Induction of Ectopic Bone Formation by Using Human Periosteal Cells in Combination with a Novel Scaffold Technology

Construction of developmentally inspired periosteum-like tissue for bone regeneration

The periosteum, a highly vascularized thin tissue, has excellent osteogenic and bone regenerative abilities. The generation of periosteum-mimicking tissue has become a novel strategy for bone defect repair and regeneration, especially in critical-sized bone defects caused by trauma and bone tumor resection. Here, we utilized a bone morphogenetic protein-2 (BMP-2)-loaded scaffold to create periosteum-like tissue (PT) in vivo, mimicking the mesenchymal condensation during native long bone development. We found that BMP-2-induced endochondral ossification plays an indispensable role in the construction of PTs. Moreover, we confirmed that BMP-2-induced PTs exhibit a similar architecture to the periosteum and harbor abundant functional periosteum-like tissue-derived cells (PTDCs), blood vessels, and osteochondral progenitor cells. Interestingly, we found that the addition of chondroitin sulfate (CS), an essential component of the extracellular matrix (ECM), could further increase the abundance and enhance the function of recruited PTDCs from the PTs and finally increase the regenerative capacity of the PTs in autologous transplantation assays, even in old mice. This novel biomimetic strategy for generating PT through in vivo endochondral ossification deserves further clinical translation.

Repair of rat cranial bone defect by using amniotic fluid-derived mesenchymal stem cells in polycaprolactone fibrous scaffolds and platelet-rich plasma

Introduction: Tissue regenerative medicine strategies, as a promising alternative has become of major interest to the reconstruction of critical size bone defects. This study evaluated the effects of the simultaneous application of polycaprolactone (PCL), amniotic fluid mesenchymal stem cells (AF-MSCs) and platelet-rich plasma (PRP) on the repair of rat cranial bone defects. Methods: The AF-MSCs were isolated at the end of the second week of pregnancy in rats. PRP obtained from rat blood and the random PCL fibrous scaffolds were prepared using the electrospinning method. Circular full thickness (5 mm) bone defects were developed on both sides of the parietal bones (animal number=24) and the scaffolds containing AF-MSCs and PRP were implanted in the right lesions. Thereafter, after eight weeks the histological and immunohistochemistry studies were performed to evaluate the bone formation and collagen type I expression. Results: The spindle-shaped mesenchymal stem cells were isolated and the electron microscope images indicated the preparation of a random PCL scaffold. Immunohistochemical findings showed that collagen type I was expressed by AF-MSCs cultured on the scaffold. The results of hematoxylin and eosin (H&E) staining indicated the formation of blood vessels in the presence of PRP. Additionally, immunofluorescence findings suggested that PRP had a positive effect on collagen type I expression. Conclusion: The simultaneous application of fibrous scaffold + AF-MSCs + PRP has positive effects on bone regeneration. This study showed that PRP can affect the formation of new blood vessels in the scaffold transplanted in the bone defect.

Effect of expanded bone marrow-derived osteoprogenitor cells seeded into polycaprolactone/tricalcium phosphate scaffolds in new bone regeneration of rabbit mandibular defects

The purpose of this study was to assess and evaluate new bone formation in rabbit marginal mandibular defects using expanded bone marrow-derived osteoprogenitor cells seeded in three-dimensional scaffolds of polycaprolactone/tricalcium phosphate (PCL/TCP). Bone marrow was harvested from the rabbit ilium and rabbit bone marrow-derived osteoprogenitor cells were isolated and expanded in standard culture medium and osteogenic medium supplement. The cells were then seeded into the PCL/TCP scaffolds and the cell/scaffold constructions were implanted into prepared defects in rabbit mandibles. PCL/TCP scaffold alone and autogenous bone graft from the mandible were also implanted into the other prepared defects. The specimens were evaluated at 4 and 8 weeks after the implantation using clinical, radiographic, and histological techniques. The results of the experimental group demonstrated more newly formed bone on the surface and in the pores of the PCL/TCP scaffolds. In addition, the osteoblasts, osteocytes, and new bone trabeculae were identified throughout the defects that were implanted with the cell/scaffold constructions. The PCL/TCP alone group was filled mostly with fibrous cells particularly in the middle region with less bone formation. These results would suggest that the derived osteotoprogenitor cells have the potential to form bone tissue when seeded onto PCL/TCP scaffolds.

Osteogenic potential of murine periosteum for critical-size cranial defects

Tissue engineering of bone has combined bespoke scaffolds and osteoinductive factors to maintain functional osteoprogenitor cells, and the periosteum has been confirmed as a satisfactory source of osteoblasts. Suitable matrices have been identified that support cell proliferation and differentiation, including demineralised bone matrix (both compatible and osteoinductive) and acellular human dermis. We have evaluated the osteogenic potential of an osteogenic unit, developed by combining periosteum, demineralised bone matrix, and acellular human dermis, in rodents with critical-size cranial defects. Briefly, remnants from the superior maxillary periosteum were used to harvest cells, which were characterised by flow cytometry and reverse retrotranscriptase-polymerase chain reaction (RT-PCR). Cells were cultured into the osteogenic unit and assessed for viability before being implanted into 3 rodents, These were compared with the control group (n=3) after three months. Histological analyses were made after staining with haematoxylin and eosin and Von Kossa, and immunostaining, and confirmed viable cells that stained for CD90, CD73, CD166, runt-related transcription factor, osteopontin, and collagen type I in the experimental group, while in the control group there was only connective tissue on the edges of the bone in the injury zone. We conclude that osteogenic unit constructs have the osteogenic and regenerative potential for use in engineering bone tissue.

Bone Tissue Engineering: Past-Present-Future

Bone is one of the few tissues to display a true potential for regeneration. Fracture healing is an obvious example where regeneration occurs through tightly regulated sequences of molecular and cellular events which recapitulate tissue formation seen during embryogenesis. Still in some instances, bone regeneration does not occur properly (i.e. critical size lesions) and an appropriate therapeutic intervention is necessary. Successful replacement of bone by tissue engineering will likely depend on the recapitulation of this flow of events. In fact, bone regeneration requires cross-talk between microenvironmental factors and cells; for example, resident mesenchymal progenitors are recruited and properly guided by soluble and insoluble signaling molecules. Tissue engineering attempts to reproduce and to mimic this natural milieu by delivering cells capable of differentiating into osteoblasts, inducing growth factors and biomaterials to support cellular attachment, proliferation, migration, and matrix deposition. In the last two decades, a significant effort has been made by the scientific community in the development of methods and protocols to repair and regenerate tissues such as bone, cartilage, tendons, and ligaments. In this same period, great advancements have been achieved in the biology of stem cells and on the mechanisms governing "stemness". Unfortunately, after two decades, effective clinical translation does not exist, besides a few limited examples. Many years have passed since cell-based regenerative therapies were first described as "promising approaches", but this definition still engulfs the present literature. Failure to envisage translational cell therapy applications in routine medical practice evidences the existence of unresolved scientific and technical struggles, some of which still puzzle researchers in the field and are presented in this chapter.

