Flexor tendon healing within the tendon sheath using bioabsorbable poly-l/d-lactide 96/4 suture. A histological in vivo study with rabbits

The bioabsorbable poly-l/d-lactide (PLDLA) 96/4 suture has good biomechanical and knot properties, and sufficient tensile strength half-life for flexor tendon repair. In the present study, the biocompatibility of PLDLA suture was compared with that of coated braided polyester suture in the rabbit flexor digitorum profundus tendon repaired within the tendon sheath. Postoperative unrestricted active mobilization was allowed. The tendons were studied histologically after 1-, 3-, 6-, 12-, 26-, and 52-week follow-ups. No differences were found in the biocompatibility between the suture materials, with only scattered multinuclear giant cells near the sutures in both groups from 6 weeks onwards. At 52 weeks, most of the PLDLA material was absorbed and the histological structure of the tendon appeared normal, whereas in the polyester repairs the suture knots filled the repair site, causing bulking of the tendon surface, and the collagen alignment appeared disoriented. The results suggest that the PLDLA 96/4 is a suitable suture material for flexor tendon repair.     

Effects of elastin-derived peptide on Achilles' tendon healing: An experimental study

Different matrix macromolecules modulate the tendon healing process. Elastin contains sequences which exhibit chemotactic activity both in vitro and in vivo. We analyzed the effects of synthetic elastin-derived peptide Val-Gly-Val-Ala-Pro-Gly suspended in a gel solution on the healing process of Achilles' tendon in a rat model. A total tenotomy at the middle 3rd was performed in 32 rats. During the suture repair the gel with (Group A) or without (Group B) the elastin-derived peptide was applied to the tendon stumps. Four animals for each period and group were killed at 10, 30, 60 and 90 days after surgery. The scar tissue was processed for histochemical, immuno-histochemical and morphometric analysis. An improved healing process with increase in cellularity and vascularity, especially at the early stage of the Achilles' tendon healing process was observed in Group A compared to Group B. The fiber alignment was also positively influenced by the factor. Immunolabeling with HAM 56 and lisozyme revealed a stronger reaction for the presence of monocyte/macrophage in Group A vs Group B especially in early stages. Chondral metaplasia and endochondral ossification occurred in the healed tissue of both group at 60 and 90 days.     

Ultrasonic assessment of extracellular matrix content in healing Achilles tendon

Although several imaging modalities have been utilized to observe tendons, assessing injured tendons by tracking the healing response over time with ultrasound is a desirable method which is yet to be realized. This study examines the use of ultrasound for non-invasive monitoring of the healing process of Achilles tendons after surgical transection. The overall extracellular matrix content of the transection site is monitored and quantified as a function of time. B-mode images (built from successive A-scan signatures) of the injury site were obtained and compared to biomechanical properties. A quantitative measure of tendon healing using the extracellular matrix (ECM) content of the injury site was analyzed using linear regression with all biomechanical measures. Contralateral tendons were used as controls. The trend in the degree of ECM regrowth in the 4 weeks following complete transection of excised tendons was found to be most closely paralleled with that of linear stiffness (R(2) = 0.987, p < .05) obtained with post-ultrasound biomechanical tests. Results suggest that ultrasound can be an effective imaging technique in assessing the degree of tendon healing, and can be used to correlate structural properties of Achilles tendons.     

Computational homogenization of regular cellular material according to classical elasticity

A two-scale computational homogenization method for deriving the effective elastic parameters of regular cell material is presented. In the present application, particle model is used as the micromechanical model and classical linear elasticity as the continuum model. The method is designed to render the same effective elastic parameters irrespective of the Representative Volume Element (RVE) used for a cell structure. This requires simultaneous fulfillment of the kinematic and kinetic conditions of computational homogenization derived in the study. Also, the relationship between the quantities of the micromechanical and continuum model needs to be invertible on a RVE. Effective elastic parameter expressions for eight planar cellular materials obtained with a typical cell as the RVE are compared to their counterparts in literature. As an application example, a new closed-form compliance expression covering e.g. the square, regular hexagon, rhombus, over-expanded hexagon, and re-entrant hexagon cell structures of literature is presented.     

