Development and characterization of a PLGA-HA composite material to fabricate 3D-printed scaffolds for bone tissue engineering

Additive manufacturing is a rising field in bone tissue engineering. Additive fabrication offers reproducibility, high precision and rapid manufacture of custom patient-specific scaffolds. The development of appropriate composite materials for biomedical applications is critical to reach clinical application of these novel biomaterials. In this work, medical grade poly(lactic-co-glycolic) acid (PLGA) was mixed with hydroxyapatite nanoparticles (nHA) to fabricate 3D porous scaffolds by Fused Deposition Modeling. We have first confirmed that the composite material could be printed in a reproductive manner. Physical characterization demonstrated a low degradation of the material during manufacturing steps and an expected loading and homogeneous distribution of nHA. In vitro biodegradation of the scaffolds showed modifications of morphological and physicochemical properties over time. The composite scaffolds were biocompatible and high cell viability was observed in vitro, as well as a maintain of cell proliferation. As expected, the addition of nHA displayed a positive impact on osteodifferentiation in vitro. Furthermore, a limited inflammatory reaction was observed after subcutaneous implantation of the materials in the rat. Overall, this study suggests that this composite material is suitable for bone tissue engineering applications.

A Unique Triculture Model to Study Osteoblasts, Osteoclasts, and Endothelial Cells

IMPACT STATEMENT

In this article, we first developed a new medium to culture together primary human osteoblastic, osteoclastic, and endothelial cells (ECs) chosen to represent the three major bone cell tissues. Indeed, no study has been conducted on primary human cells and on the phenotype/activity retention of these three primary human cell types. Thus, we established an original triculture model with osteoblastic, osteoclastic, and ECs, where not only both cell phenotype and cell activity were maintained but also cell culture homeostasis. These promising results will permit further investigations to create in vitro conditions to mimic the bone microenvironment and analyze cell interactions in ex vivo studies.

Human amniotic membrane for guided bone regeneration of calvarial defects in mice

Due to its biological properties, human amniotic membrane (hAM) is widely studied in the field of tissue engineering and regenerative medicine. hAM is already very attractive for wound healing and it may be helpful as a support for bone regeneration. However, few studies assessed its potential for guided bone regeneration (GBR). The purpose of the present study was to assess the potential of the hAM as a membrane for GBR. In vitro, cell viability in fresh and cryopreserved hAM was assessed. In vivo, we evaluated the impact of fresh versus cryopreserved hAM, using both the epithelial or the mesenchymal layer facing the defect, on bone regeneration in a critical calvarial bone defect in mice. Then, the efficacy of cryopreserved hAM associated with a bone substitute was compared to a collagen membrane currently used for GBR. In vitro, no statistical difference was observed between the conditions concerning cell viability. Without graft material, cryopreserved hAM induced more bone formation when the mesenchymal layer covered the defect compared to the defect left empty. When associated with a bone substitute, such improved bone repair was not observed. These preliminary results suggest that cryopreserved hAM has a limited potential for GBR.

Decellularized and matured esophageal scaffold for circumferential esophagus replacement: Proof of concept in a pig model

Surgical resection of the esophagus requires sacrificing a long portion of it. Its replacement by the demanding gastric pull-up or colonic interposition techniques may be avoided by using short biologic scaffolds composed of decellularized matrix (DM). The aim of this study was to prepare, characterize, and assess the in vivo remodeling of DM and its clinical impact in a preclinical model. A dynamic chemical and enzymatic decellularization protocol of porcine esophagus was set up and optimized. The resulting DM was mechanically and biologically characterized by DNA quantification, histology, and histomorphometry techniques. Then, in vitro and in vivo tests were performed, such as DM recellularization with human or porcine adipose-derived stem cells, or porcine stromal vascular fraction, and maturation in rat omentum. Finally, the DM, matured or not, was implanted as a 5-cm-long esophagus substitute in an esophagectomized pig model. The developed protocol for esophageal DM fulfilled previously established criteria of decellularization and resulted in a scaffold that maintained important biologic components and an ultrastructure consistent with a basement membrane complex. In vivo implantation was compatible with life without major clinical complications. The DM's scaffold in vitro characteristics and in vivo implantation showed a pattern of constructive remodeling mimicking major native esophageal characteristics.

Strontium-doped hydroxyapatite polysaccharide materials effect on ectopic bone formation

Previous studies performed using polysaccharide-based matrices supplemented with hydroxyapatite (HA) particles showed their ability to form in subcutaneous and intramuscular sites a mineralized and osteoid tissue. Our objectives are to optimize the HA content in the matrix and to test the combination of HA with strontium (Sr-HA) to increase the matrix bioactivity. First, non-doped Sr-HA powders were combined to the matrix at three different ratios and were implanted subcutaneously for 2 and 4 weeks. Interestingly, matrices showed radiolucent properties before implantation. Quantitative analysis of micro-CT data evidenced a significant increase of mineralized tissue formed ectopically with time of implantation and allowed us to select the best ratio of HA to polysaccharides of 30% (w/w). Then, two Sr-substitution of 8% and 50% were incorporated in the HA powders (8Sr-HA and 50Sr-HA). Both Sr-HA were chemically characterized and dispersed in matrices. In vitro studies performed with human mesenchymal stem cells (MSCs) demonstrated the absence of cytotoxicity of the Sr-doped matrices whatever the amount of incorporated Sr. They also supported osteoblastic differentiation and activated the expression of one late osteoblastic marker involved in the mineralization process i.e. osteopontin. In vivo, subcutaneous implantation of these Sr-doped matrices induced osteoid tissue and blood vessels formation.

Influence of External Beam Radiotherapy on the Properties of Polymethyl Methacrylate-Versus Silicone-Induced Membranes in a Bilateral Segmental Bone Defect in Rats

INTRODUCTION

Standard care for malignant tumors arising next to a bone structure is surgical removal with safety margins, followed by external beam radiotherapy (EBRT). Complete tumor removal can result in large bone defects. A two-step bone reconstruction technique using the induced membrane (IM) technique has proven its efficacy to bridge gap nonunion. During the first step, a spacer is placed in the bone gap. The spacer then is removed and the IM around it is filled with autologous cancellous bone graft. However, the feasibility of this technique with the addition of adjuvant EBRT between the two reconstruction steps has not yet been studied. Polymethyl methacrylate (PMMA) used to be the standard spacer material for the first step. Silicone spacers could replace them owing to their good behavior when submitted to EBRT and their easier removal from the surgical site during the second step. The aim of this study was to evaluate the influence of EBRT on the histological and biochemical properties of IM induced using PMMA or silicone as spacer.

MATERIALS AND METHODS

The analyses were performed on PMMA- or silicone-IM with and without EBRT in a 6-mm bilateral femoral defect in 32 rats. Thickness and vessel content were measured in both groups. Bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factor (VEGF) content in lysates of the crushed membranes were measured by enzyme immunoassay. Finally, alkaline phosphatase activity was analyzed in human bone marrow stromal cell cultures in contact with the same lysates.

RESULTS

EBRT did not change the histological structure of the cellular internal layer or the fibrous outer layer. The nature of the spacer only influenced IM thickness, PMMA-IM with external radiotherapy being significantly thicker. EBRT decreased the vascular density of IM but was less effective on VEGF/BMP2 production. In vitro, IM could have an osteoinductive potential on human bone marrow stem cells.

CONCLUSION

EBRT did not modify the histological properties of IMs but decreased their vascular density. VEGF and BMP2 production within IMs was not affected by EBRT. Silicone spacers are able to induce membranes with similar histological characteristics to PMMA-IM.

Layer-by-layer bioassembly of cellularized polylactic acid porous membranes for bone tissue engineering

The conventional tissue engineering is based on seeding of macroporous scaffold on its surface ("top-down" approach). The main limitation is poor cell viability in the middle of the scaffold due to poor diffusion of oxygen and nutrients and insufficient vascularization. Layer-by-Layer (LBL) bioassembly is based on "bottom-up" approach, which considers assembly of small cellularized blocks. The aim of this work was to evaluate proliferation and differentiation of human bone marrow stromal cells (HBMSCs) and endothelial progenitor cells (EPCs) in two and three dimensions (2D, 3D) using a LBL assembly of polylactic acid (PLA) scaffolds fabricated by 3D printing. 2D experiments have shown maintain of cell viability on PLA, especially when a co-cuture system was used, as well as adequate morphology of seeded cells. Early osteoblastic and endothelial differentiations were observed and cell proliferation was increased after 7 days of culture. In 3D, cell migration was observed between layers of LBL constructs, as well as an osteoblastic differentiation. These results indicate that LBL assembly of PLA layers could be suitable for BTE, in order to promote homogenous cell distribution inside the scaffold and gene expression specific to the cells implanted in the case of co-culture system.

The proangiogenic potential of a novel calcium releasing composite biomaterial: Orthotopic in vivo evaluation

Insufficient angiogenesis remains a major hurdle in current bone tissue engineering strategies. An extensive body of work has focused on the use of angiogenic factors or endothelial progenitor cells. However, these approaches are inherently complex, in terms of regulatory and methodologic implementation, and present a high cost. We have recently demonstrate the potential of electrospun poly(lactic acid) (PLA) fiber-based membranes, containing calcium phosphate (CaP) ormoglass particles, to elicit angiogenesis in vivo, in a subcutaneous model in mice. Here we have devised an injectable composite, containing CaP glass-ceramic particles, dispersed within a (Hydroxypropyl)methyl cellulose (HPMC) matrix, with the capacity to release calcium in a more sustained fashion. We show that by tuning the release of calcium in vivo, in a rat bone defect model, we could improve both bone formation and increase angiogenesis. The bone regeneration kinetics was dependent on the Ca²⁺ release rate, with the faster Ca²⁺ release composite gel showing improved bone repair at 3weeks, in relation to control. In the same line, improved angiogenesis could be observed for the same gel formulation at 6weeks post implantation. This methodology allows to integrate two fundamental processes for bone tissue regeneration while using a simple, cost effective, and safe approach.

STATEMENT OF SIGNIFICANCE

In current bone tissue engineering approaches the achievement of sufficient angiogenesis, during tissue regeneration, is a major limitation in order to attain full tissue functionality. Recently, we have shown that calcium ions, released by the degradation of calcium phosphate ormoglasses (CaP), are effective angiogenic promoters, in both in vitro and in a subcutaneous implantation model. Here, we devised an injectable composite, containing CaP glass-ceramic particles, dispersed within a HPMC matrix, enabling the release of calcium in a more sustained fashion. We show that by tuning the release of calcium in vivo, in a rat bone defect model, we could improve both bone formation and increase angiogenesis. This simple and cost effective approach holds great promise to translate to the clinics.

Preventive actions to avoid questionable research practices. Use of EERM (Ethical and Efficient Research Management) during Arrival and Departure of a co-worker★

Preventive actions for scientific misconduct and questionable research practice must be taken at an institutional level but also by scientists themselves as part of their role of science managers. We have proposed the concept of “Ethical and Efficient Research Management” and a panoply of easy to use tools which are designed to favour ethical behaviour, sound data and robust methods. Through the example of the processes “Arrival” and “Departure of a co-worker”, we show here that flow charts can help visualize critical steps in an activity and how to manage these steps in an ethical and efficient way.

The proangiogenic potential of a novel calcium releasing biomaterial: Impact on cell recruitment

In current bone tissue engineering strategies the achievement of sufficient angiogenesis during tissue regeneration is still a major limitation in order to attain full functionality. Several strategies have been described to tackle this problem, mainly by the use of angiogenic factors or endothelial progenitor cells. However, when facing a clinical scenario these approaches are inherently complex and present a high cost. As such, more cost effective alternatives are awaited. Here, we demonstrate the potential of electrospun poly(lactic acid) (PLA) fiber-based membranes, containing calcium phosphate ormoglass (CaP) particles, to elicit angiogenesis in vivo, in a subcutaneous model in mice. We show that the current approach elicited the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial. As both PLA and CaP are currently accepted for clinical application these off-the-shelf novel membranes have great potential for guided bone regeneration applications.

STATEMENT OF SIGNIFICANCE

In current bone tissue engineering approaches the achievement of sufficient angiogenesis, during tissue regeneration, is a major limitation in order to attain full tissue functionality. Recently, our group has found that calcium ions released by the degradation of calcium phosphate ormoglasses (CaP) are effective angiogenic promoters. Based on this, in this work we successfully produced hybrid fibrous mats with different contents of CaP nanoparticles and thus with different calcium ion release rates, using an ormoglass - poly(lactic acid) blend approach. We show that these matrices, upon implantation in a subcutaneous site, could elicit the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial, in a CaP dose dependent manner. This off-the-shelf cost effective approach presents great potential to translate to the clinics.

Colorectal tissue engineering: A comparative study between porcine small intestinal submucosa (SIS) and chitosan hydrogel patches

OBJECTIVE

Tissue engineering may provide new operative tools for colorectal surgery in elective indications. The aim of this study was to define a suitable bioscaffold for colorectal tissue engineering.

METHODS

We compared 2 bioscaffolds with in vitro and in vivo experiments: porcine small intestinal submucosa (SIS) versus chitosan hydrogel matrix. We assessed nontoxicity of the scaffold in vitro by using human adipose-derived stem cells (hADSC). In vivo, a 1 × 2-cm colonic wall defect was created in 16 rabbits. Animals were divided randomly into 2 groups according to the graft used, SIS or chitosan hydrogel. Graft area was explanted at 4 and 8 weeks. The end points of in vivo experiments were technical feasibility, behavior of the scaffold, in situ putative inflammatory effect, and the quality of tissue regeneration, in particular smooth muscle layer regeneration.

RESULTS

In vitro, hADSC attachment and proliferation occurred on both scaffolds without a substantial difference. After proliferation, hADSCs kept their mesenchymal stem cell characteristics. In vivo, one animal died in each group. Eight weeks after implantation, the chitosan scaffold allowed better wound healing compared with the SIS scaffold, with more effective control of inflammatory activity and an integral regeneration of the colonic wall including the smooth muscle cell layer.

CONCLUSION

The outcomes of in vitro experiments did not differ greatly between the 2 groups. Macroscopic and histologic findings, however, revealed better wound healing of the colonic wall in the chitosan group suggesting that the chitosan hydrogel could serve as a better scaffold for colorectal tissue engineering.

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.

The use of total human bone marrow fraction in a direct three-dimensional expansion approach for bone tissue engineering applications: focus on angiogenesis and osteogenesis

Current approaches in bone tissue engineering have shown limited success, mostly owing to insufficient vascularization of the construct. A common approach consists of co-culture of endothelial cells and osteoblastic cells. This strategy uses cells from different sources and differentiation states, thus increasing the complexity upstream of a clinical application. The source of reparative cells is paramount for the success of bone tissue engineering applications. In this context, stem cells obtained from human bone marrow hold much promise. Here, we analyzed the potential of human whole bone marrow cells directly expanded in a three-dimensional (3D) polymer matrix and focused on the further characterization of this heterogeneous population and on their ability to promote angiogenesis and osteogenesis, both in vitro and in vivo, in a subcutaneous model. Cellular aggregates were formed within 24 h and over the 12-day culture period expressed endothelial and bone-specific markers and a specific junctional protein. Ectopic implantation of the tissue-engineered constructs revealed osteoid tissue and vessel formation both at the periphery and within the implant. This work sheds light on the potential clinical use of human whole bone marrow for bone regeneration strategies, focusing on a simplified approach to develop a direct 3D culture without two-dimensional isolation or expansion.

The gene expression of human endothelial cells is modulated by subendothelial extracellular matrix proteins: short-term response to laminar shear stress

Vascular surgery for atherosclerosis is confronted by the lack of a suitable bypass material. Tissue engineering strives to produce bio-artificial conduits to provide resistance to thrombosis. The objectives of our study were to culture endothelial cells (EC) on composite assemblies of extracellular matrix proteins, and to evaluate the cellular phenotype under flow. Cell-adhesive assemblies were fabricated on glass slides as combinations of collagen (Co), laminin (LM), and fibronectin (FN), resulting in three samples: Co, Co/LM, and Co/FN. Surface topography, roughness, and wettability were determined. Human saphenous vein EC were harvested from cardiac patients, cultured on the assemblies and submitted to laminar shear stress (SS) of 12 dyn/cm(2) for 40, 80, and 120 min. Cell retention was assessed and qRT-PCR of adhesion genes (VE-cadherin, vinculin, KDR, CD-31 or PECAM-1, β1-integrins) and metabolic genes (t-PA, NF-κB, eNOS and MMP-1) was performed. Quantitative immunofluorescence of VE cadherin, vinculin, KDR, and vonWillebrand factor was performed after 2 and 6 h of flow. Static samples were excluded from shearing. The cells reached confluence with similar growth curves. The cells on Co/LM and Co/FN were resistant to flow up to 120 min but minor desquamation occurred on Co corresponding with temporary downregulation of VE cadherin and vinculin-mRNA and decreased fluorescence of vinculin. The cells seeded on Co/LM initially more upregulated vinculin-mRNA and also the inflammatory factor NF-κB, and the cells plated on Co/FN changed the expression profile minimally in comparison with the static control. Fluorescence of VE cadherin and vonWillebrand factor was enhanced on Co/FN. The cells cultured on Co/LM and Co/FN increased the vinculin fluorescence and expressed more VE cadherin and KDR-mRNA than the cells on Co. The cells plated on Co/FN upregulated the mRNA of VE cadherin, CD-31, and MMP 1 to a greater extent than the cells on Co/LM and they enhanced the fluorescence of VE cadherin, KDR, and vonWillebrand factor. Some of these changes sustained up to 6 h of flow, as confirmed by immunofluorescence. Combined matrices Co/LM and Co/FN seem to be more suitable for EC seeding and retention under flow. Moreover, Co/FN matrix promoted slightly more favorable cellular phenotype than Co/LM under SS of 2-6 h.

