Unit 16 Special Glass
Advanced Biomedical Materials Derived from Glasses
Since the discovery of Bioglass by Hench et al in early 1970s, various kinds of glasses and glass ceramics have found to bond to living bone, and some of them are already clinically used. For example, Bioglass in the system Na2O-CaO-SiO2-P2O5 is extensively used as periodontal implants, artificial middle ear bones etc. in USA, because of its high bioactivity. Glass ceramic AW containing apatite (Ca10(PO4)6(O,F2)) and wollastonite (CaO·SiO2) is extensively used as artificial vertebrae, intervertebral discs, iliac crests etc. In Japan, because of its high mechanical strength as well as high bioactivity. Over 5000 patients received glass ceramic AW as their bone substitutes during the last 3 years.
Even glass ceramic AW, however, can not substitute for highly loaded bones such as femoral and tibial bones, since its fracture toughness of 2.0 Mpam[1/2] at maximum. Some attempts have been made to reinforce the bioactive glasses and glass ceramics with metal fibers, metal particles or ceramic particles. Even an apatite and wollastonite containing glass ceramic reinforced with ZrO2 (Y2O3) particles, which shows highest toughness of 3.0 Mpam[1/2] among them, however, can not substitute for the highly loaded bones. Metallic materials coated with bioactive glasses and glass ceramics can substitute for them. The coated layer is, however, not stable for a long period in the body environment.
Fundamental understanding of factors governing bioactivity of glasses and glass ceramics have been greatly progressed. This enable us to design novel tough bioactive materials such as bioactive metals and organic polymers by utilizing glasses.
It has been also shown that glasses and glass ceramics can play an important role in hyperthermia treatment and radiotherapy of cancers. A chemically durable Y2O3-Al2O3-SiO2 glass microsphere, which can be activated to β emitter by neutron bombardment, is already clinically used for treatment of liver tumors in Canada. It was recently shown that ion implantation technique is useful for obtaining glasses for this purpose.
Materials for Hyperthermia Treatment
Luderer et al first reported that a ferromagnetic glass ceramic containing lithium ferrite (LiFe5O8) in a Al2O3-SiO2-P2O5 glassy matrix is useful as thermoseeds for hyperthermia treatment of cancer, since it heats the cancer locally by magnetic hysteresis loss under an alternately magnetic field, and cancer cells are destroyed above 43°C. Later the present authors showed that bioactive and ferromagnetic glass ceramic containing magnetite (Fe3O4) in a CaO-SiO2 based matrix is useful as the thermoseeds especially for bone cancers. Glass ceramics capable to generate a heat more efficiently below 50°C and to cease the generation above 50°C are now being searched by choosing an appropriate ferromagnetic or ferromagnetic phase having Curie temperature around 50°C as the crystalline phase.
Materials for Radiotherapy
Ehrhardt et al first reported that a chemically durable Y2O3-Al2O3-SiO2 glass is useful for radiotherapy of cancer. When microspheres 20 to 30 μm in size of this glass are injected to liver tumor through the hepatic artery, after Y89 in the glass is activated to β emitter Y90 with half life time of 64.1 hour by neutron bombardment, they are entrapped in the capillary bed of liver tumors and give large local radiation dose of the short ranged, highly ionizing β ray to the tumors, with little irradiation to neighboring organs. The radioactive Y90 is hardly released from the glass because of its high chemical durability. Radioactivity of the glass decays to a negligible level in 21 days because of short half time of Y90.
The short half life for Y90, however, may result in the substantial decay of radioactivity before the cancer treatment. P31 with 100% natural abundance can be activated to β emitter P32 with a little longer half life time of 14.3 days by the neutron bombardment. The biological effectiveness of P32 is about four times as large as that of Y90. Preparation of a chemically durable glass with high P2O5 content is, however, difficult by the conventional melting technique.
Such glass could be prepared by ion implantation technique. The silica glass implanted with P+ ion by more than 1×10[17]/cm2 at 50 keV released appreciable amounts of the silicon and phosphorus into a pure water at 95°C, since the phosphorus was distributed up to the glass surface and oxidized there, giving maximum concentration at a depth of 50nm. The same glass implanted with P+ ion by the same dose rate but at 200keV, however, hardly released both the silicon and phosphorus, since the phosphorus was not distributed up to the glass surface, giving maximum concentration at a depth of 200nm. This indicates that ion implantation at high energy can give a new kind of glass useful for radiotherapy of cancer.
Selected from "Proceedings of XVII International Congress on Glass Vol.1 Invited Lectures", Gong Fangtian, International Academic Publishers, 1995
Words and Expressions
bioglass 生物玻璃
clinical 临床的
bioactivity 生物活性
intervertebral disc 椎间盘
iliac 肠骨的
femoral 大腿骨的
tibial 胫骨的
hyperthermia 高热症
radiotherapy 放（射线）疗（法）
hysteresis 滞回现象
β emitter β射线源
Lithium ferrite 铁酸锂
