Biomedical subjects

G Daculsi

Publications and source records attributed to G Daculsi.

At least 55 records · Page 3Linked to original sources

PubMed2000

Influence of isostatic compression on the stability of vancomycin loaded with a calcium phosphate-implantable drug delivery device.

It is essential to prevent microbial infections after osteoarticular trauma or prosthesis implantation. As an alternative to antibiotic parenteral administration, antibiotic-loaded biomaterials allow high concentrations to be obtained in situ without systemic toxicity. Although the formulation of biphasic calcium-phosphate (BCP)-vancomycin granules by isostatic compression has recently been used to produce drug-delivery devices, the stability of vancomycin needs to be proven. In this study, vancomycin was associated with BCP powders by isostatic compression at 100, 140, or 200 MPa and then extracted or released by a rotating paddle system for 24 h. Vancomycin assays were performed by spectrophotometric and microbiological methods. The results show that all vancomycin associated with the material was recovered after extraction without degradation. Thus, vancomycin was not denaturated after application of 100, 140, or 200 MPa of isostatic compression. The results for vancomycin released from granules compressed at the three pressures were not significantly different (p =.01) whether assays were performed microbiologically or spectrophotometrically, indicating a good correlation between the two methods. This process involving high pressure appears to be a good means of developing drug delivery devices loaded with therapeutic agents without denaturating the components.

Anti-Bacterial Agents↗

PubMed2000

Ultrastructural properties of bone mineral of control and tiludronate-treated osteoporotic rat.

Bisphosphonates have been widely used in the treatment of human bone pathologies including osteoporosis. In this case, bisphosphonates have been shown to reduce bone resorption, thereby increasing the mass and mechanical resistance of bone. Determining the effects of these molecules on the properties of the bone apatite crystals could provide a better insight into the mechanism of bisphosphonate/bone interaction. The aim of this study was to determine the ultrastructural effects of a third generation bisphosphonate (tiludronate) on the morphology, size, distribution, chemical composition, and structure of apatite crystals in bone (trabecular) in a rat osteoporotic model. Four groups of rats were studied: (1) sham operated, (2) untreated ovariectomized (OVX), (3) OVX rats which received 35 mg/kg of tiludronate, (4) OVX rats which received 160 mg/kg of tiludronate. The rats of groups 3 and 4 received tiludronate orally in 2 consecutive days every week for 1 year. Scanning electron microscopy (SEM), high and low resolution transmission electron microscopy (TEM), and electron microprobe analysis (EDX) were used for the ultrastructural characterization of the bone mineral. This study demonstrated that tiludronate slightly increased the width of bone apatite crystals without changing any other crystal characteristics.

Animals↗

PubMed2000

Isostatic compression, a new process for incorporating vancomycin into biphasic calcium phosphate: comparison with a classical method.

Isostatic compression has rarely been used to load calcium-phosphate biomaterials with therapeutic agents. This report, concerning four processes associating vancomycin, compares isostatic compression 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 isostatic compression study, BCP powder was compressed at 100, 140 and 200 MPa. The blocks obtained were crushed and 200-500 microm, sieved; thus, the vancomycin solution was absorbed on these granules. Compaction of BCP and vancomycin powders gave, after crushing and sieving, granules loaded with vancomycin. In each study, 5% vancomycin was associated with BCP. Vancomycin release profiles were assessed by an in vitro culture chamber dissolution test. Physicochemical studies of BCP and vancomycin showed their structural integrity after isostatic compression. Isostatic compression prolonged vancomycin release time from 3 to 7 days and the release time became greater as isostatic pressure increased, probably because of the porosity decrease of the granules during compression.

Calcium Phosphates↗

PubMed2000

Characterization of the trabecular rat bone mineral: effect of ovariectomy and bisphosphonate treatment.

