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An analysis of soft tissue loading in the foot
492
Abstracts
most noticeable changes occurred at the proximal and distal levels. At the proximal level, the strains (stresses) were reduced and in some cases reversed from that of the intact joint. At the most distal level the strains were increased, particularly with the insertion of a long-stem prosthesis. These tests suggest that the normal load transmitting function of the tibia1 bone undergoes redistribution after total knee arthroplasty. Clinically this could result in bone resorption and/or remodelling and the possible loosening of the prosthesis. F.
MODELLING
A STRAIN ENERGY FUNaION
FOR A GUINEA PIG GALLBLADDER
N. GUZELSU (L. S. U. Medical Center, Dept. of Orthopaedics,
LA)
A theoretical model is given for the elastic response of a Guinea pig gallbladder in its passive state. It is assumed that the gallbladder is incompressible, homogeneous and isotropic. The experimental points, which are obtained by the simple tension experiment, of the gallbladder rings in different positions and orientations support the above assumptions. The experimental points of rings, under the simple tension, (axial load vs stretch) in a semilogarithmic scale suggest that an exponential type strain energy function with two physical constants (strain energy function is only the function of the second strain invariant) can adequately describe the mechanical behavior of a Guinea pig gallbladder. This work implies that the experimental curves in semi-logarithmic scales (load vs stretch) can be used for choosing the simplest exponential type strain energy function for biological tissues. AN ANALYSIS OF SOFT TISSUE LOADING
IN THE FOOT
ROY D. CROWNINSHIELD and SACHIO NAKAMURA(Biomechanics Laboratory, Orthopaedic Surgery, University of Iowa, Iowa City, IA)
Department
of
During the performance of everyday activity, the foot is subjected to repeated loading which, in many cases, represents constant trauma and misuse. The biomechanical behavior of the foot is, at present, not well understood. In particular, the magnitudes of stresses developed within the plantar skin during foot function and the dependency of these magnitudes on shoe design is not well-known. This presentation reports on a planar. large displacement and nonlinear finite element stress analysis of the foot within a shoe. The foot is modelled with a bony skeleton and plantar region of thick skin. An experimental determination of skin material properties revealed a highly nonlinear and nearly incompressible behavior. The elastic properties of the shoe sole are represented in the model by a variety of both linear and nonlinear materials. Shoe soles were considered with regard to their effect on the resulting stress developed within the plantar skin. ENHASCED
DIFFUSION IN LUSG GAS MIXING
H. D. VAN LIEW and D. J. WILKINSON(Department of Physiology, State University of New York at Buffalo, Buffalo. NY) Our goal was to discover whether convective processes, during inspiration and during the disturbances caused by each heart beat, have a significant effect on gas mixing in the lung. We compared experimental results obtained with subjects in a hyperbaric environment, in which mixing is poorer than normal, with predictions from our computer model which simulates gas diffusion in a lung-shaped vessel. The results show that the model simulations will correspond to the experimental data only if input for either diffusivity or time for diffusion is much larger than the true values. We conclude that molecular diffusion is enhanced, by a factor of about 6, by convective processes in the lung. (Supported in part by NHLBI Grant POl-HL-14414
and ONR Contract NOOO14-76-000471).
MASS TRANSPORT TO PULSATILE FLOWS IN CIRCULAR TUBES GIVE\
CUR\‘.ATL’RE I\
\ ARIOC’S
DIFFERENT PATTERNS
P. D. RICHARDSON, P. M. GALLETTI(Brown University, Providence, Rhode Island, U.S.A.) and K. TANISHITA(Tokyo Women’s Medical College, Tokyo, Japan) Mass transport through the tube-walls is enhanced when the tubes are curved instead of straight Analysis of the flow [e.g. F. T. SMITH (1975) JournalofFIuid Mechnnics 71,151 has concentrated on helical curvature where the radius remains constant. Biomedical application of curved tube devices (e.g. implantable artificial lungs may use tubes given curvature in various patterns. Mass transfer has been measured in rirro using both water and blood with
Abstracts
most noticeable changes occurred at the proximal and distal levels. At the proximal level, the strains (stresses) were reduced and in some cases reversed from that of the intact joint. At the most distal level the strains were increased, particularly with the insertion of a long-stem prosthesis. These tests suggest that the normal load transmitting function of the tibia1 bone undergoes redistribution after total knee arthroplasty. Clinically this could result in bone resorption and/or remodelling and the possible loosening of the prosthesis. F.
