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Biomedical subjects

A S Posner

Publications and source records attributed to A S Posner.

At least 19 recordsLinked to original sources
PubMed1988

The effect of glass-ceramic bone implant materials on the in vitro formation of hydroxyapatite.

The extracts of four glass-ceramic bone implant materials were investigated for dissolved material, for effects on in vitro formation of hydroxyapatite, and for surface morphology of glass-ceramic particles in scanning electron microscopy. In vitro leaching released substances that affected in vitro formation of hydroxyapatite, i.e., initiation time and growth of crystals. Leaching also changed the surface morphology of the materials. The ability of the materials to bond to bone did not correlate with the inhibition of hydroxyapatite formation by the released substances. Surface morphology and other factors at present not yet known are probably involved in controlling the bonding to bone of these ceramics.

Bone and Bones↗
PubMed1985

The structure of bone apatite surfaces.

This is a review of the surface chemistry of bone mineral and its synthetic counterpart hydroxyapatite. Small-angle x-ray scattering and low-temperature nitrogen adsorption measurements show bone mineral surfaces range from 100 to 200 m2/g. The heats of adsorption of small molecules on bone and apatite surfaces show that these materials have polarizing surfaces which form strong bonds with polar and polarizable molecules. Water is hydrogen bonded to these surfaces with energies ranging from 23 Kcal/mol, for low coverage, to 11 Kcal/mol after two full layers; the latter value shows that after two monolayers the water is bonded as strongly to the solution as it is to the apatite surface. Stearic acid in cyclohexane adsorbs on bone and apatite surfaces in a closed-packed manner with the straight-chain molecules in parallel array with the end carboxyl groups hydrogen bonded to surface electronegative ions. Synthetic hydroxyapatite has long been used in chromatography because of the bonding capacity apatite surface has for certain proteins and polynucleotides. The metabolic interplay between bone mineral and the body results from the high magnitude and high reactivity of the mineral surface.

Adsorption↗
PubMed1985

The mineral of bone.

This is a review of the chemistry and structure of synthetic, mineral, and biologic hydroxyapatites. Bone apatite has a large, reactive specific-surface and is characterized by its crystal imperfection and non-stoichiometry. Precipitated and bone hydroxyapatites are in the submicroscopic size range where their solubility decreases rapidly with a small increment of crystal growth. A discussion is given of the various mechanisms proposed for tissue mineralization. The body seems to contain a number of nucleating and inhibiting mechanisms which seem to work in concert, possibly providing redundant pathways to the mineralization of tissue.

1-Carboxyglutamic Acid↗
PubMed1984

Bone structure, composition, and mineralization.

Bone structure and function are dependent on complex interactions between cells, matrix, cell-derived factors, and systemic factors. The deposition of mineral in bone, which enables the skeleton to function properly, is described as a four-step process of matrix modification, crystal nucleation, crystal growth, and remodeling. Insight into the function of bone components in the mineralization process is provided by in vitro studies and analysis of abnormal calcifications.

Animals↗
PubMed1984

Mineral parameters in early fracture repair.

In an effort to define and characterize the initial mineralization product of fracture-healing, we studied the mineral components within a model of endochondral osseous repair. Fracture calluses from the tibiae of rats and rabbits undergoing endochondral fracture-healing were analyzed, in toto and following density fractionation, by physicochemical and crystallographic techniques. Significant changes in mineral composition, crystal size, and density occurred in the early phases of fracture repair. In the rat, two weeks after fracture, the calcium-to-phosphorus ratio was higher than that of the mineral component, possibly due to calcium-binding to some of the macromolecules known to be present. The earliest mineral was poorly crystallized hydroxyapatite with a high carbonate content. Crystal perfection improved rapidly and approached that of normal diaphyseal bone within eight weeks after endochondral fracture in both the rabbit and the rat.

Animals↗
PubMed1983

Amorphous calcium phosphate in casein micelles of bovine milk.

The calcium phosphate remaining after hydrazine deproteination of casein micelles isolated from bulk skim milk exhibits under the electron microscope a very fine and uniform granularity being formed by small subunits with a true diameter of approximately 2.5 nm. This material, which is about 10 percent by weight citrate, termed calcium phosphate citrate (CPC) complex, also contains Mg and Zn at molar ratios of 0.03 and 0.003 respectively. Radial distribution function (RDF) and infrared analyses show that CPC is a Mg-containing amorphous calcium phosphate (ACP) similar to synthetic and cytoplasmic ACP. presence of CPC in casein micelles as an amorphous colloid bonded with phosphoproteins provides the means for storing in milk large amounts of Ca (16 mM) and Pi (10 mM) in a readily utilizable form but at a higher ion concentration than found in biological solutions.

Animals↗
PubMed1982

Comparative biochemical studies of the callus matrix in immobilized and non-immobilized fractures.

