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Biomedical subjects

G Daculsi

Publications and source records attributed to G Daculsi.

At least 37 records · Page 2Linked to original sources
PubMed2003

Bilayered calcium phosphate coating to promote osseointegration of a femoral stem prosthesis.

A bilayered bioactive-gradient coating, consisting of a superficial layer of biphasic calcium phosphate (BCP) and a deep layer of hydroxyapatite (HA), promotes faster osseointegration and higher shear strength in non-loading conditions than do monolayer BCP or HA coatings. This study evaluated the biofunctionality of this coating in weight-bearing conditions at 6 and 12 months. The coating was plasma-sprayed on the metaphyseal portion of a sandblasted Ti6Al4V canine femoral prosthesis implanted using the surgical press-fit technique. An identical uncoated stem served as the control. Metaphyseal bone-to-implant apposition was increased for coated ( approximately 90% and 80% respectively at 6 and 12 months) as compared to uncoated implant ( approximately 7% at 6 and 12 months). Limited bone apposition was observed at the diaphyseal level. After 12 months, the uncoated implant interface consisted of well-organized, active fibrous tissue, whereas only inactive fibrous tissue interposition was observed at diaphyseal levels of the coated implant. At 6 months, the mineralization apposition rate (MAR) was similar, regardless of implant or bone structures. At 12 months, a significant decrease of MAR was observed around the uncoated implant. Transmission electron microscopy studies of the interface showed precipitation of biological apatite crystals in close association with mineralized collagenous bone matrix. Our results suggest a direct relationship between bioactivity and enhanced bone formation. The sandwich coating used is effective in promoting massive metaphyseal osseointegration, which ensures mechanical stability for early weight-bearing and should prevent long-term complications.

Journal Article↗
PubMed2003

Phosphate is a specific signal for ATDC5 chondrocyte maturation and apoptosis-associated mineralization: possible implication of apoptosis in the regulation of endochondral ossification.

UNLABELLED: Involvement of Pi and Ca in chondrocyte maturation was studied because their levels increase in cartilage growth plate. In vitro results showed that Pi increases type X collagen expression, and together with Ca, induces apoptosis-associated mineralization, which is similar to that analyzed in vivo, thus suggesting a role for both ions and apoptosis during endochondral ossification. INTRODUCTION: During endochondral ossification, regulation of chondrocyte maturation governs the growth of the cartilage plate. The role of inorganic phosphate (Pi), whose levels strongly increase in the hypertrophic zone of the growth plate both in intra- and extracellular compartments, on chondrocyte maturation and mineralization of the extracellular matrix has not yet been deciphered. MATERIALS AND METHODS: The murine chondrogenic cell line ATDC5 was used. Various Pi and calcium concentrations were obtained by adding NaH2PO4/Na2HPO4 and CaCl2, respectively. Mineralization was investigated by measuring calcium content in cell layer by atomic absorption spectroscopy and by analyzing crystals with transmission electron microscopy and Fourier transform infrared microspectroscopy. Cell differentiation was investigated at the mRNA level (reverse transcriptase-polymerase chain reaction [RT-PCR] analysis). Cell viability was assessed by methyl tetrazolium salt (MTS) assay and staining with cell tracker green (CTG) and ethidium homodimer-(EthD-1). Apoptosis was evidenced by DNA fragmentation and caspase activation observed in confocal microscopy, as well as Bcl-2/Bax mRNA ratio (RT-PCR analysis). RESULTS: We showed that Pi increases expression of the hypertrophic marker, type X collagen. When calcium concentration is slightly increased (like in cartilage growth plate), Pi also induces matrix mineralization that seems identical to that observed in murine growth plate cartilage and stimulates apoptosis of differentiated ATDC5 cells, with a decrease in Bcl-2/Bax mRNA ratio, DNA fragmentation, characteristic morphological features, and caspase-3 activation. In addition, the use of a competitive inhibitor of phosphate transport showed that these effects are likely dependent on Pi entry into cells through phosphate transporters. Finally, inhibition of apoptosis with ZVAD-fmk reduces pi-induced mineralization. CONCLUSIONS: These findings suggest that Pi regulates chondrocyte maturation and apoptosis-associated mineralization, highlighting a possible role for Pi in the control of skeletal development.

