In vitro assessment of a collagen/alginate composite scaffold for regenerative endodontics.

AIM: To develop a biological scaffold that could be moulded to reproduce the geometry of a gutta-percha point with precision and allow the differentiation of mesenchymal stem cells into osteoblasts to be used as a regenerative endodontic material. METHODOLOGY: A collagen/alginate composite scaffold was cast into a sodium alginate mould to produce a gutta-percha point-like cone. Prior to gelation, the cone was seeded with human stem cells from the apical papilla (SCAPs) to evaluate cell/scaffold interactions. The reconstructed tissue was characterized after 8 days in culture. Elastic modulus, tissue compaction and cell differentiation were assessed. Student t-tests and the Mann-Whitney U test were performed. RESULTS: The fabrication method developed enabled the shape of a gutta-percha point to be mimicked with great accuracy and reproducibility (P = 0.31). Stem cells seeded into this composite scaffold were able to spread, survive and proliferate (P < 0.001). Moreover, they were able to differentiate into osteoblasts and produce calcified osseous extracellular matrix (P < 0.001). The construct showed no significant contraction after 8 days, preserving its shape and tip diameter (P = 0.58). CONCLUSIONS: The composite scaffold could present substantial benefits compared to synthetic materials. It could provide a favourable healing environment in the root canal conducive for regenerative endodontics and is therefore appropriate to be evaluated in vivo in further studies.

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.

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.

New injectable self-assembled hydrogels that promote angiogenesis through a bioactive degradation product.

Hydrogels used in regenerative medicine are often designed to allow cellular infiltration, degradation, and neovascularization. Low molecular weight hydrogels (LMWHs), formed by self-assembly via non-covalent interactions, are gaining significant interest because they are soft, easy to use and injectable. We propose LMWHs as suitable body implant materials that can stimulate tissue regeneration. We produced four new LMWHs with molecular entities containing nucleic acid and lipid building blocks and analyzed the foreign body response upon subcutaneous implantation into mice. Despite being infiltrated with macrophages, none of the hydrogels triggered detrimental inflammatory responses. Most macrophages present in the hydrogel-surrounding tissue acquired an immuno-modulatory rather than inflammatory phenotype. Concomitantly, no fibrotic capsule was formed after three weeks. Our glyconucleolipid LMWHs exhibited different degradation kinetics in vivo and in vitro. LMWHs with high angiogenic properties in vivo, were found to release glyconucleoside (glucose covalently linked to thymidine via a triazole moiety) as a common by-product of in vitro LMWH degradation. Chemically synthesized glyconucleoside exhibited angiogenic properties in vitro in scratch assays with monolayers of human endothelial cells and in vivo using the chick chorioallantoic membrane assay. Collectively, LMWHs hold promise as efficient scaffolds for various regenerative applications by displaying good biointegration without causing fibrosis, and by promoting angiogenesis through the release of a pro-angiogenic degradation product. STATEMENT OF SIGNIFICANCE: The main limitations of biomaterials developed in the field of tissue engineering remains their biocompatibility and vascularisation properties. In this context, we developed injectable Low Molecular Weight Hydrogels (LMWH) exhibiting thixotropic (reversible gelation) and thermal reversible properties. LMWH having injectability is of great advantage since it allows for their delivery without wounding the surrounding tissues. The resulting gels aim at forming scaffolds that the host cells colonize without major inflammation, and that won't be insulated by a strong fibrosis reaction. Importantly, their molecular degradation releases a product (a glycosyl-nucleoside conjugate) promoting angiogenesis. In this sense, these LMWH represent an important advance in the development of biomaterials promoting tissue regeneration.

Interaction between human umbilical vein endothelial cells and human osteoprogenitors triggers pleiotropic effect that may support osteoblastic function.

Osteogenesis occurs in striking interaction with angiogenesis. There is growing evidence that endothelial cells are involved in the modulation of osteoblast differentiation. We hypothesized that primary human umbilical vein endothelial cells (HUVEC) should be able to modulate primary human osteoprogenitors (HOP) function in an in vitro co-culture model. In a previous study we demonstrated that a 3 day to 3 week co-culture stimulates HOP differentiation markers such as Alkaline Phosphatase (ALP) activity and mineralization. In the present study we addressed the effects induced by the co-culture on HOP within the first 48 hours. As a prerequisite, we validated a method based on immuno-magnetic beads to separate HOP from HUVEC after co-culture. Reverse transcription-real time quantitative PCR studies demonstrated up-regulation of the ALP expression in the co-cultured HOP, confirming previous results. Surprisingly, down-regulation of runx2 and osteocalcin was also shown. Western blot analysis revealed co-culture induced down-regulation of Connexin43 expression in both cell types. Connexin43 function may be altered in co-cultured HOP as well. Stimulation of the cAMP pathway was able to counterbalance the effect of the co-culture on the ALP activity, but was not able to rescue runx2 mRNA level. Co-culture effect on HOP transcriptome was analyzed with GEArray cDNA microarray showing endothelial cells may also modulate HOP extracellular matrix production. In accordance with previous work, we propose endothelial cells may support initial osteoblastic proliferation but do not alter the ability of the osteoblasts to produce extracellular mineralizing matrix.

