Cytocompatibility of two coating materials, amorphous alumina and silicon carbide, using human differentiated cell cultures.

The cytocompatibility of two coating materials, amorphous alumina and silicon carbide deposited by radio-frequency sputtering, was studied using alveolar bone osteoblasts and gingival fibroblasts from human healthy tissues. Cytocompatibility was assessed at the level of both the basic (attachment, proliferation and cell protein content) and the specific features (intracellular alkaline phosphatase activity and the cytoskeleton) of the cells in direct contact with the coating. Titanium was used as the reference material. The results showed that both silicon carbide and amorphous alumina are cytocompatible for human fibroblasts and osteoblasts, whereas titanium appears the least cytocompatible of all the three substrates. Moreover, the amorphous alumina coating seems slightly bioactive. It seems that these coatings, particularly amorphous alumina, could be used to protect alloys against corrosion, and consequently combine the good mechanical properties of the alloys with the good biocompatibility of the coatings. These coatings seem to perform more suitably than titanium if the strength of the bond between the coating and the underlying alloys is strong enough to give a stable composite material.

In vitro comparative evaluation under static conditions of the hemocompatibility of four types of tubing for cardiopulmonary bypass.

A comparative in vitro assessment of 4 types of tubing representative of the materials currently used in cardiopulmonary bypass (CPB) procedures was conducted under static conditions using liquid extracts of the materials or direct contact with fresh human blood or serum. The parameters monitored were biomarkers of coagulation and fibrinolytic cascades, the complement system and cell activation. Silicone and PVC tubing were shown to be non-cytotoxic and non-hemolytic. Heparin-coated PVC tubing did present a certain degree of cytotoxicity especially when in direct contact. Thrombosis was found to be significantly lower with the same heparin-coated material. To a lesser extent, platinum-cured silicone also showed a reduced thrombotic tendency. None of the materials activated platelets or the complement system. With platinum-cured silicone tubing, constant and lower leukocyte adhesion was evidenced at the different experimental time points. This could reflect reduced cell activation.

Ion exchanges in apatites for biomedical application.

The modification of the composition of apatite materials can be made by several processes corresponding to ion exchange reactions which can conveniently be adapted to current coatings and ceramics and are an alternative to setting up of new synthesis methods. In addition to high temperature thermal treatments, which can partly or almost totally replace the monovalent OH- anion of stoichiometric hydroxyapatite by any halogen ion or carbonate, aqueous processes corresponding to dissolution-reprecipitation reactions have also been proposed and used. However, the most interesting possibilities are provided by aqueous ion exchange reactions involving nanocrystalline apatites. These apatites are characterised by the existence on the crystal surface of a hydrated layer of loosely bound mineral ions which can be easily exchanged in solution. This layer offers a possibility to trap mineral ions and possibly active molecules which can modify the apatite properties. Such processes are involved in mineralised tissues and could be used in biomaterials for the release of active mineral species.

In vitro study of biodegradation of a Co-Cr alloy using a human cell culture model.

The evaluation of a potential biomaterial is based on two approaches: firstly, the study of the local and systemic effects of the biomaterial implanted in the host; and secondly the study of the behaviour of the biomaterial itself with increasing time. The progress achieved in human cell culturing allows in vitro evaluation of a new biomaterial using the human cell(s) system(s) characteristic of the tissue which it will be exposed to in vivo. This kind of approach permits the assessment of the biodegradation of a biomaterial whatever it is: metal; alloy; ceramic; glass; polymer; with or without specialized coating.... The experimental approach is as follows: discs representative of the biomaterial (surface state, cleaning, sterilization process) are manufactured in order to cover the bottom of the culture wells. Thereafter, they are either brought in the presence of complete culture medium alone, or in the presence of a subconfluent cell layer. A kinetic analysis is performed using various incubation periods at 37 degrees C. Released biodegradation products are identified and quantified, in both the medium and cell compartment, and on the other hand cytotoxicity is assessed. A Co-Cr alloy was studied over a 9-day period according to the experimental schedule, and showed a higher corrosion rate in the presence of osteoblasts in the range of 25-30%. Moreover, an intracellular uptake of both Cr and Co was detected, which will have physiological importance.

Study of the effect of the surface state on the cytocompatibility of a Co-Cr alloy using human osteoblasts and fibroblasts.

Cobalt-chromium-based alloys are widely used in oral and orthopedic implantology. Although they are relatively well tolerated, biological complications could occur which sometimes are due to the insufficient biocompatibility of the alloy. This study shows the effects of an alloy (Co (base), 28% Cr, 5.5% Mo, 1% Ni, 0.95% Si, 0.7% Fe, 0.65% Mn, 0.25% C), on differentiated human cells derived from an oral implantation site, specifically alveolar bone osteoblasts and gingival fibroblasts. The cytocompatibility of the alloy is determined by the study of cell proliferation, determination of total cell protein and intracellular alkaline phosphatase contents, cytoskeleton, and cell morphology. The alloy is presented to the cells in four different surface states: rough cast, specular polished, microbead blasted, and RF sputtered. The results demonstrate that the same material has different effects on the basal and specific cellular functions, according to its surface state. For this alloy we can classify its cytocompatibility according to its surface state in such an order: Microbead blasted much greater than specular polished greater than RF sputtered greater than rough cast.

