Search Results (29)

In this study, poly-DL-lactic acid (PDLLA) was synthesized via ring-opening polymerization (ROP) to develop a biomedical scaffold for tissue engineering. A rotary evaporator with a two-stage vacuum pump under an inert atmosphere and constant stirring was used. A factorial design with three factors (oligomerization time, ROP time, and catalyst concentration) at two levels was applied. Polymers were characterized by FTIR, capillary viscometry, ¹H-NMR, DSC, and TGA. The kinetic study revealed a first-order model, indicating that the polymerization rate depends linearly on monomer concentration. The activation energy (70.5 kJ/mol) suggests a moderate energy requirement, consistent with ring-opening polymerization, while the high pre-exponential factor (6.93 × 10⁶ min⁻¹) reflects a significant frequency of molecular collisions. The scaffold was fabricated via extrusion and 3D printing, and its morphology, porosity, mechanical properties, and contact angle were studied. The highest molecular weight PDLLA was obtained with 6 h of oligomerization, 4 h of ROP, and 1% catalyst concentration. The samples exhibited thermal stability below 40 °C, while the scaffold reached 71.6% porosity, an 85.97° contact angle, and a compressive strength of 4.24 MPa with an elastic modulus of 51.7 MPa. These findings demonstrate the scaffold’s potential for biomedical applications. Full article

Magnesium and its rare-earth alloys are extensively studied for their lightweight properties and high specific strength, making them attractive for aerospace, automotive, and biomedical applications. However, their hexagonal close-packed structure leads to a strong basal texture, limiting plasticity and formability at room temperature. Considerable research has been devoted to texture control strategies, including alloying, thermomechanical processing, and recrystallization mechanisms, yet a comprehensive understanding of their effects remains an ongoing research focus. This review summarizes recent advances in texture regulation of rare-earth magnesium alloys, focusing on the role of RE elements (Gd, Y, Nd, Ce) and non-RE elements (Zn, Ca) in modifying basal texture and enhancing mechanical properties. The influence of key processing techniques, such as extrusion, rolling, equal channel angular pressing, and rotary shear extrusion, is discussed in relation to their effects on recrystallization behavior. Additionally, the mechanisms governing texture evolution, including continuous dynamic recrystallization, discontinuous dynamic recrystallization (DDRX), and particle-stimulated nucleation, are critically examined. By integrating recent findings, this review provides a systematic perspective on alloying strategies, processing conditions, and recrystallization pathways, offering valuable insights for the development of high-performance magnesium alloys with improved formability and mechanical properties. Full article

Objectives: Apical extrusion of debris can affect the success of endodontic treatments, and the specific performance of certain retreatment systems has not been studied yet. Therefore, the aim of this in vitro study was to quantitatively assess the amount of apically extruded debris produced during retreatment procedures using three rotary NiTi retreatment systems in mature non-resorbed straight roots. Methods: Thirty extracted permanent human teeth with single straight roots were selected. The root canals were prepared with the ProTaper Next system up to size 30 and obturated with gutta-percha and AH Plus sealer using the continuous wave of condensation technique. The samples were stored for 30 days and randomized by computer sequence into three retreatment groups (n = 10): (1) ProTaper Universal Retreatment; (2) HyFlex Remover; and (3) VDW.Rotate Retreatment. Apically extruded debris was collected in Eppendorf tubes and weighed with a microbalance (10⁻⁵ g) before and after retreatment procedure. As the data were not normally distributed, the Kruskal–Wallis test was applied for comparing data among groups, with an alpha level set at α = 0.05. Dunn’s test was considered for post-hoc analyses, if appropriate. Results: Hyflex Remover was associated with the highest amount of extruded debris (0.85 ± 0.82 mg), followed by VDW.Rotate Retreatment (0.78 ± 0.41 mg) and ProTaper Universal Retreatment (0.62 ± 0.28 mg). However, the differences were not statistically significant (p > 0.05). Conclusions: All the retreatment systems tested were associated with apical extrusion of debris in vitro, with no significant quantitative differences between them, suggesting that clinicians can choose a retreatment system with features appropriate to the specific clinical situation without risk of increasing the amount of apically extruded debris. Full article

The Al-Si alloy prepared by the traditional powder metallurgy method has the problems of difficult sintering and low mechanical properties. In this paper, rotary extrusion combined with rapid solidification/powder metallurgy technology (RS/PM) is proposed and designed to produce an Al-10Si alloy. In subsequent sintering at different temperatures, better metallurgical bonding between particles can be achieved to fulfil the aim of improving the mechanical properties of the material. Additionally, the continuous preparation of materials can be achieved. Finally, it is verified that the density of the Al-10Si alloy sintered at 525 °C is 2.61 g/cm³, reaching 97.0% of the theoretical density, and the tensile strength reaches 336 MPa, which is much higher than that of the alloy prepared by the traditional casting method and powder metallurgy method. Full article

