摘要:

AbstractTensile testing of tissue strips has been used to examine the effect of simple fixation in glutaraldehyde and formaldehyde on the viscoelastic properties of bovine pericardium. To assess tissue anisotropy, tissue strips were cut at 0°, 30°, 60°, and 90° relative to the base‐to‐apex direction. Fresh anterior pericardium was modestly anisotropic, being least extensible in the base‐to‐apex direction; however, fixation removed this anisotropy. Fixation also produced a marked change in the response of the material to initial cyclic loading during preconditioning. Overall extensibility of the fixed material was significantly greater than that for the fresh tissue, consistent with a 10.7% shrinkage in aldehydes calculated from strain at fracture data. Reductions in stress relaxation and creep after fixation were noted as well, consistent with intrafibrillar crosslinking. Cyclic hysteresis and ultimate tensile strength were unaffected. Since the observed changes in the stress–strain response were largely attributable to shrinkage, control of shrinkage by physical means would allow for engineering modification of bovine pericardial mechanics for controll

ISSN:0021-9304    

DOI:10.1002/jbm.820230502

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractOur previous article suggested that control of the extensibility of aldehyde‐fixed pericardium could be achieved by controlling shrinkage during fixation. Therefore, to prevent shrinkage, we have used sandpaper‐lined plexiglass plates to clamp circular samples of bovine pericardium during fixation in glutaraldehyde, tethering them at their original dimensions. As well, we have applied transmural pressures of 50 or 100 mm Hg during fixation using a hydraulic column of glutaraldehyde solution. Strips cut at 0°, 30°, 60° and 90° to the base‐to‐apex cardiac direction have been examined for cyclic stress–strain response, stress relaxation, plastic deformation, and fracture behavior. Under physiological stresses, tethered and pressure‐fixed materials were both nearly isotropic. Tethering during fixation produced a material with extensibility nearly identical to that of fresh tissue. Plastic deformation during cyclic loading was reduced below that seen in simple fixation while stress relaxation was unchanged. Pressure‐fixation produced reduced extensibility similar to that produced in porcine aortic valve leaflets. Plastic deformation and stress relaxation were both markedly reduced. Pressure‐fixation reduced the strain at fracture, but fracture behavior was otherwise unaffected. Tethering and pressure‐fixation offer attractive means to control the mechanical behavior of bovin

ISSN:0021-9304    

DOI:10.1002/jbm.820230503

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractOur previous two articles have shown that glutaraldehyde‐fixed bovine pericardium is nearly isotropic, whether fixed without constraints, with tethering, or with pressure. In this study, we have used uniaxial stress during fixation to produce bovine pericardial material with marked tensile anisotropy. Rectangular and cruciate pericardial samples have been mechanically examined after one of four treatments: (i) fixation under 88‐kPa uniaxial stress, (ii) fixation under 176‐kPa uniaxial stress, (iii) 3 h of 176‐kPa uniaxial stress in saline followed by 24‐h fixation under the same stress, (iv) fixation under 176‐kPa uniaxial stress followed by a second fixation under 176‐kPa stress in a direction normal to the first. Strips of material were cut at 0°, 30°, 60°, and 90° to direction of the initial stress, and tested for response to cyclic loading, stress relaxation, plastic deformation, and fracture properties. Fixation under uniaxial stress produced anistropy similar to that seen in porcine aortic valve leaflets; however, the overall extensibility of the material depended on the applied stress and the aspect ratio of the stressed sample. While loading in saline produced no change, the sequential biaxial stressing produced a reduction in anisotropy, suggesting exposure of additional crosslinking sites. Uniaxial stress during fixation may be a useful method for construction of anisotropic hea

ISSN:0021-9304    

DOI:10.1002/jbm.820230504

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe fracture behavior of two types of urinary stones, namely struvite and calcium oxalate, during compression testing was studied. Scanning electron microscopy (SEM) was used to characterize the fracture surfaces. Both types of stone showed pseudo‐plastic behavior as indicated by their load‐displacement curve. The onset of nonlinear behavior was found to correspond to development of microcracks in the specimens. The compressive strength was defined as the stress calculated at the maximum load. In struvite samples, the maximum load corresponded with the development of large cracks parallel to the compressive axis. For oxalate stones a separation of the outer layer (crust) from the inner layer (core) marked the point of maximum load. The compressive strength of the struvite samples was found to depend on the orientation of lamellae relative to the loading axis. Struvite stones, when loaded parallel to the lamination direction showed a higher compressive strength than oxalate stones did. The fracture behavior and compressive strength of a model material (z‐brick) were also characterized and compared to those of the urinary s

ISSN:0021-9304    

DOI:10.1002/jbm.820230505

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractA new acetabular cup prosthesis made of alumina and bioactive glass was studied and evaluated using nondestructive and noninvasive Raman laser spectroscopy. The prosthesis consists of an alumina socket coated with a double layer of alumina beads bonded to the prosthesis with a layer of glass. Raman spectroscopy showed that both the socket and the beads are composed of α‐Al2O3(corundum), while the bioactive glass (alkaline and alkaline earth alumosilicate with a small quantity of zirconium oxide) showed this to have an intermediate structure between that of vitreous silica and that of the alkaline and alkaline earth disilicate glasses. The Raman spectra of the contact surfaces between the bioactive glass and the alumina of the assembled prosthesis and of an alumina disk coated with the same glass showed the presence of new bands which may be correlated with a chemical interaction between the components of the prosthes

ISSN:0021-9304    

DOI:10.1002/jbm.820230506

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820230507

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820230501

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY