Bone regeneration in sheep using acropora coral, a natural resorbable scaffold, and autologous mesenchymal stem cells

Sustainably cultured coral scaffold supports human bone marrow mesenchymal stromal cell osteogenesis

The current gold standard grafting material is autologous bone due to its osteoinductive and osteoconductive properties. Autograft harvesting results in donors site morbidity. Coral scaffolds offer a natural autograft alternative, sharing the density and porosity of human bone. This study investigated the biocompatibility and osteogenic potential of a novel, sustainably grown Pocillopora scaffold with human bone marrow-derived mesenchymal stromal cells (MSCs). The coral-derived scaffold displays a highly textured topography, with concavities of uniform size and a high calcium carbonate content. Large scaffold samples exhibit compressive and diametral tensile strengths in the range of trabecular bone, with strengths likely increasing for smaller particulate samples. Following the in vitro seeding of MSCs adjacent to the scaffold, the MSCs remained viable, continued proliferating and metabolising, demonstrating biocompatibility. The seeded MSCs densely covered the coral scaffold with organized, aligned cultures with a fibroblastic morphology. In vivo coral scaffolds with MSCs supported earlier bone and blood vessel formation as compared to control constructs containing TCP-HA and MSCs. This work characterized a novel, sustainably grown coral scaffold that was biocompatible with MSCs and supports their in vivo osteogenic differentiation, advancing the current repertoire of biomaterials for bone grafting.

Fabrication and characterization of 3D-printed composite scaffolds of coral-derived hydroxyapatite nanoparticles/polycaprolactone/gelatin carrying doxorubicin for bone tissue engineering

In this study, nanocomposite scaffolds of hydroxyapatite (HA)/polycaprolactone (PCL)/gelatin (Gel) with varying amounts of HA (42-52 wt. %), PCL (42-52 wt. %), and Gel (6 wt. %) were 3D printed. Subsequently, a scaffold with optimal mechanical properties was utilized as a carrier for doxorubicin (DOX) in the treatment of bone cancer. For this purpose, HA nanoparticles were first synthesized by the hydrothermal conversion of Acropora coral and characterized by using different techniques. Also, a compression test was performed to investigate the mechanical properties of the fabricated scaffolds. The mineralization of the optimal scaffold was determined by immersing it in simulated body fluid (SBF) solution for 28 days, and the biocompatibility was investigated by seeding MG-63 osteoblast-like cells on it after 1-7 days. The obtained results showed that the average size of the synthesized HA particles was about 80 nm. The compressive modulus and strength of the scaffold with 47 wt. % HA was reported to be 0.29 GPa and 9.9 MPa, respectively, which was in the range of trabecular bones. In addition, the scaffold surface was entirely coated with an apatite layer after 28 days of soaking in SBF. Also, the efficiency and loading percentage of DOX were obtained as 30.8 and 1.6%, respectively. The drug release behavior was stable for 14 days. Cytotoxicity and adhesion evaluations showed that the fabricated scaffold had no negative effects on the viability of MG-63 cells and led to their proliferation during the investigated period. From these results, it can be concluded that the HA/PCL/Gel scaffold prepared in this study, in addition to its drug release capability, has good bioactivity, mechanical properties, and biocompatibility, and can be considered a suitable option for bone tumor treatment.

The Lower in Vivo Osteogenicity of Adipose Tissue-Derived Stem Cells Correlates with a Higher Innate Immune Response

Adipose tissue-derived mesenchymal stem cells (ATSCs) have been used as an alternative to bone marrow-derived mesenchymal stem cells (BMSCs) for bone tissue engineering applications. The ability of ATSCs to promote new bone formation remains lower than that of BMSCs. This study aimed to investigate the mechanisms underlying osteogenicity differences between human ATSCs and BMSCs in ceramic constructs, focusing on the effects of inflammation on this process. In contrast to ATSC-containing constructs, which did not induce bone formation in an ectopic mouse model, BMSC constructs consistently did so. Gene expression analysis revealed that human BMSCs, concomitantly with host murine progenitors, differentiated into the osteogenic lineage early post-implantation. In contrast, ATSCs differentiated later, when few implanted viable cells remained post-implantation, while the host murine cells did not differentiate. Comparison of the inflammatory profile in the cell constructs indicated concomitant upregulation of some human and murine inflammatory genes in the ATSC-constructs compared to the BMSC-constructs during the first-week post-implantation. The high level of chemokine production by the ATSCs was confirmed at the gene and protein levels before implantation. The immune cell recruitment within the constructs was then explored post-implantation. Higher numbers of TRAP-/ MRC1 (CD206) + multinucleated giant cells, NOS2 + M1, and ARG1 + M2 macrophages were present in the ATSC constructs than in the BMSC constructs. These results proved that ATSCs are a transient source of inflammatory cytokines promoting a transient immune response post-implantation; this milieu correlates with impaired osteogenic differentiation of both the implanted ATSCs and the host osteoprogenitor cells.