Animals↗
PubMed2002

Fourier transform infrared microspectroscopic investigation of the organic and mineral constituents of peritubular dentin: a horse study.

Peritubular dentin (PTD) is a relatively dense mineralized tissue surrounding tooth dentin tubules, whose composition and mode of formation are still unclear. Fourier transform infrared microspectroscopic studies of the organic and mineral components of the highly developed horse PTD indicate that the peritubular matrix is less abundant than the intertubular matrix but is also mainly composed of collagen, which is more hydrated. These data suggest that most of the crystals are located outside the collagen fibrils and probably not associated with protein components. The crystals in PTD have nearly the same crystallinity as those in intertubular spaces, showing comparable amounts of carbonate ions, although some PO4 groups have different nonapatitic environments. Horse PTD composition is very similar to that of ITD, with collagen as the main protein component and carbonated apatite as the mineral fraction but the different proportions of these constituents and the greater water content in PTD suggest a different organization.

Animals↗
PubMed2002

In vitro characterization and in vivo properties of a carbonated apatite bone cement.

This study evaluated the in vivo behavior of an injectable calcium phosphate bone cement implanted in bone defects at the distal end of rabbit femora. After 3 weeks, samples were harvested and processed for undecalcified sectioning. Scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared microspectroscopy showed direct contact of bone and cement without soft tissue interposition, biocompatibility, and bioactivity with osteoconductive properties.

Animals↗
PubMed2002

Crystallization at the polymer/calcium-phosphate interface in a sterilized injectable bone substitute IBS.

Calcium phosphate (CaP) ceramics are the main raw materials used to elaborate blocks or granules for bone substitutes. In this study, injectable bone substitutes (IBS) were developed for applications in orthopedic or dental surgery. Sterile, ready-to-use composite containing CaP granules (biphasic calcium phosphate, BCP) and polymer (hydroxypropylmethylcellulose, HPMC) was prepared. Steam sterilization produced new phenomena at the CaP/polymer interface, resulting in crystal growth. These phenomena may constitute a model for the biomineralization study. Scanning electron microscopy showed that the formed crystallites organize themselves into a three-dimensional structure. Currently, the mechanisms of crystal growth are unknown and have been observed with only one combination of polymer/BCP ceramics after steam sterilization.

Biocompatible Materials↗
PubMed2002

Skin sensitization study of two hydroxypropyl methylcellulose components (Benecel and E4M) of an injectable bone substitute in guinea pigs.

Although initial results were promising for an injectable bone substitute (IBS) associating a hydroxypropyl methylcellulose (HPMC) polymer vector (Benecel, 2 w/w %) with biphasic calcium phosphate (BCP), a sensitization reaction occurred probably related to the degree of polymer purity. In this context, Benecel and another HPMC, E4M were investigated in the present study. The expected composition of the polymers was confirmed by gas-liquid chromatography. Studies in the guinea pig showed that Benecel has strong sensitization capacity and E4M none. Benecel manifests impurities (30 times more than E4M) in individual fibers or rounded clumps that are apparently responsible for extreme sensitization. Purification by ultracentrifugation associated with 0.2 microm filtration can decrease sensitization capacity considerably, though with a slight loss of polymer concentration. Fourier transform infrared (FTIR) analysis showed that the impurities were largely cellulose derivatives. However, extraction by organic solvent, followed by FTIR studies and micro-X analysis, detected an oily substance containing carbon and silicon associated with the cellulose derivatives. E4M, a polymer with no sensitization capacity, could replace Benecel and improve results with IBS.

Journal Article↗
PubMed2001

Association of vancomycin and calcium phosphate by dynamic compaction: in vitro characterization and microbiological activity.