MODELLING
A STRAIN ENERGY FUNaION
FOR A GUINEA PIG GALLBLADDER
N. GUZELSU (L. S. U. Medical Center, Dept. of Orthopaedics,
LA)
A theoretical model is given for the elastic response of a Guinea pig gallbladder in its passive state. It is assumed that the gallbladder is incompressible, homogeneous and isotropic. The experimental points, which are obtained by the simple tension experiment, of the gallbladder rings in different positions and orientations support the above assumptions. The experimental points of rings, under the simple tension, (axial load vs stretch) in a semilogarithmic scale suggest that an exponential type strain energy function with two physical constants (strain energy function is only the function of the second strain invariant) can adequately describe the mechanical behavior of a Guinea pig gallbladder. This work implies that the experimental curves in semi-logarithmic scales (load vs stretch) can be used for choosing the simplest exponential type strain energy function for biological tissues. AN ANALYSIS OF SOFT TISSUE LOADING
IN THE FOOT
ROY D. CROWNINSHIELD and SACHIO NAKAMURA(Biomechanics Laboratory, Orthopaedic Surgery, University of Iowa, Iowa City, IA)
Department
of
During the performance of everyday activity, the foot is subjected to repeated loading which, in many cases, represents constant trauma and misuse. The biomechanical behavior of the foot is, at present, not well understood. In particular, the magnitudes of stresses developed within the plantar skin during foot function and the dependency of these magnitudes on shoe design is not well-known. This presentation reports on a planar. large displacement and nonlinear finite element stress analysis of the foot within a shoe. The foot is modelled with a bony skeleton and plantar region of thick skin. An experimental determination of skin material properties revealed a highly nonlinear and nearly incompressible behavior. The elastic properties of the shoe sole are represented in the model by a variety of both linear and nonlinear materials. Shoe soles were considered with regard to their effect on the resulting stress developed within the plantar skin. ENHASCED
DIFFUSION IN LUSG GAS MIXING
H. D. VAN LIEW and D. J. WILKINSON(Department of Physiology, State University of New York at Buffalo, Buffalo. NY) Our goal was to discover whether convective processes, during inspiration and during the disturbances caused by each heart beat, have a significant effect on gas mixing in the lung. We compared experimental results obtained with subjects in a hyperbaric environment, in which mixing is poorer than normal, with predictions from our computer model which simulates gas diffusion in a lung-shaped vessel. The results show that the model simulations will correspond to the experimental data only if input for either diffusivity or time for diffusion is much larger than the true values. We conclude that molecular diffusion is enhanced, by a factor of about 6, by convective processes in the lung. (Supported in part by NHLBI Grant POl-HL-14414
and ONR Contract NOOO14-76-000471).
MASS TRANSPORT TO PULSATILE FLOWS IN CIRCULAR TUBES GIVE\
CUR\‘.ATL’RE I\
\ ARIOC’S
DIFFERENT PATTERNS
P. D. RICHARDSON, P. M. GALLETTI(Brown University, Providence, Rhode Island, U.S.A.) and K. TANISHITA(Tokyo Women’s Medical College, Tokyo, Japan) Mass transport through the tube-walls is enhanced when the tubes are curved instead of straight Analysis of the flow [e.g. F. T. SMITH (1975) JournalofFIuid Mechnnics 71,151 has concentrated on helical curvature where the radius remains constant. Biomedical application of curved tube devices (e.g. implantable artificial lungs may use tubes given curvature in various patterns. Mass transfer has been measured in rirro using both water and blood with