Human adipose-derived side population stem cells cultured on demineralized bone matrix for bone tissue engineering

Assembling the Puzzle Pieces. Insights for in Vitro Bone Remodeling

As a highly dynamic organ, bone changes during throughout a person's life. This process is referred to as 'bone remodeling' and it involves two stages - a well-balanced osteoclastic bone resorption and an osteoblastic bone formation. Under normal physiological conditions bone remodeling is highly regulated that ensures tight coupling between bone formation and resorption, and its disruption results in a bone metabolic disorder, most commonly osteoporosis. Though osteoporosis is one of the most prevalent skeletal ailments that affect women and men aged over 40 of all races and ethnicities, currently there are few, if any safe and effective therapeutic interventions available. Developing state-of-the-art cellular systems for bone remodeling and osteoporosis can provide important insights into the cellular and molecular mechanisms involved in skeletal homeostasis and advise better therapies for patients. This review describes osteoblastogenesis and osteoclastogenesis as two vital processes for producing mature, active bone cells in the context of interactions between cells and the bone matrix. In addition, it considers current approaches in bone tissue engineering, pointing out cell sources, core factors and matrices used in scientific practice for modeling bone diseases and testing drugs. Finally, it focuses on the challenges that bone regenerative medicine is currently facing.

The Emerging Use of ASC/Scaffold Composites for the Regeneration of Osteochondral Defects

Articular cartilage is composed of chondrocytes surrounded by a porous permeable extracellular matrix. It has a limited spontaneous healing capability post-injury which, if left untreated, can result in severe osteochondral disease. Currently, osteochondral (OC) defects are treated by bone marrow stimulation, artificial joint replacement, or transplantation of bone, cartilage, and periosteum, while autologous osteochondral transplantation is also an option; it carries the risk of donor site damage and is limited only to the treatment of small defects. Allografts may be used for larger defects; however, they have the potential to elicit an immune response. A possible alternative solution to treat osteochondral diseases involves the use of stromal/stem cells. Human adipose-derived stromal/stem cells (ASCs) can differentiate into cartilage and bone cells. The ASC can be combined with both natural and synthetic scaffolds to support cell delivery, growth, proliferation, migration, and differentiation. Combinations of both types of scaffolds along with ASCs and/or growth factors have shown promising results for the treatment of OC defects based on in vitro and in vivo experiments. Indeed, these findings have translated to several active clinical trials testing the use of ASC-scaffold composites on human subjects. The current review critically examines the literature describing ASC-scaffold composites as a potential alternative to conventional therapies for OC tissue regeneration.

Evaluation of the Growth and Differentiation of Human Fetal Osteoblasts (hFOB) Cells on Demineralized Bone Matrix (DBM)

Cells with osteogenic potential are believed to be an ideal source for bone tissue bioengineering. Large bone defects require temporary substitution of the damaged parts. In this respect, the transplantation of bone cells cultured on osteogenic substrates has been investigated. To use the natural bone matrix, one approach is the so-called demineralized bone matrix (DBM). In this study, we evaluated the interaction of human fetal osteoblasts (hFOB 1.19 cells, a human fetal osteoblastic cell line) with DBM fragments. No additional bone differentiation inducer was used other than the DBM itself. The samples were processed, had adhesion pattern evaluated and analyzed by light microscopy (cytochemical and immunocytochemical analysis) and electron microscopy (scanning and transmission). The adhesion pattern of hFOB cells on DBM was similar to what was observed on the cell culture plate. Morphological analysis showed that the hFOB cells had emitted filopodia and cellular projections on both controls and DBM. On DBM, the adhered cells emitted prolongations and migrated into the matrix. The monolayer growth pattern was observed as well as the accumulation of filamentous and reticulate extracellular materials when hFOB cells were cultured on the DBM surface. EDS analysis revealed the deposition of calcium on DBM. Immunocytochemical data showed that the hFOB cells were able to secrete extracellular matrix molecules such as fibronectin and laminin on DBM. Our data indicate that DBM successfully stimulates the osteoblastic phenotype of osteoblast-like cells and corroborate with the fact that DBM is a considerable natural matrix that promotes fractured-bone healing.

