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W C Hayes - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical analysis of the experimental artifact in trabecular bone Compressive Modulus
    Journal of Biomechanics, 1993
    Co-Authors: T M Keaveny, R E Borchers, L J Gibson, W C Hayes
    Abstract:

    Abstract A theoretical analysis was performed to characterize potential experimental artifacts in conventional compression testing of trabecular bone, where strains are based on the relative displacements of the two loading platens. We assumed that the total experimental artifact for Modulus was the sum of a damage and friction artifact and derived equations to describe these artifacts. The two unknown constants in these equations were found using a combination of data derived from linear finite element analyses and in vitro uniaxial compression tests. Subsequent finite element analyses allowed estimation of the artifacts for a wide range of specimens (cube, 1:4-3:1 aspect ratio cylinders). If friction is completely eliminated at the specimen-platen interface, the Young's Modulus of a 5 mm sized (1:1 aspect ratio dimension) specimen which has a damage artifact due to machining may be underestimated by at least 45% regardless of specimen geometry; otherwise, the platens Modulus may vary from less than 30 to over 175% of the Young's Modulus, depending upon the specimen geometry and Poisson's ratio of the bone. Increasing the specimen size reduces the artifact only slightly. Since Poisson's ratio can be large for trabecular bone and is rarely known a priori, the precision of the conventional compression test will, therefore, be poor unless friction is completely eliminated at the specimen-platen interface. However, without friction at the interface, the platens Modulus will always underestimate Young's Modulus, thereby reducing the accuracy of this test. There was also evidence that the strength may be affected by these artifacts. Taken together, these data suggest that the conventional compression test can be precise but is rarely accurate, and that inter-study comparisons should be made with caution. Use of other methods such as ultrasound or direct attachment of extensometers to material away from the platens may overcome problems with accuracy. Finally, a protocol that eliminates friction and uses a 2:1 aspect ratio specimen may optimize precision.

  • Theoretical analysis of the experimental artifact in trabecular bone Compressive Modulus.
    Journal of biomechanics, 1993
    Co-Authors: T M Keaveny, R E Borchers, L J Gibson, W C Hayes
    Abstract:

    A theoretical analysis was performed to characterize potential experimental artifacts in conventional compression testing of trabecular bone, where strains are based on the relative displacements of the two loading platens. We assumed that the total experimental artifact for Modulus was the sum of a damage and friction artifact and derived equations to describe these artifacts. The two unknown constants in these equations were found using a combination of data derived from linear finite element analyses and in vitro uniaxial compression tests. Subsequent finite element analyses allowed estimation of the artifacts for a wide range of specimens (cube, 1:4-3:1 aspect ratio cylinders). If friction is completely eliminated at the specimen-platen interface, the Young's Modulus of a 5 mm sized (1:1 aspect ratio dimension) specimen which has a damage artifact due to machining may be underestimated by at least 45% regardless of specimen geometry; otherwise, the platens Modulus may vary from less than 30 to over 175% of the Young's Modulus, depending upon the specimen geometry and Poisson's ratio of the bone. Increasing the specimen size reduces the artifact only slightly. Since Poisson's ratio can be large for trabecular bone and is rarely known a priori, the precision of the conventional compression test will, therefore, be poor unless friction is completely eliminated at the specimen-platen interface. However, without friction at the interface, the platens Modulus will always underestimate Young's Modulus, thereby reducing the accuracy of this test. There was also evidence that the strength may be affected by these artifacts.(ABSTRACT TRUNCATED AT 250 WORDS)

Jeffrey M. Catchmark - One of the best experts on this subject based on the ideXlab platform.

  • Structural properties of starch-chitosan-gelatin foams and the impact of gelatin on MC3T3 mouse osteoblast cell viability
    Journal of biological engineering, 2017
    Co-Authors: Gregory E. Risser, Brittany L. Banik, Justin L. Brown, Jeffrey M. Catchmark
    Abstract:

    This study examines the effects of adding gelatin to a starch-chitosan composite foam, focusing on the altered structural and biological properties. The Compressive Modulus of foams containing different gelatin concentrations was tested in dry, wet, and lyophilized states. MC3T3 mouse osteoblast cells were used to test the composite’s ability to support cell growth. The stability of the foams in α-MEM culture media with and without cells was also examined. It was found that for dry foams, the Compressive Modulus increased with increasing gelatin content. For foams tested in wet and lyophilized states, the Compressive Modulus peaked at a gelatin concentration of 2.5% and 5%, respectively. The growth of MC3T3 mouse osteoblast cells was tested on the foams with different gelatin concentrations. The addition of gelatin had a positive effect on the cell growth and proliferation. The composite foam containing gelatin improved cell growth and is only dissolved by the growing cells at a rate influenced by the initial concentration of gelatin added to the foam.