The introduction of nickel–titanium rotary instruments revolutionized shaping procedures as they were able to produce a well-tapered preparation while reducing operator fatigue. The major drawback of rotary instruments was the high risk of fracture due to bending and torsional stress. Thus, the creation of a glide path has been advocated and recommended by most rotary instrument manufacturers. The aim of the present review is to summarize existing knowledge on glide path preparation and identify areas where further research is needed. The primary goal is to provide a comprehensive overview of the techniques and instruments used in glide path preparation, highlighting their advantages and limitations. The secondary goal is to explore the effect of glide path creation on the overall success of endodontic treatment, particularly in terms of reducing procedural errors and improving treatment outcomes. An online search on PubMed, ScienceDirect, UCLA, and Scopus databases was conducted, and 116 articles were identified. Eligible articles were divided into nine categories based on what they researched and compared. The categories included centering ability and/or root canal transportation, cyclic fatigue resistance, glide path and shaping time, tortional stress resistance, apical extrusion of debris and/or bacteria, defects in dentine walls, file separation, postoperative pain assessment, and scouting ability and performance. Establishing a glide path reduces root canal transportation, especially with rotary methods. Reciprocating and heat-treated files offer higher fatigue resistance and shorter preparation time. Instruments with shorter pitch lengths have greater torsional strength. Preparation and coronal preflaring reduce apical debris and bacteria. Glide paths do not affect dentine microcracks, file separation, or defects but reduce immediate postoperative pain and improve cutting ability. Randomized trials are needed to assess their impact on treatment outcomes. Full article

In order to solve the traditional single-spiral fertilizer discharger issue of the fluctuation of fertilizer-discharge flow and the problem of precise fertilizer discharge, the innovative design of a cantilevered oblique placement of a fertilizer-discharging spiral structure in the form of an inclined spiral fertilizer discharger was realized, in which, through the fertilizer spiral’s full end-filled extrusion, uniform delivery of the discharge was achieved. Discrete element simulation was used to compare the fertilizer-discharge characteristics of inclined and traditional single-spiral fertilizer dischargers, and the results proved that the inclined spiral fertilizer discharger effectively reduced the fluctuation of the fertilizer-discharge flow rate. Through a theoretical analysis preformed to determine the theoretical fertilizer discharge and the main parameters affecting the uniformity of fertilizer discharge, we identified the tilting angle of the fertilizer discharger (θ) and the distance from the termination spiral blade to the fertilizer outlet (l). A two-factor, five-level quadratic generalized rotary combination experiment was conducted with two parameters (θ and l) as the experiment factors and the variation coefficient of fertilizer-discharge uniformity (σ) as the experiment indicator. The experimental results showed that for σ, θ was a highly significant effect, l was a significant effect, and σ was less than 8.5%; when θ was 35.02° and l was 16.87 mm, the fertilizer-discharge performance was better. A bench experiment was used to compare the traditional and inclined spiral fertilizer dischargers, and the results showed that the relative error of the variation coefficient between the bench and the simulation experiment under this combination was 2.28%. And compared with the traditional spiral fertilizer discharger’s σ average increase of 80.79%, the effect of fertilizer discharge was better than the traditional spiral fertilizer discharger. A fertilizer application controller was developed, and the bench performance was tested based on the measured fertilizer-discharge flow rate fitting equation of this combined inclined spiral fertilizer discharger. The results show that the electronically controlled inclined spiral fertilizer discharger has an average deviation of 3.12% from the preset value, which can be used to regulate the flow of fertilizer discharged through the fertilizer controller to realize precise fertilizer application, and this study can provide a reference for the optimal design of the spiral fertilizer discharger. Full article

Background: Andrographolide (ADG) has poor aqueous solubility and low bioavailability. This study systematically reviews the use of solid dispersion (SD) techniques to enhance the solubility and absorption of ADG, with a focus on the methods and polymers utilized. Methodology: We searched electronic databases including PubMed, Web of Science, Scopus^®, Embase and ScienceDirect Elsevier^® up to November 2023 for studies on the solubility or absorption of ADG in SD formulations. Two reviewers independently reviewed the retrieved articles and extracted data using a standardized form and synthesized the data qualitatively. Results: SD significantly improved ADG solubility with up to a 4.7-fold increase and resulted in a decrease in 50% release time (T_1/2) to less than 5 min. SD could also improve ADG absorption, as evidenced by higher C_max and AUC and reduced T_max. Notably, Soluplus-based SDs showed marked solubility and absorption enhancements. Among the five SD techniques (rotary evaporation, spray drying, hot-melt extrusion, freeze drying and vacuum drying) examined, spray drying emerged as the most effective, enabling a one-step process without the need for post-milling. Conclusions: SD techniques, particularly using Soluplus and spray drying, effectively enhance the solubility and absorption of ADG. This insight is vital for the future development of ADG-SD matrices. Full article