Hybrid Membranes of the Ureasil-Polyether Containing Glucose for Future Application in Bone Regeneration

The application of mesenchymal stem cells (MSC) in bone tissue regeneration can have unpredictable results due to the low survival of cells in the process since the lack of oxygen and nutrients promotes metabolic stress. Therefore, in this work, polymeric membranes formed by organic-inorganic hybrid materials called ureasil-polyether for modified glucose release were developed in order to overcome the problems posed by a of lack of this nutrient. Thus, membranes formed by polymeric blend of polypropylene oxide (PPO4000) and polyethylene oxide (PEO500) with 6% glucose incorporation were developed. Physical-chemical characterization techniques were performed, as well as tests that evaluated thermal properties, bioactivity, swelling, and release in SBF solution. The results of the swelling test showed an increase in membrane mass correlated with an increase in the concentration of ureasil-PEO500 in the polymeric blends. The membranes showed adequate resistance when subjected to the application of a high compression force (15 N). X-ray diffraction (XRD) evidenced peaks corresponding to orthorhombic crystalline organization, but the absence of glucose-related peaks showed characteristics of the amorphous regions of hybrid materials, likely due to solubilization. Thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses showed that the thermal events attributed to glucose and hybrid materials were similar to that seen in the literature, however when glucose was incorporated into the PEO500, an increase in rigidity occurs. In PPO400, and in the blends of both materials, there was a slight decrease in Tg values. The smaller contact angle for the ureasil-PEO500 membrane revealed the more hydrophilic character of the material compared to other membranes. The membranes showed bioactivity and hemocompatibility in vitro. The in vitro release test revealed that it is possible to control the release rate of glucose and the kinetic analysis revealed a release mechanism characteristic of anomalous transport kinetics. Thus, we can conclude that ureasil-polyether membranes have great potential to be used as a glucose release system, and their future application has the potential to optimize the bone regeneration process.

Aragonite-Polylysine: Neuro-Regenerative Scaffolds with Diverse Effects on Astrogliosis

Biomaterials, especially when coated with adhesive polymers, are a key tool for restorative medicine, being biocompatible and supportive for cell adherence, growth, and function. Aragonite skeletons of corals are biomaterials that support survival and growth of a range of cell types, including neurons and glia. However, it is not known if this scaffold affects neural cell migration or elongation of neuronal and astrocytic processes, prerequisites for initiating repair of damage in the nervous system. To address this, hippocampal cells were aggregated into neurospheres and cultivated on aragonite skeleton of the coral Trachyphyllia geoffroyi (Coral Skeleton (CS)), on naturally occurring aragonite (Geological Aragonite (GA)), and on glass, all pre-coated with the oligomer poly-D-lysine (PDL). The two aragonite matrices promoted equally strong cell migration (4.8 and 4.3-fold above glass-PDL, respectively) and axonal sprouting (1.96 and 1.95-fold above glass-PDL, respectively). However, CS-PDL had a stronger effect than GA-PDL on the promotion of astrocytic processes elongation (1.7 vs. 1.2-fold above glass-PDL, respectively) and expression of the glial fibrillary acidic protein (3.8 vs. and 1.8-fold above glass-PDL, respectively). These differences are likely to emerge from a reaction of astrocytes to the degree of roughness of the surface of the scaffold, which is higher on CS than on GA. Hence, CS-PDL and GA-PDL are scaffolds of strong capacity to derive neural cell movements and growth required for regeneration, while controlling the extent of astrocytic involvement. As such, implants of PDL-aragonites have significant potential as tools for damage repair and the reduction of scar formation in the brain following trauma or disease.

