Production of different morphologies of biocompatible polymeric materials by supercritical CO2 antisolvent techniques

High-value biocompatible-polymers have been processed with supercritical antisolvent techniques to produce solid structures of different shape and size. In particular, a class of hyaluronic acid-derived polymers (Hyaff11-p100, Hyaff11-p80, Hyaff11-p75, Hyaff 302) have been used to obtain various morphologies such as microspheres, threads, fibers, networks, and sponges. The effect of thermodynamic variables on precipitation were highlighted in some preliminary batch experiments. Then, different products were obtained by tuning the values of operating parameters. Threads and fibers were the result of a continuous supercritical antisolvent (SAS) process where a concentrated polymer solution was pumped through a micrometric nozzle: The threads showed a reticular internal structure with an adjustable type of cavity. For production of networks and sponges, the concentration of polymer plays the key role. Below a critical value it was not possible to obtain a continuous network, while above it, a structure similar to that of the natural bone with three types of internal microporosity were obtained. Again, by tuning pressure and polymer concentration, the internal porosity could be controlled. Microparticles were also produced by the SAS process, and a control of their morphology was achieved by varying the concentration of the polymer in the starting solution and the density of organic solvent-CO2 mixtures. All the products obtained by SAS have negligible content of residual solvent. A qualitative interpretation of experimental results is presented. (C) 2001 John Wiley & Sons, Inc.