Phase separation polymer scaffolds

Phase separation is another method that can be employed for the preparation of nanoscale sttucmres and is frequently used to prepare three-dimensional tissue-engineering scaffolds. Phase separation of a polymer solution can produce a polymer-rich domain and a solvent-rich domain and this morphology can be fixed by quenching under low temperamre conditions. 

Removal of the solvent through freeze-drying or extraction can produce porous polymer scaffolds. Phase separation can be induced by changing the temperature or by adding non-solvent to the polymer solution. These are known as thermally induced and non-solvent-induced phase separation, respectively. The scaffolds obtained by... 

Various fabrication methods have been developed in order to attain the 3D scaffold characteristics. In the case of synthetic polymer or polymer-matrix composite scaffolds, the methods include [47] solvent casting and particle leaching, phase separation, extrusion, gas foaming, and free form fabrication. Each method presents certain advantages with respect to others, ranging from ease of manufacture to control of the microstructure/nanostructure. Solvent casting and phase separation methods have been studied at our laboratory. 

There are several ways to prepare porous polymer scaffolds by controlled phase separation of polymer solutions in a polymer-rich phase and a polymer-poor phase. 

S., Fabrication and characterization of poly(L-lactic acid) 3D nanofibrous scaffolds with controlled architecture by liquid-liquid phase separation from a ternary polymer-solvent system. Polymer, 50, 4128, 2009. 

Using effervescent materials, the pore size of the pol5mier scaffolds can be easily controlled, and biodegradable polymer scaffolds can be more simply prepared compared to conventional methods such as salt leaching technique, phase separation technique, or gas foaming technique. 

Fig. 8. SEM micrographs of polymer scaffolds fabricated using solid-liquid phase separation (a) PLLA scaffold fabricated from 5% PLLA/dioxane solution (with local regular pore structure), (b) PLLA scaffold fabricated from 2.5% PLLA/dioxane solution (with less regular structure), (c) PLLA/HAP (hydroxyapatite) composite scaffold (PLLA/HAP 50/50) fabricated from a 2.5% PLLA/dioxane solution. Reprinted from Refs. 5 and 109. 2001, by permission of John Wiley Sons. 

Thermally induced liquid-liquid phase separation can he utilized to fabricate scaffolds for tissue engineering. For example, a solvent can be selected, where the crystallization temperature is sufficiently lower than the liquid-liquid phase separation temperature of an amorphous polymer solution. A liquid-liquid phase separation can be induced by lowering the temperature into the imstable region on the phase diagram but above the solvent crystallization temperature. For the PLA and PLGA family, a mixture of dioxane and water has been used for liquid-liquid phase separation to fabricate pol5mier scaffolds with interconnected pore structure (Fig. 12) (112,113). 

Another scaffold fabrication technique is thermally induced phase separation (TIPS) [34,46,84,147-149]. TIPS involves decreasing the temperature of a polymer solution to obtain a polymer-rich and polymer-poor phase. Following phase separation, the solvent is removed using one of a number of methods (freeze drying, evaporation) resulting in the formation of pores in the polymer stracture. TIPS can also be combined with the use of porogens to increase void fraction, have better control over pore size, or improve pore interconnectivity. 

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