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.

Chitosan-based hydrogels for developing a small-diameter vascular graft: in vitro and in vivo evaluation.

AIMS: Vascular grafts made of synthetic polymers perform poorly in small-diameter applications (cardiac and peripheral bypass). Chitosan is a biocompatible natural polymer that can provide a novel biological scaffold for tissue engineering development. The goal of this study was to demonstrate the biocompatibility of a novel chitosan preparation in vitro and in vivo, and to assess its potential as a scaffold for vascular applications. METHODS AND RESULTS: A series of experiments of increasing complexity, ranging from in vitro biocompatibility and hemocompatibility tests to in vivo studies in small and large animals (rats and sheep), was performed to provide a comprehensive analysis of chitosan hydrogels' biological properties. In vitro studies established that: (i) chitosan supported human endothelial progenitor cells adhesion, proliferation and resistance to physiological shear stress; (ii) chitosan did not activate platelets, the complement system, or the intrinsic coagulation pathway. In vivo results showed: (iii) no resorption of chitosan and no chronic inflammation at 60 days in a rat heterotopic implantation model (magnetic resonance imaging and histology); (iv) no flow obstruction (Doppler ultrasound) and no thrombus formation (histology and scanning electron microscopy) at 2 h after a carotid arteriotomy repair with chitosan patches in sheep. Finally, two chitosan tubes were implanted as carotid interposition grafts for 3 days in sheep showing that chitosan was strong enough to be sutured, to withstand arterial pressure, and no flow obstruction was observed through this short period. CONCLUSION: Chitosan-based hydrogels displayed promising in vitro biocompatibility and hemocompatibility properties as well as in vivo short-term performance.

Calcium carbonate-calcium phosphate mixed cement compositions for bone reconstruction.

The feasibility of making calcium carbonate-calcium phosphate (CaCO(3)-CaP) mixed cements, comprising at least 40% (w/w) CaCO(3) in the dry powder ingredients, has been demonstrated. Several original cement compositions were obtained by mixing metastable crystalline CaCO(3) phases with metastable amorphous or crystalline CaP powders in aqueous medium. The cements set within at most 1 h at 37 degrees C in atmosphere saturated with water. The hardened cement is microporous and exhibits weak compressive strength. The setting reaction appeared to be essentially related to the formation of a highly carbonated nanocrystalline apatite phase by reaction of the metastable CaP phase with part or almost all of the metastable CaCO(3) phase. The recrystallization of metastable CaP varieties led to a final cement consisting of a highly carbonated poorly crystalline apatite analogous to bone mineral associated with various amounts of vaterite and/or aragonite. The presence of controlled amounts of CaCO(3) with a higher solubility than that of the apatite formed in the well-developed CaP cements might be of interest to increase resorption rates in biomedical cement and favors its replacement by bone tissue. Cytotoxicity testing revealed excellent cytocompatibility of CaCO(3)-CaP mixed cement compositions.

Functionalization of biomaterials and cell to cell communication.

In the field of osseous substitution, the possibilities being offered to the surgeons prove sometimes difficult to apply in particular in the case of great losses of osseous substance. For these reasons, it is necessary to develop innovative techniques to satisfy the request increasing for substitutes and to see appearing on the market solutions combining availability, perenniality and biosecurity of the implants. The implantation of stem cells in a biomaterial opens a way of development of therapeutic substitute. Moreover, in order to optimize the rehabitation of the biomaterials by the cells and the host tissues, the second approach consists in modifying the surface of materials by the coating or the grafting of adhesive factors in order to stimulate their colonization. At least, one cannot consider a tissue mechanism of repair without a better knowledge of the respective role of the various cell populations implied in the rebuilding of this tissue and their cell to cell communication processes.

RGD-functionalized spherulites as targeted vectors captured by adherent cultured cells.