Bisphosphonates, potent inhibitors of bone resorption, have been used clinically to correct the continued loss of bone mass in osteoporosis and in other conditions. However, there has been some concern that long-term treatment with these compounds, as well as more recently developed drugs, may also decrease the rate of bone formation. Bisphosphonates, which are strongly bound to hydroxyapatite crystals, may alter the structure and reactivity of the crystals, interfere with new crystal nucleation and growth, as well as alter the short-range order of newly formed crystals. We have investigated the chemistry and structure of the solid calcium-phosphate mineral phase of lumbar vertebrae of ovariectomized, 6.5-month-old rats treated with bisphosphonates for 1 year after onset of osteopenia. Appropriate control groups were used for comparison. The techniques used to assess the mineral phase were chemical analyses, Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy, FT-IR microspectroscopy, and phosphorus-31 magic-angle-sample spinning nuclear magnetic resonance spectroscopy ((31)P MAS NMR). The (31)P MAS NMR spectra of trabecular bone of lumbar vertebrae of control, ovariectomized, and treated animals were similar. However, there were several significant differences in the results obtained by FT-IR spectroscopy of the whole tissue samples, FT-IR microspectroscopy of sections of bone, and chemical analyses. For example, whereas chemical analyses demonstrated that the CO(3) content of the mineral phase of the ovariectomized animals was decreased compared with controls, FT-IR microspectroscopy of bone sections showed no changes in the relative CO(3) content, but some changes in the environment of the CO(3) groups. However, chemical analyses of the crystals, combined with data from all three spectroscopic methods and with data from serum analysis, did indicate small changes in the mineral phase after ovariectomy, corrected after treatment with bisphosphonates. In any event, the chemical and structural data in the present studies demonstrate that the bisphosphonate, tiludronate, does not significantly alter the mineral components of bone after 1 year of treatment during the course of which bone loss was reversed.

Animals↗

PubMed2000

Chemical transformation of some biologically relevant calcium phosphates in aqueous media during a steam sterilization.

The purpose of this study was to investigate the effect of steam sterilization on some biologically relevant calcium phosphates: CaHPO4 . 2H2O (DCPD), calcium deficient apatite (CDA) and biphasic calcium phosphate (BCP). Suspensions of 0.2 g of each calcium phosphate compound with 5.0 ml of deionized water were prepared and steam sterilized in an autoclave (20 min at 121 degrees C). After sterilization the suspensions were filtered and the dried solids characterized with scanning electron microscopy, IR-spectroscopy and X-ray diffraction. The pH and calcium concentrations of the filtrates were determined with ion selective electrodes. Similar measurements were made with the same samples which were not sterilized. The sterilization procedure was found to result in the dehydration of DCPD and hydration of calcium oxide incorporated into the BCP. Solution pH was observed to change from 7.3 to 5.5 for the solutions in equilibrium with DCPD and from 8.5 to 10.6 for those in equilibrium with BCP. Minor changes both with the solid and liquid phases were found to occur during the steam sterilization of CDA. These results indicate that steam sterilization may have different effects on different calcium phosphate suspensions: it can result in dehydration of DCPD, fast hydration for CaO in BCP, but no significant effect on CDA.

Journal Article↗

PubMed2000

In situ self hardening bioactive composite for bone and dental surgery.

A new biomaterial is presented which consists of a cellulose derivative--silanised hydroxyethylcellulose (HEC-SIL) and biphasic calcium phosphate (BCP). Rheological properties of the polymer itself and its mixture with BCP are pH-dependent. At pH 10-12 HEC-SIL is liquid and undergoes quick gellation at pH < 9. Similarly, the paste of HEC-SIL and BCP is fluid and injectable at higher pH and solidifies in biological solutions. The rate of this solidification can be easily controlled by the degree of substitution of hydroxyethylcellulose with silicoalkoxy groups.

Biocompatible Materials↗

PubMed1999

Osteogenic potential in vitro of human bone marrow cells cultured on macroporous biphasic calcium phosphate ceramic.

Calcium phosphate ceramics are synthetic bone substitutes that promote bone formation by osteoconduction. However, they have shown an osteogenic potential in vivo in animal models when associated with bone marrow cells. In order to develop an osteogenic human "hybrid material," we studied the in vitro osteogenic potential of human bone marrow cells cultured on macroporous biphasic calcium phosphate (BCP) pellets in the presence of dexamethasone with or without 1alpha,25 dihydroxyvitamin D3. We were examining, in particular, their mesenchymal stem cell proliferation and hematopoietic potential. Osteogenic differentiation was evaluated in terms of alkaline phosphatase activity and immunological characterization of the extracellular matrix formed by these cells. The specimens were observed by scanning and transmission electron microscopy. Human mesenchymal stem cells proliferated on macroporous BCP ceramic, with a doubling time delayed at the beginning of the culture as compared to the cultures realized on plastic. These cells maintained a hematopoietic activity identical to that of cultures performed in plastic wells. The proliferating mesenchymal stem cells expressed an osteoblastic phenotype, as shown by alkaline phosphatase activity and the synthesis in ceramic macropores of an extracellular matrix composed of fibronectin, osteocalcin, and collagen I (but not collagen III). In addition, numerous microcrystals of apatite precipitated on the extracellular matrix, producing a mineralized fibrillar network within the ceramic not observed with cell cultures realized on plastic. These results demonstrate that human mesenchymal stem cells cultured on macroporous BCP ceramic express and conserve their osteoblastic phenotype even after one month of culture and that these osteogenic cells are able to form new bone matrix in a BCP ceramic in vitro.

