Effectiveness of scaffolds with pre-seeded mesenchymal stem cells in bone regeneration--assessment of osteogenic ability of scaffolds implanted under the periosteum of the cranial bone of rats

Mesenchymal Stem Cells, Bioactive Factors, and Scaffolds in Bone Repair: From Research Perspectives to Clinical Practice

Mesenchymal stem cell-based therapies are promising tools for bone tissue regeneration. However, tracking cells and maintaining them in the site of injury is difficult. A potential solution is to seed the cells onto a biocompatible scaffold. Construct development in bone tissue engineering is a complex step-by-step process with many variables to be optimized, such as stem cell source, osteogenic molecular factors, scaffold design, and an appropriate in vivo animal model. In this review, an MSC-based tissue engineering approach for bone repair is reported. Firstly, MSC role in bone formation and regeneration is detailed. Secondly, MSC-based bone tissue biomaterial design is analyzed from a research perspective. Finally, examples of animal preclinical and human clinical trials involving MSCs and scaffolds in bone repair are presented.

Bone Regeneration Using Rat-Derived Dedifferentiated Fat Cells Combined with Activated Platelet-Rich Plasma

Bone regeneration using mesenchymal stem cells has several limitations. We investigated adipose-derived dedifferentiated fat (DFAT) cells as an alternative, and evaluated their cell proliferation rate, osteoblast differentiation, and bone regeneration ability in combination with activated platelet-rich plasma (aPRP). Rat DFATs and aPRP were isolated using ceiling culture and centrifugation, respectively. The cell proliferation rate was measured, and the cells were cultured in an osteoblast differentiation medium under varying concentrations of aPRP for 21 days and stained with Alizarin red. Gene expression was evaluated using real time polymerase chain reaction. Critical defects were implanted with DFAT seeded gelatin sponges under aPRP, and four weeks later, the bone regeneration ability was evaluated using micro-computed tomography and hematoxylin-eosin staining. The cell proliferation rate was significantly increased by the addition of aPRP. Alizarin red staining was positive 21 days after the start of induction, with significantly higher Runt-related transcription factor 2 (Runx2) and osteocalcin (OCN) expression levels than those in the controls. A 9 mm critical defect was largely closed (60.6%) after four weeks of gelatin sponge implantation with DFAT and aPRP. Therefore, materials combining DFAT cells and aPRP may be an effective approach for bone regeneration. Further research is needed to explore the long-term effects of these materials.

Optimization of culture duration of bone marrow cells before transplantation with a β-tricalcium phosphate/recombinant collagen peptide hybrid scaffold

INTRODUCTION

Currently, various kinds of materials are used for the treatment of bone defects. In general, these materials have a problem of formativeness. The three -dimensional (3D) printing technique has been introduced to fabricate artificial bone with arbitrary shapes, but poor bone replacement is still problematic.Our group has created a β⁻tricalcium phosphate (β⁻TCP) scaffold by applying 3D printing technology. This scaffold has an arbitrary shape and an internal structure suitable for cell loading, growth, and colonization. The scaffold was coated with a recombinant collagen peptide (RCP) to promote bone replacement.As indicated by several studies, cells loaded to scaffolds promote bone regeneration, especially when they are induced osteoblastic differentiation before transplantation. In this study, culture duration for bone marrow cells was optimized before being loaded to this new scaffold material.

METHOD

Bone marrow cells isolated from C57BL/6J mice were subjected to osteogenic culture for 4, 7, and 14 days. The differentiation status of the cells was examined by alkaline phosphatase staining, alizarin red staining, and real-time RT-PCR for differentiation markers. In addition, the flow of changes in the abundance of endothelial cells and monocytes was analyzed by flow cytometry according to the culture period of bone marrow cells.Next, cells at days 4, 7, and 14 of culture were placed on a β-TCP/RCP scaffold and implanted subcutaneously into the back of C57BL/6J mice. Grafts were harvested and evaluated histologically 8 weeks later. Finally, Cells cultured for 7 days were also transplanted subperiosteally in the skull of the mouse with scaffolds.

