Bio-Medical Materials and Engineering - Volume 13, issue 1

Authors: Januszewski, Maciej | Dąbrowski, Zbigniew | Adamus, Maria | Niedźwiedzki, Tadeusz

Article Type: Research Article

Abstract: In a hematopoietic microenvironment in vivo, spatial organisation of hematopoiesis is possible due to the existence of a three‐dimensional framework, the main part of which is formed by a branching population of stromal cells. Most of the previous in vitro studies, concerning long‐term bone marrow cultures, were based on a previously prepared, flat adherent layer of stromal cells. There are only few reports concerning the three‐dimensional growth pattern of the bone marrow stroma. In the present study we used a new three‐dimensional model of the stromal cell culture. The framework for the cultured stromal cells was a structure of a …nonliving trabecular bone (Unilab Surgibone). After a period of about four weeks the stromal cells created a spatial network which filled the intertrabecular spaces of the spongy bone. Show more

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 1-9, 2003

Authors: Regimbal, R.L. | DePaula, C. Alex | Guzelsu, N.

Article Type: Research Article

Abstract: The effect of phosphate ions on the mechanical properties of plexiform bone in tension was investigated with an in‐vitro model. Bone samples were treated with saline and phosphate ion solutions for three days at 25°C and 37°C and tested in tension. The mechanical properties of the bone samples treated with phosphate were not different than controls (saline treated). Electro kinetic measurements on plexiform bone particles treated with phosphate ions at 37°C showed that phosphate ions alter electro kinetic potentials of bone particles by interacting with bone mineral as compare to saline treated particles near physiological pH. Because of the limited …diffusion properties of intact plexiform bone tissue, the tension experiments indicate that, the effect of phosphate ions on the bone mineral–matrix interface is negligible after three days treatment. On the other hand, electro kinetic measurements demonstrated that in a short period of treatment time, phosphate ions diffuse through organic matrix barrier and interact with bone mineral when plexiform bone is in the particle form. As a final experiments bone samples were tested at 37°C in three point bending configuration for three days in saline and phosphate buffer solution. The maximum tension stress generated in bending samples was about 75 percent of the tension yield stress of the samples. The creep experiments showed that the bending rigidity of bone samples tested in phosphate solution reduced in time hence the creep deformation increased compare to control samples tested in saline. This observation is attributed to the acceleration of phosphate ion diffusion into the bending samples due to micro cracks accumulation in bone tissue during the creep experiments which facilitated the phosphate ion interaction with bone mineral. Show more

Keywords: Bone, mechanical properties, phosphate ions, electrokinetic, viscoelastic behavior, bonding at the mineral–organic interface

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 11-25, 2003

Authors: Gil, F.J. | Canedo, R. | Padrós, A. | Bañeres, M.V. | Arano, J.M.

Article Type: Research Article

Abstract: The fretting corrosion of five materials for implant suprastructures (cast‐titanium, machined‐titanium, gold alloy, silver–palladium alloy and chromium–nickel alloy), was investigated in vitro, the materials being galvanically coupled to a titanium ball‐and‐socket‐joint with tetrafluoroethylene under mechanical load. Various electrochemical parameters (Ecorr , icorr , Evans diagrams, polarization resistance and Tafel slopes) were analyzed. The microstructure of the different dental materials was observed before and after corrosion processes by optical and electron microscopy. It can be observed that the mechanical load produces an important decrease of the corrosion resistance. The cast and machined titanium had the most passive current density at a …given potential and chromium–nickel alloy had the most active critical current density values. The high gold content alloys have excellent resistance corrosion, although this decreases when the gold content is lower in the alloy. The palladium alloy had a low critical current density due to the presence of gallium in this composition but a selective dissolution of copper‐rich phases was observed through energy dispersive X‐ray analysis. Show more

Keywords: Corrosion, titanium, dental alloys, ball‐and‐socket joints

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 27-34, 2003

Authors: Shibata, Nobuyuki | Tomita, Naohide | Ikeuchi, Ken

Article Type: Research Article

Abstract: Numerical simulations were carried out using a DEM‐based model under a sliding fatigue environment to investigate the influences of differences of mechanical properties between intra‐granular portions and inter‐granular portions on local stress–strain fields and to determine the effect of gamma‐irradiative degradation of UHMWPE components on delamination. The predicted stress fields in the gamma‐irradiated UHMWPE component were highly nonuniform and were quite different from those predicted in the non‐irradiated UHMWPE component. The stress distributions were intensely affected by the structural inhomogeneousness of networked grain boundaries. Marked stress concentrations were observed along subsurface grain boundaries in the gamma‐irradiated UHMWPE. The gamma‐irradiated UHMWPE …showed a steep increase in the maximum equivalent stresses for an increase in the number of sliding. As the number of sliding increased, moreover, the region where the maximum equivalent stress was observed, moved deep into the specimen. These findings suggest that fatigue damage with plastic deformation proceeds mainly at a subsurface region in the gamma‐irradiated UHMWPE and at a superficial region in the non‐irradiated one. Therefore, gamma‐irradiation is an important factor in accelerating fatigue crack initiation resulting in delamination. Show more

Keywords: Ultra‐high molecular weight polyethylene (UHMWPE), fatigue, delamination, grain boundary, numerical simulation