Biocompatible Materials↗

PubMed1999

Influence of biphasic calcium phosphate granulometry on bone ingrowth, ceramic resorption, and inflammatory reactions: preliminary in vitro and in vivo study.

Calcium-phosphate ceramics used in surgery, as bone-bonding materials, are currently available in different forms (blocks, granules, etc.). However, progress in noninvasive surgery has favored the development of injectable composite materials associating a polymeric and a dusty mineral phase. The purpose of this study was the in vivo evaluation of biphasic calcium phosphate of various grains sizes, to elucidate the role of granulometries in ceramic degradation/resorption, bone ingrowth, and inflammatory reactions. Three particle sizes were compared: 10-20, 80-100, and 200-400 microm. The 10-20-microm powders provided the best bone ingrowth, with a higher resorption/degradation rate in conjunction with stronger early inflammatory reactions. The 200-400-microm powders showed higher bone ingrowth than 80-100-microm ones, indicating that properties of cell recruitment for osseous apposition and mechanical support for bone bonding may both play a role in both ingrowth mechanisms. Our results suggest that the strong inflammatory reaction in 10-20-microm granulated powders was due to a faster reversal of the resorption/apposition sequence in bone. This may have resulted from massive release of bone ingrowth factors, which implies that the brief inflammatory process observed in the early stages of implantation was favorable to the osteoconduction process.

Bone Development↗

PubMed1999

Biological activities of sustained polymyxin B release from calcium phosphate biomaterial prepared by dynamic compaction: an in vitro study.

Calcium phosphate ceramics (CaP) have recently been proposed as a potential matrix for a bioactive drug delivery system (DDS) in which the effect in situ of a released therapeutic agent is favored by the biocompatibility, osteoconductivity, and bioresorption of the ceramic material. Polymyxin B (PMB) is a polypeptidic antibiotic which undergoes thermodamage above 60 degrees C. The dynamic compaction method was developed to consolidate the drug load on CaP powder without external heating. Two projectile velocities (50 and 25 m/s) were used here to achieve powder consolidation. Among the different techniques used to associate therapeutic agents with CaP, wet adsorption was performed before the dynamic compaction process. The PMB release profile was measured by a capillary electrophoresis technique, CaP crystallography was studied by x-ray diffraction, and CaP physicochemical analysis was performed by infrared spectroscopy. The biological activities of PMB-loaded compacted CaP were determined by the effect of the antibiotic and monocyte/macrophage degradation on compact surfaces. PMB release began after 2-3 days of incubation for blocks compacted at 25 m/s velocity and on day 5 for those compacted at 50 m/s velocity. A discrepancy was noted between the amounts of PMB released (0.5-2.1 mg) and the amounts initially compacted (2-8 mg) with CaP powder. The biological activities (antibacterial activity and inhibited lipopolysaccharide effects on monocyte/macrophage CaP degradation) of PMB released from compacted calcium-deficient apatite were unaltered. Thus, dynamic compaction allows PMB to be used with CaP ceramics without any loss in its integrity and biological effects.

Anti-Bacterial Agents↗

PubMed1999

Kinetic study of bone ingrowth and ceramic resorption associated with the implantation of different injectable calcium-phosphate bone substitutes.

This study investigated the in vivo performance of two composite injectable bone substitutes (IBS), each with different calcium-phosphate particles granulometries [40-80 (IBS 40-80) and 200-500 microm (IBS 200-500)]. These biomaterials were obtained by associating a biphasic calcium-phosphate (BCP) ceramic mineral phase with a 3% aqueous solution of a cellulosic polymer (hydroxy-propyl-methyl-cellulose). Both materials were injected for periods of 2, 3, 8, or 12 weeks into bone defects at the distal end of rabbit femurs. Quantitative results on new bone formation, BCP resorption, and staining for tartrate-resistant acid phosphatase (TRAP) activity were studied for statistical purposes. Measurements with scanning electron microscopy and image analysis showed that the final rates of newly formed bone were similar for both tested IBS after 12 weeks of implantation. Bone colonization occurred more extensively during early implantation times for IBS 40-80 than for IBS 200-500. For the latter, BCP degradation occurred regularly throughout the implantation period, whereas it was very intensive during the first 2 weeks for IBS 40-80. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than for IBS 200-500 regardless of implantation time. With the granulometry of either mineral phase, both tested IBS supported extensive bone colonization, which was greater than that previously reported for an equivalent block of macroporous BCP. The resorption-bone substitution process seemed to occur earlier and faster for IBS 40-80 than for IBS 200-500. Both tested IBS expressed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability.