RESULT

Alkaline phosphatase staining was most prominent at 7 days, and alizarin red staining was positive at 14 days. Real-time RT-PCR revealed that Runx2 and Alp peaked at 7 days, while expression of Col1a1 and Bglap was highest at 14 days. Flow cytometry indicated that endothelial cells increased from day 0 to day 7, while monocytes increased continuously from day 0 to day 14. When transplanted into mice, the scaffold with cells cultured for 7 days exhibited the most prominent osteogenesis. The scaffold, which was transplanted subperiosteally in the skull, retained its shape and was replaced with regenerated bone over a large area of the field of view.

CONCLUSION

Osteoblasts before full maturation are most efficient for bone regeneration, and the pre-culture period suitable for cells to be loaded onto a β-TCP/RCP hybrid scaffold is approximately 7 days.This β-TCP/RCP hybrid scaffolds will also be useful for bone augmentation.

In vivo bioactivity of porous polyetheretherketone with a foamed surface

The in vivo bioactivity of porous polyetheretherketone (PEEK) with a foamed surface was evaluated using rabbit femoral bone. Cylindrical porous PEEK scaffolds, with pore diameter of 550 μm and porosity of 70%, were first prepared and immersed in 98% sulfuric acid, and then washed and immersed in 3 M potassium carbonate solution used as a foaming reagent. Numerous open pores of various sizes, as well as new functional groups, were visualized on the treated PEEK surface by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Micro computed tomography (micro-CT) showed that the volumetric density of treated PEEK was higher than that of bare PEEK at 8 weeks after surgery (p<0.05). Additionally, von Kossa staining indicated ingrowth of mature new bone tissue at 4 weeks relative to the bare PEEK group. Our data indicate that surface-treated PEEK exhibited improved bioactivity in vivo.

Bone regeneration with a collagen model polypeptides/α-tricalcium phosphate sponge in a canine tibia defect model

INTRODUCTION

We evaluated the effects of synthesized collagen model polypeptides consisting of a proline-hydroxyproline-glycine (poly(PHG)) sequence combined with porous alpha-tricalcium phosphate (α-TCP) particles on bone formation in a canine tibia defect model.

MATERIALS AND METHODS

The porous α-TCP particles were mixed with a poly(PHG) solution, and the obtained sponge was then cross-linked and characterized by x-ray diffraction and scanning electron microscopy. Tibia defects were analyzed in 12 healthy beagles using microcomputed tomography and histological evaluation.

RESULTS

At 2 and 4 weeks, the volume density of new bone was higher in the poly(PHG)/α-TCP group than in poly(PHG) alone group (P < 0.05); however, there was no difference at 8 weeks (P > 0.05). Histological evaluation at 4 weeks after implantation revealed that the poly(PHG) had degraded, and newly formed bone was present on the surface of the α-TCP particles. At 8 weeks, continuous cortical bone formation with a Haversian structure covered the top of the bone defects in both groups.

CONCLUSION

This study demonstrates that the composite created using porous α-TCP particles and poly(PHG) is sufficiently adaptable for treating bone defects.

Bone tissue engineering using polyetherketoneketone scaffolds combined with autologous mesenchymal stem cells in a sheep calvarial defect model

Polyetherketoneketone (PEKK) a high performance thermoplastic polymer that is FDA-approved for cranio- and maxillo-facial as well as spineal surgery. We studied the viability, growth and osteogenic differentiation of bone marrow-derived human and sheep mesenchymal stem cells (MSC) in combination with a 3D scaffold made of PEKK using different cell-based assays. To investigate if autologous MSC, either undifferentiated or osteogenically pre-differentiated, augmented bone formation after implantation, we implanted cell-seeded 3D PEKK scaffolds into calvarial defects in sheep for 12 weeks. The volume and quality of newly formed bone were investigated using micro-computer tomography (micro-CT) and histological stainings. Our results show that the 3D PEKK scaffolds were cyto- and bio-compatible. They allowed for adherence, growth and osteogenic differentiation of human and ovine MSC. However, bone healing seemed unaffected by whether the scaffolds were seeded with MSC. Considerable amounts of newly formed bone were found in all PEKK treated groups, but a fibrous capsule was formed around the implants regardless of cell seeding with MSC.

