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We have assessed the biocompatibility of a new composite bone graft consisting of calcium phosphate cement (CPC) and poly(1actide-co-glycolide) (PLGA) microspheres (approximate diameter of 0.184.36 mm) using cell culture techniques. CPC powder is mixed with PLGA microspheres and water to yield a workable paste that could be sculpted to fit the contours of a wound. The cement then hardens into a matrix of hydroxyapatite microcrystals containing PLGA microspheres. The rationale for this design is that the microspheres will initially stabilize the graft but can then degrade to leave behind macropores for colonization by osteoblasts. The CPC matrix could then be resorbed and replaced with new bone. In the present study, osteoblast-like cells (MC3T3-El cells) were seeded onto graft specimens and evaluated with fluorescence microscopy, environmental scanning electron microscopy and the Wst-1 assay (an enzymatic assay for mitochondria1 dehydrogenase activity). Cells were able to adhere, attain a normal morphology, proliferate and remain viable when cultured on the new composite graft (CPC-PLGA) or on a control graft (CPC alone). These results suggest that our new cement consisting of CPC and PLGA microspheres is biocompatible. This is the first time that a 'polymer-in-mineral' (PLGA microspheres dispersed in a CPC matrix) cement has been formulated that is moldable, resorbable and that can form macropores after the cement has set.

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Poly(n-hexyl isocyanate) adopts a helical structure in solution and the preference of one helical sense induced by a nonracemic chiral solvent can be detected by the circular dichroism (CD) of the backbone chromophore of the polymer. Addition of an achiral or racemic cosolvent leads to a reduction of the CD intensity, which can be interpreted quantitatively as reflecting the composition of the solvent mixture in contact with the helical backbone of the polymer. Equilibrium constants characterizing the relation between the solvent composition in contact with the polymer and the bulk of the system are given for mixtures of (S)-1-chloro-2-methylbutane and a number of achiral or racemic cosolvents. The relationship between the structure of the cosolvent and the extent of the preferential solvation was surprising in several instances. The polymer was preferentially solvated by a highly branched hydrocarbon although it was a precipitant and the preferential solvation by alcohols extended up to the point of polymer precipitation. This unusual method for characterizing preferential solvation of this rod-like polymer is compared with other methods used previously on flexible chain macromolecules.