Attention In Bone Tissue Engineering Research Articles

Nanofibers and Microfibers for Osteochondral Tissue Engineering.

The use of microfibers and nanofibers allows for tailoring the scaffold properties. Electrospinning is one of the most important techniques nowadays to produce fibrous scaffolds. Microfibers and nanofibers use in scaffolds is a promising field to improve the behavior of scaffolds in osteochondral applications.

Three-dimensional porous scaffold by self-assembly of reduced graphene oxide and nano-hydroxyapatite composites for bone tissue engineering

Three-dimension (3D) porous reduced graphene oxide (RGO) scaffold has attracted increasing attention in bone tissue engineering due to its favorable osteoinductivity. In this paper, a 3D porous RGO composite was prepared from graphene oxide (GO) and nano-hydroxyapatite (nHA) via self-assembly, thus constructing biomimetic scaffold for bone defect reparation. Detailed studies were performed to evaluate its structure, cellular responses, biocompatibility and in vivo bone repair efficiency, emphasizing the influences of the composite on in vivo bone cell growth and mineralization. The as-prepared scaffold was found to significantly enhance the proliferation, alkaline phosphatase activity (ALP) and osteogenic gene expression of rat bone mesenchymal stem cells (rBMSCs). Further in vivo experiment demonstrated that the circular calvarial defects with 4 mm diameter in rabbit were successfully healed by 20% nHA incorporated RGO (nHA@RGO) porous scaffold after 6 weeks implanting, which was visibly quicker than the RGO one. The computed tomography (CT) and histological analysis showed the improved collagen deposition, cell proliferation and new bone formation occurred in the 20% nHA@RGO treated group. These results indicated that the as-prepared porous scaffold has a promising capacity to stimulate mineralization and promote the in vivo defect healing.

Sacrificed Carbon-Assisted Synthesis of β-Tricalcium Phosphate Nanostructures

β-Tricalcium phosphate (β-TCP) has attracted particular attention in bone tissue engineering because of its excellent biocompatibility, absorbability, and osteoinductivity. In the present study, β-TCP nanoparticles (NPs) and triangular cones were synthesized by a coprecipitation method combined with calcination under high temperature. Different carbon materials, including graphene oxide (GO) and activated carbon (AC), were employed as the sacrificed support in order to prevent the sintering and agglomeration during high temperature calcination. Monodispersed β-TCP NPs were obtained using GO as the sacrificed support, while β-TCP triangular cones were obtained using AC as the sacrificed support. GO not only provided anchoring sites for the nucleation and growth of the precursor through numerous oxygen-containing functional groups on the surface of nanosheets, but also promoted the nucleation and growth of β-TCP NPs by decreasing phase transformation temperature and time due to excellent thermal conductivit...

Preparation, in vitro degradability, cytotoxicity, and in vivo biocompatibility of porous hydroxyapatite whisker-reinforced poly(L-lactide) biocomposite scaffolds

Biodegradable and bioactive scaffolds with interconnected macroporous structures, suitable biodegradability, adequate mechanical property, and excellent biocompatibility have drawn increasing attention in bone tissue engineering. Hence, in this work, porous hydroxyapatite whisker-reinforced poly(L-lactide) (HA-w/PLLA) composite scaffolds with different ratios of HA and PLLA were successfully developed through compression molding and particle leaching. The microstructure, in vitro mineralization, cytocompatibility, hemocompatibility, and in vivo biocompatibility of the porous HA-w/PLLA were investigated for the first time. The SEM results revealed that these HA-w/PLLA scaffolds possessed interconnected pore structures. Compared with porous HA powder-reinforced PLLA (HA-p/PLLA) scaffolds, HA-w/PLLA scaffolds exhibited better mechanical property and in vitro bioactivity, as more formation of bone-like apatite layers were induced on these scaffolds after mineralization in SBF. Importantly, in vitro cytotoxicity displayed that porous HA-w/PLLA scaffold with HA/PLLA ratio of 1:1 (HA-w1/PLLA1) produced no deleterious effect on human mesenchymal stem cells (hMSCs), and cells performed elevated cell proliferation, indicating a good cytocompatibility. Simultaneously, well-behaved hemocompatibility and favorable in vivo biocompatibility determined from acute toxicity test and histological evaluation were also found in the porous HA-w1/PLLA1 scaffold. These findings may provide new prospects for utilizing the porous HA whisker-based biodegradable scaffolds in bone repair, replacement, and augmentation applications.