Attachment of human endothelial cells to polyester vascular grafts: pre-coating with adhesive protein assemblies and resistance to short-term shear stress

Cardiovascular prosthetic bypass grafts do not endothelialize spontaneously in humans, and so they pose a thrombotic risk. Seeding with cells improves their performance, particularly in small-caliber applications. Knitted tubular polyethylene-terephthalate (PET) vascular prostheses (6 mm) with commercial type I collagen (PET/Co) were modified in the lumen by the adsorption of laminin (LM), by coating with a fibrin network (Fb) or a combination of Fb and fibronectin (Fb/FN). Primary human saphenous vein endothelial cells were seeded (1.50 × 10(5)/cm2), cultured for 72 h and exposed to laminar shear stress 15 dyn/cm(2) for 40 and 120 min. The control static grafts were excluded from shearing. The cell adherence after 4 h on PET/Co, PET/Co +LM, PET/Co +Fb and PET/Co +Fb/FN was 22%, 30%, 19% and 27% of seeding, respectively. Compared to the static grafts, the cell density on PET/Co and PET/Co +LM dropped to 61% and 50%, respectively, after 120 min of flow. The cells on PET/Co +Fb and PET/Co +Fb/FN did not show any detachment during 2 h of shear stress. Pre-coating the clinically-used PET/Co vascular prosthesis with LM or Fb/FN adhesive protein assemblies promotes the adherence of endothelium. Cell retention under flow is improved particularly on fibrin-containing (Fb and Fb/FN) surfaces.

Attachment of human endothelial cells to polyester vascular grafts: pre-coating with adhesive protein assemblies and resistance to short-term shear stress

Cardiovascular prosthetic bypass grafts do not endothelialize spontaneously in humans, and so they pose a thrombotic risk. Seeding with cells improves their performance, particularly in small-caliber applications. Knitted tubular polyethylene-terephthalate (PET) vascular prostheses (6 mm) with commercial type I collagen (PET/Co) were modified in the lumen by the adsorption of laminin (LM), by coating with a fibrin network (Fb) or a combination of Fb and fibronectin (Fb/FN). Primary human saphenous vein endothelial cells were seeded (1.50 × 10(5)/cm2), cultured for 72 h and exposed to laminar shear stress 15 dyn/cm(2) for 40 and 120 min. The control static grafts were excluded from shearing. The cell adherence after 4 h on PET/Co, PET/Co +LM, PET/Co +Fb and PET/Co +Fb/FN was 22%, 30%, 19% and 27% of seeding, respectively. Compared to the static grafts, the cell density on PET/Co and PET/Co +LM dropped to 61% and 50%, respectively, after 120 min of flow. The cells on PET/Co +Fb and PET/Co +Fb/FN did not show any detachment during 2 h of shear stress. Pre-coating the clinically-used PET/Co vascular prosthesis with LM or Fb/FN adhesive protein assemblies promotes the adherence of endothelium. Cell retention under flow is improved particularly on fibrin-containing (Fb and Fb/FN) surfaces.

Composition and properties of silver-containing calcium carbonate-calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate-calcium phosphate (CaCO3-CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO3-CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.

IQ domain GTPase-activating protein 1 is involved in shear stress-induced progenitor-derived endothelial cell alignment

Shear stress is one of mechanical constraints which are exerted by blood flow on endothelial cells (ECs). To adapt to shear stress, ECs align in the direction of flow through adherens junction (AJ) remodeling. However, mechanisms regulating ECs alignment under shear stress are poorly understood. The scaffold protein IQ domain GTPase activating protein 1 (IQGAP1) is a scaffold protein which couples cell signaling to the actin and microtubule cytoskeletons and is involved in cell migration and adhesion. IQGAP1 also plays a role in AJ organization in epithelial cells. In this study, we investigated the potential IQGAP1 involvement in the endothelial cells alignment under shear stress. Progenitor-derived endothelial cells (PDECs), transfected (or not) with IQGAP1 small interfering RNA, were exposed to a laminar shear stress (1.2 N/m(2)) and AJ proteins (VE-cadherin and β-catenin) and IQGAP1 were labeled by immunofluorescence. We show that IQGAP1 is essential for ECs alignment under shear stress. We studied the role of IQGAP1 in AJs remodeling of PDECs exposed to shear stress by studying cell localization and IQGAP1 interactions with VE-cadherin and β-catenin by immunofluorescence and Proximity Ligation Assays. In static conditions, IQGAP1 interacts with VE-cadherin but not with β-catenin at the cell membrane. Under shear stress, IQGAP1 lost its interaction from VE-cadherin to β-catenin. This "switch" was concomitant with the loss of β-catenin/VE-cadherin interaction at the cell membrane. This work shows that IQGAP1 is essential to ECs alignment under shear stress and that AJ remodeling represents one of the mechanisms involved. These results provide a new approach to understand ECs alignment under to shear stress.

