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Simple Summary: Before calcification, the early skeletal development of both Homo sapiens and the chondrichthyan fish Raja asterias is exclusively cartilaginous. This cartilage is formed through tissue segmentation and chondrocyte mitoses. Mineral deposition in the cartilage matrix influences the stiffness and shape of the skeletal segments. In mammals, calcified cartilage serves as a scaffold for bone deposition, which is then remodeled. Conversely, chondrichthyans retain calcified cartilage as their skeletal structure, forming calcification nuclei or "tesserae". These structures adapt to aquatic locomotion. In mammals, endochondral ossification provides limb bones with the necessary stiffness for terrestrial locomotion. X-rays of marine mammals show how endochondral ossification in dolphin flippers adapts to aquatic demands, including shortening of certain bones and an increase in elements in the autopodium's central rays. Before calcification begins, the early embryonic and fetal skeletal development of both mammalian Homo sapiens and the chondrichthyan fish Raja asterias consists exclusively of cartilage. This cartilage is formed and shaped through processes involving tissue segmentation and the frequency, distribution, and orientation of chondrocyte mitoses. In the subsequent developmental phase, mineral deposition in the cartilage matrix conditions the development further. The stiffness and structural layout of the mineralized cartilage have a significant impact on the shape of the anlagen (early formative structure of a tissue, a scaffold on which the new bone is formed) and the mechanical properties of the skeletal segments. The fundamental difference between the two studied species lies in how calcified cartilage serves as a scaffold for osteoblasts to deposit bone matrix, which is then remodeled. In contrast, chondrichthyans retain the calcified cartilage as the definitive skeletal structure. This study documents the distinct mineral deposition pattern in the cartilage of the chondrichthyan R. asterias, in which calcification progresses with the formation of focal calcification nuclei or "tesserae". These are arranged on the flat surface of the endo-skeleton (crustal pattern) or aligned in columns (catenated pattern) in the radials of the appendicular skeleton. This anatomical structure is well adapted to meet the mechanical requirements of locomotion in the water column. Conversely, in terrestrial mammals, endochondral ossification (associated with the remodeling of the calcified matrix) provides limb bones with the necessary stiffness to withstand the strong bending and twisting stresses of terrestrial locomotion. In this study, radiographs of marine mammals (reproduced from previously published studies) document how the endochondral ossification in dolphin flippers adapts to the mechanical demands of aquatic locomotion. This adaptation includes the reduction in the length of the stylopodium and zeugopodium and an increase in the number of elements in the autopodium's central rays. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy (SEM) is a precious tool in materials science and morphology sciences, enabling detailed examination of materials at the nanoscale. However, precise and accurate sample repositioning during different observation sessions remains a significant challenge, impacting the quality and repeatability of SEM analyses. This study aimed to develop and evaluate a LEGO®‐based sample positioning system for SEM analysis. The system was designed to consistently identify and align features across multiple repositioning cycles, maintain accurate positioning along the z‐axis, minimize distortion, and provide repeatable and reliable results. The results indicated a high degree of precision and accuracy in the repositioning process, as evidenced by the minimal displacements, deviations in scaling and shearing, and the highly significant results (p < 0.001) obtained from the analysis of absolute translations and rotations. Moreover, the analyses were consistently replicated across six repetitions, underscoring the reliability of the observed results. While the findings suggest that the LEGO‐based sample positioning system is promising for enhancing SEM analyses' quality and repeatability, further studies are needed to optimize the system's design and evaluate its performance in different SEM applications. Ultimately, this study contributes to the ongoing efforts to develop cost‐effective, customizable, and accurate solutions for sample positioning in SEM, contributing to the advancement of materials science research and all SEM analysis requiring overtime observations of the same sample. Research Highlights: This study focused on the development and evaluation of a novel LEGO‐based sample positioning system specifically designed for SEM analysis.One of the standout features of this system is its ability to consistently identify and align features across multiple repositioning cycles, showcasing its precision and reliability.To further understand the mechanical aspects of the SEM stage, we employed the Rambold Kontroll comparator, which provided a baseline understanding of its mechanical tolerance.The registration process results were particularly noteworthy, as they revealed high accuracy with minimal displacements.Furthermore, the consistent outcomes observed across multiple repetitions emphasize the reliability and robustness of the methods we employed in this research. [ABSTRACT FROM AUTHOR]

