the coated granules followed zero-order kinetics and the release rates were significantly reduced compared with that of the original granule.

Chemical Phenomena↗
PubMed1999

Inorganic polyphosphate regulates responses of Escherichia coli to nutritional stringencies, environmental stresses and survival in the stationary phase.

The molecular mechanisms responsible for polyP accumulation in E. coli remain largely obscure. Based on the available data, a tentative model is proposed (Fig. 1; Ault-Riché et al. 1998). Inhibition by (p)ppGpp of PPX interrupts the dynamic balance between the synthesis of polyP by PPK and its hydrolysis by PPX, accounting for polyP accumulation. However, mutants lacking PhoB, the response regulator of the Pho regulon, fail to accumulate polyP even in the face of high levels of (p)ppGpp. Clearly, PhoB is required in some undefined manner. With regard to osmotic stress, the pathway to polyP accumulation is also distinct from the one identified with the activation of envZ and the associated changes in membrane functions. A tentative scheme attempting to describe the metabolic turnover of polyP is given in Fig. 4. [figure: see text] In adaptations to stress, cells must coordinate major changes in the rates of transcription, translation, and replication as well as make choices in the genes expressed (Kolter et al. 1993). PolyP could provide activated phosphates or coordinate an adaptive response by binding metals and/or specific proteins. Accumulation of polyP in E. coli and other organisms is commonly assumed to provide a reservoir of energy convertible to ATP. This seems implausible because of the turnover of ATP which consumes only a fraction of a second (Chapman and Atkinson 1977). Thus, other functions for polyP need to be considered, among them a regulatory role. PolyP, even at very low levels, is essential in E. coli for adaptations in stationary phase and for survival (Rao and Kornberg 1996). As a polyanionic polymer, polyP has chemical similarities to DNA and RNA in interactions with basic domains of proteins. Further investigation of the cellular location of polyP, its state of metabolic availability and identification of its binding partners are needed. In view of the ubiquity of polyP in eukaryotic cells (including dynamic turnover in the nuclei of some mammalian cells), studies similar to those undertaken in E. coli may reveal comparable functions.

Adaptation, Physiological↗