Handling characteristics of braided suture materials for tight tying

To establish criteria for characterizing synthetic sutures, the handling characteristics of silk suture were analyzed. The characteristics that distinguish silk suture from other braided suture materials are its good "knot security" and relatively low "tiedown resistance." Analytic consideration of knot security suggests that not only superficial friction but also resistance force produced by cross-sectional deformity of braided threads plays an important role in silk's superior performance. Results of a "pullout friction test," developed to quantitatively evaluate resistance produced by surface friction and cross-sectional deformity suggest that the superiority of silk thread can be explained in terms of high static withdrawal resistance under low loads and relatively low dynamic withdrawal resistance under high loads.

Assessment of pericardium in cardiac bioprostheses. A review

Cardiac valve bioprostheses are assessed in terms of their present and future clinical utility. The problems concerning durability basically involve early failure due to tears in the valve leaflets and late failure mainly associated with calcification of the biological tissue. New strategies for selection and chemical treatment of the biomaterials employed are analyzed, and the available knowledge regarding their mechanical behavior is reviewed. It is concluded that the durability of these devices, and thus their successful use in the future, depends on the knowledge of the interactions among the different biomaterials of which they are composed, the development of new materials, and the engineering design applied in their construction.

Characterization of hydroxyapatite and titanium coatings sputtered on Ti-6Al-4V substrate

A series of thin (<10 microm), single-layered HA/Ti coatings were deposited on Ti-6Al-4V substrate using a radio frequency magnetron-assisted sputtering system. The adhesion strength, microstructure, and chemistry of the coatings were characterized. Experimental results showed that higher Ti contents in targets or coatings resulted in higher deposition rates. When Ti was added the highly crystalline structure of monolithic HA coating was largely disrupted and the coating became amorphous-like. The highly crystalline structure of the monolithic Ti coating was also disrupted by introducing small amounts of Ca, P, and O into the coating. The HA/Ti coatings had quite uniform thicknesses and appeared smooth, dense, and well bonded to the substrate. A scanning electron microscope with an energy dispersive spectroscopy system showed that monolithic HA, 95HA/5Ti, 25HA/75Ti, and 50HA/50Ti coatings had the lowest Ca/P ratios while the 75HA/25Ti coating had the highest. The adhesion strengths of all coatings were between 60 and 80 MPa.

Influence of self-etching primer drying time on enamel bond strength of resin composites

OBJECTIVES

In clinical situations, a dentine primer is usually applied to enamel, in addition to dentine. This study was carried out to determine the influence of the air drying time of self-etching primers on their bond strength to enamel.

METHODS

Three self-etching primer systems, Fluoro Bond (FB, Shofu Inc.), Liner Bond II (LB, Kuraray Co.) and Mac Bond 2 (MB, Tokuyama Co.) were employed. Bovine mandibular incisors were mounted in self-curing resin and the enamel surfaces were wet ground with number 600 SiC paper. Following primer application, the enamel surface was dried with compressed air for 0, 2, 5, 10, 20, and 30 s from 10 cm above the enamel surface using a three-way syringe. Adhesives were applied and composites were condensed into a Teflon mold (4 x 2 mm) placed on the enamel and light activated. Ten samples per test group were stored in 37 degrees C water for 24 h, then shear tested at a crosshead speed of 1.0 mm min-1. One-way ANOVAs followed by Duncan tests (p < 0.05) were done.

RESULTS

The enamel bond strengths varied with the different air drying times and ranged from 8.2 +/- 3.2-17.4 +/- 3.0 MPa for LB, 10.9 +/- 2.8-16.3 +/- 3.3 MPa for FB, and 17.5 +/- 2.5-19.4 +/- 2.2 MPa for MB. For LB and FB, there appeared to be a minimum drying time of 10 s. LB was the most affected by drying time, while MB did not change.

CONCLUSIONS

The data suggests that the enamel bond strengths of these bonding systems can be influenced by the drying time of the primer applied prior to bond agent application and the tendency was different among the systems studied.

