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Biomedical subjects

D H Isaac

Publications and source records attributed to D H Isaac.

8 recordsLinked to original sources
PubMed1989

Osteoporotic bone microstructure by collagenase etching.

Collagenase etching has been used to show the microstructure of bone from patients suffering from primary osteoporosis. Both polished and unpolished surfaces of trabecular bone from femoral heads were treated with collagenase solution before study in the scanning electron microscope. The polished surfaces show the mineral component of this bone as small rounded units approximately 10-20 nm across, which aggregate to form a continuous phase of contiguous spheroidal particles approximately 100 nm across. Lamellations are clearly seen to be due to the removal of collagen fibres up to approximately 200 nm across, fibres in adjacent lamellae being arranged approximately perpendicular to each other. The unpolished surfaces also show small rounded units, which aggregate into rods of mineral approximately 100 nm across. Although these rods form a connected system, they are loosely packed, compatible with their being interspersed with the collagen fibres in vivo. This model for the detailed microstructure of bone is consistent with specimens from a number of other sources and shows no features unique to osteoporosis.

Aged↗
PubMed1989

Human bone microstructure studied by collagenase etching.

Bone samples from the iliac crest of patients with no signs of bone disorder were treated with collagenase to remove the collagen component and so allow detailed observation of the mineral hydroxyapatite. Both polished and unpolished surfaces were studied in the scanning electron microscope and they showed that the mineral component of bone is composed of small rounded units about 10 nm across which are fused together to form larger spheroidal units roughly 100 nm in diameter. In the unpolished surfaces these 100 nm units are seen to aggregate to form columns approximately parallel to their neighbours and with numerous interconnections forming a continuous mineral phase. The polished sections also show the hydroxyapatite as a continuous phase of contiguous spheroids and the holes from which the collagen fibres were removed are clearly revealed. Lamellations in the surface are interpreted as resulting from adjacent layers of collagen fibres having orientations approximately perpendicular to each other.

Bone and Bones↗
PubMed1988

Mineral structure and preferred orientation in the fin bones of the plaice, Pleuronectes platessa.

The technique of collagenase etching of a polished surface of plaice fin bone has been used to reveal the structural detail of the mineral component and hence to explain the preferred orientation previously deduced from X-ray diffraction experiments. High resolution electron micrographs reveal units approximately 20 nm across, which aggregate to form units approximately 100 nm across, which in turn coalesce to produce rods up to approximately 1 micron diameter and of substantial length. These rods show a preferred orientation with their axes parallel to the long axis of the bone, thus demonstrating a preferred orientation of the mineral component. Additionally, collagenase-etched transverse surfaces reveal numbers holes from which collagen fibrils parallel to the long axis of the bone have been removed, whereas similarly treated longitudinal surfaces do not show such holes. This is consistent with a predominance of collagen fibrils running along the bone axis and explains the previously observed preferred orientation of the collagen component of fish fin bones.

Animals↗
PubMed1987

Collagen fibre orientation in bovine secondary osteons by collagenase etching.

The orientation of collagen fibres in bovine secondary osteons has been investigated in the scanning electron microscope (SEM) by removal independently of firstly the mineral component and secondly the collagen fibres. Demineralization of polished transverse sections reveals a lamellar structure for the collagen component but the precise orientation of the collagen in each ring is not unequivocably determined. However, by using a collagenase solution to etch away the collagen component of a polished surface, holes are produced in the mineral revealing the former position of the fibres. The greater rigidity of the mineral component ensures that the structure does not collapse and produce artifacts. A specimen cut so that transverse and longitudinal sections are simultaneously observed allows the relationship between the structural features on each surface to be revealed. Analysis of such micrographs indicates a model for the collagen component of osteons in which the lamellar structure contains fibres with orientations alternately parallel to and circumferential to the long axis of the osteon. Tilting the samples to look directly down the holes shows that the fibres are not precisely longitudinal and circumferential but are tilted from these ideals by a variable angle (typically 20 degrees) the precise angle probably being an important factor related to the in vivo mechanical property requirements.

Animals↗
PubMed1985

Bone microstructure by collagenase etching.

A novel technique has been developed for microstructural studies of bone. The spatial organizations of the mineral and collagen fibres in bone have been a matter of discussion for some time, with numerous diverse observations arising from various preparative techniques. In this latest investigation details of the mineral structure are clearly revealed in the SEM by treating a cut and polished surface of bone with collagenase to remove the major organic component. This new procedure has minimal effect on the mineral and hence reveals microstructural detail which is far closer to that in vivo than in previous investigations. This paper concentrates on two aspects of the studies, namely the detailed morphology of the mineral component and the arrangement of the collagen fibres in the osteons of compact bone. Firstly, the mineral component is revealed as comprising 'crystallites' (approximately 20 nm diam.) which aggregate to form larger contiguous 'spheroidal particles' (approximately 100 nm diam.), which in turn form 'granules' (approximately 500 nm diam.). Secondly, the regions from which collagen fibres have been removed are clearly revealed, showing that within an osteon, alternating lamellae have collagen fibres oriented approximately parallel to and circumferential to the Haversian canal respectively.

Animals↗
PubMed1976

Polarized infrared spectra of crystalline glycosaminoglycans.

Polarized infrared spectra have been recorded for oriented, crystalline specimens of hyaluronates, chondroitin 4-sulfate and 6-sulfate, dermatan sulfate, and a cartilage proteoglycan, having different known chain conformations as determined by X-ray diffraction. The dichroism data for the vibrational modes of the amide and carboxyl groups have been interpreted with respect to the particular molecular structures.

Crystallization↗