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Haversian Systems (haversian + system)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

A Unique Microcracking Process Associated with the Inelastic Deformation of Haversian Bone

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009
Vincent Ebacher
Abstract Since the discovery of the Haversian system in human bone over three hundred years ago, researchers have been wondering about its mechanical advantages. Despite positive experimental evidences on the intervention of Haversian systems in the fracture process, the contributions of Haversian systems to bone fracture have been obscure. Here a unique microcracking process accompanying the inelastic deformation of Haversian bone is reported that may shine light on its structural advantages over other bones. When compressed transversely, the concentric bone lamellae surrounding each Haversian canal allow multiple radial microcracks and arc-shaped cracks to develop intralamellarly. Groups of circumferential arc-shaped microcracks develop in high shear zones and radiate out in oblique directions from each Haversian canal. At the cortical bone level, where the Haversian systems are randomly distributed within the interstitial matrix, multiple nucleations and stable development of such arc-shaped cracks happen to most Haversian systems progressively. As a result, Haversian bone is not sensitive to the presence of Haversian canals and demonstrates high inelastic strains at macroscopic level. [source]

Inside Front Cover: A Unique Microcracking Process Associated with the Inelastic Deformation of Haversian Bone (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009
Mater.
Human cortical bone is capable of adapting to the mechanical environment through dynamic remodeling of the Haversian systems. The presence of Haversian canals, however, also introduces stress concentration and could have detrimental effects on the fracture resistance of bone. How is the hierarchical structure in bone designed to alleviate such stress concentrations? On page 57, Vincent Ebacher and Rizhi Wang report a unique and stable microcracking process accompanying the inelastic deformation of Haversian bone. The results lead to the critical role of the well-organized bone lamellae surrounding each Haversian canal. [source]

A Unique Microcracking Process Associated with the Inelastic Deformation of Haversian Bone

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009
Vincent Ebacher
Abstract Since the discovery of the Haversian system in human bone over three hundred years ago, researchers have been wondering about its mechanical advantages. Despite positive experimental evidences on the intervention of Haversian systems in the fracture process, the contributions of Haversian systems to bone fracture have been obscure. Here a unique microcracking process accompanying the inelastic deformation of Haversian bone is reported that may shine light on its structural advantages over other bones. When compressed transversely, the concentric bone lamellae surrounding each Haversian canal allow multiple radial microcracks and arc-shaped cracks to develop intralamellarly. Groups of circumferential arc-shaped microcracks develop in high shear zones and radiate out in oblique directions from each Haversian canal. At the cortical bone level, where the Haversian systems are randomly distributed within the interstitial matrix, multiple nucleations and stable development of such arc-shaped cracks happen to most Haversian systems progressively. As a result, Haversian bone is not sensitive to the presence of Haversian canals and demonstrates high inelastic strains at macroscopic level. [source]

Behavior of dense and porous hydroxyapatite implants and tissue response in rat femoral defects

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2002
J.C.T. Andrade
Abstract Porous and dense hydroxyapatite cylinders (PHA and DHA) were implanted into cavities produced in rat femora and the sites of implantation were examined at different times over a period of 24 weeks by microradiologic and histological techniques. Microradiographs showed the presence of a layer of trabecular bone around the implants, which became more radiopaque and thinner along the experimental time. The microradiologic methodology used was suitable for the evaluation of the interface between hydroxyapatite and newly formed bone in nondecalcified materials. Microscopic observations showed that young bone grew over the surface of both types of implants after 1 and 2 weeks of surgery and that bone also grew inside PHA implants. Progressive bone absorption was observed in both types of implants after the fourth week. A layer of fibrous tissue was formed in the interface between new bone and DHA. Mature bone with haversian systems surrounded DHA implants and filled the pores of PHA implants throughout the experimental period. The pores of PHA implants were smaller than those commonly reported, which should have been a disadvantage, although it was observed that the extra cellular fluid induced disintegration of the ceramic granules, allowing the gradual growth of bone tissue into the spaces among them, without the interposition of fibrous tissue. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 62: 30,36, 2002 [source]