A tracing evoked potential estimator

The paper presents an adaptive Gaussian radial basis function neural network (RBFNN) for rapid estimation of evoked potential (EP). Usually, a recorded EP is severely contaminated by background ongoing activities of the brain. Many approaches have been reported to enhance the signal-to-noise ratio (SNR) of the recorded signal. However, non-linear methods are seldom explored due to their complexity and the fact that the non-linear characteristics of the signal are generally hard to determine. An RBFNN possesses built-in non-linear activation functions that enable the neural network to learn any function mapping. An RBFNN was carefully designed to model the EP signal. It has the advantage of being linear-in-parameter, thus a conventional adaptive method can efficiently estimate its parameters. The proposed algorithm is simple so that its convergence behaviour and performance in signal-to-noise ratio (SNR) improvement can be mathematically derived. A series of experiments carried out on simulated and human test responses confirmed the superior performance of the method. In a simulation experiment, an RBFNN having 15 hidden nodes was trained to approximate human visual EP (VEP). For detecting human brain stem auditory EP (BAEP), the approach (40 hidden nodes and convergence rate = 0.005) speeded up the estimation remarkably by using only 80 ensembles to achieve a result comparable to that obtained by averaging 1000 ensembles.

Experimental validation of arthroscopic cartilage stiffness measurement using enzymatically degraded cartilage samples

In order to evaluate the ability of the arthroscopic indentation instrument, originally developed for the measurement of cartilage stiffness during arthroscopy, to detect cartilage degeneration, we compared changes in the stiffness with the structural and constitutional alterations induced by enzymes on the tissue in vitro. The culturing of osteochondral plugs on Petri dishes was initiated in Minimum Essential Medium with Earle's salts and the baseline stiffness was measured. Then, the experimental specimens were digested using 50 microg ml(-1) trypsin for 24 h, 0.1 U ml(-1) chondroitinase ABC or 30 U ml(-1) purified collagenase (type VII) for 24 h or 48 h (n = 8-15 per group). The control specimens were incubated in the medium. After the enzyme digestion, the end-point stiffness was measured and the specimens for the microscopic analyses were processed. The proteoglycan (PG) distribution was analysed using quantitative microspectrophotometry and the quantitative evaluation of the collagen network was made using a computer-based polarized light microscopy analysis. Decrease (p < 0.05) of cartilage stiffness was found after 24 h trypsin (36%) and 48 h chondroitinase ABC (24%) digestion corresponding to a decrease (p < 0.01) of up to 80% and up to 30% in the PG content respectively. Decrease of the superficial zone collagen content or arrangement (78%, p < 0.001) after 48 h collagenase digestion also induced a decrease (30%, p < 0.001) in cartilage stiffness. We conclude that our instrument is capable of detecting early structural and compositional changes related to cartilage degeneration.

Surface fine structure of treated dentine investigated with tapping mode atomic force microscopy (TMAFM)

OBJECTIVES

The objective of this study was to investigate the surface morphology and roughness of human dentine treated with different dentine conditioning agents with tapping mode atomic force microscopy (TMAFM).

METHODS

Dentine samples from third permanent molar teeth were prepared as flat disks. The samples were treated with different conditioning agents for 15-30 s: aqueous phosphoric acid and those supplied with three commercial adhesive products. The surface morphology and roughness was measured with tapping mode atomic force microscopy, a highly resolving method which minimises unwanted side effects of conventional AFM.

RESULTS

The tubules, the areas between the tubules and the entire surface showed variations in surface morphology and roughness, depending on the conditioning agent used. These differences might affect the bonding properties of the agents in dentine/polymer systems.

CONCLUSIONS

The surface structure, such as the tubules diameters and depths, the local height differences of the surface between the tubules and the overall mean surface roughness Ra varies between samples treated with different conditioning agents. All conditioning agents, however, led to exposed and open tubules.

CLINICAL RELEVANCE

The direct observation of effects of conditioning agents on dentine is important in order to judge their performance under clinically relevant conditions-free of desiccation artefacts. A vast number of conditioning agents is available today. The differences in their actual effects on dentine surfaces, however, are less than clear to many users.

