Hollow hydroxyapatite microspheres/chitosan composite as a sustained delivery vehicle for rhBMP-2 in the treatment of bone defects

Bio-inspired polymeric iron-doped hydroxyapatite microspheres as a tunable carrier of rhBMP-2

Hybrid superparamagnetic microspheres with bone-like composition, previously developed by a bio-inspired assembling/mineralization process, are evaluated for their ability to uptake and deliver recombinant human bone morphogenetic protein-2 (rhBMP-2) in therapeutically-relevant doses along with prolonged release profiles. The comparison with hybrid non-magnetic and with non-mineralized microspheres highlights the role of nanocrystalline, nanosize mineral phases when they exhibit surface charged groups enabling the chemical linking with the growth factor and thus moderating the release kinetics. All the microspheres show excellent osteogenic ability with human mesenchymal stem cells whereas the hybrid mineralized ones show a slow and sustained release of rhBMP-2 along 14 days of soaking into cell culture medium with substantially bioactive effect, as reported by assay with C2C12 BRE-Luc cell line. It is also shown that the release extent can be modulated by the application of pulsed electromagnetic field, thus showing the potential of remote controlling the bioactivity of the new micro-devices which is promising for future application of hybrid biomimetic microspheres in precisely designed and personalized therapies.

The mechanism research of non-Smad dependent TAK1 signaling pathway in the treatment of bone defects by recombination BMP-2-loaded hollow hydroxyapatite microspheres/chitosan composite

AIMS

The present study aimed to evaluate whether the non-Smad dependent TAK1 signaling pathway (BMP-2-TAK1-p38-Osx signaling pathway) played an important role in bone repair mediated by hollow hydroxyapatite (HA) microspheres/chitosan (CS) composite.

METHODS

Firstly, the biological activity of rhBMP-2 released from the complex was investigated. Then, differentiation test of osteoblasts including ALP activity and calcium deposition, X-ray scoring and three-point bending test were performed. Finally, the mRNAs expression of TAK1, p38, Osx and osteogenic markers was tested by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

RhBMP-2 could be loaded and released from the complex in bioactive form. Additionally, the complex provided a prolonged period of time compared with HA/CS scaffolds. Serum ALP activity was significantly decreased in the TAK1 inhibitor group and p38 inhibitor group. In the X-ray radiography, bone callus was observed in rhBMP-2-loaded hollow HA microspheres/CS composite group. In the three-point bending test, load values in p38 inhibitor group decreased. In the animal model, the mRNA expression of BSP on day 90 was significantly decreased in the p38 inhibitor group and TAK1 inhibitor group. In MC3T3-E1 cells, the mRNA expression of OSX was remarkably up-regulated in both rhBMP-2 group or rhBMP-2-loaded hollow HA microspheres/CS composite group; while the mRNA expression of OSX was significantly down-regulated in TAK1 inhibitor group and p38 inhibitor group.

CONCLUSION

The BMP-2-TAK1-p38-OSX signaling pathway may play an important role in bone formation and repair mediated by rhBMP-2-loaded hollow HA microspheres/CS composite.

Study of bone repair mediated by recombination BMP-2/ recombination CXC chemokine Ligand-13-loaded hollow hydroxyapatite microspheres/chitosan composite

AIMS

The present study aimed to investigate the mechanism of bone repair mediated by recombination BMP-2 (rhBMP-2)/recombination CXC chemokine ligand-13 (rhCXCL13)-loaded hollow hydroxyapatite (HA) microspheres/chitosan (CS) composite.

MATERIALS AND METHODS

Firstly, the biological activity of rhBMP-2 and rhCXCL13 released from the complex was investigated. Secondly, the effect of rhBMP-2 sustained release solution on ALP activity and rhCXCL13 sustained release solution on cell migration of rat bone marrow mesenchyme stem cells was tested. Thirdly, osteoblasts differentiation test, X-ray scoring and three-point bending test were performed. Finally, the mRNAs expression of osteogenic marker genes and the protein expression of Runx2 was tested by reverse transcription-polymerase chain reaction (RT-PCR) and western blotting (WB), respectively.