Progress in Modern Marine Biomaterials Research

The growing demand for new, sophisticated, multifunctional materials has brought natural structural composites into focus, since they underwent a substantial optimization during long evolutionary selection pressure and adaptation processes. Marine biological materials are the most important sources of both inspiration for biomimetics and of raw materials for practical applications in technology and biomedicine. The use of marine natural products as multifunctional biomaterials is currently undergoing a renaissance in the modern materials science. The diversity of marine biomaterials, their forms and fields of application are highlighted in this review. We will discuss the challenges, solutions, and future directions of modern marine biomaterialogy using a thorough analysis of scientific sources over the past ten years.

Use of adult mesenchymal stromal cells in tissue repair: impact of physical exercise

Physical exercise (PE) has unquestionable beneficial effects on health, which likely extend into several organ-to-cell physiological processes. At the cell scale, endogenous mesenchymal stromal cells (MSCs) contribute to tissue repair, although their repair capacities may be insufficient in paucicellular or severely damaged tissues. For this reason, MSC transplantation holds great promise for tissue repair. With the goals of understanding if PE has beneficial effects on MSC biology and if PE potentiates their role in tissue repair, we reviewed literature reports regarding the effects of PE on MSC properties (specifically, proliferation, differentiation, and homing) and of a combination of PE and MSC transplantation on tissue repair (specifically neural, cartilage, and muscular tissues). Contradictory results have been reported; interpretation is complicated because various and different species, cell sources, and experimental protocols, specifically exercise programs, have been used. On the basis of these data, the effects of exercise on MSC proliferation and differentiation depend on exercise characteristics (type, intensity, duration, etc.) and on the characteristics of the tissue from which the MSCs were collected. For the in vitro studies, the level of strain (and other details of the mechanical stimulus), the time elapsed between the end of exposure to strain and MSC collection, the age of the donors, as well as the passage number at which the MSCs are evaluated also play a role. The combination of PE and MSC engraftment improves neural, cartilage, and muscular tissue recovery, but it is not clear whether the effects of MSCs and exercise are additive or synergistic.

Advances in personalized treatment of metastatic spine disease

The spine is one of the most common sites of bony metastases, and its involvement leads to significant patient morbidity. Surgical management in these patients is aimed at improving quality of life and functional status throughout the course of the disease. Resection of metastases often leads to critical size bone defects, presenting a challenge to achieving adequate bone regeneration to fill the void. Current treatment options for repairing these defects are bone grafting and commercial bone cements; however, each has associated limitations. Additionally, tumor recurrence and tumor-induced bone loss make bone regeneration particularly difficult. Systemic therapeutic delivery, such as bisphosphonates, have become standard of care to combat bone loss despite unfavorable systemic side-effects and lack of local efficacy. Developments from tissue engineering have introduced novel materials with osteoinductive and osteoconductive properties which also act as structural support scaffolds for bone regeneration. These new materials can also act as a therapeutic reservoir to sustainably release drugs locally as an alternative to systemic therapy. In this review, we outline recent advancements in tissue engineering and the role of translational research in developing implants that can fully repair bone defects while also delivering local therapeutics to curb tumor recurrence and improve patient quality of life.

The paracrine effects of human induced pluripotent stem cells promote bone-like structures via the upregulation of BMP expression in a mouse ectopic model

Use of human induced pluripotent stem cells (h-iPSCs) for bone tissue engineering is most appealing, because h-iPSCs are an inexhaustible source of osteocompetent cells. The present study investigated the contribution of undifferentiated h-iPSCs and elucidated aspects of the underlying mechanism(s) of the involvement of these cells to new bone formation. Implantation of undifferentiated h-iPSCs seeded on coral particles in ectopic sites of mice resulted in expression of osteocalcin and DMP-1, and in mineral content similar to that of the murine bone. The number of the implanted h-iPSCs decreased with time and disappeared by 30 days post-implantation. In contrast, expression of the murine osteogenic genes at day 15 and 30 post-implantation provided, for the first time, evidence that the implanted h-iPSCs affected the observed outcomes via paracrine mechanisms. Supporting evidence was provided because supernatant conditioned media from h-iPSCs (h-iPSC CM), promoted the osteogenic differentiation of human mesenchymal stem cells (h-MSCs) in vitro. Specifically, h-iPSC CM induced upregulation of the BMP-2, BMP-4 and BMP-6 genes, and promoted mineralization of the extracellular matrix. Given the current interest in the use of h-iPSCs for regenerative medicine applications, our study contributes new insights into aspects of the mechanism underlying the bone promoting capability of h-iPSCs.

