Tissue reaction to novel customized calcium silicate cement based dental implants. A pilot study in the dog

Objectives The purpose of this study was to determine the level of periodontal tissue regeneration in a canine model following post-extraction placement of an implant molded from a composite material made from extracted tooth dentin and a calcium silicate cement (CSC) material. The investigation used autologous dentin in conjunction with a CSC material to form a composite implant designed for immediate tooth replacement. Methods Two (2) beagles had a periodontal and radiographic examination performed to rule out any pre-treatment inflammation, significant periodontal disease, or mobility. Then, ination eleven (11) teeth were extracted and polyvinyl siloxane molds were made to fabricate three different types of implants: Particulate Implant (Test Group 1, n = 4), Shell Implant Alone (Test Group 2, n = 2), Shell Implant with Emdogain® (Test Group 3, n = 3). Teeth in the control group were extracted, scaled (n = 2), and then re-implanted into their respective fresh extraction sockets. At 4 weeks, a clinical, radiographic, and histologic assessment was performed. Results Clinical evaluation revealed no mobility in any of the test or control implants and no radiographic evidence of significant bone loss or active disease. Based on the MicroCT analysis, direct bone to implant contact was observed in some areas with an apparent periodontal ligament space. Implant-related inflammation, on average, was similar among all groups, with low numbers of infiltrates. Implant-related inflammatory reaction was generally minimal and not interpreted to be adverse. Conclusion The proposed novel composite materials revealed that not only do these materials demonstrate high biocompatibility, but also their successful integration in the alveolus is likely secondary to a partial ligamentous attachment. The current investigation may lead to the use of calcium silicate-based materials as custom dental implants. Further research on this novel composite’s biomechanical properties is necessary to develop the optimal material composition for use as a load-bearing dental implant.

Hydrogen-assisted cracking in GMA welding of high-strength structural steels using the modified spray arc process

High-strength structural steels are used in machine, steel, and crane construction with yield strength up to 960 MPa. However, welding of these steels requires profound knowledge of three factors in terms of avoidance of hydrogen-assisted cracking (HAC): the interaction of microstructure, local stress/strain, and local hydrogen concentration. In addition to the three main factors, the used arc process is also important for the performance of the welded joint. In the past, the conventional transitional arc process (Conv. A) was mainly used for welding of high-strength steel grades. In the past decade, the so-called modified spray arc process (Mod. SA) has been increasingly used for welding production. This modified process enables reduced seam opening angles with increased deposition rates compared with the Conv. A. Economic benefits of using this arc type are a reduction of necessary weld beads and required filler material. In the present study, the susceptibility to HAC in the heat-affected zone (HAZ) of the high-strength structural steel S960QL was investigated with the externally loaded implant test. For that purpose, both Conv. A and Mod. SA were used with same heat input at different deposition rates. Both conducted test series showed same embrittlement index “EI” of 0.21 at diffusible hydrogen concentrations of 1.3 to 1.6 ml/100 g of arc weld metal. The fracture occurred in the HAZ or in the weld metal (WM). However, the test series with Mod. SA showed a significant extension of the time to failure of several hours compared with tests carried out with Conv. A.

A novel serum: Electrophoresis method to prepare acellular corneal matrix as an artificial corneal scaffold

Introduction: The aim of this study was to develop a novel decellularization method in order to obtain an ideal scaffold with good biocompatibility. Methods: The porcine corneas were treated with human serum for 5 days or serum-electrophoresis respectively. The electrophoresis (100 V/cm) was performed in sterilized buffer containing 40-mM tris base, 18-mM glacial acetic acid, and antibiotics for 1 h at 4°C. The properties of artificial corneal scaffolds were characterized by morphological and histological examinations. The biocompatibility and biological safety were examined by subcutaneous implant test and lamellar keratoplasty. Results and conclusions: The transparency and appearance of serum-electrophoresis acellular porcine corneal matrix were better than serum acellular porcine corneal matrix. DNA and α-gal in serum-electrophoresis acellular porcine corneal matrix were more efficiently removed than those in serum acellular porcine corneal matrix (p < 0.05). The subcutaneous and corneal implantation experiments showed serum-electrophoresis acellular porcine corneal matrix had better biocompatibility compared to serum acellular porcine corneal matrix (p < 0.01). This novel serum-electrophoresis decellularization method may be valuable for preparation of xenogenic corneal tissue for clinical application.