Cell interactions between human progenitor-derived endothelial cells and human mesenchymal stem cells in a three-dimensional macroporous polysaccharide-based scaffold promote osteogenesis

Several studies have reported the benefits of mesenchymal stem cells (MSCs) for bone tissue engineering. However, vascularization remains one of the main obstacles that must be overcome to reconstruct large bone defects. In vitro prevascularization of the three-dimensional (3-D) constructs using co-cultures of human progenitor-derived endothelial cells (PDECs) with human bone marrow mesenchymal stem cells (HBMSCs) appeared as a potential strategy. However, the crosstalk between the two lineages has been studied in two-dimensional (2-D), but remains unknown in 3-D. The aim of this study is to investigate the cell interactions between PDECs and HBMSCs in a porous matrix composed of polysaccharides. This biodegradable scaffold promotes cell interactions by inducing multicellular aggregates composed of HBMSCs surrounded by PDECs. Cell aggregation contributes to the formation of junctional proteins composed of Connexin43 (Cx43) and VE-cadherin, and an activation of osteoblastic differentiation of HBMSCs stimulated by the presence of PDECs. Inhibition of Cx43 by mimetic peptide 43GAP27 induced a decrease in mRNA levels of Cx43 and all the bone-specific markers. Finally, subcutaneous implantations for 3 and 8 weeks in NOG mice revealed an increase in osteoid formation with the tissue-engineered constructs seeded with HBMSCs/PDECs compared with those loaded with HBMSCs alone. Taking together, these results demonstrate that this 3-D microenvironment favored cell communication, osteogenesis and bone formation.

A nano-hydroxyapatite--pullulan/dextran polysaccharide composite macroporous material for bone tissue engineering

Research in bone tissue engineering is focused on the development of alternatives to allogenic and autologous bone grafts that can stimulate bone healing. Here, we present scaffolds composed of the natural hydrophilic polysaccharides pullulan and dextran, supplemented or not with nanocrystalline hydroxyapatite particles (nHA). In vitro studies revealed that these matrices induced the formation of multicellular aggregates and expression of early and late bone specific markers with human bone marrow stromal cells in medium deprived of osteoinductive factors. In absence of any seeded cells, heterotopic implantation in mice and goat, revealed that only the composite macroporous scaffold (Matrix + nHA) (i) retained subcutaneously local growth factors, including Bone Morphogenetic Protein 2 (BMP2) and VEGF165, (ii) induced the deposition of a biological apatite layer, (iii) favored the formation of a dense mineralized tissue subcutaneously in mice, as well osteoid tissue after intramuscular implantation in goat. The composite scaffold was thereafter implanted in orthotopic preclinical models of critical size defects, in small and large animals, in three different bony sites, i.e. the femoral condyle of rat, a transversal mandibular defect and a tibial osteotomy in goat. The Matrix + nHA induced a highly mineralized tissue in the three models whatever the site of implantation, as well as osteoid tissue and bone tissue regeneration in direct contact to the matrix. We therefore propose this composite matrix as a material for stimulating bone cell differentiation of host mesenchymal stem cells and bone formation for orthopedic and maxillofacial surgical applications.

Interaction between a bisphosphonate, tiludronate and nanocrystalline apatite: in vitro viability and proliferation of HOP and HBMSC cells

Nanocrystalline apatites (NCA) are the inorganic components of mineralized tissues and they have been recently proposed as biomaterials for drug delivery systems. Bisphosphonates (BPs) are currently the reference drugs used to treat diseases involving bone disorders such as osteoporosis. Nevertheless, the interaction phenomena between BP molecules and apatite nanocrystals of bone are not well understood. Therefore, the adsorption characteristics have been examined and cellular activity of tiludronate molecules on NCA as models of bone mineral has been investigated. Adsorption experiments of tiludronate onto NCA were carried out and revealed a Langmuir-type adsorption isotherm. The uptake of tiludronate molecules is associated with a release of phosphate ions, indicating that the main reaction is an ion exchange process involving surface anions. The results evidence the strong affinity of BP molecules for the apatitic surface. The interactions of NCA-tiludronate associations with human osteoprogenitor cells and human bone marrow stromal cells do not reveal any cytotoxicity and evidence the activity of adsorbed tiludronate molecules. Moreover, an evolution of the physico-chemical characteristics of the apatitic substrate during biological study was observed, highlighting the existence of dynamic interactions. This work contributes to clarifying the reaction mechanisms between BPs and biomimetic apatites.

Whatever their differentiation status, human progenitor derived - or mature - endothelial cells induce osteoblastic differentiation of bone marrow stromal cells

Association of the bone-forming osteoblasts (OBs) and vascular endothelial cells (ECs) into a biomaterial composite provides a live bone graft substitute that can repair the bone defect when implanted. An intimate functional relationship exists between these cell types. This communication is crucial to the coordinated cell behaviour necessary for bone development and remodelling. Previous studies have shown that direct co-culture of primary human osteoprogenitors (HOPs) with primary human umbilical vein endothelial cells (HUVECs) stimulates HOPs differentiation and induces tubular-like networks. The present work aims to test the use of human bone marrow stromal cells (HBMSCs) co-cultured with human endothelial progenitor cells in order to assess whether progenitor-derived ECs (PDECs) could support osteoblastic differentiation as mature ECs do. Indeed, data generated from the literature by different laboratories considering these co-culture systems appear difficult to compare. Monocultures of HUVECs, HOPs, HBMSCs (in a non-orientated lineage), PDECs (from cord blood) were used as controls and four combinations of co-cultures were undertaken: HBMSCs-PDECs, HBMSCs-HUVECs, HOPs-PDECs, HOPs-HUVECs with ECs (mature or progenitor) for 6 h to 7 days. At the end of the chosen co-culture time, intracellular alkaline phosphatase (ALP) activity was detected in HOPs and HBMSCs and quantified in cell extracts. Quantitative real-time polymerase chain reaction (qPCR) of ALP was performed over time and vascular endothelial growth factor (VEGF) was measured. After 21 days, calcium deposition was observed, comparing mono- and co-cultures. We confirm that ECs induce osteoblastic differentiation of mesenchymal stem cells in vitro. Moreover, HUVECs can be replaced by PDECs, the latter being of great interest in tissue engineering.