A micromechanical fracture analysis to investigate the effect of healing particles on the overall mechanical response of a self‐healing particulate composite

A computational fracture analysis is conducted on a self‐healing particulate composite employing a finite element model of an actual microstructure. The key objective is to quantify the effects of the actual morphology and the fracture properties of the healing particles on the overall mechanical behaviour of the (MoSi₂) particle‐dispersed Yttria Stabilised Zirconia (YSZ) composite. To simulate fracture, a cohesive zone approach is utilised whereby cohesive elements are embedded throughout the finite element mesh allowing for arbitrary crack initiation and propagation in the microstructure. The fracture behaviour in terms of the composite strength and the percentage of fractured particles is reported as a function of the mismatch in fracture properties between the healing particles and the matrix as well as a function of particle/matrix interface strength and fracture energy. The study can be used as a guiding tool for designing an extrinsic self‐healing material and understanding the effect of the healing particles on the overall mechanical properties of the material.     

A comparative study of zirconium and titanium implants in rat: osseointegration and bone material quality

Permanent metal implants are widely used in human medical treatments and orthopedics, for example as hip joint replacements. They are commonly made of titanium alloys and beyond the optimization of this established material, it is also essential to explore alternative implant materials in view of improved osseointegration. The aim of our study was to characterize the implant performance of zirconium in comparison to titanium implants. Zirconium implants have been characterized in a previous study concerning material properties and surface characteristics in vitro, such as oxide layer thickness and surface roughness. In the present study, we compare bone material quality around zirconium and titanium implants in terms of osseointegration and therefore characterized bone material properties in a rat model using a multi-method approach. We used light and electron microscopy, micro Raman spectroscopy, micro X-ray fluorescence and X-ray scattering techniques to investigate the osseointegration in terms of compositional and structural properties of the newly formed bone. Regarding the mineralization level, the mineral composition, and the alignment and order of the mineral particles, our results show that the maturity of the newly formed bone after 8 weeks of implantation is already very high. In conclusion, the bone material quality obtained for zirconium implants is at least as good as for titanium. It seems that the zirconium implants can be a good candidate for using as permanent metal prosthesis for orthopedic treatments.     

A hybrid inverse method for evaluating FC-PBGA material response to thermal cycles

This study proposes a hybrid experimental-analytical inverse method that can be used to evaluate thermomechanical cyclic behavior of flip-chip plastic ball grid array modules and the constituent materials. Treating such a package as an adhesively bonded trilayer plate, the structural formulation follows and modifies an existing analytical model. A phase-shifted shadow moiré method is employed to obtain the package thermal warpage variation in responding to a temperature cycle. By correlating the modeling predicted and the experimentally measured package warpage, the application of the method leads to the determination of those uncertain material parameters including temperature dependent modulus of elasticity and coefficient of thermal expansion of the die attachment and the substrate materials. These parameters are difficult to determine otherwise due to the complexity involving the effect of package processing condition and extremely thin thickness of the adhesive layer. As the values of all material parameters are ascertained, shear and peel stresses in the module adhesive layer can also be evaluated based on the analytical model.     

A note on the impact response of a cracked orthotropic material

An approach involving potential functions is used to simplify the equations of motion for an Orthotropic material to an elementary differential equation whose solution may be used for a wide variety of problems in elastodynamics of Orthotropic materials. Solutions for the dynamic mode I and II stress intensity factors for a Griffith crack in an Orthotropic material are obtained. The new approach allows the stress intensity factors to be determined with a minimal use of integral transforms. The solutions for the stress intensity factors are shown to be the same as those obtained by previous researchers.     

Contribution of material properties of cellular components on the viscoelastic,stress-relaxation response of a cell during AFM indentation

The close relationship between the mechanical properties of biological cells, namely, elasticity, viscosity, and the state of its disease condition has been widely investigated using atomic force microscopy (AFM). In this study, computational simulation of the AFM indentation is carried out using a finite element (FE) model of an adherent cell. A parametric evaluation of the material properties of the cellular components on the viscoelastic, stress-relaxation response during AFM indentation is performed. In addition, the loading rate, the size of the nucleus, and the geometry of the cell are varied. From the present study, it is found that when comparing the material properties derived from experimental force-deflection curves, the influence of loading rates should be accommodated. It also provides a framework that can quantify the variation of the mechanical property with various stages of malignancy of the cancer cell, a potential procedure for cancer diagnosis.     