Interplay between self-assembled structure of bone morphogenetic protein-2 (BMP-2) and osteoblast functions in three-dimensional titanium alloy scaffolds: Stimulation of osteogenic activity.

Three-dimensional cellular scaffolds are receiving significant attention in bone tissue engineering to treat segmental bone defects. However, there are indications of lack of significant osteoinductive ability of three-dimensional cellular scaffolds. In this regard, the objective of the study is to elucidate the interplay between bone morphogenetic protein (BMP-2) and osteoblast functions on 3D mesh structures with different porosities and pore size that were fabricated by electron beam melting. Self-assembled dendritic microstructure with interconnected cellular-type morphology of BMP-2 on 3D scaffolds stimulated osteoblast functions including adhesion, proliferation, and mineralization, with prominent effect on 2-mm mesh. Furthermore, immunofluorescence studies demonstrated higher density and viability of osteoblasts on lower porosity mesh structure (2 mm) as compared to 3- and 4-mm mesh structures. Enhanced filopodia cellular extensions with extensive cell spreading was observed on BMP-2 treated mesh structures, a behavior that is attributed to the unique self-assembled structure of BMP-2 that effectively communicates with the cells. The study underscores the potential of BMP-2 in imparting osteoinductive capability to the 3D printed scaffolds.

Mineralization and drug release of hydroxyapatite/poly(l-lactic acid) nanocomposite scaffolds prepared by Pickering emulsion templating

Biodegradable and bioactive nanocomposite (NC) biomaterials with controlled microstructures and able to deliver special drugs have gained increasing attention in bone tissue engineering. In this study, the hydroxyapatite (HAp)/poly(l-lactic acid) (PLLA) NC scaffolds were facilely prepared using solvent evaporation from templating Pickering emulsions stabilized with PLLA-modified HAp (g-HAp) nanoparticles. Then, in vitro mineralization experiments were performed in a simulated body fluid (SBF) to evaluate the bioactivity of the NC scaffolds. Moreover, in vitro drug release of the NC scaffolds using anti-inflammatory drug (ibuprofen, IBU) as the model drug was also investigated. The results showed that the NC scaffolds possessed interconnected pore structures, which could be modulated by varying the g-HAp nanoparticle concentration. The NC scaffolds exhibited excellent bioactivity, since they induced the formation of calcium-sufficient, carbonated apatite nanoparticles on the scaffolds after mineralization in SBF for 3 days. The IBU loaded in the NC scaffolds showed a sustained release profile, and the release kinetic followed the Higuchi model with diffusion process. Thus, solvent evaporation based on Pickering emulsion droplets is a simple and effective method to prepare biodegradable and bioactive porous NC scaffolds for bone repair and replacement applications.

Coculture of peripheral blood CD34+ cell and mesenchymal stem cell sheets increase the formation of bone in calvarial critical-size defects in rabbits

The reconstruction of large bony defects remains a clinical challenge, and angiogenesis and neovascularisation are being given more attention in bone tissue engineering. In this study we cocultured peripheral blood CD34+ cells (PB-CD34+ cells), an endothelial progenitor cell/haematopoietic stem cell-enriched population, with bone marrow-derived mesenchymal stem cells (MSC) to investigate their potential for bony regeneration. Cocultured cells showed better osteogenic differentiation than MSC alone in vitro. The cocultured cells and MSC sheets were also composited with hydroxyapatite and implanted in calvarial critical-size defects in rabbits. The rabbits were killed before microcomputed tomographic (MicroCT) and histological analysis. The results showed that cocultured cell composites had promoted bony regeneration more efficiently by 8 weeks after implantation. Our results indicate that the coculture of PB-CD34+ cells and MSC increases bony regeneration in calvarial critical-size defects in rabbits, and provide a new promising therapeutic strategy to aid skeletal healing.

Reinforcing of Porous Hydroxyapatite Ceramics with Hydroxyapatite Fibres for Enhanced Bone Tissue Engineering

Porous hydroxyapatite (HA) ceramic implants have attracted attention in bone tissue engineering due to their excellent bioactivity and biocompatibility due to their chemical similarity with the mineral component of natural bone. Unfortunately, HA when is formed into porous structures exhibits very low compression strength. In this study, fabrication of porous HA ceramic scaffolds containing HA fibers is presented. The primary aim of the study is to improve mechanical properties of the scaffold by introducing the fiber with uniform component relative to the scaffold. Scanning electron microscopy was used to observe the surface morphology and pore size of the scaffold. X-ray diffraction (XRD) was used to detect the phase composition and crystallinity of the scaffold. The compressive strength was determined using a universal material test machine. The results and the characterizations demonstrate the addition of HA fiber could enhance the uniformity of mechanical properties among samples and also the strength for a given open porosity.