  • Structural properties of starch-chitosan-gelatin foams and the impact of gelatin on MC3T3 mouse osteoblast cell viability
    Journal of Biological Engineering, 2017
    Co-Authors: Gregory E. Risser, Brittany L. Banik, Justin L. Brown, Jeffrey M. Catchmark
    Abstract:

    Background This study examines the effects of adding gelatin to a starch-chitosan composite foam, focusing on the altered structural and biological properties. The Compressive Modulus of foams containing different gelatin concentrations was tested in dry, wet, and lyophilized states. MC3T3 mouse osteoblast cells were used to test the composite’s ability to support cell growth. The stability of the foams in α-MEM culture media with and without cells was also examined. Results It was found that for dry foams, the Compressive Modulus increased with increasing gelatin content. For foams tested in wet and lyophilized states, the Compressive Modulus peaked at a gelatin concentration of 2.5% and 5%, respectively. The growth of MC3T3 mouse osteoblast cells was tested on the foams with different gelatin concentrations. The addition of gelatin had a positive effect on the cell growth and proliferation. Conclusion The composite foam containing gelatin improved cell growth and is only dissolved by the growing cells at a rate influenced by the initial concentration of gelatin added to the foam.

T M Keaveny - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical analysis of the experimental artifact in trabecular bone Compressive Modulus
    Journal of Biomechanics, 1993
    Co-Authors: T M Keaveny, R E Borchers, L J Gibson, W C Hayes
    Abstract:

    Abstract A theoretical analysis was performed to characterize potential experimental artifacts in conventional compression testing of trabecular bone, where strains are based on the relative displacements of the two loading platens. We assumed that the total experimental artifact for Modulus was the sum of a damage and friction artifact and derived equations to describe these artifacts. The two unknown constants in these equations were found using a combination of data derived from linear finite element analyses and in vitro uniaxial compression tests. Subsequent finite element analyses allowed estimation of the artifacts for a wide range of specimens (cube, 1:4-3:1 aspect ratio cylinders). If friction is completely eliminated at the specimen-platen interface, the Young's Modulus of a 5 mm sized (1:1 aspect ratio dimension) specimen which has a damage artifact due to machining may be underestimated by at least 45% regardless of specimen geometry; otherwise, the platens Modulus may vary from less than 30 to over 175% of the Young's Modulus, depending upon the specimen geometry and Poisson's ratio of the bone. Increasing the specimen size reduces the artifact only slightly. Since Poisson's ratio can be large for trabecular bone and is rarely known a priori, the precision of the conventional compression test will, therefore, be poor unless friction is completely eliminated at the specimen-platen interface. However, without friction at the interface, the platens Modulus will always underestimate Young's Modulus, thereby reducing the accuracy of this test. There was also evidence that the strength may be affected by these artifacts. Taken together, these data suggest that the conventional compression test can be precise but is rarely accurate, and that inter-study comparisons should be made with caution. Use of other methods such as ultrasound or direct attachment of extensometers to material away from the platens may overcome problems with accuracy. Finally, a protocol that eliminates friction and uses a 2:1 aspect ratio specimen may optimize precision.

  • Theoretical analysis of the experimental artifact in trabecular bone Compressive Modulus.
    Journal of biomechanics, 1993
    Co-Authors: T M Keaveny, R E Borchers, L J Gibson, W C Hayes
    Abstract:

    A theoretical analysis was performed to characterize potential experimental artifacts in conventional compression testing of trabecular bone, where strains are based on the relative displacements of the two loading platens. We assumed that the total experimental artifact for Modulus was the sum of a damage and friction artifact and derived equations to describe these artifacts. The two unknown constants in these equations were found using a combination of data derived from linear finite element analyses and in vitro uniaxial compression tests. Subsequent finite element analyses allowed estimation of the artifacts for a wide range of specimens (cube, 1:4-3:1 aspect ratio cylinders). If friction is completely eliminated at the specimen-platen interface, the Young's Modulus of a 5 mm sized (1:1 aspect ratio dimension) specimen which has a damage artifact due to machining may be underestimated by at least 45% regardless of specimen geometry; otherwise, the platens Modulus may vary from less than 30 to over 175% of the Young's Modulus, depending upon the specimen geometry and Poisson's ratio of the bone. Increasing the specimen size reduces the artifact only slightly. Since Poisson's ratio can be large for trabecular bone and is rarely known a priori, the precision of the conventional compression test will, therefore, be poor unless friction is completely eliminated at the specimen-platen interface. However, without friction at the interface, the platens Modulus will always underestimate Young's Modulus, thereby reducing the accuracy of this test. There was also evidence that the strength may be affected by these artifacts.(ABSTRACT TRUNCATED AT 250 WORDS)

Gregory E. Risser - One of the best experts on this subject based on the ideXlab platform.

  • Structural properties of starch-chitosan-gelatin foams and the impact of gelatin on MC3T3 mouse osteoblast cell viability
    Journal of biological engineering, 2017
    Co-Authors: Gregory E. Risser, Brittany L. Banik, Justin L. Brown, Jeffrey M. Catchmark
    Abstract:

    This study examines the effects of adding gelatin to a starch-chitosan composite foam, focusing on the altered structural and biological properties. The Compressive Modulus of foams containing different gelatin concentrations was tested in dry, wet, and lyophilized states. MC3T3 mouse osteoblast cells were used to test the composite’s ability to support cell growth. The stability of the foams in α-MEM culture media with and without cells was also examined. It was found that for dry foams, the Compressive Modulus increased with increasing gelatin content. For foams tested in wet and lyophilized states, the Compressive Modulus peaked at a gelatin concentration of 2.5% and 5%, respectively. The growth of MC3T3 mouse osteoblast cells was tested on the foams with different gelatin concentrations. The addition of gelatin had a positive effect on the cell growth and proliferation. The composite foam containing gelatin improved cell growth and is only dissolved by the growing cells at a rate influenced by the initial concentration of gelatin added to the foam.

  • Structural properties of starch-chitosan-gelatin foams and the impact of gelatin on MC3T3 mouse osteoblast cell viability
    Journal of Biological Engineering, 2017
    Co-Authors: Gregory E. Risser, Brittany L. Banik, Justin L. Brown, Jeffrey M. Catchmark
    Abstract:

    Background This study examines the effects of adding gelatin to a starch-chitosan composite foam, focusing on the altered structural and biological properties. The Compressive Modulus of foams containing different gelatin concentrations was tested in dry, wet, and lyophilized states. MC3T3 mouse osteoblast cells were used to test the composite’s ability to support cell growth. The stability of the foams in α-MEM culture media with and without cells was also examined. Results It was found that for dry foams, the Compressive Modulus increased with increasing gelatin content. For foams tested in wet and lyophilized states, the Compressive Modulus peaked at a gelatin concentration of 2.5% and 5%, respectively. The growth of MC3T3 mouse osteoblast cells was tested on the foams with different gelatin concentrations. The addition of gelatin had a positive effect on the cell growth and proliferation. Conclusion The composite foam containing gelatin improved cell growth and is only dissolved by the growing cells at a rate influenced by the initial concentration of gelatin added to the foam.

B B Seedhom - One of the best experts on this subject based on the ideXlab platform.

  • The relationship of the Compressive Modulus of articular cartilage with its deformation response to cyclic loading: does cartilage optimize its Modulus so as to minimize the strains arising in it due to the prevalent loading regime?
    Rheumatology (Oxford England), 2001
    Co-Authors: M. K. Barker, B B Seedhom
    Abstract:

    AIM To investigate the relationship of the instantaneous Compressive Modulus with its deformation response to cyclic loading typical of that encountered at the knee joint during level walking. METHOD The study was performed on 24 osteochondral plugs taken from three unembalmed cadaveric knees. As the Compressive Modulus of cartilage has been shown to vary topographically across the knee in an established manner, the specimens were taken from specific sites on the femur and tibia of each knee. All the cartilage specimens were immersed in Hanks' salt solution at 37 degrees C and were subjected to the same cyclic loading regimen that was representative of a typical walking cycle in a specialized indentation apparatus, for over 1 h. RESULTS AND CONCLUSION The viscous and elastic components of matrix strain, the creep rate and the cartilage Compressive Modulus were measured. The latter was found to be significantly related to the strain response of cartilage to cyclic loading. Elastic strain varied exponentially with the Compressive Modulus; specimens with a Modulus less than 4 MPa experienced elastic strains in the range 0.18-0.36, whereas stiffer specimens experienced strains between 0.05 and 0.13. Viscous strain varied linearly with cartilage stiffness and was as low as 0.02 at the lower values of the Compressive Modulus but increased to 0.22 for a Compressive Modulus of 18 MN/m(2). The rate of creep under cyclic load was inversely linearly related to cartilage stiffness. The strain response of soft specimens approached steady state by 200 cycles but that of stiff specimens did not approach it until 1300 cycles. It was hypothesized that the viscous strain response of cartilage can be explained in terms of differences in permeability between specimens of different Compressive Modulus, stiffer cartilage having a lower permeability than soft cartilage.

  • The 'instantaneous' Compressive Modulus of human articular cartilage in joints of the lower limb.
    Rheumatology (Oxford England), 1999
    Co-Authors: Duncan E.t. Shepherd, B B Seedhom
    Abstract:

    Methods. The instantaneous Compressive Modulus of articular cartilage was surveyed in 11 sets of human lower limb joints obtained from the ipsilateral side. The average Modulus for the entire joint surface of each joint and the topographical variations in the Modulus within each joint were examined for all 11 sets, and subjected to statistical analysis. Results. Within each set of joints (hip, knee and ankle), the ankle always had a significantly greater mean Compressive Modulus than the hip and knee (P< 0.001‐P< 0.05). In seven sets of joints, there was no significant diVerence between the mean Compressive moduli of the knee and hip joints. In three sets of joints, the Compressive Modulus of the knee was significantly greater than that of the hip (P< 0.001‐P< 0.01), while in only one set of joints was the Compressive Modulus of the hip significantly greater than that of the knee (P< 0.01). Conclusion. The topographical variations in the cartilage instantaneous Compressive Modulus over the surfaces of the lower limb joints were matched by diVerences in the stresses occurring in diVerent areas of each joint. The results of the present study corroborate previous findings and show that the site-specific stresses and corresponding values of the instantaneous cartilage Compressive Modulus over the surfaces of lower limb joints were correlated (r = 0.82 at P< 0.01), thus adding credence to the conditioning hypothesis of cartilage by prevalent stress.

  • A technique for measuring the Compressive Modulus of articular cartilage under physiological loading rates with preliminary results
    Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 1997
    Co-Authors: Duncan E.t. Shepherd, B B Seedhom
    Abstract:

    This paper describes a technique and apparatus for measuring the Compressive Modulus of articular cartilage under physiological loading rates. The Compressive Modulus is the most relevant property to the primary function of articular cartilage i.e. load carriage. It has been determined previously from measurement of cartilage deformation under slow or almost static loading conditions. The Modulus was based on deformations occurring 2 s after the initial application of load which greatly reduces its relevance since in physiological conditions joint loading occurs within 10-150 ms. Five human knee joints have been used to test the apparatus before a major study is undertaken. The preliminary results from these joints showed that the Compressive Modulus of articular cartilage measured within physiological loading time intervals was much greater than previously reported. The Compressive Modulus at 20 ms was in the range 4.4-27 MPa and was between 32 and 75 per cent greater than its value obtained at 2 s after loading.

  • MECHANICAL CONDITIONING OF ARTICULAR CARTILAGE TO PREVALENT STRESSES
    British journal of rheumatology, 1993
    Co-Authors: J. Q. Yao, B B Seedhom
    Abstract:

    The possible correlation between joint stresses and cartilage Compressive Modulus is examined. The stresses acting upon different areas of the joints and cartilage Compressive Modulus in these areas were obtained for 15 pairs of ipsilateral human ankle and knee autopsy joint specimens. It was found that the cartilage Compressive Modulus was significantly correlated with the mechanical stress (r = 0.889 at P < 0.02 level of significance) in such a manner that cartilage subjected to higher predominant stresses was significantly stiffer than that subjected to lower predominant stresses. This was true when comparing ankle with knee joints, and also when comparing different regions within one single joint. Such a correlation is significant in that it indicates that cartilage may well be conditioned mechanically by the prevalent stress it is subject to. However, this correlation of data obtained from autopsy specimens is a necessary, but not sufficient condition, for the above hypothesis to be true. It is, therefore, concluded that further work on animals is necessary.