Simultaneous Treatment of Photobiomodulation and Demineralized Bone Matrix With Adipose-Derived Stem Cells Improve Bone Healing in an osteoporotic bone defect

Introduction: The ability of simultaneous treatment of critical-sized femoral defects (CSFDs) with photobiomodulation (PBM) and demineralized bone matrix (DBM) with or without seeded adipose-derived stem cells (ASCs) to induce bone reconstruction in ovariectomized induced osteoporotic (OVX) rats was investigated. Methods: The OVX rats with CSFD were arbitrarily separated into 6 groups: control, scaffold (S, DBM), S + PBM, S + alendronate (ALN), S + ASCs, and S + PBM + ASCs. Each group was assessed by cone beam computed tomography (CBCT) and histological examinations. Results: In the fourth week, CBCT and histological analyses revealed that the largest volume of new bone formed in the S + PBM and S + PBM + ASC groups. The S + PBM treatment relative to the S and S + ALN treatments remarkably reduced the CSFD (Mann-Whitney test, P = 0.009 and P = 0.01). Furthermore, S + PBM + ASCs treatment compared to the S and S + ALN treatments significantly decreased CSFD (Mann Whitney test, P = 0.01). In the eighth week, CBCT analysis showed that extremely enhanced bone regeneration occurred in the CSFD of the S + PBM group. Moreover, the CSFD in the S + PBM group was substantially smaller than S, S + ALN and S + ASCs groups (Mann Whitney test, P = 0.01, P = 0.02 and P = 0.009). Histological observations showed more new bone formation in the treated CSFD of S + PBM + ASCs and S + PBM groups. Conclusion: The PBM plus DBM with or without ASCs significantly enhanced bone healing in the CSFD in OVX rats compared to control, DBM alone, and ALN plus DBM groups. The PBM plus DBM with or without ASCs significantly decreased the CSFD area compared to either the solo DBM or ALN plus DBM treatments.

Micro-Computed Tomography Analysis on Administration of Mesenchymal Stem Cells - Bovine Teeth Scaffold Composites for Alveolar Bone Tissue Engineering

The tissue engineering approach for periodontal tissue regeneration using a combination of stem cells and scaffold has been vastly developed. Mesenchymal Stem Cells (MSCs) seeded with Bovine Teeth Scaffold (BTSc) can repair alveolar bone damage in periodontitis cases. The alveolar bone regeneration process was analyzed by micro-computed tomography (µ-CT) to observe the structure of bone growth and to visualize the scaffold in 3-Dimensional (3D). The purpose of this study is to analyze alveolar bone regeneration by µ-CT following the combination of MSCs and bovine teeth scaffold (MSCs-BTSc) implantation in the Wistar rat periodontitis model. Methods. MSCs were cultured from adipose-derived mesenchymal stem cells of rats. BTSc was taken from bovine teeth and freeze-dried with a particle size of 150-355 µm. MSCs were seeded on BTSc for 24 hours and transplanted in a rat model of periodontitis. Thirty-five Wistar rats were made as periodontitis models with LPS induction from P. gingivalis injected to the buccal section of interproximal gingiva between the first and the second mandibular right-molar teeth for six weeks. There were seven groups (control group, BTSc group on day 7, BTSc group on day 14, BTSc group on day 28, MSCs-BTSc group on day 7, MSCs-BTSc group on day 14, MSCs-BTSc group on day 28). The mandibular alveolar bone was analyzed and visualized in 3D with µ-CT to observe any new bone growth. Statistical Analysis. Group data were subjected to the Kruskal Wallis test followed by the Mann-Whitney (p <0.05). The µ-CT qualitative analysis shows a fibrous structure, which indicates the existence of new bone regeneration. Quantitative analysis of the periodontitis model showed a significant difference between the control model and the model with the alveolar bone resorption (p <0.05). The bone volume and density measurements revealed that the MSCs-BTSc group on day 28 formed new bone compared to other groups (p <0.05). Administration of MSCs-BTSc combination has the potential to form new alveolar bone.

Osteogenic Differentiation of Adipose-Derived Stromal Cells: From Bench to Clinics

In addition to mesenchymal stem cells, adipose-derived stem/stromal cells (ASCs) are an attractive source for a large variety of cell-based therapies. One of their most important potential applications is related to the regeneration of bone tissue thanks to their capacity to differentiate in bone cells. However, this requires a proper control of their osteogenic differentiation, which depends not only on the initial characteristics of harvested cells but also on the conditions used for their culture. In this review, we first briefly describe the preclinical and clinical trials using ASCs for bone regeneration and present the quantitative parameters used to characterize the osteogenic differentiation of ASCs. We then focus on the soluble factors influencing the osteogenic differentiation of ACS, including the steroid hormones and various growth factors, notably the most osteoinductive ones, the bone morphogenetic proteins (BMPs). Impact statement Adipose-derived stromal/stem cells are reviewed for their use in bone regeneration.

