Design of synthetic membranes aimed at promoting guided osseous regeneration

Objectives:The aim of this study is to make a porous osseous regeneration membrane intented for oral surgery which will likely facilitate colonization, fixation and growth of the osseous cells because of the presence of spaces avaible for invasion. Several method for making pores in polymer scaffolds are described in the literature. The development of these structures, usually made by ‘gas foaming'/‘salt leaching' technique, does not allow to obtain an homogeneous porosity. Therefore, we have explored a new porogen technique based on freeze-drying using a vacuum sensitive mineral salt. This novel technique was confronted to the more classical gas foaming one. Materials and method: The membrane was made of poly(DL lactide) of Mn: 90,000, Ip:2.2. The porogen was ammonium bicarbonate salt. The size of salt particles ranged from 250 to 500 µm, and they are mixed with the polymer in a 7 to 1 ratio. ‘Gas foaming'/‘salt leaching' technique : the salt was eliminated from the polymer in warm water (65°C); as it decomposes into CO2 and NH3 at this temperature to create the porosity. Freeze-drying: the porogen was totally removed by immersion in a slightly CH3COOH aqueous solution at 20°C, and then freeze-dried. Membranes of this type studied by DSC, GPC, NMR and observed by ESEM. Results: The ‘gas foaming' / ‘salt leaching' technique generated a non homogeneous porosity with a partial collapse of the foam's structure. In contrast, the freeze-drying technique showed a porosity which seemed completely interconnected. Moreover, the pores had a size similar to the crystals used to create them. Conclusion: the control of the porosity and the thickness of the membrane are two parameters that should act in favor of osteoblast colonization and osseous regeneration.