The influence of bone formation on anchoring percutaneous devices with titanium fibre mesh flanges

For man-made percutaneous devices (PD), it is known that anchoring will improve the clinical success. Previously, our Department has designed PDs that use a sheet of titanium (Ti) fibre mesh for anchoring. In nature, a very successful natural PD occurs, namely the tooth. Teeth are anchored in the alveolar bone. In the current study, we evaluated whether a sheet of (ectopic) bone can be made, and be used to anchor a skin-penetrating device. Using available tissue engineering techniques, sheets of Ti fibre mesh were loaded with osteoblast-like cells. These sheets, and non-loaded controls, were placed subcutaneously in 20 syngeneic rats. After four weeks 10 rats were sacrificed, and tissues were prepared for histology. On the other 10 rats, a percutaneous Ti bar was screwed. These rats were evaluated clinically up to eight weeks. Finally, also their tissues were prepared for histology. The results showed, that bone formation was only established in one cell-loaded implant, of the four-week group. Clinical evaluation, and the histomorphometrical data, showed no differences between cell-loaded and unloaded samples. We concluded that the combination of Ti mesh with rat bone marrow cells was not able to generate bone formation after subcutaneous implantation predictably. Thus, our original aim could not be met. On the other hand, our results did confirm the biocompatible behaviour of a PD equipped with a Ti fibre mesh anchoring flange.     

A percutaneous device to study glucose kinetics in subcutaneous tissue fluid

In the current study subcutaneous glucose kinetics were investigated in tissue fluid collected with a percutaneous device (PD). PDs containing a subcutaneous tissue chamber were implanted subcutaneously in New Zealand white rabbits. Sintered titanium fiber mesh sheets were used for subcutaneous anchorage of the PD. The bottom of the subcutaneous tissue chamber was either covered with a titanium fiber mesh sheet, a cellulose acetate membrane, or left uncovered. Subcutaneous glucose kinetics were determined after injection of octreotide and glucagon. The tissue reaction to the implants was evaluated histologically. No dynamic relationship was observed between glycaemia and subcutaneous tissue fluid glucose for all membrane covered devices. Histological evaluation showed that the presence of a seroma cavity in combination with obstruction of the membrane prevented adjustment of the subcutaneous glucose concentration in response to changes in glycaemia. In the uncovered devices, on the other hand, changes in glycaemia were reflected in subcutaneous tissue fluid. Our results prove that it is possible to measure changes in the glucose concentration in subcutaneous tissue fluid collected with a percutaneous device. Therefore, we conclude that a percutaneous device has an application as model to study the in vivo performance of implantable glucose sensors. The use of porous membranes in such devices has to be avoided.     

Comparison of the tissue reaction to implants made of a beta titanium alloy and pure titanium. Experimental study on rabbits

Commercially pure titanium (Ti cp) has been used successfully as an implant material in fracture fixation devices for many years. Ti cp is comparatively soft, but the mechanical properties, such as strength and ductility, can be adjusted by different means over a wide range. Titanium changes its crystal structure from a hexagonal (alpha) phase to the cubic (beta) phase at about 882 °C. Cubic titanium has the advantage of being very malleable (ductile), but in order to stabilize it at room temperature, additions of suitable alloying elements are required. In this study the soft tissue reaction to implants made from a beta titanium alloy (Ti–Mo–Zr–Al) with four different surface treatments is evaluated. The results are compared to Ti cp implants having the same surface conditions, and to electropolished stainless steel plates as controls. A minimum of four small plates of each group were implanted in rabbit tibiae for 3 months. Histomorphometric results show that the thickness of the soft tissue reaction layer, and the number of blood vessels, connective tissue cells (fibroblasts, fibrocytes), lymphocytes, and foreign body giant cells are not significantly different between beta titanium and Ti cp plates. For stainless steel plates the soft tissue reaction layer is thicker, and the numbers of macrophages and connective tissue cells are higher. Excellent biocompatibility was observed for this beta titanium alloy. The mechanical properties of this alloy surpass those of Ti cp, and because of the good tissue tolerance, this material seems to be advantageous and should enter into clinical testing.     