Osteogenic Differentiation and Biocompatibility of Bovine Teeth Scaffold with Rat Adipose-derived Mesenchymal Stem Cells

OBJECTIVE

Adipose-derived mesenchymal stem cells (ADMSCs) have great potential for regenerative medicine. These have been combined with biomaterials such as Bovine teeth that are preferred as a periodontal regeneration material. The main purpose of this study is to evaluate and analyze a biocompatibility test and osteogenic differentiation of bovine teeth scaffold seeded with ADMSCs in vitro.

MATERIALS AND METHODS

A true experimental study with post-test only group design was conducted. Random sampling and Lameshow's formula were used to determine the sample. The scaffold, obtained from bovine teeth as the bone graft material, was analyzed using 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and its attachment was evaluated by scanning electron microcopy (SEM) and micro-computed tomography with ADMSCs. ADMDSCs attachment present in the bovine teeth scaffold was assessed using SEM at 1-hour, 12-hour, and 24-hour intervals.

STATISTICAL ANALYSIS

Analysis of variance was used to analyze the MTT assay results (p < 0.05) based on normality and homogeneity test (p > 0.05).

RESULTS

The highest viability of cells (97.08%) was found at a concentration of 10% by means of an MTT test (p < 0.05). The results of three-dimensional bovine teeth scaffold showed the average particle size to be 500 µm. ADMSCs cell attachment to the scaffold bovine teeth showed a significant increase in the number of cells attached after 24 hours compared with those at 1 and 12 hours. Alizarin red staining showed an increase in ADMSC osteogenic differentiation after it was combined with bovine teeth scaffold.

CONCLUSION

The scaffold from bovine teeth is biocompatible and accelerates osteogenic differentiation of ADMSC.

Side Population: Its Use in the Study of Cellular Heterogeneity and as a Potential Enrichment Tool for Rare Cell Populations

There is still much to learn about the cells used for cell- and gene-based therapies in the clinical setting. Stem cells are found in virtually all tissues in the human body. As a result, cells isolated from these tissues are a heterogeneous population consisting of various subpopulations including stem cells. Several strategies have been used to isolate and define the subpopulations that constitute these heterogeneous populations, one of which is the side population (SP) assay. SP cells are identified by their ability to efflux a fluorescent dye at a rate that is greater than the main cell population. This elevated rate of dye efflux has been attributed to the expression of members of the ATP-binding cassette (ABC) transporter protein family. SP cells have been identified in various tissues. In this review, we discuss the research to date on SP cells, focussing on SP cells identified in haematopoietic stem cells, adipose-derived stromal cells, and dental pulp.

When size matters: differences in demineralized bone matrix particles affect collagen structure, mesenchymal stem cell behavior, and osteogenic potential

Demineralized bone matrix (DBM) is a natural, collagen-based, osteoinductive biomaterial. Nevertheless, there are conflicting reports on the efficacy of this product. The purpose of this study was to evaluate whether DBM collagen structure is affected by particle size and can influence DBM cytocompatibility and osteoinductivity. Sheep cortical bone was ground and particles were divided in three fractions with different sizes, defined as large (L, 1-2 mm), medium (M, 0.5-1 mm), and small (S, <0.5 mm). After demineralization, the chemical-physical analysis clearly showed a particle size-dependent alteration in collagen structure, with DBM-M being altered but not as much as DBM-S. DBM-M displayed a preferable trend in almost all biological characteristics tested, although all DBM particles revealed an optimal cytocompatibility. Subcutaneous implantation of DBM particles into immunocompromised mice resulted in bone induction only for DBM-M. When sheep MSC were seeded onto particles before implantation, all DBM particles were able to induce new bone formation with the best incidence for DBM-M and DBM-S. In conclusion, the collagen alteration in DBM-M is likely the best condition to promote bone induction in vivo. Furthermore, the choice of 0.5-1 mm particles may enable to obtain more efficient and consistent results among different research groups in bone tissue-engineering applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1019-1033, 2017.

