title: 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.
authors.affiliation: Department of Orthopedics & Physical Rehabilitation, University of Massachusetts Medical School , 55 Lake Avenue North, Worcester, Massachusetts 01655, United States.
authors.forename: Ben
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Chemical and Materials Science Group, Advanced Photon Source, Argonne National Laboratory , 9700 Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: Janae E
authors.initials: JE
authors.lastname: DeBartolo
authors.affiliation: Department of Orthopedics & Physical Rehabilitation, University of Massachusetts Medical School , 55 Lake Avenue North, Worcester, Massachusetts 01655, United States.
authors.forename: Jie
authors.identifier: http://orcid.org/0000-0001-7554-5564
authors.initials: J
authors.lastname: Song
keywords: amphiphilic biodegradable polymers; hydration-induced stiffening effect; minimal invasive surgery; shape memory; weight-bearing implantation