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.

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.

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.

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 locations of collagens with different thermal stabilities in fibrils of bovine reticular dermis.

The techniques of differential scanning calorimetry and electron microscopy were combined to locate collagens with different thermal stabilities in bovine dermis. When calfskin was heated at 1.25 degrees C/min, denatured cores developed in the fibrils at 65 degrees C, leaving native-banded sheaths.

Use of superparamagnetic particles for isolation of cells.

This report describes the preparation and characterization of synthetic ferritin-like particles produced by precipitation of magnetite from a mixture of ferrous and ferric ions in the presence of dextran. The 3-nm diameter particles, containing magnetite cores surrounded by chemisorbed dextran, had a magnetization of 46.7 emu/g of iron with Mössbauer quadrupole splitting of 2 delta = 0.

The size of collagen fibrils that stimulate platelet aggregation in human plasma.

Suspensions of collagen fibrils of different size were prepared from solutions of radioactive tropocollagen type I by either differential centrifugation or differential incubation at elevated temperature. The fractions were compared with respect to their ability to stimulate human blood platelet aggregation in plasma, their binding to human platelets, and their morphology, as seen in the electron microscope. Although small particles with a sedimentation coefficient as low as 4.

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.

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.

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.