Periostin accelerates bone healing mediated by human mesenchymal stem cell-embedded hydroxyapatite/tricalcium phosphate scaffold

BACKGROUND

Periostin, an extracellular matrix protein, is expressed in bone, more specifically, the periosteum and periodontal ligaments, and plays a key role in formation and metabolism of bone tissues. Human adipose tissue-derived mesenchymal stem cells (hASCs) have been reported to differentiate into osteoblasts and stimulate bone repair. However, the role of periostin in hASC-mediated bone healing has not been clarified. In the current study, we examined the effect of periostin on bone healing capacity of hASCs in a critical size calvarial defect model.

METHODS AND RESULTS

Recombinant periostin protein stimulated migration, adhesion, and proliferation of hASCs in vitro. Implantation of either hASCs or periostin resulted in slight, but not significant, stimulation of bone healing, whereas co-implantation of hASCs together with periostin further potentiated bone healing. In addition, the number of Ki67-positive proliferating cells was significantly increased in calvarial defects by co-implantation of both hASCs and periostin. Consistently, proliferation of administered hASCs was stimulated by co-implantation with periostin in vivo. In addition, co-delivery of hASCs with periostin resulted in markedly increased numbers of CD31-positive endothelial cells and α-SMA-positive arterioles in calvarial defects.

CONCLUSIONS

These results suggest that recombinant periostin potentiates hASC-mediated bone healing by stimulating proliferation of transplanted hASCs and angiogenesis in calvarial defects.

Enhanced Bone-Forming Activity of Side Population Cells in the Periodontal Ligament

Regeneration of alveolar bone is critical for the successful treatment of periodontal diseases. The periodontal ligament (PDL) has been widely investigated as a source of cells for the regeneration of periodontal tissues. In the present study where we attempted to develop an effective strategy for alveolar bone regeneration, we examined the osteogenic potential of side population (SP) cells, a stem cell-containing population that has been shown to be highly abundant in several kinds of tissues, in PDL cells. Isolated SP cells from the rat PDL exhibited a superior ability to differentiate into osteoblastic cells compared with non-SP (NSP) and unsorted PDL cells in vitro. The mRNA expressions of osteoblast markers and bone morphogenetic protein (BMP) 2 were significantly upregulated in SP cells and were further increased by osteogenic induction. To examine the bone-forming activity of SP cells in vivo, PDL SP cells isolated from green fluorescent protein (GFP)-transgenic rats were transplanted with hydroxyapatite (HA) disks into wild-type animals. SP cells exhibited a high ability to induce the mineralized matrix compared with NSP and unsorted PDL cells. At 12 weeks after the implantation, some of the pores in the HA disks with SP cells were filled with mineralized matrices, which were positive for bone matrix proteins, such as osteopontin, bone sialoprotein, and osteocalcin. Furthermore, osteoblast- and osteocyte-like cells on and in the bone-like mineralized matrices were GFP positive, suggesting that the matrices were directly formed by the transplanted cells. These results suggest that PDL SP cells possess enhanced osteogenic potential and could be a potential source for cell-based regenerative therapy for alveolar bone.

Adipose-derived stromal cells for osteoarticular repair: trophic function versus stem cell activity

The identification of multipotent adipose-derived stromal cells (ASC) has raised hope that tissue regeneration approaches established with bone-marrow-derived stromal cells (BMSC) can be reproduced with a cell-type that is far more accessible in large quantities. Recent detailed comparisons, however, revealed subtle functional differences between ASC and BMSC, stressing the concept of a common mesenchymal progenitor existing in a perivascular niche across all tissues. Focussing on bone and cartilage repair, this review summarises recent in vitro and in vivo studies aiming towards tissue regeneration with ASC. Advantages of good accessibility, high yield and superior growth properties are counterbalanced by an inferiority of ASC to form ectopic bone and stimulate long-bone healing along with their less pronounced osteogenic and angiogenic gene expression signature. Hence, particular emphasis is placed on establishing whether stem cell activity of ASC is so far proven and relevant for successful osteochondral regeneration, or whether trophic activity may largely determine therapeutic outcome.