Behavior of bone marrow cells cultured on three different coatings of gel-derived bioactive glass-ceramics at early stages of cell differentiation

Previous studies have shown different macrophage responses to three compact pellets (with slightly different chemical composition) of gel-derived bioactive glass-ceramics of the CaO-P2O5-SiO2 system. In the present study primary bone marrow cells directed in vitro to form osteoblastic or osteoclastic cells were cultivated on glass slides coated by these three glass-ceramics. Glass slides were used as controls. In osteoblastic cultures alkaline phosphatase activity varied, depending on the type of coatings. Northern analysis showed high mRNA expressions of bone-related proteins on both the glass-ceramics and control glass. Mineralized nodules were not formed on the control glass, but coating glass slides with the glass-ceramics promoted mineralization without any substantial differences between the types of coatings. In osteoclastic cultures, the normal morphology of tartrate resistant acid phosphatase-positive multinucleated cells on standard culture plates was altered on the control glass and the glass-ceramics. The number of these cells differed, depending on the type of coatings, with no particular differences in the arrangement of F-actin by these cells. These analyses demonstrate complete biocompatibility of the glass-ceramic coatings but not the control glass, on which the cells failed to form mineralized nodules. The phenotype expression of the cells appeared to be influenced by microstructure, surface roughness, and the general character of the coatings rather than their surface reactivity.

Innovative technology for tissue disruption by explosive-induced shock waves

We have developed a novel, less invasive, shock wave source that can be introduced into an arbitrary position in a human body percutaneously. Using this technique we can disrupt cells locally. The shock wave source consists of an explosive, an optical fiber, a balloon catheter, and a Nd:YAG laser, which generates a spherical explosive shock wave. The destructive potential of the present source for injuring tissue was confirmed and the subsequent cell elongation and split in the direction of the shock wave has been observed.

Effects of serum protein opsonization on cytokine release by titanium-alloy particles

This study tested whether macrophages respond differently to retrieved titanium-alloy particles than they do to machined titanium-alloy particles and assessed whether pretreatment of machined titanium-alloy particles with human serum would influence macrophage activation and cytokine release in vitro. Human monocyte/macrophages were isolated from normal healthy donors and exposed to increasing concentrations of machined and retrieved titanium-alloy particles. The profile of cytokine release was determined by commercially available ELISA kits. Machined titanium-alloy particles were opsonized with human serum and added to macrophage cultures. Serum protein binding was confirmed by SDS-PAGE analysis. The results showed that machined titanium-alloy particles and retrieved titanium-alloy particles stimulate a similar level of cytokine release when tested at comparable concentrations. Opsonization of the machined particles with human serum increased the macrophage release of cytokines in the first 12 h after exposure compared to nonopsonized particles. At 24 h, the opsonized particles stimulated significantly higher levels of cytokine release, but only at the greatest particle concentrations. This study demonstrates that machined titanium alloy induces a metabolic response in macrophages similar to that of titanium-alloy particles retrieved from failed total hip arthroplasty. In addition, these data show that serum protein binding to orthopedic biomaterial debris alters the macrophage reaction to the particles.

Simulation of pressure drop and energy dissipation for blood flow in a human fetal bifurcation

The pressure drop from the umbilical vein to the heart plays a vital part in human fetal circulation. The bulk of the pressure drop is believed to take place at the inlet of the ductus venosus, a short narrow branch of the umbilical vein. In this study a generalized Bernoulli formulation was deduced to estimate this pressure drop. The model contains an energy dissipation term and flow-scaled velocities and pressures. The flow-scaled variables are related to their corresponding spatial mean velocities and pressures by certain shape factors. Further, based on physiological measurements, we established a simplified, rigid-walled, three-dimensional computational model of the umbilical vein and ductus venosus bifurcation for stationary flow conditions. Simulations were carried out for Reynolds numbers and umbilical vein curvature ratios in their respective physiological ranges. The shape factors in the Bernoulli formulation were then estimated for our computational models. They showed no significant Reynolds number or curvature ratio dependency. Further, the energy dissipation in our models was estimated to constitute 24 to 31 percent of the pressure drop, depending on the Reynolds number and the curvature ratio. The energy dissipation should therefore be taken into account in pressure drop estimates.

Elastomers for biomedical applications

Current topics in elastomers for biomedical applications are reviewed. Elastomeric biomaterials, such as silicones, thermoplastic elastomers, polyolefin and polydiene elastomers, poly(vinyl chloride), natural rubber, heparinized polymers, hydrogels, polypeptides elastomers and others are described. In addition biomedical applications, such as cardiovascular devices, prosthetic devices, general medical care products, transdermal therapeutic systems, orthodontics, and ophthalmology are reviewed as well. Elastomers will find increasing use in medical products, offering biocompatibility, durability, design flexibility, and favorable performance/cost ratios. Elastomers will play a key role in medical technology of the future.