Spherulites are multilamellar vesicles consisting of concentric shells that can encapsulate small organic molecules or macromolecules. We investigate the possibility of targeting neutral spherulites to adherent culture cells by functionalizing their surface with RGD-containing ligands. The strength and specificity of association of RGD spherulites with several cell lines (EAhy 926 endothelial cell line, human umbilical vein endothelial cell (HUVEC) and human osteoprogenitor (HOP) primary cells) was studied, and the molecular interaction of RGD spherulites with the EAhy 926 cell surface was investigated. We show that, after binding to cells, spherulites are internalized.

Mineralization of regenerated cellulose hydrogels induced by human bone marrow stromal cells.

The proliferation of cultured human bone marrow stromal cells (HBMSC) on regenerated cellulose hydrogels was assessed. Regenerated cellulose hydrogels showed good rates of HBMSC proliferation, the cells exhibiting a flattened morphology, and after 22 days in culture, the cells had homogeneously colonized the surface of the materials. Moreover, since the early days in culture, between the surface of the materials and attached cells a continuous granulated hydroxyapatite layer was formed. It has been previously demonstrated in vitro, but without cells, that these materials did not mineralize. Hence, it seems that HBMSC promoted the mineralization of the surface.

Development of a resorbable macroporous cellulosic material used as hemostatic in an osseous environment.

The control of bleeding is a frequently encountered therapeutic problem, particularly during dental surgery. The most efficient substances used to resolve this problem are not risk-free because of their animal or human origins, so cellulosic materials are potentially of interest. The aim of this study was to develop a resorbable macroporous cellulosic material for use as a resorbable hemostatic agent in bone sites. The degradation and the cytocompatibility of the cellulosic material versus controls were evaluated and its behaviour in vivo was studied. An original process using calcium carbonate powder as inverse matrix was used to develop a macroporous material. In order to predegrade the cellulosic material for hemostatic use, oxidation was performed with periodate. A dialdehyde component unstable at physiological pH was thus obtained. The material was found to have cytotoxicity, biocompatibility, and resorption properties similar to control but its hemostatic power was higher.

Effect of several sterilisation techniques on homogeneous self assembled monolayers.

Understanding how cells sense their environment and are able to regulate their metabolism is of great importance for the success of biomaterials implantation. Self assembled monolayers (SAMs) are in use nowadays to model the surface of such materials. They permit the control of different surface parameters (like chemistry, surface energy and topography) enabling to get a greater insight in cells behaviour when interacting with surfaces and thus, in the future, to enhance surface properties of biomaterials. As sterilisation is the compulsory step for in vitro and in vivo assays with living biological materials, it is important to know how SAMs react under sterilisation techniques in use on biomaterials. In this work, the effect of three types of sterilisation techniques: gamma-irradiation, mostly used on biomaterials, dry heat and steam autoclaving, have been investigated on NH2 and CH3 terminated SAMs. Gamma-irradiation destructs drastically the NH2 and partially the CH3 monolayers by producing oxidative compounds (COOH, C=O, C-OH). The main product induced by gamma-irradiation on NH2 monolayers is carboxylic acid, whereas CH3 shows an important increase in the amount of alcoholic groups. This difference in deterioration is assumed to be due to the higher stability of the CH3 monolayer. Steam autoclaving to a lesser extent gives the same results on NH2 monolayers. Dry heat seems to be the most reliable technique, which can be used on such surfaces as it removes physically adsorbed organic contaminants without affecting the integrity of the surface.

A novel potential application for 99mTc-HMPAO: endothelial cell labeling for in vitro investigation of cell-biomaterial interactions.

UNLABELLED: Good adherence of endothelial cells (ECs) seeded on vascular prostheses and cell retention under flow conditions are important factors to consider in the use of functionalized prostheses in vascular surgery. Because 111In-oxine radiolabeling presents disadvantages, we wondered whether, because of its well-known physical properties, 99mTc-hexamethyl propyleneamine oxime (HMPAO or exametazime) could be used. METHODS: The cytotoxicity of unlabeled HMPAO and 99mTc-HMPAO at increasing concentrations and activities was tested on monolayers of the EC line EA-hy-926. The influence of temperature and time on tracer incorporation into cells was also tested. The optimal labeling conditions were applied to evaluate the retention of ECs seeded on polyester grafts under flow conditions by gamma camera detection. RESULTS: The activity of 10 MBq/10(6) cells corresponding to 4.5 microg/10(6) cells of unlabeled HMPAO, applied for 3 h at 37 degrees C (cellular uptake = 18%), was the best compromise between the maintenance of cell viability and metabolic activity and efficient detection by the gamma camera. Spontaneous leakage was observed and analyzed by high-performance liquid chromatography. A cell loss of 13% after 180-min exposure to shear stress was obtained. CONCLUSION: Our data thus indicate the feasibility of using such a radiolabeling technique to investigate EC-biomaterial interactions.