In vitro and in vivo angiogenic capacity of BM-MSCs/HUVECs and AT-MSCs/HUVECs cocultures

The aim of this study was to comparatively evaluate the angiogenic capacity of cocultures using either human bone marrow- or human adipose tissue-derived mesenchymal stem cells (MSCs) (BM- or AT-MSCs) with human umbilical vein endothelial cells (HUVECs) both in vitro and in vivo at early time points (i.e. days 3 and 7). In vitro, cells were either monocultured (i.e. BM-MSCs, AT-MSCs or HUVECs) or cocultured (i.e. BM-MSCs/HUVECs and AT-MSCs/HUVECs) on Thermanox® (2-dimensional, 2D) or in collagen gels (3-dimensional, 3D). For the in vivo experiment, cells (cocultures) were embedded in collagen gels and implanted subcutaneously in nude mice. For both in vitro and in vivo experiments, samples were collected on days 3 and 7 and histologically processed for hematoxylin-eosin and platelet endothelial cell adhesion molecule (PECAM-1; CD31) staining. For in vivo samples, quantitative parameters for evaluating angiogenesis included CD31-positive staining percentage, total vessel-like structure (VLS) area percentage, VLS density, and average VLS area (i.e. the size of per VLS). In vitro results showed the formation of VLS in both cocultures, while none of the monocultures showed VLS formation, irrespective of 2D or 3D culture condition. Although VLS formation occurred after in vivo implantation, no significant difference in angiogenic capacity was observed between the two cocultures, either on day 3 or on day 7. Further, VLS density decreased and anastomosis of the new human vessels with the murine host vasculature occurred over time. In conclusion, this study demonstrated that AT-MSCs/HUVECs and BM-MSCs/HUVECs have equal angiogenic capacity both in vitro and in vivo, and that vessels from donor origin can anastomose with the host vasculature within seven days of implantation.

The in vitro and in vivo effects of a low-molecular-weight fucoidan on the osteogenic capacity of human adipose-derived stromal cells

Human adipose-derived stromal cells (hASCs) may hold potential for bone tissue engineering. Osteogenic differentiation of these cells is crucial to bone formation. Low-molecular-weight fucoidan (LMWF) is a sulfated polysaccharide that potentiates several growth factors, including pro-angiogenic growth factors. To investigate whether hASC preconditioning with LMWF promoted bone repair, we compared the effects of LMWF and low-molecular-weight heparin on hASC phenotype and osteogenic differentiation. LMWF did not modify the stem-cell phenotype of hASCs but enhanced their osteogenic differentiation (formation of calcium deposits, increased activity and expression of alkaline phosphatase, and increased expression of osteopontin and runt-related transcription factor 2). However, when hASCs were exposed to LMWF before their adhesion to biphasic calcium phosphate particles and implantation in a bone-growth mouse model, no bone formation was apparent after 5 or 8 weeks, probably due to cell death. In conclusion, LMWF may hold promise for enhancing the osteogenic differentiation of hASCs before their implantation. However, concomitant vascularization would be required to enhance bone formation.

Polydopamine-assisted osteoinductive peptide immobilization of polymer scaffolds for enhanced bone regeneration by human adipose-derived stem cells

Immobilization of osteoinductive molecules, including growth factors or peptides, on polymer scaffolds is critical for improving stem cell-mediated bone tissue engineering. Such molecules provide osteogenesis-stimulating signals for stem cells. Typical methods used for polymeric scaffold modification (e.g., chemical conjugation or physical adsorption), however, have limitations (e.g., multistep, complicated procedures, material denaturation, batch-to-batch inconsistency, and inadequate conjugation) that diminish the overall efficiency of the process. Therefore, in this study, we report a biologically inspired strategy to prepare functional polymer scaffolds that efficiently regulate the osteogenic differentiation of human adipose-derived stem cells (hADSCs). Polymerization of dopamine (DA), a repeated motif observed in mussel adhesive protein, under alkaline pH conditions, allows for coating of a polydopamine (pDA) layer onto polymer scaffolds. Our study demonstrates that predeposition of a pDA layer facilitates highly efficient, simple immobilization of peptides derived from osteogenic growth factor (bone morphogenetic protein-2; BMP-2) on poly(lactic-co-glycolic acid) (PLGA) scaffolds via catechol chemistry. The BMP-2 peptide-immobilized PLGA scaffolds greatly enhanced in vitro osteogenic differentiation and calcium mineralization of hADSCs using either osteogenic medium or nonosteogenic medium. Furthermore, transplantation of hADSCs using pDA-BMP-2-PLGA scaffolds significantly promoted in vivo bone formation in critical-sized calvarial bone defects. Therefore, pDA-mediated catechol functionalization would be a simple and effective method for developing tissue engineering scaffolds exhibiting enhanced osteoinductivity. To the best of our knowledge, this is the first study demonstrating that pDA-mediated surface modification of polymer scaffolds potentiates the regenerative capacity of human stem cells for healing tissue defect in vivo.

