Minna Kellomäki, Pertti Törmälä TUT / Institute of Biomaterials Tampere, Finland

Small-sized bioabsorbable plates have been used in cranio-maxillofacial applications with good healing results. However, to improve the biological performance of the plates, several new approaches are in progress. First concept studied is to have an uneven plate surface along which tissues and cells can grow. Second concept is to use ceramic bioactive components mixed into and onto the matrix. In a third model bone morphogenetic proteins are applied together with devices. These concepts are not limited to plate-like (i.e. harder constructions) but are possible to apply them also with softer membrane structures. First concept, applying uneven surface for plates and membranes, has been studied in both hard and soft structures. A knitted structure made of poly-L,D-lactide 96/4 has been used as itself as a mesh. Neat mesh can be used in applications where no support against mechanical forces is needed or tissue fluids can flow through the device. Mesh has also been combined with plates and films. By material selection, hardness of the device can be varied and for harder structures we have used poly-L,DL-lactide 70/30 as a plate component. Softer structure using films have been made using for example copolymers of e-caprolactone and either L- or DL-lactide. Mesh is combined with solid component in a way that it remains at least partially unattached of the plate or film. Studies of these devices are in progress both in vitro and in vivo. Second concept studied at the moment is using composite material made of flexible PolyactiveÔ polymer and crushed bioactive glass. Both materials have been shown to be favourable to bony ongrowth and the combination of them is predicted to be highly bioactive. In vivo study with rabbit's cleft palate model has recently been started. Third method, applying BMPs to devices and materials, still needs further studies from technical point of view. The processing of growth factors is delicate as they are very sensitive to raised temperatures. Basically, when growth factors are supplied in a suitable media, for example in paste form, the paste could be painted on the textured surface of the plates or membranes and thus applied into the body.