Temperature impact on delayed fracture of creep-resistant steels welds

Purpose: Phenomenon of delayed fracture (or cold cracks formation) of hardenable steels weldments had been widely investigated. But temperature dependence of cracking susceptibility remained discussable, because there was no strict vision of temperature border for the cracking risk appearance, when joints are cooling after welding completion. The proposed paper aimed at assessment of dangerous temperature range at which delayed fracture, mainly for the steels with martensite formation, becomes most probable. Design/methodology/approach: The “Implant” test, conducted under isothermal conditions at the temperatures selected within the range from 160 to 20°C on cooling of the completed test weld joint, was used. Basing on the obtained thermokinetic characteristics of the cracking, the activation energy E of the fracture process was calculated. Comparing of the found E values with the close values of E for the known processes developing in steels, the explanation of the revealed cracking behaviour at different temperatures was proposed. Findings: Delayed cracking of the martensitic weld joints has started to manifest at the temperatures lower than 140°C. Dependence of the cracking period from the temperature is described by C-type curve with the minimum cracking duration within 80-100°C. Using the approach of the activation energy assessment for different temperature ranges (140 to 100°C and 80 to 20°C), the effect of the diffusible hydrogen and a martensite decay on the cracking thermokinetics was considered. Research limitations/implications: Additional investigations of the fine microstructure after different stages of the low-temperature martensite decay could be necessary for deepening understanding of a role of this process in the low-temperature heterogeneity formation and cracking susceptibility. Practical implications: Results widen data on weldability of actual for industry steels and give a ground for consideration of the technological approaches for their welding. Originality/value: Temperature border of the cold cracking risk is specified for the weldments of some commercial steels.

Local, Controlled Release In Vivo of Vascular Endothelial Growth Factor Within a Subcutaneous Scaffolded Islet Implant Reduces Early Islet Necrosis and Improves Performance of the Graft

Islet transplantation remains the only alternative to daily insulin therapy for control of type 1 diabetes (T1D) in humans. To avoid the drawbacks of intrahepatic islet transplantation, we are developing a scaffolded islet implant to transplant islets into nonhepatic sites. The implant test bed, sized for mice, consists of a limited (2-mm) thickness, large-pore polymeric sponge scaffold perforated with peripheral cavities that contain islets suspended in a collagen hydrogel. A central cavity in the scaffold holds a 2-mm diameter alginate sphere for controlled release of the angiogenic cytokine vascular endothelial growth factor ( VEGF). Host microvessels readily penetrate the scaffold and collagen gel to vascularize the islets. Here, we evaluate the performance of the implant in a subcutaneous (SC) graft site. Implants incorporating 500 syngeneic islets reversed streptozotocin-induced diabetes in mice approximately 30 d after SC placement. Controlled release of a modest quantity (20 ng) of VEGF within the implant significantly reduced the time to normoglycemia compared to control implants lacking VEGF. Investigation of underlying causes for this effect revealed that inclusion of 20 ng of VEGF in the implants significantly reduced central necrosis of islets 24 h after grafting and increased implant vascularization (measured 12 d after grafting). Collectively, our results demonstrate (1) that the scaffolded islet implant design can reverse diabetes in SC sites in the absence of prevascularization of the graft site and (2) that relatively low quantities of VEGF, delivered by controlled release within the implant, can be a useful approach to limit islet stress after grafting.

Machine GTAW Ambient Temperature Temper Bead Technique for Ni-Based Weld Overlay Repairs of Nuclear Components: Assessment of Hydrogen Cracking by Implant Test

Repair by welding of a metallic component may be required during original fabrication, following in-service inspection or during planned maintenance operations. In some instances a post-weld heat treatment (PWHT) is required. Codes/standards that cover the repair of or alterations on nuclear components, such as Section XI of the ASME Boiler & Pressure Vessel code or the French RSE-M nuclear code for in-service inspection, include provisions for waiving the need for a PWHT by using a welding technique referred to as ‘temper bead’, but in the case of in-service repairs, the practical challenges may make any heating cycles, including pre or post-heating, undesirable. So, starting from the existing temper bead procedures, repair solutions that do not require preheat, PWHT or post-heating, have been developed, particularly in the nuclear sector, referred to as ‘ambient temperature temper bead’ (ATTB). One of the most common applications of the ATTB technique is the deposition of full structural weld overlays (FSWOLs), made with Ni-based consumables on ferritic base materials, to repair piping components and nozzles susceptible to primary water stress corrosion cracking (PWSCC) and to mitigate the risk of further cracking. The ATTB technique is currently permitted for the repair of nuclear power plant components by the ASME code via Code Cases N-638-8 and N-740-2, provided the machine gas tungsten arc welding (GTAW) process is used, and it has been successfully applied on various occasions. However, the technique is currently not permitted by the RSE-M code. As the current rules in the RSE-M codes were established following experimental programs based on implant testing, the same type of tests would be expected by the French nuclear regulator to justify any changes. This paper presents the results of a research project carried out to explore the possibility of justifying the introduction of ATTB using the machine GTAW welding process to deposit austenitic weld overlays into the RSE-M code, based on implant testing. Externally loaded tests according to ISO 17642-3 (Implant test) were carried out to determine the effect of different preheat and stress levels on the cold cracking susceptibility in the parent metal. Test loads representative of actual residual stresses were determined through a review of published literature on the residual stresses associated with ATTB FSWOLs. Test pieces were obtained by depositing single beads with Inconel 52 filler metal (AWS A5.14 ERNiCrFe-7) on ASME SA 508 Grade 4N substrate. Conclusions are presented with regard to the possibility to waive preheat or to reduce the minimum preheat temperature specified for temper bead repairs, with respect to the current RSE-M code requirements. Recommendations for further work required to support a request for modification of the RSE-M code are provided.