Adipose tissue-derived mesenchymal stem cells as monocultures or cocultures with human umbilical vein endothelial cells: performance in vitro and in rat cranial defects

The aim of this study was to compare the osteogenic capacity between human adipose tissue-derived mesenchymal stem cells (AT-MSCs) and their cocultures with human umbilical vein endothelial cells (HUVECs) in vitro and their biological performance in vivo. First, the optimal cell ratio in cocultures for osteogenic differentiation was determined by seeding AT-MSCs and HUVECs in ratios varying from 100:0 to 0:100 on tissue culture plates. Afterward, AT-MSCs and AT-MSCs/HUVECs (50:50) were seeded on porous titanium fiber mesh scaffolds (Ti) for both in vitro and in vivo osteogenic evaluation. For in vitro evaluation, cell osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity and calcium assay. For in vivo evaluation, the scaffolds were implanted bilaterally into rat cranial defects (5 mm diameter) and bone formation was assessed histologically and histomorphometrically after 8 weeks. The ratio of 50:50 was chosen in the cocultures because this coculture condition retained similar amount of calcium deposition while using the least amount of AT-MSCs. Moreover, AT-MSCs showed higher osteogenic differentiation in comparison to AT-MSCs/HUVECs on Ti in vitro. Furthermore, superior bone formation was observed in AT-MSCs compared to AT-MSCs/HUVECs in rat cranial defects. In conclusion, AT-MSCs showed significantly higher osteogenic potential compared to AT-MSCs/HUVECs both in vitro and in vivo.

Autologous adipose stem cells and polylactide discs in the replacement of the rabbit temporomandibular joint disc

The temporomandibular joint (TMJ) disc lacks functional replacement after discectomy. We investigated tissue-engineered bilayer polylactide (PLA) discs and autologous adipose stem cells (ASCs) as a potential replacement for the TMJ disc. These ASC discs were pre-cultured either in control or in differentiation medium, including transforming growth factor (TGF)-β1 for one week. Prior to implantation, expression of fibrocartilaginous genes was measured by qRT-PCR. The control and differentiated ASC discs were implanted, respectively, in the right and left TMJs of rabbits for six (n = 5) and 12 months (n = 5). Thereafter, the excised TMJ areas were examined with cone beam computed tomography (CBCT) and histology. No signs of infection, inflammation or foreign body reactions were detected at histology, whereas chronic arthrosis and considerable condylar hypertrophy were observed in all operated joints at CBCT. The left condyle treated with the differentiated ASC discs appeared consistently smoother and more sclerotic than the right condyle. The ASC disc replacement resulted in dislocation and morphological changes in the rabbit TMJ. The ASC discs pre-treated with TGF-β1 enhanced the condylar integrity. While adverse tissue reactions were not shown, the authors suggest that with improved attachment and design, the PLA disc and biomaterial itself would hold potential for TMJ disc replacement.

Critical size bone defect reconstruction by an autologous 3D osteogenic-like tissue derived from differentiated adipose MSCs

For critical size bone defects and bone non-unions, bone tissue engineering using osteoblastic differentiated adipose mesenchymal stem cells (AMSCs) is limited by the need for a biomaterial to support cell transplantation. An osteoblastic three-dimensional autologous graft made of AMSCs (3D AMSC) was developed to solve this issue. This autograft was obtained by supplementing the osteoblastic differentiation medium with demineralized bone matrix. Two surgical models were developed to assess the potential of this 3D osteogenic AMSC autograft. A four-level spinal fusion using polyetheretherketone cages was designed in six pigs to assess the early phase of ossification (8-12 weeks postimplantation). In each pig, four groups were compared: cancellous bone autograft, freeze-dried irradiated cancellous pig bone, 3D AMSC, and an empty cage. A critical size femoral defect (n = 4, bone non-union confirmed 6 months postoperatively) was used to assess the 3D AMSCs' ability to achieve bone fusion. Pigs were followed by CT scan and explanted specimens were analyzed for bone tissue remodeling by micro-CT scan, micro-radiography, and histology/histomorphometry. In the spine fusion model, bone formation with the 3D AMSC was demonstrated by a significant increase in bone content. In the critical-size femoral defect model, the 3D AMSC achieved new bone formation and fusion in a poorly vascularized fibrotic environment. This custom-made 3D osteogenic AMSC autograft is a therapeutic solution for bone non-unions and for critical-size defects.

