Influence of Different Heating Regimes on the Shape-Recovery Behavior of Poly(L-Lactide) in Simulated Thermomechanical Tests

Aim Multifunctional polymer-based biomaterials, which combine degradability with a shape-memory capability and in this way enable the design of actively moving implants such as self-anchoring implants or controlled release systems, have been recently introduced. Of particular interest are approved degradable polymers such as poly(L-lactide) (PLLA), which can be easily functionalized with a shape-memory effect. In the case of semicrystalline PLLA, the glass transition can be utilized as shape-memory switching domain. Methods In this work we applied a fully atomistic molecular dynamics simulation to study the shape-memory behavior of PLLA. A heating-deformation-cooling programming procedure was applied to atomistic PLLA packing models followed by a recovery module under stress-free conditions allowing the shape recovery. The recovery was simulated by heating the samples from T _low = 250 K to T _high = 500 K with different heating rates β of 125, 40 and 4 K·ns ⁻¹ . Results We could demonstrate that the obtained strain recovery rate (R _r ) was strongly influenced by the applied simulation time and heating rate, whereby R _r values in the range from 46% to 63% were achieved. On its own the application of a heating rate of 4 K·ns ⁻¹ enabled us to determine a characteristic switching temperature of T _sw = 473 K for the modeled samples. Conclusions We anticipate that the atomistic modeling approach presented should be capable of enabling further study of T _sw with respect to the molecular structure of the investigated SMP and therefore could be applied in the context of design and development of new shape-memory (bio)materials.