Solvent-free Fabrication of Tissue Engineering Scaffolds with Immiscible Polymer Blends

A completely organic solvent-free fabrication method is developed for tissue engineering scaffolds by gas foaming of immiscible polylactic acid (PLA) and sucrose blends, followed by water leaching. PLA scaffolds with above 90% porosity and 25-200 μm pore size were fabricated. The pore size and porosity was controlled with process parameters including extrusion temperature and foaming process parameters. Dynamic mechanical analysis showed that the extrusion temperature could be used to control the scaffold strength. Both unfoamed and foamed scaffolds were used to culture glioblastoma (GBM) cells M059K. The results showed that the cells grew better in the foamed PLA scaffolds. The method presented in the paper is versatile and can be used to fabricate tissue engineering scaffolds without any residual organic solvents.

Bone Tissue Engineering with Adipose-Derived Stem Cells in Bioactive Composites of Laser-Sintered Porous Polycaprolactone Scaffolds and Platelet-Rich Plasma

Three-dimensional porous polycaprolactone (PCL) scaffolds with consistent inter-pore channels, 83% porosity and 300–400 μm pore size were fabricated via selective laser sintering. The PCL scaffold was combined with platelet-rich plasma (PRP) to form a bioactive composite and studied for potential application in bone tissue engineering using porcine adipose-derived stem cells (PASCs). The PCL/PRP/PASCs construct showed enhanced cell seeding efficiency and synergistically increased the differentiation capability of PASCs in osteogenic medium toward the osteoblast lineage, judging from elevated alkaline phosphatase activity and up-regulated osteogenic genes expression. For in vivo study, a 3 cm × 3 cm mandible defect was created in pigs and reconstructed by implanting acellular PCL scaffolds or PCL/PRP/PASCs constructs. Both groups showed new bone formation, however, the new bone volume was 5.1 times higher for PCL/PRP/PASCs 6 months post-operation. The bone density was less and loose in the acellular PCL group and the Young’s modulus was only 29% of normal bone. In contrast, continued and compact bone formation was found in PCL/PRP/PASCs and the Young’s modulus was 81% that of normal bone. Masson’s trichrome stain, immunohistochemical analysis of osteocalcin and collagen type I also confirmed new bone formation.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.

How smart do biomaterials need to be? A translational science and clinical point of view

Over the last 4 decades innovations in biomaterials and medical technology have had a sustainable impact on the development of biopolymers, titanium/stainless steel and ceramics utilized in medical devices and implants. This progress was primarily driven by issues of biocompatibility and demands for enhanced mechanical performance of permanent and non-permanent implants as well as medical devices and artificial organs. In the 21st century, the biomaterials community aims to develop advanced medical devices and implants, to establish techniques to meet these requirements, and to facilitate the treatment of older as well as younger patient cohorts. The major advances in the last 10 years from a cellular and molecular knowledge point of view provided the scientific foundation for the development of third-generation biomaterials. With the introduction of new concepts in molecular biology in the 2000s and specifically advances in genomics and proteomics, a differentiated understanding of biocompatibility slowly evolved. These cell biological discoveries significantly affected the way of biomaterials design and use. At the same time both clinical demands and patient expectations continued to grow. Therefore, the development of cutting-edge treatment strategies that alleviate or at least delay the need of implants could open up new vistas. This represents the main challenge for the biomaterials community in the 21st century. As a result, the present decade has seen the emergence of the fourth generation of biomaterials, the so-called smart or biomimetic materials. A key challenge in designing smart biomaterials is to capture the degree of complexity needed to mimic the extracellular matrix (ECM) of natural tissue. We are still a long way from recreating the molecular architecture of the ECM one to one and the dynamic mechanisms by which information is revealed in the ECM proteins in response to challenges within the host environment. This special issue on smart biomaterials lists a large number of excellent review articles which core is to present and discuss the basic sciences on the topic of smart biomaterials. On the other hand, the purpose of our review is to assess state of the art and future perspectives of the so called "smart biomaterials" from a translational science and specifically clinical point of view. Our aim is to filter out and discuss which biomedical advances and innovations help us to achieve the objective to translate smart biomaterials from bench to bedside. The authors predict that analyzing the field of smart biomaterials from a clinical point of view, looking back 50 years from now, it will show that this is our heritage in the 21st century.

The effect of PCL-TCP scaffold loaded with mesenchymal stem cells on vertical bone augmentation in dog mandible: a preliminary report

Polycaprolactone-tricalcium phosphate (PCL-TCP), a new composite scaffold, has been shown to facilitate early revascularization and speed up bone regeneration process. The objective of this study was to evaluate the effect of PCL-TCP seeded with mesenchymal stem cells (MSCs) on healing of the vertical bone critical sized defect in dog's mandible. Bone marrow aspirate from dog humerous was cultured and the stemness of the cells was examined by differentiation staining methods and flow cytometric analysis. Third passage subculture cells (5 × 10⁵ cells) were loaded on 20 × 10 × 10 mm³ and incubated for 48 h. The presence of MSCs in the pores was evaluated by scanning electron microscope. Bilateral mandibular premolar teeth were extracted in four dogs and the buccal and lingual bone plates were reduced to make a vertical defect. Cell-loaded scaffolds were fixed in right side and left side received pure PCL-TCP scaffolds as a control side defects. Histomorphometric analysis after 8 weeks of the scaffold implantation showed higher amount of lamellar bone in the test side (48.63%) than control side (17.27%) (p < 0.05).The results suggest that PCL-TCP may be an appropriate scaffold for loading MSCs in bone regeneration.

A tissue engineering solution for segmental defect regeneration in load-bearing long bones

The reconstruction of large defects (>10 mm) in humans usually relies on bone graft transplantation. Limiting factors include availability of graft material, comorbidity, and insufficient integration into the damaged bone. We compare the gold standard autograft with biodegradable composite scaffolds consisting of medical-grade polycaprolactone and tricalcium phosphate combined with autologous bone marrow-derived mesenchymal stem cells (MSCs) or recombinant human bone morphogenetic protein 7 (rhBMP-7). Critical-sized defects in sheep--a model closely resembling human bone formation and structure--were treated with autograft, rhBMP-7, or MSCs. Bridging was observed within 3 months for both the autograft and the rhBMP-7 treatment. After 12 months, biomechanical analysis and microcomputed tomography imaging showed significantly greater bone formation and superior strength for the biomaterial scaffolds loaded with rhBMP-7 compared to the autograft. Axial bone distribution was greater at the interfaces. With rhBMP-7, at 3 months, the radial bone distribution within the scaffolds was homogeneous. At 12 months, however, significantly more bone was found in the scaffold architecture, indicating bone remodeling. Scaffolds alone or with MSC inclusion did not induce levels of bone formation comparable to those of the autograft and rhBMP-7 groups. Applied clinically, this approach using rhBMP-7 could overcome autograft-associated limitations.