Dynamic behavior of bubbles during extracorporeal shock-wave lithotripsy

The interaction of air bubbles attached to gelatin surfaces, extirpated livers or abdominal aortas of rats with underwater shock waves was investigated to help clarify the tissue-damage mechanism associated with cavitation bubbles induced during extracorporeal shock-wave lithotripsy. The overpressure of the shock wave was 10.2 +/- 0.5 MPa. The initial bubble radii varied from 0.12 to 3.06 mm. The subsequent collapse of the bubbles was recorded by a high-speed camera. The liver-cell damage was histochemically evaluated. The bubble attached to gelatin or rat's liver surface migrates away from the surface with an oscillatory growth/collapse behavior after the shock-wave interaction. The penetration depth of the liquid jet into the gelatin and the radius of the subsequent damage pit on the surface depend on the initial bubble radius. The elongation and split of the nuclei in the liver parenchymal cells in the direction of the liquid jet and the increase in the cell density within the circumference of the injured region are revealed histologically.

Dental materials: 1996 literature review. Part 2

This critical review of the published literature on dental materials for the year 1996 has been compiled by the Dental Materials Panel of the UK. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, resin-bonded bridges and ceramo-metallic restorations, ceramics, denture base resins and soft lining materials, impression materials, implants materials, orthodontic materials, biomechanics and image processing, resin composites and casting investment materials and waxes). Three hundred and thirteen articles have been reviewed.

Effects of exercise at different ages on bone density and mechanical properties of femoral bone of aged mice

We determined the bone density and mechanical properties of bone specimens from 5 groups of aged mice, which had been subjected to voluntary exercise at different ages. ICR 10-week-old female mice were divided into control (C), and exercise-trained during age periods of 10-70 weeks (EE), 10-30 weeks (GPE), 30-50 weeks (MPE) and 50-70 weeks (APE). It was found that in the exercise-trained groups body weight gain was suppressed during the exercise-training period, and that de-training accelerated weight gain. Bone density was significantly higher in all the exercise-trained groups than in the C group and cortical thickness index (CTI) was higher in the exercise-trained groups, except for the APE group. Maximum breaking force, ultimate stress and elasticity in the exercise-trained groups were higher than in the C group except for the APE group, whereas deformation in the APE group had a tendency to be higher than in the other groups. Blood C-terminal parathyroid hormone, calcitonin and calcium concentrations were similar among every group, but phosphorus concentrations tended to be higher in the exercise-trained groups than in the C group. These observations suggest that exercise-training at every age suppresses age-associated bone loss, and that the effect of exercise during youth is greater than that during old age. The results of this study suggest that the effect of exercise on bone at an older age is different from that at other ages.

Bioactive surface coatings for nanoscale instruments: effects on CNS neurons

A method is described for depositing onto medical instruments highly biocompatible and bioactive surface coatings that can promote and stabilize cell attachment. The coatings were made by first depositing thin films of materials, such as diamond-like carbon, or metals, including tantalum, tungsten, platinum, gold, iridium, palladium, and brass. These surfaces were further altered to either promote or inhibit cell growth and spreading by an additional overcoat of biological materials, including the extracellular matrix proteins, laminin, fibronectin, and collagen IV. The deposition technique used a metal or carbon plasma, and the important properties of film adhesion, hardness, density, and smoothness are tailored by control of the ion bombardment energy. The films are translucent enough to permit high resolution light microscopy for rapid and detailed examination of tissue response. These bioactive substrates have been tested on primary central nervous system neurons, and the growth response is excellent. Equally successful have been our attempts to anchor neurons, without associated proliferation of non-neuronal cells, using coatings of poly-d-lysine. The method and the materials could have important ramifications in a number of areas of research and biotechnology, for example for chronic implantation of microelectrode arrays in the cerebral cortex for neuroprosthetic and neural monitoring application and for research on the human central nervous system. Possible application in nonneuronal fields, such as for coronary artery stents and pacemaker electrodes, also are discussed.