Consumer response to the tris controversy: A research study

The purpose of the research was to study the possible long-term effects of the public controversy that arose when the most widely used flame retardant (FR) finish. Tris, was first identified as a potential carcinogen. Parents of children enrolled in 15 selected nursery schools and day care centers in Rhode Island were surveyed to determine changes in their practices and in their attitudes toward the use of FR finishes for children's sleepwear. Almost 85% of the 269 respondents had heard or read about problems with FR chemicals. Of these, only 68% remembered that Tris was considered to be a carcinogen and/or health hazard and only 20% reported appropriate changes, such as reading labels, in their purchasing behavior. Absence of Health Risk was the primary consideration used in the purchase of children's sleepwear followed, in order, by Flame Retardancy, Comfort, Durability. Price, Ease of Care and Attractiveness. Despite the problems with Tris, most respondents felt strongly that FR garments should be available for a variety of population groups. They were less convinced that the government should set flammability standards and the majority wanted the freedom to choose between flame retardant and non-flame retardant garments for themselves and their children. Cluster and chi square analyses based on the criteria used in the selection of children's sleepwear showed seven distinct patterns of response but few significant differences between the clusters in respect to opinions and practices. Additional chi square analyses did, however, show some relationships between demographic variables and respondents' shopping practices, understanding of terminology, sources of information and opinions regarding the importance of FR garments and the expansion of government regulation. Many consumers appeared to be confused by the controversy. Specific recommendations for dealing with such problems need to be presented in a variety of media in order to reach different segments of the population; the often misunderstood term “flame resistant” should be retired from use; some non-toxic FR garments should be made available to all population groups: labels and promotional materials should be more informative; consideration should be given to the long-range health, safety and cost effectiveness of government regulations and more research should be conducted to increase understanding of consumer behavior.     

Fibrous wound repair associated with biodegradable poly-L/D-lactide copolymer implants: study of the expression of tenascin and cellular fibronectin

Extracellular matrix (ECM) proteins are known to play a role in inflammatory and hyperplastic processes. Our aim in the present study was to study the distribution of tenascin (Tn), cellular fibronectins (cFn) and myofibroblasts around biodegradable poly-L/D-lactide (PLA) implants with monoclonal antibodies (MAb). Ethylene-oxide and gamma-irradiation sterilized PLA plate-type implants were inserted into the dorsal subcutaneous tissue of ten adult rabbits. Follow-up times were 4, 12, 16, 36 and 48 wk. Only some inflammatory cells were observed. In electron microscopy, a close coherence between the implant and the stromal tissue was seen. Immunoreactivity for Tn, cFn and -actin was detected as a distinct layer bordering the implant, regardless of the sterilization method for the first 36 wk. From week 36 onwards, Tn immunoreactivity was downregulated while cFn immunoreactivity still persisted. A moderate upregulation for myofibroblasts was seen on the week 48 specimens, when hydrolysation of PLA implant had started. The persistent content of myofibroblasts, Tn and cFn suggests a prolonged wound healing produced by PLA implants. The absence of Tn at the week 48 specimens suggests that cFn, rather than Tn may be needed for -actin-mediated contraction by myofibroblasts.     

人耳对信号频率瞬时变化的听觉响应研究

从探讨人耳在噪声背景中听测具有复杂时间－频率结构的主动声呐信号的模型出发，研究了人耳对信号频率发生短时间变化的感觉灵敏性问题。根据在８５０～１１３０Ｈｚ频段内的测量结果，得出了人耳听觉对频率变化响应的模糊区域由τ△Ｆ＝１～２决定。这里τ和△Ｆ分别是指信号频率变化的时间间隔及变化的差值。当τｔ△Ｆ≤１时，人耳感觉不到频率的瞬变，而当，τ△Ｆ≥２时则能十分清楚地分辨。     

The correct analysis of shocks in a cellular material

Cellular materials have applications for impact and blast protection. Under impact/impulsive loading the response of the cellular solid can be controlled by compaction (or shock, see Tan et al. (2005) 3 and 4) waves. Different analytical and computational solutions have been produced to model this behaviour but these solutions provide conflicting predictions for the response of the material in certain loading scenarios. The different analytical approaches are discussed using two simple examples for clarity. The differences between apparently similar “models” are clarified. In particular, it is argued that mass-spring models are not capable of modelling the discontinuities that exist in a compaction wave in a cellular material.     