Dynamic compaction has rarely been used to produce drug-delivery devices in granule form. This report considered four processes associating vancomycin and compared dynamic compaction with wet granulation, a classical method. In the wet granulation study, vancomycin was associated with biphasic calcium-phosphate (BCP) granules either by adsorption or incorporation with a new granulation. In the dynamic compaction study, BCP powder was compacted at 1.1, 1.5 and 1.9 MPa. The compacts obtained were crushed and sieved (200-500 microm), and the vancomycin solution was adsorbed on the resulting granules. After crushing and sieving, the compaction of BCP and vancomycin powders produced vancomycin-loaded granules. In each study, 4.76% of vancomycin was associated with BCP. Granules were characterized in terms of porosity, vancomycin release and vancomycin biological activity. Physicochemical studies of BCP and vancomycin showed their structural integrity after dynamic compaction, which prolonged vancomycin release time from 1 to 6 days. However, a microbiological assay indicated that vancomycin had been altered since only 27.7% was found to be active.

Anti-Bacterial Agents↗
PubMed2001

A new injectable bone substitute combining poly(epsilon-caprolactone) microparticles with biphasic calcium phosphate granules.

Previous studies have shown the effectiveness of an injectable bone substitute (IBS) composed of biphasic calcium phosphate in 2% hydroxypropyl methylcellulose gel (50/50 w/w). A therapeutic agent in the form of a drug can be added to the biomaterial by encapsulation into microparticles to protect the active agent, control its release and preserve the material rheological properties. Poly(epsilon-caprolactone) was used in this study because of its biocompatibility and resorbability, as tested in orthopaedic implants and surgical sutures. Particles (80-200 microm) were manufactured by a solvent evaporation-extraction process (1 g of polymer, 11-15 ml methylene chloride, with a stirring speed of 400-600 rpm) and introduced into the IBS in a 5-50% (V/V) range. Injectability was evaluated by texture analysis. With less than 45% of particles, the material had rheological properties similar to those of the reference IBS, whereas injectability decreased markedly with more than 45% of particles. A preliminary in vitro release study showed that this type of triphasic IBS could be efficient for drug delivery systems with osteoconduction properties.

Anti-Bacterial Agents↗
PubMed2001

Fourier transform infrared microspectroscopic investigation of the maturation of nonstoichiometric apatites in mineralized tissues: a horse dentin study.

Fourier transform infrared microspectroscopy (FTIRM) was used to study carbonated apatite/collagen interactions and maturation in horse secondary dentin. Unlike human dentin, this model contains no peritubular material around the odontoblastic processes and is thus quite similar to bone in composition, but not subject to tissue turnover. Crystals close to the mineralization front were very immature, showing high HPO(4) and very low CO(3) levels. Carbonate ions were located essentially in very labile, reactive environments, probably on the crystal surface. Removal of some of the HPO(4) ions from crystals during maturation was linked to an increase in total carbonate content. The CO(3) ions in labile environments decreased, probably after incorporation into more organized regions of the lattice. However, this increase of total carbonate content was associated with greater mineral crystallinity, confirming findings in other studies of synthetic apatite maturation in vitro. The good correlation between these results and those of in vitro experiments suggests that crystal maturation is essentially due to physicochemical processes and that the organic matrix controls only crystal size, multiplication, and/or organization.

Animals↗
PubMed2001

Light scattering experiments on aqueous solutions of selected cellulose ethers: contribution to the study of polymer-mineral interactions in a new injectable biomaterial.

Hydroxypropylmethylcellulose (HPMC) is used as a ligand for a bioactive calcium phosphate ceramic (the filler) in a ready-to-use injectable sterilized biomaterial for bone and dental surgery. Light scattering experiments were usually used to study high water-soluble polymers and to determine the basic macromolecular parameters. In order to gain a deeper understanding of polymer/mineral interactions in this type of material, we have investigated the effect of divalent and trivalent ions (Ca(2+), PO(4)(3-)) and steam sterilization on dilute solutions of HPMC and hydroxyethylcellulose (HEC). The sterilization process may cause some degradation of HEC taking into account its high molecular weight and some rigidity of the polymer chain. Moreover, in the case of HPMC, the changes in the conformations rather than degradation process are supposed. These effects of degradation and flocculation are strengthened in alkaline medium. Experimental data suggested the formation of chelate complexes between Ca(2+) and HPMC which improve its affinity to the mineral blend and consolidate the injectable biomaterial even in the case of its hydration by biological fluid.

