Fabrication and characterization of poly(l-lactic acid) gels induced by fibrous complex crystallization with solvents

Complex crystal induced gelation of poly(l-lactic acid) (PLLA) solutions was studied for a series of solvents, including N,N-dimethylformamide (DMF). By cooling the solutions prepared at elevated temperatures, PLLA gels were produced in solvents that induced complex crystals (ε-crystals) with PLLA. Fibrous structure of PLLA in the gel with DMF was observed by polarizing optical microscopy, field emission electron microscopy, and atomic force microscopy. Upon heating, the crystal form of PLLA in the DMF gel changed from ε-crystal to α-crystal, the major crystal form in common untreated PLLA films, but the morphology and high elastic modulus of the gel remained until the α-crystal dissolved at higher temperature. In addition, a solvent exchanging method was developed, which allowed PLLA gels to be prepared in other useful solvents that do not induce ε-crystals without losing the morphology and mechanical properties. [Display omitted]