Wear of polyethylene cups in total hip arthroplasty: a parametric mathematical model

This paper presents a parametric mathematical model of the head-cup wear coupling in total hip arthroplasty (THA). The model evaluates the dependence of acetabular volumetric wear upon the characteristic parameters of patient and hip prosthesis. Archard's law is assumed to calculate the wear coupling behaviour. The wear factor is taken from pin-on-disc wear tests as a function of materials and finishing of the articular joint. The forces acting on the hip joint are taken from experimental data found in the literature whilst the load distribution is calculated under the hypotheses of perfectly rigid ideal wear coupling. The sliding distance is obtained by combining the three elementary displacements -- due to rotations around the three axes -- at the generic bearing surface location. The simulations show that the polymeric wear volume per step cycle decreases ranging from fast walking speeds to low running speeds, it increases linearly with patient body weight and with femoral head diameter, it decreases slightly for positive variations of the socket inclination angle and it increases exponentially with femoral head roughness. The volumetric wear rate per year calculated for a standard reference patient is 5.8 mm3. The relevant iso-wear maps show a marginal pattern with the maximum located near the cup superior borderline. At the instant of peak load, the iso-stress maps show a paracentral pattern with the maximum superior to the cup polar point, and the iso-sliding distance maps show a marginal pattern with two maxima located near the cup's superior and inferior borderlines.

The viscoelastic behavior of the non-degenerate human lumbar nucleus pulposus in shear

The viscoelastic behavior of the nucleus pulposus was determined in shear under transient and dynamic conditions and was modeled using a linear viscoelastic model with a variable amplitude relaxation spectrum. During stress-relaxation tests, the shear stress of the nucleus pulposus relaxed nearly to zero indicative of the fluid nature of the tissue. Under dynamic conditions, however, the nucleus pulposus exhibited predominantly 'solid-like' behavior with values for dynamic modulus (magnitude of G*) ranging from 7 to 20 kPa and loss angle (delta) ranging from 23 to 30 degrees over the range of angular frequencies tested (1-100 rad s-1). This frequency-sensitive viscoelastic behavior is likely to be related to the highly polydisperse populations of nucleus pulposus molecular constituents. The stress-relaxation behavior, which was not linear on a semi-log plot (in the range t1 << t << t2), required a variable amplitude relaxation spectrum capable of describing this frequency sensitive behavior. The stress-relaxation behavior was well described by this linear viscoelastic model with variable amplitude relaxation spectrum; however, the dynamic moduli were underpredicted by the model which may be related to non-linearities in the material behavior.

The influence of the blunting of the apex on the flow in a vertebro-basilar junction model

The apex of human vertebro-basilar junctions can be sharp-edged or blunted. In the present study, the effect of blunted apex on the flow in vertebro-basilar junction models is investigated. We compared the flow phenomena in a series of junction models with blunted apices and confluence angles 45, 85, and 125 deg with the flow phenomena in a series of junction models with sharp-edged apices and the same range of confluence angles, studied in a previous paper (Ravensbergen et al., 1996b). The blunting of the apex appears to have an effect on the size of the local recirculation area near the apex and the prevailing low velocities. Large recirculation areas are found in the models with blunted apices, especially in those with small confluence angles. In addition, the blunting of the apex has no influence on the flow further downstream, nor on the structure and strength of the secondary flow field. Furthermore, a blunted apex appears to be a geometric risk factor for atherosclerosis. This supports the hypotheses that recirculation areas and low wall shear stress influence the development of atherosclerotic plaques.

Gentamicin-loaded hydraulic calcium phosphate bone cement as antibiotic delivery system

A hydraulic calcium phosphate cement made of beta-tricalcium phosphate [beta-Ca3(PO4)2], monocalcium phosphate monohydrate [Ca(H2PO4)2-H2O], and water was used as a delivery system for the antibiotic gentamicin sulfate (GS). GS, added as powder or as aqueous solution, was very beneficial to the physicochemical properties of the cement. The setting time increased from 2 to 4.5 min with 3% (w/w) GS and then slowly decreased to 3.75 min with 16% (w/w) GS. The tensile strength increased from 0.4 to 1.6 MPa with 16% (w/w) GS. These effects were attributed to the presence of sulfate ions in GS. The release of GS from the cement was measured in a pH 7.4 phosphate-buffered saline solution at 37 degrees C by USP paddle method. Factors such as cement porosity, GS content and presence of sulfate ions or polymeric additives were investigated. The amount of GS released was roughly proportional to the square root of time up to approximately 50% release. Afterwards, the release rate markedly slowed down to zero. In all but two cement formulations, the total dose of GS was released within 7 days, indicating that no irreversible binding occurred between the cement paste and the antibiotic. When small amounts of hydroxypropylcellulose or poly(acrylic acid) were added to the cement, the maximum fraction released was a few percent lower than the total GS dose, suggesting some binding between the polymer and GS. The GS release rate was strongly influenced by the presence of sulfate ions in the cement paste and by the cement porosity. The higher the sulfate ion content of the cement paste, the lowe the GS release rate. This influence was attributed to the finer cement micro-structure induced by the presence of sulfate ions. Furthermore, when the initial cement porosity was increased from 38 to 69%, the release rate almost tripled (0.16 to 0.45 h-1/2). Finally, the biological activity of GS in the cement was maintained, as measured by assaying the release medium.