A histomorphometric comparison of the muscular tissue reaction to stainless steel,pure titanium and titanium alloy implant materials

Thein vivo tissue reaction to titanium and titanium-based alloys using quantitative histomorphometry was investigated. According to the guidelines for biomaterials testing suggested by ISO, 2 mm × 6 mm cylindrical specimens of chemically pure (CP) Ti, TiO₂, electrolytically coated Ti, Ti6Al4V, TiO₂-coated Ti6Al4V, TiN physical vapour deposition-coated Ti6Al4V and Ti5Al2.5Fe were implanted in the paravertebral muscles of rats, for 1–52 weeks, 316L stainless steel being used as a control implant material. After PMMA embedding, electrochemical dissolution of the implants, microtome sectioning and Masson's trichrome staining, the tissue reaction was assayed using a semi-automatic method based on the digitization of both the encapsulating membrane contours and the different cell types located within it. All materials induced a close tissue reaction. There was no statistical difference between the tested materials regarding the time-evolution of the inflammatory cells. However, when comparing CP Ti with 316L, a significant difference was found in the fibrocyte kinetics: in the short term, fibrocyte densities were lower for 316L, while beyond 12 weeks, they exhibited higher values than CP Ti. To a lesser extent, a similar observation was made when comparing CP Ti with Ti5Al12.5Fe. No statistical difference was found in the comparison of CP Ti with Ti6Al4V. The membrane thickness was identical for all tested materials and appeared not to be time-dependent.     

Evaluation of a roadside impairment test device using alcohol

The main objective of this study was to compare the performance of a portable impairment test device known as roadside impairment testing apparatus (RITA) with the field impairment tests (FIT) that are used at the roadside by UK police. One hundred and twenty two healthy volunteers aged 18-70 years took part in this two-period crossover evaluation. The volunteers received a dose of alcohol and placebo, in the form of a drink, on separate days. Doses were calculated to produce blood alcohol concentrations of 90 mg/100 ml and RITA and FIT testing was carried out between 30 and 75 min post-drink. FIT was found to have a diagnostic accuracy of 62.7%. However, there was a substantial age effect for FIT scores, with volunteers aged over 40 showing failure rates on placebo similar to the failure rates on alcohol of younger volunteers. The accuracy of RITA was between 66 and 70%, not significantly higher than that of FIT. However, RITA did not show a marked age effect. Advantageously, this could result in fewer false positives being recorded if RITA were deployed at the roadside. Horizontal gaze nystagmus (HGN) was also investigated and posted an accuracy of 74%. The inclusion of HGN as one component of a UK roadside impairment test battery warrants further exploration with other drugs.     

Magnetic resonance imaging of a tissue/implanted device biointerface using in vivo microdialysis sampling

Real-time in vivo images of magnetic resonance contrast agent diffusion from implanted microdialysis probes were obtained by magnetic resonance (MR) microscopy. A gadolinium-containing contrast agent (Gd-DTPA) was infused through microdialysis probes implanted into the subcutaneous space of male Sprague-Dawley rats. The infusion of Gd-DTPA alters the T1 relaxation time for water protons near the microdialysis probe, thus causing an increase in brightness around the probe. Steady state concentration profiles of Gd-DTPA around the microdialysis probe were attained within 10 min. The distance for the diffusion of Gd-DTPA away from the probe was calculated to be approximately 1400 microm on the basis of an image intensity analysis. A 5-cm field of view was used with a 256 x 256 matrix, giving a voxel volume of 0.190 mm3 (195 microm x 195 microm x 5,000 microm). These experiments demonstrate the ability of magnetic resonance microscopy to obtain real-time images of Gd-DTPA diffusion around implanted microdialysis probes. This noninvasive technique may be useful for determining how fibrous encapsulation during long-term implantation may affect localized mass transport at a biointerface.     