Functional upregulation of granulocytes labeled with technetium-99m-HMPAO and indium-111-oxinate.

UNLABELLED: Indium-111-oxinate-labeled granulocytes have been used in vivo for several years for the detection of abscesses. Technetium-99-m-hexamethylpropyleneamine oxime (99mTc-HMPAO) labeling has more recently been described. METHODS: The influence of radiolabeling by both radiotracers on adhesion glycoprotein CD11b quantification was studied in quiescent and formyl-methionylleucylphenylalanine (fMLP)-activated neutrophils (PMN). Adhesion was assessed on human umbilical endothelial cells (HUVEC) as well as the repercussion of the granulocyte labeling on HUVEC viability (neutral red) and metabolic activity (MTT). Chemotaxis of PMN was evaluated by measuring migration under agarose with fMLP as chemoattractant. We also measured phagocytosis and the production of hydrogen peroxide induced by staphylococcus aureus. RESULTS: Whereas whole functional integrity is maintained after labeling, most of the functions (CD11b expression, adhesion, HUVEC metabolic activity) are up-regulated while chemotaxis is decreased in the presence of both radiotracers. Indium-111-oxinate induces larger alterations than 99mTc-HMPAO. CONCLUSION: These data were obtained in normal volunteers. In patients, alterations due to the in vitro labeling procedure, in addition to potential functional alterations caused by the underlying pathology, should be taken into account during image interpretation.

Colonization of a calcium phosphate/elastin-solubilized peptide-collagen composite material by human osteoblasts.

The evaluation of the suitability of a new biomaterial as a possible substitute for bone tissue is described here. This biomaterial is based on calcium phosphate particles linked to an artificial connective matrix, the elastin-solubilized peptides (ESP) associated with type I and III collagens. This work demonstrates the feasibility of shaping this composite material into discs, describes its microstructural characteristics, and evaluates its capacity as a substrate for the proliferation of human osteoblasts without loss of their phenotypic expression.

Evaluation of an in vitro endothelialized vascular graft under pulsatile shear stress with a novel radiolabeling procedure.

OBJECTIVE: To improve the hemocompatibility of vascular grafts, endothelial cell (EC) seeding of biomaterials prior to implantation is critical. The current in vitro study was designed to investigate such a feasibility on a collagen-coated heparin-bonded graft and to evaluate cell detachment upon pulsatile shear stress. MATERIALS AND METHODS: Endothelial cells (EA-hy-926) were seeded onto grafts. The endothelialization of the grafts was evaluated by the [3H]-thymidine incorporation, scanning electron microscopy (SEM) and histological examinations. After in situ EC radiolabeling with a novel 99mTc technique, the prostheses were exposed to pulsatile shear stress (0.27 N/m2), mimicking the shear rate occurring in a superficial femoral artery, for 3 h in a flow circuit and EC loss quantified by gamma camera detection. RESULTS: Complete EC coverage was achieved after 5 days. Three hours of artificial perfusion resulted in a low EC loss (12.9+/-0.8%, n = 7). SEM shows EC withstanding shear stress in valleys of prosthesis circumvolutions. CONCLUSIONS: These satisfactory results could be explained by the high affinity of EC for heparinized surfaces in addition to cell surface receptors involved in adhesion to collagen.

Evaluation of cell colonization on biomaterials: preventing cell attachment to plastic containers.

In biocompatibility evaluation involving cell culture models, we use samples of biomaterials of different forms and sizes. During cell seeding onto biomaterials of an inadequate size to cover the bottom of the culture wells completely, cells have the opportunity to attach to the plastic. As described in this report with two culture models and two biomaterials, we use an agarose gel sublayer to prevent this phenomenon.

New artificial connective matrix-like structure made of elastin solubilized peptides and collagens: elaboration, biochemical and structural properties.

Several improvements of the basic reaction between elastin peptides and type III collagen, specially the addition of heparan sulphate proteoglycans, are presented. The consequent elaboration of either cell culture support or membranes are described and illustrated by scanning electron microscopy. The material produced possesses composition, very well organized lamellar structure and some properties quite close to natural membranes such as subendothelial tissue.

New artificial connective matrix-like structure: thrombogenicity and use as endothelial cell culture support.

The recently described artificial connective matrix made of elastin solubilized peptides, type I+III collagens and connective proteins is shown to have structural and biological properties very close to the natural arterial subendothelium: the capacity to promote endothelial cell cultures maintaining their phenotype expression and its non-thrombogenicity. This new bioactive composite material could be used to replace arteries.