Methods for the treatment of collagenous tissues for bioprostheses

Collagenous tissue as a biomaterial possesses many favourable characteristics and advantages over synthetic materials. The resemblance to human tissue suggests that it has a performance advantage over alternative materials. This advantage has been exploited to produce clinical devices that have been implanted in patients for more than a quarter of a century. The method of treating collagenous tissue for bioprostheses has developed from crude exposure of tissue to chemicals to a sophisticated level of considering the biochemical, chemical, engineering and clinical aspects of the process. This review focuses on the various chemical and physical treatments that have made the bioprostheses possible, highlighting the chemical agents and the cross-linking mechanism involved.

In vitro bone formation by rat marrow cell culture

Fresh marrow cells were obtained from the femora Fischer rats and cultured in a medium containing 15% fetal calf serum (FCS) to leach confluent. After trypsinization, cells were subcultured at a cell density of 100 x 10(3)/35 mm well in the presence of FCS, 10 mM beta-glycerophosphate, 82 micrograms/mL ascorbic acid phosphate, and 10(-8)M dexamethasone (Dex). Osteoblastic cells and microscopic mineralized nodules began to appear at about 1 week after the subculture, and at 2 weeks many macroscopic nodules that showed high alkaline phosphatase activity (ALP) and appearance of bone Gla protein (BGP) mRNA were evident. As demonstrated by in situ hybridization, the mRNA was manifested by cuboid-shaped cells (osteoblastic cells). X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) showed the mineralization of fine crystals of hydroxyapatite comparable to natural rat bone mineral. In contrast to these findings, subculture done under the same conditions except for the lack of Dex did not show mineralized nodules, nor did they show the osteoblastic phenotype expression. These analyses indicate that Dex-induced mineralization using rat bone marrow cell culture is an in vitro counterpart of bone formed in vivo. Such a culture is useful for investigating materials/ osteogenic cells interactions.

Histomorphological reaction of bone to different concentrations of phagocytosable particles of high-density polyethylene and Ti-6Al-4V alloy in vivo

Wear debris has been implicated in the pathogenesis of loosening and osteolysis of total joint replacements by stimulating a foreign body and chronic inflammatory reaction capable of bone resorption. Whether increasing concentrations of wear particles have an adverse biological effect on bone has not been elucidated. We performed a histomorphological and semi-quantitative morphometric analysis of the reaction of bone to different concentrations of phagocytosable particles of high-density polyethylene (HDPE) and titanium 6-aluminium 4-vanadium alloy (Ti-6Al-4V) implanted in the rabbit tibia. The Ti-6Al-4V particles had a diameter of 4.0 +/- 4.4 microns (mean +/- SD); the HDPE particles averaged 4.7 +/- 2.1 microns. Suspensions of 10(6)-10(9) particles per ml were mixed in saline, sterilized, and introduced through a drill hole into the proximal tibia of 30 mature female rabbits. Controls included drilled, but non-implantable limbs. The animals were killed at 16 weeks and histological sections were made of the implant area. Histomorphological assessment was carried out using an interactive image analysis system. The parameters assessed included the presence of histiocytes, foreign body giant cells and inflammatory cells, the location and number of particles, the presence of haematopoeitic elements, fat or necrosis of the marrow, whether healing of the cortical window had taken place, and whether there was evidence of formation or resorption of bone by the periosteum, cortex and marrow. A semi-quantitative rating system was employed. Phagocytosable particles of Ti-6Al-4V and HDPE, in concentrations of 10(6)-10(9) particles per ml, evoked a histiocytic reaction without extensive fibrosis, necrosis or granuloma formation. This reaction occurred without disturbing the normal repair processes of bone formation and resorption to the surgical insult. A clear dose-response effect on the histological parameters assessed in this study was not noted. Using the present model, by 16 weeks, a similar "one time' particle load could be accommodated. The ongoing generation of particulate debris over a more extended period of time might be necessary before the remodelling processes of bone would be disturbed.