The potential of human fetal mesenchymal stem cells for off-the-shelf bone tissue engineering application

Mesenchymal stem cells (MSCs) have become one of the most promising cell sources for bone tissue engineering (BTE) applications. In this review, we first highlight recent progress in the understanding of MSC biology, their in vivo niche, multi-faceted contribution to fracture healing and bone re-modelling, and their role in BTE. A literature review from clinicaltrials.gov and Pubmed on clinical usage of MSC for both orthopedic and non-orthopedic indications suggests that translational use of MSC for BTE indications is likely to bear fruit in the ensuing decade. Last, we disscuss the profound influence of ontological and antomical origins of MSC on their proliferation and osteogenesis and demonstrated human fetal MSC (hfMSC) as a superior cellular candidate for off-the-shelf BTE applications. This relates to their superior proliferation capacity, more robust osteogenic potential and lower immunogenecity, as compared to MSC from perinatal and postnatal sources. Furthermore, we discuss our experience in developing a hfMSC based BTE strategy with the integrated use of bioreactor-based dynamic priming within macroporous scaffolds, now ready for evaluation in clinical trials. In conclusion, hfMSC is likely the most promising cell source for allogeneic based BTE application, with proven advantages compared to other MSC based ones.

Fabrication of tissue engineering scaffolds through solid-state foaming of immiscible polymer blends

In scaffold-based tissue engineering, the fabrication process is important for producing suitable microstructures for seeded cells to grow and reformulate. In this paper, we present a new approach to scaffold fabrication by combining the solid-state foaming and the immiscible polymer-blending method. The proposed approach has the advantage of being versatile and able to create a wide range of pore size and porosity. The proposed method is studied with polylactic acid (PLA) and polystyrene (PS) blends. The interconnected porous structure was created by first foaming the PLA/PS blend and then extracting the PS phase. The solid-state foaming experiments were conducted under various conditions to achieve the desired pore sizes. It is shown that the PS phase of the PLA/PS blend can be extracted much faster in the foamed samples and the pore size of the scaffolds can be easily controlled with proper gas foaming parameters. The average pore size achieved in the foaming process ranged from 20 to 70 µm. After PS extraction, both pore size and porosity can be further improved. For example, the pore size and porosity increased from 48 µm and 49% to 59 µm and 67%, respectively, after the PS extraction process. The fabricated porous scaffolds were used to culture human osteoblast cells. Cells grew well and gradually formed a fibrous structure. The combined solid-state foaming and immiscible polymer blending method provides a new technique for fabricating tissue-engineering scaffolds.

Scaffolds based bone tissue engineering: the role of chitosan

As life expectancy increases, malfunction or loss of tissue caused by injury or disease leads to reduced quality of life in many patients at significant socioeconomic cost. Even though major progress has been made in the field of bone tissue engineering, present therapies, such as bone grafts, still have limitations. Current research on biodegradable polymers is emerging, combining these structures with osteogenic cells, as an alternative to autologous bone grafts. Different types of biodegradable materials have been proposed for the preparation of three-dimensional porous scaffolds for bone tissue engineering. Among them, natural polymers are one of the most attractive options, mainly due to their similarities with extracellular matrix, chemical versatility, good biological performance, and inherent cellular interactions. In this review, special attention is given to chitosan as a biomaterial for bone tissue engineering applications. An extensive literature survey was performed on the preparation of chitosan scaffolds and their in vitro biological performance as well as their potential to facilitate in vivo bone regeneration. The present review also aims to offer the reader a general overview of all components needed to engineer new bone tissue. It gives a brief background on bone biology, followed by an explanation of all components in bone tissue engineering, as well as describing different tissue engineering strategies. Moreover, also discussed are the typical models used to evaluate in vitro functionality of a tissue-engineered construct and in vivo models to assess the potential to regenerate bone tissue are discussed.

Dimensional change of the healed periosteum on surgically created defects

PURPOSE

The final goal of regenerative periodontal therapy is to restore the structure and function of the periodontium destroyed or lost due to periodontitis. However, the role of periosteum in periodontal regeneration was relatively neglected while bone repair in the skeleton occurs as a result of a significant contribution from the periosteum. The aim of this study is to understand the histological characteristics of periosteum and compare the native periosteum with the repaired periosteum after elevating flap or after surgical intervention with flap elevation.

METHODS

Buccal and lingual mucoperiosteal flaps were reflected to surgically create critical-size, "box-type" (4 mm width, 5 mm depth), one-wall, intrabony defects at the distal aspect of the 2nd and the mesial aspect of the 4th mandibular premolars in the right and left jaw quadrants. Animals were sacrificed after 24 weeks.

RESULTS

THE RESULTS FROM THIS STUDY ARE AS FOLLOWS: 1) thickness of periosteum showed difference as follows (P<0.05): control group (0.45±0.22 mm)>flap-elevation group (0.36±0.07 mm)>defect formation group (0.26±0.03 mm), 2) thickness of gingival tissue showed difference as follows (P<0.05): defect formation group (3.15±0.40 mm)>flap-elevation group (2.02±0.25 mm)>control group (1.88±0.27 mm), 3) higher cellular activity was observed in defect formation group and flap-elevation groups than control group, 4) the number of blood vessles was higher in defect formation group than control group.

CONCLUSIONS

In conclusion, prolonged operation with increased surgical trauma seems to decrease the thickness of repaired periosteum and increase the thickness of gingiva. More blood vessles and high cellular activity were observed in defect formation group.

High tibial osteotomy using polycaprolactone-tricalcium phosphate polymer wedge in a micro pig model

Medial open-wedge high tibial osteotomy has been gaining popularity in recent years, but adequate supporting material is required in the osteotomy gap for early weight-bearing and rapid union. The purpose of this study was to investigate whether the implantation of a polycaprolactone-tricalcium phosphate composite scaffold wedge would enhance healing of the osteotomy in a micro pig model. We carried out open-wedge high tibial osteotomies in 12 micro pigs aged from 12 to 16 months. A scaffold wedge was inserted into six of the osteotomies while the other six were left open. Bone healing was evaluated after three and six months using plain radiographs, CT scans, measurement of the bone mineral density and histological examination.

Complete bone union was obtained at six months in both groups. There was no collapse at the osteotomy site, loss of correction or failure of fixation in either group. Staining with haematoxylin and eosin demonstrated that there was infiltration of new bone tissue into the macropores and along the periphery of the implanted scaffold in the scaffold group. The CT scans and measurement of the bone mineral density showed that at six months specimens in the scaffold group had a higher bone mineral density than in the control group, although the implantation of the polycaprolactone-tricalcium phosphate composite scaffold wedge did not enhance healing of the osteotomy.

