Leeya Engel

Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function

In cardiac tissue engineering approaches to treat myocardial infarction, cardiac cells are seeded within three-dimensional porous scaffolds to create functional cardiac patches. However, current cardiac patches do not allow for online monitoring and reporting of engineered-tissue performance, and do not interfere to deliver signals for patch activation or to enable its integration with the host. Here, we report an engineered cardiac patch that integrates cardiac cells with flexible, free-standing electronics and a 3D nanocomposite scaffold. The patch exhibited robust electronic properties, enabling the recording of cellular electrical activities and the on-demand provision of electrical stimulation for synchronizing cell contraction. We also show that electroactive polymers containing biological factors can be deposited on designated electrodes to release drugs in the patch microenvironment on-demand. We expect that the integration of complex electronics within cardiac patches will eventually provide therapeutic control and regulation of cardiac function.

Freestanding smooth micron-scale polydimethylsiloxane (PDMS) membranes by thermal imprinting

We report on a novel fabrication process based on thermal imprinting for the formation of micron-scale, freestanding, dielectric layers of poly(dimethylsiloxane). This technique is the basis for three-dimensional elastomeric membrane micro-electro-mechanical system applications where the structural material is part of the actuator and the lateral expansion is by vertically applied bias. We have fabricated freestanding smooth defect-free membranes with thicknesses in the range of 0.4?4.8 ?m and with diameters of centimeters order of magnitude. A curve was plotted to calibrate the thickness of the elastomer layer to the pressure of the imprint. The adhesion between the polymer and the silicon (Si) chips surface was reduced by the deposition of a hydrophobic dodecyl-trichlorosilane monolayer on the chips prior to imprinting. The ability to detach the membrane from the chips after imprinting is critical for the production of layers that are freestanding. Additionally, we demonstrate the feasibility of patterning the membranes at the time of imprinting to create freestanding patterned micron-scale membranes. A simple device made up of a freestanding circular membrane with electrodes on the circumference demonstrating the application of the method is presented here. The devices electromechanical characteristics are presented as well.

Thermoplastic nanoimprint lithography of electroactive polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) for micro/nanoscale sensors and actuators

Thermoplastic nanoimprint lithography has been used for the first time, to the best of our knowledge, as a method for transferring nanoscale patterns to electroactive polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)]. PVDF, its copolymers, and terpolymers cannot be processed using conventional lithography techniques because of their solubility in most organic solvents and photoresist developers. In this work, line-shaped patterns with widths of 60 to 100 nm were formed in the thermoplastic polymer by thermal compression using a previously patterned and treated silicon (Si) stamp. Annealing of the polymer under compression in a nanoimprinter following imprint resulted in a 10-fold improvement in the surface roughness of the polymer relative to spin-coated layers of P(VDF-TrFE-CFE). Patterning of distinct polymer structures on Si substrates (without residual layer) was achieved for micron scale structures. The processes presented here comprise a basis for the integration of P(VDF-TrFE-CFE) as an active material in nanoscale sensors and actuators.

A Cardiovascular Occlusion Method Based on the Use of a Smart Hydrogel

Smart hydrogels for biomedical applications are highly researched materials. However, integrating them into a device for implantation is difficult. This paper investigates an integrated delivery device designed to deliver an electro-responsive hydrogel to a target location inside a blood vessel with the purpose of creating an occlusion. The paper describes the synthesis and characterization of a Pluronic/methacrylic acid sodium salt electro-responsive hydrogel. Application of an electrical bias decelerates the expansion of the hydrogel. An integrated delivery system was manufactured to deliver the hydrogel to the target location in the body. Ex vivo and in vivo experiments in the carotid artery of sheep were used to validate the concept. The hydrogel was able to completely occlude the blood vessel reducing the blood flow from 245 to 0 ml/min after implantation. Ex vivo experiments showed that the hydrogel was able to withstand physiological blood pressures of > 270 mm·Hg without dislodgement. The results showed that the electro-responsive hydrogel used in this paper can be used to create a long-term occlusion in a blood vessel without any apparent side effects. The delivery system developed is a promising device for the delivery of electro-responsive hydrogels.