Bio-Medical Materials and Engineering - Volume 18, issue 2

Authors: İnceoğlu, Serkan | Kılınçer, Cumhur | McLain, Robert F.

Article Type: Research Article

Abstract: Stress relaxation during pullout of a pedicle screw decreases the peak load and stiffness of the bone–screw interface. However, it is unknown whether this can be generalized to all types of screw designs. This study aimed to show whether screw design altered the effects of stress relaxation on the mechanical performance of the pedicle screw during pullout. Twelve calf vertebrae were obtained: six vertebrae were instrumented with 7.5×40 mm conical pedicle screws and the other six with 5.0×40 mm cylindrical pedicle screws. The screws with two different designs were pulled out using either a standard pullout or a stress relaxation …pullout protocol. Both bone–screw interfaces had lower stiffness in the stress relaxation pullout model than in the standard pullout model, but it was significant in only the cylindrical design group (P<0.05). However, the stress relaxation and standard pullout models did not yield any difference in peak loads in either screw type. Although stress relaxation at the bone–screw interface can alter the mechanical performance of the screw, this may be eliminated by modifying the screw design. A better understanding of viscoelastic properties of the bone–screw interface may help improve implant design and thus, clinical outcomes. Show more

Keywords: Pedicle, pedicle screw, pullout, stress relaxation, viscoelasticity, spine

DOI: 10.3233/BME-2008-0508

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 53-60, 2008

Authors: Übeyli, Elif Derya

Article Type: Research Article

Abstract: The automated diagnostic systems employing diverse and composite features for electrocardiogram (ECG) signals were analyzed and their accuracies were determined. Because of the importance of making the right decision, classification procedures classifying the ECG signals with high accuracy were investigated. The classification accuracies of multilayer perceptron neural network (MLPNN), recurrent neural network (RNN), and mixture of experts (ME) trained on composite features and modified mixture of experts (MME) trained on diverse features were compared. The inputs of these automated diagnostic systems were composed of diverse or composite features (wavelet coefficients and power levels of the power spectral density estimates obtained …by the eigenvector methods) and were chosen according to the network structures. The conclusions of this study demonstrated that the MME trained on diverse features achieved accuracy rates which were higher than that of the other automated diagnostic systems trained on composite features. Show more

Keywords: Diverse features, composite features, electrocardiogram (ECG) signals, automated diagnostic systems, wavelet coefficients, eigenvector methods

DOI: 10.3233/BME-2008-0509

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 61-72, 2008

Authors: Pylios, T. | Shepherd, D.E.T.

Article Type: Research Article

Abstract: The metacarpophalangeal (MCP) joint is crucial for hand function, but the joints are frequently affected by arthritis, leading to pain and disability. Joint replacement implants are used to replace the diseased MCP joint. This paper presents an investigation of applying the soft layered concept in the design of a new MCP joint replacement implant. Analytical methods were used to investigate the minimum film thickness for a novel MCP joint with a soft layer. The effect of load, entraining velocity, radial clearance, radius of the metacarpal head, elastic modulus and thickness of the soft layer were investigated. The soft layered joints …show an enhanced predicted film thickness and some evidence of fluid film lubrication that should help to reduce wear rates. It may be beneficial for future MCP joint implant designs to utilise the soft layered joint concept. Show more

Keywords: Arthritis, joint replacement, lubrication analysis, metacarpophalangeal joint, soft layered joints