In vitro properties of a chitosan-bonded bone-filling paste: studies on solubility of calcium phosphate compounds

The present study investigated properties of various mixtures of organic acids (malic and malonic) and calcium phosphate compounds (beta-tricalcium phosphate, ashed bovine bone, and synthetic hydroxyapatite) with the objective of determining the optimum combination of organic acid and calcium phosphate compound for components of a chitosan-bonded bone-filling paste. beta-tricalcium phosphate was decomposed by malic acid and malonic acid, but these two acids did not decompose synthetic hydroxyapatite and ashed bovine bone. Assessment of ion release from a set paste containing either synthetic hydroxyapatite or ashed bovine bone indicated that only calcium ions were appreciably released after storing and stirring the set paste in physiologic saline for 7 days.

Helmets in surgical history

The relevance of historical experience is evident in a consideration of helmets designed for head protection in war, industry, sport and road transport. Modern helmets are designed to minimize the risk of brain damage by penetration and by blunt impact; where facial or ocular injury is likely, facial protection may be provided by visors, goggles or full-face helmets. The effectiveness of helmets should be monitored by studies of actual injuries; historically, surgeons have done this, in war and peace, for centuries.

Tissue engineering scaffolds using superstructures

Here, scaffolds as cell and tissue carriers are approached from an engineering point of view, emphasizing material superstructuring in the design of supports. Superstructure engineering provides optimal spatial and nutritional conditions for cell maintenance by the arrangement of structural elements (e.g. pores or fibres) so as to vary the order of cell to cell contact. This approach is illustrated in the design of several scaffolds: knitted fabrics as three-dimensional superstructures for optimized osteosynthesis implants, a new injectable open porous implant system, an angiopolar non-degradable ceramic cell carrier, and an injectable or microsurgically implantable entangled carrier system. The implications for tissue engineering are discussed.

Demineralized bone matrix as a template for mineral--organic composites

Mineralizing biological tissues are complex bioceramic-biopolymer composites engineered for a variety of functions. The organic and inorganic constituents, morphology, location, orientation, crystallinity and interactions exhibit materials or extremely fine microstructure, unique mechanical and physical properties with high strength and fracture toughness compared to the individual constituents. An understanding of mineralization, ultrastructural organization and interfacial bonding forces in mineralizing biological composite tissues, such as bone, may provide new strategies and techniques for the production of a novel class of man-made organic-ceramic composites. The present study explores the use of the organic matrix remaining after removal of the mineral phase by chelation with EDTA or solubilizing in HCl as a template for mineral deposition and the production of mineral-organic composites. Different pH conditions are employed to alter the inorganic phase which is deposited within the organic matrix. Mechanical testing and ultrastructural evaluations are carried out for characterization.

Role of cyclic plastic deformation in the wear of UHMWPE acetabular cups

The mechanisms of wear in ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator-tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet-like flakes from initial machining marks, and the other by the formation of fine ripple and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations.

Detection of brainstem auditory evoked potential by adaptive filtering

A method of detecting brainstem auditory evoked potential (BAEP) using adaptive signal enhancement (ASE) is proposed and tested in humans and cats. The ASE in this system estimates the signal component of the primary input, which is correlated with the reference input to the adaptive filter. The reference input is carefully designed to make an optimal and rapid estimation of the signal corrupted with noise, such as ongoing EEG. With a good choice of reference input, it is possible to track the variability of BAEP efficiently and rapidly. Moreover, the number of repetitions required could be markedly reduced and the result of the system is superior to that of ensemble averaging (EA). To detect BAEP in cats, only 30 ensemble averages are needed to obtain a reasonable reference input to the adaptive filter, and, for humans, 350-750 ensemble averages are sufficient for a satisfactory result. Using the LMS adaptive algorithm, individual BAEP can be obtained in real-time.

Effects of creep value and occlusal force on marginal adaptation of amalgam filling

Creep of amalgam is thought to be a factor determining poor marginal adaptation. Clarification of the relationship between creep of amalgam in the cavity and creep value (American Dental Association specification no. 1; ADA #1) is essential to an understanding of the mechanism of marginal fracture and service life. However, only elastic stress analyses of amalgam in a cavity have been reported in the dental field. Therefore, the creep of amalgam in a class I cavity was simulated by an axisymmetric elastic creep finite-element method. The stress and time dependencies of the creep rate of amalgam were incorporated into this calculation. Creep values of 1.0 and 3.0% (ADA #1) were selected as amalgam properties. When the occlusal force on the amalgam filling was assumed in the vertical direction along the axis of the tooth, the rate of extrusion and rate of opening of the gap at the cavity margin were revealed by the simulation. The computed results show that the gap and extrusion were developed in direct proportion of the creep value and proportionally with the square of the occlusal force. Simulated results are in agreement with clinical findings of the service lives of restorations, i.e., a poor adaptation to the margin can be seen for 4-to-10-year-old amalgam fillings.