The evaluation of a biphasic osteochondral implant coupled with an electrospun membrane in a large animal model

Conventional clinical therapies are unable to resolve osteochondral defects adequately; hence, tissue engineering solutions are sought to address the challenge. A biphasic implant that was seeded with mesenchymal stem cells (MSCs) and coupled with an electrospun membrane was evaluated as an alternative. This dual phase construct comprised of a polycaprolactone (PCL) cartilage scaffold and a PCL-tricalcium phosphate osseous matrix. Autologous MSCs were seeded into the entire implant via fibrin and the construct was inserted into critically sized osteochondral defects located at the medial condyle and patellar groove of pigs. The defect was resurfaced with a PCL-collagen electrospun mesh, which served as a substitute for periosteal flap in preventing cell leakage. Controls without either implanted MSCs or resurfacing membrane were included. After 6 months, cartilaginous repair was observed with a low occurrence of fibrocartilage at the medial condyle. Osteochondral repair was promoted and host cartilage degeneration was arrested as shown by superior glycosaminoglycan maintenance. This positive morphological outcome was supported by a higher relative Young's modulus, which indicated functional cartilage restoration. Bone ingrowth and remodeling occurred in all groups, with a higher degree of mineralization in the experimental group. Tissue repair was compromised in the absence of the implanted cells or the resurfacing membrane. Moreover, healing was inferior at the patellar groove when compared with the medial condyle and this was attributed to the native biomechanical features.

Evaluation of the osteogenic potential and vascularization of 3D poly(3)hydroxybutyrate scaffolds subcutaneously implanted in nude rats

The aim of this study was to evaluate the osteogenic potential and the vascularization of embroidered, tissue engineered, and cell-seeded 3D poly(3)hydroxybutyrate (PHB) scaffolds in nude rats. Collagen I (coll I)- and collagen I/chondroitin sulfate (coll I/CS)-coated PHB scaffolds were seeded with human mesenchymal stem cells (hMSCs). Proliferation and differentiation were characterized by different biochemical assays in vitro. For animal experiments, the cells were cultivated on coll I- or coll I/CS-coated scaffolds and either expanded or osteogenically differentiated. Scaffolds were piled up to create a 3D scaffold pad and implanted subcutaneously into nude rats. In vitro hMSC showed proliferation and differentiation on PHB scaffolds. Alkaline phosphatase (ALP) and calcium increased in the differentiation medium and in the presence of coll I/CS. In vivo blood vessels were found in the scaffold-stack. Histological/immunohistological analyses of explanted scaffolds showed osteogenic markers such as osteopontin, osteonectin, and coll I around the PHB fibers. Coll I/CS-coated scaffolds with expanded hMSC showed higher values of ALP and calcium than the other combinations. Embroidered PHB scaffolds, coated with extracellular matrix components, provided an adequate environment and, therefore, a template for hMSC which could be differentiated in osteogenic direction.

Progenitor and stem cells for bone and cartilage regeneration

Research in regenerative medicine is developing at a significantly quick pace. Cell-based bone and cartilage replacement is an evolving therapy aiming at the treatment of patients who suffer from limb amputation, damaged tissues and various bone and cartilage-related disorders. Stem cells are undifferentiated cells with the capability to regenerate into one or more committed cell lineages. Stem cells isolated from multiple sources have been finding widespread use to advance the field of tissue repair. The present review gives a comprehensive overview of the developments in stem cells originating from different tissues and suggests future prospects for functional bone and cartilage tissue regeneration.

In vivo bone formation in silk fibroin and chitosan blend scaffolds via ectopically grafted periosteum as a cell source: a pilot study

Reconstruction of a critical size bone defect in the head and neck after trauma or tumor resection remains challenging. While certain defects, such as isolated orbital floor fractures, may be reconstructed with alloplastic biomaterials, larger defects or those involving load bearing bones usually require autologous tissue reconstruction. Vascularized bone free flaps remain the gold standard for large bone defects of the head and neck. These are generally lengthy, complicated, multi-step procedures that require subspecialty expertise to assure optimal outcomes.1 Invariably any procedure where autologous bone is harvested carries with it donor site morbidity.2 To spare the patient this additional morbidity and avoid potential complications associated with the harvest of this tissue, an alternative source for bone that would be sufficient to fill a critical-sized defect is needed.

Quantitative screening of engineered implants in a long bone defect model in rabbits

We have standardized a long bone defect model in rabbits to quantitatively compare the bone healing performance of engineered biological implants and have tested the bone healing efficiency of porous cylindrical scaffolds (ø-h, 6-20 mm [diameter 6 mm, height 20 mm] porosity, 70%) that were produced from hydroxyapatite (HA), titanium (Ti), and a novel biodegradable polymer-bioceramic composite (PH70alphaTCP). Scaffolds were perfused with or without 20 x 10(6) rabbit periosteal cells (RPCs) in a bioreactor and implanted in a standardized 2 cm defect in rabbit tibiae. X-rays revealed that new bone had formed at 3 weeks after creation of the defects. At sacrifice after 10 weeks, bone corticalization was observed in the majority of animals. Although PH70alphaTCP scaffolds did not inhibit callus formation, histomorphometric analysis revealed that there was no bone within the biomaterial, in contrast to HA and Ti scaffolds (bone volume ranging from 10% to 25%). We found that Ti and HA scaffold had good osteoconductive properties, but only HA scaffolds seeded with RPCs contributed to long bone mechanical functionality, with the maximum energy and angle being 308% and 155% greater than in control defects without scaffold.

Adhesion, proliferation, and osteogenic differentiation of a mouse mesenchymal stem cell line (BMC9) seeded on novel melt-based chitosan/polyester 3D porous scaffolds

The aim of the present work was to study the biological behavior of a mouse mesenchymal stem cell line when seeded and cultured under osteogenic conditions onto novel processed melt-based chitosan scaffolds. Scaffolds were produced by compression molding, followed by salt leaching. Scanning electron microscopy (SEM) observations and microCT analysis showed the pore sizes ranging between 250 and 500 microm and the interconnectivity of the porous structure. The chitosan-poly(butylenes succinate) scaffolds presented high mechanical properties, similar to the ones of trabecular bone (E1% approximately 75 MPa). Cytotoxicity assays were carried out using standard tests (accordingly to ISO/EN 10993 part 5 guidelines), namely, MTS test with a 24 h extraction period, revealing that L929 cells had similar metabolic activities to that obtained for the negative control. Cell culture studies were conducted using a mouse mesenchymal stem cell line (BMC9). Cells were seeded onto the scaffold and allowed to proliferate for 3 weeks under osteogenic conditions. SEM observations demonstrated that cells were able to proliferate and massively colonize the scaffolds structure. The cell viability assay MTS demonstrated that BMC9 cells were viable after 3 weeks of culture. The cells clearly evidenced a positive differentiation toward the osteogenic lineage, as confirmed by the high ALP activity levels. Moreover, energy dispersive spectroscopy (EDS) analysis revealed the presence of Ca and P in the elaborated extracellular matrix (ECM). These combined results indicate that the novel melt-based chitosan/polyester scaffolds support the adhesion, proliferation, and osteogenic differentiation of the mouse MSCs and shows adequate physicochemical and biological properties for being used as scaffolds in bone tissue engineering-related strategies.

