synthesis-programmable-main-chain-liquid-crystalline-elastomers-using

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline ...

University of Colorado Denver

Dye-containing polymers are highly desired for a number of commercially and medically relevant applications, such as sensors, medical devices, and drug delivery. In particular, dyes that emit light in the NIR region of the electromagnetic spectrum are of great interest due to the window of transparency for mammalian soft tissue in this range. While the incorporation of dyes into polymeric hosts by diffusion is a method that has been widely used, this approach is problematic in that it lacks uniformity and control over the incorporation. Here, we sought to develop NIR-emitting polymeric materials with high fluorescence intensity, addressing the problem of uniformity by incorporating the dye in a polymer host using dissolution in a mutual solvent and subsequent electrospinning into a fibrous web. This web could be prepared as a free-standing film, a coating or, as we will show, a shrink-wrap medical device label. The primary findings of this study were that an optimal concentration of dye in the polymer host exists, that the fluorescence intensity for fibrous webs greatly exceed that of comparable cast films, and that the dye-containing webs feature water-triggered contraction of use for application to medical devices, such as feeding tubes or catheters.

Fabrication of a light-emitting shape memory polymeric web containing indocyanine green.

Research in the field of shape memory polymers has recently witnessed the introduction of increasing complexity of material response, including such phenomena as triple/multishape behavior, temperature memory, and reversible actuation. Ordinarily, such complexity in physical behaviour is achieved through comparable complexity in material composition and synthesis. Seeking to achieve a triple shape behaviour with a simple route to materials synthesis, we introduce here a method that utilizes polymerization induced phase separation (PIPS) to yield the requisite combination of microstructure and composition. Thus, two blends incorporating epoxy and poly(ε-caprolactone) were developed using commercially available reactants, one featuring a semicrystalline epoxy and the other featuring an amorphous epoxy. We show that both blends exhibited distinct transition temperatures and three modulus-temperature plateaus needed for triple shape behaviour. Despite these similarities, their physical character at room temperature is vastly different: the semicrystalline epoxy material is elastomeric and the amorphous epoxy material is highly stiff. Characterization of the triple shape behaviour revealed an ability of both systems to fix two separate deformations independently, one by PCL crystallization and a second one by epoxy crystallization or vitrification, and recover both programmed shapes separately upon heating. Given the simplicity of fabrication, we envision application as multi-shape coatings, adhesives, and films.

Properties of triple shape memory composites prepared via polymerization-induced phase separation.

Soft, anisotropic materials, such as myocardium in the heart and the extracellular matrix surrounding cells, are commonly found in nature. This anisotropy leads to specialized responses and is imperative to material functionality, yet few soft materials exhibiting similar anisotropy have been developed. Our group introduced an anisotropic shape memory elastomeric composite (A-SMEC) composed of non-woven, aligned polymer fibers embedded in an elastomeric matrix. The composite exhibited shape memory (SM) behavior with significant anisotropy in room-temperature shape fixing. Here, we exploit this anisotropy by bonding together laminates with oblique anisotropy such that tensile deformation at room temperature - mechanical programming - results in coiling. This response is a breakthrough in mechanical programming, since non-affine shape change is achieved by simply stretching the layered A-SMECs at room temperature. We will show that pitch and curvature of curled geometries depend on fiber orientations and the degree of strain programmed into the material. To validate experimental results, a model was developed that captures the viscoplastic response of A-SMECs. Theoretical results correlated well with experimental data, supporting our conclusions and ensuring attainability of predictable curling geometries. We envision these smart, soft, shape changing materials will have aerospace and medical applications.

Article	Year
Fabrication of a light-emitting shape memory polymeric web containing indocyanine green. Journal of biomedical materials research. Part B, Applied biomaterials\| PubMed ID: 24449265	2014
Properties of triple shape memory composites prepared via polymerization-induced phase separation. Soft matter\| PubMed ID: 24695693	2014
Mechanically programmed shape change in laminated elastomeric composites. Soft matter\| PubMed ID: 26086682	2015

Amir H. Torbati

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