One of the holy grails in tissue engineering is developing scaffolds that will support robust vascular growth. Apropos to Eileen’s earlier story about a new award for Larry Hench, a research group with members from the University of Erlangen-Nuremberg and Imperial College London has, for the first time demonstrated that a type of bioactive scaffold based on 45S5 Bioglass just might be able to foster the right type of vascularization that surgeons are looking for in implant design.
By way of background, it might first be worth looking at the just-published interview I did with Hench, the Bioglass inventor. In this Bulletin article, Hench describes the emergence of what he call the “third generation” of biomedical glasses and other bioceramics, which are defined by their ability to achieve a controlled release of biological stimuli that triggers the body’s intrinsic repair mechanisms.
The composition of Bioglass often appears to have this third-generation ability, and the new research I mentioned above, published in Tissue Engineering C (doi:0.1089/ten.tec.2012.0572), is an important new example. The goal of the study was to investigate—in cooperation with Dr. Raymund E. Horch, head of the Department of Plastic and Hand Surgery in Erlangen and Dr. Andreas Arkudas, from the same department—the angiogenic effects of bioactive glass in a relevant in vivo model.
In brief, the group tested the scaffold and grew tissue using an arteriovenous loop (AVL) model in rats. An AV loop is a commonly used hybrid blood vessel, formed via microsurgery, which joins a small arterial vessel with a vein counterpart. The AVL stays connected to the animal.
The researchers made the scaffolds by first using 45S5 Bioglass powder and applying a foam replica technique developed by the group of Aldo R. Boccaccini, an ACerS Fellow and head of the Institute of Biomaterials in Erlangen. They then filled this Bioglass-derived granular matrix with fibrin gel. Finally, they placed the scaffold in a small Teflon isolation chamber containing the AVL. They left the AVL–Teflon isolation chamber in the rats, which, they say, tolerated the material well.
After about three weeks, they removed the isolation chamber from the rats and examined the resultant combination of scaffold and newly grown tissue using microcomputed tomography and histology. To their delight, they found extensive axial vascularization of the matrix, confirming the significant potential of the material in tissue engineering applications. Furthermore, because other research has shown that the presence of Bioglass generally can have a positive effect on the growth of new bone tissue, this in vivo study, in particular, suggests that it should be possible to use the 45S5 for the development of vascularized bone tissue.
The fact that the group found axial vascularization shouldn’t be missed. This is a key finding that allows the microsurgical transfer of the biomaterial independent of local conditions at the recipient site. In addition, they found that the newly grown microvessels were immature and had consistent, small diameters, meaning that they would be prime for continued growth once implantation occurs. Implantation could occur as easily as transplanting the entire AVL pedicle to another site where, for example, bone or another type of tissue repair is needed.
The hope is that this technique, or one similar, could be used to engineer tissue to address large-bone defects and eventually replace the practice of harvesting bone graft material from, for example, a patient’s pelvis, a method that often causes additional and serious medical complications.