Tissue regeneration requires 3-dimensional (3D) smart materials as scaffolds to promote transport of nutrients. To mimic mechanical properties of extracellular matrices, biocompatible polymers have been widely studied and a diverse range of 3D scaffolds have been produced. We propose the use of responsive polymeric materials to create dynamic substrates for cell culture, which goes beyond designing only a physical static 3D scaffold. Here, we demonstrated that lactone- and lactide-based star block-copolymers (SBCs), where a liquid crystal (LC) moiety has been attached as a side-group, can be crosslinked to obtain Liquid Crystal Elastomers (LCEs) with a porous architecture using a salt-leaching method to promote cell infiltration. The obtained SmA LCE-based fully interconnected-porous foams exhibit a Young modulus of 0.23 ± 0.07 MPa and a biodegradability rate of around 20% after 15 weeks both of which are optimized to mimic native environments. We present cell culture results showing growth and proliferation of neurons on the scaffold after four weeks. This research provides a new platform to analyse LCE scaffold-cell interactions where the presence of liquid crystal moieties promotes cell alignment paving the way for a stimulated brain-like tissue.
This investigation highlights the potential for electrospun nanofiber mats and self-assembled nanofiber networks to be interfaced synergistically to induce hygromorphic behaviour. Control poly(vinyl alcohol) (PVA) electrospun active layers and 1,3:2,4-di-p-methylbenyliedene sorbitol (MDBS) self-assembled passive layers encapsulated in an ethylene oxide-epichlorohydrin (EO-EPI) copolymer matrix were fabricated to examine the influence of composition on the properties guiding hygromorphism, such as water transport, layer thickness, and layer modulus. Experimentally determined material constants were utilized in conjunction with mathematical modeling to determine ideal layer properties. It was revealed that the active layer with the highest PVA content exhibited the fastest water transport, and the passive layer with the highest MDBS content displayed the slowest water transport. However, the hygromorphic bilayer fabricated utilizing the lowest PVA content and the highest MDBS fraction was predicted to induce the highest change in curvature due to the lower modulus and thickness of the PVA nanofiber active layer. Decreasing the MDBS content reduced the passive layer modulus while increasing water transport, which theoretically reduced the overall bilayer curvature. The hygromorphic bilayer composites fabricated using these ideal control layers exhibited folding bias and response variations dependent upon active layer composition and imposed folding directions. By utilizing the favorable force balances between the active layer with the lower PVA content and the passive layer with the highest MDBS amount in conjunction with folding bias in a non-preferential direction, it was possible to achieve hygromorphic unfolding and refolding with hydration. Through modelling and individual layer examination, a unique platform built on two independent fiber networks has been designed to achieve biomimetic hygromorphism in synthetic bilayer composites.
Intelligence of living and nonliving systems is often characterized by the ability to communicate through signal and response. In the polymer science community, this intelligence is realized through the reaction of a material construct to environmental triggers. These smart materials are modeled after natural materials, which utilize matrix–fiber architectures to detect stimuli, release small molecules, or alter their macroscopic morphology in response to stimuli. As such, researchers have designed matrix–fiber composites, which function as release vehicles, sensors or switches, and actuators. Through the examination of the architecture and environmental triggering of these natural muses, the fundamental design parameters necessary for functional response in matrix–fiber composites and the ability to utilize these composites in targeted applications are highlighted. Opportunities for innovation in composite design are also discussed.
Natural systems utilize nanofiber architectures to guide water transport, tune mechanical properties, and actuate in response to their environment. In order to harness these properties, a hygromorphic bilayer composite comprised of a self-assembled fiber network and an aligned electrospun fiber network was fabricated. Molecular gel self-assembly was utilized to increase hydrophobicity and strength in one layer, while aligned electrospun poly(vinyl alcohol) (PVA) nanofibers increased the rate of hydration and facilitated tunable actuation in the other. Interfacing these two fiber networks in a poly(ethylene oxide-co-epichlorohydrin) (EO-EPI) matrix led to hydration-driven actuation with tunable curvature. Specifically, variations in fiber alignment were achieved by cutting at 0, 90, and 45 degree angles in relation to the length edge of the composite. Along with the ability to program the natural curvature, the utilization of aligned nanofibers increased water transport compared to random nanofiber systems, resulting in a reduction in response time from 20+ minutes to 2-3 minutes.
Multiscale
investigation of molecular gel additives in polymer
matrices guides understanding of how solution-state assemblies result
in mechanically enhanced, solid-state nanocomposites. Model polymers,
poly(ethylene oxide-co-epichlorohydrin) (EO–EPI)
and poly(vinyl acetate) (PVAc), were utilized as matrices and reinforced
by cholesterol–pyridine (CP) nanofiber networks. The CP nanofillers
suppress ethylene oxide segment melting for EO–EPI composites,
whereas for PVAc nanocomposites, cause a polymer–gel dissociation
transition. Incorporation of crystalline CP fiber networks led to
an order of magnitude increase in tensile storage modulus due to restrictions
on polymer chain mobility. This decrease in molecular mobility was
confirmed by decreased loss moduli for both EO–EPI and PVAc
composites. Excitingly, PVAc nanocomposites display an additional
relaxation mode caused by release of PVAc chains from the transient
molecular gel assembly. For both EO–EPI and PVAc composites,
bulk flow can be suppressed to temperatures up to 100 °C by simply
increasing the CP concentration.
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