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Biomedical subjects

K W Davy

Publications and source records attributed to K W Davy.

27 records · Page 2Linked to original sources
PubMed1987

The mechanical properties of elastomeric poly(alkyl methacrylate)s.

A range of poly(alkyl methacrylate)s in the range C5 to C13 with varying degrees of crosslinking, have been studied with respect to stress-strain behaviour. Where the extensions to break were sufficiently high, stress-strain properties conformed well to the statistical theory of rubber elasticity, the Mooney/Rivlin C2 term being sensibly zero. All materials studied were very elastic, exhibiting extremely little permanent set. The energy to break decreases very rapidly as the homologous series is ascended, and 0.5% crosslinking agent is perfectly adequate to give elastic properties. Hence either n-pentyl or hexyl methacrylates are to be preferred in soft prosthesis formulations on mechanical grounds.

Acrylates↗
PubMed1987

Polymerization shrinkage of methacrylate esters.

The polymerization shrinkage of a range of poly(n-alkyl methacrylates) in the range C1 to C16, some of their isomers and the polymers of cyclic and heterocyclic methacrylates have been measured using densitometry. The percentage volume shrinkage decreases with the size of the substituent side group. This proved to reflect the fact that the change in molar volume on polymerizing a methacrylate ester is reasonably constant at 22 cc/mol irrespective of the geometry of the substituent group. However, the glass transition temperature of the polymer depends very critically on the geometry of the side group. Hence one method for the development of low shrinkage glassy polymers is to investigate methacrylate esters of large molar volume, but with side group geometry that results in a high glass transition temperature. Polymerization shrinkage can be used to determine the degree of conversion of a polymer, using the value of 22 cc/mol as the change in molar volume.

Acrylates↗
PubMed1986

Water absorption characteristics of some unfilled resins.

The water absorption characteristics of resins, upon which many composite filling materials are based, have been studied. In general, the equilibrium uptake is less than that predicted from the water absorption of composite filling materials, if it is assumed that the polymer alone absorbs the water. Also, whereas there are very large differences between sorption and desorption diffusion coefficients in composites, there is very little difference in the case of unfilled resins. Furthermore, sorption in the case of composites is generally very much slower near equilibrium than predicted. These phenomena are all explicable because composite filling materials contain water soluble impurities which enhance uptake, which is ultimately determined by a balance between osmotic and elastic pressures. This implies the existence of internal strains in composites.

Absorption↗
PubMed1985

Cephalosporin resistance in Pseudomonas aeruginosa, with special reference to the proposed trapping of antibiotics by beta-lactamase.

Resistance of Pseudomonas aeruginosa strains to newer cephalosporins is often associated with stable derepression of synthesis of the chromosomal beta-lactamase. Similar resistance is developed by enzyme inducible (i.e. normal) strains in response to beta-lactamase inducers. By comparing the responses of otherwise isogenic P. aeruginosa beta-lactamase inducibility mutants to antipseudomonal cephalosporins alone or in combination with potent beta-lactamase inducers we confirmed that resistance to cefotaxime, ceftriaxone, cefoperazone, and ceftazidime and latamoxef was caused by beta-lactamase action. The low-level resistance to carbenicillin and cefsulodin which was exhibited by some fully beta-lactamase derepressed strains was not confirmed to be beta-lactamase determined and may have reflected concurrent target or permeability changes. The mechanism whereby the enzyme protected the cell against cefotaxime and ceftriaxone was also investigated. These agents are reportedly stable to the enzyme and some workers have suggested that resistance entails their being trapped rather than hydrolysed. However, the use of a novel model of cellular beta-lactamase function indicated that a hydrolytic resistance mechanism remained likely.

Cefotaxime↗
PubMed1984

Pseudomonas aeruginosa beta-lactamase as a defence against azlocillin, mezlocillin and piperacillin.

Azlocillin, mezlocillin and piperacillin are weak substrates for the chromosomal beta-lactamase of Pseudomonas aeruginosa, and hydrolysis kinetics were calculated. Enzyme function in the living cell was studied by comparing antibiotic activity against a typical Ps. aeruginosa strain with inducible beta-lactamase expression with antibiotic activity against beta-lactamase uninducible and constitutive mutants. The inducible organism was less sensitive than its uninducible mutant to all three agents; this difference was more apparent at high inocula than low and in broth than in agar. These differences involved both enzyme induction and selection of genotypically enzyme derepressed variants. The penicillins were not, however, efficient beta-lactamase inducers at low concentrations and their activity against the inducible organism was antagonized by more potent inducers. Secondary inducers did not antagonize antibiotic activity against beta-lactamase uninducible and constitutive organisms. The beta-lactamase constitutive mutants were highly resistant to the three antibiotics tested.

Azlocillin↗
PubMed1977

Applications of gas-liquid chromatography in protein chemistry. II. Determination of amide residues in nanomolar amounts of proteins.

A method for the quantitative determination of amide residues in nanomolar amounts of proteins is described, based on dilute acid hydrolysis at 100 degrees, followed by isothermal gas-liquid chromatography of the ammonia released by on-column neutralisation of the hydrolysate and quantitation by means of a conductometric detector. Amide contents are given for twenty well characterised proteins, as well as for asparagine and glutamine.

Amides↗
PubMed1976

Applications of gas-liquid chromatography in protein chemistry. Determination of C-terminal sequences on nanomolar amounts of proteins.

A method for the determination of C-terminal amino acids and C-terminal amino acid sequences in nanomolar amounts of proteins is described, based on carboxypeptidase A digestion of the protein, followed by removal of the partially digested protein and quantitative gas-liquid chromatographic determination of the amino acids released after known time intervals. Sequences deduced from the kinetics of release of specific amino acids are compared with the known C-terminal sequences of well-characterized proteins.

Amino Acid Sequence↗