Investigations into the Material Characteristics of Selected Plastics Manufactured Using SLA-Type Additive Methods.

In this study, the authors performed a strength analysis of seven groups of commercially available materials based on SLS incremental technology. Test samples were made with Original PRUSA SL1S printers, with 10 samples of each type from 7 resins selected for testing. The tests were carried out on an MTS Bionix machine in a static tensile test, during which the basic mechanical properties were determined. This is also a preliminary study to determine material constants in the Johnson-Cook strength model. The authors then performed numerical simulations to mirror the experimental tests in order to tune the rheological model. In addition, a fracture criterion was determined based on a hybrid FEM/SPH numerical method. This allowed for the expansion of material libraries currently used in numerical simulations, as well as the sensitivity of the materials' models. In subsequent studies, in order to determine the nature of material destruction, analysis of fracture surfaces was performed using a scanning electron microscope (SEM). The final study was a biocompatibility test to assess the biological properties of the material. The conducted research made it possible to determine the strength properties of resins currently used in 3D printers, expand the libraries of material models in the computational environment (with an error rate of less than 5%), as well as observe the nature of the cracks formed and biocompatibility in the context of predicting the use of these materials for biomedical applications.

Investigation into Changes of Microstructure and Abrasive Wear Resistance Occurring in High Manganese Steel X120Mn12 during Isothermal Annealing and Re-Austenitisation Process.

Hadfield steel, under unit pressure conditions, strengthens itself by forming a high density dislocation structure, which results in increased resistance to dynamic impact wear. However, under abrasion conditions, the homogeneous microstructure of the cast steel is insufficient to achieve the expected service life. The aim of the research is to conduct a comparative analysis of the material in its as-delivered state and after two-stage heat treatment (isothermal annealing followed by re-austenitisation). It was found that after isothermal annealing of X120Mn12 grade steel at a temperature of 510 °C, a microstructure with a complex morphology consisting of colonies of fine-grained pearlite, (Fe,Mn)3C carbides distributed along the grain boundaries of the former austenite and needle-like (Fe,Mn)3C carbides was obtained in the austenite matrix. The subsequent thermal treatment of the steel with the use of supersaturating annealing at 900 °C resulted in a heterogeneous microstructure consisting of evenly distributed globular carbide precipitations in a matrix of considerably finer austenite grains in comparison with the as-delivered original state. As a result of the final microstructural changes achieved, a 16.4% increase in abrasion resistance was obtained compared to the delivered condition.

Deposition of Biocompatible Polymers by 3D Printing (FDM) on Titanium Alloy.

Nowadays, the replacement of a hip joint is a standard surgical procedure. However, researchers have continuingly been trying to upgrade endoprostheses and make them more similar to natural joints. The use of 3D printing could be helpful in such cases, since 3D-printed elements could mimic the natural lubrication mechanism of the meniscus. In this paper, we propose a method to deposit plastics directly on titanium alloy using 3D printing (FDM). This procedure allows one to obtain endoprostheses that are more similar to natural joints, easier to manufacture and have fewer components. During the research, biocompatible polymers suitable for 3D FDM printing were used, namely polylactide (PLA) and polyamide (PA). The research included tensile and shear tests of metal-polymer bonds, friction coefficient measurements and microscopic observations. The friction coefficient measurements revealed that only PA was promising for endoprostheses (the friction coefficient for PLA was too high). The strength tests and microscopic observations showed that PLA and PA deposition by 3D FDM printing directly on Ti6Al4V titanium alloy is possible; however, the achieved bonding strength and repeatability of the process were unsatisfactory. Nevertheless, the benefits arising from application of this method mean that it is worthwhile to continue working on this issue.

Printable and Machinable Dental Restorative Composites for CAD/CAM Application-Comparison of Mechanical Properties, Fractographic, Texture and Fractal Dimension Analysis.

Thanks to the continuous development of light-curing resin composites it is now possible to print permanent single-tooth restorations. The purpose of this study was to compare resin composites for milling -Gandio Blocks (GR), Brilliant Crios (CR) and Enamic (EN) with resin composite for 3D printing-Varseo Smile Crown plus (VSC). Three-point bending was used to measure flexural strength (σf) and flexural modulus (Ef). The microhardness was measured using a Vickers method, while fractographic, microstructural, texture and fractal dimension (FD) analyses were performed using SEM, optical microscope and picture analysis methods. The values of σf ranged from 118.96 (±2.81) MPa for EN to 186.02 (±10.49) MPa for GR, and the values of Ef ranged from 4.37 (±0.8) GPa for VSC to 28.55 (±0.34) GPa for EN. HV01 ranged from 25.8 (±0.7) for VSC to 273.42 (±27.11) for EN. The filler content ranged from 19-24 vol. % for VSC to 70-80 vol. % for GR and EN. The observed fractures are typical for brittle materials. The correlation between FD of materials microstructure and Ef was observed. σf of the printed resin depends on layers orientation and is significantly lower than σf of GR and CR. Ef of the printed material is significantly lower than Ef of blocks for milling.

