Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics

Abstract

Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain-machine interfaces. This paper describes a material strategy for a type of biointerfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal

Thermal Release Transfer Printing for Stretchable Conformal Bioelectronics

“…As shown in Figure 3 a, the conformal contact issue of neural electrode array can be simplified as how to keep a membrane wrapping around a cylinder with certain radius. The formula of the conformal critical diameter is shown as the following5 $\gamma \ge {\gamma }_{\mathrm{normalc}}=\frac{EI}{R^{2}b}$where γ is the adhesion energy per unit area, b is the width of PI pad ( b = 3690 µm, Figure S7, Supporting Information). γ is about 10 mJ m −2 , according to the reported values for wet interfaces 5.…”

“…As the core of neurophysiologic monitoring, realizing high‐quality signal collection is an important topic in the research of neural electrode arrays. Related researches have indicated that stretchable/flexible neural electrode arrays, with their excellent mechanical and electrical performance, are superior candidates for the next generation of implantable devices 3, 4, 5, 6, 7, 8, 9, 10, 11. The successful development of stretchable/flexible neural electrode arrays hinges on good conformal contact between the array and the tissue, which enables excellent mechanical and electrical properties,3 as well as low‐cost, stable, and high‐throughput manufactural techniques.…”

“…Moreover, many implementations of stretchable/flexible bioelectronics employ polyimide (PI), a polymer with excellent mechanical properties and thermostability,1 as a flexible passivation layer to reinforce the metal layers 52. The insufficient strong to weak adhesion ratio of kinetic control strategy requires an additional thin layer of polymethyl methacrylate (PMMA) as a sacrificial layer on the donor substrate before the fabrication of the bioelectronics to decrease the interfacial adhesion between the bioelectronics membrane and the substrate 5, 35, 53, 54. Extra processing steps related to the fabrication and removal of the sacrificial layer increase the complicacy of the process.…”

“…By utilizing the large strong to weak adhesion ratio of TRT, the metal/PI based microdevices can be picked up directly from PI/glass interface using a sacrificial‐layer‐free process, and printed onto a PDMS substrate by thermal treatment. Due to the small Van der Waals force between the conventional PDMS stamp and microdevices, the retrieval of the metal/PI‐based microdevices cannot be accomplished by the common kinetically controlled transfer printing method if no sacrificial layer is fabricated 5, 54. Using the thermal release transfer printing approach, a stretchable neural electrode array on ultrathin elastomeric substrate has been designed and fabricated.…”

Flexible Photodetectors Based on 1D Inorganic Nanostructures

“…Stretchable electronic devices have great advances for implantable devices in the human body 164, 165, 166. Stretchable devices, such as pressure sensors, gas sensors and PDs, could also be used in industry, bio‐organs, and under harsh environments 167, 168, 169, 170.…”