Osseointegration of two types of titanium cylinders with geometric or trabecular microarchitecture: A nanotomographic and histomorphometric study

Porous biomaterials promote osseointegration. We have prepared porous titanium cylinders by additive manufacturing from titanium beads. Two types of morphology were tested: cylinders with geometric pores or mimicking trabecular microarchitecture. Cylinders were decontaminated and cleaned by HF/HNO₃ to remove unmelted balls. Surgical implantation in ewes was performed under general anesthesia and the animals were housed for 90 and 270days. The femoral condyles were collected and analyzed by nanoCT, embedded in pMMA and analyzed by histomorphometry. No significant difference was found in terms of bone volume or bone/titanium interface between the two types of cylinders. There was no evolution over time except for the mineralization rates which decreased, reflecting the effect of the aging of the animals. The influence of the pores (geometrical or "natural") did not influence osseointegration. HF/HNO₃ etching treatments are effective on the outermost surfaces but do not seem to reach the central cavities of the samples. Finally, osseointegration seems to occur only in the few millimeters around the periphery of the implants and does not extend in the center. This is explained by the absence of stress transmission within the very rigid metal cylinders, preventing bone modeling and remodeling.

Two androecious mutations reveal the crucial role of ethylene receptors in the initiation of female flower development in Cucurbita pepo

Ethylene is the key regulator of sex determination in monoecious species of the family Cucurbitaceae. This hormone determines which individual floral meristems develop as female or male flowers and the female flowering transition. The sex determination genes discovered so far code for ethylene biosynthesis enzymes, but little is known about the importance of ethylene signaling components. In this paper we characterize two novel ethylene-insensitive mutations (etr1a-1 and etr1b) which block the female flowering transition of Cucurbita pepo; this makes plants produce male flowers indefinitely (androecy). Two missense mutations in the ethylene-binding domain of the ethylene receptors CpETR1A or CpETR1B were identified as the causal mutations of these phenotypes by using whole-genome resequencing. The distinctive phenotypes of single and double mutants for four etr mutations have demonstrated that the final level of ethylene insensitivity depends upon the strength and dosage of mutant alleles for at least three cooperating ETR genes, and that the level of ethylene insensitivity determines the final sex phenotype of the plant. The sex phenotype ranges from monoecy in ethylene-sensitive wild-type plants to androecy in the strongest ethylene-insensitive ones, via andromonoecy in partially ethylene-insensitive plants. The induction of female flowering transition was found to be associated with upregulation of CpACS11, CpACO2 and CpACS27, three ethylene biosynthesis genes required for female flower development. A model is proposed herein, integrating both ethylene biosynthesis and receptor genes into the genetic network which regulates sex determination in C. pepo.

The ethylene receptors CpETR1A and CpETR2B cooperate in the control of sex determination in Cucurbita pepo

High-throughput screening of an ethyl methanesulfonate-generated mutant collection of Cucurbita pepo using the ethylene triple-response test resulted in the identification of two semi-dominant ethylene-insensitive mutants: etr1a and etr2b. Both mutations altered sex determination mechanisms, promoting conversion of female into bisexual or hermaphrodite flowers, and monoecy into andromonoecy, thereby delaying the transition to female flowering and reducing the number of pistillate flowers per plant. The mutations also altered the growth rate and maturity of petals and carpels in pistillate flowers, lengthening the time required for flowers to reach anthesis, as well as stimulating the growth rate of ovaries and the parthenocarpic development of fruits. Whole-genome sequencing allowed identification of the causal mutation of the phenotypes as two missense mutations in the coding region of CpETR1A and CpETR2B, each one corresponding to one of the duplicates of ethylene receptor genes highly homologous to Arabidopsis ETR1 and ETR2. The phenotypes of homozygous and heterozygous single- and double-mutant plants indicated that the two ethylene receptors cooperate in the control of the ethylene response. The level of ethylene insensitivity, which was determined by the strength of each mutant allele and the dose of wild-type and mutant etr1a and etr2b alleles, correlated with the degree of phenotypic changes in the mutants.

Mapping a Partial Andromonoecy Locus in Citrullus lanatus Using BSA-Seq and GWAS Approaches

The sexual expression of watermelon plants is the result of the distribution and occurrence of male, female, bisexual and hermaphrodite flowers on the main and secondary stems. Plants can be monoecious (producing male and female flowers), andromonoecious (producing male and hermaphrodite flowers), or partially andromonoecious (producing male, female, bisexual, and hermaphrodite flowers) within the same plant. Sex determination of individual floral buds and the distribution of the different flower types on the plant, are both controlled by ethylene. A single missense mutation in the ethylene biosynthesis gene CitACS4, is able to promote the conversion of female into hermaphrodite flowers, and therefore of monoecy (genotype MM) into partial andromonoecy (genotype Mm) or andromonoecy (genotype mm). We phenotyped and genotyped, for the M/m locus, a panel of 207 C. lanatus accessions, including five inbreds and hybrids, and found several accessions that were repeatedly phenotyped as PA (partially andromonoecious) in several locations and different years, despite being MM. A cosegregation analysis between a SNV in CitACS4 and the PA phenotype, demonstrated that the occurrence of bisexual and hermaphrodite flowers in a PA line is not dependent on CitACS4, but conferred by an unlinked recessive gene which we called pa. Two different approaches were performed to map the pa gene in the genome of C. lanatus: bulk segregant analysis sequencing (BSA-seq) and genome wide association analysis studies (GWAS). The BSA-seq study was performed using two contrasting bulks, the monoecious M-bulk and the partially andromonoecious PA-bulk, each one generated by pooling DNA from 20 F2 plants. For GWAS, 122 accessions from USDA gene bank, already re-sequenced by genotyping by sequencing (GBS), were used. The combination of the two approaches indicates that pa maps onto a genomic region expanding across 32.24-36.44 Mb in chromosome 1 of watermelon. Fine mapping narrowed down the pa locus to a 867 Kb genomic region containing 101 genes. A number of candidate genes were selected, not only for their function in ethylene biosynthesis and signalling as well as their role in flower development and sex determination, but also by the impact of the SNPs and indels differentially detected in the two sequenced bulks.

Hyaluronic Acid Stimulates Osseointegration of β-TCP in Young and Old Ewes

Cross-linked hyaluronic acid (HyAR) increases the local concentration of growth factors. We compared β-TCP osseointegration in old and young ewes with/without HyAR addition. A blind tunnel was drilled on the medial femoral condyle of each knee in nine young and nine old ewes and was filled with β-TCP, β-TCP + HyAR or left unfilled. Double labeling with calcein allowed histodynamic analysis. Ewes were sacrificed at 84 days and the knees were harvested. MicroCT provided histomorphometric parameters: trabecular bone volume, residual volume of biomaterial. Histodynamic parameters were: mineralization rate, mineralized surfaces, bone formation rate. A non-parametric ANOVA and post hoc test analyzed differences between subgroups. Osseointegration of β-TCP was similar in the aged/young grafted groups. Trabecular bone volume was significantly increased versus ungrafted animals (p < 0.001). There were no significant difference for bone volume, residual volume of biomaterial and histodynamic parameters when a single parameter was considered but additional effects of β-TCP and HyAR were evidenced by 3D analysis. Addition of HyAR to ß-TCP does not significantly increase bone volume but tends to increase histodynamic parameters. However, considering the reduction of osteoblastic activity in aged animals, β-TCP, and HyAR boosts osteoblastic activity. HyAR leads to an equivalent response between young and old animals.

Polyhydroxyalkanoate (PHBV) fibers obtained by a wet spinning method: Good in vitro cytocompatibility but absence of in vivo biocompatibility when used as a bone graft

Polyhydroxyalkanoates (PHAs) are biomaterials widely investigated for tissue-engineering applications. In this regard, we describe a method to prepare fibers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by a wet-spinning technique. Polymer fibers were used to test the cytocompatibility of the material in vitro. We have investigated their behavior in vitro in presence of the osteoblast-like (SaOs2) and macrophage (J774.2) cell lines. The PHBV fibers used were 100-200μm in diameter and offered a large surface for cell adhesion, similar to that they encounter when apposed onto a bone trabeculae. The fiber surface possessed a suitable roughness, a factor known to favor the adherence of cells, particularly osteoblasts. PHBV fibers were degraded in vitro by J774.2 cells as erosion pits were observable by transmission electron microscopy. The fibers were also colonisable by SaOs2 cells, which can spread and develop onto their surface. However, despite this good cytocompatibility observed in vitro, implantation in a bone defect drilled in rabbit femoral condyles showed that the material was only biotolerated without any sign of osteoconduction or degradation in vivo. We can conclude that PHBV is cytocompatible but is not suitable to be used as a bone graft as it does not favor osteoconduction and is not resorbed by bone marrow macrophages.

The sex-determining gene CitACS4 is a pleiotropic regulator of flower and fruit development in watermelon (Citrullus lanatus)

In the species of the Cucurbitaceae family, the occurrence of separate male and female flowers in the same plant (monoecy) is controlled by an ethylene biosynthesis ACS gene, which specifically suppresses the development of stamen in the female flower. In watermelon, a mutation of loss of function in CitACS4 promotes the conversion of female into hermaphrodite flowers, and of monoecious into andromonoecious plants. We have studied whether the ethylene produced by CitACS4 enzyme could also be involved in other ethylene-regulated traits, including pistillate flowering transition and the number of female flowers per plant, the development of floral organs other than stamens, as well as fruit and seed set, and fruit development. A linkage analysis approach was performed in three independent F2 populations segregating for the two alleles of the gene (M, monoecious; m, andromonoecious), and the different traits under study. The CitACS4m allele not only cosegregated with andromonoecy, but also with earlier pistillate transition, an increased number of pistillate flowers per plant, and a slower growth and maturation of petals and carpels, which delayed anthesis time in hermaphrodite flowers. The m allele was also found to be linked to a reduced fruit set, which was not caused by a deficiency in pollination or fertilization. The gene also affected the longitudinal and transverse growth rates of the ovary and fruit, which means that fruits from andromonoecious plants (mm) were rounder than those from monoecious (MM) ones. Taken together, these data indicate that the locus defined by the ethylene biosynthesis and sex-determining gene CitACS4 acts as a pleiotropic regulator of the complete development of the pistillate flower and the earlier development of the fruit.

Microcomputed tomography (microCT) and histology of the mandibular canal in human and laboratory animals

The inferior alveolar nerve (IAN) is a sensitive branch of the trigeminal nerve. It has an intra-bone path in the mandible, inside the mandibular canal, where it is accompanied by lymph, venous and arterial vessels. We have studied the mandibular canal in human mandibles and in some laboratory animals (mice, rats, rabbits and cats). Microcomputed tomography evidenced that the walls of the canal are made with thin plates of trabecular bone with numerous fenestrations. This aspect is evidenced in dentate subjects and become more evident in edentulous subjects with atrophy of the alveolar bone. In rats and mice, the wall of the canal is also clearly composed of trabecular plates coming from the surrounding alveolar bone of the mandible. In the rabbit, similar findings are also observed but the trajectory of the canal is more difficult to identify. In the cat, the floor of the canal is composed of the cortical bone from the basilar cortex of the mandible and the roof has a trabecular nature. Vascular injections of gelatin-barium evidenced the arterial trajectories inside the bone in rats and humans. Undecalcified bone sections in human evidenced the histological aspect of the IAN and its connective sheets. Some nervous bundles can be observed outside the epineurium. Bone remodeling is observed on the wall of the mandibular canal. These descriptive findings have a clinical relevance in dental implantology or mandibular surgery.