Macroporous scaffolds associated with cells to construct a hybrid biomaterial for bone tissue engineering

Bone tissue has the ability to heal without a scar and to remodel, which promotes three basic functions: locomotion, protection of internal organs and mineral homeostasis. Although bone regeneration is highly efficient, some clinical situations - such as large bone defects - require specific treatments in order to promote bone healing. Allogenic or autologous bone grafts have been used in these procedures with limited success and, based on this, bone tissue-engineering approaches have been investigated extensively. Tissue engineering has been defined as the application of principles and techniques of the life sciences and engineering to the design, modification and growth of living tissues using biomaterials, cells and growth factors, alone or in combination. The association of cells with porous scaffolds to produce 3D hybrid osteogenic constructs is a common subject in bone tissue-engineering research and will be the focus of this review. We will present some aspects of bone biology, the cells and scaffolds used to engineer bone, and techniques to fabricate the hybrid biomaterial.

Therapeutic ultrasound induces periosteal ossification without apparent changes in cartilage

Low intensity pulsed ultrasound (LIPUS) is an extremely useful noninvasive treatment which halves the duration of fracture healing when the bone is exposed once a day for 20 min. To elucidate the direct reactions of bone and cartilage, dissected rat femora were immobilized in culture dish wells, exposed to LIPUS from a certain angle every day, and the local pattern of ossification was analyzed in relation to the ultrasound. Daily 20-min exposures were started 24 hr after isolation of the femora, and at days 5, 10, and 15, samples were harvested for measurements, morphological, and histochemical analyses. While the gross features of the samples were identical to the untreated controls, extended mineralization of the periosteum was observed with alizarin red staining, antiosteocalcin immunohistochemical staining, and micro-three dimensional computed tomography. Interestingly, the newly deposited mineral was found perpendicular to the ultrasound path, strongly suggesting that LIPUS accelerates periosteal bone formation. Zones of epiphyseal cartilage and hypertrophic and calcified cartilage did not exhibit any differences with and without this exposure. LIPUS also did not influence the secreted proteoglycan components or amounts in the culture medium. The absence of any additional longitudinal growth of the femur demonstrated that LIPUS did not accelerate endochondral bone formation. We conclude that cartilage alone does not directly respond to therapeutic ultrasound, whereas the periosteum does.

Bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) transfection to human periosteal cells enhances osteoblast differentiation and bone formation

Periosteum has been demonstrated to contain mesenchymal progenitor cells differentiating to osteoblasts, and both bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) may play important roles in cell-based approaches to bone regeneration. The purpose of this study was to evaluate the feasibility and efficacy of BMP-2 and/or VEGF on periosteal cell differentiation to osteoblasts in vitro and ectopic bone formation in vivo. Human periosteum-derived cells were transfected with BMP-2, VEGF, BMP-2 + VEGF, or vehicle as a control by non-viral gene transfer and then cultured and implanted to nude mice intramuscularly. Real-time polymerase chain reaction analysis of the culture revealed that transgenes for BMP-2 and BMP-2 + VEGF induced more mRNA expression of alkaline phosphatase, collagen type I, and osteocalcin than VEGF and vehicle treatments; additionally, alizarin red S staining, alkaline phosphatase staining, and alkaline phosphatase activity were significantly higher in the BMP-2 + VEGF transgene than in the other versions. After implantation, ectopic bone was observed at 4 weeks and greatly increased at 8 weeks in all groups. In particular, the combination of BMP-2 and VEGF formed significantly more bone at 4 weeks, and VEGF transfection resulted in more blood vessels relative to the conditions without VEGF. Thus, VEGF might enhance BMP2-induced bone formation through modulation of angiogenesis.

Periosteal cells compared with autologous cancellous bone in lumbar segmental fusion

OBJECT

Despite modern stabilization techniques and the use of autologous cancellous bone, bone consolidation does not occur in 10-15% of spinal fusion operations. There is also considerable donor site morbidity. Therefore, there is a definite need for material that has a larger measure of osteoinductivity, osteoconductivity, and osteogenic potential.

METHODS

In this study, 24 patients with degenerative spinal disease underwent single-level circumferential lumbar fusion. The patients were randomly placed in 2 groups, each with different cage filling (Group 1, autologous iliac crest cancellous bone; Group 2, autologous periosteal cells in a fibrin/polyglactin-poly-p-dioxanone fleece). After 3, 6, 9, and 12 months, the patients underwent clinical (Oswestry Disability Index, patient satisfaction, willingness to undergo the operation again, visual analog scale for pain) and radiological (plain and flexion/extension radiographic and thin-layer computed tomography [CT]) examinations.

RESULTS

The 6-month CT scans and 9-month radiographs obtained in Group 2 patients showed a significantly higher rate of fusion than those in Group 1 patients. Aside from this, there were no further significant differences. After 12 months, radiographic results showed a fusion rate of 80% in Group 1 and 90% in Group 2. No implant- or transplant-related complications were observed.

CONCLUSIONS

The use of autologous periosteal cells on carrier material with osteoinductive and osteoconductive properties showed comparable results with autologous cancellous bone and better results with regard to consolidation at 6-9 months postoperatively. The shorter consolidation time, as well as lower donor site morbidity, justifies the clinical use and further development of this tissue-engineering strategy.

Cell guidance in tissue engineering: SDF-1 mediates site-directed homing of mesenchymal stem cells within three-dimensional polycaprolactone scaffolds

Cell guidance is a new tissue engineering concept aimed at total in vivo tissue engineering without the need for cell seeding. This technique aims to create a biomimetic environment through constant delivery of cytokines to different areas of an implanted scaffold, such that site-specific homing of cells can be achieved. In this study, expression of CXCR4 on mesenchymal stem cells (MSCs) was characterized by immunohistochemistry and flow cytometry, subsequent to which chemotaxis toward stromal cell-derived factor 1 (SDF-1) was demonstrated. In a subsequent three-dimensional in vitro study, MSCs were shown to migrate within a polycaprolactone scaffold in response to SDF-1, such that polarized tissue formation could be achieved. A customized cytokine microdelivery system comprising a reservoir housing system and microneedle apparatus was fabricated to ensure constant delivery of SDF-1 to the scaffold. Following on this experiment, we demonstrated in an in vivo rat bone tissue engineering model that a cytokine combination consisting of vascular endothelial growth factor, SDF-1, and bone morphogenetic protein-6 delivered at 10-day intervals through the microneedle apparatus could lead to tissue formation through migrating cell fronts, with evidence of angiogenesis and vascularization without the need for cell seeding on scaffolds prior to implantation. In summary, cell guidance offers an advancement in cellular methodology for tissue engineering, and promises a novel, minimally invasive option for tissue regeneration.

