Shape Recovery with Concomitant Mechanical Strengthening of Amphiphilic Shape Memory Polymers in Warm Water

Abstract

Maintaining adequate or enhancing mechanical properties of shape memory polymers (SMPs) after shape recovery in an aqueous environment are greatly desired for biomedical applications of SMPs as self-fitting tissue scaffolds or minimally invasive surgical implants. Here we report stable temporary shape fixing and facile shape recovery of biodegradable triblock amphiphilic SMPs containing a poly(ethylene glycol) (PEG) center block and flanking poly(lactic acid) or poly(lactic-co-glycolic acid) blocks in warm water, accompanied by concomitant enhanced mechanical strengths. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD), and small-angle X-ray scattering (SAXS) analyses revealed that the unique stiffening of the amphiphilic SMPs upon hydration was due to hydration-driven microphase separation and PEG crystallization. We further demonstrated that the chemical composition of degradable blocks in these SMPs could be tailored to affect the persistence of hydration-induced stiffening upon subsequent dehydration. These properties combined open new horizons for these amphiphilic SMPs for smart weight-bearing in vivo applications (e.g., as self-fitting intervertebral discs). This study also provides a new material design strategy to strengthen polymers in aqueous environment in general.

Biodegradable Shape Memory Polymers in Medicine

“…There are several important medical applications that currently use BSMPs (outside of the major applications discussed above) that could use further development. Examples include an orthodontics arch wire for aligning teeth, an implantable (fallopian tube) contraception device, an annuloplasty ring for the treatment of mitral valve insufficiency, an actuator, and an artificial spinal disc . The last two examples highlight some of the unique functions achievable with SMPs that have been underexplored for medical applications.…”

“…d) Stiffening of the hydrated spinal disk. Adapted with permission . Copyright 2017, American Chemical Society.…”

3D‐Printed Biomaterials for Guided Tissue Regeneration

“…To address this challenge, biodegradable polymers incorporating hydrophilic segments such as PEG have been developed to increase their aqueous wettability, and blending with HA and calcium phosphates to impart osteoconductivity and mitigate immunogenicity of the acidic degradation products of PLA. We recently developed triblock amphiphilic copolymers of PLA–PEG–PLA (PELA) and PLGA–PEG–PLGA (PELGA), which exhibited unique hydration‐induced stiffening behavior (due to hydration‐driven microphase separation and crystallization) and thermally responsive shape‐memory properties ( Figure A) . Being thermoplastics, these amphiphilic polymers and their mineral composites were readily 3D printed into unmineralized (inhibiting cell adhesion due to the low‐fouling property of PEG), mineralized (supporting attachment and osteogenesis of bone‐marrow‐derived stromal cell (BMSC) (Figure B)), and mineralized/unmineralized biphasic constructs (Figure C).…”

Carbon nanotubes array reinforced shape‐memory epoxy with fast responses to low‐power microwaves

“…Most SMPs are thermo‐triggered, which may be not practical when outer heating sources are not available . So researchers attempted to expand the actuation routes of SMPs, that is, from thermal to non‐thermal triggering (such as electricity, magnetism, light, water, and microwave). Functional nanofillers that can transform other types of energy into heat are usually needed for the realization of nonthermal activation of SMPs .…”