Austenite Grain Growth Analysis in a Welded Joint of High-Strength Martensitic Abrasion-Resistant Steel Hardox 450.

The paper presents the results of tests of a welded joint of Hardox 450 steel, belonging to the group of weldable high-strength boron steels with increased resistance to abrasive wear. As a result of the conducted research, apart from the basic structural indicators, an attempt was made to determine the correlation between the grain size of the prior austenite in the characteristic weld zones and its basic mechanical properties, such as yield point, tensile strength, percentage elongation after fracture, reduction of area, and impact strength. The scope of research quoted above was carried out for a welded joint of the considered steel at delivery state (directly after welding), in the normalising annealed state, as well as in water-quenched state, using different austenitisation temperatures in the range of 900-1200 °C. The results obtained showed a large influence of the parameters of the applied thermal heat treatment on the selected structural and mechanical properties of the welded joint.

Changes in muscle length and orientation after orthognathic surgeries using a bilateral sagittal split osteotomy as an example.

PURPOSE: The aim of the present study was to analyze the changes in the angular positions and lengths of the mandibular elevator muscles due to the displacement of bone segments after bilateral sagittal split osteotomy. Additionally, the impact of changes in mandibular geometry on the values of occlusal forces and mandibular condyle loading was considered. The combined geometric and force analysis makes a valuable contribution to the operating conditions of the system affected by the changes. METHODS: The considerations were based on elementary principles of analytical geometry and the analysis was performed for two craniofacial geometries. RESULTS: For the rotation of the proximal segment, the greatest differences in angular position concern the masseter muscle during roll rotation (11.7°). Significant changes in muscle length occurred during pitch rotation and amounted to 3.7 mm. Translation of the distal segment by 10 mm changed the angle of the pterygoid muscle by 30.2° in the coronal plane and 18.7° in the sagittal plane, simultaneously changing its direction to that of the opposite. Posterior translation (10 mm) caused an elongation of the muscle by 4.7 mm and anterior translation caused a shortening by 2.6 mm. For the mandible with elongated geometry, lower values of occlusion forces and increased reaction forces in the condyle were observed. CONCLUSIONS: The analysis revealed significant changes in the orientation and length of the masticatory muscles, and thus, their potential impact on the functioning conditions of the masticatory system.

The occurrence of strain symptoms in the lumbosacral region and pelvis during pregnancy and after childbirth.

OBJECTIVE: The etiology and pathology of pain in the lumbosacral region and pelvis of pregnant women during and after pregnancy have not been fully determined. This study evaluated if lower back pain during pregnancy and after childbirth is connected with static alterations in the alignment of the pelvis, dysfunction of sacroiliac joints, and irritation of the pelvic ligaments and spine in the lumbosacral region. METHODS: This study was carried out on a group of 30 women in their eighth month of pregnancy and through 3 months after childbirth. Techniques of manual examination were used to determine the strain. Static alteration of the pelvis was evaluated in both the sitting and standing positions on the basis of alignment of the posterior superior iliac spines. Irritation of the iliolumbar ligaments, sacrotuberous, sacroiliac, and interspinous ligaments was evaluated by means of pressure palpation. Disorders of sacroiliac joint function were evaluated with the Patrick FABERE test, the standing Gillet test, and the standing and sitting flexion tests. RESULTS: The most frequently irritated ligaments in the lumbar region are interspinous (60%), iliolumbar (40%), and sacroiliac (36%). CONCLUSIONS: In women, in their eighth month of pregnancy and after childbirth, disorders of static alterations in pelvis alignment and sacroiliac joint dysfunction may occur. The state of pregnancy may result in strain symptoms in the lumbosacral region and pelvis with variable pain intensifying in various static positions.

Effect of silica precursors-type on mechanical properties of sol-gel coatings.

Reversion to narrowing, called restenosis, still remains an important problem of coronary angioplasty. Analysis of the problem revealed that the application of surface layers aimed at creating on the stent surface a neutral barrier between its metallic framework and tissues of the blood-vascular system is decidedly best to impede the restenosis. They also play the role of medicine carriers. This article presents a new sol-gel technology, to be applied in coronary stent coatings. Currently, this is one of the most progressive methods allowing the modification of surface layers of metallic biomaterials. The results presented prove that due to a proper selection of silica precursors it is possible to obtain continuous, smooth, plastic deformation-resistant sol-gel coatings, which additionally are characterised by very close adherence to the base material, nanometer thickness and low degree of surface development.

Microscopic and histological analysis of the processes occurring in the aperture and wall of a coronary vessel after stent implantation.

The serious problem of angioplasty is restenosis, which relates to approx. 15-30% of all the patients subjected to the procedure. The present research was inspired by an attempt to explain this phenomenon and to analyse its causes. Two coronary arteries coming from the patients after stent implantation were subjected to analysis using light and electron microscopy. As a result of expansion of the stent and pressing the implant metallic structure into the artery wall, it comes to breaking the endothelium continuity, uncovering the structures of the intercellular matrix and the internal membrane and, consequently, to creation of a thrombus in the damaged area. As a result of the tissue response, the extracellular matrix is created and neointime formed.