Electrochemical degradation of polycyclic aromatic hydrocarbons in creosote solution using ruthenium oxide on titanium expanded mesh anode

In this study, expanded titanium (Ti) covered with ruthenium oxide (RuO(2)) electrode was used to anodically oxidize polycyclic aromatic hydrocarbons (PAH) in creosote solution. Synthetic creosote-oily solution (COS) was prepared with distilled water and a commercial creosote solution in the presence of an amphoteric surfactant; Cocamidopropylhydroxysultaine (CAS). Electrolysis was carried out using a parallelepipedic electrolytic 1.5-L cell containing five anodes (Ti/RuO(2)) and five cathodes (stainless steel, 316 L) alternated in the electrode pack. The effects of initial pH, temperature, retention time, supporting electrolyte, current density and initial PAH concentration on the process performance were examined. Experimental results revealed that a current density of 9.23 mA cm(-2) was beneficial for PAH oxidation. The sum of PAH concentrations for 16 PAHs could be optimally diminished up to 80-82% while imposing a residence time in the electrolysis cell of 90 min. There was not a significant effect of the electrolyte (Na(2)SO(4)) concentration on oxidation efficiency in the investigated range of 500-4000 mg/L. However, an addition of 500 mg Na(2)SO(4)L(-1) was required to reduce the energy consumption and the treatment cost. Besides, there was no effect of initial PAH concentration on oxidation efficiency in the investigated range of 270-540 mg PAHL(-1). Alkaline media was not favourable for PAH oxidation, whereas high performance of PAH degradation could be recorded without initial pH adjustment (original pH around 6.0). Likewise, under optimal conditions, 84% of petroleum hydrocarbon (C(10)-C(50)) was removed, whereas removal yields of 69% and 62% have been measured for O&G and COD, respectively. Microtox and Daphnia biotests showed that electrochemical oxidation using Ti/RuO(2) could be efficiently used to reduce more than 90% of the COS toxicity.     

Evaluation of directional mesh bias in concrete fracture simulations using continuum damage models

In the present comparative study, we investigate the influence of directional mesh bias on the results of failure simulations performed with isotropic and anisotropic damage models. Several fracture tests leading to curved crack trajectories are simulated on different meshes. The isotropic damage model with a realistic biaxial strength envelope for concrete is highly sensitive to the mesh orientation, even for fine meshes. The sensitivity is reduced if the definition of the damage-driving variable (equivalent strain) is based on the modified von Mises criterion, but the corresponding biaxial strength envelope is not realistic for concrete. The anisotropic damage models used in this study capture reasonably well arbitrary crack trajectories even if the biaxial strength envelope remains close to typical experimental data. Their superior performance can be at least partially attributed to their ability to capture dilatancy under shear, which is revealed by a comparative analysis of the behavior of individual models under shear with restricted or free volume expansion.     

Salvage of exhausted neck access using a novel inside‐out device in dialysis‐dependent patients

Chronic central venous occlusion represents a challenge for upper body central dialysis access for both surgical and endovascular interventions. The Surfacer (Surfacer Inside‐Out Access Catheter System) is a novel technique that offers a device‐based solution over various physician‐modified techniques in salvaging exhausted right‐sided neck veins for catheter placement. We report a retrospective series of four cases in which this system is used to gain upper body venous access from a single center in Singapore. This report seeks to integrate the understanding of the technical aspects of a new inside‐out device and its utility in recanalization of occluded right‐sided neck veins as it relates to Asian patients.     

Dynamics of bone tissue mineralization in porous titanium and the mechanical properties of a titanium-bone tissue composite

We studied the dynamics of bone tissue mineralization in the pores of a titanium matrix and the mechanical properties of the resulting titanium-bone tissue composite. It is shown that the mineralization process is virtually accomplished within six months after implantation of a porous titanium article into the organism. As the pores and channels in the titanium matrix are filled with bone tissue, the material becomes a composite with mechanical properties higher as compared to those of the porous implant or bone tissue.     