Altered nanofeature size dictates stem cell differentiation

The differentiation of stem cells can be modulated by physical factors such as the micro- and nano-topography of the extracellular matrix. One important goal in stem cell research is to understand the concept that directs differentiation into a specific cell lineage in the nanoscale environment. Here, we demonstrate that such paths exist by controlling only the micro- and nano-topography of polymer surfaces. Altering the depth (on a nanometric scale) of micro-patterned surface structures allowed increased adhesion of human mesenchymal stem cells (hMSCs) with specific differentiation into osteoblasts, in the absence of osteogenic medium. Small (10 nm) depth patterns promoted cell adhesion without noticeable differentiation, whereas larger depth patterns (100 nm) elicited a collective cell organization, which induced selective differentiation into osteoblast-like cells. This latter response was dictated by stress through focal-adhesion-induced reorganization of F-actin filaments. The results have significant implications for understanding the architectural effects of the in vivo microenvironment and also for the therapeutic use of stem cells.

Carbon nanotubes have a deleterious effect on the nose: the first in vitro data

BACKGROUND

The information currently available concerning carbon nanotubes toxicity is disturbing and conflicting. Moreover, little is known about their effect on the nasal cavities, which are the first target for nanoparticles.

MATERIAL AND METHOD

We investigated the cytotoxicity (50 to 0.5 microg/mL) of double-walled carbon nanotube with two independent tests (MTT, Wst-1) on normal human nasal epithelial cells after 12-day exposure (control untreated nasal cells and A549). Nasal cell differentiation function, oxidative stress, the morphological features of cells in contact with DWCNTs and the localizations of the latter were also investigated.

RESULTS

Exposure revealed a dose-dependent decrease in cell metabolic activity and cell growth. In nearly all conditions, normal human nasal epithelial cells were more sensitive than malignant ones. Even with both tests, the cytotoxic threshold dose could not be accurately determined because of dye adsorption by DWCNTs. Nasal cells showed stronger cytokeratin 7 and persistent UEA-I immunostaining. Cytokeratin 19 production was increased at 25 microg/mL and mucus production was stimulated from 0.5 microg/mL. A significant increase in Reactive Oxygen Species was observed from 25 microg/mL. The cell plasma membrane showed several holes and DWCNTs were present in the cytoplasm.

CONCLUSION

DWCNTs seem to have a deleterious effect on nasal cells after 12-day exposure.

Magnetic resonance imaging tracking of human adipose derived stromal cells within three-dimensional scaffolds for bone tissue engineering

For bone tissue engineering, human Adipose Derived Stem Cells (hADSCs) are proposed to be associated with a scaffold for promoting bone regeneration. After implantation, cellularised scaffolds require a non-invasive method for monitoring their fate in vivo. The purpose of this study was to use Magnetic Resonance Imaging (MRI)-based tracking of these cells, labelled with magnetic agents for in vivo longitudinal assessment. hADSCs were isolated from adipose tissue and labelled with USPIO-rhodamine (Ultrasmall SuperParamagnetic Iron Oxide). USPIO internalisation, absence of toxicity towards hADSCs, and osteogenic differentiation of the labelled cells were evaluated in standard culture conditions. Labelled cells were then seeded within a 3D porous polysaccharide-based scaffold and imaged in vitro using fluorescence microscopy and MRI. Cellularised scaffolds were implanted subcutaneously in nude mice and MRI analyses were performed from 1 to 28 d after implantation. In vitro, no effect of USPIO labelling on cell viability and osteogenic differentiation was found. USPIO were efficiently internalised by hADSCs and generated a high T2* contrast. In vivo MRI revealed that hADSCs remain detectable until 28 d after implantation and could migrate from the scaffold and colonise the area around it. These data suggested that this scaffold might behave as a cell carrier capable of both holding a cell fraction and delivering cells to the site of implantation. In addition, the present findings evidenced that MRI is a reliable technique to validate cell-seeding procedures in 3D porous scaffolds, and to assess the fate of hADSCs transplanted in vivo.

Human progenitor-derived endothelial cells vs. venous endothelial cells for vascular tissue engineering: an in vitro study

The isolation of endothelial progenitor cells from human peripheral blood generates a great hope in vascular tissue engineering because of particular benefit when compared with mature endothelial cells. We explored the capability of progenitor-derived endothelial cells (PDECs) to line fibrin and collagen scaffolds in comparison with human saphenous and umbilical cord vein endothelial cells (HSVECs and HUVECs): (a) in a static situation, allowing definition of the optimal cell culture conditions with different media and cell-seeding densities to check cell behaviour; (b) under shear stress conditions (flow chambers or tubular vascular constructs), allowing investigation of cell response and mRNA expression on both substrates by oligonucleotide microarray analysis and quantitative real-time PCR. Well characterized PDECs: (a) could not be expanded adequately with the usual mature ECs culture media; (b) were able to colonize and grow on fibrin glue; (c) exhibited higher resistance to oxidative stress than HSVECs and HUVECs; (d) withstood physiological shear stress when lining both substrates in flow chambers, and their gene expression was regulated; (e) colonized a collagen-impregnated vascular prosthesis and were able to sense mechanical forces. Our results provide an improved qualification of PDECs for vascular tissue engineering.

