[Failure analysis as basis for quality assurance strategies in implant technology]. / Schadensanalyse als Basis für Qualitätssicherungsstrategien in der Implantattechnologie.

BACKGROUND: Implant safety is a topic gaining more and more public interest. Implants are safety relevant medical devices which in the case of failure can lead to life-threatening situations. OBJECTIVES: A well-founded failure analysis requires expert knowledge not only of materials and implant design but also a qualified explantation procedure and storage conditions. METHODS: A selective literature search was carried out putting the main emphasis on implant failure analysis supplemented with own investigations. RESULTS: The reasons for implant breakdown are mostly failures of materials and in the manufacturing process. In some cases false material combinations can lead to tribocorrosion effects under cyclic loading. CONCLUSION: The increased level of knowledge gained from complex analyses of failed implants produces valuable evidence for better quality management.

[Tongue fixation system for therapy of sleeping disorders. A feasibility study]. / Implantatgebundene Zungenfixierung zur Therapie schlafbezogener Atmungsstörungen. Eine Machbarkeitsstudie.

INTRODUCTION: Forward displacement of the tongue is a verified principle in the therapy of sleep disorders which prevents the tongue from sinking backwards thus avoiding obstruction of the upper respiratory tract during sleep. In this feasibility study a novel oral appliance which connects to a pin implanted within the tongue was investigated. METHODS: A new tongue positioning system using previously implanted tongue piercings as a pivot was developed. By pulling the tongue forward the oral device prevents airway obstruction. In our study we fitted 10 subjects who already had the tongue pierced with the developed oral device. The subjects underwent two nights of polysomnography with and without using the tongue positioning system. Wearing comfort and side effects were evaluated using a questionnaire. Moderate alcohol consumption was used to provoke snoring or apnea in the subjects. Tongue positioning with and without the device was visualized with oropharyngeal MRI. RESULTS: Subjects did not report any discomfort or side effects wearing the device. Subjects showed only moderate snoring or apnea after alcohol consumption and snoring after alcohol consumption was reduced with the device. The average apnea/hypopnea index (AHI) was 0.8/h without the device. Using the device led to an increase of apnea in the subjects. MRI visualization showed that the device did not keep the upper airway space opened by fixing the tongue. CONCLUSION: The effectiveness of the tongue positioning system should be improved by a modification which should be investigated in patients with preexisting sleep disorders.

Temporal bone investigations on landmarks for conventional or endosteal insertion of cochlear electrodes.

CONCLUSION: Our anatomical findings place special emphasis on the requirement to follow an infero-anterior approach to the round window, to expose the scala tympani safely for 'normal' cochlear implantation. It is also known how easily the basilar membrane may be accidentally damaged, despite exercising considerable caution in the approach used. With regard to an 'endosteal electrode' it can be stated that there are no really specific indicators to locate the spiral ligament, or each of the scalae, on the lateral aspect of the tissue layer encasing the cochlea. For the concept of an endosteal electrode, however, the soft tissue layer of the lateral aspect of the cochlea is considered to be sufficiently thick to serve as a physical barrier between the electrode and the inner ear fluid. OBJECTIVES: To re-evaluate surgical techniques of gaining access to the scala tympani for cochlear implantation (cochleostomy, 'fenestration'). There are two reasons for this study. First, recent publications show that in a significant number of patients the electrode array was unintentionally inserted into the 'wrong' scala (sc. vestibuli). Second, dealing with an alternative concept proposed by Lehnhardt for patients with residual hearing ('endosteal electrode'), the anatomical site of the spiral ligament should be known. In a study on human temporal bones the topography of the middle and inner ear is revised with regard to the presence of anatomical or surgical landmarks that may guide the surgeon. MATERIALS AND METHODS: Anatomical examinations were performed on 10 temporal bones (5 fresh specimens and 5 fixed in formalin), in which the bone of the promontory was carefully milled. The consistency of identification and the relative location of specific surgical indicators or landmarks such as 'blue lines' and 'gray lines' were evaluated for 10 temporal bones. Furthermore, the projection of the lateral attachment of the basilar membrane on the promontory was determined with regard to round window anatomy. RESULTS: In all cases, a major blue line indicated the lateral aspect of the basal cochlear turn while milling the promontorial bone. In a limited number of cases (20%), an additional gray line potentially indicated the spiral ligament before the last shell of bone was removed. In 80% of the cases it was possible to remove the bony layer and leave the endosteum intact as a precondition for a potential endosteal electrode insertion. In addition, through the examination of these models, the relative anatomical location of structures, such as the scala vestibuli, scala tympani, spiral ligament, and basilar membrane, is reviewed.

Structural alterations of adhesion mediating components in cells cultured on poly-beta-hydroxy butyric acid.

