Histological aspects in bone regeneration of an association with porous hydroxyapatite and bone marrow cells

Preparation of gradient-type biological tissue-polymer complex for interlinking device

The aim of this study was to investigate the monomer absorption behavior of decellularized dermis and prepare a gradient-type decellularized dermis-polymer complex. Decellularized dermis was prepared using sodium dodecyl sulfate, and its monomer absorption behavior was investigated using three types of hydrophobic monomer with different surface free energies. The results show that monomer absorption depends strongly on the tissue structure, regardless of the surface free energy, and the amount of absorbed monomer can be increased by sonication. Based on these results, we prepared a gradient-type decellularized dermis-poly(methyl methacrylate) complex by controlling the permeation time of the methyl methacrylate monomer and polymerization initiator into the decellularized dermis. The mechanical strength of this complex gradually increased from the dermis side to the polymer side, and combined the physical characteristics of the dermis and the polymer.

Bone marrow-derived mesenchymal stem cells assembled with low-dose BMP-2 in a three-dimensional hybrid construct enhances posterolateral spinal fusion in syngeneic rats

BACKGROUND CONTEXT

The combination of potent osteoinductive growth factor, functional osteoblastic cells, and osteoconductive materials to induce bone formation is a well-established concept in bone tissue engineering. However, supraphysiological dose of growth factor, such as recombinant human bone morphogenetic protein 2 (rhBMP-2), which is necessary in contemporary clinical application, have been reported to result in severe side effects.

PURPOSE

We hypothesize that the synergistic osteoinductive capacity of low-dose bone morphogenetic protein 2 (BMP-2) combined with undifferentiated bone marrow-derived stromal cells (BMSCs) is comparable to that of osteogenically differentiated BMSCs when used in a rodent model of posterolateral spinal fusion.

STUDY DESIGN/SETTING

A prospective study using a rodent model of posterolateral spinal fusion was carried out.

PATIENT SAMPLE

Thirty-six syngeneic Fischer rats comprised the patient sample.

METHODS

Six groups of implants were evaluated as follows (n=6): (1) 10 µg BMP-2 with undifferentiated BMSCs; (2) 10 µg BMP-2 with osteogenic-differentiated BMSCs; (3) 2.5 µg BMP-2 with undifferentiated BMSCs; (4) 2.5 µg BMP-2 with osteogenic-differentiated BMSCs; (5) 0.5 µg BMP-2 with undifferentiated BMSCs; and (6) 0.5 µg BMP-2 with osteogenic-differentiated BMSCs. Optimal in vitro osteogenic differentiation of BMSCs was determined by quantitative real-time polymerase chain reaction (qRT-PCR) gene analysis whereas in vivo bone formation capacity was evaluated by manual palpation, micro-computed tomography, and histology.

RESULTS

Rat BMSCs cultured in fibrin matrix that was loaded into the pores of medical-grade poly epsilon caprolactone tricalcium phosphate scaffolds differentiated toward osteogenic lineage by expressing osterix, runt-related transcription factor 2, and osteocalcium mRNA when supplemented with dexamethasone, ascorbic acid, and β-glycerophosphate. Whereas qRT-PCR revealed optimal increase in osteogenic genes expression after 7 days of in vitro culture, in vivo transplantation study showed that pre-differentiation of BMSCs before transplantation failed to promote posterolateral spinal fusion when co-delivered with low-dose BMP-2 (1/6 or 17% fusion rate). In contrast, combined delivery of undifferentiated BMSCs with low-dose BMP-2 (2.5 µg) demonstrated significantly higher fusion rate (4/6 or 67%) as well as significantly increased volume of new bone formation (p<.05).

CONCLUSION

In summary, this study supports the combination of undifferentiated BMSCs and low-dose rhBMP-2 for bone tissue engineering construct.