Multipotent adult progenitor cell-loaded demineralized bone matrix for bone tissue engineering

Multipotent adult progenitor cells (MAPCs) from bone marrow have been shown to be capable of forming bone, cartilage and other connective tissues. In addition, MAPCs differentiate into lineages that are different from their germ layers of origin. Previous studies showed the ability of MAPCs to improve cardiac function and control allogenic-reactive responses associated with acute graft versus host disease. In the current study, we evaluated the ability of MAPCs to produce bone matrix on demineralized bone allograft substrates. Specifically, MAPCs expressed alkaline phosphatase, produced extracellular matrix proteins and deposited calcium-containing mineral on demineralized bone matrices. Furthermore, the addition of MAPCs on demineralized bone matrix (DBM) scaffolds enhanced osteoinductivity of the carrier in a rat ectopic pouch model. These results demonstrated the potential of MAPCs as a new approach for bone repair in tissue-engineering applications.

Leveraging "raw materials" as building blocks and bioactive signals in regenerative medicine

Components found within the extracellular matrix (ECM) have emerged as an essential subset of biomaterials for tissue engineering scaffolds. Collagen, glycosaminoglycans, bioceramics, and ECM-based matrices are the main categories of "raw materials" used in a wide variety of tissue engineering strategies. The advantages of raw materials include their inherent ability to create a microenvironment that contains physical, chemical, and mechanical cues similar to native tissue, which prove unmatched by synthetic biomaterials alone. Moreover, these raw materials provide a head start in the regeneration of tissues by providing building blocks to be bioresorbed and incorporated into the tissue as opposed to being biodegraded into waste products and removed. This article reviews the strategies and applications of employing raw materials as components of tissue engineering constructs. Utilizing raw materials holds the potential to provide both a scaffold and a signal, perhaps even without the addition of exogenous growth factors or cytokines. Raw materials contain endogenous proteins that may also help to improve the translational success of tissue engineering solutions to progress from laboratory bench to clinical therapies. Traditionally, the tissue engineering triad has included cells, signals, and materials. Whether raw materials represent their own new paradigm or are categorized as a bridge between signals and materials, it is clear that they have emerged as a leading strategy in regenerative medicine. The common use of raw materials in commercial products as well as their growing presence in the research community speak to their potential. However, there has heretofore not been a coordinated or organized effort to classify these approaches, and as such we recommend that the use of raw materials be introduced into the collective consciousness of our field as a recognized classification of regenerative medicine strategies.

Demineralized bone matrix as a vehicle for delivering endogenous and exogenous therapeutics in bone repair

As a unique human bone extract approved for implant use, demineralized bone matrix (DBM) retains substantial amounts of endogenous osteoconductive and osteoinductive proteins. Commercial preparations of DBM represent a clinically accessible, familiar, widely used and degradable bone-filling device, available in composite solid, strip/piece, and semi-solid paste forms. Surgically placed and/or injected, DBM releases its constituent compounds to bone sites with some evidence for inducing new bone formation and accelerating healing. Significantly, DBM also has preclinical history as a drug carrier by direct loading and delivery of several important classes of therapeutics. Exogenous bioactive agents, including small molecule drugs, protein and peptide drugs, nucleic acid drugs and transgenes and therapeutic cells have been formulated within DBM and released to bone sites to enhance DBM's intrinsic biological activity. Local release of these agents from DBM directly to surgical sites in bone provides improved control of dosing and targeting of both endogenous and exogenous bioactivity in the context of bone healing using a clinically familiar product. Given DBM's long clinical track record and commercial accessibility in standard forms and sources, opportunities to formulate DBM as a versatile matrix to deliver therapeutic agents locally to bone sites in orthopedic repair and regenerative medicine contexts are attractive.

Adipose-derived stem cells combined with a demineralized cancellous bone substrate for bone regeneration