Immune modulation by the hepatitis C virus core protein

Hepatitis C virus (HCV) infection is currently the most important cause of chronic viral hepatitis in the world and one of the most frequent indications for liver transplantation. HCV uses different strategies to evade the innate and adaptive immune response, and this evasion plays a key role in determining viral persistence. Several HCV viral proteins have been described as immune modulators. In this review, we will focus on the effect of HCV nucleocapsid core protein in the function of immune cells and its correlation with the findings observed in HCV chronically infected patients. Effects on immune cell function related to both extracellular and intracellular HCV core localization will be considered. This review provides an updated perspective on the mechanisms involved in HCV evasion related to one single HCV protein, which could become a key tool in the development of new antiviral strategies able to control and/or eradicate HCV infection.

Overexpression of a flower-specific aerolysin-like protein from the dioecious plant Rumex acetosa alters flower development and induces male sterility in transgenic tobacco

Sex determination in Rumex acetosa, a dioecious plant with a complex XY1 Y2 sex chromosome system (females are XX and males are XY1 Y2 ), is not controlled by an active Y chromosome but depends on the ratio between the number of X chromosomes and autosomes. To gain insight into the molecular mechanisms of sex determination, we generated a subtracted cDNA library enriched in genes specifically or predominantly expressed in female floral buds in early stages of development, when sex determination mechanisms come into play. In the present paper, we report the molecular and functional characterization of FEM32, a gene encoding a protein that shares a common architecture with proteins in different plants, animals, bacteria and fungi of the aerolysin superfamily; many of these function as β pore-forming toxins. The expression analysis, assessed by northern blot, RT-PCR and in situ hybridization, demonstrates that this gene is specifically expressed in flowers in both early and late stages of development, although its transcripts accumulate much more in female flowers than in male flowers. The ectopic expression of FEM32 under both the constitutive promoter 35S and the flower-specific promoter AP3 in transgenic tobacco showed no obvious alteration in vegetative development but was able to alter floral organ growth and pollen fertility. The 35S::FEM32 and AP3::FEM32 transgenic lines showed a reduction in stamen development and pollen viability, as well as a diminution in fruit set, fruit development and seed production. Compared with other floral organs, pistil development was, however, enhanced in plants overexpressing FEM32. According to these effects, it is likely that FEM32 functions in Rumex by arresting stamen and pollen development during female flower development. The aerolysin-like pore-forming proteins of eukaryotes are mainly involved in defence mechanisms against bacteria, fungi and insects and are also involved in apoptosis and programmed cell death (PCD), a mechanism that could explain the role of FEM32 in Rumex sex determination.

The Ethylene Biosynthesis Gene CitACS4 Regulates Monoecy/Andromonoecy in Watermelon (Citrullus lanatus)

Monoecious and andromonoecious cultivars of watermelon are characterised by the production of male and female flower or male and hermaphrodite flowers, respectively. The segregation analysis in the offspring of crosses between monoecious and andromonoecious lines has demonstrated that this trait is controlled by a single gene pair, being the monoecious allele M semi-dominant to the andromonoecious allele A. The two studied F1 hybrids (MA) had a predominantly monoecious phenotype since both produced not only female flowers, but also bisexual flowers with incomplete stamens, and hermaphrodite flowers with pollen. Given that in other cucurbit species andromonoecy is conferred by mutations in the ethylene biosynthesis genes CmACS7, CsACS2 and CpACS27A we have cloned and characterised CitACS4, the watermelon gene showing the highest similarity with the formers. CitACS4 encoded for a type ACS type III enzyme that is predominantly expressed in pistillate flowers of watermelon. In the andromonoecious line we have detected a missense mutation in a very conserved residue of CitACS4 (C364W) that cosegregates with the andromonoecious phenotype in two independent F2 populations, concomitantly with a reduction in ethylene production in the floral buds that will develop as hermaphrodite flowers. The gene does not however co-segregates with other sex expression traits regulated by ethylene in this species, including pistillate flowering transition and the number of pistillate flowers per plant. These data indicate that CitAC4 is likely to be involved in the biosynthesis of the ethylene required for stamen arrest during the development of female flowers. The C364W mutation would reduce the production of ethylene in pistillate floral buds, promoting the conversion of female into hermaphrodite flowers, and therefore of monoecy into andromonoecy.

Identification of functional, short-lived isoform of linker for activation of T cells (LAT)

Linker for activation of T cells (LAT) is a transmembrane adaptor protein playing a key role in the development, activation and maintenance of peripheral homeostasis of T cells. In this study we identified a functional isoform of LAT. It originates from an intron 6 retention event generating an in-frame splice variant of LAT mRNA denoted as LATi6. Comparison of LATi6 expression in peripheral blood leukocytes of human and several other mammalian species revealed that it varied from being virtually absent in the mouse to being predominant in the cow. Analysis of LAT isoform frequency expressed from minigene splicing reporters carrying loss- or gain-of-function point mutations within intronic polyguanine sequences showed that these elements are critical for controlling the intron 6 removal. The protein product of LATi6 isoform (LATi6) ectopically expressed in LAT-deficient JCam 2.5 cell line localized correctly to subcellular compartments and supported T-cell receptor signaling but differed from the canonical LAT protein by displaying a shorter half-life and mediating an increased interleukin-2 secretion upon prolonged CD3/CD28 crosslinking. Altogether, our data suggest that the appearance of LATi6 isoform is an evolutionary innovation that may contribute to a more efficient proofreading control of effector T-cell response.

