Technology and Health Care - Volume 14, issue 4-5

Authors: Yang, T.H.J. | Leung, S.K.W. | Phipps, S. | Reuben, R.L. | McNeill, S.A. | Habib, F.K. | Schnieder, A. | Stevens, R.

Article Type: Research Article

Abstract: In vitro macro- and micro-indentation test systems have been designed to measure the dynamic micro-mechanical properties of human prostate tissues at actuation frequencies between 5 Hz and 30 Hz, and 0.5 Hz and 20 Hz, respectively. The development of in vitro test systems was aimed at assessing the capacity of such an in vivo medical probe to provide information useful for the diagnosis of various prostate diseases. The macro-indentation test system is an established one, which we have used to determine structure-property relationships in human and canine prostate tissues and here we use it to validate a newly-developed …micro-indentation test system using a tissue phantom. Mechanical testing was also carried out on sections of prostate tissue harvested from cystectomy and radical prostatectomy, diagnosed with bladder cancer and benign prostatic hyperplasia. Dynamic probing under displacement control was carried at pre-strains between 5% and 8% for macro-probing and at 5% pre-strain for micro-probing, and the general effect of pre-strain on the dynamic mechanical properties (described by the amplitude ratio between stress and strain, and the phase lag between strain and stress) of phantom and prostate tissues is presented. Specific point probing on epithelial and stromal histological components was also carried out showing a significant difference between the amplitude ratios of epithelial and stromal components for actuation frequencies exceeding 5 Hz. However, no significant difference was found between phase lags for epithelial and stromal tissues. Show more

Keywords: Dynamic modulus, soft tissue biomechanics, BPH, prostate

DOI: 10.3233/THC-2006-144-511

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 281-296, 2006

Authors: Lakshmanan, V. | Yang, T.H.J. | Reuben, R.L. | Hammer, J. | Else, R.W.

Article Type: Research Article

Abstract: The overall aim of this study is to establish relationships between the histology of biological tissues and their mechanical properties, especially their dynamic modulus. The emphasis is on the physical scale of the probe used in relation to the size of the histological features in the material of interest. The selection of a model system (connective tissue) is described along with a corresponding gelatin-based system in which the make-up of the material can be “engineered” reproducibly. Next three experimental rigs are described with regard to their suitability for making measurements at a variety of scales; the micro-scale, the …meso-scale and the macro-scale. Finally, some preliminary measurements on the micro-scale rig are presented and preliminary conclusions drawn on the methodology. Show more

Keywords: AFM, tissue-mimic, structure-property relationships, biological materials

DOI: 10.3233/THC-2006-144-512

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 297-309, 2006

Authors: Bursa, Jiri | Lebis, Radek | Janicek, Premysl

Article Type: Research Article

Abstract: The paper deals with problems related to computational modelling of stress-strain states in vascular smooth muscle cells (SMCs). First, motivation for stress-strain analysis of SMCs is presented. Problems of their structure, geometry, constitutive models and initial (stress-free) state are analyzed on the basis of anatomical, histological and physiological knowledge. Various types of computational FE models of SMCs are presented; their constitutive models are identified on the basis of published mechanical tests carried out with SMCs cultured in vitro. Results of two models are presented; the former is a homogeneous model of the cell tension test with hyperelastic constitutive relations of …the cell material. The latter model is more complex, it comprehends cortical and deep cytoskeleton, modelled as a tensegrity structure, and homogeneous linear elastic nucleus and remaining cytoplasm; it is used in computational modelling of indentation test. Perspectives, assumptions and limitations of computational modelling of SMCs under physiological load are discussed. Show more

