Morphological and Dimensional Characteristics of Bone Mineral Crystals

Ultra-low binder content 3D printed calcium phosphate graphene scaffolds as resorbable, osteoinductive matrices that support bone formation in vivo

Bone regenerative engineering could replace autografts; however, no synthetic material fulfills all design criteria. Nanocarbons incorporated into three-dimensional printed (3DP) matrices can improve properties, but incorporation is constrained to low wt%. Further, unmodified nanocarbons have limited osteogenic potential. Functionalization to calcium phosphate graphene (CaPG) imparts osteoinductivity and osteoconductivity, but loading into matrices remained limited. This work presents ultra-high content (90%), 3DP-CaPG matrices. 3DP-CaPG matrices are highly porous (95%), moderately stiff (3 MPa), and mechanically robust. In vitro, they are cytocompatible and induce osteogenic differentiation of human mesenchymal stem cells (hMSCs), indicated by alkaline phosphatase, mineralization, and COL1α1 expression. In vivo, bone regeneration was studied using a transgenic fluorescent-reporter mouse non-union calvarial defect model. 3DP-CaPG stimulates cellular ingrowth, retains donor cells, and induces osteogenic differentiation. Histology shows TRAP staining around struts, suggesting potential osteoclast activity. Apparent resorption of 3DP-CaPG was observed and presented no toxicity. 3DP-CaPG represents an advancement towards a synthetic bone regeneration matrix.

Biomimetic Silk Fibroin Hydrogels Strengthened by Silica Nanoparticles Distributed Nanofibers Facilitate Bone Repair

Various materials are utilized as artificial substitutes for bone repair. In this study, a silk fibroin (SF) hydrogel reinforced by short silica nanoparticles (SiNPs)-distributed-silk fibroin nanofibers (SiNPs@NFs), which exhibits a superior osteoinductive property, is fabricated for treating bone defects. SF acts as the base part of the composite scaffold to mimic the extracellular matrix (ECM), which is the organic component of a native bone. The distribution of SiNPs clusters within the composite hydrogel partially mimics the distribution of mineral crystals within the ECM. Incorporation of SiNPs@NFs enhances the mechanical properties of the composite hydrogel. In addition, the composite hydrogel provides a biocompatible microenvironment for cell adhesion, proliferation, and osteogenic differentiation in vitro. In vivo studies confirm that the successful repair is achieved with the formation of a large amount of new bone in the large-sized cranial defects that are treated with the composite hydrogel. In conclusion, the SiNPs@NFs-reinforced-hydrogel fabricated in this study has the potential for use in bone tissue engineering.

Nanostructure of bone tissue probed with Ca 2p and O 1s NEXAFS spectroscopy

X-ray absorption spectroscopy is applied to investigate relationships between hierarchical organization of the skeleton and nanostructure of femoral bone in knee compartments and to understand the osteoarthritis (OA) related changes at the subcellular level. Our focus is on local electronic and atomic and molecular architectonics of the medial and lateral condyles of the femur resected during total knee arthroplasty in patients with medial compartmental knee OA. The element-specific and site-dependent peculiarities in spectral distributions of oscillator strength for core-to-valence transitions are revealed. The near Ca 2p and O 1s edges x-ray absorption fine structure (Ca 2p and O 1s NEXAFS) spectra of the saw cuts demonstrate substantial redistributions in intact and OA damaged areas on the proximal side, and on the proximal and distal sides of the samples. Examining the O 1s NEXAFS spectra new chemical bonds are revealed on the proximal surface in the OA areas. Strong intra-atomic intershell Ca2+ 2 p 3 / 2 , 1 / 2 5 3 d 1 interaction specifies the great similarity of the Ca 2p NEXAFS spectra. Their analysis performed in combination with the x-ray photoelectron data has demonstrated the formation of non-apatite calcium in the OA areas of the samples. It is shown that NEXAFS spectroscopy is a powerful tool for deeper understanding relationship between hierarchical skeletal organization and nanostructure of native bone. Perspectives for development of novel methods for medical imaging and diagnosis of subchondral bone at the nanolevel are discussed.

Local electronic structure and nanolevel hierarchical organization of bone tissue: theory and NEXAFS study

Theoretical and experimental investigations of native bone are carried out to understand relationships between its hierarchical organization and local electronic and atomic structure of the mineralized phase. The 3D superlattice model of a coplanar assembly of the hydroxyapatite (HAP) nanocrystallites separated by the hydrated nanolayers is introduced to account the interplay of short-, long- and super-range order parameters in bone tissue. The model is applied to (i) predict and rationalize the HAP-to-bone spectral changes in the electronic structure and (ii) describe the mechanisms ensuring the link of the hierarchical organization with the electronic structure of the mineralized phase in bone. To check the predictions the near-edge x-ray absorption fine structure (NEXAFS) at the Ca 2p, P 2p and O 1s thresholds is measured for native bone and compared with NEXAFS for reference compounds. The NEXAFS analysis has demonstrated the essential hierarchy induced HAP-to-bone red shifts of the Ca and P 2p-to-valence transitions. The lowest O 1s excitation line at 532.2 eV in bone is assigned with superposition of core transitions in the hydroxide OH^-(H₂O) _m anions, Ca²⁺(H₂O) _n cations, the carboxyl groups inside the collagen and [PO₄]^2- and [PO₄]^- anions with unsaturated P-O bonds.

Effect of hydrazine deproteination on bone mineral phase: A critical view

Over the last 30 years several techniques have been developed to separate bone matrix and bone mineral, in order to allow for a study of each component independently of the other. Preservation of original characteristics of the phase studied after isolation has always been a great challenge for all such techniques. The hydrazine deproteination procedure, first proposed by Termine, has been one of the processes most widely used for studying bone mineral. It is found to be one of the most effective, notwithstanding controversy over its efficiency in bone deproteination and criticism regarding possible changes it could make to the characteristics of bone mineral. In this work, we have studied the possible chemical and physical alterations caused by the hydrazine deproteination process to bone mineral from rats and to other materials of biological interest. Materials were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), inductive coupled plasma-optical emission spectroscopy (ICP-OES), C-H-N analysis and infrared spectroscopy (FTIR), before and after hydrazine deproteination. Finally, here we present a comprehensive discussion on the criticism of hydrazine deproteination. The experimental results obtained in this work, even when compared to the results in the literature, show that most widespread criticism to the hydrazine deproteination process is not completely justified.