Welcome to the Glass Age

47 phosphate and soluble silica (Figure 3.3). Bonding with damaged bone occurs because a bone mineral-like calcium phosphate layer forms on the surface of the glass [2]. As it is so similar to bone mineral, the cells of the body’s immune system do not see it as foreign, so fibrous encapsulation does not occur. As this calcium phosphate layer grows, it integrates with collagen fibrils of the damaged host bone and is incorporated into the healing bone. The effect of the dissolution ions was discovered when Hench, his co-workers, and the company wanting to market Bioglass at the time (NovaBone Products, US), started to investigate why Bioglass worked so well in terms of encouraging high quality bone repair. In cell culture experiments, they found that the dissolution products, particularly silica species and calcium ions, stimulated human bone cells at the genetic level to produce more bone matrix [3]. We are now celebrating more than 50 years of its invention, although many fewer years of clinical use. The original 45S5 Bioglass has been implanted in more than 1.5 million patients who were suffering from bone defects, usually as a result of surgery removing abscesses or tumours, but sometimes due to fractures not healing by conventional treatments. In these clinical applications, Bioglass as a “medical device” is usually a white powder in a sterile and hermetically sealed sachet (Figure 3.4). Surgeons tend to blend the microparticles with blood, and once the blood begins to clot, the mixture can be pressed into the hole in the bone. Since bioglass particulate was launched to market, several rival products have been released, such as Biogran (Orthovita, US), Unigraft ® (Unicare Biomedical, US), GlassBone (Noraker, France), which are alternative 45S5 Bioglass products, and BonAlive ® , which has the S53P4 composition (53.8 mol% (53 wt%) SiO 2 , 21.8 mol% CaO, 22.7 mol% Na 2 O, 1.7 mol% P 2 O 5 , BonAlive Biomaterials, Finland). Most have been used in a similar manner, but BonAlive ® has also shown benefits in patients with deep bone infections, known as chronic osteomyelitis. The infections are termed Figure 3.4. Bioglass products for orthopaedic applications: NovaBone particulate (left), BonAlive granules (top right) and BonAlive putty (bottom right). Source: Julian R. Jones.