DOI: 10.3233/THC-2006-144-513

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 311-320, 2006

Authors: Glinkowski, Wojciech | Górecki, Andrzej

Article Type: Research Article

Abstract: Introduction: The use of noninvasive, acoustic methods like ultrasonometry is becoming increasingly interesting in the quantitative assessment of fracture healing. A reliable measurement technique has been described using ultrasonic transducers placed across the fracture gap. Ultrasonic image aiming is useful for accurate transducers location, on both sides of the gap. The study was designed to assess the clinical application of measurement of ultrasonic wave propagation through the fracture callus. Material and Methods: Contact testing was performed with a prototype ultrasonic bone tester UTTK-01 device. The measuring technique was validated experimentally on human long bones in vitro, as well …on volunteers. Twenty four diaphyseal fractures of long bones were prospectively assessed. Transducers put on a fixed distance frame were properly placed with ultrasonographic focusing. Results: Average ultrasound propagation time was 1917 m/s. The measured values for fractures rose with time after injury. The average speed of sound measured between 10th and 21st day after fracture was 1200,85 m/s, after 7 to 8 weeks – 1559,35 m/s, after 12 weeks – 1640,64 m/s, after 16 weeks – 1735,72 m/s. Conclusions: We conclude that the technique for measuring long bone ultrasound velocity with ultrasonographic centering on the fracture gap allows repetitive positioning of ultrasonic transducers for measurement. Ultrasonic measurement of bone union may support or modify clinical decision. However, further studies are required to make the ultrasonometric method easier and more user friendly for clinical studies. Show more

Keywords: Fracture healing, assessment, monitoring, cortical bone, quantitative ultrasound, ultrasonometry

DOI: 10.3233/THC-2006-144-514

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 321-333, 2006

Authors: Blythe, A. | Tasker, T. | Zioupos, P.

Article Type: Research Article

Abstract: The performance of ACL grafts in both the short and long term is only as good as the condition of the graft at the time of surgery. If the graft lengthens under load at the two fixation ends incorporation will take longer to occur. Previous studies have shown that the various grafts currently used are strong enough. However, data on strength came primarily from quasistatic single pull to failure tests with, in some cases, modest cycling to precondition the grafts. The present study examined the in-vitro biomechanical behaviour of model ACL grafts, which have been fatigue cycled to failure over …a wide range of loads in physiological ambient conditions. Load/deformation curves and the stretch of the grafts was continuously recorded until final rupture. The grafts demonstrated typical creep-rupture like behaviour with elongation (non-recoverable stretch) and loss of stiffness leading to gradual failure. Some of the graft designs were consistently shown to elongate up to 20 mm in length within the first 2000 cycles at moderate physiological loads and a further 10 mm of elongation occurred between the initial preconditioned state and just prior to complete rupture. Not enough attention has been paid previously to the likely long term elongation patterns of ACL grafts post-surgery and even after the usual empirical preconditioning has been performed by the surgeon. Increased graft dimensions may result in recurrent knee instability and may also lead to failure of the graft to incorporate. Preconditioning in-vitro may still be a way to remove some slack and prepare the graft for its operational environment by stiffening in particular the tissue/fixation interface for those grafts that use soft polymer fixation ends. Show more

Keywords: ACL grafts, in-vitro biomechanical performance, (pre)conditioning, elongation, laxity

DOI: 10.3233/THC-2006-144-515

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 335-347, 2006

Authors: Mefti, Nacim | Ganghoffer, Jean François | Haussy, Bernard

Article Type: Research Article

Abstract: Cell adhesion plays an important role in biology: essentially with regard to immunizing defence and the transport of medicinal substances toward specific zones. The focus is here on the mechanical description of adhesion kinetics, in terms of the failure and creation of connections during the rolling phenomenon. Hence, we consider the case of a single cell, which is linked to a rigid substratum. A 2D model is established. We consider that the contact zone cell-wall is rectilinear and composed of vertical fibers and two horizontal rigid beams (complex cell membrane- fibers-vein wall). These connections are modeled by elastic …springs having identical elastic properties (e.g stiffness), but different failure strengths. The cell is subjected to the flow of plasma, which can generate the rolling phenomenon; we accordingly consider two distinct zones, one associated with the failure of the old fibers and one with the creation of the new fibers (in the direction opposite to the flow). Several interactions are taken into account in this model: van der Waals (attractive) and electrostatic (repulsive) forces and the effects of fluid pressure, assimilated into a periodic point force applied to the interface zone. We also study the vibration induced failure in the contact zone without mechanical damping using the principle of virtual work and a failure criterion to establish the equation of motion and the time evolution of the failure (dynamical approach). Rupture of a fiber can occur if the stress applied to the fiber is above a certain limit. These limits are determinated with using a probabilistic approach by use of a spectral method to simulate a stochastic and Gaussian field. Modeling of the creation of new fibers is also achieved by the combination of a dynamical and probabilistic method and a kinematical criterion. On the basis of these elements, numerical simulations are developed, that elucidate the rupture and rolling phenomena. Show more

Keywords: Cel, adhesion, failure, probabilistic description, fiber, time dependence

DOI: 10.3233/THC-2006-144-516

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 349-358, 2006

Authors: Lee, T.C. | O'Brien, F.J. | Gunnlaugsson, T. | Parkesh, R. | Taylor, D.

