Described in recent and upcoming journal articles,* the new technology provides a method for making scaffolds for bone tissue. The scaffold is seeded with a patient's own cells and is formed with a cement paste made of minerals also found in natural bone. The paste is mixed with beads of a natural polymer (made from seaweed) filled with bone cells. The paste is shaped or injected into a bone cavity and then allowed to harden with the encapsulated cells dispersed throughout the structure. The natural polymer beads gradually dissolve when exposed to the body's fluids, creating a scaffold that is filled by the now released bone cells.
The cement, a calcium phosphate material, is strengthened by adding chitosan, a biopolymer extracted from crustacean shells. The implant is further reinforced to about the same strength as spongy natural bone by covering it with several layers of a biodegradable fiber mesh already used in clinical practice.
"Bone cells are very smart," says Hockin Xu, of the ADAF and principal investigator for the project. "They can tell the difference between materials that are bioactive compared to bioinert polymers. Our material is designed to be similar to mineral in bone so that cells readily attach to the scaffold." The researchers used mouse bone cells in their experiments, but in practice surgeons would use cells cultured from patient samples. In addition to creating pores in the hardened cement, the natural polymer beads protect the cells during the 30 minutes required for the cement to harden. Future experiments will develop methods for improving the material's mechanical properties by using smaller encapsulating beads that biodegrade at a predictable rate.
NIST and the American Dental Association Foundation have conducted cooperative research on dental and medical materials since 1928. ADAF researchers focus on development of new dental materials, while NIST specializes in the development of improved technologies and methods for measuring materials properties.
The research was funded by the National Institute of Dental and Craniofacial Facial Research, NIST and ADAF.
*E.F. Burgera, H.H.K. Xu and M.D. Weir. Injectable and rapid-setting calcium phosphate bone cement with dicalcium phosphate dihydrate. Journal of Biomedical Materials Research B. April 2006.
H.H.K. Xu, M.D. Weir, E.F. Burguera and A.M. Fraser. Injectable and macroporous calcium phosphate cement scaffold. Biomaterials. In press.
M.D. Weir, H.H.K. Xu, and C.G. Simon, Jr. Strong calcium phosphate cement-chitosan-mesh construct containing cell-encapsulating hydrogel beads for bone tissue engineering, Journal of Biomedical Materials Research A. In press.