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 35-45, 2003

Authors: Shibata, Nobuyuki | Tomita, Naohide | Ikeuchi, Ken

Article Type: Research Article

Abstract: To examine the effects of a networked substructure of granular agglomerate on a style of destruction in prosthetic ultra‐high molecular weight polyethylene (UHMWPE), uniaxial tensile simulations were carried out using the numerical model based on the discrete element method (DEM). The numerical simulations were performed taking the difference of mechanical characteristics between inter‐granular and intra‐granular portions of UHMWPE into consideration. A significant increase in stress and strain was observed along grain boundaries where micro cracks were initiated. This finding suggests that the large difference of mechanical properties between intra‐granular and inter‐granular portions causes significantly increased local stresses and strains in …the vicinity of grain boundaries. The tensile simulation resulted in intra‐granular destruction, which had good agreement with a result of previous experimental observation. This is presumably because the directions of principal shear stresses do not coincide with those at stress‐concentrated grain boundaries. The dependence of the style of material destruction on forms of loading application could be explained by the relationship between directions of principal shear stress and reorientations of stress‐concentrated grain boundaries. Show more

Keywords: Ultra‐high molecular weight polyethylene (UHMWPE), numerical simulation, stress concentration, grain boundary, uniaxial tension

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 47-57, 2003

Authors: Soman, N. | Banerjee, R.

Article Type: Research Article

Abstract: Vitreoretinal pathologies remain the significant leading cause of blindness, after cataract, throughout the world. Biomaterials as a whole, and vitreous substitutes in particular, have had a major role to play in vitreoretinal surgery. History has witnessed the advent of vitreous substitutes from collagen and hyaluronic acid to gases, silicone oils and perfluorocarbon liquids and now to polymer hydrogels. Such a long list only underscores the fact that we have been found wanting in our quest for an ideal vitreous substitute. This review focuses on the merits and demerits of various vitreous substitutes, which have been tried to date, clinical as …well as experimental. The properties required of an ideal substitute and the performance of the vitreous substitutes with respect to these criteria have been described. Finally, the concluding note dwells on the future directions for biomaterial research in the posterior segment of the eye and undermines the role of tissue engineering in vitreoretinal regeneration. Show more

Keywords: Vitreous, biomaterials, collagen and hyaluronic acid, silicone oil, polymer hydrogels

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 59-74, 2003

Authors: Lewis, Gladius

Article Type: Research Article

Abstract: The finite element analysis method was used to perform a sensitivity study of the effect of the materials used for the two layers of the outsole (high‐density polyethylene, HDPE, and polyurethane, PU) of a “solid rocker‐bottom” design of a therapeutic shoe on the responses (stresses and displacements) of a model of the shoe. It was found that the aforementioned materials choice affected the model responses in a noticeable manner. For example, when HDPE was used for the top layer of the outsole, the von Mises stress at the interface between the bottom of the foot and the top layer of …the insole ranged from being about 8% lower to being about 62% higher compared to when PU was used. The implications of this finding are discussed. Show more

Keywords: Therapeutic shoes, finite element analysis, von Mises stress

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 75-81, 2003

Authors: Ozeki, K. | Yuhta, T. | Aoki, H. | Fukui, Y.

Article Type: Research Article

Abstract: Hydroxyapatite (HA) and other calcium phosphates were synthesized on titanium plates by a solid–gas state reaction of sputtered CaO and vaporized P2 O5 . The calcium phosphates formed were HA, β‐tricalcium phosphate (β‐TCP; Ca3 (PO4 )2 ), β‐calcium pyrophosphate (β‐PYR; Ca2 P2 O7 ), and β‐calcium metaphosphate (β‐MET; Ca2 (PO3 )2 ). Their formation depended on the ratio of the sputtered CaO and the reacting P2 O5 . For a mole ratio of CaO/P2 O5 =4 (Ca/P=2), an HA film was synthesized. The surface roughness increased by over seven times after the solid–gas state reaction from Ra = 0.16±0.02 μm …(for the CaO film) to Ra = 1.15±0.25 μm (for the reacted film). The synthesized HA film‐coated titanium plates and control non‐coated titanium plates were implanted in the femora of two dogs for a period of two, four and 12 weeks, and observed using a soft X‐ray radiograph and histological sections. New bone formation was observed without any connective tissue at four weeks around the HA film, whereas over the 12 week experimental period, there was no new bone formation around the control and connective tissue was observed over all periods, reaching a thickness of more than 200 μm at 12 weeks. Show more

Keywords: Sputtered CaO, hydroxyapatite, vaporized P$_{2}$O$_{5}$, osteocompatibility

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 83-90, 2003

Authors: Mesfar, W. | Shirazi‐Adl, A. | Dammak, M.

Article Type: Research Article

Abstract: Proper isotropic and anisotropic friction constitutive equations are developed based on previous friction measurements at cancellous bone–porous coated implant interfaces exhibiting nonlinear load–displacement curves. The simulated friction response is dependent on relative tangential displacements in both orthogonal directions. The interface constitutive matrix contains cross‐stiffness terms identical in isotropic friction but different in anisotropic friction. These terms are due mainly to nonlinearity in response and vanish in unidirectional friction along a principal direction and in cases with Coulomb or linear friction. The interface ultimate resistance is evaluated by an elliptic criterion which becomes circular in isotropic cases. These constitutive relations …are implemented in a finite element program which is employed to analyze a bone cube sliding on top of a porous‐surfaced metallic plate, an experimental model used in our earlier measurements. The results for both isotropic and anisotropic frictions demonstrate the coupling between two orthogonal directions. The direction of resultant displacement under a variable load coincides with that of the load only when the friction is isotropic with coupling terms considered. In anisotropic friction, the resultant displacement occurs in a direction different from that of loading. Our previous bi‐directional measurements corroborate well the findings of this study. Show more

Keywords: Nonlinear friction, interface, coupling, finite element method, constitutive equations

Citation: Bio-Medical Materials and Engineering, vol. 13, no. 1, pp. 91-101, 2003