Effect of the Bone Morphogenetic Protein-2 Doses on the Osteogenic Potential of Human Multipotent Stromal Cells- Containing Tissue Engineered Constructs

IMPACT STATEMENT

A strategy for improving the efficacy of stem cell-based bone tissue engineering (TE) constructs is to combine bone morphogenetic protein-2 (BMP-2) with multipotent stromal cells (MSC). Previous studies on the potential cooperative effect of BMP-2 with human multipotent stromal cells (hMSCs) on bone formation in vivo have, however, shown contradictory results likely due to the various and/or inappropriate BMP-2 doses. Our results provided evidence that the addition of BMP-2 at low dose only was beneficial to improve the osteogenic potential of hMSCs-containing TE constructs, whereas BMP-2 delivered at high dose overcame the advantage of combining this growth factor with hMSCs. This new knowledge will help in designing improved combination strategies for tissue regeneration with better clinical outcomes.

Synthetic and Marine-Derived Porous Scaffolds for Bone Tissue Engineering

Bone is a vascularized and connective tissue. The cortical bone is the main part responsible for the support and protection of the remaining systems and organs of the body. The trabecular spongy bone serves as the storage of ions and bone marrow. As a dynamic tissue, bone is in a constant remodelling process to adapt to the mechanical demands and to repair small lesions that may occur. Nevertheless, due to the increased incidence of bone disorders, the need for bone grafts has been growing over the past decades and the development of an ideal bone graft with optimal properties remains a clinical challenge. This review addresses the bone properties (morphology, composition, and their repair and regeneration capacity) and puts the focus on the potential strategies for developing bone repair and regeneration materials. It describes the requirements for designing a suitable scaffold material, types of materials (polymers, ceramics, and composites), and techniques to obtain the porous structures (additive manufacturing techniques like robocasting or derived from marine skeletons) for bone tissue engineering applications. Overall, the main objective of this review is to gather the knowledge on the materials and methods used for the production of scaffolds for bone tissue engineering and to highlight the potential of natural porous structures such as marine skeletons as promising alternative bone graft substitute materials without any further mineralogical changes, or after partial or total transformation into calcium phosphate.

Tissue Engineering and Cell-Based Therapies for Fractures and Bone Defects

Bone fractures and segmental bone defects are a significant source of patient morbidity and place a staggering economic burden on the healthcare system. The annual cost of treating bone defects in the US has been estimated to be $5 billion, while enormous costs are spent on bone grafts for bone injuries, tumors, and other pathologies associated with defective fracture healing. Autologous bone grafts represent the gold standard for the treatment of bone defects. However, they are associated with variable clinical outcomes, postsurgical morbidity, especially at the donor site, and increased surgical costs. In an effort to circumvent these limitations, tissue engineering and cell-based therapies have been proposed as alternatives to induce and promote bone repair. This review focuses on the recent advances in bone tissue engineering (BTE), specifically looking at its role in treating delayed fracture healing (non-unions) and the resulting segmental bone defects. Herein we discuss: (1) the processes of endochondral and intramembranous bone formation; (2) the role of stem cells, looking specifically at mesenchymal (MSC), embryonic (ESC), and induced pluripotent (iPSC) stem cells as viable building blocks to engineer bone implants; (3) the biomaterials used to direct tissue growth, with a focus on ceramic, biodegradable polymers, and composite materials; (4) the growth factors and molecular signals used to induce differentiation of stem cells into the osteoblastic lineage, which ultimately leads to active bone formation; and (5) the mechanical stimulation protocols used to maintain the integrity of the bone repair and their role in successful cell engraftment. Finally, a couple clinical scenarios are presented (non-unions and avascular necrosis—AVN), to illustrate how novel cell-based therapy approaches can be used. A thorough understanding of tissue engineering and cell-based therapies may allow for better incorporation of these potential therapeutic approaches in bone defects allowing for proper bone repair and regeneration.

