TY  - JOUR
A1  - Ghobadi, Ehsan
A1  - Heuchel, Matthias
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Influence of different heating regimes on the shape-recovery behavior of poly(L-lactide) in simulated thermomechanical tests
JF  - Journal of applied biomaterials & functional materials
N2  - 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 beta 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.
KW  - Molecular modeling
KW  - Polymers
KW  - Shape-memory effect
Y1  - 2012
U6  - https://doi.org/10.5301/JABFM.2012.10440
SN  - 2280-8000
VL  - 10
IS  - 3
SP  - 259
EP  - 264
PB  - Wichtig
CY  - Milano
ER  - 
TY  - JOUR
A1  - Wang, Li
A1  - Heuchel, Matthias
A1  - Fang, Liang
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Influence of a polyester coating of magnetic nanoparticles on magnetic heating behavior of shape-memory polymer-based composites
JF  - Journal of applied biomaterials & functional materials
N2  - Background: Magnetic composites of thermosensitive shape-memory polymers (SMPs) and magnetite nanoparticles (MNPs) allow noncontact actuation of the shape-memory effect in an alternating magnetic field. In this study, we investigated whether the magnetic heating capability of cross-linked poly(epsilon-caprolactone)/MNP composites (cPCLC) could be improved by covalent coating of MNPs with oligo(epsilon-caprolactone) (OCL).
 Methods: Two different types of cPCLC containing uncoated and OCL-coated MNP with identical magnetite weight content were prepared by thermally induced polymerization of poly(epsilon-caprolactone) diisocyanatoethyl methacrylate. Both cPCLCs exhibited a melting transition at T-m = 48 degrees C, which could be used as switching transition.
 Results: The dispersion of the embedded nanoparticles within the polymer matrix could be substantially improved, when the OCL-coated MNPs were used, as visualized by scanning electron microscopy. We could further demonstrate that in this way the maximal achievable bulk temperature (T-bulk) obtained within the cPCLC test specimen in magnetic heating experiments at a magnetic field strength of H = 30 kA.m(-1) could be increased from T bulk = 48 degrees C to T bulk = 74 degrees C.
KW  - Magnetic composites
KW  - Magnetite nanoparticles
KW  - Polymer networks
KW  - Shape-memory effect
Y1  - 2012
U6  - https://doi.org/10.5301/JABFM.2012.10293
SN  - 2280-8000
VL  - 10
IS  - 3
SP  - 203
EP  - 209
PB  - Wichtig
CY  - Milano
ER  -