Chemically-Conjugated Bone Morphogenetic Protein-2 on Three-Dimensional Polycaprolactone Scaffolds Stimulates Osteogenic Activity in Bone Marrow Stromal Cells

Poly(ε-caprolactone) (PCL) has received considerable attention in bone tissue engineering. However, the lack of osteoinductive ability of PCL limits its application. The aim of this study was to directly attach bone morphogenetic protein-2 (BMP-2) to PCL scaffolds by a crosslinking conjugation method and to investigate whether the bound BMP-2 maintained bioactivity in vitro. Immunofluorescent staining against BMP-2 and quantitative enzyme-linked immunosorbent assay measurements demonstrated that BMP-2 was successfully immobilized on the PCL three-dimensional scaffold by aminolysis and subsequent chemical conjugation. Conjugation produced much higher immobilization efficiency than the physical adsorption. Conjugated BMP-2 release from the PCL scaffolds was significantly slower than that from BMP-2-adsorbed PCL scaffolds over 15 days, which resulted in more BMP-2 locally retained on the conjugated scaffold. Further, the downstream Smads pathway was upregulated in bone marrow stromal cells cultured on the BMP-2-conjugated PCL scaffolds. Finally, gene expression of osteogenic markers (alkaline phosphatase, osteoclacin, and type I collagen) was upregulated in bone marrow stromal cells cultured on the PCL scaffolds with BMP-2 conjugation, but not on PCL scaffolds after BMP-2 adsorption. Therefore, our finding demonstrated that BMP-2 conjugation on polyester scaffolds is a feasible way to impart scaffolds with osteoinductive capability.

Efficient Cell-seeding into Scaffolds Improves Bone Formation

Bone marrow stromal cells (BMSCs)/β-tricalcium phosphate (β-TCP) composites have attracted a great deal of attention in bone tissue engineering. If more effective bone regeneration is to be achieved, efficient cell-seeding systems need to be clarified. In this study, we investigated the number of cells contained in composites, and the in vitro/vivo osteogenic differentiation capacity of composites using 4 conventional systems of seeding rat BMSCs into β-TCP: soak, low-pressure, pipette, and syringe systems. The highest number of cells was contained in the composites from the syringe group. Moreover, after two-week osteogenic induction in vitro, the composites in the syringe group exhibited the highest osteogenic potential, which continued at 8 weeks after subcutaneous implantation in vivo. Our results indicated that efficient and appropriate cell-seeding could improve in vitro/vivo bone formation in composites and thus make a potential clinical contribution to successful bone tissue engineering. Abbreviations: BMSCs, bone marrow stromal cells; β-TCP, β-tricalcium phosphate; S-D, Sprague-Dawley; kPa, kilopascal; ALP, alkaline phosphatase; N, Newton; DNA, deoxyribonucleic acid; OCN, osteocalcin; ANOVA, analysis of variance; PLSD, protected least-significant difference; and HE, hematoxylin and eosin.

Origin of Osteoblasts Involved in the Mechanism of Ectopic Bone Formation Induced by KUSA/A1 Cells with Honeycomb Carrier

The basic principle of bone tissue engineering is to use seeded stem cells in porous scaffold. Stem cells can proliferate and differentiate into various types of mature cells. A kind of stem cell called KUSA/A1 is a marrow stromal cell, capable of differentiating into three mesenchymal phenotypes: osteocyte, adipocyte, and myocyte by treating with 5-azacytidine in cell culture. Moreover, it has been reported that the mechanism of bone induction by KUSA/A1 cells is similar to intramembranous ossification. In order to clarify the origin of osteoblasts implicated in new bone formation, KUSA/A1 cells alone and combined with Honeycomb carrier were implanted in Transgenic Green Fluorescent Protein mice (GFP) mice. The presence of GFP positive host cells with osteoblastic morphology as well as GFP negative cells, clearly of KUSA/A1 cells in origin were observed around the bony trabeculae. These results indicated that the new bone was not only produced by KUSA/A1 cells but also by host cells from the surrounding connective tissues. To our knowledge, this is the first study to describe that host cells play an important role in ectopic bone induced by implanted marrow stromal cells, which would need special attention in bone tissue engineering.