Applications of condensed matter understanding to medical tissues and disease progression: Elemental analysis and structural integrity of tissue scaffolds

Properties of Cartilage-Subchondral Bone Junctions: A Narrative Review with Specific Focus on the Growth Plate

OBJECTIVE

The purpose of this narrative review is to summarize what is currently known about the structural, chemical, and mechanical properties of cartilage-bone interfaces, which provide tissue integrity across a bimaterial interface of 2 very different structural materials. Maintaining these mechanical interfaces is a key factor for normal bone growth and articular cartilage function and maintenance.

MATERIALS AND METHODS

A comprehensive search was conducted using Google Scholar and PubMed/Medline with a specific focus on the growth plate cartilage-subchondral bone interface. All original articles, reviews in journals, and book chapters were considered. Following a review of the overall structural and functional characteristics of the physis, the literature on histological studies of both articular and growth plate chondro-osseous junctions is briefly reviewed. Next the literature on biochemical properties of these interfaces is reviewed, specifically the literature on elemental analyses across the cartilage-subchondral bone junctions. The literature on biomechanical studies of these junctions at the articular and physeal interfaces is also reviewed and compared.

RESULTS

Unlike the interface between articular cartilage and bone, growth plate cartilage has 2 chondro-osseous junctions. The reserve zone of the mature growth plate is intimately connected to a plate of subchondral bone on the epiphyseal side. This interface resembles that between the subchondral bone and articular cartilage, although much less is known about its makeup and formation.

CONCLUSION

There is a notably paucity of information available on the structural and mechanical properties of reserve zone-subchondral epiphyseal bone interface. This review reveals that further studies are needed on the microstructural and mechanical properties of chondro-osseous junction with the reserve zone.

Correlative Imaging of Trace Elements and Intact Molecular Species in a Single-Tissue Sample at the 50 μm Scale

Elemental and molecular imaging play a crucial role in understanding disease pathogenesis. To accurately correlate elemental and molecular markers, it is desirable to perform sequential elemental and molecular imaging on a single-tissue section. However, very little is known about the impact of performing these measurements in sequence. In this work, we highlight some of the challenges and successes associated with performing elemental mapping in sequence with mass spectrometry imaging. Specifically, the feasibility of molecular mapping using the mass spectrometry imaging (MSI) techniques matrix-assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) in sequence with the elemental mapping technique particle-induced X-ray emission (PIXE) is explored. Challenges for integration include substrate compatibility, as well as delocalization and spectral changes. We demonstrate that while sequential imaging comes with some compromises, sequential DESI-PIXE imaging is sufficient to correlate sulfur, iron, and lipid markers in a single tissue section at the 50 μm scale.

Bioinspired Structural Hierarchy within Macroscopic Volumes of Synthetic Composites

A key challenge in developing bioinspired composites is the fabrication of well-defined 3D hierarchical structures ranging from nano to the macroscale. Herein, the development of a synthetic polymer-apatite composite realized by integrating bottom-up self-assembly and additive manufacturing (AM) is described. The resulting composite exhibits a bioinspired hierarchical structure over its 3D macroscopic volume. The composite is assembled in a bottom-up manner, where periodic nanoscale assemblies of organic micellar fibrils and inorganic apatite nanocrystals are organized as bundles of mineralized microstructures. These microstructural bundles are preferentially oriented throughout the macroscopic volume of the material via extrusion based AM. The obtained structural hierarchy is investigated in 3D using electron microscopy and small angle X-ray scattering tensor tomography and correlated to the structural hierarchy and anisotropy observed in biological tissues such as bone and the bone-cartilage interface. This work demonstrates the possibility to form polymer-apatite composites with a well-defined hierarchical structure throughout its macroscopic volume, which is crucial for the development of mechanically optimized materials for applications such as bone and osteochondral implants.

Bone calcium/phosphorus ratio determination using dual energy X-ray method

Non-invasive dual energy methods have been used extensively on osteoporosis diagnosis estimating parameters, such as, Bone Mineral Density (BMD) and Bone Mineral Content (BMC). In this study, an X-ray dual energy method (XRDE) was developed for the estimation of the bone Calcium-to-Phosphorous (Ca/P) mass ratio, as a bone quality index. The optimized irradiation parameters were assessed by performing analytical model simulations. X-ray tube output, filter material and thickness were used as input parameters. A single exposure technique, combined with K-edge filtering, was applied. The optimal X-ray spectra were selected according to the resulted precision and accuracy values. Experimental evaluation was performed on an XRDE system incorporating a Cadmium Telluride (CdTe) photon counting detector and three bone phantoms with different nominal mass Ca/P ratios. Additionally, the phantoms' mass Ca/P ratios were validated with energy-dispersive X-ray spectroscopy (EDX). Simulation results showed that the optimum filter atomic number (Z) ranges between 57 and 70. The optimum spectrum was obtained at 100 kVp, filtered with Cerium (Ce), with a surface density of 0.88 g/cm(2). All Ca/P ratio measurements were found to be accurate to within 1.6% of the nominal values, while the precision ranged between 0.91 and 1.37%. The accuracy and precision values of the proposed non-invasive method contributes to the assessment of the bone quality state through the mass Ca/P ratio determination.

Evaluation of particle-induced X-ray emission and particle-induced γ-ray emission of quartz grains for forensic trace sediment analysis

The independent verification in a forensics context of quartz grain morphological typing by scanning electron microscopy was demonstrated using particle-induced X-ray emission (PIXE) and particle-induced γ-ray emission (PIGE). Surface texture analysis by electron microscopy and high-sensitivity trace element mapping by PIXE and PIGE are independent analytical techniques for identifying the provenance of quartz in sediment samples in forensic investigations. Trace element profiling of the quartz grain matrix separately from the quartz grain inclusions served to differentiate grains of different provenance and indeed went some way toward discriminating between different quartz grain types identified in a single sample of one known forensic provenance. These results confirm the feasibility of independently verifying the provenance of critical samples from forensic cases.

Ca/P concentration ratio at different sites of normal and osteoporotic rabbit bones evaluated by Auger and energy dispersive X-ray spectroscopy

Osteoporosis is a systemic skeletal disorder associated with reduced bone mineral density and the consequent high risk of bone fractures. Current practice relates osteoporosis largely with absolute mass loss. The assessment of variations in chemical composition in terms of the main elements comprising the bone mineral and its effect on the bone's quality is usually neglected. In this study, we evaluate the ratio of the main elements of bone mineral, calcium (Ca), and phosphorus (P), as a suitable in vitro biomarker for induced osteoporosis. The Ca/P concentration ratio was measured at different sites of normal and osteoporotic rabbit bones using two spectroscopic techniques: Auger electron spectroscopy (AES) and energy-dispersive X-ray spectroscopy (EDX). Results showed that there is no significant difference between samples from different genders or among cortical bone sites. On the contrary, we found that the Ca/P ratio of trabecular bone sections is comparable to cortical sections with induced osteoporosis. Ca/P ratio values are positively related to induced bone loss; furthermore, a different degree of correlation between Ca and P in cortical and trabecular bone is evident. This study also discusses the applicability of AES and EDX to the semiquantitative measurements of bone mineral's main elements along with the critical experimental parameters.