3D visualization of the sintered 6P53B glass scaffolds using the Advanced Light Source’s synchrotron X-ray microcomputed tomography (left and top right) and a corresponding scanning electron microscopy image (bottom right). Credit: LBL.
Researchers in the glass and ceramics field seem to be stepping up the search for materials and fabrication techniques that can deliver strong, well-tolerated, customizable and, it’s hoped, inexpensive scaffolds for bone replacement and regeneration. The end product typically should be something that can serve as a temporary host for normal tissue to form matrices (that support and encourage cell growth, nutrient transport, vascularization, etc.) and also can be resorbed by the body in a planned and therapeutic way.
And, when looking at bones, one has to consider that not all of them function the same way. For example, the strength of tissue in long, load bearing bones (in the axis of the length of the bone) needs to be quite high.
The folks at the Lawrence Berkeley National Lab recently described some of the joint work its Advanced Light Source facility is doing with researchers at Imperial College London in using a special bioactive glass material—6P53B—and “robocasting” processing technique to produce samples that are both highly porous and strong (in the sense of compressive strength).
Those interested in this topic typically want to know how glass compositions compare to the well known 45S5 (“Bioglass”) glass material developed by Larry Hench. The main difference is that the 6P53B has K2O and MgO that is absent in Bioglass, and contains more SiO2; on the other hand, Bioglass has more Na2O and CaO.
LBL has been working on using robocasting of 6P53B scaffolds and doing in vitro testing since at least 2006. Robocasting is a method of computer-controlled 3D deposition or “printing” of a slurry “ink” that has glass powder suspended in it. The computer builds a 3D structure layer-by-layer. Several other groups are using similar ink jet printing-like techniques for bioimplantable materials. Of robocasting, LBL researchers say on the ALS website, “This technique allows patterning and controlled fabrication, creating the scaffold following a computer model, and sintering the glass into the desired composition and shape. Therefore, it is possible to design glass scaffolds with variable degradation rates to match that of bone growth and remodeling.”
The LBL and Imperial College groups claims to be finding success in building scaffolds with compressive strengths in the range of what’s required for long, dense bones (~136 MPa), while retaining enough porosity to encourage cell growth and ion exchange. They report on their website, “The strength of this porous glass scaffold is ~100 times that of polymer scaffolds and 4–5 times that of ceramic and glass scaffolds with comparable porosities previously reported in the literature. The glass scaffold’s biological performance in both small animals (mice) and big (miniature pigs) is currently under systematic evaluation at the University of California, San Francisco.”