Introduction: Shape memory polymers are a class of smart materials capable of transitioning from a programmed temporary shape back to its permanent shape when stimulated. while shape memory polymers have been developed to be degradable and biocompatible, none feature a reconfigurable permanent shape. We have developed a new, soft, biocompatible and biodegradable reconfigurable shape memory elastomeric composite featuring a polyanhydride (PAH) matrix and electrospun poly(ε-caprolactone) (PCL) fibers. This composite is capable of resetting its permanent shape as well as triggering shape recovery at body temperature. Materials: PCL, 4-pentenoic anhydride (PNA), pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), azobisisobutyronitrile (AIBN), chloroform, N,N-dimethylformamide (DMF), trimethylolpropane diallyl ether (TMPDAE), and 1,6-hexanediol diacrylate (HDDA) were used as received. Thermoplastic polyurethane PCL was synthesized using 3,4-dihydroxy-1-butene, hexamethylene diisocyanate, toluene and poly(ε-caprolactone) diol. Methods: PCL was electrospun from solution prepared by dissolving PCL in chloroform/DMF. The PAH monomer was prepared by mixing PNA with PETMP (2:1 molar ratio) and AIBN. The PCL fiber mat was then imbibed with the PAH monomer, followed by UV and thermal curing of the PAH matrix. The shape memory properties were characterized quantitatively using a defined thermomechanical cycling method using a dynamic mechanical analyzer. Degradation of the composite was monitored by measuring the mass loss over time and evaluating the PCL content using differential scanning calorimetry. Scanning electron microscopy (SEM) was used to evaluate the morphological changes during degradation. Results and Discussion: The PAH elastomer was found to reconfigure its crosslinked structure toward a stress-free state when strained at temperatures greater than 40 °C, with stress relaxation completing over a time that decreased with increasing temperature. This reconfiguration in the solid state is due to dynamic covalent exchange reactions involving anhydride groups. Such reconfiguration did not occur when the elastomer was synthesized devoid of anhydride groups; i.e., using HDDA or TMPDAE instead of PNA. When combined with PCL fibers, PAH-PCL composite exhibited one way shape memory before and after shape resetting through melting and recrystallization of PCL. The thermal parameters of these shape memory cycles can be tuned by replacing PCL with a hard-block-free PCL-based polyurethane exhibiting a lower melting transition. Near-complete degradation of the PAH matrix occured after approximately four days, with about 92% of composite comprised of PCL compared to 18% prior to degradation. Microstructural analysis reveals a change in the erosion mechanics from surface erosion of the pure matrix to apparent bulk degradation for the composite. The composite maintained its fixed shape throughout degradation. Conclusions: Our polyanhydride elastomer is capable of resetting new permanent shapes, erasing any 'memory' of previous shapes. Incorporation of this elastomer as a matrix structured with PCL fibers provides a new reconfigurable elastomeric shape memory biomaterial capable of reprogramming its original shape as well as degrading in PBS at physiological conditions while maintaining a programmed shape.
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