A case of polyostotic osteosarcoma with kidney metastases in a dog: histopathology and microcomputed tomographic analysis

A 7-year- old sexually intact female Leonberg dog was evaluated for chronic lameness of the right forelimb. The bitch showed mild hyperthermia (39.3°C), a decrease in its activity, a capricious appetite, a high weight loss (4 kg in 15 days) and a right foreleg lameness. A careful clinical examination revealed a deformation of the right proximal humerus and right tibia. Radiographic examination of the right tibia, right humerus showed osteolysis of both cortical and trabecular bone with a periosteal bone proliferation in the vicinal soft tissues. The owner having refused a bone biopsy, a treatment with NSAIDs and antibiotics was prescribed. After a marked improvement during the first two weeks, an increase in lameness and activity was observed. At that time, the owner accepted the bone biopsy. Histopathologic examination evidenced an osteosarcoma but the amount of available tissue was limited. Due to the poor prognosis, he declined treatment and decided to euthanize the dog. An osteosarcoma with a large chondroid component was observed at autopsy together with ossifying kidney metastases. Histological findings revealed a grade III osteosarcoma. Conventional and undecalcified histology and X-ray microcomputed tomography findings evidenced a large and partially mineralized osteoid part with a sunburst extension in the soft tissues. This is the first time that microCT and undecalcified analyses of an osteosarcoma are presented. The osteolytic and metaplastic bone foci were easily demonstrated by this method.

Changes in exhaled nitric oxide after inhalation challenge with occupational agents

BACKGROUND AND OBJECTIVE

The use of fractional exhaled nitric oxide (FeNO) concentration has been proposed as a surrogate marker for monitoring airway response to specific inhalation challenge (SIC). We investigated the usefulness of FeNO measurements for monitoring airway response to SIC with occupational agents. Materialandmethods: Workers with suspected occupational asthma were recruited to undergo SIC with occupational agents and subsequently FeNO testing at baseline and 24 hours.

RESULTS

Sixty-eight patients were evaluated, 45 of whom had a positive SIC. SIC-positive patients showed a significant increase in FeNO 24 hours postchallenge, with an increase ratio of 1.25 (95% CI, 1.05-1.48; P=.01); no increase was seen in patients with a negative SIC (P=.08). The predictive capacity of variations in FeNO showed that for each unit increase in FeNO, the probability of a positive SIC rose by 4%. A baseline FeNO value of 25 ppb predicted a positive SIC with 60% sensitivity and 80% specificity. The increase in %FeNO cutoff point providing maximal sensitivity and specificity for predicting a positive SIC was 41% (sensitivity 50%, specificity 95%).

CONCLUSIONS

We demonstrated that asthmatic reactions induced by occupational agents during SICs are associated with a consistent increase in FeNO. However, the predictive diagnostic capacity of FeNO measurements is low. While FeNO may aid in the interpretation of SIC in some cases, it cannot be used as a general surrogate marker to predict or to assess SICs with occupational agents.

Tropomyosin IgE-positive results are a good predictor of shrimp allergy

BACKGROUND

Shrimp is a common cause of food allergy. Our aims were to determine the value of IgE antibodies in the diagnosis of shrimp allergy and to study red shrimp (Solenocera melantho) tropomyosin both as a new allergen and as a cross-reactive IgE-binding protein.

METHODS

We have studied 45 subjects. Skin prick test (SPT) was carried out in all subjects, and specific IgE (sIgE) to shrimp, recombinant and natural shrimp tropomyosins rPen a 1 and nPen m 1, recombinant Der p 10, and Dermatophagoides pteronyssinus was assessed by fluoroimmunoassay and/or immunoblotting. Double-blind, placebo-controlled food challenges were carried out to confirm diagnosis of shrimp allergy. Also, in vitro inhibition tests were performed to evaluate cross-reactivity.

RESULTS

Shrimp allergy was confirmed in 18 shrimp-allergic patients. Skin prick test and IgE antibodies to shrimp were positive in all shrimp-allergic patients; sIgE to rPen a 1 was detected in 98% of these patients. Of the 18 shrimp-tolerant patients, 61% had positive SPT to shrimp, 55% were IgE-positive to shrimp, and 33% showed IgE antibodies to rPen a 1. Determination of IgE to rPen a 1 yielded a positive predictive value of 0.72 and a negative predictive value of 0.91.

CONCLUSION

IgE levels to rPen a 1 provided additional value to the diagnosis of shrimp allergy. Some allergens in mite extract are recognized by patients who are allergic to shrimp, though their clinical relevance remains unknown.

Does milling one-piece titanium dental implants induce osteocyte and osteoclast changes?

One-piece dental implants avoid adverse effects sometimes associated with the traditional implant-abutment interface and may provide a suitable alternative to two-piece implants; however, one-piece implants often need in situ milling, which may exacerbate cell apoptosis from excessive heat at the bone-implant interface and induce secondary crestal bone loss. Twelve implants were placed in the metaphyses of two sheep under general anesthesia. Six implants were milled with a diamond bur while the other six implants remained intact. Animals were euthanized after four days, and bone blocks were harvested. Bone samples were studied without decalcification. Osteocytes were stained with Hoechst 33342 and osteoclasts by the TRAcP reaction. Both cell types, in the cortical and trabecular bone around the implant's cervical region, were counted utilizing morphometric methods. Values were compared to areas at a distance from the cervical region. No difference was observed between milled and unmilled implants, which suggested that the amount of generated heat did not provoke osteocyte loss or induce osteoclastogenesis. Intraoral abutment preparations did not increase cellular apoptosis at the bone-implant interface after four days in the ovine model.

