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Biomedical subjects

M Dard

Publications and source records attributed to M Dard.

At least 19 recordsLinked to original sources
PubMed2005

Functionalization of dental implant surfaces using adhesion molecules.

The aim of the present study was to test the hypothesis that organic coating of titanium screw implants that provides binding sites for integrin receptors can enhance periimplant bone formation. Ten adult female foxhounds received experimental titanium screw implants in the mandible 3 months after removal of all premolar teeth. Four types of implants were evaluated in each animal: (1) implants with machined titanium surface, (2) implants coated with collagen I, (3) implants with collagen I and cyclic RGD peptide coating (Arg-Gly-Asp) with low RGD concentrations (100 micromol/mL), and (4) implants with collagen I and RGD coating with high RGD concentrations (1000 micromol/mL). Periimplant bone regeneration was assessed histomorphometrically after 1 and 3 months in five dogs each by measuring bone implant contact (BIC) and the volume density of the newly formed periimplant bone (BVD). After 1 month, BIC was significantly enhanced only in the group of implants coated with the higher concentration of RGD peptides (p = 0.026). Volume density of the newly formed periimplant bone was significantly higher in all implants with organic coating. No significant difference was found between collagen coating and RGD coatings. After 3 months, BIC was significantly higher in all implants with organic coating than in implants with machined surfaces. Periimplant BVD was significantly increased in all coated implants in comparison to machined surfaces also. It was concluded that organic coating of machined screw implant surfaces providing binding sites for integrin receptors can enhance bone implant contact and periimplant bone formation.

Animals↗
PubMed2004

Repair of calvarial defects in rats by prefabricated hydroxyapatite cement implants.

The aim of the present study was to test the hypothesis that calvarial defects can be repaired by using preformed implants of calcium phosphate bone cement (CPBC) in rats. Sixty adult female Sprague-Dawley rats received full-thickness calvarial nonhealing defects with a diameter of 8 mm. Three different CPBCs were used: group 1: tetracalcium phosphate-based powder; group 2: a blend of amorphous and crystalline calcium phosphate precursors; and group 3: an alpha-tricalcium phosphate (alpha-TCP)-based powder. Implants were left to cure for 25-40 min at room temperature in a silicon mold of 7.9 mm and inserted press fit into the defects. Fifteen animals served as unfilled controls. After 13, 26, and 52 weeks, the material was analyzed qualitatively by using surface-stained undecalcified thick-section specimens and quantitatively by using semiautomated histometry. Kruskal-Wallis tests were applied to compare mean values of periimplant bone formation at a significance level of p < 0.05. Three implants of group 1 fractured during insertion. Resorption of CPBC without complementary bone formation was noticed in these implants. Unfractured implants were resorbed with simultaneous apposition of bone on the implant surface. After 52 weeks, the resorption rate varied between 23.1 and 39.3%. Periimplant bone formation increased continuously on average around all implant types, but it reached statistical significance only in group 2. The results showed that repair of calvarial defects can be achieved by preformed CPBC implants. The rate of resorption of preformed implants is, however, much lower than that reported for in vivo cured CPBC.

Animals↗
PubMed2004

Cyclo-(DfKRG) peptide grafting onto Ti-6Al-4V: physical characterization and interest towards human osteoprogenitor cells adhesion.

In the present paper, specific interest has been devoted to the design of new hybrid materials associating Ti-6Al-4V alloy and osteoprogenitor cells through the grafting of two RGD containing peptides displaying a different conformation (linear RGD and cyclo-DfKRG) onto titanium surface. Biomimetic modification was performed by means of a three-step reaction procedure: silanization with APTES, cross-linking with SMP and finally immobilization of peptides thanks to thiol bonding. The whole process was performed in anhydrous conditions to ensure homogeneous biomolecules layout as well as to guarantee a sufficient amount of biomolecules grafted onto surfaces. The efficiency of this new route for biomimetic modification of titanium surface was demonstrated by measuring the adhesion between 1 and 24 h of osteoprogenitor cells isolated from HBMSC. Benefits of the as-proposed method were related to the high concentration of peptides grafted onto the surface (around 20 pmol/mm(2)) as well as to the capacity of cyclo-DfKRG peptide to interact with integrin receptors. Moreover, High Resolution beta-imager (using [(35)S]-Cys) has exhibited the stability of peptides grafted onto the surface when treated in harsh conditions.