Animals↗

PubMed1999

Role of fibronectin during biological apatite crystal nucleation: ultrastructural characterization.

The role of adhesion molecules like osteopontin and bone sialoprotein, both containing the Arg-Gly-Asp sequence have been shown to have a role in mineral formation, whereas fibronectin (FN), another adhesive protein, was never studied during the mineralization processes. The formation and maturation of biological apatite crystals are under matrix control, and one of the roles of specific crystal proteins is to control the nucleation and growth of biological apatite during the mineralization process (promotion or inhibition). In the case of calcium phosphate ceramic used as a bone substitute, a dissolution-precipitation process occurs after implantation before the bone ingrowth and bone mineralization. The early precipitation consists of common biological apatite crystals. These crystals are the result of secondary nucleation and a heteroepitaxic growth process on synthetic residual crystals. In in vivo studies, hydroxyapatite crystals were implanted subcutaneously into mice for 1 or 2 weeks. Fibronectin immunogold labeling of the newly formed crystals on surfaces of high-resolution transmission electron microscopy sections of retrieved implants revealed the close association of these precipitated crystals with FN. In in vitro experiments using a solution of human FN incubated in the presence of calcium phosphate crystals, we obtained apatite crystal precipitation. The fibronectin network observed in high-resolution transmission electron microscopy showed numerous clusters of very small particles (1 nm in diameter and 2 nm in length), whereas the same experiment realized as control on albumin revealed no crystal precipitation. These results demonstrate for the first time the role of FN in early biological crystal nucleation. This process could have important biological significance in accounting for ectopic calcification, primary nucleation in calcified tissue, and bone ingrowth on calcium phosphate ceramics.

Animals↗

PubMed1999

Ultrastructural study of apatite precipitation in implanted calcium phosphate ceramic: influence of the implantation site.

Macroporous biphasic calcium phosphate (MBCP) blocks were implanted into rabbit trabecular bone and muscle, recovered 18 weeks later, and then observed and analyzed by transmission electron microscopy (TEM), electron diffraction, and electron microprobes. The results showed that (1) apatitic microcrystals appeared by secondary nucleation in both bone and muscle sites; (2) precipitated microcrystals were aggregated around ceramic crystals in bone sites but distributed randomly and without orientation in micropores in muscle sites; (3) the ratio of calcium to phosphorus was higher for microcrystals in bone than muscle sites; and (4) precipitated microcrystals around beta-tricalcium phosphate (beta-TCP) crystals were less aggregated and dense than those around hydroxyapatite (HA). These findings suggest that microenvironmental parameters such as fluid circulation and the interaction of ceramics with proteins or cells affect the physicochemical dissolution/reprecipitation process. Epitaxic growth of apatitic microcrystals seems more favorable from HA than beta-TCP.

Animals↗

PubMed1999

Influence of a cellulosic ether carrier on the structure of biphasic calcium phosphate ceramic particles in an injectable composite material.

An injectable composite material based on biphasic calcium phosphate (BCP) and a nonionic cellulose ether has been elaborated for use in percutaneous surgery for spine fusion. This paper reports the characterization results of this material by spectroscopic techniques including X-ray diffraction (XRD), infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) fitted with an energy dispersive X-Ray analysis system and high-resolution transmission electron microscopy (HR-TEM). From FTIR and XPS results, it was observed that the adhesion between the polymer and the ceramic might be insured by oxygen bridging developed through an ionic bonding between calcium ions and (C-O) groups of the polymer. Moreover, XPS showed attraction of Ca2+ ions in the polymer matrix, while the ceramic surface was modified in a HPO4(2-) -rich layer. These results suggest a possible dissolution/precipitation process at the interface ceramic/polymer. HR-TEM observations supported this hypothesis, showing a light contrasted fringe at the surface of the ceramic grains in the composite paste. As well, changes in the XRD spectra could indicate a small decrease in the crystal size of the BCP powder through the contact to polymer solution. In addition, SEM observation showed a decrease of the initial BCP granulometry. Aggregates of 80-200 microm seemed to be mostly dissociated in micrograins. The ceramic grains were coated with and bonded between each other by the polymer matrix, which acted as spacer in between the ceramic grains, creating a macroporous-like material structure.

Biocompatible Materials↗

PubMed1999

Effects of fibronectin on hydroxyapatite formation.