Ectopic bone formation in cell-seeded poly(ethylene oxide)/poly(butylene terephthalate) copolymer scaffolds of varying porosity

Scaffolds from poly(ethylene oxide) and poly(butylene terephthalate), PEOT/PBT, with a PEO molecular weight of 1,000 and a PEOT content of 70 weight% (1000PEOT70PBT30) were prepared by leaching salt particles (425-500 microm). Scaffolds of 73.5, 80.6 and 85.0% porosity were treated with a CO(2) gas plasma and seeded with rat bone marrow stromal cells (BMSCs). After in vitro culture for 7 days (d) in an osteogenic medium the scaffolds were subcutaneously implanted for 4 weeks in nude mice. Poly(D, L-lactide) (PDLLA) and biphasic calcium phosphate (BCP) scaffolds were included as references. After 4 weeks (wks) all scaffolds showed ectopic formation of bone and bone marrow. For the scaffolds of different porosities, no significant differences were observed in the relative amounts of bone (7-9%) and bone marrow (6-11%) formed, even though micro computed tomography (mu-CT) data showed considerable differences in accessible pore volume and surface area. 1000PEOT70PBT30 scaffolds with a porosity of 85% could not maintain their original shape in vivo. Surprisingly, 1000PEOT70PBT30 scaffolds with a porosity of 73.5% showed cartilage formation. This cartilage formation is most likely due to poorly accessible pores in the scaffolds, as was observed in histological sections. mu-CT data showed a considerably smaller accessible pore volume (as a fraction of the total volume) than in 1000PEOT70PBT30 scaffolds of 80.6 and 85.0% porosity. BMSC seeded PDLLA (83.5% porosity) and BCP scaffolds (29% porosity) always showed considerably more bone and bone marrow formation (bone marrow formation is approximately 40%) and less fibrous tissue ingrowth than the 1000PEOT70PBT30 scaffolds. The scaffold material itself can be of great influence. In more hydrophobic and rigid scaffolds like the PDLLA or BCP scaffolds, the accessibility of the pore structure is more likely to be preserved under the prevailing physiological conditions than in the case of hydrophilic 1000PEOT70PBT30 scaffolds. Scaffolds prepared from other PEOT/PBT polymer compositions, might prove to be more suited.

Combination of platelet-rich plasma with polycaprolactone-tricalcium phosphate scaffolds for segmental bone defect repair

Porous scaffold biomaterials may offer a clinical alternative to bone grafts; however, scaffolds alone are typically insufficient to heal large bone defects. Numerous studies have demonstrated that osteoinductive growth factor or gene delivery significantly improves bone repair. However, given the important role of vascularization during bone regeneration, it may also be beneficial to incorporate factors that promote vascular ingrowth into constructs. In this study, a strategy combining structural polycaprolactone-20% tricalcium phosphate (PCL-TCP) composite scaffolds with platelet-rich plasma (PRP) was tested. Following bilateral implantation of constructs into 8 mm rat nonunion femoral defects, 3D vascular and bone ingrowth were quantified at 3 and 12 weeks using contrast-enhanced microcomputed tomography (micro-CT) imaging. At week 3, PRP-treated femurs displayed 70.3% higher vascular volume fraction than control femurs. Interestingly, bone volume fraction (BVF) was significantly higher for the empty scaffold group at the early time point. At 12 weeks, BVF measurements between the two groups were statistically equivalent. However, a greater proportion of PRP-treated femurs (83%) achieved bone union as compared to empty scaffold controls (33%). Consistent with this observation, biomechanical evaluation of functional integration also revealed a significantly higher torsional stiffness observed for PRP-treated defects compared to empty scaffolds. Ultimate torque at failure was not improved, however, perhaps due to the slow resorption profile of the scaffold material. Histological evaluation illustrated infiltration of vascularized connective tissue and bone in both groups. Given that bone ingrowth into untreated defects in this model is minimal, PCL-TCP scaffolds were clearly able to promote bone ingrowth but failed to consistently bridge the defect. The addition of PRP to PCL-TCP scaffolds accelerated early vascular ingrowth and improved longer-term functional integration. Taken together, the results of this study suggest that the use of PRP, alone or in combination with other bioactive components, may be an effective approach to augment the ability of porous biomaterial scaffolds to repair orthotopic defects.

Influence ofIn VitroCultivation on the Integration of Cell-Matrix Constructs After Subcutaneous Implantation

Dynamic cultivation of scaffolds loaded with undifferentiated stem cells can lead toward osteogenic differentiation in vivo. The aim of this study was to examine the influence of different in vitro cultivation setups on the integration of cell-matrix constructs after subcutaneous implantation. Human mesenchymal stem cells (hMSC) were inoculated on clinically approved scaffolds. These cell-matrix constructs were then cultured under static (12 hours or 14 days) or dynamic (14 days) conditions, followed by paravertebral subcutaneous implantation in athymic nude mice. After 2 weeks and 12 weeks the constructs and selected organs were harvested for histological evaluation, and qualitative and quantitative polymerase chain reaction (PCR). Histological analysis showed good integration of cell-matrix constructs independent of culture conditions and a differential effect of static and dynamic in vitro culture on fat cell formation in vivo. Human DNA (hDNA) was detected in explanted cell-matrix constructs at all time points with a significant decrease in human cells on the constructs compared to the initial amount of cells seeded. No hDNA was detected in the explanted organs. In conclusion, we could prove the survival of hMSC on scaffolds after in vitro cultivation and consecutive implantation in vivo. While the amount of adipose tissue increased after static cultivation, we could not achieve osteogenic differentiation.

Osteogenic potential of cultured human periosteum-derived cells – A pilot study of human cell transplantation into a rat calvarial defect model

BACKGROUND

Periosteum shows osteogenic potential and has received considerable attention as a grafting material for the repair of bone and joint defects. The osteogenic potential of cultured periosteal cells has also been reported. The findings of bone formation induced by cultured human periosteum-derived cells using a rat model are presented.

MATERIAL AND METHODS

Human mandibular periosteum was placed into a culture medium with 10% foetal bovine serum for 14 days. After reaching confluence, periosteal cells were re-suspended with 0.25% trypsin/EDTA and then re-cultured three dimensionally on a collagen sponge. The periosteal cell/collagen complex was grafted into rat calvarial defects and an immunosuppressant (FK506, 1.0 mg/kg/day) was administered intramuscularly. At 2, 3, and 5 weeks postoperatively, grafted tissue was extirpated and compared histologically and radiographically with tissue from a collagen-only grafted group.

RESULTS

In the experimental group, periosteal cells had proliferated and differentiated into osteogenic cells by 2 weeks post grafting. At 3 weeks, new bone formation was evident. By 5 weeks, bone growth was observed and new calcification was detected in the defect.

CONCLUSION

Cultured human periosteum-derived cells showed osteogenic potential in a xenogeneic graft model using rat calvarial defects.