Modulation of stem cell differentiation with biomaterials

Differentiation of stem cells can be controlled with interactions with microenvironments of the stem cells. The interactions contain various signals including soluble growth factor signal, cell adhesion signal, and mechanical signal, which can modulate differentiation of stem cells. Biomaterials can provide these types of signals to induce desirable cellular differentiation. Biomaterials can deliver soluble growth factors locally to stem cells at a controlled rate for a long period. Stem cell adhesion to specific adhesion molecules presented by biomaterials can induce specific differentiation. Mechanical signals can be delivered to stem cells seeded onto biomaterial scaffolds. These approaches would be invaluable for direction of stem cell differentiation and in vivo tissue regeneration using stem cells.

Calcium phosphate bioceramics fabricated from extracted human teeth for tooth tissue engineering

Bioceramic tooth powders were prepared via heat treatment of extracted human teeth using sintering temperatures between 600°C and 1200°C, and their properties were investigated for potential tooth tissue engineering. The sintered human tooth powders were characterized using thermal analysis (thermogravimetric analysis (TG) and differential thermal analysis (DTA)), field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and Fourier transformed infrared (FTIR) spectroscopy. Additionally, the phase constitutions and chemical homogeneities of the composite samples were examined using a quantitative chemical analysis with inductively coupled plasma spectroscopy. The results revealed that the annealing process produced useful hydroxyapatite-based bioceramic biomaterials when annealed above 1000°C. The FTIR spectra and the TG/DTA thermograms of the tooth powders indicated the presence of organic compounds, which were completely removed after annealing at temperatures above 1000°C. The tooth powders annealed between 1000°C and 1200°C had good characteristics as bioceramic biomaterials. Furthermore, the biocompatibility of each tooth powder was evaluated using in vitro and in vivo techniques; our results indicate that the prepared human tooth powders have great potential for tooth tissue engineering applications.

Enhancement of in vivo bone regeneration efficacy of osteogenically undifferentiated human cord blood mesenchymal stem cells

We hypothesized that bone morphogenetic protein-2 (BMP-2) would significantly enhance in vivo bone formation efficacy of osteogenically undifferentiated human cord blood mesenchymal stem cells (hCBMSCs). To test this hypothesis, poly(lactic-co-glycolic acid)/hydroxyapatite (PLGA/HA) scaffolds (group 1), BMP-2-loaded PLGA/HA scaffolds (group 2), undifferentiated hCBMSCs seeded on PLGA/HA scaffolds (group 3), undifferentiated hCBMSCs seeded on BMP-2-loaded PLGA/HA scaffolds (group 4), and osteogenically differentiated hCBMSCs seeded on PLGA/HA scaffolds (group 5) were implanted into dorsal, subcutaneous spaces of athymic mice for 8 weeks. Histological analysis showed that group 4 exhibited the largest bone formation area. RT-PCR analysis showed that human mRNA expression of osteoblastic markers such as ALP and osteocalcin in group 4 was higher than that of the other groups. Mouse osteoblastic markers of the host cells in the implants were also expressed more in group 4 than in the other groups. This study demonstrated that hCBMSCs that were not differentiated osteogenically in vitro prior to transplantation regenerate bone negligibly in vivo and that transplantation of osteogenically undifferentiated hCBMSCs with BMP-2 delivery results in much more extensive bone formation in vivo than that of undifferentiated or osteogenically differentiated hCBMSCs.

Differentiation of bone marrow stromal cells into osteoblasts in a self-assembling peptide hydrogel: in vitro and in vivo studies

A prerequisite of tissue engineering approaches with regard to autograft is a suitable scaffold that can harbor cells and signals. Conventionally, such scaffolds have been prepared as 3D scaffolds prefabricated from synthetic or natural biomaterials. RAD16 has been introduced as a new biomaterial, where synthetic peptides self-assemble to form a hydrogel. In this study, RAD16 was examined in terms of osteogenic efficacy and feasibility of ectopic mineralization. Two hundred and seventy-one RAD16 was cocultured with 1 × 10(6) bone marrow cells from the femurs of 6-week-old Wistar male rats in alpha minimum essential medium supplemented with or without dexamethasone. Second, the same volume of the RAD16 construct hosting the cells with or without hydroxyapatite (HA) particles was treated in the dexamethasone medium as well, prepared in a Teflon tube, and implanted subcutaneously. Cell proliferation was prominent in the RAD16 coculture with dexamethasone at 1 week and significantly decreased by 2 weeks, whereas the other combinations remained or inclined, and their osteogenic differentiation was accelerated up to 2 weeks, as seen in increasing alkaline phosphatase (ALP) activity and mRNAs of ALP, OPN, and OCN. The RAD16 implant prepared with HA particles allowed more osteoblast-like cells and blood cells to grow inside, which was accompanied by elevating OPN gene expression and the stronger peak of VEGF gene expression at 2 weeks. Furthermore, more OPN mRNA signal was detected around the RAD16 containing HA particles by 4 weeks. On the other hand, the RAD16 alone represented lower expression of OPN gene. During the experiment, however, no ectopic mineralization was observed in both groups. Conclusively, it was suggested that the RAD16 showed feasibility of serving as a matrix for osteogenic differentiation of cocultured bone marrow cells in vitro and in vivo. Proceeding of exploration and modification of RAD16 are continuously required for cell-based tissue engineering.

