Modified Hyaluronic Acid-Laminin-Hydrogel as Luminal Filler for Clinically Approved Hollow Nerve Guides in a Rat Critical Defect Size Model

Hollow nerve guidance conduits are approved for clinical use for defect lengths of up to 3 cm. This is because also in pre-clinical evaluation they are less effective in the support of nerve regeneration over critical defect lengths. Hydrogel luminal fillers are thought to improve the regeneration outcome by providing an optimized matrix inside bioartificial nerve grafts. We evaluated here a modified hyaluronic acid-laminin-hydrogel (M-HAL) as luminal filler for two clinically approved hollow nerve guides. Collagen-based and chitosan-based nerve guides were filled with M-HAL in two different concentrations and the regeneration outcome comprehensively studied in the acute repair rat sciatic nerve 15 mm critical defect size model. Autologous nerve graft (ANG) repair served as gold-standard control. At 120 days post-surgery, all ANG rats demonstrated electrodiagnostically detectable motor recovery. Both concentrations of the hydrogel luminal filler induced improved regeneration outcome over empty nerve guides. However, neither combination with collagen- nor chitosan-based nerve guides resulted in functional recovery comparable to the ANG repair. In contrast to our previous studies, we demonstrate here that M-HAL slightly improved the overall performance of either empty nerve guide type in the critical defect size model.

Statistical properties of defect-dependent detachment strength in bioinspired dry adhesives

Dry adhesives using surface microstructures inspired by climbing animals have been recognized for their potentially novel capabilities, with relevance to a range of applications including pick-and-place handling. Past work has suggested that performance may be strongly dependent on variability in the critical defect size among fibrillar sub-contacts. However, it has not been directly verified that the resulting adhesive strength distribution is well described by the statistical theory of fracture used. Using in situ contact visualization, we characterize adhesive strength on a fibril-by-fibril basis for a synthetic fibrillar adhesive. Two distinct detachment mechanisms are observed. The fundamental, design-dependent mechanism involves defect propagation from within the contact. The secondary mechanism involves defect propagation from fabrication imperfections at the perimeter. The existence of two defect populations complicates characterization of the statistical properties. This is addressed by using the mean order ranking method to isolate the fundamental mechanism. The statistical properties obtained are subsequently used within a bimodal framework, allowing description of the secondary mechanism. Implications for performance are discussed, including the improvement of strength associated with elimination of fabrication imperfections. This statistical analysis of defect-dependent detachment represents a more complete approach to the characterization of fibrillar adhesives, offering new insight for design and fabrication.

The effect of microstructural heterogeneities on the High Cycle Fatigue scatter of cast aluminium alloys: from an elementary volume to the structure

Cast Al-Si alloys have been widely used in automobile applications thanks to their low density and excellent thermal conductivity. A lot of components made of these alloys are subjected to cyclic loads which can lead to fatigue failure. Furthermore, the well know size effect in fatigue, whereby the fatigue strength is reduced in proportion to an increase in size, can be important. This is caused by a higher probability of initiating a crack in larger specimens (i.e. statistical size effect). This paper analyses the role of casting defects on the statistical size effect. For that, a uniaxial fatigue testing campaign (R=0.1) has been conducted using two cast aluminium alloys, fabricated by different casting processes (gravity die casting and lost foam casting), associated with the T7 heat treatment, and with different degrees of porosity. Different specimens (smooth and notched) with different stressed volumes have been investigated. The first part of this article is dedicated to the experimental characterization of the statistical size effect in both alloys via the concept of the Highly Stressed Volume. The second part investigates the effect of the Highly Stressed Volume on the critical defect size via diagram of Kitagawa-Takahashi. The results show that the presence of statistical size effect is strongly linked to the characteristics of the pore population present in the alloy. A numerical approach, linking the observed pore distribution to the volume of loaded material, is proposed and discussed.

Influence of as-built surface and heat treatment on the fatigue resistance of Additively Layer Manufacturing (ALM) AlSi10Mg alloy.

This work concerns the fatigue resistance of a AlSi10Mg material produced by additive manufacturing, and more precisely the competition between as built manufacturing surface and as-machined surface on the fatigue resistance. Samples were built by a powder-bed process with an EOS-M280 machine using standard in two configurations (0° and 90°) in order to evaluate the impact of building direction on fatigue life. The impact of as-built surface on fatigue behavior is quantified for each specimen configuration. A T6 heat treatment is performed on samples in order to evaluate the impact of microstructure on fatigue behavior. For each configurations, the S-N curves is determined in as-built and T6 materials with a load ratio R= -1. The fracture surfaces are carefully analyzed in order to determine the critical defect size for each sample. A Kitagawa type diagram representing the fatigue limit as a function of the defect size is derived from these measurements. All the results were compared to those obtained in asmachined samples.

Use of Nuclear Mechanical Design Codes and Fracture Mechanics Procedures for the UK EPR™ at Hinkley Point C

Structures, systems and components that are important to nuclear safety are designed, manufactured, constructed, installed, commissioned, quality assured, maintained, tested and inspected to the appropriate standards. The codes and standards need to be evaluated to determine their applicability, adequacy and sufficiency. The consideration of a conservative design is one important element of the Safety Case. This is generally used together with high manufacturing quality, the use of proven materials, inspection, functional testing and defect tolerability. In a UK Safety Case, the assessment of fracture risk of those mechanical components whose likelihood of gross failure is so low that can be discounted requires the determination of the actual critical defect size in order to compare it with the detectable defect size used for inspections. For the UK EPR™ the 2007 Edition of the RCC-M Code including Addenda 2008, 2009 and 2010 will be the design code of reference and the RSE-M Code version 2010 Appendix 5 will form the basis of the methodology used for standard fracture mechanics assessments of the UK EPR™. Previously, the UK nuclear structural integrity community has used the ASME Code Section III for the UK previous PWR and the R6 procedure for fracture mechanics assessments. This paper explains the choice of these two codes for the UK EPR™ and the work carried out to date by EDF Energy to demonstrate its compliance with the UK expectations for components critical to safety.

A New Retention Method for Sub-10 nm Liquid Filtration Using Fluorescent CdSe QDs

As advances are made in the lithographic patterning process and critical defect size continues to shrink, new filters are required to remove particles in the sub-10 nm size range. Membrane filtration separates unwanted particles from a fluid by retaining particles on the membrane surface and pores, in much the same manner as a sieve. One key parameter of membrane performance is pore size, usually expressed as pore diameter. However, for nanofiltration, especially for the membranes whose pore size measures under 30 nm, manufacturers may use different methods to rate the membranes pore. Considering the different chemical structures of membranes, the vast combination of materials, and the methods of manufacturing, it is highly unlikely that a universal method can be used for all combinations.