Biofunctionality of MBCP ceramic granules (TricOs) plus fibrin sealant (Tisseel) versus MBCP ceramic granules as a filler of large periprosthetic bone defects: an investigative ovine study

We aimed to quantify bone colonization toward an untreated titanium implant with primary stability following filling of the defect with micromacroporous biphasic calcium phosphate (MBCP) granules (TricOs) or MBCP granules mixed with fibrin sealant (Tisseel). Medial arthrotomy was performed on the knees of 20 sheep to create a bone defect (16 mm deep; 10 mm diameter), followed by anchorage of a titanium screw. Defects were filled with TricOs or TricOs-Tisseel granules, a perforated MBCP washer, a titanium washer and titanium screw. Sheep were euthanized at 3, 6, 12 and 26 weeks. From Week 12 onwards, the percentage of bone in contact with the 8 mm anchorage part of the screw increased in both groups, confirming its primary stability. At 26 weeks, whereas bone colonization was similar in both groups, biodegradation of ceramic was more rapid in the TricOs-Tisseel group (P = 0.0422). The centripetal nature of bone colonization was evident. Bone contact with the titanium implant surface was negligible. In conclusion, the use of a model that reproduces a large metaphyseal bone defect around a titanium implant with primary stability, filled with a mixture of either TricOs ceramic granules or TricOs granules mixed with Tisseel fibrin sealant, suggests that the addition of fibrin to TricOs enhances bone filling surgical technology.

Radiation effects on bone healing and reconstruction: interpretation of the literature

OBJECTIVE

Reconstructing irradiated mandibles with biomaterials is still a challenge but little investigated. We collected data that could help us understand studies in the field of regeneration with biomaterials and irradiated bone.

STUDY DESIGN

Systematic review of the literature.

RESULTS

Delay and duration of radiation delivery and total equivalent dose are the most variable parameters in the various studies, resulting in confusion when interpreting the literature. Most reproducible experiments show that radiation reduces osteogenic cell numbers, alters cytokine capacity, and delays and damages bone remodeling. Interindividual variations and how such changes become irreversible lesions are still uncertain. In the case of regeneration using biomaterials, most studies have addressed the question of reconstruction in previously irradiated bone. The results show that osseointegration is often possible, although the failure rate is higher. The sooner the implantation takes place after the end of the radiation, the higher the likelihood of failure. Few studies have focused on primary reconstruction followed by early irradiation, and most of the currently available engineering models would be altered by radiation. Good outcomes have been obtained with bone morphogenetic protein and with total bone marrow transplanation.

CONCLUSION

This review points out the difficulties in achieving reproducible experiments and interpreting literature in this underinvestigated field.

Developments in injectable multiphasic biomaterials. The performance of microporous biphasic calcium phosphate granules and hydrogels

Calcium phosphate bioceramic granules associated with hydrosoluble polymers were developed as bone substitutes for various maxillofacial and orthopaedic applications. These injectable bone substitutes, support and regenerate bone tissue and resorb after implantation. The efficiency of these multiphasic materials is due to the osteogenic and osteoconductive properties of the microporous biphasic calcium phosphate. The associated hydrosoluble polymers are considered as carriers in order to achieve the rheological properties of injectable bone substitutes (IBS). In this study, we used 2 semi synthetic hydrosoluble polymers of polysaccharidic origin. The hydroxy propyl methyl cellulose (HPMC), with and without silane, was combined with microporous BCP granules. The presence of silane induced considerable gelation of the suspension. The 2 IBS used (without gelation, IBS1, with gelation, IBS2) were implanted in critical size femoral epiphysis defects in rabbits. No foreign body reactions were observed in either sample. However, because of the higher density from gelation, cell colonisation followed by bone tissue ingrowth was delayed over time with IBS2 compared to the IBS1 without gelation. The results showed resorption of the BCP granule and bone ingrowth at the expense of both IBS with different kinetics. This study demonstrates that the hydrogel cannot be considered merely as a carrier. The gelation process delayed cell and tissue colonisation by slow degradation of the HPMC Si, compared to the faster release of HPMC with IBS1, in turn inducing faster permeability and spaces for tissue ingrowth between the BCP granules.

Bone growth in rapid prototyped porous titanium implants

Two porous titanium implants with a pore size diameter of 800 and 1200 microm (Ti800 and Ti1200) and an interconnected network were manufactured using rapid prototyping. Their dimensions and structure matched those of the computer assisted design. The porosity of the implants was around 60%. Their compressive strength and Young's modulus were around 80 MPa and 2.7 GPa, respectively. These values are comparable to those of cortical bone. The implants were implanted bilaterally in the femoral epiphysis of 15 New Zealand White rabbits. After 3 and 8 weeks, abundant bone formation was found inside the rapid prototyped porous titanium implants. For the Ti1200 implants, bone ingrowth was (23.9 +/- 3.5)% and (10.3 +/- 2.8)%, respectively. A significant statistical difference (p < 0.05) was found for bone ingrowth in the Ti1200 between the two delays. The percentage of bone directly apposited on titanium was (35.8 +/- 5.4)% and (30.5 +/- 5.0)%. No significant difference was found for bone-implant contact between the different time periods and pore sizes. This work demonstrates that manufacturing macroporous titanium implants with controlled shape and porosity using a rapid prototyping method is possible and that this technique is a good candidate for orthopedic and maxillofacial applications.

[Experimental evaluation of microscan assessment of bone fusion]

PURPOSE OF THE STUDY

Certain confirmation of bone fusion remains difficult to obtain after arthrodesis despite progress in imaging techniques. Microscanning enables both qualitative and quantitative analysis of the bone microarchitecture. The purpose of this study was to evaluate this technique using a cervical arthrodesis with an intersomatic cage on an animal model and to validate results with histological analysis and electron scan microscopy (SEM).

MATERIAL AND METHODS

C3-C4 discectomy was performed in 8 goats divided into two groups. In group 1 (3 animals), PEEK cages were inserted without bone graft. In group 2 (5 goats) the same cage was inserted and filled with an autologous iliac graft. The animals were sacrificed at six months. The instrumented levels were analyzed with a microscan. Histological slides were obtained and SEM performed.