Background: All endodontic treatment techniques are associated with the extrusion of debris into periradicular tissues through the apex. The extrusion of apical debris can lead to delayed healing or even therapy failure. It is possible to reduce the extrusion into periapical tissues through various approaches. The objective of this systematic review is to evaluate whether, in cases of non-surgical endodontic retreatment, reciprocating instruments cause greater extrusion of debris compared to instruments with continuous rotation. Methods: A search was conducted on PubMed, Ovid MEDLINE, and the Web of Science. The inclusion criterion was in vitro studies comparing apical extrusion in endodontically treated elements using continuously rotating and reciprocating files. Results: The search on scientific databases yielded 164 results, out of which only 16 were eligible for evaluation after screening. Conclusions: The authors of the research included in this review do not agree on the results obtained. Based on the articles analyzed in this systematic review, it remains unclear whether continuous rotation or reciprocating movement of the endodontic instrument can lead to significant differences in apical debris extrusion; it is not possible to provide a clear clinical recommendation regarding the choice of instrument movement for endodontic procedures. Full article

Bubble growth processes are highly influenced by the elongational viscosity of the blowing agent-loaded polymer melt. Therefore, the elongational viscosity is an important parameter for the development of new polymers for foaming applications, as well as for the prediction of bubble growth processes. Thus, knowledge of the initial expansion and deformation behavior in dependency on the polymer, the blowing agent concentration, and the process conditions is necessary. This study presents a novel method for the in-line observation and analysis of the initial expansion and deformation behavior within the bead foam extrusion process. For this purpose, nitrogen as the blowing agent was injected into the polymer melt (PS and PLA) during the extrusion process. The in-line observation system consists of a borescope equipped with a camera, which was integrated into the water box of an underwater pelletizer. The camera is controlled by a developed trigger by means of angular step signal analysis of a rotary encoder on the cutter shaft of the underwater pelletizer. Thus, images can be taken at any time during the foaming process depending on the cutter position to the die outlet. It is shown that the developed method provides reliable results and that the differences of the initial expansion and deformation behavior during bubble growth can be analyzed in-line in dependency on real foaming process conditions and the type of polymer used. Full article

In the realm of engineering rotary excavation, the rigid and brittle nature of the Polycrystal Diamond Compact (PDC) layer poses challenges to the impact resistance of conical teeth. This hinders their widespread adoption and utilization. In this paper, the Abaqus simulation is used. By optimizing the parameters of the radius of the cone top arc, we analyzed the changing law of the parameters of large-diameter D30 series conical PDC teeth, such as the equivalent force, impact force, and energy absorption of the conical teeth during the impact process, and optimized the best structure of the conical PDC teeth. After being subjected to a high temperature and high pressure, we synthesized the specimen for impact testing and analyzed the PDC layer crack extension and fracture failure. The findings reveal the emergence of a stress ring below the compacted area of the conical tooth. As the radius of the cone top arc increases, so does the area of the stress ring. When R ≥ 10 mm, the maximum stress change is minimal, and at R = 10 mm, the stress change in its top unit is relatively smooth. Optimal impact resistance is achieved, withstanding a total impact work value of 7500 J. Extrusion cracks appear in the combined layer part of PDC layers I and II, but the crack source is easy to produce in the combined layer of PDC layer II and the alloy matrix and extends to both sides, and the right side extends to the surface of the conical tooth in a “dragon-claw”. The failure morphology of the conical teeth includes ring shedding at the top of the PDC layer, the lateral spalling of the PDC layer, and the overall cracking of the conical teeth. Through this study, we aim to promote the popularization and application of large-diameter conical PDC teeth in the field of engineering rotary excavation. Full article

To meet the demand for more extensive applications of Mg alloys, a Mg-5Al-2Ca-1Mn-0.5Zn alloy without RE was prepared in this paper, and its mechanical properties were further improved by conventional hot extrusion and subsequent rotary swaging. The results show that the hardness of the alloy decreases along the radial central region after rotary swaging. The strength and hardness of the central area are lower, but the ductility is higher. The yield strength and ultimate tensile strength of the alloy in the peripheral area after rotary swaging reach 352 MPa and 386 MPa, respectively, while the elongation remains at 9.6%, exhibiting better strength–ductility synergy. The grain refinement and dislocation increase caused by rotary swaging promoted strength improvement. The activation of non-basal slips during rotary swaging is an important reason for the alloy to maintain good plasticity while improving strength. Full article

