In vitro and in vivo assessment of nanostructured porous biphasic calcium phosphate ceramics for promoting osteogenesis in an osteoporotic environment

Fusion Rate of Biphasic Calcium Phosphate Bone Graft with Needle-Shaped Submicron Surface Topography in Interbody Lumbar Fusion for Degenerative Disc Disease: A Single-Center Retrospective Review

BACKGROUND

Calcium phosphate bone grafts are emerging as alternatives to autologous bone grafts in lumbar spinal fusion. This study evaluates the 12-month fusion rate and clinical outcomes of lumbar interbody fusion using synthetic biphasic calcium phosphate with submicron needle-shaped surface topography (BCP<μm).

METHODS

A retrospective review identified patients who underwent lumbar interbody arthrodesis with BCP<μm, with or without autograft. Fusion was assessed by an independent neuroradiologist using a computed tomography alphanumeric classification based on bridging bone on 12-month postoperative computed tomography. Secondary outcomes included changes in visual analog scale, length of stay, and fusion of all treated levels.

RESULTS

Fifty-five patients with 93 treated levels were analyzed (average age: 62.78 years; body mass index: 28.73 kg/m2). Patients had an average of 3 comorbidities and a median of 2 levels fused. Procedures included anterior (52 levels), transforaminal (22 levels), and lateral lumbar interbody fusion (19 levels). Fusion occurred in 95.70% of levels without evidence of fixation failure. Fusion rates were unaffected by procedure type (P = 0.965) or supplemental autograft use (P = 1.00). Complications were reported in 4 patients. Six-month postoperative visual analog scale improved by a mean of 25.10 (P < 0.0001).

CONCLUSIONS

This study demonstrates a high fusion rate (95.70%) and low complication rate in a diverse patient population with multiple comorbidities, suggesting BCP<μm is a viable graft material for lumbar interbody fusion.

Bone Cell Exosomes and Emerging Strategies in Bone Engineering

Bone tissue remodeling is a highly regulated process balancing bone formation and resorption through complex cellular crosstalk between resident bone and microenvironment cells. This cellular communication is mediated by direct cell and cell–matrix contact, autocrine, endocrine, and paracrine receptor mediated mechanisms such as local soluble signaling molecules and extracellular vesicles including nanometer sized exosomes. An impairment in this balanced process leads to development of pathological conditions. Bone tissue engineering is an emerging interdisciplinary field with potential to address bone defects and disorders by synthesizing three-dimensional bone substitutes embedded with cells for clinical implantation. However, current cell-based therapeutic approaches have faced hurdles due to safety and ethical concerns, challenging their clinical translation. Recent studies on exosome-regulated bone homeostasis and regeneration have gained interest as prospective cell free therapy in conjugation with tissue engineered bone grafts. However, exosome research is still in its nascent stages of bone tissue engineering. In this review, we specifically describe the role of exosomes secreted by cells within bone microenvironment such as osteoblasts, osteocytes, osteoclasts, mesenchymal stem cell cells, immune cells, endothelial cells, and even tumor cells during bone homeostasis and crosstalk. We also review exosome-based osteoinductive functionalization strategies for various bone-based biomaterials such as ceramics, polymers, and metals in bone tissue engineering. We further highlight biomaterials as carrier agents for exosome delivery to bone defect sites and, finally, the influence of various biomaterials in modulation of cell exosome secretome.

Osteogenic effects of the bioactive small molecules and minerals in the scaffold-based bone tissue engineering

Reconstruction of the damaged bone is a striking challenge in the medical field. The bone grafts as a current treatment is associated with inherent limitations; hence, the bone tissue engineering as an alternative therapeutic approach has been considered in the recent decades. Bone tissue engineering aims at replacing the lost tissue and restoring its function by recapitulating the natural regeneration process. Concerted participation and combination of the biocompatible materials, osteoprogenitor/ stem cells and bioactive factors closely mimic the bone microenvironment. The bioactive factors regulate the cell behavior and they induce the stem cells to osteogenic differentiation by activating specific signaling cascades. Growth factors (GFs) are the most important bioactive molecules and mediators of the natural bone repair process. Although these soluble factors have approved applications in the bone regeneration, however, there are several limitations such as the instability, high dose requirements, and serious side effects which could restrict their clinical usage. Alternatively, a new generation of bioactive molecules with the osteogenic properties are used. The non-peptide organic or inorganic molecules are physiologically stable and non-immunogenic due to their small size. Many of them are obtained from the natural resources and some are synthesized through the chemical methods. As a result, these molecules have been introduced as the cost-effective osteogenic agents in the bone tissue regeneration. In this paper, three groups of these bioactive agents including the organic small molecules, minerals and metallic nanoparticles have been investigated, considering their function in accelerating the bone regeneration. We review the recent in vitro and in vivo studies that utilized the osteogenic molecules to promote the bone formation in the scaffold-based bone tissue engineering systems.