Bone-Forming Capacity and Biodistribution of Bone Marrow-Derived Stromal Cells Directly Loaded into Scaffolds: A Novel and Easy Approach for Clinical Application of Bone Regeneration

In the context of clinical applications of bone regeneration, cell seeding into scaffolds needs to be safe and easy. Moreover, cell density also plays a crucial role in the development of efficient bone tissue engineering constructs. The aim of this study was to develop and evaluate a simple and rapid cell seeding procedure on hydroxyapatite/ β-tricalcium phosphate (HA/βTCP), as well as define optimal cell density and control the biodistribution of grafted cells. To this end, human bone marrow-derived stromal cells (hBMSCs) were seeded on HA/βTCP scaffolds, and we have compared bone formation using an ectopic model. Our results demonstrated a significantly higher bone-forming capacity of hBMSCs directly loaded on HA/βTCP during surgery compared to hBMSCs preseeded for 7 days in vitro on HA/βTCP before ectopic implantation. The extent of new bone formation increases with increasing hBMSC densities quantitatively, qualitatively, and in frequency. Also, this study showed that grafted hBMSCs remained confined to the implantation site and did not spread toward other tissues, such as liver, spleen, lungs, heart, and kidneys. In conclusion, direct cell loading into a scaffold during surgery is more efficient for bone regeneration, as well as quick and safe. Therefore direct cell loading is suitable for clinical requirements and cell production control, making it a promising approach for orthopedic applications. Moreover, our results have provided evidence that the formation of a mature bone organ containing hematopoietic islets needs a sufficiently high local density of grafted hBMSCs, which should guide the optimal dose of cells for clinical use.

Stem cell recruitment after injury: lessons for regenerative medicine

Tissue repair and regeneration are thought to involve resident cell proliferation as well as the selective recruitment of circulating stem and progenitor cell populations through complex signaling cascades. Many of these recruited cells originate from the bone marrow, and specific subpopulations of bone marrow cells have been isolated and used to augment adult tissue regeneration in preclinical models. Clinical studies of cell-based therapies have reported mixed results, however, and a variety of approaches to enhance the regenerative capacity of stem cell therapies are being developed based on emerging insights into the mechanisms of progenitor cell biology and recruitment following injury. This article discusses the function and mechanisms of recruitment of important bone marrow-derived stem and progenitor cell populations following injury, as well as the emerging therapeutic applications targeting these cells.

Radial-flow bioreactor enables uniform proliferation of human mesenchymal stem cells throughout a three-dimensional scaffold

Mesenchymal stem cells (MSCs) obtained from human bone marrow are pluripotent and have been expanded and differentiated into several kinds of mesodermal tissue in vitro. To create bioartificial tissues and organs for implantation, it is necessary to induce proliferation in such cells. In this study, a radial-flow bioreactor (RFB) was used to induce three-dimensional (3D) expansion of human MSCs (hMSCs) on a large scaffold. The effect of this expansion on cellular characteristics was investigated. To produce precultured sheets, the hMSCs were first seeded onto type 1 collagen sheets and incubated for 12 h, after which they were placed in the RFB for fabrication of scaffolds. The culture medium was circulated at 3 mL/min, and the cells were dynamically cultured for 1 week at 37°C. As a control, static cultivation in a culture dish was also carried out. Cellular expansion and characteristics were analyzed. Alkaline phosphatase (ALP) activity in the hMSCs was also investigated after dynamic culture in an osteogenesis induction medium to explore their potential for osteogenic differentiation. At 1 week of dynamic cultivation, a >60% increase was observed in a number of cells together with a uniform distribution throughout the scaffolds compared with under static conditions; no change in hMSC markers was observed. The hMSCs retained the ability for osteogenic differentiation after culture in the RFB. The present results indicate that 3D dynamic culture in an RFB enables uniform expansion of hMSCs with no change in cellular characteristics, suggesting the usefulness of this technique in tissue engineering.

Dynamic culture improves MSC adhesion on freeze-dried bone as a scaffold for bone engineering

AIM

To investigate the interaction between mesenchymal stem cells (MSCs) and bone grafts using two different cultivation methods: static and dynamic.