Polymers may serve as a biodegradable material in tissue engineering. To assess the biocompatibility of poly-beta-hydroxy butyric acid (PHB), we studied the structural organization of cellular molecules involved in adhesion using osteoblastic and epithelial cell lines. On PHB, both cell lines revealed a rounded cell shape due to reduced spreading. The filamentous organization of the actin cytoskeleton was impaired. In double immunofluorescence analyses we demostrated that the colocalization of the fibronectin fibrils with the actin filaments was lost in cultures on PHB. Similarly, collagen II distribution was altered, whereas the organization of collagen I was not obviously affected. Further evidence for impaired structural organization was obtained for the beta1-integrin receptor and vinculin which mediate the interaction of the cytoskeleton with the extracellular matrix. In confluent epithelial cells, the tight junction protein ZO-1 showed a larger lateral extension in the cell-cell contacts when cells were grown on PHB. Because structural organization of components which mediate cell-matrix and cell-cell adhesion controls cell physiology these parameters could be a sensitive indicator for the biocompatibility of implant materials.

Laser cutting: influence on morphological and physicochemical properties of polyhydroxybutyrate.

Polyhydroxybutyrate (PHB) is a biocompatible and resorbable implant material. For these reasons, it has been used for the fabrication of temporary stents, bone plates, nails and screws (Peng et al. Biomaterials 1996;17:685). In some cases, the brittle mechanical properties of PHB homopolymer limit its application. A typical plasticizer, triethylcitrate (TEC), was used to overcome such limitations by making the material more pliable. In the past few years, CO2-laser cutting of PHB was used in the manufacturing of small medical devices such as stents. Embrittlement of plasticized PHB tubes has been observed, after laser machining. Consequently, the physicochemical and morphological properties of laser-processed surfaces and cut edges of plasticized polymer samples were examined to determine the extent of changes in polymer properties as a result of laser machining. These studies included determination of the depth of the laser-induced heat affected zone by polariscopy of thin polymer sections. Molecular weight changes and changes in the TEC content as a function of distance from the laser-cut edge were determined. In a preliminary test, the cellular response to the processed material was investigated by cell culture study of L929 mouse fibroblasts on laser-machined surfaces. The heat-affected zone was readily classified into four different regions with a total depth of about 60 to 100 microm (Klamp, Master Thesis, University of Rostock, 1998). These results correspond well with the chemical analysis and molecular weight measurements. Furthermore, it was found that cells grew preferentially on the laser-machined area. These findings have significant implications for the manufacture of medical implants from PHB by laser machining.

Beyond fast mapping: young children's extensions of novel words and novel facts.

L. Markson and P. Bloom (1997) concluded that there was evidence against a dedicated system for word learning on the basis of their finding that children remembered a novel word and a novel fact equally well. However, a word-learning system involves more than recognition memory; it must also provide a means to guide the extension of words to additional exemplars, and words and facts may differ with regard to extendibility. Two studies are reported in which 2-4-year-old children learned novel words and novel facts for unfamiliar objects and then were asked to extend the words and facts to additional exemplars of the training objects. In both studies, children extended the novel word to significantly more category members than they extended the novel fact. The results show that by 2 years of age, children honor the necessary extendibility of novel count nouns but are uncertain about the extendibility of arbitrary facts.

Assessment of explanted PTCA balloons.

The data presented here are part of a on-going study to define the surface characteristics and properties of explanted PTCA catheters in a further effort to address some of the ramifications of the re-use issue. PTCA balloon catheter were examined after angioplasty in one hundred and sixty-eight patients (n = 168). This series included six balloon types from three manufacturers. The fresh fixed and dehydrated balloons were examined at first with light microscopy and then in a scanning electron microscope. X-ray semiquantitative microanalysis and FT-IR-ATR analysis were also performed on the balloons. Because most blood proteins are water soluble, we examined unfixed balloons with a protein silver staining kit for detection of adhered proteins described by Heukeshoven. A further method for protein detection is the Lowry-analysis. With this method water insoluble proteins can be observed. Our study has shown convincingly that all deployed angioplasty catheters were coated with adherent protein layers. Plaque particles were found embedded in the surfaces of most of the balloons examined. Fissuring and micro tearing of balloon surfaces was noted. FT-IR-ATR analyses of the blood contacted balloon surfaces did not show any peaks indicative of proteins on the balloon surface. The silver staining method also did not show any evidence of protein adsorption on the balloons. On the other hand, the Lowry-analysis yielded clear evidence that water insoluble proteins were adherent to the balloon surfaces. The average measured protein concentration was 17 microg/ml.

The loss of stiffness as osteoporosis progresses.