Alloys↗
PubMed2004

Grafting RGD containing peptides onto hydroxyapatite to promote osteoblastic cells adhesion.

Ceramics possess osteoconductive properties but exhibit no intrinsic osteoinductive capacity. Consequently, they are unable to induce new bone formation in extra osseous sites. In order to develop bone substitutes with osteogenic properties, one promising approach consists of creating hybrid materials by associating in vitro biomaterials with osteoprogenitor cells. With this aim, we have developed a novel strategy of biomimetic modification to enhance osseointegration of hydroxyapatite (HA) implants. RGD-containing peptides displaying different conformations (linear GRGDSPC and cyclo-DfKRG) were grafted onto HA surface by means of a three-step reaction procedure: silanisation with APTES, cross-linking with N-succinimidyl-3-maleimidopropionate and finally immobilisation of peptides thanks to thiol bonding. Whole process was performed in anhydrous conditions to ensure the reproducibility of the chemical functionalisation. The three-step reaction procedure was characterised by high resolution X-ray photoelectron spectroscopy. Efficiency of this biomimetic modification was finally demonstrated by measuring the adhesion of osteoprogenitor cells isolated from HBMSC onto HA surface.

Amino Acid Sequence↗
PubMed2003

Electrochemically assisted deposition of thin calcium phosphate coatings at near-physiological pH and temperature.

An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca(2+) / H(x)PO(4) ((3-x)-))-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36 degrees C). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (approximately 30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology.

Alloys↗
PubMed2003

Biological performance of biomimetic calcium phosphate coating of titanium implants in the dog mandible.

The aim of the present study was to analyze the in vivo effect of biomimetic calcium phosphate coating of titanium implants on periimplant bone formation and bone-/implant contact. Five types of implants were used: 1) Ti6Al4V implants with a polished surface; 2) Ti6Al4V implants with collagen coating; 3) Ti6Al4V implants with a mineralized collagen layer; 4) Ti6Al4V implants with sequential coating of hydroxyapatite (HA) and collagen; and 5) Ti6Al4V implants with HA coating only. All implants had square cross sections with an oblique diameter of 4.6 mm and were inserted press fit into trephine burr holes of 4.6 mm in the mandibles of ten beagle dogs. The implants of five animals each were evaluated after a healing period of 1 month and 3 months, respectively, during which time sequential fluorochrome labeling of bone formation had been performed. Bone formation was evaluated by morphometric measurement of the newly formed bone around the implants and the percentage of implant bone contact. After 1 month, there was a significantly higher percentage of mean bone/implant contact in the HA-coated implants compared to those with polished surface and those with the collagen-coated surface. After 3 months, these differences were not present anymore. Bone apposition was significantly higher next to implants with sequential HA/collagen coating compared to polished surfaces and mineralized collagen layer. It is concluded that biomimetic coating of titanium implants with HA has shown the clearest trend to increase bone-implant contact in the early ingrowth period. The addition of collagen to an HA coating layer may hold some promise when used as sequential HA/collagen coating with mineralized collagen as the surface layer.

Alloys↗
PubMed2003

A cyclo peptide activates signaling events and promotes growth and the production of the bone matrix.

The interaction of bone cells and their underlying extracellular matrix impacts biological processes such as maintenance of tissue integrity. The biological recognition of the extracellular matrix by attached cells is mediated by the activity of integrins that recognize adhesive-specific domains. The most widely recognized adhesive motif is the RGD sequence, common to many of the adhesive matrix molecules. Here, we show that cyclo DFKRG which was previously selected to increase cell adhesion of human bone marrow stromal cells (HBMSC), increases both cell differentiation and mineralization through activation of tyrosine kinases, focal adhesion kinase (p(125)FAK) and Mitogen Activated Protein (MAP) kinases.