The role of vascular actors in two dimensional dialogue of human bone marrow stromal cell and endothelial cell for inducing self-assembled network

Angiogenesis is very important for vascularized tissue engineering. In this study, we found that a two-dimensional co-culture of human bone marrow stromal cell (HBMSC) and human umbical vein endothelial cell (HUVEC) is able to stimulate the migration of co-cultured HUVEC and induce self-assembled network formation. During this process, expression of vascular endothelial growth factor (VEGF₁₆₅) was upregulated in co-cultured HBMSC. Meanwhile, VEGF₁₆₅-receptor2 (KDR) and urokinase-type plasminogen activator (uPA) were upregulated in co-cultured HUVEC. Functional studies show that neutralization of VEGF₁₆₅ blocked the migration and the rearrangement of the cells and downregulated the expression of uPA and its receptor. Blocking of vascular endothelial-cadherin (VE-cad) did not affect the migration of co-cultured HUVEC but suppressed the self-assembled network formation. In conclusion, co-cultures upregulated the expression of VEGF₁₆₅ in co-cultured HBMSC; VEGF₁₆₅ then activated uPA in co-cultured HUVEC, which might be responsible for initiating the migration and the self-assembled network formation with the participation of VE-cad. All of these results indicated that only the direct contact of HBMSC and HUVEC and their respective dialogue are sufficient to stimulate secretion of soluble factors and to activate molecules that are critical for self-assembled network formation which show a great application potential for vascularization in tissue engineering.

Role of neural-cadherin in early osteoblastic differentiation of human bone marrow stromal cells cocultured with human umbilical vein endothelial cells

In our previous studies, roles of gap junction and vascular endothelial growth factor in the cross-talking of human bone marrow stromal cells (HBMSCs) and human umbilical vein endothelial cells (HUVECs) have been extensively studied. The present study focused on the investigation of the roles of neural (N)-cadherin in early differentiation of HBMSCs in direct-contact cocultures with HUVECs for 24 and 48 h. Quantitative real-time polymerase chain reaction, immunofluorescence, Western blot, as well as functional studies were applied to perform the studies at both protein and gene levels. Results showed that cocultured cells expressed much higher N-cadherin than monocultured cells after 24 and 48 h of culture. We observed that N-cadherin concentrated in the membrane of cocultured HBMSCs (co-HBMSCs) while distributed within the cytoplasm of monocultured HBMSCs, which indicated that the cell-cell adhesion was improved between cocultured cells. In addition, more beta-catenin was found to translocate into the cocultured cells nuclei and more T cell factor-1 (TCF-1) were detected in cocultured cells than in the monocultured cells. Moreover, mRNA levels of early osteoblastic markers including alkaline phosphatase (ALP) and type I collagen (Col-I) of co-HBMSCs were significantly upregulated, whereas neutralization of N-cadherin led to a downregulation of ALP and Col-I in both of the HBMSCs and co-HBMSCs compared with untreated cells. Taking our findings together it can be concluded that cocultures of HBMSCs with HUVECs increased N-cadherin expression and improved cell-cell adhesion. Whether this applies only to osteoprogenitor cells or to all the cell types in the culture will need to be determined by further studies. Subsequently, signaling transduction might be induced with the participation of beta-catenin and TCF-1. With the N-cadherin-mediated cell-cell adhesion and signaling transductions, the early osteoblastic differentiation of co-HBMSCs was significantly upregulated.

Laser assisted bioprinting of engineered tissue with high cell density and microscale organization

Over this decade, cell printing strategy has emerged as one of the promising approaches to organize cells in two and three dimensional engineered tissues. High resolution and high speed organization of cells are some of the key requirements for the successful fabrication of cell-containing two or three dimensional constructs. So far, none of the available cell printing technologies has shown an ability to concomitantly print cells at a cell-level resolution and at a kHz range speed. We have studied the effect of the viscosity of the bioink, laser energy, and laser printing speed on the resolution of cell printing. Accordingly, we demonstrate that a laser assisted cell printer can deposit cells with a microscale resolution, at a speed of 5 kHz and with computer assisted geometric control. We have successfully implemented such a cell printing precision to print miniaturized tissue like layouts with de novo high cell density and micro scale organization.

High-throughput laser printing of cells and biomaterials for tissue engineering

In parallel with ink-jet printing and bioplotting, biological laser printing (BioLP) using laser-induced forward transfer has emerged as an alternative method in the assembly and micropatterning of biomaterials and cells. This paper presents results of high-throughput laser printing of a biopolymer (sodium alginate), biomaterials (nano-sized hydroxyapatite (HA) synthesized by wet precipitation) and human endothelial cells (EA.hy926), thus demonstrating the interest in this technique for three-dimensional tissue construction. A rapid prototyping workstation equipped with an IR pulsed laser (tau=30 ns, lambda=1064 nm, f=1-100 kHz), galvanometric mirrors (scanning speed up to 2000 mm s(-1)) and micrometric translation stages (x, y, z) was set up. The droplet generation process was controlled by monitoring laser fluence, focalization conditions and writing speed, to take into account its mechanism, which is driven mainly by bubble dynamics. Droplets 70 microm in diameter and containing around five to seven living cells per droplet were obtained, thereby minimizing the dead volume of the hydrogel that surrounds the cells. In addition to cell transfer, the potential of using high-throughput BioLP for creating well-defined nano-sized HA patterns is demonstrated. Finally, bioprinting efficiency criteria (speed, volume, resolution, integrability) for the purpose of tissue engineering are discussed.