The routine diagnosis of osteoporosis is based on radiological measurements of bone mineral content. An osteoporotic failure is influenced both by a loss of mineralized bone and internal bone structure. The structure cannot be estimated by bone reconstruction based on standard radiological equipment. To investigate the influence of structure on cancellous bone stiffness, a new finite element model of cancellous bone is developed. The model describes a cancellous bone unit as an open-celled structure. Trabecular length, trabecular thickness, diameter of trabecular connections, relative lattice disorder and relative bone loss determine the real architecture. Using this model, the loss of stiffness as a result of trabecular thinning and loss of trabecular connections is estimated. The volume fraction as a scalar value for a volume can not be a marker for orthotropic stiffness changes. A formula in the form Y = e(a *1 n(X) + b) can describe the correlation between cancellous bone stiffness and volume fraction. These formulas are appropriate for those cases, when the loss of bone mineral (decrease in trabecular thickness) is closely connected to a loss of structure (increasingly perforated trabecular network).

Assessment of mechanical properties and biocompatibility of Pellethane.

Pellethane CPR 2363-80A nonreinforced (PUR), non-reinforced and twice sterilized (PUR F2), reinforced with Dacron (Dm), Grisuten (DG) and glassfibre (PUG) and fabricated under different conditions have been examinated. Tests included uniaxial tension at 310 K, torsional movement from 293 to 319 K, X-ray structure, SEM, visual surface clotting, thrombocyte adhesion and degree of albumenisation. Typical in vitro results were: modulus of elasticity E [MPa] (PUR: 1.33, Dm: 4.22, DG: 1.86, PUG: 622.5), tensile strength delta B [MPa] (43.4, 12.5, 21.7, 24.9), elongation at break delta [%] (1122, 109, 660, 479), dynamic modulus of sliding G', G" [MPa] at 293 K (8.7, 0.4/ 15.9, 0.9/ 12.1, 1.3/ 17.1, 1.5), damping tan delta (0.13, 0.1, 0.16, 0.12), orientational degree at 5% elongation fx [%] (PUR: 0.5), low thrombogenicity and high degree of albumenisation. The results indicate a strong dependency of mechanical and biocompatibility properties on membrane and housing fabrication. The most effective combination is a thin PUR membrane and a PUG housing fabricated under special conditions.

[Biomaterials in urology]. / Biowerkstoffe in der Urologie.

Biomaterials are defined as non-living materials which are used in interaction with biological systems. Especially in the field of urology, biomaterials are applied in urinary diversion, urinary incontinence, erectile dysfunction, and as cosmetic prostheses. Biomaterial-tissue interaction is caused by the physical and chemical characteristics of the biomaterial, its degradation, and the resulting protein denaturation. General requirements include biocompatibility and functionality and the avoidance of carcinogenic, mutagenic, toxic, and allergic reactions. This is most important when there is permanent contact between urine and epithelial tissue, which may lead to biofilminfection and incrustation. Continuous modification of known materials, inauguration of new materials, as well as the possibilities of tissue engineering will determine their development in the years to come.

[Polyurethane or silicone as long-term implant substance--a critical evaluation]. / Polyurethan oder Silikon als Langzeitimplantatwerkstoff--eine kritische Wertung.

Long-term implants made from thermoplastic elastomers have a long history of clinical use. Among other rubber materials, such as polyolefin rubber, much of the demand for rubber-like biomaterials is met by silicone and polyurethane elastomers. The last two elastomers both have sufficient biocompatibility for long-term applications, but differ in terms of biodegradability. Inadequate resistance to degradation almost always leads to implant function loss, which may even threaten the patient's life. Long-term implantation studies in the rat show different mechanisms of biodegradation for polyurethane and silicone. Polyurethane shown deep fissures in the surface, compared with erosion of silicone surfaces. Mechanical and electrical parameters determined to evaluate degradation, additionally show differences in the extent of damage occurring.

[A measuring procedure for experimental determination of tensile strength of catheters and flexible probes]. / Messverfahren zur experimentellen Bestimmung der Biegesteifigkeit von Kathetern und flexiblen Sonden.

In order to obtain a more objective description of the properties usually subsumed under such terms as the "handling" of catheters, it is necessary to measure the significant parameter bending stiffness. A contact-free method of recording the oscillations of rod-shaped elements is presented. The stiffness EI can be calculated from the measured characteristic frequency. The logarithmic decrement can be derived from the damped natural oscillation and the damping properties of the catheter thus characterised. In addition, a consideration of imposed oscillations can be employed to calculate resonance frequency. A computer-driven measuring set-up employing a CCD line camera for the non-contact recording of oscillations of rodshaped elements, together with the software required is presented. The measuring principle and possible errors are discussed and a measurement described by way of an example.

[Comparative analysis of in vitro test procedures for evaluating hemocompatibility of cardiovascular stents]. / Vergleichende Analyse von in vitro Testverfahren zur Beurteilung der Hämokompatibilität von kardiovaskulären Stents.