Characterizing the fibre/matrix interface of carbon fibre-reinforced composites using a single fibre pull-out test

A single fibre pull-out technique has been used to determine the interfacial bond strength of carbon fibres embedded in epoxy resin. A method is presented whereby the maximum interfacial bond shear stress may be evaluated from the simple measurement of the pull-out force and fibre dimensions. Additional information may also be obtained concerning the interface morphology. The results obtained demonstrate the feasibility of the method and good agreement between theory and experiment.     

Evaluation of internal contamination levels after a radiological dispersal device incident using portal monitors

Following a radioactive dispersal device (RDD) incident, it may be necessary to evaluate the internal contamination levels of a large number of potentially affected individuals to determine if immediate medical follow-up is necessary. Since the current laboratory capacity to screen for internal contamination is limited, rapid field screening methods can be useful in prioritising individuals. This study evaluated the suitability of a radiation portal monitor for such screening. A model of the portal monitor was created for use with models of six anthropomorphic phantoms in Monte Carlo N-Particle Transport Code Version 5 (MCNP) X-5 Monte Carlo Team (MCNP-A General Monte Carlo N-Particle Transport Code Version 5. LA-CP-03-0245. Vol. 2. Los Alamos National Laboratory, 2004.). The count rates of the portal monitor were simulated for inhalation and ingestion of likely radionuclides from an RDD for each of the phantoms. The time-dependant organ concentrations of the radionuclides were determined using Dose and Risk Calculation Software Eckerman, Leggett, Cristy, Nelson, Ryman, Sjoreen and Ward (Dose and Risk Calculation Software Ver. 8.4. ORNL/TM-2001/190. Oak Ridge National Laboratory, 2006.). Portal monitor count rates corresponding to a committed effective dose E(50) of 10 mSv are reported.     

Validation of the modified rule of mixtures using a combination of fibre orientation and fibre length measurements

The goal of this study was to investigate the fibre orientation distribution (FOD), and subsequent mechanical properties, of an injection moulded plate with two different number averaged fibre lengths, termed in this paper medium (1.35 mm) and long (2.40 mm). Fibre orientation measurements (FOD) were made using the 2D elliptical section method and an in-house developed image analyser. The samples were injected from a pin gate located at the centre and top of the plate. Expansion flow on the divergent flow front from this pin gate resulted in a core region with circumferential alignment, while through thickness shear resulted in the usual realignment of fibres in the flow direction either side of the core, termed the shell layers. Two interesting aspects were discovered from these measurements. First, and most importantly, the FOD was found to be independent of the two fibre lengths in this study, and so predominantly controlled by the mould shape and the interaction with the flow front. Second, the fibres in the core region were found to be much closer packed than those in the shell regions.The interaction between the flow front and the mould shape resulted in a range of FOD across the moulded plate, from equal in-plane orientation at the centre of the plate, to highly aligned at the plate edge. This gave a very useful set of samples from which to test out the well known modified rule of mixtures (MROM). Often the fibre orientation distribution cannot be measured directly, but indirectly using the modified rule of mixtures model in reverse. The samples from this moulding (at two different average fibre lengths) gave an excellent opportunity to validate this often used approach.Both the tensile modulus and strength (measured parallel to the injection direction) were found to show a strong correlation with the measured fibre orientation, with a significant increase in both measures between the centre and the edge of both plates. The increased length of the ‘long’ fibre plate was found to give only a small increase in tensile modulus but a much larger increase in tensile strength.The tensile modulus showed a linear dependence with the measured fourth order orientation tensor average, 〈cos⁴ θ〉, with respect to the injection direction of the plate, as predicted by the modified rule of mixtures. Excellent agreement was found between the measured modulus and the predictions from the modified rule of mixtures, based only on measured quantities (matrix modulus, fibre fraction and average fibre length) for both plates.     