Mesenchymal stem cells (MSCs) isolated from cadaveric adipose tissue can be obtained in large quantities, and have been reported in the literature to be capable of inducing bone formation in vivo and ex vivo.( 1-6 ) The hypothesis tested whether a demineralized cancellous bone matrix (DCBM) can provide an effective substrate for selection and retention of stem cells derived from the stromal vascular fraction (SVF) of adipose. Human cadaveric adipose tissue was recovered from a donor and digested. The resulting SVF-containing MSCs were seeded onto the demineralized bone allografts, after which the nonadherent cells were washed off. The MSCs were characterized using a flow cytometer and tri-lineage differentiation (osteogenesis, chondrogenesis, and adipogenesis) in vitro. The stem cell-seeded allografts were also characterized for cell number, adherence to the DCBM, osteogenic activity (alkaline phosphatase and Alizarin Red staining), and bone morphorgenic protein (BMP) quantity. Flow cytometry identified a mean total of 7.2% MSCs in SVF and 87.2% MSCs after culture. The stem cells showed the capability of differentiating into bone, cartilage, and fat. On the 21 stem cell-seeded bone allografts, there were consistent, attached, viable cells (100,744±22,762 cells/cube). An assessment of donor age, gender, and body mass index revealed no significant differences in cell numbers. Enzyme-linked immunosorbent assay revealed the presence of BMP-2 and BMP-7. In conclusion, this bone graft contains three key elements for bone regeneration: adhered osteogenic stem cells, 3D osteoconductive bone scaffold, and osteoinductive BMP signal. It therefore has the potential to be effective for bone regeneration.

Restoration of critical-size defects in the rabbit mandible using porous nanohydroxyapatite-polyamide scaffolds

Composite nanohydroxyapatite/polyamide (n-HA/PA) biomaterials have been indicated for bone defect reconstruction, where PA is added to enhance the toughness of n-HA. However, a comprehensive understanding of the biological performance of this implant material remains to be determined. In this study, the biological activity of n-HA/PA biomaterials was characterized in vitro by assessing the growth of bone marrow stromal cells (BMSCs), and in an in vivo rabbit model. To evaluate the n-HA/PA performance under different osteogenic conditions in vivo, implants were inserted to critical-size bone defects in the angle and body of the rabbit mandible. To determine the necessity of ectogenic BMSC-n-HA/PA hybrids at different implantation sites, both raw n-HA/PA materials and BMSC-seeded n-HA/PA hybrids were implanted. Bone formation was detected by radiology and histological studies. The results showed that n-HA/PA composites had great bioactivity, demonstrating significant BMSC proliferation, active alkaline phosphatase secretion, and stimulating the expression of osteogenic proteins (bone morphogenetic protein 2 [BMP2], osteoprotegerin [OPG], osteopontin [OPN], collagen type I [Col I], and osteocalcin [OCN]), in comparison to the control (polyethylene). At marrow-rich implantation sites (mandibular body), the amount of new bone formation was significant, but was not enhanced by the presence of BMSCs in the BMSC-n-HA/PA hybrids. However, the BMSC-n-HA/PA hybrids were essential for promoting bone formation in marrow-poor sites (mandibular angle). In conclusion, n-HA/PA biomaterials, which offer the advantage of enhanced mechanical performance over n-HA, exhibit significant bioactivity, including the capacity for bone regeneration at marrow-poor sites when implanted in combination with BMSCs.

Stem cells, mature adipocytes, and extracellular scaffold: what does each contribute to fat graft survival?

BACKGROUND

Soft tissue engineering offers new perspectives for improving fat graft survival, for which the appropriate association of cells and scaffold seems essential. This study aimed to analyze the survival of free-cell grafts compared with adipose-derived stem cells (ASCs) seeded on collagen scaffolds.

METHODS

Adipose tissue from a single volunteer was used for the following preparations: purified adipose tissue, isolated mature adipocytes (free-cell graft), cultured ASCs without scaffold (free-cell graft), collagen scaffold only, cultured ASCs in collagen scaffold without and with bioactive factors, and freshly-isolated ASCs in collagen scaffold. These were grafted on 18 nude mice for 2 months, after which specimens were evaluated grossly and histologically using hematoxylin-phloxine-safran (HPS), Oil-Red-O, and antivimentin labeling. Specimens and animals were weighed before implantation and after explantation, and weight values were statistically analyzed.

RESULTS

Free-cell grafts (mature adipocytes and free ASCs) showed complete resorption in 50 and 60% of the animals (remaining weight fraction was 22.5 and 5.3%, respectively). The survival of purified adipose tissue was 81.8% (statistically greater compared with free-cell grafts; p < 0.05). In the ASCs-scaffold association, the remaining weight fractions (87.3-70.4%) were statistically greater than in free-cell grafts (5.3-22.5%; p < 0.05), but the difference between ASC-scaffolds and fat grafts was not statistically significant. These results were confirmed by clinical and histologic observations.

CONCLUSION

Three-dimensional collagen scaffolds seem to improve survival of ASCs compared with free-cell grafts (adipocytes and free ASCs).