Direct Transfer Printing of Water Hydrolyzable Metals onto Silk Fibroin Substrates through Thermal‐Reflow‐Based Adhesion

Abstract

join a number of other polymeric hydrogel and fi lm materials (PCL, PLGA, Collagen, and others) as advantageous options for highly compliant biological/technological interfaces. [25][26][27][28][29] In a recent example, silk has enabled fl exible and fully bioresorbable electronic and optical devices that show promise for implantable diagnostics and therapeutics, where silk remains a substrate material of unique utility. [29][30][31][32] Bioelectronic and biooptical devices based on silk and other polymeric systems are fabricated by integrating thin-fi lm device components made from metals and semiconductors with polymer substrates. The metal and semiconductor based components are most often manufactured via established micro-and nanofabrication techniques, and can be interfaced with polymeric substrates by a number of methods including inkjet printing, [ 21 ] direct deposition with a shadow mask, [ 31,32 ] and several transfer-print-based strategies. [ 25,[33][34][35] In the case of silk, additional encapsulating layers and/or doped therapeutics can then be incorporated to add functionality, and adjustment of silk's material polymorphism can tune the device behavior and degradation rate in vivo.However, there remain limitations to existing fabrication methods for substrate/device interfaces. Direct shadow-mask deposition on often leads to poor mechanical performance because the hydrated networks common to compliant biological polymers dry out and become brittle at the low pressures required for deposition. [ 5 ] Inkjet printing lacks the resolution for use with many microelectronic and optical devices and despite recent improvements remains limited in the variety of electronic materials that can be processed as inks. [36][37][38] This leaves transfer printing as the most advantageous interfacing strategy for building bioelectronics on polymer substrates such as silk.Transfer printing on silk is commonly accomplished in one of several ways. In the fi rst method, a silicon wafer is coated with a layer of fl uorosilane (FOTS) to limit adhesion and the device is built on top. Aqueous silk solution is directly cast on the surface and allowed to dry overnight. The limited adhesion of the device to the silanized wafer helps it to peel up with the dried silk, transferring it onto the silk as a substrate. [ 34 ] This method can be effective for large scale devices, In recent years, the use of biopolymers as interface materials between inorganic electronics and biological tissues has increased, which has necessitated the integration of micro-and nanofabrication techniques with these unconventional materials. This combination has led to devices with intriguing operational characteristics such as so-called "transient" bioresorbable devices. Here, a method is investigated which leverages the thermal refl ow characteristics of non-beta-sheet crystallized silk fi broin protein fi lms to transfer print electronic components onto bioresorbable silk substrates. This is accomplished by applying heat and pressure to the interface o...

A Thermal‐Reflow‐Based Low‐Temperature, High‐Pressure Sintering of Lyophilized Silk Fibroin for the Fast Fabrication of Biosubstrates

“…The overall process can be considered to be a flow of material that, from the micrographs, seems to behave as a viscous fluid until it reaches a solid form. This corresponds to previous studies that report this phenomenon when fibroin temperature is raised above the T g …”

“…Water, in this phenomenon, acts as plasticizer decreasing the glass transition temperature ( T g ) and, consequently, the energy needed to activate thermal reflow . In wet fibroin films, this principle has been used to imprint microstructures and hydrolysable metal microstructures using a hot mold, to produce laminates of stacked films by compression, and, more recently, to produce a fibroin device with a programmable degradation time . Even if the T g of fibroin is reported to decrease down to 40 °C in some conditions, none of the above processes report the use of a such low temperature.…”

Engineering the Future of Silk Materials through Advanced Manufacturing

“…The combination of manufacturing technology and biomaterials offers new methods to engineer biomaterials and biomanufacturing. Numerous research efforts have been invested in the biomanufacturing, inspired by the existing integrated circuit manufacturing and microelectromechanical system fabrication, and multiscale manufacturing for silk biomaterial has been developed, including electron‐beam lithography (EBL),c ion‐beam lithography (IBL), soft lithography (SL), nanoimprinting lithography (NIL), self‐assembly, scanning probe lithography, multiphoton lithography (MPL), direct pattern transfer, bioinspired spinning, covering from nanoscale to macroscale. Biomanufacturing, a highly interdisciplinary field, seeks to create novel bioarchitectures as functional devices and interfaces, and attempts to integrate inorganic and organic components for new properties and functions, which have the potential for a wide variety of biological research topics and medical applications.…”

Combining Living Microorganisms with Regenerated Silk Provides Nanofibril-Based Thin Films with Heat-Responsive Wrinkled States for Smart Food Packaging

“…The polymorphism of silk fibroin (i.e., random coil, silk I, and silk II structures) can be also tailored by controlling the content of β-sheet crystals to enable the correct gas exchange and water vapour permeability through silk-based membranes [ 11 , 12 , 13 ]. Among the different fabrication methods, transfer printing is the most known method for interfacing silk on soft substrates [ 14 ]. In this regard, the hidden strength and stiffness of natural honeycomb walls constructed from recycled silk and wax secreted by worker bees [ 15 , 16 , 17 ] is reminiscent of modern fiber-reinforced composite laminates.…”