RESULTS

Nonunion was observed in the three animals with an empty cage (group 1) while only one animal in group 2 presented nonunion. Histology and SEM confirmed the diagnosis established with the microscan which also enabled a 3D analysis of the sample and study of the trabecular architecture of the intersomatic graft.

DISCUSSION

The microscan enabled a micrometric analysis of the sample. This is the only technique enabling 3D analysis (slices can be obtained in the three planes for 3D reconstruction) for both qualitative and quantitative assessment. Analysis of the trabecular microstructure constitutes a major progress in evaluating the mechanical value of the fusion. The sample is not destroyed and can be studied further with other biomechanical techniques.

CONCLUSION

Microscanning is an important technical advancement for the analysis of bone fusion. Future applications will undoubtedly be numerous (follow-up after arthrodesis, analysis of the mechanical quality of a graft). In vivo applications will probably be adapted soon.

[Study of two types of dental implants for immediate loading (expansion implants and locking pin implants) in the Beagle dog]

Titanium implants have become a treatment of choice for total or partially edentulous patients. The method, however, requires a double surgical time and the placement of the dental prosthesis after a healing phase of 3 to 6 months during which the patients have a toothless mandible with the top of the implants emerging at the gengiva. Immediate loading of standard implants is responsible for micromotions which induce implant failure. New designs of implants would allow an immediate anchoring in the bone, would prevent the shearing forces and would precociously authorize the setting of the prosthesis. We made an experimental study in the Beagle dog. After partial tooth removal, two types of implants were placed (expansion implants and locking pin implants). After 2 weeks, the implants were covered with a gold-palladium prosthesis and left in place during 12 weeks. After sacrifice, a study by resonance frequency (ISQ) and histomorphometry was done. The two types of implants were covered by the same quantity with bone (volume and interface) without interposition of fibrous tissue. The locking pin implants were associated with an increase in the ISQ parameter of stability, higher than that of the expansion implants. The locking pin implant, tested in the dog which has a chewing function close to man, appears interesting for the immediate loading with dental prosthesis.

Small-animal models for testing macroporous ceramic bone substitutes

The aim of this study was to compare the bone colonization of a macroporous biphasic calcium phosphate (MBCP) ceramic in different sites (femur, tibia, and calvaria) in two animal species (rats and rabbits). A critical size defect model was used in all cases with implantation for 21 days. Bone colonization in the empty and MBCP-filled defects was measured with the use of backscattered electron microscopy (BSEM). In the empty cavities, bone healing remained on the edges, and did not bridge the critical size defects. Bone growth was observed in all the implantation sites in rats (approximately 13.6-36.6% of the total defect area, with ceramic ranging from 46.1 to 51.9%). The bone colonization appeared statistically higher in the femur of rabbits (48.5%) than in the tibia (12.6%) and calvaria (22.9%) sites. This slightly higher degree of bone healing was related to differences in the bone architecture of the implantation sites. Concerning the comparison between animal species, bone colonization appeared greater in rabbits than in rats for the femoral site (48.5% vs. 29.6%). For the other two sites (the tibia and calvaria), there was no statistically significant difference. The increased bone ingrowth observed in rabbit femurs might be due to the large bone surface area in contact with the MBCP ceramics. The femoral epiphysis of rabbits is therefore a favorable model for testing the bone-bonding capacity of materials, but a comparison with other implantation sites is subject to bias. This study shows that well-conducted and fully validated models with the use of small animals are essential in the development of new bone substitutes.

Noninvasive bone replacement with a new injectable calcium phosphate biomaterial

The use of injectable calcium phosphate (CaP) biomaterials in noninvasive surgery should provide efficient bone colonization and implantation. Two different kinds of injectable biomaterials are presently under development: ionic hydraulic bone cements that harden in vivo after injection, and an association of biphasic calcium phosphate (BCP) ceramic granules and a water-soluble polymer vehicle (a technique particularly investigated by our group), providing an injectable CaP bone substitute (IBS). In our study, we compared these two approaches, using physicochemical characterizations and in vivo evaluations in light microscopy, scanning electron microscopy, and three-dimensional microtomography with synchrotron technology. Three weeks after implantation in rabbit bone, both biomaterials showed perfect biocompatibility and bioactivity, but new bone formation and degradation of the biomaterial were significantly greater for BCP granules than for ionic cement. Newly formed bone developed, binding the BCP granules together, whereas new bone grew only on the surface of the cement, which remained dense, with no obvious degradation 3 weeks after implantation. This study confirms that BCP granules carried by a cellulosic polymer conserve bioactivity and are conducive to earlier and more extensive bone substitution than a carbonated-hydroxyapatite bone cement. The presence of intergranular spaces in the BCP preparation, as shown on microtomography imaging, seems particularly favorable, allowing body fluids to reach each BCP granule immediately after implantation. Thus, the IBS functions as a completely interconnected ceramic with total open macroporosity. This new bone replacement approach should facilitate microinvasive bone surgery and local delivery of bone therapy agents.

Calcium-deficient apatite: a first in vivo study concerning bone ingrowth

Biphasic calcium phosphate (BCP) materials are increasingly used to restore bone loss in surgery. Calcium-deficient apatites (CDA), the precursors of BCP, are closer in structure to biological apatites and can be associated with therapeutic agents to form drug-delivery systems. The purpose of this first in vivo study of CDA was to evaluate the osteoconductive properties of two composites, consisting of 40-80 microm granules carried by a cellulose-derived polymer, used to fill critical size bone defects in rabbit femoral ends. Animals were sacrificed 2 or 3 weeks after implantation. Histomorphometric analysis of scanning electron microscopy implant surface files was performed using gray level threshold that distinguish between bone or materials (white) and noncalcified tissue (black). Quantitative results for new bone formation showed no significant differences between the composites or the implantation periods. However, nearly all of the CDA disappeared early while supporting more extensive bone colonization than biphasic calcium phosphates implanted in the same conditions.