Article Type: Research Article

Abstract: Mechanobiology is concerned with the relationships between mechanical forces and biological processes. Bone adapts to altered mechanical loading by modelling and remodelling. Microdamage is a stimulus for adaptation as shown by a sheep overload model. If microdamage accumulates it leads to fracture failure, notably in osteoporosis. Detection methods, based on chelating fluorochromes and radiopaque agents, will enable microdamage to be quantified and, along with bone mass, aid in fracture prediction and prevention. Mechanobiological principles can be utilised to create tissue engineered bone grafts in cases of bone loss due to trauma, malignancy or resorption.

DOI: 10.3233/THC-2006-144-517

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 359-365, 2006

Authors: Taylor, David | Hazenberg, Jan | Lee, T. Clive

Article Type: Research Article

Abstract: Bone is able to detect its strain environment and respond accordingly. In particular it is able to adapt to over-use and under-use by bone deposition or resorption. How can bone sense strain? Various physical mechanisms have been proposed for the so-called cellular transducer, but there is no conclusive proof for any one of them. This paper examines the theories and evidence, with particular reference to a new theory proposed by the authors, involving damage to cellular processes by microcracks. Experiments on bone samples ex-vivo showed that cracks cannot fracture osteocytes, but that cellular processes which span the crack can be …broken. A theoretical model was developed for predicting the number of broken processes as a function of crack size and applied stress. This showed that signals emitted by fractured processes could be used to detect cracks which needed repairing and to provide information on the overall level of damage which could be used to initiate repair and adaptation responses. Show more

Keywords: Bone, adaptation, cellular transducer, remodelling, microdamage

DOI: 10.3233/THC-2006-144-518

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 367-377, 2006

Authors: Racila, M. | Crolet, J.M.

Article Type: Research Article

Abstract: It is well known that long term behavior of implants depends on bone remodeling. In the absence of a model of this phenomenon, few numerical simulations take into account bone remodeling. Some laws have been proposed but they cannot be used in the essential area surrounding the implant. We propose a multi-scale approach: cortical bone is structured in a hierarchical way consisting of five levels. The cortical part of a given bone is made up of various areas having different physical properties adapted to locally existing conditions. A Bony Elementary Volume denotes the elementary part of such a …zone which constitutes our first level. The other levels are in conformity with our previous studies: osteon, lamella, fibre and fibril. This latter is composed by collagen and hydroxyapatite (Hap) occurring in a viscous liquid containing mineral ions. Mathematical homogenisation theory is used to determine equivalent macroscopic properties of a BEV, knowing the physical properties of collagen and Hap and the architectural description of this bony structure. For improving the performance of our simulation software, a new behavior law has been introduced with no continuity between the various levels. The effect of the fluid at the nanoscopic scale is modeled by a constant pressure. Recent developments allow us to determine the magnitude of various entities at nanoscopic scale from information at the macroscopic level. Realized simulations show that the assumption of constant pressure is not sufficient to characterize the nanoscopic mechanical behaviour. This point needs a more complex model with the introduction of a coupling between structure and fluid. This aspect is in development. Show more

DOI: 10.3233/THC-2006-144-519

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 379-392, 2006

Authors: Hazenberg, Jan G. | Taylor, David | Lee, T. Clive

Article Type: Research Article

Abstract: It is well known for almost half a century that bones contain microcracks. Very little is known about the crack growth behaviour of very small cracks, e.g. the stage before they become macroscopically long. The aim of this work was to investigate the dynamic crack growth behaviour of sub-millimetre microcracks in cortical bone. It was found that slow stable crack growth occurs in specimens subjected to static loading conditions. Crack growth direction was dominated by the local fibre orientation of the bones. Crack angles varied between 10 and 36 degrees of the long axis of the bone. Short cracks were …found to show periods of rapid growth followed by intervals of temporary crack arrest. Histological analysis showed that crack arrest occurred due to vascular canals in the bone. During these periods of crack arrest, crack opening displacements increased until the local strain was sufficient to overcome these features. These observations indicate a mechanism for growth of small cracks in bone at constant stress, involving microstructural barriers, time-dependent deformation of material near the crack tip and strain-controlled propagation. Show more

Keywords: Microcracks, crack growth, microstructure

DOI: 10.3233/THC-2006-144-520

Citation: Technology and Health Care, vol. 14, no. 4-5, pp. 393-402, 2006