Control of PLA Stereoisomers-Based Polyurethane Elastomers as Highly Efficient Shape Memory Materials

Abstract

Poly(lactic acid) (PLA) has received increasing attention in the development of shape memory polymers (SMPs) due to its excellent physical properties and good biocompatibility. However, the intrinsically increased crystallinity of PLA at higher deformation ratios still remains a significant challenge, which remarkably restricts the chain mobility and reduces shape recovery efficiency. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for modulation of PLA toward a favorable property by incorporating different PLA stereoisomers in one macromolecular architecture. In this paper, we report a completely amorphous PLA poly(ester urethane) elastomer that exhibits excellent shape fixity (>99%) and shape recovery (>99%) in a time frame of seconds. By means of adjusting the stereoisomeric ratios and control over architecture, the resultant poly(PLLA/PDLLA urethane)s (PLDU) elastomers show a single glass transition temperature (T g ), as the only thermal event, in the range of 38−46 °C in a predictable manner. The elastic moduli of PLDU elastomers display a 100-fold loss during the sharp transition from a glassy to a rubbery state with temperature alternation across their corresponding T g , indicating a successful manipulation of the thermo-mechanical properties by temperature as required in thermally induced SMPs. In addition, all samples display a typical elastomeric behavior with elongation at break (ε b ) greater than 400%. The effect of the stereoisomer content on the tensile modulus and elastic mechanical behavior were also systematically investigated. Together with the prominent degradation property, the new PLDU elastomers developed in this study show great potential for biomedical applications as shape memory implants.

Shape memory polyurethanes with oxidation-induced degradation: In vivo and in vitro correlations for endovascular material applications

“…Without a solvent, sufficient temperature is required for movement of the polymer backbone, which allows for shape change associated with the return the entropic maximum that determines the primary shape of the material. In the presence of a solvent that can interrupt the hydrogen bonding, such as water or ethanol, the required temperature for the shape to change to occur is dramatically reduced, and shape recovery can be achieved at lower temperatures through the use of solvent as opposed to a purely thermally-driven recovery mechanism, due to the increased mobility of the crosslinking segments with disruption of the hydrogen bonded urethane and urea segments [40,41,48,49]. …”

Nano‐Star‐Shaped Polymers for Drug Delivery Applications

“…Polymer, in general, has been one of the go‐to classes of materials to be used as controlled drug delivery vehicles due to its myriad of properties including biocompatibility, the ability to functionalize, and ease of synthesis . With newer polymerization techniques developed over the years, we now have improved control over the structures of synthesized macromolecules, especially those of the star‐shaped polymers, which has allowed us to functionalize and recombine various arm architectures to suit various needs .…”

Relationship between the crystallization behavior of poly(ethylene glycol) and stereocomplex crystallization of poly(L‐lactic acid)/poly(D‐lactic acid)

“…reported better mechanical and thermomechanical properties of PLA in PLLA‐PEG‐PLLA/PDLA‐PEG‐PDLA blends, which can be attributed to the increased diffusion ability and decreased diffusion pathway of enantiomeric chains. Besides PEG, some other functional components are also used to improve the properties of PLA SCs; examples are star‐like hybrid POSS‐(PDMAEMA‐ b ‐PDLA) 8 copolymer, PLA‐based polyurethane elastomers, linear–dendritic‐like amphiphilic poly( d ‐ or l ‐lactide)‐ b ‐poly(acrylic acid) copolymers, and so on.…”