Micromechanical spectroscopy of cartilage proteoglycans: hydration.

Proteoglycan subunits extracted from calf cartilage have been studied with a high resolving power mechanical spectroscopy: the Thermostimulated Creep (TSC). The influence of hydration on TSC spectra shows the existence of two types of bound water: the weakly bound water increases the inertia of proteoglycan and stiffens their structure; the strongly bound water is responsible to a compensation law indicating the existence of a resonance phenomenon at the physiological temperature. Because of the looseness of bonds in weakly bound water, an increase of the local pressure may induce, in vivo, a release of water in tissues. This hypothesis explains perfectly the role of a water pump of proteoglycans in cartilage.

In vitro kinetic evaluation of titanium alloy biodegradation.

The present controlled in vitro experiment evaluated the dissolution kinetics of titanium (Ti), aluminum (Al) and vanadium (V). Titanium alloy (Ti90Al6V4) dental implants were inserted in 1.8 ml sterile tubes, containing equal volumes of NaCl 0.9% (w/v) and human serum. Metallic elements released by the atomic process of corrosion were measured at pH 7.2 and 37 C by atomic absorption spectrophotometer at 1, 3, 6, 9, 15, 21, 27, 33, 42, 51, 60, 69, 78, 87 and 96 days. Ti dissolution averaged 16+/-5 ng/cm2/day and 1565 ng/cm2 over the experimental period. Al dissolution was stable at 9+/-5 ng/cm2/day and averaged 945 ng/cm2 over the 96-day period. V dissolution was stable at 0.15+/-0.18 ng/cm2/day after the sixth day of incubation and averaged 42 ng/cm2 over the 96-day period. Major disparities in atomic dissolution were detected among implants. No local or systemic reaction to titanium has been documented. In contrast, 4% toxic V and 6% Al may suffice to elicit local and systemic reactions or inhibit cellular proliferation and differentiation.

Effect of a derivatized dextran on human osteoblast growth and phenotype expression.

Water soluble derivatized dextran named E9 with a molecular weight of 45,000 g l-1 containing 58% methyl carboxylic acid unit, 19% benzylamide unit, and 26% sulfonate with a specific anticoagulant activity of 0.29 IU mg-1 was studied for its effects on human osteoblast growth and phenotype expression for short-term treatment. At concentrations between 1 ng ml-1 and 1 microgram ml-1 E9 has no effect on DNA synthesis whereas at higher concentrations DNA synthesis is inhibited in a dose related fashion (87% for 400 micrograms ml-1). For concentrations which do not modify osteoblast growth, E9 promotes alkaline phosphatase activity, type I collagen and osteocalcin synthesis with a maximum effect for 0.1-1 microgram ml-1. It has a synergistic effect with hPTH increasing AMPc. Moreover, osteonectin synthesis was enhanced in a dose-dependent manner between 0.1 and 5 micrograms ml-1. These results seem to indicate that E9 is able to stimulate human osteoblast phenotype expression and could be useful in clinical applications.

In vitro evaluation of an epoxy resin's cytocompatibility using cell lines and human differentiated cells.

The cytocompatibility of a polyepoxy resin (Elf Aquitaine) has been studied using both cell lines and human differentiated cell cultures. The human models were gingival fibroblasts and bone osteoblasts, while the cell lines were Hela cells and 3T3 Balb/c cells. Basal cytocompatibility was assessed by estimation of the cell proliferation, total cell protein content, cell membrane sub-lysis, and cell attachment and spreading. Specific cytocompatibility concerning human osteoblasts, from both alveolar and trabecular bone, was determined by measuring the intracellular alkaline phosphatase activity. Resin colonization by the cells was studied by both TEM and SEM. The behaviour of the two cell lines reveals a significant level of discrepancy, whereas the behaviour of human cells, whatever the model, is comparable; however, osteoblasts look more sensitive. Moreover, the results show that this epoxy resin exhibits a moderate cytocompatibility which could be the result of the cytotoxicity of early released products, associated with the considerable surface roughness.

Corrosion protection of metal implants by hard biocompatible ceramic coatings deposited by radio-frequency sputtering.

Most metals used for orthopaedic and stomatology implants and prostheses belong to the families of titanium or nickel-based and cobalt-based superalloys designed for advanced technology industries (e.g. space, aeronautic and nuclear industries). Ideal materials should be as insoluble and biologically compatible as possible. In the present paper the corrosion behaviour of Ni-Cr and Co-Cr alloys in biological media is evaluated through potentiodynamic polarization tests. It is shown that these metals exhibit some minor release of the component elements and degradation products, which may induce cytotoxic and allergic effects. The corrosion resistance of these alloys can be strongly enhanced by hard ceramic coatings deposited by radio-frequency sputtering. The biocompatibility of coated and uncoated metals is compared from differentiated human cell cultures.