Low-dose BMP-2 and MSC dual delivery onto coral scaffold for critical-size bone defect regeneration in sheep

Tissue-engineered constructs (TECs) combining resorbable calcium-based scaffolds and mesenchymal stem cells (MSCs) have the capability to regenerate large bone defects. Inconsistent results have, however, been observed, with a lack of osteoinductivity as a possible cause of failure. This study aimed to evaluate the impact of the addition of low-dose bone morphogenetic protein-2 (BMP-2) to MSC-coral-TECs on the healing of clinically relevant segmental bone defects in sheep. Coral granules were either seeded with autologous MSCs (bone marrow-derived) or loaded with BMP-2. A 25-mm-long metatarsal bone defect was created and stabilized with a plate in 18 sheep. Defects were filled with one of the following TECs: (i) BMP (n = 5); (ii) MSC (n = 7); or (iii) MSC-BMP (n = 6). Radiographic follow-up was performed until animal sacrifice at 4 months. Bone formation and scaffold resorption were assessed by micro-CT and histological analysis. Bone union with nearly complete scaffold resorption was observed in 1/5, 2/7, and 3/6 animals, when BMP-, MSC-, and MSC-BMP-TECs were implanted, respectively. The amount of newly formed bone was not statistically different between groups: 1074 mm³ [970-2478 mm³ ], 1155 mm³ [970-2595 mm³ ], and 2343 mm³ [931-3276 mm³ ] for BMP-, MSC-, and MSC-BMP-TECs, respectively. Increased scaffold resorption rate using BMP-TECs was the only potential side effect observed. In conclusion, although the dual delivery of MSCs and BMP-2 onto a coral scaffold further increased bone formation and bone union when compared to single treatment, results were non-significant. Only 50% of the defects healed, demonstrating the need for further refinement of this strategy before clinical use. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2637-2645, 2017.

The Role of Three-Dimensional Scaffolds in Treating Long Bone Defects: Evidence from Preclinical and Clinical Literature-A Systematic Review

Long bone defects represent a clinical challenge. Bone tissue engineering (BTE) has been developed to overcome problems associated with conventional methods. The aim of this study was to assess the BTE strategies available in preclinical and clinical settings and the current evidence supporting this approach. A systematic literature screening was performed on PubMed database, searching for both preclinical (only on large animals) and clinical studies. The following string was used: "(Scaffold OR Implant) AND (Long bone defect OR segmental bone defect OR large bone defect OR bone loss defect)." The search retrieved a total of 1573 articles: 51 preclinical and 4 clinical studies were included. The great amount of preclinical papers published over the past few years showed promising findings in terms of radiological and histological evidence. Unfortunately, this in vivo situation is not reflected by a corresponding clinical impact, with few published papers, highly heterogeneous and with small patient populations. Several aspects should be further investigated to translate positive preclinical findings into clinical protocols: the identification of the best biomaterial, with both biological and biomechanical suitable properties, and the selection of the best choice between cells, GFs, or their combination through standardized models to be validated by randomized trials.

A comparative study of tissue-engineered constructs from Acropora and Porites coral in a large animal bone defect model

Objectives

To compare the therapeutic potential of tissue-engineered constructs (TECs) combining mesenchymal stem cells (MSCs) and coral granules from either Acropora or Porites to repair large bone defects.

Materials and Methods

Bone marrow-derived, autologous MSCs were seeded on Acropora or Porites coral granules in a perfusion bioreactor. Acropora-TECs (n = 7), Porites-TECs (n = 6) and bone autografts (n = 2) were then implanted into 25 mm long metatarsal diaphyseal defects in sheep. Bimonthly radiographic follow-up was completed until killing four months post-operatively. Explants were subsequently processed for microCT and histology to assess bone formation and coral bioresorption. Statistical analyses comprised Mann-Whitney, t-test and Kruskal–Wallis tests. Data were expressed as mean and standard deviation.

Results

A two-fold increaseof newly formed bone volume was observed for Acropora-TECs when compared with Porites-TECs (14 sd 1089 mm³versus 782 sd 507 mm³; p = 0.09). Bone union was consistent with autograft (1960 sd 518 mm³). The kinetics of bioresorption and bioresorption rates at four months were different for Acropora-TECs and Porites-TECs (81% sd 5% versus 94% sd 6%; p = 0.04). In comparing the defects that healed with those that did not, we observed that, when major bioresorption of coral at two months occurs and a scaffold material bioresorption rate superior to 90% at four months is achieved, bone nonunion consistently occurred using coral-based TECs.

Discussion

Bone regeneration in critical-size defects could be obtained with full bioresorption of the scaffold using coral-based TECs in a large animal model. The superior performance of Acropora-TECs brings us closer to a clinical application, probably because of more suitable bioresorption kinetics. However, nonunion still occurred in nearly half of the bone defects.