Bone Matrix↗
PubMed2002

Function of linear and cyclic RGD-containing peptides in osteoprogenitor cells adhesion process.

Cell adhesion directly influences cell growth, differentiation and migration as well as morphogenesis, integrity and repair. The extracellular matrix (ECM) elaborated by osteoblast cells constitutes a regulator of the cell adhesion process and then of the related phenomenon. These regulatory effects of ECM are mediated through integrins and some of them are able to bind RGD sequences. The aim of this study was to determine the role of the sequence and the structure of RGD-containing peptides (linear and cyclic) as well as their role in the cell adhesion process. Cell adhesion assays onto ECM proteins coated surfaces were performed using a range of linear and cyclic RGD-containing peptides. We showed a different human osteoprogenitor cell adhesion according to the coating for ECM proteins and for RGD-peptides. Inhibition assays using peptides showed different responses depending on the coated protein. Depending on the amino-acid sequence and the structure of the peptides (cyclic linear), we observed 100% inhibition of cell adhesion onto vitronectin. These results suggest the importance of sequence, structure and conformation of the peptide, which may play a crucial function in the ligand/receptor interaction and/or in the stability of the interaction.

Adult↗
PubMed2001

Evaluation of the effect of three calcium phosphate powders on osteoblast cells.

The aim of the present study was to assess the effect of three calcium phosphate powders entering in the composition of bone substitute materials on osteoblast-cells activity. These powders were hydroxyapatite (HA) widely used as a biomaterial, nanocrystalline carbonate apatite (C A) very close to bone mineral crystals, and an experimental one: calcium phosphate cement-1 (CPC-1) composed of an amorphous Ca-P phase and brushite. The powders were physico-chemically characterized. The very reactive CPC-1 powder became transformed in cell culture medium: recrystallization of amorphous precursors and hydrolysis of brushite into poorly crystalline apatite occurred. Osteoblast-cells activity was evaluated: for low level of calcium phosphates (>100 microg/ml) CPC-1 enhanced proliferation and, to a lesser degree, differentiation on alkaline phosphatase activity. For 100 microg/ml of powders we observed a great alteration of biological activity of the osteoblasts: evaluation of proliferation indicated an inhibition for all samples, and a decrease of two differentiation markers: alkaline phosphatase activity and osteocalcin release were noticed, suggesting a down regulation due to the presence of large amount of mineral powder.

Journal Article↗
PubMed2001

Adsorption of vascular endothelial growth factor to two different apatitic materials and its release.

The aim of our study was to assess the ability of calcium phosphate powders to serve as growth factor carriers. Vascular endothelial growth factor (VEGF), in particular, is locally involved in the bone formation process throughout osteoblast differentiation. Two different apatitic substrates were tested: hydroxyapatite (HA), widely used as biomaterial, and nanocrystalline carbonated apatite (CA), which has a composition similar to bone mineral crystals. These materials have been compared for their VEGF adsorption and release properties. The adsorption of the growth factor was higher on CA than on HA probably due to differences of both the proteins and the powders involved. The specific activity of the VEGF released was also tested to determine the available activity for cells in contact with these materials. Interestingly, the bioactivity of the VEGF released from CA quantified on fetal bovine aortic endothelial cells (FBAE) by evaluating the proliferation activity, exhibited no marked difference compared to native VEGF. Qualitatively, VEGF adsorbed on CA material induced well-defined collagen type I immunostaining on osteoblast cells compared to the staining obtained after VEGF adsorption on HA.

Journal Article↗
PubMed2000

[Pilot study of controlled liberation of growth factors from polylactide implants].

