title: Influence of different heating regimes on the shape-recovery behavior of poly(L-lactide) in simulated thermomechanical tests.
abstract: OBJECTIVE
  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 Tlow = 250 K to Thigh = 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 (Rr) was strongly influenced by the applied simulation time and heating rate, whereby Rr 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 Tsw = 473 K for the modeled samples.
  
  
  CONCLUSIONS
  We anticipate that the atomistic modeling approach presented should be capable of enabling further study of Tsw 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.
authors.affiliation: Center for Biomaterial Development and Berlin-Brandenburg Centre for Regenerative Therapies, Institute of Polymer Research, Helmholtz-Zentrum Geesthacht, Teltow, Germany.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Ghobadi
authors.forename: Matthias
authors.initials: M
authors.lastname: Heuchel
authors.forename: Karl
authors.initials: K
authors.lastname: Kratz
authors.forename: Andreas
authors.initials: A
authors.lastname: Lendlein
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D011091:Polyesters / Q000737:chemistry*; D044366:Transition Temperature
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; C033616:poly(lactide)