The free surface of the articular cartilage must withstand compressive and shearing forces, maintain a low friction coefficient and allow oxygen and metabolites to reach the underlying matrix. In many ways it is critical to the physiology of the whole tissue and its disruption always involves deep pathological alterations and loss of the joint integrity. Being very difficult to image with section‐based conventional techniques, it was often described by previous research in conflicting terms or entirely overlooked. High‐magnification face‐on observations with high resolution scanning electron microscopy and with scanning probe microscopy revealed a very thin, delicate superficial layer rich in glycoconjugates, which may explain the very low friction coefficient of the tissue but which was very easily altered and/or dissolved in the preparation. Beneath this superficial sheet lies a thicker coat of thin, highly uniform, slightly wavy collagen fibrils lying parallel to the surface and mutually interconnected by a huge number of interfibrillar glycosaminoglycan bridges. These bridges and the collagen fibrils form an extended reticular structure able to redistribute tensile and compressive stress across a larger area of the surface and hence a greater volume of tissue. [ABSTRACT FROM AUTHOR]

Direct laser metal forming (DLMF) is a procedure in which a high-power laser beam is directed on a metal powder bed and programmed to fuse particles according to a computer-aided design file, thus generating a thin metal layer. With DLMF, it is now possible to fabricate dental implants with a superficial porous surface. The aim of the present study was to evaluate the peri-implant soft tissues around human-retrieved DLMF dental implants. Collagen fibers, in the form of bundles, were oriented perpendicularly to a distance of 100 μm from the surface, where they became parallel, running in several directions. In some portions, only a few collagen fiber bundles appeared to be oriented perpendicularly or obliquely to the plane of the section. Collagen fibers appeared to form a dense chaotic three-dimensional network running in different, more or less parallel directions to the surface. Under scanning electron microscopy, an intimate contact of the fibrous matrix with the implant surface was evident, and some collagen bundles could be seen to bind directly to the metal surface. By changing the surface microtexture, it was possible to change the response of the peri-implant soft tissues. [ABSTRACT FROM AUTHOR]

The aim of the present study was a light and scanning electron microscopy (SEM) evaluation of the peri-implant tissues around sandblasted, acid-etched implants, retrieved from man, after a loading period of 5 and 10 years, respectively. Two implants (Leone Implant System) had been retrieved for a fracture of the prosthetic superstructure respectively after 5 and 10 years of loading. Both implants were stable before retrieval and had been retrieved using a 5-mm trephine bur. One implant was treated to obtain thin ground sections, while the other underwent evaluation under SEM. Compact, mature lamellar bone was present over most of the implant perimeter in close contact with the implant surface and with many remodeling areas. Under SEM, small concavities, completely filled by mineralized bone, were present on the implant surface. The present histologic results showed that these implants were well integrated over the long term, and the peri-implant bone was undergoing continuous remodeling at the interface. [ABSTRACT FROM AUTHOR]

The 'fate' of growth plate hypertrophic chondrocytes has been long debated with two opposing theories: cell apoptosis or survival with transformation into osteogenic cells. This study was carried out on the proximal tibial growth plate of rabbits using light microscopy, scanning and transmission electron microscopy. We focused particularly on the orientation of the specimens included in order to define the mineral deposition and the vascular invasion lines and obtain histological and ultrastructural images at the corresponding height of the plate. Chondrocyte morphology transformation through the maturation process (characterized by vesicles and then large cytoplasmic lacunae before condensation, fragmentation and disappearance of the nuclear chromatin) did not correspond to that observed in the 'in vitro' apoptosis models. These findings rather suggested the passage of free water from the cartilage matrix into a still live cell (swelling). The level of these changes suggested a close relationship with the mineral deposition line. Furthermore, the study provided evidence that the metaphyseal capillaries could advance inside the columns of stacked hypertrophic chondrocytes (delimited by the intercolumnar septa) without the need for calcified matrix resorption because the thin transverse septa between the stacked chondrocyte (below the mineral deposition line) were not calcified. The zonal distribution of cell types (hypertrophic chondrocytes, osteoblasts, osteoclasts and macrophages) did not reveal osteoclasts or chondroclasts at this level. Morphological and morphometric analysis recorded globular masses of an amorphous, necrotic material in a zone 0–70 μm below the vascular invasion line occasionally surrounded by a membrane (indicated as 'hypertrophic chondrocyte ghosts'). These masses and the same material not bound by a membrane were surrounded by a large number of macrophages and other blood cell precursors, suggesting this could be the cause of macrophage recall and activation. The most recent hypotheses based on genetic and lineage tracing studies stating that hypertrophic chondrocytes can survive and transform into osteoblasts and osteocytes (trans‐differentiation) were not confirmed by the ultrastructural morphology or by the zonal comparative counting and distribution of cell types below the vascular invasion line. [ABSTRACT FROM AUTHOR]