There is increasing evidence that noncollagenous matrix proteins initiate bone mineralization in vivo. Fibronectin, which is present during the early phases of mineralization, may contribute to this process in bone tissues. In this context, the mineralization potential of fibronectin was tested in an agarose gel precipitation system and a metastable calcium phosphate solution. The protein inhibited the precipitation of calcium phosphate crystals in solution but had no apparent effect in gel. Conversely, fibronectin stimulated crystal formation when apatite powder was used to seed crystal growth in gel. Although these results in vitro do not clearly indicate that fibronectin is involved in the mineralization process, they are consistent with in vivo events. Free fibronectin (e.g. in biological fluids) could inhibit crystal growth but might also activate the mineralization process when absorbed on apatite powder in a bone environment and areas of ectopic mineralization.

Animals↗

PubMed1999

Biphasic calcium phosphate/hydrosoluble polymer composites: a new concept for bone and dental substitution biomaterials.

Calcium phosphate materials have been increasingly employed in orthopedic and dental applications in recent years and are now being developed for use in noninvasive surgery or as carriers for drug delivery systems. We developed an injectable bone substitute (IBS) constituted of biphasic calcium phosphate and a hydrosoluble polymer as a carrier. In vivo biocompatibility and biofunctionality of IBS were tested in rabbits using implants in osseous and nonosseous areas. The results obtained demonstrated that the concept of IBS, a filler without initial mechanical properties but able to be rapidly resorbed and replaced by newly formed bone, can be applied to new surgical applications in orthopedic surgery, maxillofacial surgery, and dentistry for pulp capping and root filling.

Animals↗

PubMed1999

Short-term effects of mineral particle sizes on cellular degradation activity after implantation of injectable calcium phosphate biomaterials and the consequences for bone substitution.

This in vivo study investigated the influence of two calcium phosphate particle sizes (40-80 microm and 200-500 microm) on the cellular degradation activity associated with the bone substitution process of two injectable bone substitutes (IBS). The tested biomaterials were obtained by associating a biphasic calcium phosphate (BCP) ceramic mineral phase and a 3% aqueous solution of a cellulosic polymer (hydroxypropylmethylcellulose). Both were injected into osseous defects at the distal end of rabbit femurs for 2- and 3-week periods. Quantitative results for tartrate-resistant acid phosphatase (TRAP) cellular activity, new bone formation, and ceramic resorption were studied for statistical purposes. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than IBS 200-500, regardless of implantation time. BCP degradation was quite marked during the first 2 weeks for IBS 40-80, and bone colonization occurred more extensively for IBS 40-80 than for IBS 200-500. The resorption-bone substitution process occurred earlier and faster for IBS 40-80 than IBS 200-500. Both tested IBS displayed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability. Differences in calcium phosphate particle sizes influenced cellular degradation activity and ceramic resorption but were compatible with efficient bone substitution.

Acid Phosphatase↗

PubMed1999

Injectable bone substitute using a hydrophilic polymer.

We studied a new injectable biomaterial for bone and dental surgery consisting of a hydrophilic polymer as matrix and bioactive calcium phosphate (CaP) ceramics as fillers. This material is composed of complex fluids whose flow is determined by the laws of rheology. We investigated the macromolecular effects on this composite in a tube. The stability of the polymer and the mixture is essential to the production of a ready-to-use injectable biomaterial. These flow properties are necessary to obtain CaP bioactivity in a dental canal or bone defect during percutaneous surgery. Macromolecules provide spaces between CaP ceramic granules and facilitate the role of the biological agents of bone substitution.

Animals↗

PubMed1999

Elaboration conditions influence physicochemical properties and in vivo bioactivity of macroporous biphasic calcium phosphate ceramics.

Two different preparations of biphasic calcium phosphate (BCP) were characterized in vitro: BCP1 from a mechanical mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) powders, and BCP2 from calcination of a calcium-deficient apatite (CDA). The structural, physicochemical and mechanical parameters of these two preparations were investigated, and two different macroporous BCP1 (MBCP1) and BCP2 MBCP2) implants were manufactured and implanted in rabbit bone for in vivo bioactivity studies. Scanning electron microscopy observations showed that MBCP1 implants had a significantly higher degradation rate (P<0.0001) than MBCP2 implants. This was probably caused by the presence of calcium oxide impurities in BCP1 and the more intimate mixture and stable ultrastructure of BCP2. No significant difference about the newly formed bone rate in these two BCP preparations was observed. Very slight variations in sintering conditions appeared to influence the biodegradation behavior of the two MBCP implants despite their identical HA/-TCP ratios and similar porosity. Precise and complete in vitro characterization enabled us to understand and predict in vivo degradation behavior.

Journal Article↗