Journal Article↗
PubMed2001

Macroporous biphasic calcium phosphate ceramics versus injectable bone substitute: a comparative study 3 and 8 weeks after implantation in rabbit bone.

Macroporous biphasic calcium phosphate ceramics (MBCP) and a calcium phosphate injectable bone substitute (IBS), obtained by the association of biphasic calcium phosphate (BCP) ceramic granules and an aqueous solution of a cellulosic polymer, were compared in the same animal model. The two tested biomaterials were implanted in distal femoral osseous defects in rabbits. Qualitative and quantitative histological evaluation was performed three and eight weeks after implantation to investigate bone colonization and ceramic biodegradation associated with the two bone substitutes. Both biomaterials expressed osteoconduction properties and supported the apposition of a well-mineralized lamellar newly-formed bone. Bone colonization occurred much earlier and faster for IBS than for MBCP implants, although the respective rates of newly-formed bone after eight weeks of implantation did not differ significantly. For both biomaterials, ceramic resorption occurred regularly throughout the implantation period, though to a greater extent with IBS than with MBCP implants. The associated polymer in IBS produced intergranular spaces allowing body fluids to reach each BCP ceramic granule immediately after implantation, which may have favored osteoblastic activity, new bone formation and ceramic resorption. This completely interconnected open macroporosity could account for the earlier and more satisfactory bone substitution achieved with IBS.

Journal Article↗
PubMed2001

Interaction between hydroxypropyl methylcellulose and biphasic calcium phosphate after steam sterilisation: capillary gas chromatography studies.

The purpose of this study was to check the chemical stability of an injectable bone substitute (IBS) composed of a 50/50 w/w mixture of 2.92% hydroxypropyl methylcellulose (HPMC) solution in deionized water containing biphasic calcium phosphate (BCP) granules (60% hydroxyapatite/40% beta-tricalcium phosphate w/w). After separation of the organic and mineral phases, capillary gas chromatography (GC) was used to study the possible modification of HPMC due to the contact with BCP granules following steam sterilisation and 32 days storage at room temperature. HPMC was extracted from IBS in aqueous medium, and a dialytic method was then used to extract calcium phosphate salts from the HPMC. The percentage of HPMC extracted from BCP was 98.5%+/-0.5%, as measured by UV. GC showed no chemical modifications after steam sterilisation and storage.

Biocompatible Materials↗
PubMed2001

Study of the maturation of the organic (type I collagen) and mineral (nonstoichiometric apatite) constituents of a calcified tissue (dentin) as a function of location: a Fourier transform infrared microspectroscopic investigation.

Fourier transform infrared microspectroscopy (FTIRM) was used to investigate the organic and mineral phases of a calcified tissue (dentin) as a function of its location from predentin toward enamel. Thin dentin slices (decalcified or not) were fixed in formaldehyde and embedded in glycolmethylmethacrylate (GMA). Fixation did not denature collagen, and GMA did not interact with organic or mineral constituents of dentin. The v1v3 PO4 domain was studied in particular in order to estimate mineral maturity and amide I, II, A, and B to obtain data on protein conformation. The results showed that dentin apatite became increasingly mature (stoichiometric) from the mineralization front toward the enamel, especially through loss of HPO4(2-) groups and vacancies. Moreover, collagen fibrils became less and less hydrated, suggesting that intrafibrillar mineralization partially dehydrated the collagen. Combined study of the organic and mineral fractions of calcified tissues may help clarify their relationships in physiological and pathological tissues.

Adolescent↗
PubMed2001

[Autografts versus biomaterials for ossiculoplasty with normal stapes; a comparative analysis of functional outcome in 100 cases].

Ossicular graft is usually considered as the reference for surgical substitution in ossiculoplasties. Nevertheless, according to the infectious risks, nothing but autografts or synthetic prosthetic substitutes should be used nowadays. Authors compare hearing results for 100 patients after ossiculoplasty with either ossicular autograft or calcium-phospathe chain reconstruction. Audiometric results were retreived using both Glasgow Benefit Plot study and post-operative air-bone gap thresholds closure. Significant hearing improvement was statistically demonstrated in both conditions, and 60% of the patients had a post-operative hearing gain. Autograft ossicular reconstructions did not show to provide higher results. Biocompatibility and functionnal properties of calcium-phosphate materials retreived in this study, indicate that those ceramic substitutes should be considered as the best alternative to autografts.