In vivo study on hydroxyapatite scaffolds with trabecular architecture for bone repair

The objective of this research was to investigate the bone formation and angio-conductive potential of hydroxyapatite (HA) scaffolds closely matched to trabecular bone in a canine segmental defect after 3 and 12 weeks post implantation. Histomorphometric comparisons were made between naturally forming trabecular bone (control) and defects implanted with scaffolds fabricated with micro-size (M-HA) and nano-size HA (N-HA) ceramic surfaces. Scaffold architecture was similar to trabecular bone formed in control defects at 3 weeks. No significant differences were identified between the two HA scaffolds; however, significant bone in-growth was observed by 12 weeks with 43.9 +/- 4.1% and 50.4 +/- 8.8% of the cross-sectional area filled with mineralized bone in M-HA and N-HA scaffolds, respectively. Partially organized, lamellar collagen fibrils were identified by birefringence under cross-polarized light at both 3 and 12 weeks post implantation. Substantial blood vessel infiltration was identified in the scaffolds and compared with the distribution and diameter of vessels in the surrounding cortical bone. Vessels were less numerous but significantly larger than native cortical Haversian and Volkmann canals reflecting the scaffold architecture where open spaces allowed interconnected channels of bone to form. This study demonstrated the potential of trabecular bone modeled, highly porous and interconnected, HA scaffolds for regenerative orthopedics.

Bone morphogenetic protein-2 enhances bone regeneration mediated by transplantation of osteogenically undifferentiated bone marrow-derived mesenchymal stem cells

We have hypothesized that human bone marrow-derived mesenchymal stem cells (BMMSCs), that are not osteogenically differentiated prior to implantation, would regenerate bone extensively in vivo once exogenous bone morphogenetic protein-2 (BMP-2) was delivered to the implantation site. BMP-2 released from heparin-conjugated poly(lactic-co-glycolic acid) (HCPLGA) scaffolds stimulates osteogenic differentiation of cultured BMMSCs. Upon implantation, undifferentiated BMMSCs on BMP-2-loaded HCPLGA scaffolds induce far more extensive bone formation than either undifferentiated BMMSCs or osteogenically differentiated BMMSCs on HCPLGA scaffolds. These BMP-2-loaded HCPLGA scaffolds could prove invaluable for in vivo regeneration of bone from undifferentiated human BMMSCs.

Effects of trabecular calcium phosphate scaffolds on stress signaling in osteoblast precursor cells

The objective of this research was to investigate stress-signaling patterns in response to two-dimensional (2-D) and three-dimensional (3-D) calcium phosphate (CP) materials using human embryonic palatal mesenchyme cells (HEPM, CRL-1486, ATCC, Manassas, VA), an osteoblast precursor cell line. Control discs and scaffolds were fabricated from hydroxyapatite and beta tri-CP ceramics. Phospho-specific antibody cell-based ELISA technique was utilized on members of the mitogen-activated protein kinase cascade including; the extracellular signal-regulated kinases (ERK1/2), p38, c-Jun N-terminal kinase (JNK), and the anti-apoptosis mediator protein kinase B (AKT). Quantification of these signals was evaluated during the early attachment phase of osteoblast precursor cells. In this study, it was observed that 3-D CP scaffolds significantly activated the stress mediators p38 and JNK but not ERK1/2. This signal trend was matched with an up-regulation in AKT, suggesting the ability of cells to manage high stress signals in response to 3-D CP architecture and that 3-D CP scaffolds are necessary for studies simulating a natural trabecular bone organization. The absence of these signals in 2-D CP surfaces indicated the importance of local architecture conditions on cell stress response. It was concluded from this study that osteoblast precursor cells cultured in 3-D CP scaffolds experience greater stress-signaling patterns when compared to 2-D CP surfaces.