DOI: 10.3233/BME-2008-0510

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 73-82, 2008

Authors: Lewis, Gladius | Son, Yang

Article Type: Research Article

Abstract: Heat-conduction isothermal microcalorimetry was used to measure the exothermic heat flow rate (Q) from the powder of a widely used commercially-available acrylic bone cement, Palacos® R, when it interacted with ambient laboratory air, as a function of time, t, in the calorimeter, for up to 200 h. Four variants of the powder were used, these being unsterilized, sterilized using ethylene oxide gas, γ-irradiated, in ambient air, with a minimum dosage of 2.5 Mrad, and γ-irradiated, in ambient air, with a minimum dosage of 4.5 Mrad. In each case, the powder variant was tested after being stored on the shelf, …under ambient conditions, for 2 days, 3 weeks and 9 months immediately following sterilization. Best-fit correlations between Q and t for each powder variant were determined. Then, this relationship was integrated over the period 14 h≤t≤200 h to give an estimate of the “effective” heat flow, Qeff . For powder variants tested 2 days after being sterilized, the difference in their thermal stabilities (Qeff ranged from 0.19±0.01 to 0.62±0.03 μJ/g, respectively) was significant in the case of some pairs and not for others. However, for powders tested either 3 weeks or 9 months following sterilization, there was no significant difference between the means of Qeff (they ranged from 0.18±0.01 to 0.31±0.07 μJ/g) for any pair. These results suggest that an acrylic bone cement in which the powder is EtO-sterilized may be mixed with the liquid monomer for use in cemented arthroplasties after any length of time of shelf storage of the powder, under ambient conditions, whereas, for powders that are γ-irradiated and then stored under the same conditions, at least 3 weeks should elapse before they are used in these procedures. Show more

Keywords: Acrylic bone cement, sterilization, isothermal microcalorimetry

DOI: 10.3233/BME-2008-0511

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 83-90, 2008

Authors: Palmieri, Annalisa | Pezzetti, Furio | Brunelli, Giorgio | Martinelli, Marcella | Scapoli, Luca | Arlotti, Marzia | Masiero, Elena | Carinci, Francesco

Article Type: Research Article

Abstract: Porous polyethylene (PP or Medpor® ) is an alloplastic material worldwide used for craniofacial reconstruction. Although several clinical studies are available, there is a lack as regard the genetic effects. Because PP is always fixed on bone and the mechanism by which PP acts on osteoblasts is unknown, we therefore attempted to address this question by using microRNA microarray techniques to investigate the translation regulation in osteoblasts exposed to PP. The miRNA oligonucleotide microarray provides a novel method to carry out genome-wide microRNA profiling in human samples. By using miRNA microarrays containing 329 probe designed from Human miRNA sequence, …we identified in osteoblast-like cells line (MG-63) cultured with Medpor® (Porex Corporation, Fairburn, Georgia, USA) several miRNA which expression is significantly modified. We identified 16 up-regulated miRNA (i.e. mir-337, mir-515-3p, mir-377, mir-153, mir-367, mir-152, let-7b, mir-92, mir-155, mir-424, mir-148b, mir-368, mir-18b, mir-520d, mir-20b, mir-128a) and 2 down-regulated miRNA (i.e. mir-143, mir-32). The data reported are, to our knowledge, the first study on translation regulation in osteoblasts exposed to PP. They can be relevant to better understand the molecular mechanism of bone regeneration and as a model for comparing other materials with similar clinical effects. Show more

Keywords: Alloplastic material, porous polyethylene, miRNA, microarray, gene expression

DOI: 10.3233/BME-2008-0512

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 91-97, 2008

Authors: Ishida, Hitoshi | Satou, Toshio | Tsuji, Kiichi | Kawashima, Norimichi | Takemura, Hideo | Kosaki, Yasuhiro | Shiratori, Seimei | Agishi, Tetuzou

Article Type: Research Article

Abstract: Recently, expired gases are analyzed non-invasively for monitoring the substances in the blood. Breath ammonia has been shown to correlate with BUN (blood urea nitrogen) and Cr (creatinine), both of which are indicators of solute removal in hemodialysis. In this study, breath ammonia concentration was continuously measured using a crystal oscillator QCM (quartz crystal microbalance) during the expiration of patients undergoing dialysis treatment. The results show that NH3 (ammonia) decreased gradually as the treatment proceeded. A strong correlation was observed between changes in the frequency of the QCM gas sensor and both the pre-dialysis BUN level (r=0.71, p<0.05) …and the post-dialysis BUN level (r=0.90, p<0.05). NH3 was found to fall precipitously during dialysis. The differences were statistically significant. In addition, we found a statistically significant correlation between BUN and NH3 in expired gas. These results suggest that continuous measurement of NH3 is useful to assess the status of solute removal during hemodialysis. Show more

Keywords: Expired gas, non-invasive analysis, hemodialysis, QCM, BUN, Cr

DOI: 10.3233/BME-2008-0513

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 2, pp. 99-106, 2008