Cite this article: A. Decambron, M. Manassero, M. Bensidhoum, B. Lecuelle, D. Logeart-Avramoglou, H. Petite, V. Viateau. A comparative study of tissue-engineered constructs from Acropora and Porites coral in a large animal bone defect model. Bone Joint Res 2017;6:208–215. DOI: 10.1302/2046-3758.64.BJR-2016-0236.R1.

Is there a role of coral bone substitutes in bone repair?

Xenogeneic bone graft materials are an alternative to autologous bone grafting. Among such implants, coralline-derived bone grafts substitutes have a long track record as safe, biocompatible and osteoconductive graft materials. In this review, we present the available literature surrounding their use with special focus on the commercially available graft materials. Corals thanks to their chemical and structural characteristics similar to those of the human cancellous bone have shown great potential but clinical data presented to date is ambiguous with both positive and negative outcomes reported. Correct formulation and design of the graft to ensure adequate osteo-activity and resorption appear intrinsic to a successful outcome.

Natural and Synthetic Coral Biomineralization for Human Bone Revitalization

Coral skeletons can regenerate replacement human bone in nonload-bearing excavated skeletal locations. A combination of multiscale, interconnected pores and channels and highly bioactive surface chemistry has established corals as an important alternative to using healthy host bone replacements. Here, we highlight how coral skeletal systems are being remolded into new calcified structures or synthetic corals by biomimetic processes, as places for the organized permeation of bone tissue cells and blood vessels. Progressive technologies in coral aquaculture and self-organization inorganic chemistry are helping to modify natural corals and create synthetic coral architectures able to accelerate bone regeneration with proper host integration at more skeletal locations, adapted to recent surgical techniques and used to treat intrinsic skeletal deformities and metabolic conditions.

A Selective Cell Population from Dermis Strengthens Bone Regeneration

Finding appropriate seed cells for bone tissue engineering remains a significant challenge. Considering that skin is the largest organ, we hypothesized that human bone morphogenetic protein receptor type IB (BmprIB)+ dermal cells could have enhanced osteogenic capacity in the healing of critical-sized calvarial defects in an immunodeficient mouse model. In this study, immunohistochemical staining revealed that BmprIB was expressed throughout reticular dermal cells; the positive expression rate of BmprIB was 3.5% ± 0.4% in freshly separated dermal cells, by flow cytometry. Furthermore, in vitro osteogenic capacity of BmprIB+ cells was confirmed by osteogenic-related staining and marker gene expression compared with unsorted dermal cells. In vivo osteogenic capacity was demonstrated by implantation of human BmprIB+ cell/coral constructs in the treatment of 4-mm diameter calvarial defects in an immunodeficient mouse model compared with implantation of unsorted cell/coral constructs and coral scaffold alone. These results indicate that the selective cell population BmprIB from human dermis is a promising osteogenic progenitor cell that can be a large-quantity and high-quality cell source for bone tissue engineering and regeneration. Stem Cells Translational Medicine 2017;6:306-315.

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

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

Agent-based modeling of osteogenic differentiation of mesenchymal stem cells in porous biomaterials

Mesenchymal stem cells (MSC) have shown promise in tissue engineering applications due to their potential for differentiating into mesenchymal tissues such as osteocytes, chondrocytes, and adipocytes and releasing proteins to promote tissue regeneration. One application involves seeding MSCs in biomaterial scaffolds to promote osteogenesis in the repair of bone defects following implantation. However, predicting in vivo survival and differentiation of MSCs in biomaterials is challenging. Rapid and stable vascularization of scaffolds is required to supply nutrients and oxygen that MSCs need to survive as well as to go through osteogenic differentiation. The objective of this study is to develop an agent-based model and simulator that can be used to investigate the effects of using gradient growth factors on survival and differentiation of MSCs seeded in scaffolds. An agent-based model is developed to simulate the MSC behavior. The effect of vascular endothelial growth factor (VEGF) and bone morphogenic protein-2 (BMP-2) on both survival and osteogenic differentiation is studied. Results showed that the survival ratio of MSCs can be enhanced by increasing VEGF concentration. BMP-2 caused a slight increase on survival ratio. Osteogenesis strongly depends on the VEGF concentration as well because of its effect on vascularization. BMP-2 increased the osteogenic differentiation of MSCs.

