<p>Microscale acoustofluidic resonators have been adapted for various applications in medicine and engineering and they have potential to be integrated in medical implants. In fabrication of these devices, various materials have been used, among which polymers are most suitable for implantation. Polymeric microfabricated devices can be biocompatible, hemocompatible, and bioresorbable. These properties are advantageous for medical implants that are minimally invasive. Moreover, in a minimally invasive delivery, folding an implant is crucial, which requires a device with high elasticity and a small form factor. Various polymers offer these properties such as Polydimethylsiloxane (PDMS). While numerous works have reported on polymeric or stretchable electronic implants for a minimally invasive delivery, limited works have focused on stretchable acoustic microresonators adapted for a transcatheter delivery. Here we report on a novel method for miniaturization of the overall thickness of acoustofluidic microcavities embedded in Polydimethylsiloxane (PDMS) such that they form a stretchable thin film with a thickness ranging from 100 microns to 1 mm. This cost-effective method is demonstrated by adding/bonding layer by layer thin PDMS films, which results in a network of isolated or connected microcavities, with a minimal thickness. In this process, each layer of patterned PDMS is fabricated by spin coating or casting PDMS on templates, curing the PDMS film, releasing the film and then transferring/bonding it on another PDMS film. The templates are fabricated using a photolithography process on silicon wafers. To facilitate the release of the cured PDMS films sacrificial layers are spin coated on the templates. Multiple surface treatment techniques are employed and assessed for bonding the thin PDMS layers. Subsequently, air-filled periodic cylindrical microcavities are realized with a hexagonal lattice and they are demonstrated with critical dimensions ranging from 50 to 500 microns. The film-like devices could be folded, passed through a Fr-12 catheter, deployed, and finally be unfolded. This process mimics transcatheter delivery of a minimally invasive implant, as well as frictional forces typically applied to the implant. The dislodged films are then optically characterized for finding any failure. It is shown than films with surface area as large as 2 cm<sup>2</sup>&nbsp;can be deployed without any failure. Finally, the cross-sectional dimensions of the microresonators are optically characterized. It is shown that the dimensions of the microcavities across a device varies &lt; ~ 10 % in each device. Our results suggest the possibility of fabrication and integration of film-like acoustic microresonators in minimally invasive implants with acoustic communications.&nbsp;</p>

Fabrication of Polymeric Arrays of Film-Like Microcavities With a Small Form Factor Suitable for Minimally Invasive Implants

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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