Biomedical subjects

A F Mak

Publications and source records attributed to A F Mak.

43 records · Page 3Linked to original sources

PubMed1986

The apparent viscoelastic behavior of articular cartilage--the contributions from the intrinsic matrix viscoelasticity and interstitial fluid flows.

Articular cartilage was modeled rheologically as a biphasic poroviscoelastic material. A specific integral-type linear viscoelastic model was used to describe the constitutive relation of the collagen-proteoglycan matrix in shear. For bulk deformation, the matrix was assumed either to be linearly elastic, or viscoelastic with an identical reduced relaxation spectrum as in shear. The interstitial fluid was considered to be incompressible and inviscid. The creep and the rate-controlled stress-relaxation experiments on articular cartilage under confined compression were analyzed using this model. Using the material data available in the literature, it was concluded that both the interstitial fluid flow and the intrinsic matrix viscoelasticity contribute significantly to the apparent viscoelastic behavior of this tissue under confined compression.

Animals↗

PubMed1986

Unconfined compression of hydrated viscoelastic tissues: a biphasic poroviscoelastic analysis.

A biphasic poroviscoelastic theory was used to analyze the unconfined compression creep and stress relaxation of a hydrated viscoelastic tissue. The intrinsic shear properties of the tissue matrix was described by an integral-type viscoelastic constitutive law while the intrinsic bulk property of the matrix was assumed to be linearly elastic. Parametric data were presented to show how the two major energy dissipative mechanisms, namely the interstitial fluid flow and the intrinsic matrix viscoelasticity, may each contribute to the apparent viscoelastic behavior of the whole tissue under unconfined compression. The hydraulic permeability of the tissue was found to enter in only as a scaling factor for time.

Biomechanical Phenomena↗

PubMed1984

Viscoelastic properties of proteoglycan subunits and aggregates in varying solution concentrations.

Using a cone-on-plate mechanical spectrometer, we have measured the linear and non-linear rheological properties of cartilage proteoglycan solutions at concentrations similar to those found in situ. Solutions of bovine nasal cartilage proteoglycan subunits (22S) and aggregates (79S) were studied at concentrations ranging from 10 to 50 mg ml-1. We determined: (1) the complex viscoelastic shear modulus G (omega) under small amplitude (0.02 radians) oscillatory excitation at frequencies (omega) ranging from 1.0 to 20.0 Hz, (2) the non-linear shear rate (gamma) dependent apparent viscosity napp (gamma) in continuous shear, and (3) the non-linear shear rate dependent primary normal stress difference sigma 1 (gamma) in continuous shear. Both the apparent viscosity and normal stress difference were measured over four decades of shear rates ranging from 0.25 to 250 s-1. Analysis of the experimental results were performed using a variety of materially objective non-linear viscoelastic constitutive laws. We found that the non-linear, four-coefficient Oldroyd rate-type model was most effective for describing the measured flow characteristics of proteoglycan subunit and aggregate solutions. Values of the relaxation time lambda 1, retardation time lambda 2, zero shear viscosity no, and nonlinear viscosity parameter muo were computed for the aggregate and subunit solutions at all of the solute concentrations used. The four independent material coefficients showed marked dependence on the two different molecular conformations, i.e. aggregate or subunit, of proteoglycans in solution.

Animals↗

PubMedDate not supplied

Effects of knee bracing on the sensorimotor function of subjects with anterior cruciate ligament reconstruction.

The sensorimotor performance of the knee joint in 31 subjects who had undergone unilateral anterior cruciate ligament reconstruction at least 5 months previously was tested under three bracing conditions, 1) the DonJoy Legend brace, 2) a mechanical placebo brace, and 3) no brace, in random order. The accuracy of the subjects' ability to reproduce specified knee joint angles was tested as well as the isokinetic performance of their knee muscles at 60 and 180 deg/sec. The results showed that subjects with the brace or placebo brace performed similarly in reproducing the knee joint positions, but both groups performed better than the subjects without a brace. Isokinetic tests revealed no difference among the three groups in extensor and flexor peak torque production at 60 deg/sec or total work done by the extensors and flexors at 60 and 180 deg/sec. These results suggest that knee bracing can improve the static proprioception of the knee joint, but not the muscle contractile function, in subjects with anterior cruciate ligament reconstruction under isokinetic testing conditions. The finding of similar performances for joint angle reproduction in the brace and placebo brace groups suggests that the apparent improvement in proprioception with knee bracing was not due to the mechanical restraining action of the brace.