Fracture healing in both non-immobilized and immobilized rat fracture callus, though different radiographically and histologically; is characterized by similar biochemical changes in the ground substance. Although the callus formed in the immobilized model is appreciably smaller than that formed when the fracture is not immobilized, the chemical composition of the organic matrix of the existing callus undergoes similar modifications regardless of fixation and histological response. Previous studies of endochondral fracture repair have demonstrated an elevation in fracture callus hexosamine content during the early stages of healing of the non-immobilized fracture. This corresponded histologically to a predominance of cartilaginous tissue in the callus matrix. In the present study, the biochemistry, histology, and roentgenographic features of stabilized and non-stabilized rat fractures are compared. Similar elevations in hexosamine are noted at two weeks in both models. These elevations are attributed to changes in proteoglycan rather than glycoprotein concentration of the tissue.

Animals↗
PubMed1982

Calcium-acidic phospholipid-phosphate complexes in diseased and normal human bone.

Ca-acidic phospholipid-PO4 complexes promote in vitro hydroxyapatite nucleation and/or growth and are believed to have similar functions in vivo. The complexed acidic phospholipid content of human bones has been studied in femoral heads obtained at surgery from patients with osteonecrosis and osteoarthritis and compared with age-matched, disease-free control bones. The content of Ca-acidic phospholipid-PO4 complexes was elevated in bones that were judged on the basis of radiographic and histological data to be actively making new bone. These data suggest that the relative concentration of Ca-acidic phospholipid-PO4 in bone may be related to the rate at which bone is being made and mineralized.

Adolescent↗
PubMed1982

Optimal conditions for Ca-acidic phospholipid-PO4 formation.

Calcium-acidic phospholipid-phosphate complexes (Ca-PL-PO4) cause hydroxyapatite (HA) deposition in vitro. The acidic phospholipids--phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG), and diphosphatidylglycerol (DPG)--all form Ca-PL-PO4 complexes: Nonacidic phospholipids--sphingomyelin (SPL), phosphatidylcholine (PC) and phosphatidylethanolamine (PE)--do not form Ca-PL-PO4 and do not induce hydroxyapatite (HA) deposition in low ionic strength metastable calcium phosphate solution or in synthetic lymph. The extent to which each of the acidic phospholipids reacts with calcium and inorganic phosphate, and the chemical composition of the Ca-PL-PO4 complexes is a function of pH, solution composition, the nature of the phospholipid, and the method of isolation. The addition of inorganic phosphate prior to or in combination with calcium appears to be an absolute requirement for Ca-PL-PO4 formation.

Calcium↗
PubMed1981

Formation and structure of Ca-deficient hydroxyapatite.

When amorphous calcium phosphate (ACP) was transformed to crystalline hydroxyapatite (HA) in a series of aqueous slurry concentrations ranging from low to high, the higher slurry concentrations produced more Ca-deficient HA as measured by Ca/P ratio and heat-produced pyrophosphate. We feel that the excess solution phosphate produced in the higher slurry transformations results in lower Ca/P ratio HA. It has been suggested that an ACP is the precursor to bone apatite. Regulation of the in vivo ACP slurry concentration could then control the stoichiometry and, therefore, the metabolic activity of bone apatite. X-ray radial distribution function (RDF) analyses showed that CO3(2-) substitution in HA creates far greater structural distortions than do Ca deficiencies. The latter, however, do produce small, but observable, structural distortions when compared to stoichiometric HA. It now seems clear that the RDF of bone apatite can be modeled by a synthetic, Ca-deficient, CO3(2-)-containing HA.

Calcium↗
PubMed1980

Effect of magnesium on lipid-induced calcification: an in vitro model for bone mineralization.

The effect of Mg on hydroxyapatite proliferation induced by phosphatidyl serine, phosphatidyl inositol, and calcium-acidic phospholipid-phosphate complexes has been studied in metastable calcium phosphate solutions of constant ionic strength and variable Mg/Ca ratio. Mg inhibits formation of the Ca-acidic phospholipid phosphate complexes, probably by competing with Ca for sites on the phospholipid molecules. Once the complexed acidic phospholipids were present, Mg has no effect on the proliferation of hydroxyapatite. This is shown by the invariant first-order rate constant for the disappearance of CA during hydroxyapatite proliferation (kCa = 0.0037 h-1) in solutions with Mg/Ca weight ratios ranging 0/1 to 10/1. These studies suggest that the presence of Mg does affect in vivo calcification and that the initiation of calcification by means of a Ca-PL-PO4 complex may be dependent on the Mg/Ca ratio in the calcifying tissue.

Bone and Bones↗
PubMed1979

Effect of diphosphonates on hydroxyapatite formation induced by calcium-phospholipid-phosphate complexes.

The diphosphonates disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP) and disodium dichloromethylene diphosphonate (Cl2MDP) prevent hydroxyapatite (HA) formation in metastable calcium phosphate solutions, induced by calcium-phospholipid-phosphate complexes and by the acidic phospholipids phosphatidyl serine and phosphatidyl inositol. The diphosphonates appear to act not only as HA crystal poisons but also as surfactants which probably change the nature of the lipid micelle and the charge and conformational properties of the lipid molecules. The surfactants sodium dodecyl sulfate (SDS) and Non-Idet P-40 (NP-40), like the diphosphonates, prevent HA formation by the acidic phospholipids and complexed lipids, but do not act as HA surface poisons. The lipid surfactant lyso-phosphatidyl serine did not induce HA formation from solution. The relevance of the ability of the diphosphonates to act as lipid surfactants to the in vivo use of these agents is discussed.

Calcium↗