A comparative analysis of scaffold material modifications for load-bearing applications in bone tissue engineering

To facilitate optimal application of appropriate scaffold architectures for clinical trials, there is a need to compare different scaffold modifications under similar experimental conditions. In this study was assessed the effectiveness of poly-e-caprolactone (PCL) scaffolds fabricated by fused deposition modelling (FDM), with varying material modifications, for the purposes of bone tissue engineering. The incorporation of hydroxyapatite (HA) in PCL scaffolds, as well as precalcification through immersion in a simulated body fluid (SBF) to produce a biomimetic apatite coating on the scaffolds, was assessed. A series of in vitro studies spanning 3 weeks as well as in vivo studies utilizing a subcutaneous nude mouse model were carried out. PCL and HA-PCL scaffolds demonstrated increasing tissue growth extending throughout the implants, as well as superior mechanical strength and mineralization, as evidenced by X-ray imaging after 14 weeks in vivo. No significant difference was found between PCL and HA-PCL scaffolds. Precalcification with SBF did not result in increased osteoconductivity and cell proliferation as previously reported. Conversely, tensile forces exerted by tissue sheets bridging adjacent struts of the PCL scaffold caused flaking of the apatite coating that resulted in impaired cell attachment, growth and mineralization. The results suggest that scaffolds fabricated by FDM may have load-bearing applications.

rh-BMP2-induced ectopic bone for grafting critical size defects: a preliminary histological evaluation in rat calvariae

The aim of this study was to evaluate histologically the biological usefulness of recombinant human BMP2 (rh-BMP2)-induced ectopically-formed bone as graft material to repair a bone defect model, compared with autogenous bone and frozen allogeneic bone. Forty-five male Wistar rats were used, which were divided into three graft groups. Each of the three graft groups was divided into three observation period groups (3, 6 and 9 weeks after graft). All rats underwent craniotomy to create a bone defect, and then received a bone graft. In the rh-BMP2-induced ectopic bone graft group, marked bone formation was seen from 3 weeks after graft. In the autogenous bone graft group, marked bone formation was seen from 6 weeks after graft. In the group that received a frozen allogeneic bone graft, marked bone formation was seen from 9 weeks after graft. At 3, 6 and 9 weeks after graft, newly formed bone area was significantly greater in the tissue engineered bone (TEB) group than in the auto or frozen allogeneic bone (FAB) group. rh-BMP2-induced ectopically-formed bone graft exhibited better osteoconductivity than autogenous bone graft and frozen allogeneic bone graft. These histological findings indicate that rh-BMP2-induced ectopically-formed bone is suitable as bone graft material.

Ectopic bone formation in nude rats using human osteoblasts seeded poly(3)hydroxybutyrate embroidery and hydroxyapatite-collagen tapes constructs

PURPOSE

The aim of this study was to evaluate the ectopic bone formation using tissue engineered cell-seeded constructs with two different scaffolds and primary human maxillary osteoblasts in nude rats over an implantation period of up to 96 days.

MATERIAL AND METHODS

Collagen I-coated Poly(3)hydroxybutyrate (PHB) embroidery and hydroxyapatite (HAP) collagen tapes were seeded with primary human maxillary osteoblasts (hOB) and implanted into athymic rnu/run rats. A total of 72 implants were placed into the back muscles of 18 rats. 24, 48 and 96 days after implantation, histological and histomorphometric analyses were made. The osteoblastic character of the cells was confirmed by immunocytochemistry and RT-PCR for osteocalcin.

RESULTS

Histological analysis demonstrated that all cell-seeded constructs induced ectopic bone formation after 24, 48 and 96 days of implantation. There was more mineralized tissue in PHB constructs than in HAP-collagen tapes (at day 24; p < 0.05). Bone formation decreased with the increasing length of the implantation period. Osteocalcin expression verified the osteoblastic character of the cell-seeded constructs after implantation time. No bone formation and no osteocalcin expression were found in the control groups.

CONCLUSIONS

Cell-seeded constructs either with PHB embroidery or HAP-collagen tapes can induce ectopic bone formation. However, the amount of bone formed decreased with increasing length of implantation.

Species Specificity of Ectopic Bone Formation Using Periosteum-Derived Mesenchymal Progenitor Cells

To investigate novel cell-based bone-engineering approaches using rabbit as a preclinical animal model, we compared the osteogenic potential of rabbit periosteum-derived cells (RPDCs) and human periosteum-derived cells (HPDCs) in vitro and in vivo. Adherent periosteal cells from both species were expanded in vitro and subsequently treated with osteogenic medium or bone morphogenetic protein 6 (BMP6). Alkaline phosphatase (ALP) activity was measured, and alizarin red staining was performed to evaluate osteogenic differentiation. In vivo ectopic bone formation was assessed by seeding 5x10(6) periosteal cells, grown in osteogenic conditions, in a Collagraft carrier and subsequent implantation subcutaneously in athymic mice. In vitro, growth analysis indicated that RPDCs expanded faster and were smaller than HPDCs under the same culture conditions. Osteogenic medium did not affect the ALP activity of HPDCs or RPDCs. In contrast, BMP6 stimulated ALP activity in cultured RPDCs and HPDCs but at different rates. In vivo, HPDCs gave rise to extensive bone formation, whereas RPDCs failed to make bone. In vivo, cell tracking revealed that engraftment and survival of HPDCs and RPDCs after 8 weeks in the implant were limited. Some HPDCs were incorporated into the newly formed bone. RPDCs and HPDCs displayed distinct growth characteristics and osteogenic differentiation capacity in vitro and in vivo under the culture conditions used. Our data indicate potential limitations of use of the rabbit as a preclinical model for cell-based treatments for bone repair.

3D scaffolds for bone marrow stem cell support in bone repair

Bone tissue repair is one of the major concerns of regenerative medicine. The current need for tissue replacements has necessitated the development of a new science termed ‘bone tissue engineering’. The basic organization of bone tissue requires the design and fabrication of a porous 3D structure or ‘scaffold’ to contain the bone-forming cells. This scaffold should be formulated from biocompatible, osteoconductive materials that are not immunoreactive. 3D scaffolds provide the necessary support for cells to proliferate and maintain their capacity to differentiate and scaffolds containing bone marrow-derived osteoprogenitors can be employed within implants to enhance bone repair. The complex construct is intended to mimic the native in vivo microenvironment and this demands construction of bioactive scaffolds that are also capable of supporting vascularization as well as cell proliferation and osteogenic differentiation. 3D bioactive scaffolds containing committed osteoprogenitors can provide a promising surgical tool for bone tissue engineering directed at orthopedic and cranio-maxillofacial clinical applications.