METHODS

MSCs were isolated from rat bone marrow. MSC culture was analyzed according to the morphology, cell differentiation potential, and surface molecular markers. Before cell culture, freeze-dried bone (FDB) was maintained in culture for 3 d in order to verify culture medium pH. MSCs were co-cultured with FDB using two different cultivation methods: static co-culture (two-dimensional) and dynamic co-culture (three-dimensional). After 24 h of cultivation by dynamic or static methods, histological analysis of Cell adhesion on FDB was performed. Cell viability was assessed by the Trypan Blue exclusion method on days 0, 3 and 6 after dynamic or static culture. Adherent cells were detached from FDB surface, stained with Trypan Blue, and quantified to determine whether the cells remained on the graft surface in prolonged non-dynamic culture. Statistical analyses were performed with SPSS and a P < 0.05 was considered significant.

RESULTS

The results showed a clear potential for adipogenic and osteogenic differentiation of MSC cultures. Rat MSCs were positive for CD44, CD90 and CD29 and negative for CD34, CD45 and CD11bc. FDBs were maintained in culture for 3 d and the results showed there was no significant variation in the culture medium pH with FDB compared to pure medium pH (P > 0.05). In histological analysis, there was a significant difference in the amount of adhered cells on FDB between the two cultivation methods (P < 0.05). The MSCs in the dynamic co-culture method demonstrated greater adhesion on the bone surface than in static co-culture method. On day 0, the cell viability in the dynamic system was significantly higher than in the static system (P < 0.05). There was a statistical difference in cell viability between days 0, 3 and 6 after dynamic culture (P < 0.05). In static culture, cell viability on day 6 was significantly lower than on day 3 and 0 (P < 0.05).

CONCLUSION

An alternative cultivation method was developed to improve the MSCs adhesion on FDB, demonstrating that dynamic co-culture provides a superior environment over static conditions.

Effects on bone regeneration when collagen model polypeptides are combined with various sizes of alpha-tricalcium phosphate particles

We evaluated the effects on bone formation of combining synthesized collagen model polypeptides consisting of a Pro-Hyp-Gly [poly(PHG)] sequence and alpha-tricalcium phosphate (α-TCP) particles with various median sizes (large: 580.8 μm; small: 136.2 μm; or large and small mixed: 499.3 μm) in a skull defect model in mini-pigs. Quantitative image analyses for the volume density (VD) of new bone revealed that the VD in each α-TCP group was significantly higher than that in the poly(PHG) control group, with the mixed group showing the highest VD among all the groups at 4 weeks after implantation. Histological assessments revealed that the small α-TCP particles were almost completely degraded at 8 weeks. At 12 weeks, all sizes of α-TCP particles were completely degraded and remodeling of the lamellar bone was observed. The present findings suggest that particle size may influence the success of bone formation in defects.

Controlling multipotent stromal cell migration by integrating "course-graining" materials and "fine-tuning" small molecules via decision tree signal-response modeling

Biomimetic scaffolds have been proposed as a means to facilitate tissue regeneration by multi-potent stromal cells (MSCs). Effective scaffold colonization requires a control of multiple MSC responses including survival, proliferation, differentiation, and migration. As MSC migration is relatively unstudied in this context, we present here a multi-level approach to its understanding and control, integratively tuning cell speed and directional persistence to achieve maximal mean free path (MFP) of migration. This approach employs data-driven computational modeling to ascertain small molecule drug treatments that can enhance MFP on a given materials substratum. Using poly(methyl methacrylate)-graft-poly(ethylene oxide) polymer surfaces tethered with epidermal growth factor (tEGF) and systematically adsorbed with fibronectin, vitronectin, or collagen-I to present hTERT-immortalized human MSCs with growth factor and extracellular matrix cues, we measured cell motility properties along with signaling activities of EGFR, ERK, Akt, and FAK on 19 different substrate conditions. Speed was consistent on collagen/tEGF substrates, but low associated directional persistence limited MFP. Decision tree modeling successfully predicted that ERK inhibition should enhance MFP on collagen/tEGF substrates by increasing persistence. Thus, we demonstrated a two-tiered approach to control MSC migration: materials-based "coarse-graining" complemented by small molecule "fine-tuning".