ADAMI, RENATA

CARDEA, STEFANO

DE MARCO, Iolanda

REVERCHON, Ernesto

English

Archivio della Ricerca - Università di Salerno

 1 Nanosized and nanostructured polymers by supercritical fluid processing  E. Reverchon, R. Adami, S. Cardea, I. De Marco Università degli studi di Salerno, Dipartimento di Ingegneria Chimica e Alimentare, Via Ponte Don Melillo, Fisciano (SA), Italy  Supercritical fluids have been applied in several fie ds, among these pharmaceuticals, fine chemicals, food, polymers and cosmetics [1-5]. Polymers are particularly interesting: they are a transversal field since they are of interest alone r in combination with, for example, pharmaceutical compounds to give products with improved technological characteristics. We are presently working on polymers and biopolymers at nanoscale dimensions using supercritical fluids assisted processes with two major objectives: the production of polymer nanoparticles and of nanostructured polymers. To obtain these goals we are applying supercritical antisolvent precipitation (SAS) to produce polymer nanoparticles, alone or in combinatio  with pharmaceutical compounds and supercritical gel drying to obtain polymer and biopolymer gels combined with other materials with the final aim to produce polymeric scaffolds to be us d for bone repair and substitution. SAS as nanonization technique for polymers SAS has mainly been used to produce microparticles of several kind of compounds [6,7]; whereas, its use to produce nanoparticles is less documented. Scientific information on the use of this technique for the production of polymers nanoparticles is even more limited [3,8]. However, in a recent paper we have indicated some general rules to produce nanoparticles by SAS [9]. They can be summarized as: near zero solubility of the solid solute in the fluid solution supercritical CO2+liquid solvent formed in the precipitation vessel and precipitation conditions above the mixture critical point (MCP). These conditions are relatively simple to be obtained for several polymers, especially when they have a high molecular weight. For example, we obtained nanoparticles of dextran, inulin, HYAFF, HPMA, PVA with mean diameters ranging between 55 and 140 nm. In figure 1 an example of PVA nanoparticles produced by SAS at 200 bar, 45°C is reported.  2  figure 1. SEM image of PVA precipitated from EtOH by SAS at 45°C, 200 bar and 1 wt%. The major limitation of this process is the possible lowering of the glass transition temperature (Tg) of the polymer due to the presence of SC-CO2 [10] that can induce the coalescence of polymer nanoparticles at T>Tg. Composite gels drying for scaffolding applications Several polymers can produce gels when their solution in a liquid solvent is, for example, fast cooled. The resulting material (gel) is a solid nanometric structure formed by the polymer embedded in the liquid solvent. Gel drying can be a very complex operation, since the solvent elimination has to be performed at supercritical conditions for the solvent, to avoid the collapse of the solid structure due to the surface tension of the evaporating liquid. It has been demonstrated that a very simple process for polymeric gels drying is the use of SC-CO2. A SC-solution with the liquid solvent is formed, then the fluid solution is eliminated using pure SC-CO2 [11]. This process preserves very well the gel nanostructure and 3D structure; it also allows the fast and complete elimination of the solvent. Working on bio-polymeric gels we have also induced the formation of macro-voids (of micrometric dimensions), while preserving the shape and nanostructure of the gel. Operating in this manner, w  think that it is possible to simulate either themicrostructure either the nanostructure of human boes. Since an open pores microstructure that is formed by nanometric filaments that mimics the structure of the bones has been produced. We have also added hydroxyapatite crystals in the structure, that are one of the inorganic constituents of human bones. An example of 3D scaffold of PLLA obtained using this process is reported in figure 2.  3  figure 2. SEM image of PLLA scaffolds at 33°C, 200 bar, 10 wt% from gel with porogen diameter 250-500 µm. Mechanical, micro and nanostructural properties of these PLLA scaffolds can allow the temporary substitution of bones and the subsequent growth of osteocites coming from the patients, with the aim to reproduce the original bone structure. Cellular growth experiments are in progress. References  [1] J. Jung, M. Perrut, Particle design using supercritical fluids: Literature and patent survey, J. Supercrit. Fluids, 20(2001) 179.  [2] A. Shariati, C.J. Peters, Recent developments in particle design using supercritical fluids, Current Opinion in Solid State & Materials Science, 7(2003) 371.  [3] S.-D. Yeo, E. Kiran, Formation of polymer particles with supercritical fluids: A review, J. Supercrit. Fluids, 34(2005) 287.  [4] D.L. Tomasko, H. Li, D. Liu, X. Han, M.J. Wingert, L.J. Lee, K.W. Koelling, A review of CO2 applications in the processing of polymers, Industrial & Engineering Chemistry Research, 42(2003) 6431.  [5] Z. Knez, E. Weidner, Particles formation and particle design using supercritical fluids, Current Opinion in Solid State & Materials Science, 7(2003) 353.  [6] E. Reverchon, Supercritical antisolvent precipitation of micro- and nano-particles, J. Supercrit. Fluids, 15(1999 ) 1.  [7] F. Dehghani, N.R. Foster, Dense gas anti-solvent processes for pharmaceutical formulation, Current Opinion in Solid State & Materials Science, 7(2003) 363.  [8] E. Reverchon, R. Adami, Nanomaterials and supercritical fluids, J. Supercrit. Fluids, 37(2006) 1.  [9] E. Reverchon, I. De Marco, E. Torino, Nanoparticles production by supercritical antisolvent precipitation: A general interpretation, J. Supercrit. Fluids, In Press, Corrected Proof(2007). [10] A.I. Cooper, Polymer synthesis and processing using supercritical carbon dioxide, J. Mater. Chem., 10(2000) 207. [11] C. Daniel, D. Alfano, V. Venditto, S. Cardea, E. Reverchon, D. Larobina, G. Mensitieri, G. Guerra, Aerogels with a microporous crystalline host phase, Advanced Materials (Weinheim, Germany), 17(2005) 1515. 

Nanosized and nanostructured polymers by supercritical fluid processing

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Nanosized and nanostructured polymers by supercritical fluid processing

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