Adolescent↗
PubMed2001

Scanning electron microscopic description of cellular activity and mineral changes in feline odontoclastic resorptive lesions.

The cellular activity and changes in mineral composition of dental tissues involved in feline odontoclastic resorptive lesions were investigated. Teeth with at least 1 lesion (n = 10) were extracted from 10 different cats that were presented primarily for chronic gingivostomatitis and/or severe periodontal disease. Scanning electron microscopic methods were used to determine the presence of resorptive cells in 8 teeth while 2 teeth were evaluated for pathologic changes in dental mineral composition. Observations were complicated by the presence of organic wear on the dental surfaces, however resorptive cells could be clearly identified in feline odontoclastic resorptive lesions. Resorptive cells had morphologic features indicative of "osteoclast-like" cells or odontoclasts. Resorptive cell activity created a resorption area of darker dentin continuous with physiologic dentin. The darker dentin area seemed poorly mineralized and showed a significantly lower calcium/phosphorous ratio compared with adjacent physiologic denting in 1 tooth. A significantly higher level of magnesium combined with available carbonate ions may have increased the solubility in areas of darker dentin.

Animals↗
PubMed2000

Biphasic calcium phosphates: influence of three synthesis parameters on the HA/beta-TCP ratio.

Hydroxyapatite (HA) contents measurements were conducted on eight biphasic calcium phosphate (BCP) samples obtained by sintering calcium-deficient apatite formed previously by hydrolyzing a dicalcium phosphate dihydrate (DCPD) powder. We evaluated the influences and interactions of three synthesis factors: alkalinity, process duration, and concentration of the water suspension in DCPD. Those parameters were varied simultaneously between two limit levels. Experiments used a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. FDM showed that HA content, in a defined experimental area, can be described by a first-order polynomial equation in which the initial alcalinity and the DCPD/water ratio are the major influences. Experiment prove that pH measured at the end of the hydrolysis was predictive of the HA content in the final BCP. This study leads up to an isoresponse line diagram which will allow the synthesis of some BCP with fitted HA/beta-tricalcium phosphate ratios.

Biocompatible Materials↗
PubMed2000

Crystal polymer interaction with new injectable bone substitute; SEM and Hr TEM study.

A composite constituted of calcium phosphate (CaP) granules and a hydrophilic polymer as a carrier (hydroxy-propyl-methyl cellulose, HPMC) was developed to be an injectable bone substitute (IBS, CNRS patent). IBS is a composite and not an ionic cement. The composite obtained is ready to use and sterile. Chemical interactions between organic and inorganic components appeared during the association of the two. The interactions of the CaP and the polymer have been studied using scanning electron microscopy (SEM), electron microprobe (EDX), and high-resolution transmission electron microscopy (HrTEM) SEM revealed a degradation of the granules into smaller particles while EDX was unable to show significant changes in the Ca/P ratio during aging of the composite. With Hr TEM, however, we observed hydrolysis (process of dissolution and precipitation) from the surface to about 13 nm into the HA crystals and occasional dissolution with precipitation of beta-TCP crystals. In HA, the first zone of interaction consisted of a single layer of small globular crystals of 2 to 3 nm in diameter. Numerous lattice patterns in all three axes could be observed. Under the globular crystals zone, the inter-reticular distances of the single crystals appeared enlarged by 1.2% (from 0.817 to 0.827 nm). The enlargement seems to correspond to diffusion of HPO(4) into the crystal lattice. In beta-TCP crystals, dissolution was observed to be several nanometers deep, but globular surface precipitation rarely was observed. With time or after steam sterilization, no changes were observed. These data demonstrate the strong interactions of the hydrophylic polymer with calcium phosphate, but only in the first several nanometers of thickness.

Bone Substitutes↗