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Biomedical subjects

H A Paschall

Publications and source records attributed to H A Paschall.

6 recordsLinked to original sources
PubMed1976

The influence of surface chemistry on implant interface histology: a theoretical basis for implant materials selection.

A theory is proposed stating that an ideal implant material must have a dynamic surface chemistry that induces histological changes at the implant interface which would normally occur if the implant were not present. Evidence for the validity of this theory is provided with a series of bone-implant studies which result in stable interfacial osteogenesis under specific implant surface chemistry conditions. Insufficient or excess surface ion concentrations produce negative osteogenesis and fixation results. Implantation of osteogenic implants in soft tissues also produces undesirable histological responses as proposed in the theory. A variety of surface chemical analyses of the implant are reviewed which provide a scientific basis for the implant surface theory.

Animals↗
PubMed1975

Electron microscopic observations of 20 human osteosarcomas.

Twenty primary osteosarcomas of bone and two osteosarcomas metastatic to the lung were examined by electron microscopy. The tumor cells, whether from an area exhibiting chondroid, osteoid or collagenous matrix, showed common abnormalities in configuration and fine structure. The cells tended to be spindle-shaped with centralized nuclei. The nucleus was enlarged, irregular in shape, and frequently lobulated. The choromatin was dense and arranged around the periphery of the nucleus. There was a large prominent, irregularly shaped nucleolus. Smooth membranes were sparse to absent. The rough endoplasmic reticulum was abundant, disorderly, and tended to be markedly dilated in mature cells. The mitochondria were numerous, variable in size and configuration, and were intimately surrounded by rough endoplasmic reticulum. The collagenous matrix was disorganized with the fibers and bundles randomly oriented and arranged. No structures definitely identifiable as virus-particles were seen. However, microstructures resembling unenveloped nucleocapsids of paramyxo- or related viruses were noted. All fine structure abnormalities could be associated with an increased metabolic rate and/or with abnormal protein and enzyme synthesis. No definitive diagnostic features were found. The fine structure of cell cultures derived from the osteosarcomas in this study was similar to that of the fresh tissue. No virus-like particles were seen in any of these cell lines.

Bone Matrix↗
PubMed1967

Changes in the fine structure of bone cells after the administration of parathyroid extract.

This paper describes the effect of parathyroid extract on the fine structure of bone cells in the proximal metaphysis of the tibia. The extract was given to rats intraperitoneally, in single or repeated doses of 1-14 units (USP) per gram body weight, over short or extended periods, and the tissue was examined between 6 and 26 hr after the commencement of injection. During this period, osteoblasts showed the greatest changes. Their mitochondria became swollen and contained dense granules; both rough- and smooth-surfaced vesicles were distended; ribosomes were separated from the membranes; and various dense bodies appeared in the cytoplasm. Osteocytes were similarly but less affected, and osteoclasts differed little from those in normal animals. Eventually after repeated injections, the fine structure of many of the cells was disrupted. These changes were accompanied by erosion of the bony trabeculae without any great increase in numbers of osteoclasts. It is possible that the alterations in fine structure were the result of damage to the cells by the parathyroid extract. However, since the extract did not seem to stimulate classical osteoclastic activity, the mitochondrial swelling and dense bodies could have been related to the removal of mineral and matrix, respectively.

Animals↗