Enhancement of bone ingrowth in a titanium fiber mesh implant by rhBMP-2 and hyaluronic acid

The present study was designed to evaluate the efficacy of high molecular weight hyaluronic acid (HA) used as a carrier of recombinant human bone morphogenetic protein-2 (rhBMP-2) adsorbed to a titanium fiber mesh implant (TFMI) in vivo. The quantity of HA in the TFMI rapidly decreased during the initial 3-day period after implantation. BMP particles were trapped by the meshwork of HA as observed by scanning electron microscopy (SEM). TFMIs containing LF-6, HA, rhBMP-2, or HA combined with rhBMP-2 were implanted on the cranium of rats. Analysis of digitized SEM images of samples obtained six weeks post-implantation was performed to determine the area occupied by new bone. The area fraction of Ca relative to that of the pores of TFMI in the HA group was larger than that in the Ti group (p<0.05). The area fraction of Ca in both the BMP and HA+BMP groups was larger than that in both the Ti and HA groups (p<0.01), and that in the HA+BMP group was larger than that in the BMP group (p<0.05). It is suggested that HA is not only an effective carrier of BMP, but also it may have a positive effect on the generation of new bone in the TFMI. © 2001 Kluwer Academic Publishers     

A percutaneous device as model to study the in vivo performance of implantable amperometric glucose sensors

Glucose kinetics were investigated in subcutaneous tissue of rabbits, in which a percutaneous device was implanted. The device was used for collection of tissue fluid and as carrier of an amperometric glucose sensor. Changes in glycaemia were reflected in subcutaneous tissue fluid. However, a limited number of responses of the implanted sensors were observed. Histologic evaluation showed thin fibrous capsules surrounding the implants. Accumulations of inflammatory cells were observed inside the subcutaneous chamber. The experiments again showed that changes in blood glucose concentration can be measured in subcutaneous tissue fluid collected with a percutaneous device. Nevertheless, implanted glucose sensors could not reliably monitor these changes. Supported by our histological observations and sufficient in vitro performance, we suppose that the cellular reaction to the sensor plays an important role in this poor in vivo performance. In combination with adsorption of tissue fluid proteins, this results in a reversible deactivation of implanted sensors. The exact mechanisms involved in this process are currently unknown and need further investigation.     

Histologic evaluation of the soft tissue response to sintered austenitic stainless steel fibre structures

Recently it has been supposed that the soft tissue response to fibre mesh materials can be influenced by changing the flexibility and/or porosity of these materials. Therefore, to test this hypothesis, small sintered stainless steel (316L) fibre web implants with varying flexibilities and porosities were inserted subcutaneously into the dorsum of rabbits. The implants were left in situ for 15 weeks. Histological and tissue compatibility evaluations were performed. It was found that the best tissue reaction developed around the most porous fibre web material. Nevertheless, because of the possible occurrence of corrosion phenomena, the real existence of a relationship between implant porosity and connective tissue behaviour is still not clear.     

Optimisation of fibre steering in composite laminates using a genetic algorithm

An optimization procedure using a genetic algorithm has been applied to define the optimum orientation of fibres in a uni-directional laminate in which the fibres were allowed to vary continuously across the domain. The domain was divided into two-dimensional finite elements and anisotropic properties corresponding to a carbon fibre laminate with all layers aligned in the zero element axis direction were applied to the laminate. The orientation of the material axis on each element was then prescribed as an independent variable for the genetic algorithm.     

Tissue reaction to bone plates made of pure titanium: a prospective,quantitative clinical study

In 54 patients fractures of the long bones were stabilized with limited-contact dynamic compression plates (LC-DCP) made of titanium. The implant surfaces were anodized to an interference colour of gold. The surface morphology effects the tissue response to the implant and was therefore examined. At implant retrieval, about 18 months post operatively (range 11 to 27), samples of the soft tissue layer covering the plate were excised and analysed by histomorphometrical means. The aim was to study the soft tissue reactions at the implant site and further to correlate it to the clinical symptoms of the patients. At retrieval the plates were covered by a connective tissue layer of 2 mm thickness on average. In patients with local pain a comparatively significant higher number of round cells (p=0.001) and macrophages (p=0.01) was found. This is consistent with a chronic granulomatous inflammatory reaction. The localized tissue discoloration observed in about half of the patients was confirmed as being due to titanium, but it was not the focus of a cellular reaction and was not correlated with pain. In general the implant showed good biocompatibility with excellent or good clinical results in 96% of patients.