Repair of osteochondral defects with autologous chondrocytes seeded onto bioceramic scaffold in sheep

At present, the most popular biomaterials used in cartilage tissue engineering are synthetic polymers. However, problems-such as acidic by-product accumulation and side effects in local or systemic inflammatory reactions during in vivo degradation-are drawing much attention. The polymers are also highly hydrophobic and degrade within 4 weeks, allowing insufficient time to support neocartilage formation. All these have made polymers less promising in clinical application. In this study, we tested a new bioceramic scaffold made of artificial synthesized powder of beta-tricalcium phosphate (beta-TCP) in a sheep model. Osteochondral defects were filled with a bioceramic-chondrocyte construct and neocartilage tissue completely resurfaced the cartilage defects after 24 weeks. Typical hyaline cartilage structure was generated in the engineered cartilage. Biodegradation of bioceramic was notable, leading to bioceramic fragmentation and particle formation. Numerous ceramic particles (size, 0.5-1.9 microm) and numerous macrophages were observed at the ceramic-tissue interface as well as in the marrow tissue. No macrophages were visible in the neocartilage tissue. Although long-term in vivo study is needed to further determine the pathological sequences of the beta-TCP-based cartilage construct, this study suggests that this bioceramic might be used to repair chondral or osteochondral defects and could be used as a scaffold for cartilage tissue engineering.

Biomaterial challenges and approaches to stem cell use in bone reconstructive surgery

As life expectancy increases, so does the need to treat large bone defects. New biomaterials combined with osteogenic cells are now being developed as an alternative to autogenous bone grafts. The goal is to make the stem cells adhere to the scaffold, and then grow to differentiate into functional osteogenic cells and organize into healthy bone as the scaffold degrades. Decisive improvements have been made in the fields of stem cell biology, 3-D scaffold fabrication and tissue engineering, but the ideal bone substitute that fulfils all functional and safety requirements has yet to be developed.

In vitro control of human bone marrow stromal cells for bone tissue engineering

For the clinical application of cultured human mesenchymal stem cells (MSCs), cells must have minimal contact with fetal calf serum (FCS) because it might be a potential vector for contamination by adventitious agents. The use of human plasma and serum for clinical applications also continues to give rise to considerable concerns with respect to the transmission of known and unknown human infectious agents. With the objective of clinical applications of cultured human MSCs, we tested the ability of autologous plasma, AB human serum, FCS, and artificial serum substitutes containing animal-derived proteins (Ultroser G) or vegetable-derived proteins (Prolifix S6) to permit their growth and differentiation in vitro. To conserve as much autologous plasma as possible, we attempted to mix it at decreasing concentrations with the serum substitute containing vegetable-derived mitogenic factors. Under control conditions, by day 10 all the fibroblast colony-forming units (CFU-Fs) were alkaline phosphatase (ALP) positive. However, their number and size were highly variable among donors. Better CFU-F formation was obtained with Ultroser G, and with human AB serum and autologous plasma mixed at, respectively, 5 and 1% with Prolifix S6. The effects of these mixtures on CFU-F formation demonstrate synergy, with the human serum or plasma supplying the factors that favor differentiation of MSCs while Prolifix S6 supplies the mitogenic factors. Finally, we demonstrated the possibility of controlling human MSC growth and differentiation in vitro. Notably, by means of a minimal quantity of human serum or human plasma mixed with a new serum substitute containing vegetable-derived proteins, we displayed growth and differentiation of human MSCs comparable to that obtained with FCS or serum substitutes containing animal-derived proteins. These results will have crucial significance for future applications of cultured human MSCs in bone tissue engineering.