Distinctive Capillary Action by Micro-channels in Bone-like Templates can Enhance Recruitment of Cells for Restoration of Large Bony Defect

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not occur. With conventional templates, the absence of internal micro-channels results in the lack of cell infiltration, distribution, and inhabitance deep inside the templates. Hence, a highly porous and uniformly interconnected trabecular-bone-like template with micro-channels (biogenic microenvironment template; BMT) has been developed to address these obstacles. The novel BMT was created by innovative concepts (capillary action) and fabricated with a sponge-template coating technique. The BMT consists of several structural components: inter-connected primary-pores (300-400 µm) that mimic pores in trabecular bone, micro-channels (25-70 µm) within each trabecula, and nanopores (100-400 nm) on the surface to allow cells to anchor. Moreover, the BMT has been documented by mechanical test study to have similar mechanical strength properties to those of human trabecular bone (~3.8 MPa)¹².

The BMT exhibited high absorption, retention, and habitation of cells throughout the bridge-shaped (Π) templates (3 cm height and 4 cm length). The cells that were initially seeded into one end of the templates immediately mobilized to the other end (10 cm distance) by capillary action of the BMT on the cell media. After 4 hr, the cells homogenously occupied the entire BMT and exhibited normal cellular behavior. The capillary action accounted for the infiltration of the cells suspended in the media and the distribution (active migration) throughout the BMT. Having observed these capabilities of the BMT, we project that BMTs will absorb bone marrow cells, growth factors, and nutrients from the periphery under physiological conditions.

The BMT may resolve current limitations via rapid infiltration, homogenous distribution and inhabitance of cells in large, volumetric templates to repair massive skeletal defects.

Comparative study of membranes induced by PMMA or silicone in rats, and influence of external radiotherapy

The induced membrane technique has been used for long bone defect reconstruction after traumatism. One of the major drawbacks of this method is the difficult removal of the polymethyl methacrylate spacer after membrane formation. We therefore replaced the stiff PMMA spacer with a semi-flexible medical grade silicone spacer. This study aimed to compare subcutaneously formed membranes, induced by PMMA and silicone, in the irradiated or not irradiated areas within 28 rats that received the spacers. Histological analysis was performed to evaluate the composition of the membrane and to quantify the amount of vessels. Histomorphometric measurements were used to evaluate membranes' thickness, while fibrosis and inflammation were scored. The expression of VEGF and BMP-2 in lysates of the crushed membranes was determined by Western blotting. ALP expression was analyzed in HBMSC cultures in contact with the same lysates. Non-irradiated membranes induced by the two spacer types were non-inflammatory, fibrous and organized in layers. Irradiation did not change the macroscopic properties of membranes that were induced by silicone, while PMMA induced membranes were sensitive to the radiotherapy, resulting in thicker, strongly inflammatory membranes. Irradiated membranes showed an overall reduced osteogenic potential. Medical grade silicone is safe for the use in radiotherapy and might therefore be of great advantage for patients in need of cancer treatment.

Evaluation of the osteoinductive potential of a bio-inspired scaffold mimicking the osteogenic niche for bone augmentation

Augmentation of regenerative osteogenesis represents a premier clinical need, as hundreds of thousands of patients are left with insufficient healing of bony defects related to a host of insults ranging from congenital abnormalities to traumatic injury to surgically-induced deficits. A synthetic material that closely mimics the composition and structure of the human osteogenic niche represents great potential to successfully address this high demand. In this study, a magnesium-doped hydroxyapatite/type I collagen scaffold was fabricated through a biologically-inspired mineralization process and designed to mimic human trabecular bone. The composition of the scaffold was fully characterized by XRD, FTIR, ICP and TGA, and compared to human bone. Also, the scaffold microstructure was evaluated by SEM, while its nano-structure and nano-mechanical properties were evaluated by AFM. Human bone marrow-derived mesenchymal stem cells were used to test the in vitro capability of the scaffold to promote osteogenic differentiation. The cell/scaffold constructs were cultured up to 7 days and the adhesion, organization and proliferation of the cells were evaluated. The ability of the scaffold to induce osteogenic differentiation of the cells was assessed over 3 weeks and the correlate gene expression for classic genes of osteogenesis was assessed. Finally, when tested in an ectopic model in rabbit, the scaffold produced a large volume of trabecular bone in only two weeks, that subsequently underwent maturation over time as expected, with increased mature cortical bone formation, supporting its ability to promote bone regeneration in clinically-relevant scenarios. Altogether, these results confirm a high level of structural mimicry by the scaffold to the composition and structure of human osteogenic niche that translated to faster and more efficient osteoinduction in vivo--features that suggest such a biomaterial may have great utility in future clinical applications where bone regeneration is required.

