Carl G. Simon, Jr.,1 William F. Guthrie2 and Francis W. Wang 1
1Polymers Division, NIST, Gaithersburg, MD.
2Statistical Engineering Division, NIST, Gaithersburg, MD
In order to improve the effectiveness of calcium phosphate cement (CPC),
we have developed a method to seed osteoblasts into the cement. CPC
powder is mixed with water to form a paste that can be shaped to fit a
bone defect in situ. The paste hardens in 30 min, reacts to form
hydroxyapatite and is replaced with new bone. Reacted CPC is biocompatible
but unreacted CPC paste was found to be toxic when placed on cell monolayers
(MC3T3-E1 cells). In contrast, when cells were indirectly exposed
to CPC paste using a porous membrane or by placing a coverslip containing
adherent cells onto a bed of CPC paste, the unreacted CPC was nontoxic.
These results suggested that gel encapsulation of the cells might protect
them from the CPC paste. Thus, cells were encapsulated in alginate
beads (3.6 mm dia.), mixed with CPC paste and incubated overnight.
Both vital staining (calcein-AM and ethidium homodimer-1) and the Wst-1
assay (measures dehydrogenase activity) showed that cell survival in alginate
beads that were mixed with CPC was the same as in untreated control beads.
These results suggest that gel encapsulation could be used as a mechanism
to protect cells for seeding into CPC.