58 Scientific Research

In vivo engineering of organs: The bone bioreactor

The original paper on which this TEDTalk is based, it mainly focuses on the development of the ability to create space between the bone structure and the periosteum by injecting a biocompatible calcium-alginate gel that crosslinked in situ, creating a “bioreactor” in the bone structure which can then be removed and implanted elsewhere for bone regrowth and regeneration. This method also allows for minimal to no effect on the original donor site.  The events accompanying neo-bone formation are achieved without local or systemic administration of growth factors, other biomolecules or cell isolation and transplantation, and creates engineering bone which is biomechanically identical to native bone. New bone was harvested after 6 weeks and then transplanted into other bone defects with no morbidity at the donor site.

Characterization Technique

Alginate-based gel systems have many applications and can have adjusted properties depending on their use case. Properties such as gelation kinetics, homogeneity, and Young’s modulus can be optimized and adjusted through changing calcium salt concentrations, gelling-ion selection, and guluronic acid concentration. In the original research, four different alginates were used to create gel systems. High G-content alginates are combined with calcium salts to create a gel system which supports bone growth in the periosteum, which were then used in this TEDTalk to create bone growth which can be transplanted for use in bone grafts. Higher G-content alginates

Bioprintable Alginate/Gelatin Hydrogel 3D In Vitro Model Systems Induce Cell Spheroid Formation – JoVE

Calcium Salt Characterization

Both CaSO4 and CaCl2 were used to induce gelation in alginate-based gel systems. Research suggests that CaSO4-induced gelation occurred over longer time periods, up to several hours. Precipitates of CaSO4 were also observed in these gels, which could decrease homogeneity in the gel, leading to undesirable mechanical characteristics when implanted.

CaCl2 as a gelling ion is much faster when compared to CaSO4, and much more suitable for use in bone genesis. Gels formed using a 2% ion concentration had much more stable mechanical properties compared to other concentrations.