Within the scope of this study existing in vitro techniques for testing the hemocompatibility of coronary stents were analysed and optimised. Static and quasi-stationary systems were compared to a pulsed flow model with respect to platelet activity. The streamlines were visualized by dye injection. Blood flow was measured by ultrasonic Doppler velocity meter and electromagnetic flow meter. Uncoated stainless steel (316 L) stents were tested. Surrogate parameters of the hemocompatibility were the change in surface morphology after blood contact and the rise of biomechanical activation markers as C3a and beta-thromboglobulin. The results were correlated to the stent design and to the flow characteristics of the test systems.

Optimization of the neck region of dental implants with a bioactive, resorbable coating.

With the goal of shortening the postoperative healing phase and the minimization of the risk of peri-implantitis around dental implants, a polymer coating, with improved surface biocompatibility in the region of soft tissue penetration by the implant, was investigated. The polymer used was the relatively slowly resorbable poly-beta-hydroxybuterate (PHB) whose surface was further activated in a NH3--plasma. The influence of surface roughness of the substrate (commercially pure titanium) as well as the influence of the edge radii on the test samples was determined in prior studies. These studies formed the basis for an optimised coating process. In-vitro biocompatibility was determined using a human gingival primary cell culture. Surface morphology was determined with SEM and AFM to complement the cell culture studies.

Dental implants and immediate loading: multivariate analysis of success factors.

OBJECTIVES: The authors had for aim to examine factors potentially influencing the success of immediate implant placement and loading. MATERIALS AND METHODS: One hundred and ninety-five consecutive patients (16.5 to 80.4 years of age) were provided with 310 prostheses supported by 896 immediately loaded implants. The mean follow-up was 27.5 months. Univariate and multivariate Cox regression was performed to analyze potential modifiers of implant success. RESULTS: The overall implant success rate was 96.7%. The statistically significant modifiers of success on multivariate analysis (P<0.05) were duration of functional use (P<0.001), type of superstructure (P<0.001), implant-abutment connection (P<0.001), and maxilla versus mandible (P=0.026). None of the other investigated factors (age, gender, implant location/design/length) were statistically significant modifiers of success. DISCUSSION: Our study results demonstrate high success rates for immediately loaded implants whatever types and superstructure used. Prosthetic designs and their implementation have a significant effect on the success rate of implant-supported restoration, with adjusted hazard ratios of up to 51. Maxilla versus mandible was the only significant non-external modifier when using an adjusted hazard ratio of 2.75.

Detection of tympanic membrane movement using film patch with integrated strain gauge, assessed by optical coherence tomography: experimental study.

OBJECTIVE: We report an ex vivo and in vivo experimental study of a device designed to measure tympanic membrane movement under normal and pathological conditions, assessed using optical coherence tomography. MATERIALS AND METHODS: We designed two types of flexible, round film patch with integrated strain gauge, to be attached to the tympanic membrane in order to measure tympanic membrane movement. Tympanic membrane attachment was assessed using optical coherence tomography. The devices were tested experimentally using an ex vivo model with varying middle-ear pressure. RESULTS: Optical coherence tomography reliably assessed attachment of the film patch to the tympanic membrane, before and after middle-ear pressure changes. Strain gauge voltage changes were directly proportional to middle-ear pressure recordings, for low pressure changes. Tympanic membrane perforations smaller than 2 mm could be sealed off with the film patch. CONCLUSION: Attachment of the film patch with integrated strain gauge to the tympanic membrane was not ideal. Nevertheless, the strain gauge was able to precisely detect small pressure changes within the middle ear, in this experimental model.

Minimal cross-infection risk through Icare rebound tonometer probes: a useful tool for IOP-screenings in developing countries.

AIMS: Recently, a new rebound tonometer has been introduced into the market, which might be useful for glaucoma screenings in developing countries. Disposable probes, that are potentially reusable, are recommended by the manufacturer. Our study aimed to address the question of microbial transmission risks if the probes are reused. METHODS: IOP measurements were obtained from 100 healthy eyes. The used probes were inoculated on broth and culture media. In addition, 10 probes were analyzed using environmental scanning electron microscopy in saturated hydrogen-steam atmosphere after usage and wipe disinfection technique with Sekusept 4% solution or Isopropanol 70%. RESULTS: No bacterial or fungal growth could be detected in any of the inoculated agar plates or broth tubes. No microorganisms, clumps of cells, or single intact epithelium cells were detected in any of the probes using environmental scanning electron microscopy. Cell debris was detected on seven probes; three probes were completely free of any residual cell elements. CONCLUSION: Transmission of possibly infective material through reused probes is significantly less than for reusable Goldmann probes if the same sterilization protocols are applied. Re-usage of the probes appears safe and is helpful in avoiding unnecessary costs.