Induced membrane for treatment of critical sized bone defect: a review of experimental and clinical experiences

PURPOSE

The purpose of this study was to review experimental and clinical experiences about the use of an induced membrane to address critical bone size defect of the limbs.

METHODS

From a review of published experimental and clinical data and from our clinical experience, we present the key data about the use of an induced membrane to address critical bone size defect of the limbs.

RESULTS

After reviewing the concept of critical sized bone defect, we present the different indications of an induced membrane, the key points of the surgical technique and the strategy of bone grafting given the indication, localization and importance of the critical sized bone defect. Finally, we discuss the perspective of the use of an induced membrane with various bone substitutes.

CONCLUSIONS

The use of an induced membrane to treat critical sized bone defects of the limbs is a simple, reliable and reproducible technique. Certain technical steps should be pointed out and observed with great caution in order to avoid any pitfalls. This technique will probably be a key step for facilitating bone inclusion of new bone substitutes proposed by recent bioengineering.

Different Culture Media Affect Proliferation, Surface Epitope Expression, and Differentiation of Ovine MSC

Orthopedic implants including engineered bone tissue are commonly tested in sheep. To avoid rejection of heterologous or xenogeneic cells, autologous cells are preferably used, that is, ovine mesenchymal stem cells (oMSC). Unlike human MSC, ovine MSC are not well studied regarding isolation, expansion, and characterization. Here we investigated the impact of culture media composition on growth characteristics, differentiation, and surface antigen expression of oMSC. The culture media varied in fetal calf serum (FCS) content and in the addition of supplements and/or additional epidermal growth factor (EGF). We found that FCS strongly influenced oMSC proliferation and that specific combinations of supplemental factors (MCDB-201, ITS-plus, dexamethasone, and L-ascorbic acid) determined the expression of surface epitopes. We compared two published protocols for oMSC differentiation towards the osteogenic, adipogenic, and chondrogenic fate and found (i) considerable donor to donor variations, (ii) protocol-dependent variations, and (iii) variations resulting from the preculture medium composition. Our results indicate that the isolation and culture of oMSC in different growth media are highly variable regarding oMSC phenotype and behaviour. Furthermore, variations from donor to donor critically influence growth rate, surface marker expression, and differentiation.

In vivo bone regeneration using tubular perfusion system bioreactor cultured nanofibrous scaffolds

The use of bioreactors for the in vitro culture of constructs for bone tissue engineering has become prevalent as these systems may improve the growth and differentiation of a cultured cell population. Here we utilize a tubular perfusion system (TPS) bioreactor for the in vitro culture of human mesenchymal stem cells (hMSCs) and implant the cultured constructs into rat femoral condyle defects. Using nanofibrous electrospun poly(lactic-co-glycolic acid)/poly(ε-caprolactone) scaffolds, hMSCs were cultured for 10 days in vitro in the TPS bioreactor with cellular and acellular scaffolds cultured statically for 10 days as a control. After 3 and 6 weeks of in vivo culture, explants were removed and subjected to histomorphometric analysis. Results indicated more rapid bone regeneration in defects implanted with bioreactor cultured scaffolds with a new bone area of 1.23 ± 0.35 mm(2) at 21 days compared to 0.99 ± 0.43 mm(2) and 0.50 ± 0.29 mm(2) in defects implanted with statically cultured scaffolds and acellular scaffolds, respectively. At the 21 day timepoint, statistical differences (p<0.05) were only observed between defects implanted with cell containing scaffolds and the acellular control. After 42 days, however, defects implanted with TPS cultured scaffolds had the greatest new bone area with 1.72 ± 0.40 mm(2). Defects implanted with statically cultured and acellular scaffolds had a new bone area of 1.26 ± 0.43 mm(2) and 1.19 ± 0.33 mm(2), respectively. The increase in bone growth observed in defects implanted with TPS cultured scaffolds was statistically significant (p<0.05) when compared to both the static and acellular groups at this timepoint. This study demonstrates the efficacy of the TPS bioreactor to improve bone tissue regeneration and highlights the benefits of utilizing perfusion bioreactor systems to culture MSCs for bone tissue engineering.