Human Circulating Peripheral Blood Mononuclear Cells for Calvarial Bone Tissue Engineering

BACKGROUND

Large-scale production of engineered tissues requires an adequate source of expandable cells. Current strategies that involve harvesting of cells from donor tissue or bone marrow for tissue engineering are invasive and unfeasible for obtaining large quantities of cells in a clinical setting. Peripheral blood has been reported to contain circulating hematopoietic cells as well as, in significantly smaller quantities, mesenchymal cells

METHODS

An adherent subset of CD14+ mononuclear cells was isolated from human peripheral venous blood and characterized in vitro by light microscopy, immunohistochemistry, flow cytometry, and quantitative differentiation assays. These cells were then evaluated for the purposes of tissue engineering in a rat calvarial defect model, in combination with biodegradable polymer matrices made from poly-e-caprolactone. Specimens were analyzed 6 weeks after implantation with histologic analysis, microcomputed tomography, and HLA immunostaining.

RESULTS

CD14+ mononuclear cells were induced to differentiate into osteoblast-like cells in vitro, with areas of mineralization. In a rat calvarial defect model, tissue-engineered bone with evidence of mineralization was formed within 6 weeks. HLA immunohistochemistry demonstrated that de novo bone formation originated from the transplanted human cells.

CONCLUSIONS

These findings show, for the first time, to our knowledge, the derivation of bone from human blood. They also demonstrate the utility of circulating mononuclear cells as a minimally invasive, potentially unlimited pool of cells for tissue engineering and organ regeneration.

In vitro osteogenic differentiation and in vivo bone-forming capacity of human isogenic jaw periosteal cells and bone marrow stromal cells

OBJECTIVE

To compare the in vitro osteogenic differentiation and in vivo ectopic bone forming capacity of human bone marrow stromal cells (BMSCs) and jaw periosteal cells (JPCs), and to identify molecular predictors of their osteogenic capacity.

SUMMARY BACKGROUND DATA

JPC could be an appealing alternative to BMSC for the engineering of cell-based osteoinductive grafts because of the relatively easy access to tissue with minimal morbidity. However, the extent of osteogenic capacity of JPC has not yet been established or compared with that of BMSC.

METHODS

BMSCs and JPCs from the same donors (N = 9), expanded for 2 passages, were cultured for 3 weeks in osteogenic medium either in monolayers (Model I) or within 3-dimensional porous ceramic scaffolds, following embedding in fibrin gel (Model II). Cell-fibrin-ceramic constructs were also implanted ectopically in nude mice for 8 weeks (Model III). Cell differentiation in vitro was assessed biochemically and by real-time RT-PCR. Bone formation in vivo was quantified by computerized histomorphometry.

RESULTS

JPCs had lower alkaline phosphatase activity, deposited smaller amounts of calcium (Model I), and expressed lower mRNA levels of bone sialoprotein, osteopontin, and osterix (Models I and II) than BMSCs. JPCs produced ectopic bone tissue at lower frequency and amounts (Model III) than BMSCs. Bone sialoprotein, osteopontin, and osterix mRNA levels by BMSCs or JPCs in Model II were markedly higher than in Model I and significantly more expressed by cells that generated bone tissue in Model III.

CONCLUSIONS

Our data indicate that JPCs, although displaying features of osteogenic cells, would not be as reliable as BMSCs for cell-based bone tissue engineering, and suggest that expression of osteoblast-related markers in vitro could be used to predict whether cells would be osteoinductive in vivo.

An in vitro evaluation of PCL-TCP composites as delivery systems for platelet-rich plasma

In this study, we first investigated the in vitro degradation properties of biodegradable, bioresorbable polycaprolactone-20% tricalcium phosphate (PCL-TCP) composites immersed in simulated body fluid (SBF) and phosphate buffered saline (PBS). Then, the release profiles of the growth factors present in platelet-rich plasma (PRP) loaded onto the composites incubated in SBF and PBS were compared. Composites immersed in both buffers showed water uptake of 13.7%+/-0.75 at day 1, followed by a constant uptake of 12.1%+/-0.3 until day 12. Henceforth the water uptake declined for SBF- and increased for PBS-soaked composites. The weight loss data did not reveal any trend. SBF- and PBS-soaked samples displayed 1-2% weight loss for 2 and 5 of the ten time points measured respectively. The original protein retention (PR) of the composites was 49.1%+/-1.50. After immersion in SBF and PBS for 4 weeks, the PR was augmented to 88.5%+/-1.40 and 69.1%+/-1.40 correspondingly. PRP after activation contained 164.7+/-24.8, 194+/-43 and 18.3+/-4.75 ng/ml of TGF-beta1, PDGF-BB and IGF-1. Microscopic analysis verified the attachment of PRP to the rods and pores of the composites. Interestingly, the buffers played an important role in determining the release profiles of TGF and PDGF. Firstly, PBS-soaked composites manifested a tri-phasic burst-like profile that was absent in SBF. Secondly, SBF-soaked composites experienced delayed release of the growth factors and total release was not achieved (64.4% for TGF and 60.5% for PDGF), whereas total release was realized for PBS-soaked composites. Lastly, release profiles from SBF-soaked composites were growth factor mediated in terms of their amounts and sizes. This was not observed for PBS-soaked composites. IGF-1, on the other hand, exhibited a progressive reduction in levels over the entire experimental period for both buffers. The mechanisms of release were theorized to be a combination of diffusion, degradation and bioactivity. Since SBF is analogous to our body fluids in terms of its ionic constituents, we expect the elution profiles derived from SBF-soaked samples to more accurately emulate the in vivo situation. In conclusion, this study has deemed PCL-TCP composites as suitable delivery systems for platelet-rich plasma.

Expression pattern of the chromosome 21 transcription factor Ets2 in cell-seeded three-dimensional bone constructs

The ability to generate new bone for reconstructive surgery use is a major clinical need. Tissue engineering with osteoprogenitor cells isolated from the patient's periosteum and seeded into bioresorbable scaffolds offers a promising approach to the generation of skeletal tissue. To our knowledge, there is no description about the expression of Ets2 in tissue engineered "bone neotissue." The aim of our study was to manufacture cell-seeded three-dimensional bone constructs with human periosteal cells on poly (lactic-co-glycolic acid) polymer fleeces to describe the expression pattern of Ets2 and its target genes osteocalcin and osteopontin; expression analysis of type I collagen, core-binding factor-1, alkaline phosphatase, and osteonectin; the ability of matrix mineralization and ALP enzymatic activity showed the osteogenic character of the constructs. A significant correlation between the expression of Ets2 and osteopontin mRNA (r = -0.70; p < 0.05) could be shown. A 1.35-fold increase of Ets2 expression from days 1 to 9 was detected, followed by a slight decrease from days 11 to 15. Until the end of the culture period, the expression of Ets2 reached a comparable high level as detected on day 9. In contrast, the expression level of osteopontin mRNA reached a maximum at day 7, followed by a progressive 3.04-fold decrease until day 21. This study shows for the first time that Ets2 gene and its transcriptional target genes are expressed in tissue-engineered bone constructs. These findings have the potential to provide much-needed information about the role and function of Ets2 in human osteogenesis processes and creation of "bone neotissue."