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.

Platelet aggregation induced by the C-terminal peptide of thrombospondin-1 requires the docking protein LAT but is largely independent of alphaIIb/beta3

Thrombospondin-1 (TSP1) is abundantly secreted during platelet activation and plays a role in irreversible platelet aggregation. A peptide derived from the C-terminal domain of TSP1, RFYVVMWK (RFY) can activate human platelets at least in part via its binding to integrin-associated protein. Although integrin-associated protein is known to physically interact with alphaIIb/beta3, we found that this major platelet integrin had only a partial implication in RFY-mediated platelet aggregation. Accordingly, RFY induced a significant Glanzmann type I thrombasthenic platelet aggregation. The alphaIIb/beta3-dependent part of platelet aggregation induced by RFY was mainly due to secreted ADP and thromboxane A2. In the absence of alphaIIb/beta3 and fibrinogen, RFY stimulated a rapid tyrosine phosphorylation of a set of proteins, including Syk, linker for activation of T cells (LAT) and phospholipase Cgamma2. This signaling pathway was critical for RFY-mediated platelet activation as revealed by the use of pharmacological inhibitors as well as LAT-deficient mouse platelets. Phosphoinositide 3-kinase activation was also required for RFY-mediated platelet aggregation. Our results unravel a new alphaIIb/beta3 and fibrinogen-independent mechanism for platelet aggregation in response to the active peptide from the C-terminal domain of TSP1.

Enhanced bone integration of implants with increased surface roughness: a long term study in the sheep

OBJECTIVES

This study evaluated the quality and the remodeling of bone around commercially pure titanium implants after 3, 6, 12 and 18 month implantation periods in the sheep.

METHODS

Twelve animals were implanted in the cortico-trabecular areas of both femurs. Each femur received four implants with a rough surface (type 1) in the right femur and four with a smooth surface (type 2) in the left one. Bone blocks containing the implants were studied by histomorphometry on undecalcified specimens. The amount of bone around implants was measured (bone volume, fractional woven bone volume, bone thickness, contact interface) together with osteoblastic activity (mineral apposition rates, bone formation rates) and resorption activity (eroded surfaces).

RESULTS

No significant differences could be observed for the two types of implants between 3 and 6 months. At 12 and 18 months, bone volume and contact interface were still increasing and there was always a tendency for type 1 implants to be associated with higher values. On the contrary, mineral apposition rate, bone formation rates and eroded surfaces decreased in the referent area in contact with the implant; this phenomenon of 'return to the normal' was more evident with type 1 implants. The remodeling process appears to increase bone quality and bone-titanium interface around implants in long term periods.

CONCLUSIONS

The net bone quantity necessary to immobilize implants is obtained rapidly but the adapting process to mechanical strength can lead to a small but persistent increase in bone volume around implants. Although the differences between type 1 and type 2 implants were often small or statistically insignificant, the rougher type 1 implants seemed to be associated with stronger bone response.

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.

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.

Altered expression of CD43-hexasaccharide isoform on peripheral T lymphocytes from HIV-infected individuals

OBJECTIVE

To examine if peripheral T lymphocytes from HIV-infected individuals show abnormalities in the surface expression of CD43, the major sialoglycoprotein of leukocytes.

DESIGN

A series of 86 HIV-positive individuals was studied. The subjects, grouped by their peripheral CD4 cell count, were in different stages of the disease as defined by the Centers for Disease Control and Prevention (CDC).

METHODS

Peripheral leukocytes and isolated lymphocytes were examined by double and triple immunofluorescence flow cytometric and Western blot analyses with monoclonal antibodies, which discriminate between CD43 isoforms.

RESULTS

We found elevated percentages of the surface expression of CD43-hexasaccharide isoform on T lymphocytes from 82 out of 86 individuals tested. Increasing percentages are progressively found in CDC groups 1, 2 and 3 patients. The expression of the molecule is remarkably biased towards the CD8 cell subpopulation. The percentage of cells bearing human leukocyte antigen-DR locus molecules (HLA-DR) is also augmented. Two subsets expressing T305 have been identified: a minor subset that co-expresses HLA-DR and T305; and a second population formed by the majority of T305-positive cells, which lack surface HLA-DR. Finally, we found CD43 bands with altered electrophoretic mobility in lysates from peripheral lymphocytes from all HIV-positive individuals tested.

CONCLUSION

The augmented expression of CD43-hexasaccharides and the observed cellular distribution suggest an important regulatory role for this molecule in HIV-specific responses.

HLA-B2702 (77-83/83-77) peptide binds to beta-tubulin on human NK cells and blocks their cytotoxic capacity

It has been described that peptides derived from a highly conserved region of the alpha1 helix of the first domain of HLA class I Ags exhibit immunomodulatory capacity blocking both T and NK cell cytotoxicity. In vivo treatment with these peptides prolongs survival of MHC-mismatched allografts. However, the molecular bases of these effects are still unclear. In this study, we further analyze the mechanisms by which the dimeric peptide HLA-B2702 (77-83/83-77) induces suppression of NK cell cytotoxicity. This peptide inhibits natural and redirected lysis mediated by NK cells without significantly affecting effector-target cell binding. We have also isolated and sequenced a protein that binds this inhibitory peptide, which structurally corresponds to beta-tubulin. Tubulin is the major protein of microtubules and is involved in target cell killing. Furthermore, B2702 peptide promotes GTP-independent tubulin assembly, producing aggregates that cannot be depolymerized by cold. Treatment of NK cells with Taxol or demecolcine, which interfere with microtubule organization, also prevents NK cell cytotoxicity. Taken together, these results support the hypothesis that the peptide B2702 (77-83/83-77) exerts its inhibitory effect on NK cell cytotoxicity by inducing polymerization of microtubules and interfering with their normal assembly/disassembly dynamics.