The aim of the present study was to test polylactic acid material as a controlled release carrier for polypeptide growth factors. Basic fibroblast growth factor (bFGF) was incorporated into DL polylactic acid (PLA) pellets under hyperbaric CO2 pressure in two different ways. (1) Lyophilized bFGF was crushed and mixed with PLA granules, filled into cylindric moulds of 5 x 3 mm, and submitted to hyperbaric CO2 pressure. (2) Lyophilized bFGF was reconstituted in phosphate buffer, mixed with PLA granules, and relyophilized. In vitro assessment of bFGF release from the PLA implants by immunoassay showed that loading of PLA with crushed lyophilized bFGF resulted in a rapid and high release, while loading by solubilized bFGF and relyophilization led to a low and more regular release of the polypeptide growth factor.

Drug Carriers↗
PubMed2000

Tools for tissue engineering of mineralized oral structures.

This paper presents a short review of three groups of tools which can be or are used for the tissue engineering of mineralized oral structures: growth factor delivery systems (GFDS) and surface bioactivation with covalent bound peptides or with nanomechanically linked proteins. According to the reported personal experience of the authors, GFDS have to face the following challenging issue before being used routinely in dentistry, e.g., as a tool for reparative dentinogenesis or bone healing: adaptation of the GFDS design to the tissue where it will be implanted in order to deliver the right dose of growth factor (GF) at the right time. The bioactivation of surfaces, for example of dental implants, with covalent bound peptides or nanomechanically linked proteins represents a second innovative way to improve dental health in the future. Here we report on the experimental use of cyclic RGD peptides grafted on polymethylmethacrylate to improve osteoblast adhesion. Furthermore, we show the potential advantage of immobilizing and incorporating collagen I on titanium implant surfaces. These techniques or a combination of them will help to create improvements, for example, of dental implants in the near future. They will also help to promote bone and dentin regeneration.

Alveolar Process↗
PubMed2000

Various evaluation techniques of newly formed bone in porous hydroxyapatite loaded with human bone marrow cells implanted in an extra-osseous site.

The purpose of this work was to develop qualitative methods for in situ analysis of bone formation in an osteoconductive hydroxyapatite matrix (ENDOBON), loaded with human bone marrow cells (HBMSC) implanted subcutaneously in athymic mice. Samples were taken before implantation (T0), 1, 2, 4 and 6 weeks after implantation. Bone-biomaterial interaction were investigated on undecalcified sections by histological, cytochemical, immunological and molecular biology methodologies. Histological observations were performed in order to observe inflammatory cells, vessels, newly formed bone, woven and lamellar bone. Enzymohistochemistry was carried out to detect positive tartrate resistant acid phosphatase activity (TRAP+). Immunohistochemistry using antibodies against type I collagen and osteocalcin permitted us to characterize the content of the matrix elaborated within the implant. Moreover, in situ hybridization was carried out to discriminate, the implanted human cells from the murine cells, and to evaluate the function of these human cells in osteogenesis. Results demonstrated an early formation of lamellar bone only in the pores of the studied HAP loaded with HBMSC. This bone contained a matrix showing positive reaction for type I collagen and osteocalcin. In situ hybridization identified some of these cells as human cells. At 6 weeks, examination of histological results showed persistance of lamellar bone in the implants. We only found TRAP+ activity in the materials loaded with human bone marrow cells. Molecular hybridization no longer revealed positive cells for the human DNA probe. All these results indicate that the various evaluation techniques performed on undecalcified sections, permit us to evaluate the response of human bone marrow cells in HAP implanted into mice.

Animals↗
PubMed2000

Guided bone regeneration around endosseous implants using a resorbable membrane vs a PTFE membrane.