KEY FINDINGS

RhBMP-2 could significantly promote the proliferation and differentiation, and RhCXCL13 could promote the migration of rat bone marrow MSCs. Detection of ALP activity and calcium salt deposition showed that rhBMP-2 and rhCXCL13 could significantly improve the biological activity and promote cell differentiation ability. X-ray scoring of radius and flexural strength test showed that rhBMP-2 and rhCXCL13 could promote bone healing and improve the bending resistance of bone tissue. The in vitro molecular experiments including RT-PCR and WB further demonstrated the roles of rhBMP-2 and rhCXCL13 in bone formation and bone repair.

SIGNIFICANCE

Our results indicated that the hollow HA microspheres/CS composite could be effective as a delivery vehicle for rhBMP-2 and rhCXCL13 in bone regeneration and bone repair. In this process, rhBMP-2 may promote bone regeneration by regulating bone marrow MSCs cells recruited by rhCXCL13.

Bone morphogenetic protein-2 sustained delivery by hydrogels with microspheres repairs rabbit mandibular defects

Mandible defect is a difficult issue in dental surgery owing to limited therapeutic options. Recombinant human bone morphogenetic protein-2 (rhBMP2) is osteoinductive in bone regeneration. This article prepared chitosan/collagen hydrogels with rhBMP2-incorporated gelatin microsphere (GMs) for a sustained release of rhBMP2 to induce bone regeneration in rabbits. In experiments, mandibular defects of 8 mm in diameter and 3 mm in depth were surgically prepared on the right cheek of 27 rabbits. Either chitosan/collagen hydrogels alone, rhBMP2-incorporated hydrogels, or hydrogels with rhBMP2-incorporated GMs were implanted to the defect sites. The animals were euthanized at 2, 6, 12 weeks following surgery. In results, scanning electronic microscope images revealled spherical GMs. The complex delivery systems, hydrogels with rhBMP2-incorporated GMs, exhibited ideal release profiles in vitro. The complex delivery systems resulted in apparent new bone formation within 12 weeks, as evidenced by computed tomography and histological observations. All these results demonstrated that the chitosan/collagen hydrogels with rhBMP2-incorporated GMs had a better capacity to heal mandible defects than other two hydrogel scaffolds. Chitosan/collagen hydrogels with rhBMP2-incorporated GMs might be potential carriers of rhBMP2 for accelerating the repair of mandibular defects.

Scaffolds for bone regeneration made of hydroxyapatite microspheres in a collagen matrix

Biomimetic scaffolds with a structural and chemical composition similar to native bone tissue may be promising for bone tissue regeneration. In the present work hydroxyapatite mesoporous microspheres (mHA) were incorporated into collagen scaffolds containing an ordered interconnected macroporosity. The mHA were obtained by spray drying of a nano hydroxyapatite slurry prepared by the precipitation technique. X-ray diffraction (XRD) analysis revealed that the microspheres were composed only of hydroxyapatite (HA) phase, and energy-dispersive x-ray spectroscopy (EDS) analysis revealed the Ca/P ratio to be 1.69 which is near the value for pure HA. The obtained microspheres had an average diameter of 6 μm, a specific surface area of 40 m(2)/g as measured by Brunauer-Emmett-Teller (BET) analysis, and Barrett-Joyner-Halenda (BJH) analysis showed a mesoporous structure with an average pore diameter of 16 nm. Collagen/HA-microsphere (Col/mHA) composite scaffolds were prepared by freeze-drying followed by dehydrothermal crosslinking. SEM observations of Col/mHA scaffolds revealed HA microspheres embedded within a porous collagen matrix with a pore size ranging from a few microns up to 200 μm, which was also confirmed by histological staining of sections of paraffin embedded scaffolds. The compressive modulus of the composite scaffold at low and high strain values was 1.7 and 2.8 times, respectively, that of pure collagen scaffolds. Cell proliferation measured by the MTT assay showed more than a 3-fold increase in cell number within the scaffolds after 15 days of culture for both pure collagen scaffolds and Col/mHA composite scaffolds. Attractive properties of this composite scaffold include the potential to load the microspheres for drug delivery and the controllability of the pore structure at various length scales.