Successful outcome of pulp therapy depends on good chemomechanical preparation of the canals. This is completed with the help of various upcoming rotary and hand files. However, during this preparation, there might be an apical extrusion of the debris which may result in postoperative complications. The aim of this study was to evaluate and compare the number of debris apically extruded during canal preparation using two different pediatric rotary file systems and conventional hand file systems in primary teeth. 60 primary maxillary central incisors that were extracted due to trauma or untreated dental caries with no signs of resorption were taken. Canal preparation was executed using three different file systems: Group A: Group A hand K file system, Group B Kedo S Plus, Group C Kedo SG Blue. For each of these files using the Myers and Montgomery model, the pre- and post-weight of the eppendorf tube was assessed to quantify the number of apical debris. The maximum extrusion of apical debris was noticed with the Hand K-file system. The least debris was noticed in the Kedo S Plus file system. Statistical analysis revealed that there were highly significant differences in apical extrusion and debris when comparing hand files and rotary files and also between the two rotary files used. Apical debris collection is an unavoidable outcome of canal instrumentation. Among the file systems compared, rotary files had lesser extrusion when compared to hand files. Among the rotary files, Kedo S plus showed normal extrusion compared to SG Blue. Full article

To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that microseismic events occur and accumulate frequently in the surrounding rock and some overlying key layers of the GSR. Large deformation is experienced in the middle part of roadway near the solid coal side, the middle and upper parts of the roadway near the coal pillar side, and the roadway floor. The overlying strata of the GSR are fractured to form a composite structure as “low-level cantilever beam and high-level masonry beam”. The coal pillar is squeezed and effected by the composite beam structure and the rotation moment M, causing serious bulge in middle and upper part of the coal pillar side. The stability of the solid coal side of the roadway is affected by the stress transferred from gangue contact point. Numerical simulation shows that the immediate roof and key layer breakage are induced by the mining of the 30,501 working face. Shear and tension failures happen in the GSR due to overburden subsidence and rotary extrusion. The stress and displacement at the middle and upper of the roadway on the coal pillar side are larger than the other area. Compared with the solid coal side, the coal on the coal pillar side is obviously more fractured, with a lower bearing capacity. The peak stress in the coal pillar shows up 2 m away from the roadway, which is close to the length of bolt support. The mining-induced stress and the stress transferred from gangue contact point are the direct reasons for solid coal bulge beside the roadway. The peak stress on the solid coal side is located 7 m away from the roadway, at the gangue contact point where overburden fractures. The overburden strata loads and the transferred stress near the gangue contact point are transferred from the sides to the roadway floor. Their coupling effect with the in situ horizontal stress acts as the force source for the plastic floor heave. Full article

A study of the effect of rotary swaging (RS) on the microstructure and properties of the pre-extruded and pre-quenched Cu-0.5%Cr-0.08%Zr alloy was performed. RS leads to the formation of an ultrafine-grained (UFG) microstructure. UFG structure formation caused by RS increases the ultimate tensile strength (UTS) up to 443 ± 5 MPa and 597 ± 9 MPa for pre-quenched and pre-extruded alloys, respectively. Additionally, the reduction in ductility occurs after RS. It should be noted that UTS is increased for a pre-quenched alloy, while the strength of a pre-extruded alloy is dropped. The growth of UTS for the pre-quenched alloy is associated with the precipitation of fine Cr particles, whereas the recovery processes in the pre-extruded alloy induce the reduction in its UTS. An additional advantage of RS is an increase in the fatigue limit of the pre-quenched alloy up to 265 MPa, and of the pre-extruded alloy up to 345 MPa. The combination of extrusion and RS allows for the increase of the UTS of the Cu-0.5%Cr-0.08%Zr alloy up to 597 ± 9 MPa, while the levels of ductility and electrical conductivity are 10.9 ± 0.9% and 82.0 ± 1.7% IACS, respectively. Full article

In large ports, shipyards, and other places of handling operations, gantry cranes are widely used. As a typical slewing crane, its slewing-bearing large gear ring is prone to tooth breakage problems due to the existence of long-term complex alternating load. This paper presents a new fault analysis method based on the gear position accuracy error. Firstly, the relative displacement relationship between the pinion and large gear ring and the large gear ring gear teeth stress nature were analyzed through the establishment of the rotary table structure, slewing bearing, and cylinder structure assembly finite element model. In addition, a dynamic data acquisition instrument and resistance strain gauge data were separately applied to analyze the pinion and large gear ring displacement along with cylinder structure stress for the test position accuracy error. The final results show that under the frontal load condition, the horizontal displacement deviation of the pinion gear and the large gear ring is approximately 2.9 mm, which leads to an increase of 23% in the stress value of the upper tooth root at the engagement of the large gear ring, causing extrusion and accelerating the fatigue and even fracture of the gear teeth. Full article