Shape-Morphing Liquid Crystal Elastomer-Based Tissue Adhesives

Current tissue adhesives for wound management face ongoing challenges and limitations such as insufficient adhesion strength to soft and wet tissue and poor mechanical properties. Chemical-based adhesives, such as cyanoacrylates, provide high bond strength but can elicit an inflammatory response due to toxic monomers. Alternatively, mechanical systems are commercially available for clinical applications, such as sutures and staples, but these approaches can cause excessive penetration trauma. Recently, microneedle (MN) array adhesives have been developed. These mechanical adhesives offer enhanced tissue adhesion while reducing trauma and clinician time. We are developing shape-morphing liquid crystal elastomer (LCE) based microscale tissue adhesives, capable of providing strong fixation to soft and wet tissue through mechanical interlocking. The key advantage of this approach is that we can create sub-millimeter scale polymeric structures with controlled forms that can be used as MN adhesives. We employ thiol-ene click chemistry to synthesize liquid crystal elastomers capable of crystallizing after polymerization. The combination of liquid crystallinity and semicrystallinity enables these microneedles to not only exbibit large and programmable deformation strain but also high elastic modulus and toughness. Directed self-assembly is used to spatially pattern the molecular orientation of the material prior to crosslinking. This orientation dictates the shape of the polymer at body temperature. In this manner, flat sheets are able to morph into their programmed out-of-plane bent state when released from the underlying glass carrier without requiring an external stimulus. These curved needles are then inserted into the model tissue of interest. The relationship between microneedle curvature and adhesion will be discussed. The semicrystalline LCE-based MN arrays have sufficient strength to first be able to puncture and then mechanically adhere to both agarose tissue model as well as chicken tissue. The maximum pull-out force of an LCE-based microneedle is 9.6 ± 0.9 mN force per needle in an agarose tissue model. We expect that by leveraging this class of stimuli-responsive polymers, we can enable microneedle arrays to provide a safe and effective strategy for high-strength tissue adhesion.