Published online by Cambridge University Press: 10 February 2011
Extrusion freeform fabrication is a 3-D layerwise writing technique for forming objects directly under the control of a CAD program. This method is one of a family of rapid prototyping methods which include stereolithography, selective laser sintering and fused deposition modeling. This system can be used to build shapes, layer by layer, from hydrogels of agarose, polyacrylamide or other cross-linked water-soluble acrylic polymers.
Mineralization can be induced in these gels by first building a part from an aqueous gel slurry containing calcium sulfate powder. This part is then immersed in a carbonate or phosphate solution which diffuses into the gel and precipitates calcite or calcium phosphates as the sulfate slowly dissolves. The resulting material contains 5-10 vol% mineral, 5 vol% agarose and 85-90 vol% water. On drying a bone-like composite is formed. If the original part is not a solid but a mesh of connected struts, the drying step results in a stronger part.