Biodegradation of tricalcium phosphate ceramics by osteoclasts

Biodegradable Cements for Bone Regeneration

Bone cements such as polymethyl methacrylate and calcium phosphates have been widely used for the reconstruction of bone. Despite their remarkable clinical success, the low degradation rate of these materials hampers a broader clinical use. Matching the degradation rate of the materials with neo bone formation remains a challenge for bone-repairing materials. Moreover, questions such as the mechanism of degradation and how the composition of the materials contribute to the degradation property remain unanswered. Therefore, the review provides an overview of currently used biodegradable bone cements such as calcium phosphates (CaP), calcium sulfates and organic-inorganic composites. The possible degradation mechanism and clinical performance of the biodegradable cements are summarized. This paper reviews up-to-date research and applications of biodegradable cements, hoping to provide researchers in the field with inspirations and references.

Tissue-engineered bone formation in vivo for artificial laminae of the vertebral arch using β-tricalcium phosphate bioceramics seeded with mesenchymal stem cells

STUDY DESIGN

A rabbit laminectomy model was used to evaluate the efficacy of artificial laminae of vertebral arch using bone marrow-derived mesenchymal stem cells (MSCs) transplanted in porous beta-calcium phosphates (β-TCP) bioceramics.

OBJECTIVE

The aim of this study was to establish artificial lamina of the vertebral arch for bone tissue engineering using β-TCP bioceramics seeded with MSCs in a rabbit model of decompressive laminectomy.

SUMMARY OF BACKGROUND DATA

Decompressive laminectomy may induce various degrees of scar tissue and adhesion formation in the epidural space, and thus is the most common cause of failed back surgery syndrome. However, there is no effective method of bone defect treatment to control and reduce the scar tissue formation.

METHODS

MSCs were harvested from New Zealand rabbits (2-week old) by femoral bone marrow extraction. These cells were seeded into porous β-TCP bioceramics and cultivated for up to 3 weeks in the presence of osteogenic supplements. Segmental defects (20 × 8 mm) were created in 48 adult New Zealand rabbits that underwent laminectomy at the L5 to L6 levels. The animals were transplanted with cell media (control), β-TCP bioceramics (group I), or MSC-loaded β-TCP bioceramics (group II). Bone formation was evaluated after operation using scanning electron microscopy, computed tomography, magnetic resonance imaging, histomorphometry, and immunohistochemistry.

RESULTS

Scanning electron microscopy showed that MSCs filled the pores and surfaces of bioceramics in MSC-loaded β-TCP. In addition, significant increases in bone formation were observed in group II compared with other groups. Computed tomography and magnetic resonance imaging at 16 weeks showed that the artificial lamina of the vertebral arch was successfully formed. Hematoxylin-eosin and Masson trichrome staining were used to show the artificial laminae of the vertebral arch and the degraded bioceramics. In addition, immunohistochemistry results showed that the expression of bone morphogenetic protein-2 increased significantly in group II compared with group I at 2,4, and 8 weeks after implantation (P < 0.05).

CONCLUSION

β-TCP bioceramics seeded with MSCs are a promising source of tissue-engineered bone for the artificial lamina of the vertebral arch.

Bioactive glass foam scaffolds are remodelled by osteoclasts and support the formation of mineralized matrix and vascular networks in vitro

Remodelling of scaffolds and new bone formation is critical for effective bone regeneration. Herein is reported the first demonstration of resorption pits due to osteoclast activity on the surface of sol-gel bioactive glass foam scaffolds. Bioactive glass foam scaffolds are known to have osteogenic potential and suitable pore networks for bone regeneration. Degradation of the scaffolds is known to be initially solution mediated, but for effective bone regeneration, remodelling of the scaffold by osteoclasts and vascularisation of the scaffold is necessary. The culture of C7 macrophages on a bioactive glass scaffold induces the cells to differentiate into (TRAP(+ve) ) osteoclasts. They then form distinctive resorption pits within 3 weeks, while MC3T3-E1 pre-osteoblasts deposit mineralized osteoid on their surfaces in co-culture. The scaffolds are of the 70S30C (70 mol% SiO2 , 30 mol% CaO) composition, with modal pore and interconnect diameters of 373 μm and 172 μm respectively (quantified by X-ray micro-tomography and 3D image analysis). The release of soluble silica and calcium ions from 70S30C scaffolds induces an increase in osteoblast numbers as determined via the MTT assay. Scaffolds also support growth of endothelial cells on their surface and tube formation (characteristic of functional microvasculature) following 4 days in culture. This data supports the hypothesis that 70S30C bioactive glass scaffolds promote the differentiation of the 3 main cell types involved in vascularized bone regeneration.

In vivo mechanisms of hydroxyapatite ceramic degradation by osteoclasts: fine structural microscopy

In the present study the in vivo mechanism of calcium-phosphate (CaP) ceramic degradation has been investigated by means of transmission electron microscopy. The results revealed osteoclast-mediated degradation of hydroxyapatite ceramic implanted into sheep bone by simultaneous resorption and phagocytosis. After 6 weeks of implantation, osteoclasts were localized immediately beneath the ceramic surface. They had formed resorption lacunae and exhibited typical ultrastructural features, such as the ruffled border, the clear zone, and the dorsal microvilli. Their resorption capacity also had become evident by alterations of the electron density and the shape of the CaP crystals localized within the acidic microenvironment of the ruffled border. Moreover, the osteoclasts simultaneously were capable of phagocytosing the resorbed CaP crystals. The formation of endophagosomes was performed (1) by the uptake of particles into large intracellular vacuoles, which were generated by deep invagination of the membranes of the osteoclastic ruffled border, and (2) by the encircling of particles due to the development of pseudopodia-like plasmaprotrusions of the ruffled border. The formation of endophagosomes was followed by the in situ fragmentation of the inclusion material, which subsequently was released into the extracellular space and phagocytosed by macrophages.