Adult↗

PubMedDate not supplied

State-of-the-art research in lower-limb prosthetic biomechanics-socket interface: a review.

Scientific studies have been conducted to quantify attributes that may be important in the creation of more functional and comfortable lower-limb prostheses. The prosthesis socket, a human-machine interface, has to be designed properly to achieve satisfactory load transmission, stability, and efficient control for mobility. The biomechanical understanding of the interaction between prosthetic socket and the residual limb is fundamental to such goals. The purpose of this paper is to review the recent research literature on socket biomechanics, including socket pressure measurement, friction-related phenomena and associated properties, computational modeling, and limb tissue responses to external mechanical loads and other physical conditions at the interface. There is no doubt that improved biomechanical understanding has advanced the science of socket fitting. However, the most recent advances in the understanding of stresses experienced at the residual limb have not yet led to enough clinical consensus that could fundamentally alter clinical practice. Efforts should be made to systematically identify the major discrepancies. Further research should be directed to address the critical controversies and the associated technical challenges. Developments should be guided to offer clinicians the quantification and visualization of the interaction between the residual limb and the prosthetic socket. An understanding of comfort and optimal load transfer as patterns of socket interface stress could culminate in socket design expert systems.

Amputation Stumps↗

PubMedDate not supplied

State-of-the-art methods for geometric and biomechanical assessments of residual limbs: a review.

A review is presented on the state-of-the-art methods for geometric and biomechanical assessments of residual limb tissues. Residual limb assessments are needed throughout different stages of prosthetic management, namely preamputation, residual limb maturation, prosthetic design, prosthetic fitting, and subsequent follow-ups. Geometric assessments include the monitoring of the volumetric change as the residual limb matures after amputation. Geometric and biomechanical assessments of the residual limb are important considerations in prosthetic design. Quantitative geometric and biomechanical assessments are becoming more important in the development of a computer-aided system for prosthetic socket design. It is noted that, except for the external shape measurements of residual limbs, most of the instruments used in residual limb assessment are not particularly cost-effective for clinical applications in prosthetics. Further developments are needed to facilitate the incorporation of the internal geometric assessments and biomechanical assessments into the current computer-aided design systems for clinical prosthetics.

Amputation Stumps↗

PubMedDate not supplied

EMG analysis of voluntary elbow movements in subjects with spasticity.

Surface electromyography (EMG) signals were measured from the biceps brachii (BIC), the brachioradialis (BRD) and the triceps brachii (TRI) of seven young adults with pure spastic quadriplegia and eight normal individuals. The signals were analyzed in both the time domain and the frequency domain. The subjects sat in an adjustable chair and were asked to perform two voluntary tasks involving the elbow joint. For task A, the subjects moved the hand from the proximal target plate to the distal target plate and then back to the proximal one along the table plane. For task B, the subject followed the sound of a metronome (0.5 Hz), perform 5 elbow flexion/extension cycles in the vertical plane. Certain quantitative parameters were identified as statistically significant in describing quantitatively the condition of spasticity. Compared to the normal subjects, the spastic subjects showed significantly higher EMG activities for both the elbow flexors and extensor. The stretch/shortening (S/S) ratios for BRD and TRI were significantly different from those of the normal subjects. The power spectra analysis showed higher mean power frequency (MPF). MPF of BIC and TRI were uncorrelated for normal subjects, but correlated for the spastic subjects. It is speculated that low motor unit discharge rate and fiber type abnormalities may account for these differences.

Adult↗