The aim of the present experimental pilot study was to assess bone regeneration underneath resorbable barrier membranes vs non-resorbable extended polytetrafluoroethylene (ePTFE) membranes in peri-implant defects. Two implants were inserted into surgically created defects on each side of the mandibles of 6 adult beagle dogs 3 months after extraction of all premolar teeth. One implant on each side was covered with a porous polylactic acid membrane or a ePTFE membrane, respectively, while the second implant served as control. Fluorochrome labelling was administered during the 1st, 5th, 12th and the 18th week. Three animals each were evaluated after 3 and 6 months. Bone regeneration was assessed by measuring the distance from the first fluorochrome label to the level of the regenerated bone immediately adjacent to the implant surface and to the top of the newly formed alveolar contour both on the lingual and buccal side. The increase in bone height was significantly higher compared to the controls under both barrier membranes after 3 months at the top of the alveolar crest but not immediately adjacent to the implant surface. After 6 months, bone height was significantly increased only at the top of the alveolar contour underneath the ePTFE membranes, while bone underneath the polylactic acid membranes showed signs of superficial resorption. It is concluded that guided bone regeneration underneath barrier membranes can restore alveolar bone contour but is not necessarily associated with a higher bone/implant contact. The use of resorbable membranes may be associated with untoward biological effects at later stages, when membrane degradation starts due to degradation products of the polymer material or decreasing membrane stability. Future efforts have to refine the relation between degradation kinetics, membrane porosity and mechanical properties of degradable barrier membranes to improve membrane performance.

Absorbable Implants↗
PubMed1999

Induced tissue integration of bone implants by coating with bone selective RGD-peptides in vitro and in vivo studies.

The optimal function of medical implant materials used in tissue substitution is often limited due to its healing properties. This effect is linked to reduced interactions of the implants with the surrounding tissue. Implant surfaces biologically functionalized with arginine-glycine-aspartic acid (RGD) peptides, a class of cellular adhesion factors, are described in this paper. The RGD-peptides are either bound via bovine serum albumin linking on culture plastic dishes as a model surface or via acrylic acid coupling on PMMA surface as a potential implant material. Resulting functionalized surfaces aquire the capability to bind cultured osteoblasts in high levels and show high proliferation rates in vitro. These results are observed for osteoblast cultures as well as from different species with different preparation procedures. A critical minimum distance between the bioactive portion of the RGD-peptides and the implant surface of 3.0-3.5 nm is crucial for the induction of an optimum cell binding process. In vivo animal studies in the rabbit show that newly formed bone tissue generated a direct contact with the RGD-peptide coated implants. In contrast uncoated implants are separated from newly formed bone tissue by a fibrous tissue layer thereby preventing the formation of a direct implant-bone bonding.

Journal Article↗
PubMed1998

Basic fibroblast growth factor adsorption and release properties of calcium phosphate.

Basic fibroblast growth factor (bFGF) is well known as a potent angiogenic factor playing a crucial role in wound-healing processes. Apatitic substrates such as hydroxyapatite and carbonated apatite (CA) could be potential carriers of growth factors because of their physicochemical similarities to bone mineral. These materials have been compared for their bFGF adsorption and release properties. The adsorption of the growth factor was higher on carbonated apatite than on hydroxyapatite, probably owing to environments with labile nonapatitic CO3(2-) and HPO4(2-) groups, along with a higher specific surface area which gives the CA a higher surface reactivity. These environments can be exchanged very rapidly, leading to the release of bFGF. The controlled release of adsorbed growth factor from carbonated apatite could provide means of improving bone healing in the future.

Adsorption↗
PubMed1997

In vitro growth of human adult bone-derived cells on hydroxyapatite plasma-sprayed coatings.

The growth of adult human bone-derived cells on hydroxyapatite (HA) plasma-sprayed coatings was investigated. Such cells were difficult to grow on original plasma-sprayed coatings, even following rinsing and rubbing down. We obtained cell growth only on samples previously immersed 15 or 22 days in complete culture medium. We describe a dissolution/precipitation phenomenon on the HA coating surface assessed by modifications of Ca and P concentrations in the culture medium, by the transformation of the HA coating into carbonated HA (X-ray diffraction and infrared spectrometry and by the presence demonstrated by scanning electron microscopy of spherocrystallites on the HA after 15 days of immersion. Our results show that adult human bone-derived cells are apparently particularly sensitive to the changes in the coating surface induced by liquid immersion. We raise the question of the limits of in vitro investigations on bioactive ceramics such as HA plasma-sprayed coatings susceptible to modification by simple immersion in aqueous solutions such as cell culture medium or physiologic saline.

Adult↗