Demonstrating the mechanism and efficacy of water‐induced shape memory and the influence of water on the thermal properties of oriented poly(d,l‐lactide)

Achieving water-induced shape-memory property in poly(D,L-lactide) (PDLLA), generated by means of advanced process- ing methods, opens possibilities to develop novel bioresorbable medical devices with shape-memory properties activated by the human body without external heat. The main phenomena that affect the molecular movements that enable the water-induced shape- memory effect in an oriented PDLLA in an aqueous environment at physiological temperature are related to the water driven disrup- tion of the intermolecular dipole-dipole and/or hydrogen bonding of the oriented PDLLA chains and the subsequent decrease of the glass transition temperature (Tg) to the range of physiological temperature. The diffused water in the polymer matrix decreased the energy needed to finish the glass transition process explaining the higher shape-recovery rate of the c-irradiated PDLLA with respect to the non-c-irradiated PDLLA in an aqueous environment at physiological temperatures. The water-induced decrease in the Tg was thermally reversible. The efficacy of the generated shape-memory was tested with PDLLA shape-memory nails in a pullout test, in which the pullout force of the PDLLA nails increased 360% during a seven day test period in vitro at 37C. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4209-4218, 2013