Takao Yamamuro

Apatite coating on ceramics, metals and polymers utilizing a biological process

A novel method of apatite coating is presented. The main characteristics of the method are that the apatite layer obtained consists of bone-like apatite and can be coated on various substrates including ceramics, metals and organic polymers. Coating is carried out in a simulated body fluid, the ion concentrations, temperature and pH of which are adjusted to almost equal to those of human blood plasma, using a plate of CaO, SiO2-based glass as a source of nucleating agent of apatite on the surfaces of substrates. The apatite layer obtained, formed in a similar environment to that in the body, is thus expected to show higher bone-bonding ability than that formed by conventional methods, and this method is applicable to various materials having different mechanical properties.

Mechanical properties of a new type of apatite-containing glass−ceramic for prosthetic application

A new type of apatite-containing glass-ceramic in the system MgO-CaO-SiO2-P2O5 can form a tight chemical bond with bones and has a high mechanical strength. The cause for its high mechanical strength was examined by comparing mechanical properties of the glass-ceramics which have an identical chemical composition and different microstructures. It was found that the mechanical strength of the apatite-containing glass-ceramics is considerably increased by the precipitation ofβ-wollastonite crystals due to an increase in fracture surface energy resulting in an increase in fracture toughness.

Fatigue and life-time of bioactive glass-ceramic A-W containing apatite and wollastonite

High-strength bioactive glass-ceramic A-W containing apatite and wollastonite shows the least dynamic fatigue among glass and glass-ceramics of the same composition and of different structure in a simulated body fluid at 38.5° C. An avenge life-time estimated from the fatigue of glass-ceramic A-W is 10 yews under continuous loading of bending stress of 65 MPa in the simulated body fluid, whereas that of a sintered dense hydroxyapatite ceramic is only 1 min. Articles of the glass-ceramic which withstand the stress of 215 M Pa in an inert atmosphere are guaranteed for 10 years life-time in the body environment. The glass-ceramic shows an increase in strength, without having an appreciable change in fatigue, when placed in the simulated body fluid without being loaded. Its practical life-time can therefore be expected to be much longer than that estimated above.

Quantitative study on osteoconduction of apatite-wollastonite containing glass ceramic granules, hydroxyapatite granules and alumina granules

The osteoconductive potential of apatite-wollastonite containing glass ceramic (A-W.GC), hydroxyapatite (HA), and alumina (AL) was quantitatively evaluated by implanting them as granules into rat tibiae. The amount of mature bone formed in contact with the ceramics varied depending on the ceramic materials; it reached a plateau earliest in A-W.GC and latest in AL. The bone mass at the interface showed the same results. The osteoconductive potential was suggested to be higher in bioactive ceramics than in bioinert ceramics, and to be related to the formation rate of the surface apatite layer of the bioactive ceramics.

Bonding behavior of a glass-ceramic containing apatite and wollastonite in segmental replacement of the rabbit tibia under load-bearing conditions.

Glass-ceramic implants containing apatite and wollastonite were studied under load-bearing conditions in a segmental replacement model in the tibia of the rabbit. Alumina-ceramic implants were used as a control. A sixteen-millimeter segment of the middle of the shaft of the tibia was resected at a point distal to the junction of the tibia and the fibula. The defect was replaced by a fifteen-millimeter-long hollow, cylindrical implant that was fixed by intramedullary nailing using a Kirschner wire. Two groups of eight rabbits each (one group with a glass-ceramic implant and the other with an alumina implant) were killed twelve weeks after implantation. Two similar groups were killed twenty-five weeks after implantation. The segment of the tibia that contained the implant was excised and tension-tested. The load to failure of glass-ceramic implants containing apatite and wollastonite increased with time. The loads to failure of the glass-ceramic and alumina implants at twelve weeks after implantation were 19.8 +/- 7.06 and zero newtons, respectively. The loads to failure of glass-ceramic and alumina implants at twenty-five weeks after implantation were 126.4 +/- 32.54 and 19.6 +/- 13.92 newtons, respectively. No glass-ceramic implants broke. A calcium-phosphorus layer at the interface of the glass-ceramic and the bone was observed by scanning electron microscopy and electron-probe microanalysis. There was no interposition of soft tissue between the glass-ceramic and the bone, as observed by Giemsa surface staining.

Replacement of the lumbar vertebrae of sheep with ceramic prostheses

We prepared a prosthesis for the replacement of the lumbar vertebrae of sheep, using apatite- and wollastonite-containing glass-ceramic. The material is stronger than human cortical bone and has the special feature of chemical bonding to bone. Ten sheep underwent replacement of L3 and L4 vertebrae, without bone grafting. The animals were killed at intervals from three months to 27 months after operation, and the interface between the prosthesis and bone was examined radiologically, histologically and crystallographically. Bone bonding with the prosthesis had occurred in half the implants. It took at least one year for bonding to be complete, but an apatite layer on the surface of the prosthesis was observed as early as three months after the operation, suggesting the possibility of much earlier bone bonding if more rigid fixation of the prosthesis had been provided.

The bonding of glass ceramics to bone

SummaryIn this study the bonding behaviour of glass ceramics, containing apatite and wollastonite, to bone tissue is shown to vary depending on the amount of alumina they contain. We have experimented with three types of material: A·W-GC, AW-6 and AW-AL. Rectangular plates were implanted into the tibiae of rabbits. Ten weeks later a segment of bone around the plate was removed for examination, and the load of breaking by traction (failure load) was measured by an autograph. This was lowest for AW-AL and highest for A·W-GC (with AW-6 in between), and the figures differed significantly from each other (P<0.01). The interface was examined by a scanning electron micro-analyser and an energy dispersive X-ray micro-analyser (SEM-EPMA) and the reactive zone, the calcium-phosphorus rich layer, was assessed. Silicon and magnesium decreased, the calcium did not change, and the phosphorus increased. The reactive zone of A·W-GC was wider than that of AW-6. A Ca-P rich layer was not present between AW-AL and the bone. It is suggested that the strong bonding between glass-ceramics and bone was made through the formation of the Ca-P rich layer.RésuméCette étude montre que la liaison entre les céramiques, contenant de lapatite et de la wollastonite, et le tissue osseux, varient en fonction de la quantité dalumine quelles contiennent. Nous avons expérimenté trois types de matériaux: AW-GC, AW-6 et AW-AL. Des plaques rectangulaires ont été insérées dans des tibias de lapin. Dix jours plus tard on a découpé, en vue dexamen, un segment dos autour de la plaque. La charge de rupture par traction a été mesurée. Elle est la plus basse pour le AW-AL et la plus élevée pour le AW-GC (le AW-6 est entre deux) et les chiffres diffèrent significativement lun de lautre (P<0,01). Linterface a été examinée par micro-analyse électronique et radiologique et la zone réactive, la couche riche en calcium et phosphore a été étudiée. Le silicium et le magnésium avaient diminué, le calcium était resté stable et le phosphore avait augmenté. La zone réactive de lAW-GC était plus large que celle de lAW-6. Il nexistait pas de couche phopho-calcique entre lAW-AL et los. Il semble que la forte liaison entre la céramique et los soit due à la formation dune importante couche phopho-calcique.