In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied. Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks. PCR demonstrated the disappearance of the provirus. Histologically, inflammatory lesions were observed in the transduced livers. Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene. This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.

Functional expression of CD43 on human natural killer cells

CD43 is the major leukocyte sialoglyco-protein that plays important functional roles in neutrophils and lymphocytes. However, the expression of CD43 on human natural killer (NK) cells and its participation in the regulation of NK activity has not been studied. We have therefore investigated the expression of CD43 isoforms on human NK cell subpopulations as well as the role of this molecule in NK cell activation and cytotoxicity. We found that CD56bright and CD56dim NK cells express different sialylated forms of CD43, observing that activation of the CD56bright NK cells induces the change of tetrasaccharide O-glycans to hexasaccharide O-glycans on CD43. Cross-linking of the molecule with mAbs results in a metalloprotease-dependent loss of CD43 from the NK cell surface, whereas soluble anti-CD43 mAbs induce a vigorous NK cell proliferation. This property is distinct from T cells, which proliferate after CD43 cross-linking only in the presence of monocytes. Occupancy of the CD43 receptor on NK cells transduces specific signals, leading to enhanced killing activity and tyrosine phosphorylation and de-phosphorylation of several substrates. We therefore propose that CD43 significantly contributes to the regulation of the NK cell function by participating in the control of effector/target interactions and, if pertinent, by transducing activation signals.

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.

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.

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.

A new injectable calcium phosphate biomaterial for immediate bone filling of extraction sockets: a preliminary study in dogs

BACKGROUND

Many different bone substitutes, such as autografts, allografts or synthetic biomaterials have been proposed to restore alveolar bone loss and support efficient placement of dental implants. This experimental study evaluated the osteoconductive properties of an injectable bone substitute (IBS) composed of a polymeric carrier and a calcium phosphate mineral phase, used to fill mandibular and maxillary canine extraction sockets.

METHODS

The polymer was a cellulose derivative (methyl-hydroxy-propyl-cellulose, MHPC), and the mineral phase consisted of granules of biphasic calcium phosphate (BCP) ceramics 200 to 500 microm in diameter. Mandibular and maxillary premolars extracted from 3 dogs (a total of 60 extraction sites) were immediately treated with the IBS or left unfilled as control sites. Animals were sacrificed 3 months after implantation and all extraction sockets were prepared for histological evaluation.

RESULTS

Qualitative histological studies showed that the IBS was able to support the extensive apposition of well-mineralized newly formed lamellar bone over the entire socket surface and appeared to prevent alveolar ridge bone loss in treated extraction sites. Quantitative evaluation showed that the amount of newly formed bone was significantly higher in mandibular than maxillary extraction sockets for both treated and control sites.

CONCLUSIONS

An injectable bone substitute composed of a polymeric carrier and calcium phosphate was effective in enhancing the bone fill of extraction sockets. This approach may prove promising for periodontal lesions. The material expressed osteoconductive capacities, and the biological properties of the mineral phase were conserved.

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.

Expression of killer inhibitory receptors on cytotoxic cells from HIV-1-infected individuals

Dysfunction of cytotoxic activity of T and natural killer (NK) lymphocytes is a main immunological feature in patients with AIDS, but its basis are not well understood. It has been recently described that T and NK cell-mediated cytotoxicity can be regulated by HLA killer inhibitory receptors (KIR). In this work, we have determined on cytotoxic T cells and NK cells from HIV-1-infected individuals the expression of the following KIR molecules: p58, p70, and ILT2 (immunoglobulin-like family KIR) as well as CD94 and NKG2A (C-lectin-type family KIR). With some exceptions, no significant changes were found on the expression of immunoglobulin-like KIR in either CD8+ or CD56+ cells. Interestingly, the percentages of CD8+ and CD56+ cells expressing CD94 were significantly increased in these individuals. We also show that, in vitro, IL-10 up-regulates CD94 expression on CD8+ and CD56+ cells obtained from normal individuals, suggesting that the augmented expression observed in HIV-infected individuals could be related to the high levels of IL-10 previously described in HIV-1-infected individuals.

The early remodeling phases around titanium implants: a histomorphometric assessment of bone quality in a 3- and 6-month study in sheep

The purpose of this study was to evaluate the quality of the bone matrix around commercially pure titanium implants at 3 and 6 months postplacement in sheep. Implants were placed in the corticotrabecular areas of both femurs in 6 animals. Each animal received 4 Euroteknika implants in the right femur and 4 Nobel Biocare implants in the left femur. Bone blocks containing the implants were studied undecalcified after being embedded in methylmethacrylate. Sections were stained with toluidine blue and basic fuchsin. The amount of bone around the implants, the contact interface between the implant and bone, and the mineral apposition rates were measured. The fractional amount of woven bone could be quantified because of its high glycosaminoglycan content. No differences could be observed between the 2 types of implants. Total bone volume did not increase around both types of implants between 3 and 6 months, indicating that ankylosis was rapidly achieved. In contrast, in the area in contact with the implant, the bone-titanium interface drastically increased and the mineral apposition rate decreased. The fractional volume of woven bone around implants was considerably reduced after 6 months. Bone quality around implants was improved at 6 months (volume of woven bone near zero), and true osteonic structures were observed in close contact with titanium. The remodeling process appeared to improve bone quality and increase the bone-titanium interface around implants, while the net bone quantity necessary to immobilize implants was achieved rapidly and remained unchanged.