Porous, robocast glass scaffolds produced by scientists at Missouri University of Science and Technology not only bear significant weight but have been shown to promote bone ingrowth. Credit: B.A. Rupert/MS&T.
Invention of the original 45S5 Bioglass in the late 1960s marked a watershed moment in the history of biomedical engineering. The material’s ability to bond with bone made it a boon to folks suffering with sensitive teeth (when it’s included, for example, in toothpaste formulations) and other maladies. But, as revolutionary as it is in nonstructural applications, the material is not suited to load-bearing use.
Scientists have worked to change that with varying degrees of success. Researchers at Missouri University of Science and Technology (Rolla) have developed bioglass scaffolds capable of bearing significant loads in the arms, legs and other weight-bearing parts of the body, according to this news release.
Lead researcher Mohamed N. Rahaman, professor of materials science and engineering and director of the Center for Biomedical Science and Engineering at MS&T, says the advance is the first glass implant material that is both strong enough to bear weight and also promotes bone ingrowth, thus opening new possibilities for bone repair. “Right now, there is no synthetic material that is practical for structural bone repair,” he says in the release.
In previous work, the researchers developed a glass scaffold strong enough to handle the weight and pressure of repetitive motions such as walking or lifting. Published in the journal Acta Biomaterialia (DOI: 10.1016/j.actbio.2013.03.039), their most recent study was aimed at determining how well the material would integrate with bone and promote bone growth.
The researchers used robocasting to fabricate porous scaffolds of silicate 13-93 bioactive glass with compressive strength comparable to human cortical bone. Featuring a grid-like microstructure with porosity of 50 percent, filament width of 330 μm, and pore width of 300 μm, the scaffolds were tested by implanting them into sections of the calvarial bones (skullcaps) of laboratory rats.
The skullcap is not a load-bearing bone, but it consists primarily of cortical bone. The aim of this research was to demonstrate how the material would interact with cortical bone, the type of material that makes up most of the long, weight-bearing bones of the body such as those in the arms and legs. “You can have the strongest material in the world, but it also must encourage bone growth in a reasonable amount of time,” says Rahaman, who defines a reasonable time frame for completely regenerating an injured bone into one that can bear weight as three to six months.
In testing, the amount of new bone formed in implants composed of the as-fabricated scaffolds was 32% of the available area after six weeks. Pretreating the scaffolds in an aqueous phosphate solution for one, three, and six days to convert the scaffolds’ surface layer to hydroxyapatite before implantation enhanced new bone formation to 46, 57, and 45 percent, respectively. New bone formation in scaffolds pretreated for one, three, and six days and loaded with 1 μg/defect of bone morphogenetic protein-2 was 65, 61, and 64 percent, respectively.
“The results show that converting a surface layer of the glass to hydroxyapatite or loading the surface-treated scaffolds with BMP-2 can significantly improve the capacity of 13-93 bioactive glass scaffolds to regenerate bone in an osseous defect,” the researchers write. “Based on their mechanical properties evaluated previously and their capacity to regenerate bone found in this study, these 13-93 bioactive glass scaffolds, pretreated or loaded with BMP-2, are promising in structural bone repair.”
The scientists are now experimenting with true load-bearing bones by testing the 13-93 bioglass implants in rat femurs. Future studies will examine how composition changes to the glass scaffolds might enhance other desirable properties. For example, the scientists expect doping the glass with copper will promote blood vessel growth, while silver additions should give it antibacterial properties.