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Biomedical subjects

P L Kronick

Publications and source records attributed to P L Kronick.

12 recordsLinked to original sources
PubMed1996

Thermal stabilization of collagen fibers by calcification.

Mineralized collagenous tissue is known to be more stable than soft collagenous tissue both mechanically and thermally. We find that the denaturation temperature of collagen in bone scanned in differential scanning calorimetry at 5 degrees C/min is 155 degrees C, 90 degrees C higher than that in skin. Furthermore, when the bone is partially demineralized with citrate, a discrete intermediate denaturation temperature appears at 113 degrees C, indicating that the mineral is retained at preferential binding sites in the collagen until it is completely leached out. It is shown by electron microscopy that these sites are located in the overlap regions of the collagen fibrils. Collagen in bovine hide can be synthetically mineralized in vitro by impregnation with calcium acid phosphate solution, followed by raising the pH, causing the phosphate to precipitate. Some of the collagen in this synthetically calcified tissue has an elevated denaturation temperature, 104 degrees C. This temperature compares favorably with collagen that is tanned with chromium oxide-sulfate complexes. Calcium phosphate in synthetically mineralized hide, hydroxyapatite in bone, and chromium oxide-sulfate complexes in leather might share the same mechanism of thermal stabilization.

Animals↗
PubMed1994

Matrix macromolecules that affect the viscoelasticity of calfskin.

The chemical basis of viscoelasticity of bovine skin was explored by mechanical relaxation spectroscopy after selective enzymatic degradation. Measurements covered a wide range of time scales because water was replaced in the tissue with aqueous mixtures of ethylene glycol, which maintained a water-like electrical environment for the charged macromolecules down to -50 degrees C. Macromolecular components that couple the fibrils to the interfibrillar matrix contribute about half the values of the resultant storage and loss moduli, while removal of components that are readily extractable, so perhaps free in the matrix, did not alter these mechanical quantities or their relaxations. The precision of the method reveals the effects of fibril-attached matrix, when conventional methods of mechanical testing fail.

Animals↗
PubMed1991

Quantification of vertical-fiber defect in cattle hide by small-angle light scattering.

Vertical-fiber defect (VFD), an abnormal arrangement of collagen fibers in hides of certain cattle breeds, is still not fully understood. Prior work has been limited to subjective histological examinations from hide biopsies. A device using small angle light scattering (SALS) was used to quantify the collagen fiber orientation of sections taken from hide biopsies. Sections were chosen from the Hereford cattle breed and classified by conventional observation as belonging to either the normal, intermediate, or vertical phenotypes. The vertical fibers occur only in the upper reticular dermis, with the fibers in the lower reticular dermis lying parallel to the plane of the hide in all phenotypes. By SALS the vertical phenotype was found to be significantly different from the normal phenotype, whilst the intermediate phenotype was found to be structurally indistinguishable from the vertical one. No evidence was found for the existence of other phenotypes.

Animals↗
PubMed1988

Analysis of the effects of pH and tensile deformation on the small-deformation modulus of calf skin.

A dynamic technique was used to measure the elastic modulus of the reticular dermis of calf skin at a small (0.1%), non-perturbing oscillating deformation. The elastic modulus increases by over an order of magnitude when the tissue is stretched by only 10% before the measurement is made. The results are interpreted by a stochastic model of fiber orientation that includes the orientation of fibers and their straightening out from slack configurations into the load-bearing structure. An equation is derived that accurately describes the course of the modulus-extension curve over a range of pH from 3 to 11, and allows the calculations of the properties and configurations of the slack fibers. One of these is the Young's modulus of a fiber, which agrees well with the previous determinations in neutral medium.

Animals↗
PubMed1979

Direct measurement of the amount of bound collagen which stimulates platelet aggregation.

The amount of collagen which binds to platelets has been correlated with aggregating activity in a platelet aggregometer. Aggregating activity requires only 0.22 microgram/ml (0.35 microgram/10(9) cells) of collagen bound, the reaction saturating with 4.9 microgram/ml (7.9 microgram/10(9) cells). On the basis of the fraction of collagen bound and its hydroxyproline/proline ratio, it is concluded that the activity resides in the type I collagen component.

Binding Sites↗
PubMed1978

Magnetic microspheres prepared by redox polymerization used in a cell separation based on gangliosides.

A facile method is described for making magnetic microspheres that bind specifically to cell surfaces, in order to separate cells magnetophoretically. Control over the sizes of the spheres is effected by using their magnetic cores as part of a redox polymerization system. The use of the microspheres is demonstrated with a separation involving C-1300 neuroblastoma cells, 10% of which express the ganglioside GM1 in their membranes. The GM1-containing cells were separated with better than 99% purity, while the deficient cells were obtained at least 98% pure. The separation, which was carried out under sterile conditions, required only 6 minutes.

Cell Line↗
PubMed1977

Reactions of human platelets with microspheres of poly(hydroxymethyl methacrylate) and polyacrylamide.

We have studied the contact interaction of platelets with hydrogels. In the form of microspheres, 0.6-1.0 mu, poly(glycol methacrylate) (polyHEMA) and poly(methyl methacrylate) beads cause platelets to aggregate at concentrations of about 10(8) beads/ml. Polyacrylamide and (20/80) poly(acrylamide-HEMA) copolymer were ineffective in aggregating platelets. The admixture of 20% methacrylate to polyHEMA rendered the beads inactive. Blood plasma components other than fibrinogen were found essential to the interaction of the beads with platelets. Near-infrared spectra of the hydrogels polyacrylamide and polyHEMA showed the water hydrogen bonds to be the same for both and different from those in pure water. The monomer HEMA is an inhibitor of platelet aggregation and the release reaction at levels of 0.1%. It is concluded that the two hydrogels have different blood compatibilities, which depend more on the network structures than the water structures in the respective gels.

Acrylamides↗