Polyelectrolyte multilayer films allow seeded human progenitor-derived endothelial cells to remain functional under shear stress in vitro

There is considerable interest in making multilayer films for various applications, among which are cell contacting biomaterials, allowing new opportunities to prepare functionalized biomaterials. In this study we have explored the capability of poly(sodium-4-styrene sulfonate)/poly(allylamine hydrochloride) polyelectrolyte multilayer films (PMFs) as functional coatings for human progenitor-derived endothelial cells (PDECs), since the latter are a potential source of endothelial-type cells to be used in bioartificial vascular substitutes. We performed investigations with PDECs derived from peripheral blood and characterized as endothelial cells. After forming a confluent monolayer on PMFs they were exposed to laminar pulsatile physiological shear stress. We investigated whether PDECs were able to withstand shear stress and to respond at the mRNA (microarray analysis) and protein levels (thrombomodulin and tissue factor functional activity), in comparison with collagen I and fibrin glue used as controls. After shear stress the PDECs remained spread on the substrates, with a resulting increase in the number of expressed genes. Considering the functional significance of our findings for the regulation of coagulation and fibrinolytic factors, mRNA tissue plasminogen activator and thrombomodulin, profibrinolytic and thrombin inhibiting respectively, were overexpressed in PDECs after 6h shear stress. von Willebrand factor showed down-regulation, while tissue factor was up-regulated. We can speculate that PMFs could favour anti-thrombogenic activity by PDECs because activated protein C generation, measuring thrombomodulin activity, was particularly high on PMFs, but unchanged after 6h shear stress. Thus, PMFs could represent suitable coatings able to provide functional surfaces for endothelialization with PDECs.

Biphasic calcium phosphate to repair nasal septum: the first in vitro and in vivo study

Our objective was to evaluate the cytocompatibility and biocompatibility of biphasic calcium phosphate (BCP) in the nasal respiratory airway. In vitro, the attachment rate was quantified on BCP disks with normal human epithelial cells at 1, 3 and 24 h by determining N-acetyl beta-D-hexosaminidase activity. Proliferative activity of cells was indirectly assessed by MTT assay at 3, 9, 15 and 21 days. Plastic surfaces were used as positive control. In vivo, 15 rabbits underwent anterior nasal septum perforation and 10 septa were repaired with BCP disks. Five non-implanted animals were sacrificed at 3 months. Two groups of five implanted animals were sacrificed at 1 and 2 months. The surface of new airway mucosa covering BCP disks was evaluated macroscopically. During both steps, light microscopy, immunohistochemistry and scanning electron microscopy were performed. Statistical analysis was performed with the Mann-Whitney U-test. In vitro, at 1 and 3 h, the attachment rates were significantly better than on the plastic surface (p < 10(-2)). Mitochondrial activity increased on both surfaces but began 6 days later than on plastic. After 21 days of culture, cells were confluent and formed a monolayer covering the implant even in the bottom of the pores. In vivo, no perforations in the control group closed spontaneously. The mean rate of closure was 63% in the 1 month group and 64% in the 2 month group (p > 0.05). Implants were invaded by inflammatory reaction covered by incomplete differentiated respiratory epithelium. Throughout the study, all immunohistochemical findings remained positive. These data suggest a good affinity between BCP and nasal epithelial cells. BCP could be used to rebuild nasal septa.

Absence of bone sialoprotein (BSP) impairs cortical defect repair in mouse long bone

Matrix proteins of the SIBLING family interact with bone cells and with bone mineral and are thus in a key position to regulate bone development, remodeling and repair. Within this family, bone sialoprotein (BSP) is highly expressed by osteoblasts, hypertrophic chondrocytes and osteoclasts. We recently reported that mice lacking BSP (BSP-/-) have very low trabecular bone turnover. In the present study, we set up an experimental model of bone repair by drilling a 1 mm diameter hole in the cortical bone of femurs in both BSP-/- and +/+ mice. A non-invasive MRI imaging and bone quantification procedure was designed to follow bone regeneration, and these data were extended by microCT imaging and histomorphometry on undecalcified sections for analysis at cellular level. These combined approaches revealed that the repair process as reflected in defect-refilling in the cortical area was significantly delayed in BSP-/- mice compared to +/+ mice. Concomitantly, histomorphometry showed that formation, mineralization and remodeling of repair (primary) bone in the medulla were delayed in BSP-/- mice, with lower osteoid and osteoclast surfaces at day 15. In conclusion, the absence of BSP delays bone repair at least in part by impairing both new bone formation and osteoclast activity.

Cyclo-DfKRG peptide modulates in vitro and in vivo behavior of human osteoprogenitor cells on titanium alloys

The first aim of the present study was to investigate the capacity of a cyclo-DfKRG-coated hydroxyapatite-titanium alloy (Ti-HA-RGD) to activate in vitro human osteoprogenitor cells adhesion and differentiation. The second purpose was to examine in vivo the role of a autologous cell seeding on cyclo-DfKRG-functionalized materials to provide bone repair after implantation in femoral condyle of rabbits. Our in vitro results have demonstrated that both titanium alloy functionalized with hydroxyapatite (Ti-HA-RGD and Ti-HA) contributed to higher cell adhesion than titanium alloy alone respectively 85 and 55% vs 15% compared to tissue culture polystyrene after one hour of cell seeding. As for differentiation, after 3 days of culture, Ti-HA presented the highest increase of ALP mRNA of all surfaces studied. Ti-HA-RGD showed an intermediate value about half as high as Ti-HA. Moreover after 3 days, both Ti-HA and Ti-HA-RGD surfaces showed the highest increase of cbfa1 mRNA expression. Two weeks following implantation, in vivo findings revealed that percentage of lacunae contact observed with pre-cellularized Ti-HA-RGD samples remains significantly lower than with Ti-HA group (10.5+/-9.6 % vs 33.7+/-11.5 %, P<0.03). Meanwhile, RGD peptide coating had no significant additional effect on the bone implant contact and area. Moreover, histomorphometry analysis revealed that implantation of pre-cellularized RGD coated materials with ROP cells increased significantly peri-implant fibrous area (24+/-11.6% vs 3+/-1.7% for Ti-HA-RGD, P<0.02). RGD coatings demonstrated osteoblastic adhesion, differentiation and in vivo bone regeneration at most equivalent to HA coatings.