The goals of bone tissue engineering are to apply biomaterial scaffolds with adhered cells, such as osteoblasts, bone marrow stromal stem cells, or chondrocytes, to repair, regenerate, and restore the functions of damaged bone tissue or to replace those tissues with porous engineered biomaterials. Over recent decades, a diverse class of biomaterials has been applied in bone tissue engineering field. Porous hydroxyapatite bioceramic is currently receiving significant attention as a bone tissue engineering substitute because of its biological characteristics, including biocompatibility, bioactivity, osteoconduction, and vasculogenesis. This biomaterial has a three-dimensional structure with interconnected spherical pores of uniform size, which encourages bone ingrowth and achieves good integration of the material and the host bone over time. However, the compressive strength and elastic modulus of porous hydroxyapatite scaffolds generally weaken as the porosity increases, in both in vitro and in vivo testing. Zirconia can be used to toughen hydroxyapatite materials for bone repair and replacement because of its unique biomechanical properties, including compressive strength and fracture toughness. Additionally, a zirconia chitosan hybrid containing bone morphogenetic protein-2 and mesenchymal stem cells derived from induced pluripotent stem cells has been used as a coating material adhered to surface of scaffolds to promote bone regeneration and repair. Here, we provide a succinct review of zirconia toughened hydroxyapatite biomaterial scaffolds that incorporate bone morphogenetic protein-2 and mesenchymal stem cells for bone tissue engineering and describe the biomaterials that are currently being investigated based on the recent literature and our own data.
New porous gradient hydroxyapatite/zirconia composites can promote the repair of bony defect, and induce bone tissue to ingrow into the pores, which may be applied widely to the treatment of bony defect in the future.
The purpose of this study was to establish methods for isolation, culture, expansion, and characterization of rat hair follicle stem cells (rHFSCs). Hair follicles were harvested from 1-week-old Sprague-Dawley rats and digested with dispase and collagenase IV. The bulge of the hair follicle was dissected under a microscope and cultured in Dulbecco's modified Eagle's medium/F12 supplemented with KnockOut™ Serum Replacement serum substitute, penicillin-streptomycin, L-glutamine, non-essential amino acids, epidermal growth factor, basic fibroblast growth factor, polyhydric alcohol, and hydrocortisone. The rHFSCs were purified using adhesion to collagen IV. Cells were characterized by detecting marker genes with immunofluorescent staining and real-time polymerase chain reaction (PCR). The proliferation and vitality of rHFSCs at different passages were evaluated. The cultured rHFSCs showed typical cobblestone morphology with good adhesion and colony-forming ability. Expression of keratin 15, integrin α6, and integrin β1 were shown by immunocytochemistry staining. On day 1-2, the cells were in the latent phase. On day 5-6, the cells were in the logarithmic phase. Cell vitality gradually decreased from the 7th passage. Real-time PCR showed that the purified rHFSCs had good vitality and proliferative capacity and contained no keratinocytes. Highly purified rHFSCs can be obtained using tissue culture and adhesion to collagen IV. The cultured cells had good proliferative capacity and could therefore be a useful cell source for tissue-engineered hair follicles, vessels, and skin.
A new HA/ZrO2-based porous bioceramic artificial vertebral body (AVB), carried a recombinant human bone morphogenetic protein-2 (rhBMP-2)/chitosan slow-release hydrogel was prepared to repair vertebral bone defect in beagles. An ionic cross-linking was used to prepare the chitosan hydrogel (CS gel) as the rhBMP-2 slow-release carrier. The vertebral body defects were implanted with the rhBMP-2-loaded AVB in group A, or a non-drug-loaded AVB in group B, or autologous iliac in group C. The encapsulation rate of rhBMP-2 in rhBMP-2-loaded CS gel was 91.88±1.53%, with a drug load of 39.84±2.34 ng/mg. At 6, 12, 24 weeks postoperatively, radiography showed that the bone calluses gradually increased with time in group A, where the artificial vertebral body had completely fused with host-bone at 24 weeks after surgery. In group C, an apparent bone remodeling was occurred in the early stages, and the graft-bone and host-bone had also fused completely at 24 weeks postoperatively. In group B, fusion occurred less than in groups A and C. At 24 weeks after surgery, micro-computed tomography (Micro-CT) revealed that the volume of newly-formed bone in group A was significantly more than in group B (p<0.05). At 24 weeks after surgery, ultra-compressive strengths of the operated segments were 14.03±1.66 MPa in group A, 8.62±1.24 MPa in group B, and 13.78±1.43 MPa in group C. Groups A and C were both significantly higher than group B (p < 0.05). At 24 weeks postoperatively, the hard tissue sections showed that the AVB of group A had tightly fused with host bone, and that pores of the AVB had been filled with abundant nearly mature bone, and that the new bone structured similarly to a trabecular framework, which was similar to that in group C. In contrast, implant fusion of the AVB in group B was not as apparent as group A. In conclusion, the novel HA/ZrO2-based porous bioceramic AVB carried the rhBMP-2-loaded CS gel can promote the repair of bony defect, and induce bone tissue to grow into the pores, which may replace iliac bone grafts as commonly applied in clinical practice.
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