A model material approach to the study of fracture process zone of quasi-brittle materials

A new approach to study the fracture of quasi-brittle materials is introduced: the design and testing of model materials. By model material is understood a material with enlarged microstructure and which material parameters, such as stacking and mechanical properties of particles and cohesion force, can be fully controlled. In this paper a first example to the model materials approach is presented, consisting in 5 mm steel particles bonded in a precise stacking with an epoxy-based glue. It is shown how it is possible to correlate the different fracture mechanisms and ultimate peak load of the model material to the particle pair force and to the fracture process zone size. It is also seen how a quasi-brittle behaviour is produced in the presence of mechanisms that induced the crack to shift fracture planes, that is, in presence of energy dissipative mechanisms.     

A cellular concrete material used for thorough cleaning of wastewater generated in electroplating process

Heavy metals are of special concern because of their toxicity and negative impact on living organisms. An active porous material for adsorption of heavy metals from aqueous solutions has been manufactured. The material is a sort of cellular concrete with some iron containing industrial dust as an additive. The dust is a result of cleaning of metal elements in the mining machinery production process. Several adsorbents were manufactured. For the adsorbents, the kinetics of batch process of removal of Cu, Zn, Cr and Ni ions from aqueous solutions has been investigated. Laboratory tests of the sorption material were promising. The process is quick; within several minutes the material uptakes over 70% of metal contained in the solution. A trial of continuous treatment of effluents from electroplating facility has been conducted in industry. The employed material demonstrated high cleaning ability firmly binding Cu, Zn, Cr and Ni ions. A sulfuric acid solution of pH value corresponding to the “acid rain”, leached only insignificant amounts of these metals.     

A computational study of the piezoelectric response due to the material effect in periodic, single island thin films and the geometric effect in periodic, bi-island thin films

The electromechanical response of a square-periodic array of circular piezoelectric (PE) thin films alternating with non-piezoelectric (NPE) films is studied in this paper. The material effects are studied for four film/substrate combinations in absence of NPE films for which it is found that if d_zxx ? d_zzz (z-axis being normal to the interfacial plane between the film and the substrate), it results in reduced substrate bending leading to reduced degradation in the electromechanical response of the thin film. The bi-island structure is studied for zinc oxide on strontium titanate, and, in general, it is seen that the NPE films not only reduce degradation of the electromechanical response of the PE films but also increase their internal stresses; the effect on the former is less than the latter. These effects are most prominent when the circular NPE thin films fill the space between the PE thin films and are elastically very stiff compared to the substrate.     

A parametric study of material damping in fibre-reinforced plastics

In this paper, the important parameters causing energy dissipation in unidirectional glass fibre-reinforced epoxy laminae are investigated. Three parameters are considered: matrix and fibre damping and the effect of the interface. An energy balance approach is used to find closed-form relationships between material properties and design parameters. This approach shows that the fibre or matrix contribution to damping lies in the partition of elastic strain energy, which is highly dependent on the elastic properties of the fibres and matrix. A three-phase model is developed which clearly shows that a poor quality interface, with low elastic stiffnesses, has a significant effect on the energy damping capacity of the unidirectional laminate. However, in the case of a normal quality interface, more sensitive and accurate damping measurement methods are needed to identify the contribution of interface damping to the global laminate damping behaviour.     

A penetration test to study the mechanical response of mortar in ancient masonry buildings

A simple method for studying the mechanical response of the mortar in existing masonry buildings is presented herein. The method is based on the measurement of the penetration depth increment of a steel probe (4 mm diameter) at each hammer blow (impact energy=2.2 J). Numerous tests were carried out on different laboratory specimens in order to formulate a relationship between the compressive strength and the probe penetration rate, and a series of tests on actual masonry elements confirmed that the proposed relationship is sound.

---

Résumé On présente une méthode d’essai simple pour évaluer la resistance à la compression des mortiers des murs existants. La méthode proposée ici est basée sur la mesure de la profondeur de pénétration d’une sonde d’acier (4 mm de diamètre), à chaque coup de scléromètre (énergie d’impact=2,2 Joule). Les résultats de nombreux essais effectués sur des éprouvettes construites en laboratoire ont permis d’obtenir une relation entre la résistance à la compression du mortier et la vitesse de pénétration de la sonde. En outre, la validité de cette méthode a été confirmée par une série d’essais effectués sur des murs existants.