The effect of in vitro fluoride ion treatment on the ultrasonic properties of cortical bone

The mechanical properties of composites are influenced, in part, by the volume fraction, orientation, constituent mechanical properties, and interfacial bonding. Cortical bone tissue represents a short-fibered biological composite where the hydroxyapatite phase is embedded in an organic matrix composed of type I collagen and other noncollagenous proteins. Destructive mechanical testing has revealed that fluoride ion treatment significantly lowers the Z-axis tensile and compressive properties of cortical bone through a constituent interfacial debonding mechanism. The present ultrasonic data indicates that fluoride ion treatment significantly alters the longitudinal velocity in the Z-axis as well as the circumferential and radial axes of cortical bone. This suggests that the distribution of constituents and interfacial bonding amongst them may contribute to the anisotropic nature of bone tissue.

Flow visualization in the Baylor total artificial heart

To analyze the flow patterns of the left and right blood chambers of the total artificial heart (TAH), flow visualization studies were performed. Two setup levels were used for the flow visualization studies. For estimating the global flow patterns, the pumps were illuminated using incandescent light, and the patterns were recorded by either videotape or photography. To evaluate sectional flow patterns, a laser light was applied, and the pump could be scanned segmentally. The flow patterns were recorded by a high-speed camera. A signal was also used that synchronized the timing of the camera shutter to the pusher-plate movement signal. In the left pump chamber, major stagnations were observed in the middle area of the inflow site. To solve this problem, a modification was made that changed the inflow direction appropriately. After evaluation of the inflow port direction, a proper flow pattern was obtained, which was validated by a global flow visualization study. Furthermore, both pump chambers indicated excellent flow patterns as obtained by a segmental flow visualization study method utilizing a laser light. The Baylor TAH demonstrated excellent flow patterns in flow visualization studies, with antithrombogenicity expected. These flow visualization studies are very useful not only for validations of global flow patterns but also for validations of local areas of stagnation in various blood pumps.

The effects of diamond-like carbon coatings on macrophages, fibroblasts and osteoblast-like cells in vitro

The elaboration of metallic and polymeric particles from the wear of joint replacement components is widely implicated in the pathogensis of aseptic loosening of these implants. Diamond-like carbon (DLC) coatings show great potential as wear-retardant coatings and may offer a possible solution to this problem. We have studied the effects of DLC coatings on cells derived from the tissues that surround a total joint replacement (macrophages, fibroblasts and osteoblast-like cells). There was no evidence that DLC coatings, deposited on a variety of different substrates, caused cytotoxicity in vitro. Cells grown on the coated substrates exhibited normal cellular growth and morphology. DLC coatings are biocompatible in vitro and should now be tested in animal models to determine their behaviour in vivo.

Errors in the estimation of arterial wall shear rates that result from curve fitting of velocity profiles

An analysis was performed to determine the error that results from the estimation of the wall shear rates based on linear and quadratic curve-fittings of the measured velocity profiles. For steady, fully developed flow in a straight vessel, the error for the linear method is linearly related to the distance between the probe and the wall, dr1, and the error for the quadratic method is zero. With pulsatile flow, especially a physiological pulsatile flow in a large artery, the thickness of the velocity boundary layer, delta is small, and the error in the estimation of wall shear based on curve fitting is much higher than that with steady flow. In addition, there is a phase lag between the actual shear rate and the measured one. In oscillatory flow, the error increases with the distance ratio dr1/delta and, for a quadratic method, also with the distance ratio dr2/dr1, where dr2 is the distance of the second probe from the wall. The quadratic method has a distinct advantage in accuracy over the linear method when dr1/delta << 1, i.e. when the first velocity point is well within the boundary layer. The use of this analysis in arterial flow involves many simplifications, including Newtonian fluid, rigid walls, and the linear summation of the harmonic components, and can provide more qualitative than quantitative guidance.